ICE STRENGTHENED HULL STRUCTURE OF MERCHANT VESSELS
Naval and Ocean Engineering Master Thesis
2020
Author: Samuel Ruiz Capel
Supervisor: José Enrique Gutiérrez Romero
Co-supervisor: Kaj Antero Riska
2
Acknowledgements ... 12
Summary ... 13
1. Introduction ... 14
2. Hull Scantling through Ice Class Regulations ... 19
2.1. Sample Vessel: M/S EIRA ... 19
2.2. Finish-Swedish Ice Class Rules (FSICR) ... 21
2.2.1. Engine Output ... 22
2.2.2. Hull Structural Design ... 24
2.2.3. Ice Load and Ice Pressure ... 27
2.2.4. Shell Plating ... 29
2.2.5. Transverse Frames ... 29
2.2.6. Ice Stringers ... 31
2.2.7. Web Frames ... 31
3. Model Development ... 34
3.1. Initial Model ... 34
3.2. Contact Force ... 40
3.3. Frame Formulation ... 47
3.3.1. Bending Moment for Simply Supported Frames ... 50
3.3.2. Bending Moment for Fixed Frames ... 52
3.4. Frame Types and Section Modulus Calculation ... 54
3.4.1. Bulb Flat Profiles ... 54
3.4.2. Commercial Angles (L Profiles) ... 56
3.4.3. Custom-Built T Profiles ... 56
3.5. Shell Plating ... 57
3.5.1. Concentrated Loads ... 57
3.5.2. Single Location Loads. ... 58
4. Optimization Process ... 61
5. Experimental Tests: Ice Resistance in Floating Ice ... 68
5.1. Introduction ... 68
3
6. Results and Comparison ... 81
6.1. Results through the Finish-Swedish Ice Class Rules (FSICR) ... 81
6.2. Results through the Direct Calculation Method (DCM) ... 85
6.2.1. Results for the Contact Force ... 85
6.2.2. Results for the Optimization Process ... 92
6.3. Results for the Direct Calculation Model Validation ... 110
7. Summary, Conclusions and Discussion ... 112
7.1. Summary and Conclusions ... 112
7.2. Discussion ... 114
7.3. Future Work ... 116
APPENDICES ... 119
Appendix I. CO2 Emissions by Means of Transport ... 119
Appendix II. Definition of Ice Classes for Different Institutions ... 120
Appendix III. Resolution of Equations ... 125
a) Hull Angles Calculation ... 125
b) Resolution of the Euler Equations ... 127
Appendix IV. Properties of the Standard Profiles ... 129
Appendix V. Characteristics of the Impact for the Worst Scenario ... 131
Appendix VI. Design Space for Different Situations ... 132
a) Design Space for each Profile Type ... 132
b) Design Space for Security Coefficient ... 135
c) Sample Vessel DCM Optimization ... 137
Appendix VII. Sea Ice Nomenclature ... 140
References ... 142
4
Figure 1. Value of extra EU countries trade in goods (left) and tonnes (right), by mode of transport, between 2002 and 2019 (% of total) (Eurostat, 2020). ... 14 Figure 2. Total anthropogenic GHG emissions (GtCO2 eq/yr) by economic sectors. The circle shows direct
GHG emission shares (in % of total anthropogenic GHG emissions) from electricity and heat production are attributed to sectors of final energy use. ‘Other Energy’ refers to all GHG emission sources in the energy sector other than electricity and heat production (IPCC b, 2014). ... 15 Figure 3. Direct GHG emissions of the transport sector (shown here by transport mode) rose 250 % from
2.8 Gt CO2eq worldwide in 1970 to 7.0 Gt CO2eq in 2010 (IPCC, 2014). ... 15 Figure 4. General arrangement of the profile of the ship ‘M/S EIRA’ (Jumeau & Riska, 2018) ... 19 Figure 5. Features of the selected vessel: ‘M/S EIRA’ (ESL Shipping, 2020;
https://www.eslshipping.com/fleet/ships/m-s-eira). ... 20 Figure 6. Determination of the geometric parameters of the hull. If the ship has a bulbous bow, then ϕ1=
90º (TRAFI, 2016). ... 23 Figure 7. Ice load distribution on a ship's side (TRAFI, 2016). ... 25 Figure 8. Definition of the frame span (left) and frame spacing (right) for curved members (TRAFI, 2016).
... 25 Figure 9. Different regions for the ice strengthening defined by the FSICR (TRAFI, 2016). ... 26 Figure 10. Sketch of the approximation of the ice belt in the bow region of a ship to the idealized simplified
flat panels. The ice belt in the bow region of the ship is the red area, which is the only area considered in the ice strengthening in ice class ships. In the idealization of two flat panels (each of them being one side of the vessel), they are fully reinforced with strengthened members. ... 27 Figure 11. Sketch for the calculation of the maximum shear force (𝑄) on the web frame (TRAFI, 2016).
... 32 Figure 12. Hull angles definition, unified from IACS, C. G. Daley and FSICR (adapted from IACS, 2019).
... 34 Figure 13. Representation of local angles for the collision between the ship (left) and the ice floe (right) in
3D. ... 35 Figure 14. Definition of main dimensions of the sample ice floe (adapted from Jumeau & Riska, 2018). 35 Figure 15. Representation of the ship's shape and axes to develop the impact model (adapted from Popov
et al. 1967). ... 37 Figure 16. Diagram of impact taking translation, crushing and bending into account. Cross section of the
ship and the ice floe with a vertical plane containing the hull’s normal vector (adapted from Popov et al., 1967). ... 38 Figure 17. Representation of a beam on elastic foundation (adapted from Hetényi, 1979). ... 38 Figure 18. Collision point distances (𝑥𝑝, 𝑦𝑝, 𝑧𝑝) to the centre of gravity of the ship (Os) and floe (Oif; 𝑥𝑝2,
𝑦𝑝2, 𝑧𝑝2) and ice plate approach to the finite beam (blue: approached beam; black: original floe) (adapted from Jumeau & Riska, 2018). ... 39 Figure 19. Sketch of the collision point geometry and direction cosines of the ship (Daley, 1999). ... 40 Figure 20. Sketch of the collision point geometry and direction cosines of the ice floe (Dolny, 2018). ... 40 Figure 21. Nominal contact geometry during the collision of the ship with an ice floe corner. The impact is
assumed to be symmetric respect with the diagonal axis of the floe, with thickness enough to keep a triangular area for all the studied cases and without taking the curvature of the ship into account (Daley, 2000). ... 43 Figure 22. Simple representation of the framing system on the hull side of a ship. Ice stringers in the
direction of the ships’ length and ice transverse frames in the direction of the ships’ depth (Jumeau &
Riska, 2018). ... 48 Figure 23. Sketch of the process of impact between ship and ice. Triangular crushed area on the ice's corner
and bending forces which might produce the fracture of the ice floe (Daley, 2000). ... 48 Figure 24. Ice load patch configuration, the width of the load patch area being in the direction of the ship’s
length and its height in the direction of the ships’ depth. Evolution with time of the load patch (left):
1) Load patch when 𝑤 < 𝑠; 2) Load patch when 𝑤 = 𝑠; 3) Load patch when 𝑤 > 𝑠; Load division in two cases when the framing configuration allows a load patch area 3 (right): case 1) rectangular load, green triangles are excluded and its load is supported by the next frame; case 2) Triangular load (dapted from Jumeau & Riska, 2018). ... 49
5
a simply supported frame (adapted from Jumeau & Riska, 2018). ... 51 Figure 27. Idealization of the moment produced by a partially distributed varying (triangular) load on a
simply supported frame (adapted from Jumeau & Riska, 2018). ... 51 Figure 28. Ice load distribution on a fixed frame at both ends when the horizontal dimension of the load
patch area is greater than the frame spacing (adapted from Jumeau & Riska, 2018). ... 52 Figure 29. Idealization of the moment produced by a uniformly partially distributed (rectangular) load on
a frame fixed at both ends (adapted from Jumeau & Riska, 2018). ... 52 Figure 30. Idealization of the moment produced by a partially distributed varying (triangular) load on a
frame fixed at both ends (adapted from Jumeau & Riska, 2018). ... 53 Figure 31. Definition of the main parameters and dimensions of a bulb flat profile (adapted from UAHE,
2007). ... 55 Figure 32. Definition of the main parameters and dimensions of commercial L profiles (adapted from
UAHE, 2007). ... 56 Figure 33. Definition of main parameters and dimensions of a custom-built T profile. ... 56 Figure 34. Parameters definition for a panel and the footprint created by a partially concentrated load
(adapted from Hughes & Paik, 2010). ... 58 Figure 35. Load patch on the shell plate due to impact against a wedge shaped ice floe. Left: when the frame
spacing is larger than the width of the load patch 𝑊 < 𝑠. Right: when the frame spacing is smaller than the width of the load patch 𝑊 > 𝑠. ... 60 Figure 36. MATLAB code performance for the process of hull's weight optimization. ... 62 Figure 37. Comparison between the hypothetic bow region of a real ship and the idealized dimensions of
the flat panels (blue broken line). ... 66 Figure 38. Maps of linear trends (in ºC per decade) of Arctic (a, c) and Antarctic (e, g) sea surface
