Browsing by Author "Patel, M. H."

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    Aerodynamic forces on high speed multi-hulled marine vehicles
    (Cranfield University, 2008-12) Williams, A. G. W.; Patel, M. H.
    The need for high-speed high-payload craft has led to a considerable interest in vehicles capable of bridging the gap between conventional ships and aircraft. One such concept uses the forward motion of the craft to create aerodynamic forces on a wing-like structure, and hence, alleviate the overall drag by reducing the wetted area. This research focuses on the use of suitably shaped multihull geometries to achieve e cient aerodynamic lift for high-speed sea vessels. The problem is rst studied in two dimensions using a simpli ed analytical approach and CFD modeling. The work is then extended into three dimensions and a nal aerodynamic model is produced for a complete hull form, including the e ects of hydrodynamic surfaces above the water. The aerodynamic analysis demonstrates that signi cant e ciency can be achieved through careful shaping of the side hull and cross deck, with lift-to-drag ratios of nearly 50 for a complete aerodynamic hull con guration. Further analysis is carried out using a hybrid vehicle stability model to determine the e ect of such aerodynamic alleviation on a theoretical planing hull vessel. Comparisons are made using the Savitsky planing model, and from this it is found that the resistance can be almost halved for a fty metre, three hundred tonne vehicle with aerodynamic alleviation traveling at 70 knots. A comparative study is made for the hybrid vehicle with regards to size, speed and weight, whilst attempting to match the proportion of aerodynamic lift with speed to a theoretical optimum. From this the likely con gurations for future development are identi ed.
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    Dynamics of marine vehicles with aerodynamic surfaces
    (Cranfield University, 2008-11) Collu, Maurizio; Patel, M. H.; Trarieux, F.
    An assessment of the relative speeds and payload capacities of airborne and waterborne vehicles highlights a gap which can be usefully filled by a new vehicle concept, utilizing both hydrodynamic and aerodynamic forces. A high speed marine vehicle equipped with aerodynamic surfaces (called an AAMV, 'Aerodynamically Alleviated Marine Vehicle') is one such concept. The development of this type of vehicle requires a mathematical framework to characterize its dynamics taking account of both aerodynamic and hydrodynamic forces. This thesis presents the development of unified and consistent equations of equilibrium and equations of motion to predict the dynamic performance of such AAMV configurations. An overview of the models of dynamics developed for Wing In Ground effect 'WIGe' vehicles and high speed marine vehicles (planing craft) is given first. Starting from these models, a generic AAMV configuration is proposed and a kinematics framework is developed. Then, taking into account the aerodynamic, hydrostatic and hydrodynamic forces acting on the AAMV, equations of equilibrium are derived and solved. This is followed by deriving and solving the full equations of motion, using a small perturbation assumption. A static stability criterion, specific for the AAMV configuration, has been developed. This mathematical framework and its results are implemented in MATLAB and validated against theoretical and experimental data. The resultant capability for analysing novel AAMV configurations is presented through two parametric analysis. The analysis demonstrate that these models offer a powerful AAMV design tool.