CFD-based Numerical Analysis of Amphibious Vehicle Hydrodynamics during Turning Motion

To enhance vehicle/road safety, rollover warning and control systems have received considerable research interest in recent years, especially for vehicles with high center of gravity (CG). Accurate and reliable estimates of the relevant vehicle states facilitate the design of such systems. This paper investigates the state estimation for rollover avoidance, in which the relevant states include vehicle roll velocity and roll angle, as well as sideslip velocity and yaw velocity. The main challenge of the design comes from the fact that, under near-rollover situations, vehicle dynamics is complex and nonlinear. Not only vehicle suspension and tires are in their nonlinear region, but also vehicle yaw, sideslip and roll motions are highly coupled. In addition, the estimation needs to deal with sensor biases and sensor nonlinearity under this extreme condition. To address those issues, this paper proposes a vehicle state estimation design that consists of three parts: a sensor pre-filter, an Extended Kalman filter (EKF), and a sideslip velocity estimator. The sensor pre-processor removes sensor biases by utilizing the Recursive Least Square technique with a varying forgetting factor. The EKF is designed based on a linear yaw/sideslip/roll model, and its feedback gains are further scheduled based on vehicle lateral acceleration in order to reduce the effects of increased model inaccuracy as vehicle roll motion becomes more severe. The sideslip velocity estimator adjusts the sideslip velocity estimated by the EKF to extend the estimation to the nonlinear region. Both simulation and vehicle fishhook testing have been used to verify the effectiveness of the design.

This paper compares performance predictions from a Reynolds Averaged Navier Stokes (RANS) based Velocity Prediction Program (VPP) to on the water testing of a J70. The J70 has been outfitted with a system to determine sail flying shapes, apparent wind conditions and performance data. The on the water testing is conducted in both racing and controlled sailing conditions. Data taken during racing conditions is analyzed to determine optimal performance envelopes while data taken in controlled conditions is used to match exact sailing and VPP states. The data acquisition system combines a number of standard marine sensors including a sonic anemometer, a GPS, a digital compass, an accelerometer and a gyroscope with custom sensors that measure rudder and boom angles as well as a custom sail shape acquisition system. The RANS based VPP developed by Doyle CFD has three main components; an aerodynamic force model, a hydrodynamic force model and an algorithm to balance the forces. The force balance routine uses four degrees of freedom; boat speed, yaw, heel and rudder angle to balance the aerodynamic and hydrodynamic forces for a given true wind speed and angle. The force models are derived from RANS CFD data calculated using OpenFOAM. The aerodynamic forces are calculated using steady state RANS as a function of apparent wind angle, apparent wind speed and sail flying shape. The VPP force model is derived by fitting response surfaces to this data. The aerodynamic CFD is run with sail flying shapes recorded from on the water testing. Using accurate flying shapes is critical for picking out slight aerodynamic differences in sail and rig setup. The hydrodynamic CFD data points are calculated using RANS Volume of Fluid CFD (VOF) as a function of boat speed, rudder angle, yaw angle, heel angle and displacement. Response surfaces are generated from a 64 data point array of RANS VOF simulations.

Unmanned Aerial Vehicles are extensively exploited for diverse applications importantly surveillance, defence and military, photography. Development of unmanned amphibious vehicle with integrating features of hovercraft principles and multirotor to navigate along and above the water surface, land surface and flying in the air is challenging demand. This article presents conceptual design of amphibious vehicle for the payload capacity of 7 kg with an endurance of 20 minutes and provision for mounting water sampler to collect water samples in remote water bodies. Structural strength characteristics of each part of the amphibious vehicle and integrity of same are analysed by Finite Element Analysis. FEA results indicated that the designed amphibious vehicle structure is well within the stress limit and minimal displacement is obtained. Based on structural analysis materials for various parts of the amphibious vehicle are determined and integrated structure is analysed.

Little attention has been given to the study of sport sailing. A new trend in performance analysis of cyclic sports involves examining steadiness between cycles. Therefore, the aims of this study were as follows: to determine which technical aspects differ between Olympic and regional-level sailors to maximise performance in the ILCA class, and to analyse whether steadiness in these technical variables is enhanced in athletes at a higher competitive level. A total of 36 ILCA sailors participated in the study—8 from Olympic teams and 28 from regional competitions – performing a sailing test on a simulator. Performance and technical variables, such as speed, heading angle, boom angle, heel angle, rudder angle, and hiking effort were assessed. Additionally, short-term and long-term steadiness of these variables were analysed. Olympic sailors demonstrated superior performance by higher speed, greater hiking effort, and lower heading, boom, heel, and rudder angles (p < 0.05). Furthermore, Olympic sailors exhibited greater steadiness in some technical variables (p < 0.05). In conclusion, Olympic sailors outperform regional sailors in specific linear tests due to higher speed influenced by technical aspects related to the mechanical behaviour of the boat and the ability to maintain more consistent force values and steadier technical aspects.

By establishing bus simplify coordinate system model and equivalent mechanical model, inertial forces and external forces are analyzed through vehicle lateral movement and vehicle's yaw motion and roll motion. Three degrees of freedom linear motion equation of vehicle is established taking into account lateral motion, yawing movement and rolling motion of vehicle and it can be solved by using method of state space equation. Vehicle dynamic characteristics are analyzed by using this method and programming with Matlab. Vehicle in steering wheel angle step response is analyzed under the conditions of different tire wheel cornering stiffness, moment of inertia, height of center of mass. The results show that increasing rear wheel cornering stiffness, reducing front wheel cornering stiffness and center of mass height, which can effectively improve stability of vehicle. Simulation results provide a theoretical basis and reference for the selection and design of vehicle.