temperature (SST) for 1982−2017 in March (a, e) and September (c, g). (b, d, f, h) same as (a, c, e, g), but for the linear trends of sea ice concentration (in % per decade). Stippled regions indicate the trends that are statistically insignificant. Dashed circles indicate the Arctic/Antarctic Circle. Beneath each map of linear trend shows the time series of SST (area-averaged north of 40º N/ south of 40º S) or sea ice extent in the northern/southern hemisphere. Black, green, blue, orange, and red curves indicate observations, Coupled Model Intercomparison Project Phase 5 (CMIP5) historical simulation, Representative Concentration Pathway (RCP)2.6, RCP4.5, and RCP8.5 projections respectively; shading indicates ± standard deviation of multi-models (IPCC, 2019). ... 68 Figure 39. Arctic routes for shipping: Northeast Passage (orange), Northwest Passage (red), Northern Sea
Route (white broken line) and Trans-Polar Sea Route (dark blue). ... 70 Figure 40. Model basin (CEHINAV) of Naval Architecture Department of Technical University of Madrid,
in Madrid (Spain). In the image, boxes containing the artificial ice are found at both sides, prepared for the experimentation. Fresh water around 15 ºC (𝜌 = 1000 kg/m3). ... 73 Figure 41. Different ice patch coverage for the towing tank and propulsion tests in the confined zone (25 x
3.8 m). From top to bottom: 30 %, 45 % and 60 %. For the top coverage only big blocks have been used because the number of small blocks was too low. Both paraffin wax block sizes are used for the latter cases. ... 74 Figure 42. Wooden model of the B.I.O. Hespérides built by CEHINAV for the experimental tests in the
model basin. ... 75 Figure 43. Carriage-model joint system during the experimentation in simulated ice. Main image:
installation inside the model; yellow-bordered image: detail of the Cardan system; bottom-right image: joint system from the outside. ... 76 Figure 44. Virtual representation of a test configuration. The carriage jointly to the model is shown moving
through the simulated ice with paraffin wax blocks towards the end of the confined zone. Carriage model courtesy of CEHINAV. ... 77 Figure 45. Model running jointly with the carriage during a towing tank test with artificial ice. Both block
types are found in the image with the black stickers to later determine their positions. ... 78 Figure 46. Ice resistance over time for the model obtained through isolated impact tests at a speed of 0.222
m/s. ... 78
6
m/s. ... 79 Figure 49. Impact capture from the cameras situated right opposite the bow of the model (impact’s
coordinates) and from an aerial view (block orientation). ... 80 Figure 50. Evolution through time of the displacement and its different components in the impact's direction
during the collision for the basic scenario. The highest value of the components of the displacement is due to bending (adapted from Jumeau & Riska, 2018). ... 85 Figure 51. Evolution through time of the contact force and bending force during the collision for the basic
scenario. Note how the contact force (blue) is higher than the force needed to break the ice floe (fracture force, red) at the end of the impact, when it is stabilized and reaches its maximum value.
However, the vertical component of the contact force (bending force, green) does not surpass the value of the fracture force at any point of time, meaning that the floe does not collapse (adapted from Jumeau & Riska, 2018). ... 86 Figure 52. Evolution through time of the impact’s velocity divided into its different components in the
impact's direction during the collision for the basic scenario. The velocity of the ship is transmitted to the ice floe, which experiments different effects along the time until it equalizes the value of the ship’s speed (adapted from Jumeau & Riska, 2018). ... 86 Figure 53. Influence of the ship’s speed on the contact force for the basic scenario. The bending force (blue)
remains under the fracture force curve (grey) for 5 knots, meaning that the ice floe does not break and the model is valid for the studied cases (adapted from Jumeau & Riska, 2018). ... 87 Figure 54. Influence of the waterline angle on the contact force for the basic scenario. The higher the
waterline angle, the higher the produced force during the impact until a moment in which the floe breaks (adapted from Jumeau & Riska, 2018). ... 87 Figure 55. Influence of the sheer angle on the contact force for the basic scenario. There is a clear decrease
of the contact force with the augmentation of the sheer angle or the reduction of the buttock angle (adapted from Jumeau & Riska, 2018). ... 88 Figure 56. Influence of the ice floe thickness on the contact force for the basic scenario. In this case, the
fracture force changes since it is directly dependent on the ice thickness. The contact force increases with a smooth slope, as does the fracture force which increases as an exponential function. With small thicknesses the ice floe fractures, increasing its resilience with the augmentation of the thickness until the force needed to be applied during the impact is higher than the generated bending force, thus the floe remains intact (thicknesses above 0.9 m) (adapted from Jumeau & Riska, 2018). ... 88 Figure 57. Influence of the ice floe length on the contact force for the basic scenario. The higher the length,
the higher the contact force. The floe breaks with a length slightly above the selected value for the ice floe length to be used in the calculation. Since the model does not consider ice breaking, the values of the contact force correspondent to values of bending force above the value of the fracture force cannot be trusted (adapted from Jumeau & Riska, 2018). ... 89 Figure 58. Influence of the ice floe width on the contact force for the basic scenario. The influence of the
ice floe width follows a similar trend to that of the ice floe length. The higher the width, the higher the contact force. The same considerations are taken into account if the floe breaks. ... 89 Figure 59. Influence of the ice floe edge opening angle on the contact force for the basic scenario. The trend
for this parameter follows an ‘S’ shaped curve. Larger ice edge opening angles provide larger contact areas. Since the contact force is dependent on the contact area, it rises with the increase of the ice edge opening angle. The change in the mass of the ice floe due to a change in the contact force has not been taken into account (adapted from Jumeau & Riska, 2018). ... 90 Figure 60. Influence of the pressure-area exponent on the contact force for the basic scenario. The variation
of the 𝑛 exponent throughout the typical values it usually adopts shows a diminution of the contact force as the pressure-area exponent grows. This trend opposes the results shown in experiments carried out by other authors and is extensively discussed in the final chapter (adapted from Jumeau &
Riska, 2018). ... 90 Figure 61. Influence of the ice load application point or load patch location on the maximum bending
moment produced on a simply supported frame for the basic scenario and the structural configuration of the sample vessel. The bending moments obtained when applying a rectangular (blue) and triangular (orange) load on a simply supported frame tend to have a maximum around the mid-span
7
Figure 62. Influence of the ice load application point or load patch location on the maximum bending moment produced on a fixed frame at both ends for the basic scenario and the structural configuration of the sample vessel. The three curves shown in this figure are calculated as the sum of the bending moments obtained through the application of the triangular and rectangular loads for each situation (left end, middle beam and right end). The highest value of these three curves is selected as the maximum bending moment for fixed frames, coincident with situation 1. This value of maximum moment is reached around the mid-span of the frame, at a value between 1.2-1.4 m from the right end (adapted from Jumeau & Riska, 2018). ... 91 Figure 63. Influence of the ice load application point or load patch location on the maximum averaged
bending moment produced on an averaged simply supported and fixed frame for the basic scenario and the structural configuration of the sample vessel. As shown in the preceding graphs, the value of the load patch location which gives the maximum bending moment is different for each type of frame support. Thus, the average bending moment has been calculated by using the values of the bending moment of the two supporting systems for each load patch location, instead of the simple average of their maximum bending moments (which would give a wrong value). This approach gives a maximum average bending moment at around mid-span of the frame (1 m) (adapted from Jumeau & Riska, 2018). ... 92 Figure 64. From whole design space to feasible designs for the basic case and a simply supported frames.
