Á REAS PROTEGIDAS

5 11 | -- |XXXX| |XXXX|ELM1|

-- | |

| |_Compulsory Data Category Keyword(A4) |

|_Optional User Identifier(A2)

6.3. Element Topology Data Record

2 5 7 11 16 21 31 41

- --- -- ---- --- --- |X| | |QPPL| DIFF| |(30)(11,1)(71,1)(72,1)(12,1) - --- -- ---- --- --- |X| | |TUBE| | |(10)(11,3)(71,3)(2)(1)

- --- -- ---- --- --- |X| | |DISC| | |(1)(11)(71)(1)

- --- -- ---- --- --- | | | | | |

| | | | | |

| | | | | (3)Columns 21-80 free format data for | | | | | generating NODE,MATERIAL,and GEOMETRIC | | | | | GROUP NUMBERS. Format(60A1)

| | | | |

| | | | |_(2)Element Group Number(I5) | | | |

Element Topology - ELM* (Data Category 2)

| | | |_(4) DIFF identifier (diffracting plates only)

(1) The element type (always four characters) provides the classification for a particular element, i.e. the number of nodes, and whether material and geometric properties are required. Valid codes for element types are QPPL, TPPL, TUBE, PMAS, PBOY, FPNT, DISC and STUB as shown below:

Geometric Property

(2) The element group number associated with each element is used to divide the elements defining the structure into groups. Groups can be used for plotting and to identify special sets of elements (see The ILID Data Record - Suppression of Irregular Frequencies (p. 54) and The VLID Data Record - Suppres-sion of Standing Waves. (p. 51)), but the group number may be left blank if desired.

(3) Free Format data generation is achieved by specifying several bracketed sets of Topological variables in columns 21-80. The number of bracketed sets is given by

Number of Sets = 1 + (Number of Nodes) + 1 if a Material Group is required

+ 1 if a Geometry Group is required In general we have a format of

N - Number of elements to be generated

N₁ - Starting Node number, Material Group number or Geometric Group number N₂ - Increment of N₁ for each element generated

N₃ - Increment of N₂ for each element generated

Element Topology Data Record

For the i^th element of the N elements generated (whether the set applies to a node number, material or geometric group number) each bracketed set will produce the number

Note

• The nodes defining TPPL and QPPL elements must be ordered in a counterclockwise direction from the perspective of an observer external to the structure.

• In an Aqwa-Line data file,QPPL and TPPL elements which are below the still water line in the Aqwa-Line analysis position must be denoted as diffracting elements by entering the identifier DIFF in columns 12 to 15.

• For structures which cross the waterline, the top row of diffracting plate elements must have their top edges aligned with the still water line (i.e. diffracting plates must not cross the still water line).

6.3.1. The QPPL Element

Quadrilateral pressure plate of zero thickness.

Element generates pressure and hydrostatic forces only.

6.3.2. The TPPL Element

Triangular pressure plate of zero thickness.

Element generates pressure and hydrostatic forces only.

Element Topology - ELM* (Data Category 2)

6.3.3. The TUBE Element

Tubular element with uniform circular cross-section and constant wall thickness.

Forces on this element are calculated using Morison’s equation.

Open TUBE elements are considered to have open ends. The water surface inside the TUBE is at the same level as the surface outside. The transverse added mass is based on the outside diameter, but the axial added mass only uses the cross-sectional area of the TUBE material.

TUBE elements have an axial drag coefficient of 0.016 that cannot be changed.

6.3.4. The STUB Element

Slender tube element. The STUB element differs from the TUBE element in the following respects:

• STUB elements permit tubes of non-circular cross-section to be modeled, by allowing the tube properties (diameter, drag coefficient, and added mass coefficient) to be specified in two directions at right angles.

• Longer lengths of tube can be input, as the program automatically subdivides STUB elements into sections of shorter length for integration purposes.

STUB elements should only be employed if the mean diameter is small compared to the length.

The local axis of the element runs from Node 1 to Node 2 (origin at Node 1). The perpendicular from Node 3 to the local X-axis, together with the local X-axis itself, defines the Xplane, and hence the Z-axis. The local Y-axis forms a right-handed set.

If any Z parameter for a STUB is omitted or set to zero it will default to the equivalent Y value.

Element Topology Data Record

If the STUB area is omitted or set to zero, the program will assume a circular cross-section if diameter Y and diameter Z are equal. If they are unequal, the cross-section is assumed to be rectangular and area will be set to the rectangular cross-sectional area. The area for the STUB element is used to calculate the displaced mass per unit length and buoyancy force. It is also used to calculate the Froude-Krylov force and default added mass. The area for the STUB element is used in the calculation of defaults for drag and added mass coefficients. Although the program will accept any value for area, warnings are issued if the value is greater than 1.05 * rectangular area or less than 0.95 * circular area.

6.3.5. The DISC Element

A circular disc element with no thickness and no mass. The DISC element has a drag coefficient and added mass coefficient in its normal direction. To add mass, the user can define a PMAS element and attach it to the DISC element.

The DISC element has two nodes; the first defines the center of the element and the second gives the normal direction of the element.

The force on a DISC element has two components: added mass force and drag force. As DISC elements have no thickness, the Froude-Krylov force and hydrostatic force are zero. This is different from a TUBE end on which the Froude-Krylov force and hydrostatic force are non-zero and therefore are calculated in Aqwa. The application point of the force is at the centroid of the DISC element when fully submerged, and at the force center computed by the program if partially submerged. The direction of the force on a DISC is parallel to the normal direction of the DISC.

6.3.6. The PMAS Element

Point mess element having internal mass with the center of mass coincident with a given node and specified values of second moments of mass inertia. The PMAS element generates mass forces only.

6.3.7. The PBOY Element

External point buoyancy element without mass. The PBOY element generates hydrostatic displacement forces only.

6.3.8. The FPNT Element

External fluid field point element. This element gives the pressure head amplitude at a specified point in the external fluid domain. When the element is at the water surface, it corresponds to the amplitude of the water surface elevation. Only applicable in Aqwa-Line with a radiation/diffraction analysis is run.

If a hydrodynamic database is imported from a previous run it is not possible to calculate the water surface elevation.

FPNT elements are defined in the LSA axes and move with the structure in which they are defined.

Element Topology - ELM* (Data Category 2)

FPNT elements are subject to symmetry commands.

i.e. 30 elements are generated each with 4 node numbers where Element 1 nodes are 11,71,72,12

Element 2 nodes are 12,72,73,13 Element 3 nodes are 13,73,74,14 etc.

Note

N3 is zero in all cases, which is very common.

Example 2

Element 1: nodes are 11,71; Material Group = 2; Geometry Group = 1

Element Topology Data Record

Element 2: nodes are 14,74; Material Group = 2; Geometry Group = 1 Element 3: nodes are 17,77; Material Group = 2 ; Geometry Group = 1 etc.

Note

N2 (as well as N3) is zero for the material/geometric group number increments, which is very common. This means that all 10 elements will have the same material and geometric prop-erties.

Example 3

For the DISC element, the data (1)(11)(71)(1)

will generate one DISC element as indicated by the number in the first pair of brackets. The centroid position of the disc is defined by the first node number (node 11) and the normal direction of the disc is decided by the vector from the first node (11) to the second node (71). It should be noted that whether the normal vector defined as from node 11 to 71 or from node 71 to 11 has no effect on the results. The last number in the DISC data record is the geometry property group number for this DISC which is to be defined in Geometric Properties - GEOM (Data Category 4) (p. 61) (DISC has no material properties).