Browsing by Author "Patel, Minoo H."

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    High Speed Marine Vehicles With Aerodynamic Surfaces: Development of a Dynamic Model for a Novel Configuration.
    (2008-05-06T00:00:00Z) Collu, Maurizio; Patel, Minoo H.; Trarieux, Florent
    A research programme on high speed marine vehicles fitted with aerodynamic surfaces started in Cranfield University in 2005. One of the configurations analyzed is a high speed prismatic planing hull with one or more aerodynamic surfaces; it is called a hybrid vehicle (HV). Two mathematical models have been developed for the dynamic behavior which is a combination of the very different behaviors of aircraft and ships. The first model estimates the equilibrium attitude of the HV at a certain speed. A parametric analysis for the influence of the configuration on the performance of the HV has been conducted (1). With the second model, the authors propose a set of ordinary differential equations of motion, derived in the frame of small-disturbance stability theory which has been used to investigate the longitudinal dynamic stability of the HV (2). Ref. (1) and (2) present a complete description of the mathematical models, while this article summarizes the methodology adopted to develop these dynamic models and gives a brief summary of the results. (1) COLLU, M., PATEL, M. H., TRARIEUX, F., A Mathematical Model to analyze the Static Stability of Hybrid (Aero- hydrodynamically supported) vehicles., 8th Symposium on High Speed Marine Vehicles 2008 (HSMV08), Naples, Italy, 2008. (2) COLLU, M., PATEL, M. H., TRARIEUX, F., A Unified Mathematical Model for High Speed Hybrid (Air and Water- borne) Vehicles., 2nd International Conference on Marine Research and Transportation, 2007.
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    Investigations with a bandwidth measure for fatigue assessment of the Foinaven dynamic umbilical including VIV
    (Elsevier Science B.V., Amsterdam., 2006-10-01T00:00:00Z) Trarieux, Florent; Lyons, G. J.; Patel, Minoo H.
    An innovative use of a method to detect Vortex Induced Vibration (VIV) bandwidth in the curvature data of subsea flexible risers and umbilicals is presented. The parameter epsilon gives a valuable estimate of the bandwidth of signals such as VIV as a single value which may be used to track the behaviour with time and against other measures such as current speed. The method is conveniently based on a peak counting approach originally used in a marine context by Cartwright and Longuet-Higgins. Low epsilon values close to zero indicate a narrow-band process whereas values near unity indicate a broad-band process. Curvature and environmental data were gathered by the Foinaven Umbilical Monitoring System (FUMS) installed on the Foinaven Petrojarl IV floating production unit located in the Atlantic margin, west of Shetland. The VIV frequency range owing to current excitation considered is that in the range 0.2–2 Hz. This paper presents analyses showing the correlation of the epsilon bandwidth parameter with standard deviation of curvature, current speed and spectral analysis results for extended periods measured on the Foinaven dynamic umbilical. Examination of the number of frequencies and their values using spectrograms over long periods enable interesting interpretation of the build-up and decay of the VIV behaviour. These data are also reduced to the predominant peak frequencies, and standard deviation along with epsilon to provide a compact description of the VIV behaviour over 10 min intervals. Clear frequency and amplitude shifts can be observed as VIV varies with current ebb and flow. The behaviour is usefully described using only epsilon, standard deviation, and peak frequencies. The importance of epsilon for fatigue damage assessment is demonstrated through a formulation derived by Wirsching and Light. Strong VIV regimes are often characterized by an intense activity around a particular frequency and the impact of such relatively narrow-band events on the fatigue life of the structure is clearly demonstrated. This paper also presents the relative contributions of mooring, and waves/vessel motions, and VIV to fatigue damage. Although wave excitation remains the main source of fatigue, VIV appears to potentially contribute to a significant part of the overall fatigue damag
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    The longitudinal static stability of an aerodynamically alleviated marine vehicle, a mathematical model
    (Royal Society, 2010-04-08T00:00:00Z) Collu, Maurizio; Patel, Minoo H.; Trarieux, Florent
    An assessment of the relative speeds and payload capacities of airborne and waterborne vehicles highlights a gap that can be usefully filled by a new vehicle concept, utilizing both hydrodynamic and aerodynamic forces. A high- speed marine vehicle equipped with aerodynamic surfaces is one such concept. In 1904, Bryan & Williams (Bryan & Williams 1904 Proc. R. Soc. Lond. 73, 100-116 (doi: 10.1098/rspl.1904.0017)) published an article on the longitudinal dynamics of aerial gliders, and this approach remains the foundation of all the mathematical models studying the dynamics of airborne vehicles. In 1932, Perring & Glauert (Perring & Glauert 1932 Reports and Memoranda no. 1493) presented a mathematical approach to study the dynamics of seaplanes experiencing the planing effect. From this work, planing theory has developed. The authors propose a unified mathematical model to study the longitudinal stability of a high-speed planing marine vehicle with aerodynamic surfaces. A kinematics framework is developed. Then, taking into account the aerodynamic, hydrostatic and hydrodynamic forces, the full equations of motion, using a small perturbation assumption, are derived and solved specifically for this concept. This technique reveals a new static stability criterion that can be used to characterize the longitudinal stability of high-speed planing vehicles with aerodynamic surfaces.
