Supercavitating Vehicle Research Articles

Research on the encounter motion of super-cavitating vehicles

In this paper, the super-cavitating phenomenon under the effect of two vehicles’ encounter motion processes is numerically studied. Particular attention is given to the influence of the vertical gaps between the vehicle, the cavitation number, and the slenderness ratio on the cavity profile and radial force of the object. Several numerical models are built to study the cavity evolution process and the force acting on the vehicle to explore the influence mechanism of two vehicles’ encounter motion on supercavitating flow. The study shows that the cavity around the vehicle is primarily affected by the vertical gaps and cavitation number, but is relatively weakly affected by the slenderness ratio. Several impact laws are acquired in the paper. The relationship between cavity fracture time and vertical gaps is approximately a power function and obeys the law of t = 5.433h0.3688. The concept of the time of the maximum radial force occurrence and the cavitation number follows the formula of t = 4.86e0.3688σ. The relationship between the maximum radial force occurrence position and the cavitation number is a function of Ln and consistent with the law n = −0.799ln(σ) + 8.427.

A Numerical Investigation of Supercavitation Vehicle’s Hydrodynamic Noise

This paper presents the simulation results of the acoustic field around an underwater supercavitation vehicle under various operating conditions and analyzes the cavitation phenomenon and the hydrodynamic noise spectrum. Regarding the ventilated cavitation phenomenon, the simulation shows that low vehicle speed can reduce the threshold of the ventilated supercavitation, and high background pressure can enhance the stability of the supercavitation structure. As for hydrodynamic noise, firstly, the simulation results reveal that when cavitation occurs, the noise spectrum exhibits several characteristic peaks near 1 kHz and between 3 and 10 kHz. The overall noise amplitude demonstrates a descending trend between 10 and 40 kHz. Further, under natural cavitation conditions, a characteristic peak is detectable between 40 and 80 kHz. The influence of the operating conditions on the noise is essentially achieved by altering the scale of the cavitation flow: with the growth of the bubble flow scale, the noise between 3 and 10 kHz first increases and then decreases due to its own pulsation and the masking effect, while the noise between 10 to 40 kHz substantially reduces. On the other hand, if the scale expansion of bubble flow is related to the increase of ventilation flow, the noise amplitude near 1 kHz will increase significantly. These results provide theoretical support for studying the supercavitation vehicles’ noise and applying the ventilated supercavitation technology.

Numerical Simulation of Cavitation and Damping Force Characteristics for a High-Speed Supercavitation Vehicle

In this study, an attempt has been made to investigate the supercavitation and hydrodynamic characteristics of high-speed vehicles. A homogeneous equilibrium flow model and a Schnerr–Sauer model based on the Reynolds-averaged Navier–Stokes method are used. Grid-independent inspection and comparison with experimental data in the literature have been carried out to verify the accuracy of numerical methods. The effect of the navigation speed and angle of attack on the cavitation morphology and dynamic characteristics has been investigated. It has been demonstrated that the angle of attack has a remarkable influence on the wet surface and hydrodynamic force, whereas navigation speed has little effect on the position force of the vehicle under the circumstance of no wet surface. The hydrodynamic force changes periodically with the swing of the vehicle, but its maximum is greater than that for the direct navigation state at the same attack angle. Moreover, the damping effect obviously affects the hydrodynamic force amplitude and movement trend.

Optimization of the maximum range of supercavitating vehicles based on a genetic algorithm

Range is an important indicator for measuring the performance of supercavitating vehicles (SCAVs), which is closely related to the hydrodynamic layout of vehicles. The motion state, cavitating flow and control surfaces of a vehicle, which are key factors that affect the hydrodynamic distribution, have an important impact on the range. A range optimization model is established for a SCAV on a straight and level trajectory, wherein the optimal variables include the cavitator number, speed of motion, diameter and deflection angle of the cavitator, pitch angle and fin deflection angle. The global search performance of the adaptive genetic algorithm is improved by segmenting the main optimization variables and performing multiple optimizations in each segment, thereby resulting in the development of a program called the genetic-ZouLiu code (GE-ZL Code). Based on the optimization model, some geometric characteristic and motion parameters of natural and ventilated SCAVs are optimized to the maximum ranges using the GE-ZL Code. Analyses are performed to determine the influences of the navigation depth and slenderness ratio of the vehicle on the optimization results, i.e., the change trends of the optimization variables and the maximum range with the change in the navigation depth and slenderness ratio. Additionally, the optimization results of the two vehicles are compared and analyzed. Furthermore, based on the optimization results, the relationships among the cavitator diameters, column body diameters and full lengths of the vehicles are formulated using the nonlinear least square method. Based on the analyses of the afterbody force characteristics, the study also shows that the SCAV can rely on only the deflections of the cavitator and fin to achieve good horizontal straight navigation without other wetted afterbodies by optimizing geometric characteristic and motion parameters.