The instability criteria are not considered here. ... 104 Figure 65. From whole design space to feasible designs for the basic case and a simply supported frames.
Many designs have been removed from the latter graph due to the fact that they do not fulfil the instability criteria. ... 105 Figure 66. Pareto front on the feasible designs for the basic scenario using simply supported frames
assumption. The three selected designs are pointed on the Pareto front (purple = most resistant design;
grey = light-resistant design; orange = lightest design). ... 106 Figure 67. Pareto front on the feasible designs for the basic scenario using fixed frames assumption. The
three selected designs are pointed on the Pareto front (purple = most resistant design; grey = light- resistant design; orange = lightest design). ... 106 Figure 68. Pareto front on the feasible designs for the basic scenario using maximum averaged bending
moments. The three selected designs are pointed on the Pareto front (purple = most resistant design;
grey = light-resistant design; orange = lightest design). ... 107 Figure 69. Pareto front on the feasible designs for the worst scenario using simply supported frames
assumption. The three selected designs are pointed on the Pareto front (purple = most resistant design;
grey = light-resistant design; orange = lightest design). ... 107 Figure 70. Pareto front on the feasible designs for the worst scenario using fixed frames assumption. The
three selected designs are pointed on the Pareto front (purple = most resistant design; grey = light- resistant design; orange = lightest design). ... 108 Figure 71. Pareto front on the feasible designs for the worst scenario using averaged maximum bending
moments. The three selected designs are pointed on the Pareto front (purple = most resistant design;
grey = light-resistant design; orange = lightest design). ... 108 Figure 72. Pareto fronts of all design spaces obtained for the basic design scenario under the three
supporting system assumptions. A hypothetical Pareto front of the whole considered cases would be a mix of these curves. The optimal approach would delimit the designs closer to the axes titles on the graph. A more conservative approach would include those designs that are closer to the legend on the graph. Designs with the same weight correspond to the same, or very similar structural configuration.
The best of the optimal designs are those that are the lightest and are presented within the three Pareto fronts. ... 109 Figure 73. Pareto fronts of all design spaces obtained for the worst design scenario under the three
supporting system assumptions. A hypothetical Pareto front of the whole considered cases would be a mix of these values. The optimal approach would delimit the designs closer to the axes titles on the graph. A more conservative approach would include those designs that are closer to the legend on the graph. Designs with the same weight correspond to the same, or very similar structural configuration.
8
Figure 75. Proposed ice load model for ice stringers. The load patch on the hull plate is shown for two situations and beneath each of them, their correspondent ice load are idealized. When the structural configuration consists of frames separated by more than the width of the load patch (a), the entire load is applied on the ice stringer. This load is applied to the length of the stringer in contact with the load patch (𝑙𝑖𝑠). Then, the ice load applied to the ice stringer (c) is the sum of: a rectangular area within the base of the triangular load patch in contact with the stringer (dark blue area, a and c); the rest of area belonging the base of the triangle, which is not directly in contact with the stringer (red triangles, a) but it is uniformly distributed over the length in contact (red rectangle, c); and a triangular area (light blue, a) correspondent to a varying load applied to the frame (light blue triangle, c). The same occurs when the structural configuration consists of frames which are at a distance lower than the width of the load patch (b, d). In this case, the ice load is partially shared (green triangles, b) with the adjacent ice stringer, since ice stringers are assumed to support the load enclosed between the two transverse frames limiting their length. This means that the area not directly in contact with the length of the stringer is smaller, thus the height of its distributed area over the beam (red rectangle, d). The same approaches for direct design of ice stringers could be used in all possible cases, taking account of the particularities of the ice load when the position of the ice stringer changes in depth or the frame spacing is smaller. ... 117 Figure 76. Typical ranges of direct CO2 emissions per passenger kilometre and per tonne-kilometre for
freight, for the main transport modes when fuelled by fossil fuels including thermal electricity generation for rail (IPCC, 2014). ... 119 Figure 77. Illustration of hull areas on a round bilge form ship with an ice knife, defined according to
ASPPR (Transport Canada, 1995). ... 120 Figure 78. Russian Register hull regions for ice strengthening of ice class ships: a) Ships designed for both
bow- and stern-first year ice operation; b) ships designed only for stern-first year ice operation (RS, 2020). ... 121 Figure 79. Russian Register hull regions for ice strengthening of Arctic double acting ships with ice class
mark Icebreaker in the class notation (RS, 2020). ... 122 Figure 80. Hull area extents of the strengthened regions for Polar Class vessels (IACS, 2019). ... 124 Figure 81. Representation of the hull angles of the vessel: left) water plane; middle) section plane; right)
profile plane (Jumeau & Riska, 2018). ... 125 Figure 82. Representation of the normal angle to the hull in the waterplane (left) and in the section plane
(right) (Jumeau & Riska, 2018). ... 126 Figure 83. Evolution over time of the displacement and its different components in the impact's direction
during the collision for the worst scenario. ... 131 Figure 84. Evolution over time of the impact’s velocity divided into its different components in the impact's
direction during the collision for the worst scenario. ... 131 Figure 85. Evolution over time of the contact force and bending force during the collision for the worst
scenario. Note how the contact force (blue) is higher than the force needed to break the ice floe (fracture force, red). However, the vertical component of the contact force (bending force, green) does not pass the value of the fracture force at any point of time, meaning that the floe does not collapse.
... 132 Figure 86. Whole design space for bulb flat profiles using the basic scenario and a simply supported frame.
