Trans RINA, Vol 152, Part A2, Intl J Maritime Eng, Apr-Jun 2010


optimum curve is an estimate of the smooth line through these points. HV1 shows the lift produced by the equivalent


size and weight of hybrid vehicle as


calculated by the stability model. It can be seen that HV1 does not produce enough aerodynamic support to be at optimum drag.


The HV2 is a version of the hybrid vehicle using


optimised lift coefficients and a modification to the geometry. For this vehicle it was assumed that the lift coefficient could be controlled at each speed via control surfaces. The lift coefficients used are shown in Table 1. To achieve these optimum values a maximum lift coefficient of 1.45 was used at 50knots. This should be entirely achievable given that slightly higher values have already been achieved without further optimisation or the use of control surfaces or trailing edge flaps. One difference with the modified coefficient of lift is that the value is reduced in the latter stages to prevent total take- off.


Speed in knots


CL Cushion pressure %


0 1 0


10 1 1.6 20 1 6.2 30 1 13.9 40 1.4 50 1.45 60 1.4 70 1.2 80 0.98 90 0.79 100 0.64


It was found that significant produced by careful


levels of lift can be design of a ducted hull, with


aerodynamic lift coefficients over 1.4 at only moderate angles of attack and L/D ratios of nearly 50 for a full aero-hydro model of the AAMV concept.


Preliminary stability and performance analysis showed that the AAMV concept can provide a significant improvement over a conventional planing hull, with a total drag reduction of 45% at top speed.


The AAMV proved to be unstable beyond 80 knots in this configuration and it was shown that control surfaces would be needed to maintain greater cruise speeds. It was also noted that better performance could be achieved with control surfaces.


The AAMV concept was compared to the optimised INCAT vessels with aerostatic support and it was found that aerodynamic support can be made to fit the optimum levels required. However, either the level of lift produced must be further increased, the weight of the vehicle reduced, or the size increased. Most likely a combination of the three would be required.


34.8 56.4 78.4 91.5 97.6 99.5 99.6


Table 1: Lift coefficients used to obtain an optimal aerodynamic support curve.


Unfortunately, the most effective way to achieve the desired optimum lift fraction was to change the geometry of the ship. HV2 has an increased length of 150m, with the same length to beam ratio of 2 used for the previous hybrid AAMV configurations. By extending the length of the AAMV the aerodynamic force is greatly increased and the take off speed is much easier to achieve. However, the extra length must be at the cost of payload, or better use of structural design and materials.


7. CONCLUSIONS


The concept of aerodynamic alleviation of marine vehicles has been studied and it has been found that the standard model of a wing in ground effect


is not


necessarily valid for a multihull vehicle. In such a situation it was found that a ducted flow was more appropriate and that the side-hull shape must therefore be an integral part of the design as well as the cross deck.


6.


The AAMV concept shows promise for reducing the drag of high-speed multihull. With an increasing demand on ships to achieve higher speeds, and the knowledge that the present design is an early concept which it may be hoped will be much improved, it seems likely that the AAMV may provide a realistic avenue of development for high-speed sea travel.


8. 1.


REFERENCES


MOORE, N. J. WILSON, P. A. PETERS, A. ‘An Investigation into Wing In Ground Effect Airfoil Geometry’, RTO SCI Symposium on “Challenges


in 2. 3. 4. 5. Dynamics, Systems


Identification, Control and Handling Qualities for Land, Air, Sea and Space Vehicles", (RTO- MP-095), 2002. Berlin, Germany. BALOW, F. GUGLIELMO, J.


‘Design and evaluation of a midsize wing in ground effect transport’, Technical report, AIAA, 1993.


CLARK, D. ELLSWORTH, W. MEYER, J. ‘Quest for speed at sea’, Naval Surface Centre, Carderock Division Technical Digest, 2004.


LAZAUSKAS, L. ‘Hydrodynamics of advanced high-speed sealift vessels’, Master's thesis, University of Adelaide, 2005.


DOCTORS, L. ‘Analysis of the efficiency of an ekranocat: A very-high-speed catamaran with aerodynamic alleviation’, Royal Institution of Naval Architects, 1997.


TRILLO, R. ‘High speed over water, ideas from the past, present and future’, First international conference on FAST, pp 17-34, 1991.


SIVIER, K.


©2010: The Royal Institution of Naval Architects


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