Stability Analysis of a Fractional-Order High-Speed Supercavitating Vehicle Model with Delay

A novel fractional-order model (FOM) of a high-speed super-cavitating vehicle (HSSV) with the nature of memory is proposed and investigated in this paper. This FOM can describe the behavior of the HSSV superior to the integer-order model by the memory effects of fractional-order derivatives. The fractional order plays the role of the advection delay, which is ignored in most of the prior studies. This new model takes into account the effect of advection delay while preserving the nonlinearity of the mathematical equations. It allows the analysis of nonlinear equations describing the vehicle with ease when eliminating the delay term in its equations. By using the fractional order to avoid the approximation of the delay term, the proposed FOM can also preserve the nature of the time delay. The numerical simulations have been carried out to study the behavior of the proposed model through the transient responses and bifurcation diagrams concerning the fractional-order and vehicle speed. The bifurcation diagrams provide useful information for a better control and design of new supper super-cavitating vehicles. The similar behaviors between the proposed model and prior ones validate the FOM while some discrepancies suggest that more appropriate controllers should be designed based on this new model.

Bow rudder of cavitator attached with a non-symmetric anti-roll fin for strong manoeuvring underwater supercavitating vehicles

ABSTRACT The hydrodynamic control of strong manoeuvring supercavitating vehicles (SVs) is challenging because unwanted changes in the aft planning contacts may result in destabilising forces and moments. In this paper, the disadvantages of the existing hydrodynamic layout of stern rudders are revealed. A novel hydrodynamic layout was proposed using a non-symmetric anti-roll fin installed to the lower part of a conical cavitator bow rudder to create high agility SVs. The conical cavitator bow rudder with two degrees of freedom in the vertical and horizontal planes was employed to manoeuvre pitch and yaw. Deflecting together with the cavitator, the anti-roll fin generates most of the anti-roll moment. The differential motion between the anti-roll fin and the cavitator provides the small residual moment. Adopting this layout, finless SVs could be designed, and the efficiency of the rudder system was remarkably improved. Simulations of an SV validated the effectiveness of the proposed layout.

A novel hydrodynamic layout of front vertical rudders for maneuvering underwater supercavitating vehicles

Owing to the complex hydrodynamic characteristics of the water/cavity/vehicle systems, supercavitating vehicles (SVs) feature slope-discontinuous force characteristics at the afterbody, presenting challenges to the hydrodynamic control of such maneuverable and highly agile vehicles. In this paper, the disadvantages of the existing SV hydrodynamic layout are revealed via rudder efficiency analysis, and a novel hydrodynamic layout of front vertical rudders for high agility maneuvering SVs is proposed. In this layout, the vertical rudders are fixed behind the cavitator at the bow. The rudder efficiency is improved remarkably without increasing the degree of freedom of the cavitator, and the valuable space in the cavitator is reserved. From the unit step response characteristics, it is observed that using the novel hydrodynamic layout affords approximately twice the sideslip angle and five times the yaw rate compared to those using the existing layout. Free motion experiments are carried out with an SV with a preset vertical rudder angle, and the feasibility of the proposed hydrodynamic layout is validated.

Dynamic features of kinetic energy supercavitating vehicles

Stability is an important issue for the application of kinetic energy supercavitating vehicles. Interactions of supercavitating vehicles with their fluid environment are exceptionally complex. Traditionally, the kinetic modeling is established in the longitudinal plane, which is inevitable to lose some important features of 6DOF dynamic system. On the basis of general dynamics theory, a 6DOF dynamic system is established for kinetic supercavitating vehicles. Credibility of this model assesses through experiments and empirical estimation equation. The conception of limit-angle and χ-χlim chart are proposed for analyzing the stability of kinetic supercavity vehicles. The instability mechanism is discussed and the calculation method of velocity stable range is given. These works provide the theoretical basis for the engineering. Besides, the cavity cross and position where the tail-slap occurs is visualized in three-dimensional Cartesian coordinates, which could provide a reference for further research on the ballistic dispersion of supercavitating vehicles. Additionally, the further regular of the angular velocity is found. When the vehicle moves in supercavity the hydrodynamic point of the cavitator would change, which changes the angular velocity.