No instability criteria are considered. Total number of evaluated designs = 66960. ... 132 Figure 87. Whole design space for commercial L profiles using the basic scenario and a simply supported
frame. No instability criteria are considered. Total number of evaluated designs = 52080. ... 133 Figure 88. Whole design space for custom-built T profiles using the basic scenario and a simply supported
frame. No instability criteria are considered. Total number of evaluated designs = 307520. ... 133 Figure 89. Whole design space for bulb flat profiles using the basic scenario and a simply supported frame.
The designs which do not fulfil the instability criteria have been removed. ... 134 Figure 90. Whole design space for commercial L profiles using the basic scenario and a simply supported
frame. The designs which do not fulfil the instability criteria have been removed. ... 134 Figure 91. Whole design space for custom-built T profiles using the basic scenario and a simply supported
frame. The designs which do not fulfil the instability criteria have been removed. ... 135
9
clearly noted a displacement towards right, increasing the required yield stress of the designs. This displacement is larger for the designs which are further from the ordinates axis. ... 135 Figure 93. Design space zoomed for the basic case using the simply supported frames approach. Yellow
points are the designs considered in the thesis for all profile types (bulb flats, L and T profiles). Blue, black and green points are the same designs, but using a security coefficient equal to 2 (2𝐹𝑚𝑎𝑥). It is clearly noted a displacement towards right, increasing the required yield stress of the designs. This displacement is larger for the designs which are further from the ordinates axis. ... 136 Figure 94. Design space for the basic case using the simply supported frames approach. Yellow points are
the designs considered in the project for all profile types (bulb flats, L and T profiles). Blue, black and green points are the same designs, but using a security coefficient equal to 2 (2𝐹𝑚𝑎𝑥). It is clearly noted a displacement towards right, increasing the required yield stress of the designs. This displacement is larger for the designs which are further from the ordinates axis. Almost all the lightest design considered in the project do not appear in the feasible design space. However, most of the most resistant designs are still in the range of feasible designs. ... 136 Figure 95. Feasible designs for the ‘M/S EIRA’ configuration (𝑠=0.4 m; 𝐿=2 m) for the basic scenario and
simply supported frames assumption. ... 137 Figure 96. Feasible designs for the ‘M/S EIRA’ configuration (𝑠=0.4 m; 𝐿=2 m) for the basic scenario and
fixed frames assumption. ... 137 Figure 97. Feasible designs for the ‘M/S EIRA’ configuration (𝑠=0.4 m; 𝐿=2 m) for the basic scenario and
averaged supporting system assumption. These graphs contain almost the same points, thus are the same designs. The difference between them is that they have a different capacity to withstand impact depending on the bending moment, that is, the supporting assumption. This means that the whole group of points moves towards right or left. ... 138 Figure 98. Feasible designs for the ‘M/S EIRA’ configuration (𝑠=0.4 m; 𝐿=2 m) for the worst scenario and
simply supported frames assumption. ... 138 Figure 99. Feasible designs for the ‘M/S EIRA’ configuration (𝑠=0.4 m; 𝐿=2 m) for the worst scenario and
fixed frames assumption. ... 139 Figure 100. Feasible designs for the ‘M/S EIRA’ configuration (𝑠=0.4 m; 𝐿=2 m) for the worst scenario
and average supporting system assumption. These graphs contain almost the same points, thus are the same designs. The difference between them is that they have a different capacity to withstand impact depending on the bending moment, that is, the supporting assumption. This means that the whole group of points moves towards right or left. ... 139 Figure 101. Open drift (floating ice in which the ice concentration is 4/10 to 6/10; left) and very open drift
(floating ice in which the concentration is 1/10 to 3/10 and water preponderates over ice; right) ice in Denmark, according to Sea Ice Nomenclature (WMO, 2014). ... 140 Figure 102. Ice patch (an area of floating ice less than 10 km; left, Denmark) and brash ice (accumulations
of floating ice made up of fragments not more than 2 m across, the wreckage of other forms of ice;
right, Japan), according to Sea Ice Nomenclature (WMO, 2014). ... 140 Figure 103. Ice cake (floating ice less than 20 m across; left, Germany) and medium first year ice (sea ice
of not more than one winter's growth, developing from young ice, with thickness 70-120 cm; right, Canada), according to Sea Ice Nomenclature (WMO, 2014). ... 140 Figure 104. Small ice floes (any contiguous piece of sea ice 20-100 m across; left, Canada) and level ice
(sea ice which has not been affected by deformation; right, Sweden), according to Sea Ice Nomenclature (WMO, 2014). ... 141 Figure 105. Ice ridge concentration (concentration of all kinds of sea ice piled haphazardly one piece over
another to form an uneven surface; left, Japan) and iceberg (massive piece of ice of greatly varying shape, protruding more than 5 m above sea-level, which has broken away from a glacier and which may be afloat or aground; right, US), according to Sea Ice Nomenclature (WMO, 2014). ... 141
10
Table 1. Known parameters of the vessel ‘M/S EIRA’ (adapted from Jumeau & Riska, 2018). ... 19
Table 2. Main parameters needed to determine the engine output of the ship, according to TRAFI (2016). ... 23
Table 3. Values of 𝐾𝑒 for conventional propulsion systems (TRAFI, 2016). ... 24
Table 4. Values of coefficients for the determination of 𝐶1 and 𝐶2 (TRAFI, 2016). ... 24
Table 5. Values of ℎ𝑖 and ℎ for the different ice classes (TRAFI, 2016) ... 27
Table 6. Values of 𝑎 and 𝑏 to calculate 𝐶𝑑 for different hull regions (TRAFI, 2016). ... 28
Table 7. Values of 𝐶𝑝 for different hull regions (TRAFI, 2016). ... 28
Table 8. Values of la for different structural elements (TRAFI, 2016). ... 28
Table 9. Values of 𝑚0 for different boundary conditions (TRAFI, 2016). ... 30
Table 10. Values of factors 𝛼 and 𝛾 (TRAFI, 2016). ... 33
Table 11. Features and parameters to define the ice floe according to the model (Jumeau & Riska, 2018). ... 36
Table 12. Calculation of the section modulus (𝑍) of a bulb flat profile. ... 55
Table 13. Calculation of the section modulus (𝑍) of a custom-built T profile. ... 57
Table 14. Parameters of the ship needed to calculate the contact force. ... 63
Table 15. Parameters of the ice floe needed to calculate the contact force. ... 63
Table 16. Parameters of the structural configuration and the features of the impact to calculate the contact force. ... 63
Table 17. Main dimensions of the CEHINAV’s model basin in Madrid. ... 73
Table 18. Physical and mechanical properties of the paraffin wax blocks. Correspondence with real ice floes size. ... 74
Table 19. Real vessel and model characteristics. ... 75
Table 20. Experimental matrix for the resistance tests with simulated ice. ... 76
Table 21. General input data to determine the hull scantlings through the FSICR. Data regarding the hull shape, propeller structural configuration and other features is shown. ... 81
Table 22. Output data for the calculation of the hull scantlings through the FSICR. Values of the parameters to calculate the engine output, ice pressure and ice load. ... 82
Table 23. Output data for the calculation of the hull scantlings through the FSICR. Values of the parameters to calculate the properties of the shell plate, transverse frames and ice stringers. ... 83
Table 24. Output data for the calculation of the hull scantlings through the FSICR. Values of the parameters to calculate the features of the web frames and the total weights. ... 84
Table 25. General input data to calculate the contact force during the impact, the bending moment and the resulting structural configuration. ... 92
Table 26. General output data for the model to calculate the contact force. ... 94
Table 27. Results of the contact force calculation and load patch for the basic scenario and simply supported frames. Structural configuration of the selected potential designs. ... 95
Table 28. Results of the contact force calculation and load patch for the basic scenario and fixed frames. Structural configuration of the selected potential designs. ... 96
Table 29. Results of the contact force calculation and load patch for the basic scenario and averaged simply supported and fixed frames. Structural configuration of the selected potential designs. ... 97
Table 30. Results of the contact force calculation and load patch for the worst scenario and simply supported frames. Structural configuration of the selected potential designs. ... 99
Table 31. Results of the contact force calculation and load patch for the worst scenario and fixed frames. Structural configuration of the selected potential designs. ... 100
Table 32. Results of the contact force calculation and load patch for the worst scenario and averaged simply supported and fixed frames. Structural configuration of the selected potential designs. ... 101
Table 33. Summary of weights and required yield stress for the designs calculated through the DCM and comparison to the weight obtained through the FSICR. ... 103
Table 34. Potential weight reduction of the bow region compared to the weight calculated through the FSICR. ... 103
Table 35. Input/output data for the contact force model and the towing tank test at a speed of 0.222 m/s. Impact 2. ... 110
11
Impact 3. ... 111 Table 38. Input/output data for the contact force model and the towing tank test at a speed of 0.533 m/s.