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    A Mathematical Model to Analyze the Static Stability of Hybrid (Aero- Hydrodynamically Supported) Vehicles.
    (2008-05-21T00:00:00Z) Collu, Maurizio; Patel, Minoo H.; Trarieux, Florent
    Among the new concepts developed for high speed marine vehicles over the last two decades, the "aerodynamic alleviation" approach consists in using an aerodynamic surface to "alleviate" the weight sustained by the hydrodynamic lift. Such vehicle experiences aerodynamic and hydrodynamic forces of the same order of magnitude, therefore the dynamic models developed for airborne and waterborne vehicles are not suitable. Considering a vehicle having a high-speed prismatic planing hull and one or more aerodynamic surfaces, the authors propose two mathematical methods. The first one calculates the equilibrium attitude of the vehicle at a given speed and its numerical implementation has been used to undertake a parametric analysis of the influence of some configuration characteristics on performances. The second method analyzes the static stability of the HV. Starting from the dynamic analysis previously proposed by the authors, the characteristic polynomial of the HV dynamics is derived and a static stability criterion is proposed.
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    Post-buckling behaviour of slender structures with a bi-linear bending moment-curvature relationship
    (Elsevier, 2007-04) Vaz, M. A.; Patel, Minoo H.
    Certain classes of slender structures of complex cross-section or fabricated from specialised materials can exhibit a bi-linear bending moment–curvature relationship that has a strong influence on their global structural behaviour. This condition may be encountered, for instance, in (a) non-linear elastic or inelastic post-buckling problems if the cross-section stiffness may be well approximated by a bi-linear model; (b) multi-layered structures such as stranded cables, power transmission lines, umbilical cables and flexible pipes where the drop in the bending stiffness is associated with an internal friction mechanism. This paper presents a mathematical formulation and an analytical solution for such slender structures with a bi-linear bending moment versus curvature constitutive behaviour and subjected to axial terminal forces. A set of five first-order non-linear ordinary differential equations are derived from considering geometrical compatibility, equilibrium of forces and moments and constitutive equations, with hinged boundary conditions prescribed at both ends, resulting a complex two-point boundary value problem. The variables are non-dimensionalised and solutions are developed for monotonic and unloading conditions. The results are presented in non-dimensional graphs for a range of critical curvatures and reductions in bending stiffness, and it is shown how these parameters affect the structure's post-buckling behaviour.
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    A Unified Mathematical Model for High Speed Hybrid (Air and Water-borne) Vehicles.
    (2007-06-01T00:00:00Z) Collu, Maurizio; Patel, Minoo H.; Trarieux, Florent
    During the last two decades, the interest in civil and military high speed marine vehicles has lead to several new configurations. Some of them exploit a combination of aerodynamic and hydrodynamic forces to sustain part of the weight of the craft, leading to a hybrid vehicle (HV). This paper focuses on the study of the longitudinal high-speed dynamics of such hybrid vehicles. Since airborne and waterborne vehicles belong to two distinct areas of research, they have been investigated with a rather different approach. The authors propose a unified mathematical model to represent the kinematics suitable for hybrid vehicles, including a detailed analysis of the aerodynamic and hydrodynamic forces acting on the vehicle. Then a set of ordinary differential equations of motion is derived in the frame of small-disturbance stability theory, leading to the Cauchy standard form. An illustrative example of a hybrid vehicle (KUDU II) is analyzed with the proposed method.