Longitudinal maneuvering motions of the supercavitating vehicle

As the supercavitating flows theory and technology developing, to develop a supercavitating vehicle with maneuverability is a significant trend. In order to achieve this goal, it is prerequisite to establish a dynamics model, reflecting the supercavitating flows’ unsteady characteristics and the supercavitating vehicle’s dynamics characteristics as much as possible, and an effective control method. The maneuvering supercavity model proposed in our previous work, where the gravity effect model is further improved here, is applied to the vehicle dynamics modeling in the longitudinal motions. Based on the dynamics model, a numerical method that integrates the fourth order Runge–Kutta algorithm with the cavitation number correction algorithm, the exactly feedback linearizing control and the linear quadratic regulator methods is proposed to simulate the level flight, climbing and diving of the vehicle. Numerical results confirm that the developed dynamics model and numerical method are effective for the vehicle’s maneuvering motions and that the method with control laws is robust to velocity perturbation and trajectory mutation.

Design of Pose Controller of Underwater Supercavitating Vehicles Based on Variable Structure

On the basis of dynamic modeling for underwater supercavitating vehicles, the paper designed controllers adopting variable structure control strategy whose robustness can suppress unknown disturbance caused by imprecision existed in dynamic modeling. Theory analysis and simulation show that the controller designed can make pose angle track course angle of trajectory steadily, realize decoupling controlling between three pose moving subsystems and have good robustness for outside interference and model’s error, which assure that supercavitating vehicles have good maneuverability.

A Robust Impulsive Control Strategy of Supercavitating Vehicles in Changing Systems

Supercavitation is a hydrodynamic phenomenon in which an underwater body is almost entirely inside the cavity wall. Since the density of the gas is much lower than that of water, skin friction drag can be reduced considerably. We develop controllers to control a supercavitating vehicle, which is a high-speed vehicle with a cavitator at its nose. We designed controllers based on impulsive inputs, which are used to change the pitch of the vehicle slightly. This slight pitch change is desirable, since a large pitch change can lead to instability of the vehicle due to large planing force. Moreover, our impulsive controllers are robust to disturbances. In practice, the vehicle consumed its fuel to move forward. This fuel consumption led to changing parameters of the vehicle, such as mass. To handle this changing system, we used fuzzy impulsive controllers. We ran simulations to verify the effectiveness of our controllers.

Global approximation based adaptive RBF neural network control for supercavitating vehicles

A global approximation based adaptive radial basis function (RBF) neural network control strategy is proposed for the trajectory tracking control of supercavitating vehicles (SV). A nominal model is built firstly with the unknown disturbance. Next, the control scheme is established consisting of a computed torque controller (CTC) for the practical vehicle and an RBF neural network controller to estimate model error between the practical vehicle and the nominal model. The network weights are adapted by employing a Lyapunov-based design. Then it is shown by the Lyapunov theory that the trajectory tracking errors asymptotically converge to a small neighborhood of zero. The control performance of the proposed controller is illustrated by simulation.

Drag reduction of a rapid vehicle in supercavitating flow

Supercavitation is one of the most attractive technologies to achieve high speed for underwater vehicles. However, the multiphase flow with high-speed around the supercavitating vehicle (SCV) is difficult to simulate accurately. In this paper, we use modified the turbulent viscosity formula in the Standard K-Epsilon (SKE) turbulent model to simulate the supercavitating flow. The numerical results of flow over several typical cavitators are in agreement with the experimental data and theoretical prediction. In the last part, a flying SCV was studied by unsteady numerical simulation. The selected computation setup corresponds to an outdoor supercavitating experiment. Only very limited experimental data was recorded due to the difficulties under the circumstance of high-speed underwater condition. However, the numerical simulation recovers the whole scenario, the results are qualitatively reasonable by comparing to the experimental observations. The drag reduction capacity of supercavitation is evaluated by comparing with a moving vehicle launching at the same speed but without supercavitation. The results show that the supercavitation reduces the drag of the vehicle dramatically.

Catastrophe characteristics and control of pitching supercavitating vehicles at fixed depths

The existence of the cavity and of a nonlinear planing force results in catastrophe phenomena and causes an instant loss of stability for the supercavitating vehicle during the travel process. To analyze the catastrophe characteristics, the least-squares method is exploited in order to approximate the nonlinear planing force, and the simplified model of the pitching supercavitating vehicle at fixed depths is established. According to the splitting lemma, the cusp catastrophe potential function is built for the pitching supercavitating vehicle at fixed depths and the critical condition of the catastrophe is obtained. A dynamic washout filter-aided feedback is used to control the catastrophe phenomena of the vehicle, and the simulation result shows that the control method is effective and feasible.

흡입 유로 형상이 터보펌프의 성능 및 캐비테이션에 미치는 영향에 관한 실험적 연구

Super-cavitating vehicle which is operating under water speeds up to 100m/s. In this process super-cavitation around body reduces frictional resistance. This paper introduces experimental study on different width of suction path as there is a warhead in the torpedo. Hydraulic performances of turbopump at non-cavitating condition does not display a significant differences depending on different width of suction path. However, cavitation performance of each model shows obvious differences in the same condition of experience. In case of radial inlet, the value of critical NPSH(which indicates 3% head drop) increases about 20% in comparison of axial inlet.