Impact 6. ... 111 Table 39. Input/output data for the contact force model and the towing tank test at a speed of 0.533 m/s.
Impact 10. ... 111 Table 40. Categories based upon the purpose for which a vessel is designed according to ASPPR (Transport
Canada, 1995). ... 120 Table 41. . Russian Register ice classes and their descriptions, depending on the vessel operational area
(RS, 2019). ... 121 Table 42. Hull strengthened regions required for ships designed for both bow- and stern-first year ice
operation (RS, 2020). ... 122 Table 43. Russian Register hull strengthened regions required for ships designed for only stern-first year
ice operation (RS, 2020). ... 123 Table 44. Russian Register hull strengthened regions requirements of Ice Classes, Arctic and Icebreaker
vessels (RS, 2016). ... 123 Table 45. Polar Class classification and description (IACS, 2016). ... 124 Table 46. Properties of the angle profiles (Lp) used for the weight estimation through the direct calculation
method, adapted from AENOR (UAHE, 2007). ... 129 Table 47. Properties of the bulb flat profiles (Bp) used for the weight estimation through the direct
calculation method, adapted from AENOR (UAHE, 2007). ... 130
12
Every single stage in life always comes to an end. This thesis represents the end of not only my master’s degree but also my life as a student during which I have enjoyed some of the best moments of my life and, I have to say, some of the most difficult.
I would like to thank all the people I have met during my years as a student: the professors who have taught me what I know today and the friends who have given me wonderful memories.
Thanks to my professors during the first year of my master’s degree in Spain (UPCT), who have enabled me to be self-sufficient and better prepared for professional life.
Thanks to the professors I have had during the second year of my master’s degree in Norway (NTNU), to whom I owe much of the acquired knowledge used in this master thesis. Many thanks to Professor Bjørnar Pettersen, for helping me during the first stages of the thesis.
Many thanks to Carolyn Harrison Ganberg, for revising the thesis in search of any mistakes I may have made during the writing of these lines.
Many thanks to all my friends, who have supported me during the time I have spent writing this document. Especially to Simón Carrillo Segura, who has contributed towards some technical parts of the optimization program; and to Pablo Romero Tello, for his continuous advice and support.
Special thanks to my supervisors Kaj Riska and Jose Enrique Gutiérrez Romero; the former for providing the method used in the optimization process, giving insight and motivation to do this thesis and for his wise advise, and to the latter for following the development of my projects, his support, advice and inexhaustible trust during the time I have known him and for introducing me to the world of research and the experimental field.
Lastly, with all my heart I give thanks to my family, especially my parents, for their continuous encouragement during my daily life and their understanding for the time I needed during the writing of this thesis.
Remarks:
I wish to thank the CEHINAV Research Group, who provided facilities at UPM in order to conduct the experimental tests. Special thanks to Luis Pérez Rojas, Ricardo Abad and a special mention to Juan Luis Chacón Gómez for providing their assistance in the realization of the tests.
Thanks to CIMNE Naval Group, specially Borja Serván Camas and Julio García Espinosa for their support during the experimentation and the project development. Thanks to Pablo Romero Tello, Jerónimo Esteve Pérez and Juan José Hernández Ortega for their help during the development and preparation of the towing tank tests and to Carlos López Pavón for providing useful material for the experimentation capture system.
Finally, many thanks to the Spanish Ministry of Economy and Competitiveness for funding and making possible the experimental campaign under Grants RTI2018-094744-A-C22, to the NICESHIP team and once again, to José Enrique Gutiérrez Romero, for including me.
13
The rising trend towards globalisation and the increases in the transport of freight has resulted in connections being established between almost every point on the planet. Sea transport is the most in-demand means of freight transport and, given the growing opportunities for both exploitation and protection by stakeholders in the Arctic area, ships now venture further into the higher latitudes on both sides of the Equator. Polar navigation (Arctic and Antarctic) requires more powerful ships with increased hull strengthening capable of overcoming the additional resistance presented by sea ice and able to withstand the impacts of the many ice formations that might appear.
The increase in capability of the ship to overcome the resistance whilst moving through the ice infested waters plus the extra weight of its structure due to the higher strengthening, requires greater power. More power implies heavier engines and adequate strengthening involves significant amounts of steel for the construction of the ship. Consequently, the added requirements needed by ice-going vessels entail higher emissions of pollutants into the atmosphere, greater initial investment for shipbuilding and huge operational costs.
Vessels are usually classified by institutions called Classification Societies. The construction of polar class ships must be in accordance with certain special sets of rules that define the required features of ice capable vessels. The creation of these regulations is based on the experience gained throughout the years by studying ice model tests, ice navigation features and damage to ships when navigating through ice. The Finish-Swedish Ice Class Rules (FSICR) are most commonly used to design the structure of polar vessels. These rules have been used to calculate the hull scantlings of a sample ship through regulations for the most strengthened part of it: the bow region. In order to optimize and obtain a decrease in the total weight of these ships whilst maintaining an adequate grade of hull strengthening, the hull scantlings of the same sample vessel are obtained by means of a direct calculation method. Assuming an impact between a ship and an ice floe, the resultant contact force of the collision is calculated and with it, the hull scantlings and the weight of the bow region. The results estimate a decrease in the weight of the bow region of the ship of up to 40.26 % depending on the approach used to calculate it. The optimization method developed is shown to be effective.
Knowing the real resistance a ship has to face when navigating in ice is the key factor in determining the necessary power and size of the engine that is required. Too small an engine are not sufficient to propel the ship through the ice conditions encountered during the voyage. An engine larger than required results in having to move more weight than needed, higher initial and operational costs and more pollution. Some experiments are conducted to determine the ship’s resistance in floating ice in order to provide data to validate a numerical tool. The experiments are carried out in a traditional basin facility and they consist of towing tank tests of a ship’s model for different concentrations of artificial ice simulated by the use of paraffin wax. The results of the resistance obtained in the experiments in the presence of simulated ice turns out to increase with the concentration of paraffin wax blocks and the model’s speed.
Finally, some of the tests results are used to try to validate the direct calculation method and give an approach to the estimation of the ship’s model resistance. However, the big differences in the assumptions provide a huge deviation in the results, and are unable to validate the direct calculation model under the proposed conditions.
