Herramientas EDA hardware

The HSM01 was a model of the 112 m INCAT full-scale vessel with a design displacement of 2500 tonne. Based on the size and capabilities of the AMC test facility, the chosen scale ratio was defined as 1/44.8, resulting in a model of length 2.5 m and mass of 27.12 kg. The model was designed to have each demihull split into three segments, the segment cuts being at 40% and 60% of the model length from the transom. The two demihulls and the wetdecks (mounted between the hulls) were joined using transverse aluminium beams. The three segments were connected using aluminium elastic links, strain gauges fitted to these links allowed the vertical bending moments (VBM) to be measured. An outline of the model is presented in Figure 3.1.

Figure ‎3.1: The first AMC-UTas segmented catamaran model HSM01 with its main components and elastic links

Aft wetdeck

Elastic links Centrebow transverse beams

Aft Segment Mid Segment FWD Segment

Centrebow Segment Backbone beams

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The model was constructed using sandwich panels of carbon fibre and Divinycell foam core, whilst the elastic links were fabricated from aluminium square section fitting into a hollow square section backbone beam embedded into each segment. This backbone beam ensured that each segment was rigid and flexibility only occurred at the segment gaps through the elastic links.

The elastic link dimensions were designed to ensure that the whipping vibratory response replicated the full-scale vessel behaviour. Since the 112 m WPC was not built at the time of HSM01 design, the measured modal frequencies of the 86 m and 96 m INCAT catamaran were extrapolated to obtain an estimate of first longitudinal mode whipping frequency based on the 112 m catamaran. Hence, from the similarity scaling, the target modal frequency of the HSM01 was designed to be 13.79 Hz from similarity scaling [50]. As also seen in Table 3.1, following the sea trials of the 112 m WPC, the average frequency was measured to be 2.29 Hz [51], corresponding to 15.33 Hz at the model scale. It was recommended that stiffer links should be used in the future to provide a more accurate structural representation of the full scale vessel [50].

Table ‎3.1: First longitudinal modal frequency of the 112 m vessel and its scaled values for 2.5 m model

Vessel

First longitudinal modal frequency

Predicted Before construction Measured after construction

112 m vessel, Hull 064 2.06 Hz 2.29 Hz

Scaled value for 2.5 m model 13.79 Hz 15.33 Hz

The centrebow was isolated from the forward demihull segments so that slam loads could be measured. Two transverse beams with four elastic links located the centrebow and measured the vertical loads on the centre bow. The centrebow was also fitted with pressure transducers on the archway to measure slam pressures.

The model HSM01 was tested in various sea conditions to measure motions, loads and slamming behaviour in both regular and irregular waves as follows:

- Investigation of mode shapes and the effect of hydroelasticity on vessel motions at varying speeds in regular waves by Matsubara and Lavroff [50, 51, 99-101].

- Pressure mapping on the centrebow section at various speeds and wave heights in order to produce full-scale load cases for finite element analysis models by Amin [20].

- Global motions, VBM and slam loads in regular waves by Matsubara and Lavroff [50, 51]. - Vessel response in irregular waves and the characterisation of slamming behaviour by French

and Winkler [1, 102, 103].

Although scaling the slam loads is difficult, the results from this extensive set of experiments have been verified against full-scale results. One interesting result is that both the model and full-scale INCAT vessels have experienced slams with a magnitude greater than the vessel displacement [1]. Figure 3.2 shows some structural elements of HSM01 where a longitudinal cantilever beam connects the aft wetdeck tray to the mid segment transverse beams; the aft tow post was attached to this beam.

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Figure ‎3.2: HSM01 transverse beam and cross-deck system. Two aluminium transverse beams connected to demihull backbone beams hold the demihulls together in mid segment. Aft wetdeck is attached to another cantilever

beam extended from mid segment

By reviewing the model design, construction techniques and the test results from HSM01, the following issues were considered:

- It was noted through studying videos of test runs that the model, when tested at higher speeds, tended to run horizontally into waves rather than slam vertically caused by pitch and heave motions. This indicated that there could be a significant horizontal slamming force present on the centrebow. However, the HSM01 centrebow force measuring system could only measure vertical slam components. Hence, to better understand and measure slam forces it was recommended that loads in both the horizontal and vertical directions be measured.

- The centrebow force calibration of the HSM01 required the introduction of correction factors due to internal structural cross-torques and friction generated at the hinge supports of the bow transverse beams [51, 104]. It was proposed that a major review on the centrebow load measuring system should be completed to provide a more direct measurement system. This would also help to understand why there was uncertainty in the slam magnitudes measured in equivalent sea conditions [1, 102].

- A longitudinal cantilever beam connected the aft wetdeck tray to the mid segment. Since the aft wetdeck was actually a member of the mid segment, as demonstrated in Figure 3.3, any vertical wave forces on the aft wetdeck would be transferred to the mid segment instead of the aft segments. It was proposed that the connection between the aft wetdeck and mid segment be eliminated so transferring the loads to the segments realistically.

Aluminium transverse beams

Flat wetdeck pieces Backbone beams _{Tow post bases}

Longitudinal cantilever beam

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- The robust and light weight properties of the carbon-fibre with Divinicell foam core. The resin was infused to carbon-fibre sandwich by vacuuming technique. More than 2,300 runs in slamming conditions were completed in the towing tank and model test basin. The model went under repair only in one case which the model disconnected from the tow post and struck the towing tank wall.

- The friction locked ball joint mount used for towing the model was replaced with a mechanically locked connection to increase the safety and avoid disconnecting from the tow post in heavy seas.

- The number of structural elements and instruments used in the model HSM01 increased the model light weight and therefore the model was difficult to trim. It was necessary to use a 3D solid modelling CAD package to enhance design efficiently and track the masses and LCG of the many structural elements.

- The effectiveness of the sealing method between segment gaps was to be improved. Using double sided tapes on the hull, applying light latex to seal the gap and on top each side, the use of water proof sticky tapes was found to be satisfactory. However, in some gap junctions such as where the forward cut and centrebow gap meet, especial care has to be taken to avoid leakage without transferring any loads across the flexible seal.

Figure ‎3.3: Aft wetdeck in HSM01 is attached to a cantilever beam extended from mid segment. In case of wave loading on the aft wetdeck, the VBMs are transferred to both sides of the mid segment