Thermoelastic Ultrasonic Actuator With Piezoresistive Sensing and Integrated Through-Silicon Vias

This paper presents technology development toward the goal of a micromachined acoustic proximity sensor for real-time cavity monitoring of underwater high-speed super-cavitating vehicles. Low-resistance polysilicon-based through-silicon vias (TSVs) have been integrated with the device to enable backside contacts for drive and sense circuitry. The sensor and vias were fabricated in a complementary-metal-oxide-semiconductor compatible process using deep reactive ion etching, producing a 1-mm-diameter composite diaphragm and 20-μm-diameter high-aspect-ratio TSVs on a silicon-on-insulator wafer. The diaphragm incorporates a central resistive heater for thermoelastic actuation and diffused piezoresistors for sensing acoustic pressure perturbations. Electrical, mechanical, and acoustic characterizations of the device indicate a transmitter source level of 50 dB (ref 20 μPa) at an operating frequency of 60 kHz, a flat-bandwidth receiving sensitivity of 0.98 μV/(V · Pa), a flat frequency response over the measured range of 1-20 kHz, a linear response from 60 to 140 dB, negligible leakage current for the junction-isolated diffused piezoresistors (<; 14 pA at -10 V), low interconnect resistance of 14 Ω, and a minimum detectable pressure of 31.9 dB for a 1-Hz bin centered at 60 kHz, at a bias of 9 V.

Study on Numerical Simulation Method for Motion of Supercavitation Vehicles

A calculation method was developed to predict motion of supercavitation vehicles based on the computational fluid dynamics (CFD) model. Control equation of supercavitating flow and motion equations of vehicles are coupling solved through self-made software. This method can directly obtain hydrodynamic data of the vehicle and accurately predict instantaneous motion attitude and trajectory of the vehicle. The simulation results of a supercavitation vehicle motion process show that this method can predict interaction between vehicle and cavity surface and periodic tail beat phenomenon, which accord with experiment results. Furthermore, the periodic variation of vehicle attack angle, which is found in experimental studies, is also caught though simulation. This further proves that the method developed in this paper has an ability to accurately simulate motion of supercavitation vehicles underwater.

Structure Buckling Reliability Analysis for the Underwater Super-Speed Supercavitating Vehicle

An approach to the structure buckling reliability analysis for the underwater super-speed supercavitating vehicle is proposed in this paper. The circular ribbed part-cabin of the vehicle is simplified as the thin cylindrical shell with variable thickness. The critical buckling load coefficient of the thin cylindrical shell is solved by using semi-analytical FEM (finite element method). The structure buckling reliability index is obtained by SFEM (Stochastic Finite Element Method) combining Limit Step Length Iteration Method. A numerical example is given to analyze influences of the number of circular ribs, the coefficient of variation of elastic modulus and the coefficient of variation of the thickness of the thin shell on the structure buckling reliability index.

A Three-Component Model Suitable for Natural and Ventilated Cavitation

A three-component model based on mass transfer equation is proposed to simulate both the natural and ventilated cavitations. In the present cavitation model, the content of nuclei in the local flow field is updated synchronously, and is coupled with the Rayleigh–Plesset equation so as to capture the cavity development. The proposed model is applied for simulating the cavitating flow around a super-cavitating vehicle in different cavitation conditions. In the case of the natural cavitation simulation, the predicted cavitation characteristics including the cavity length and cavity diameter agrees fairly well with the analytical results. In the case of the mixed cavitation simulation, the gas ventilation obviously influences the development of cavity. With the increase of the gas ventilated rate, the natural cavitation is suppressed remarkably, and a super cavitation is formed even at a relatively larger natural cavitation number.

Linear, parameter-varying control of a supercavitating vehicle

A systematic approach to parameter-dependent control synthesis of a high-speed supercavitation vehicle (HSSV) is presented. The aim of the control design is to provide robust reference tracking across a large flight envelope, while directly accounting for the interaction of liquid and gas phases with the vehicle. A nonlinear dynamic HSSV model is presented and discussed relative to the actual vehicle. A linear, parameter-varying (LPV) controller is synthesized for angle rate tracking in the presence of model uncertainty. The control design takes advantage of coupling in the governing equations to achieve improved performance. Multiple LPV controllers synthesized for smaller overlapping regions of the parameter space are blended together, providing a single controller for the full flight envelope. Time-domain simulations implemented on high-fidelity simulations, provide insight into the performance and robustness of the proposed scheme.