Keywords: weight optimization, hull strengthening, ice impact, FSICR, ice-going vessels, Arctic navigation, ship-ice interaction, ships’ ice resistance.
1. Introduction
As early human societies began to develop beyond a subsistence level lifestyle giving rise to the production of surplus goods, the increasing complexity of human interaction and communication led to an exchange of goods and services. Trading started as the simple exchange of one product or service for another and ultimately to the invention of common currencies that could be used in the exchange of goods and services from a wider area. Trading activities necessitated the movement of freight between communities and this was initially accomplished by the development of trade routes and the use of haulage animals giving rise to our modern transport systems. However, more importantly, many ancient trading societies were located close to the sea or rivers and these people quickly realized the advantages of moving freight by water. This led to the invention of the ship, one of our oldest forms of transport.
The earliest historical records of waterborne vessels date back as far as 4000 B.C. Originally a boat could be as simple as a single log or several logs tied into a basic raft. Ship design continued to evolve throughout history from wooden ships propelled by oars and sails to steel vessels propelled by steam and current engines or electrical batteries (Encyclopaedia Britannica, 2020).
Nowadays, freight transport is carried out by road, rail, air or sea. This is also applicable to passenger transport. The highest volumes of movement of freight worldwide are those carried out by ships, due to lower costs. Sea transport accounted for around half of all goods traded between the European Union (EU) and the rest of the world in 2019 (Eurostat, 2020).
Figure 1. Value of extra EU countries trade in goods (left) and tonnes (right), by mode of transport, between 2002 and 2019 (% of total) (Eurostat, 2020).
Most vehicles used for transport obtain their energy for movement from the combustion of fossil fuels. This combustion liberates CO2 and other elements known as greenhouse gases (GHG), which actively contribute to the climate change and global warming accelerated by human activities. According to IPCC (2014; 2014 b) around 14 % of these emissions are due to transportation (Figure 2), of which 9.26 % correspond to international and coastal shipping (Figure 3).
15
Figure 2. Total anthropogenic GHG emissions (GtCO2 eq/yr) by economic sectors. The circle shows direct GHG emission shares (in % of total anthropogenic GHG emissions) from electricity and heat production are attributed to sectors of final energy use. ‘Other Energy’ refers to all GHG emission sources in the energy sector other than electricity and heat production (IPCC b, 2014).
Figure 3. Direct GHG emissions of the transport sector (shown here by transport mode) rose 250 % from 2.8 Gt CO2eq worldwide in 1970 to 7.0 Gt CO2eq in 2010 (IPCC, 2014).
As shown in Figure 3, the largest proportion of GHG emissions is produced by road transport, followed by waterborne vessels. Although ships produce the second largest amount of pollutant emissions to the atmosphere, the total amount of CO2 emissions per passenger-kilometre and tonnes-kilometre is one of the lowest, just behind rail transportation (see Figure 76). This means that moving the same quantity of freight or the same number of passengers through transport means other than ships or rail would significantly increase the amount of emissions. However, freight volumes and emissions produced by transport are expected to increase by a factor of 3.9 to 2050 (ITF, 2015), which would have an unfortunately significant impact on the environment.
Due to the increase in trade transport and sea transport being the preferred option, marine traffic is becoming increasingly widespread, encompassing most coastal areas worldwide. Furthermore, the increasing global warming accelerated by human activities producing pollutant emissions of GHG are melting larger areas of polar ice extents in summer. This melting is opening up new shipping routes through remote points on Earth such as the Arctic Ocean (IPCC, 2020). As ships navigate through northernmost or southernmost routes, they reach latitudes where additional hazards, notably sea ice, may have to be overcome.
Sea ice is any form of ice found at sea which has originated from the freezing of sea water. Many forms of sea ice can be presented depending on size, origin, concentration, age, stage of development, etc. These forms give a wide number of different definitions for sea ice defined by the World Meteorological Organization (WMO, 2014). If sea ice impacts a vessel navigating in ice covered waters, it can cause severe damage to the structure of the ship.
In order to avoid damage to the hull, ice-going vessels must be designed according to existing rules whose aim is to provide safe ship operation and protection of the polar environment by addressing the risks presented in polar waters. The risks of navigating ice infested waters under extreme climate conditions are wider than only the impact of ice itself: topside icing, the congealing of fluids in different systems due to low temperatures and the inexperience of crew members in polar waters among others. These hazards necessitate special requirements regarding the ship’s structure, power, subdivision and stability, hull strengthening and considerations concerning equipment and navigation among others (IMO, 2014).
16
Due to geographical reasons, countries surrounding Arctic waters started to develop rules appropriate for ice-going ships. Each system of rule is unique attending to design scenarios, ice load and strengthening formulations, structural regions, etc. Some of these rules are briefly described as follows (Daley, 2014):
Finish-Swedish Ice Class Rules (FSICR): developed by the Finnish Transport Safety Agency (TRAFI, Finland) and the Swedish Transport Agency (STA, Sweden) were the first rules for ice strengthened vessels. They were created for ships operating in the Baltic Sea, having 6 different ice classes defined as ice class III, II, IC, IB, IA and IA Super, in order of increased strengthening.
These ice classes apply to ships which need ice breaker assistance and to vessels able to navigate in level ice 1 m thick (mid channel of brash ice). The ice load model is based on empirical pressure results from tests carried out in the Baltic Sea, for which reason they are considered to be sub- Arctic or Baltic rules. The hull strengthening is divided into 3 main regions (bow, mid-body, aft) and 2 subareas within the bow region (fore foot and upper bow ice belt). Hull scantlings are obtained through formulation based on elastic response of bending for plates and frames (TRAFI, 2016).
Arctic Shipping Pollution Prevention Regulations (ASPPR): developed by Transport Canada for ships navigating Canadian Arctic waters. They have 4 ice classes defined as category or CAC 4, 3, 2 and 1, in order of increasing self-independence for navigation in ice. These ice classes correspond to a range of ships operating in transit or controlled icebreaking in first year ice and ships navigating in multiyear ice with no restrictions in operation. The ice load model is based on a model consisting of a combination of heavy ramming and pressure-area effect. There are 4 main regions of hull strengthening (bow, skeg, mid-body/stern, and bottom). Hull scantlings are obtained through formulation based on plastic response of folding plates and bending and shear for frames (Transport Canada, 1995).
Russian Rules (RS): developed by the Russian Maritime Register of Shipping (RS, Russia) for the classification and construction of sea-going ships in Russian waters (Arctic and sub-Arctic).
They have 9 different ice classes defined as Ice 1, 2, and 3 for non-Arctic conditions and Arc 4, 5, 6, 7, 8 and 9 for navigation including Arctic conditions, in order of increasing thickness of ice and extreme conditions of the operational area (Arctic or non-Arctic). In addition, they include 4 icebreaker classes defined as Icebreaker 6 and 7 (8 and 9) in order of increasing capability to overcome extreme ice conditions. The hull strengthening adapted is divided into 10 main regions based on damage surveys: 4 divisions in the longitudinal direction (A or forward, A1 or intermediate, B or mid-ship and C or aft), the 3 parts abaft the bow region being also divided in 4 regions (from top to bottom, I, II, III and IV). These regions vary depending on the ice class and the icebreaking mode of the vessel (bow or stern operation). The ice load model is based on Popov et al. (1967) glancing impact load and Kurdyumov & Kheisin (1976) extrusion model. Hull scantlings are obtained by using equations based on plastic response of folding plates and bending for frames (RS, 2016; 2019; 2020).
Unified Requirements for Polar Class (IACS UR): developed by the International Association of Classification Societies (IACS) with the aim of unifying all requirements of the existing ice class rules, in cooperation with experts from Finland, Canada, Russia and some Classification Societies for ships navigating in ice covered waters (Arctic, Antarctic). They consist of 7 different Polar Classes defined as PC 7, 6, 5, 4, 3, 2 and 1, in order of increasing strengthening for tougher ice conditions. The hull strengthening is divided into 4 regions in the longitudinal direction (bow, bow intermediate, mid-body and stern). Each one of these regions, except for the bow region, is divided into 3 regions in the vertical direction (ice belt, lower and bottom). The ice load model is based on the Popov et al. (1967) glancing model and the pressure-area effect. Hull scantlings are calculated through plastic model for folding plates and bending and shear forces in one end for frames (IACS, 2016; 2019).
17
Features of the hull’s regions and the type of vessel class are shown in detail in Appendix II. Some classification societies also have polar codes, for example the American Bureau of Shipping (ABS), Det Norske Veritas (DNV), Germanischer Lloyd (GL; both of them unified in the DNV- GL rules) among many others. Most classification societies have adopted the IACS rules for vessels in Arctic navigation and multiyear ice and the FSICR for their first year ice classes. Other organizations have developed rules for offshore activities in Arctic conditions, such as the International Organization for Standardization (ISO 19906: Arctic offshore structures) and the American Petroleum Institute (API PR 2N: Planning, Designing and Constructing Structures and Pipelines for Arctic Conditions) (Riska, 2018 b).
As can be deduced from the above description of the ice class rules each institution uses its own model to estimate proper hull scantlings. Conservative security factors are used and increased thicknesses are recommended based on observation of ice-going ships throughout the years. The impact produced by level ice is not usually a risk, since its thickness and properties are included in the design rules. However, risk may be presented when occasionally hitting undetected larger ice floes. Aiming to obtain an adequate approach to the forces exerted by the ice on the hull of ice capable vessels, some models have been developed for the impact between ship and ice. These models are used to estimate the ice load on different structural elements of a ship and to determine the required thicknesses and configuration (distribution of its structural elements), which can be used as a basis for the development of the ice class rules or direct design.
Popov et al. (1967) developed a model which set the basis for the ice class rules of the Russian Maritime Register of Shipping. Popov’s model is used for obtaining ice loads acting on the side of a ship’s hull whilst sailing in ice. Some assumptions are made for the ship and floe in order to simplify the model, such as the ship being symmetric with respect to its centreline and the ice floe being round in shape. The two bodies are considered as rigid bodies with the possibility of a movement range of 6 degree of freedom (DoF), this 3D system being reduced to a simpler 1D system in the normal direction of the impact to the shell. This reduction is done through the use of reduced mass and velocity coefficients in the contact force direction. Then, by using an energy method and a penetration model, the contact or crushing force is calculated. No sliding or friction is taken into consideration.
The complexity of the crushing prompted researchers to devise new tests in order to understand the ice crushing process. Crushing is understood as a non-continuous process including elastic contact, damage to the solid, fracture, re-breaking of trapped ice, and extrusion of granular material. Joensuu & Riska (1989) conducted experimental tests for crushing in Helsinki, at Wärtsilä Arctic Research Centre (WARC) in 1988. They used a high resolution system to measure the pressure forces contained in piezoelectric polyvinylidene fluoride (PVDF) film sensors and a transparent plate to observe the ice-indenter contact. As results of these tests, they observed that the ice in contact with the indenter was thin and line-like. They also saw that the recorded signal had triangular peaks that grew in size when the indentation increased. Daley (1991) created a simple model for crushing that was able to reproduce most of the results obtained by Joensuu &
Riska (1989). His model treated ice edge failure as a hierarchy of failures, each being superseded by the failure of the supporting mechanism and did not contain extrusion considerations.
A number of reports made for the Finish-Canadian joint research team, Daley et al., (1997), focused on the study of ice loads and models for obtaining ice forces and ship response during ramming and shoulder collision, based on the authors’ previous work. They give an overview of the forces and ship motions during ramming and shoulder collision.
Daley (1999; 2001) proposed an energy based collision method for different ice floe shapes and impact types (shoulder, head-on). The method is based on Popov’s energy method, introducing the concept of pressure-area relationship for the indentation on the ice.
18
Bueno (2012) presented a modelling framework in Ship Structures Committee (SSC-465) for modelling impact of sea ice on ships and offshore structures. The model, based on previous elastic-plastic response of structures and fracture mechanics advances, is developed by using the Extended Finite Element Method (X-FEM) and compared to typical FEM analysis techniques. A similar model was previously presented by Daley & Kim (2010) considering structural local plastic deformation in the energy balance.
Dolny (2018) presented in Ship Structures Committee (SSC-473) a direct calculation method for determining the technical safe speed for light ice strengthened vessels operating in ice. The method is based on the Popov et al. (1967) model with the updated idea of pressure-area effects, as presented by Daley (1999; 2001). It gives an update for a software tool to determine safe speed depending on different ice scenarios called Direct Design for Polar Ship (DDePS). This Microsoft Excel based spreadsheet tool uses all the modern collision models found in IACS UR for different impact types and ice floes shapes.
There is a risk of impact with a large ice floe that can cause damage to the hull of vessels navigating in ice covered waters. This risk is reduced by increasing the strengthening of these ships through augmented thicknesses for their structural elements according to a proper ice class.
Ice class regulations tend to be quite conservative at the moment of assigning hull scantlings. This may turn into an excessive increase of steel weight and, consequently, rising pollutant emissions and operational and constructive costs. The second chapter of the report presents a method for hull scantlings calculation through one of the most popular ice class regulations (FSICR) for a sample vessel.
The present thesis aims to use a direct calculation method based on Popov et al. (1967) model and the load patch concept, which is developed throughout the third chapter of the document. This method is used for estimating the contact force produced by a ship impacting an ice floe. This force is used for determining hull scantlings through direct calculation methods for plating and framing. When the direct calculation method is defined, hull scantlings are optimized by using the direct formulation and different hull configuration and framing type. The forth chapter of the report describes a process to determine the maximum potential for weight reduction, and thus a decrease in emissions and cost savings. In addition, the hull scantlings calculated through the FSICR are used to obtain the weight of the vessel for the sake of comparison with that of the direct calculated designs.
Given the importance of the proper determination of the ice resistance for a ship, the last descriptive part of the document gives insight into the state of art research for this topic and presents the experiments carried out in Madrid (Spain) at CEHINAV’s towing tank. These model tests shown in the fifth chapter were conducted for floating ice conditions simulated with artificial ice, using paraffin wax. Some tests for single impact were run in order to obtain data to try to validate the direct calculation model for impact between a ship and an ice floe.
Finally, the results and conclusions deduced for the ship structure, impact model and model validation are presented and discussed in the final part of the thesis.
2. Hull Scantling through Ice Class Regulations
2.1. Sample Vessel: M/S EIRA
In order to address the hull scantling of a ship through any set of rules, some parameters of the ship need to be known. The selected vessel for the hull scantling is the bulk-carrier ‘M/S EIRA’, a vessel of the company ‘ESL Shipping’, shown in Figure 4. This vessel was built in 2001 by Tsuneishi Shipbuilding Co. Ltd, Japan, and currently sails under the flag of Finland for bulk trading between Nordic Countries (Finland, Sweden, Denmark). The vessel was classified by the classification society Lloyd’s Register and constructed using the transverse framing system. Due to the nature of the winters in the geographical area in which the ship is intended to operate, it was built to comply with the ice class IA Super of the Finish-Swedish Ice Class Rules (ESL Shipping, 2020). For this reason it has been selected as a sample ship for the hull scantling calculation and, in addition, for some of the necessary parameters (see Table 1 and Figure 5) used to develop the direct calculation method.
Figure 4. General arrangement of the profile of the ship ‘M/S EIRA’ (Jumeau & Riska, 2018)
Table 1. Known parameters of the vessel ‘M/S EIRA’ (adapted from Jumeau & Riska, 2018).
Parameter Symbol Value (units)
Length over all 𝐿𝑂𝐴 157.00 m
Length between perpendiculars 𝐿𝑝𝑝 148.00 m
Breadth 𝐵 24.60 m
Draught 𝑇 9.03 m
Depth 𝐷 13.00 m
Displacement Δ 26000 t
Sheer angle 𝛾 45º
Waterline angle 𝛼 45º
Frame spacing 𝑠 0.40 m
Frame span 𝐿 2.00 m
Block coefficient 𝐶𝑏 0.85
Water plane coefficient 𝐶𝑤𝑝 0.95
Mid-ship section coefficient 𝐶𝑚 0.99
Yield stress 𝜎𝑦 315 N/mm²
Density of ice steel 𝜌𝑖𝑠 7860 Kg/m3
20
Figure 5. Features of the selected vessel: ‘M/S EIRA’ (ESL Shipping, 2020; https://www.eslshipping.com/fleet/ships/m-s-eira).
21
2.2. Finish-Swedish Ice Class Rules (FSICR)
During the era of wooden sailing ships, ice navigation in high latitudes used to be a seasonal adventure in winter. Ships were able to navigate avoiding ice but not breaking it. When steel, steam and propellers started to be used to build and power ships, ice could be forced to break.
Real winter navigation started in the Great Lakes (USA), in the mid-19th century. The increasing maritime traffic in the area made evident the need of assistance for low ice capable merchant vessels, giving birth to the first icebreakers. The first steam-powered icebreaking ship was the
‘City Boat Nº 1’, built by the city of Philadelphia in 1837. In Europe, the first dedicated metal- hull icebreaker, the ‘Russian Pilot’ appeared in 1864 (Riska & Kämäräinen, 2011). An economically significant scale was reached by the end of mid-19th century, which made it necessary to regulate the construction and use of ships intended for ice. Year-round navigation in the Baltic Sea started in 1877 with the introduction of the ship ‘Express II’ sailing between the ports of Turku and Stockholm (Riska, 2010).
The oldest regulations concerning navigation through ice infested waters (‘Imperial Statutes’) were developed by Finland in 1890, (Finland being a part of Russia at the time). Initially, they were only a set of recommendations related to the construction and fitting out of ships for winter navigation. Since the development of the rules, they have included many updates. In 1920 the first Finish ice class rules for shipping were created in which scantlings were set as some relative increase in the open water scantlings. Later, in 1932, three ice classes were introduced (IA, IB, IC) as well as ice class II corresponding to open water ships and ice class III corresponding to barges. The next significant change came in 1965, with the introduction of the superior ice class IA Super. After having noticed that the strengthening for these ships was too weak based on the evidence of damage caused to ships, a large ice damage survey was carried out. As a result, Finland and Sweden made an agreement and jointly developed the Finish-Swedish Ice Class Rules in 1971, in order to give adequate strengthening to ice-going ships and to manage the maritime traffic in winter. In 1985, the hull rules changed with the introduction of a new idea relating to ice load height. The ice performance requirement changed in 2002, requiring a minimum speed of 5 knots in a brash channel according to the design class. In 2006 the rules were updated with regard to the ice waterlines and in 2008 new machinery rules were introduced. The rules were updated in 2010 in order to streamline the hull rules. The latest update of the rules was made in 2017, to include new azimuthing requirements for operating in ice (Riska & Kämäräinen, 2011;
TRAFI, 2016).
Experiences of winter navigation in the Baltic Sea have been collected throughout the years and safety measures and knowledge have been consequently adopted, as is presented in the rules document ‘Ice Class Regulations and the Application Thereof’, published by the Finnish Transport Safety Agency (TRAFI, 2016). An equivalence between the Finish-Swedish ice classes and other Classification Societies or institutions is found in the guidelines published by TRAFI (2016 b). The rules are hereby presented with this chapter to give an insight into the calculation methodology of the hull scantlings of the selected ship. In order to do that, ice classes, engine output and the procedures for the calculation of the thicknesses for hull members are described as found in the rules. Tables with input values, assumptions and results are further presented in section 6.1.
The document details the regulations on the requirements concerning structure, engine output and other ice navigation considerations for ships belonging to different ice classes, on the methods for determining ice classes and on differences between ice classes. These classes are differentiated in the document found in Section 1.8 of the rules described by TRAFI (2016), as follows:
22
a) Ice class IA Super: ships with such a structure, engine output and other properties that they are normally capable of navigating in difficult ice conditions without the assistance of icebreakers.
b) Ice class IA: ships with such a structure, engine output and other properties that they are capable of navigating in difficult ice conditions, with the assistance of icebreakers when necessary.
c) Ice class IB: ships with such a structure, engine output and other properties that they are capable of navigating in moderate ice conditions, with the assistance of icebreakers when necessary.
d) Ice class IC: ships with such a structure, engine output and other properties that they are capable of navigating in light ice conditions, with the assistance of icebreakers when necessary.
e) Ice class II: ships that have a steel hull and that are structurally fit for navigation in the open sea and that, despite not being strengthened for navigation in ice, are capable of navigating in very light ice conditions using their own propulsion machinery.
f) Ice class III: ships that do not belong to the ice classes referred to in paragraphs a)-e).
Ice class draughts as defined in Chapter 2 of the rules are the upper ice waterline (UIWL), that shall be the envelope of the highest points of the waterlines at which the ship is intended to operate in ice; the lower ice waterline (LIWL), that shall be the envelope of the lowest points of the waterlines at which the ship is intended to operate in ice. They may be a broken line.
As previously mentioned, the selected vessel belongs to the ice class with the highest hull strengthening which is considered by these rules: IA Super. Henceforth, requirements concerning engine output and hull structure are presented for this ice class. Firstly, the required engine output must be calculated for this type of ship being able to navigate in a brash ice channel at a speed of at least 5 knots. Once the engine output and the ice load for the selected ice class are known, the ice pressures applied to the hull produced by a ship of such features and power are determined.
With the ice loads applied to each single member of the hull (plate, frames, stringers and web frames) the whole ship’s scantlings can be calculated, the bow region being the case of studio in this thesis.
2.2.1. Engine Output
The engine output 𝑃 is defined in Chapter 3 of the rules as the total maximum output the propulsion machinery can continuously deliver to the propeller (or propellers). The output of the machinery must be taken as a reduced output of the total power if it is restricted by technical means or any applicable regulations, or increased output if additional power sources are available for propulsion power in addition to the main engine (TRAFI, 2016).
The engine output shall not be less than that determined by the formulation below and in no case less than 2800 kW for ice class vessels IA super. In order to use the formulas proposed by the rules, parameters and dimensions of the ship must be defined as shown in the image and table below.