Mobile manipulators have reduced maneuverability and risk rolling over when operated at high speeds. One of the main contributing factors is the higher center of gravity (CG) due to the manipulator arm. This paper proposes a new dynamic weight-shifting method that uses the manipulator arm on the mobile robot to improve maneuverability and reduce rollover risk. A control law is developed such that the manipulator arm keeps a low CG and the contribution of the reaction moments from its inertia is small in comparison to the reaction moments due to gravity. A linear dynamic model is used to analyze the effect of the arm design (link length, mass, etc.) on the roll dynamics. A higher fidelity nonlinear simulation is used to evaluate roll reduction and the impact on handling dynamics. Last, the dynamic weight-shifting method is implemented in hardware. With regard to reducing rollover risk, simulation results from the nonlinear model (NLM) show a 29% reduction in wheel normal load transfer by using the proposed method. In terms of improving maneuverability, experimental results with hardware demonstrate a 13% increase in lateral acceleration when using dynamic weight-shifting. By reducing the vehicle's roll motion, dynamic weight-shifting can increase safe operating speeds and maneuverability.

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;Amphibious vehicles are widely used in civil and military scenarios due to their excellent driving performance in water and on land, unique application scenarios and rapid response capabilities. In the field of civil rescue, the hydrodynamic performance of amphibious vehicles directly affects the speed and accuracy of rescue, and is also related to the life safety of rescuers. In the existing research on the hydrodynamic performance of amphibious vehicles, seakeeping performance has always been the focus of research by researchers and amphibious vehicle manufacturers, but most of the existing research focuses on the navigation performance of amphibious vehicles in still water. In actual application scenarios, amphibious vehicles often face complex water conditions when performing emergency rescue tasks, so it is very important to study the navigation performance of amphibious vehicles in waves. Aiming at the goal of studying the navigation performance of amphibious vehicles in waves, this paper first establishes a simplified model of amphibious vehicle. Then, based on computational fluid dynamics numerical simulation, the seakeeping performance of amphibious vehicles at different speeds and wavelengths were studied by using overlapping grid and numerical wave generation methods. Then obtained the data of resistance, vertical acceleration of the center of gravity, pitch and heave at different speed and wavelength, and the flow field and free surface waveform of the amphibious vehicle were also obtained. The results show that the driving resistance of low-speed amphibious vehicle in water increases with the increase of speed. With the increase of speed, the vertical acceleration RAO of the center of gravity, pitch RAO and heave RAO of the amphibious vehicle will also increase. The ratio of wavelength to vehicle length also has a profound influence on the longitudinal motion of amphibious vehicles. The maximum value of vertical acceleration RAO of the center of gravity appears when λ/L is 3.5, but the pitch RAO and heave RAO increase when value of λ/L increases.&lt;/div&gt;&lt;/div&gt;

Abstract. The Nacra-17 catamaran is currently the only type of multihull that participates in the Olympic Games. It features semi-L-shaped daggerboards, allowing the boat to foil. For maximizing boat speed, the sailors have to cope with a large set of trimming parameters. Boat speed depends on sail trim, but additional trim parameters also have a strong impact on boat speed: the rake of the daggerboard and the rudder, the platform trim and heel angle and the rudder angle. The project described here tries to assist the sailors in finding an optimized set of trim parameters. This is done with the help of a proprietary velocity prediction program, which - besides solving for equilibrium of all forces acting on the boat - searches for the set of daggerboard and rudder rake, rudder angle, heel angle and platform trim, for which performance yields a maximum. The paper describes the method as well as some of the results.

The unique structural configurations of amphibious vehicles, designed for dual land–water operations, pose significant challenges for hydrodynamic stability during water navigation. This study systematically investigated the hydrodynamic performance and motion response of a light high-speed amphibious vehicle (HSAV-II) under oblique inflow conditions. The working conditions of HSAV-II drift with five incoming flow angles (β) (0°, 5°, 10°, 15° and 20°) were considered. The computational fluid dynamics method, based on the steady Reynolds mean Navier–Stokes equation and the shear stress transport k-ω turbulence model, was used to simulate the viscous flow field. The computational domain was divided by a trim mesh, and the overset grid technique was used to analyze the coupled motion of the amphibious vehicle. Following verification of mesh independence and calculation method reliability, the flow field distributions were examined for a range of β. The results show that capsizing thresholds were identified through hydrodynamic analysis: heave motion transitioned to planing mode at Fr ≥ 0.711, whereas roll instability intensified abruptly beyond this speed. Asymmetric vortices and wave-breaking effects induced significant resistance amplification beyond β ≥ 10°, with transverse force stability limits exceeded at β &amp;gt; 15°. Pressure redistribution toward the bow coupled with lift effects triggered coupled instabilities. Free wave surface asymmetry and velocity contour interactions intensified above β = 15°, culminating in critical roll failure at β = 20° (Fr = 1.271). This study reveals the interrelation mechanisms among the pressure distribution, free wave surface, and velocity contour of the flow field during oblique navigation, providing theoretical guidance for amphibious vehicle stability enhancement under extreme maneuvers.

BACKGROUND: amphibious wheeled transport and technological complexes (AWTTC) are critically important for rescue and other special operations, but their speed on water is limited due to high wheel resistance and suboptimal hydrodynamics. Existing studies do not take into account the planing mode in a comprehensive manner. AIMS: the objective of this work is to develop a mathematical model of the movement of an amphibious vehicle on water in the planing mode, which takes into account not only hydrostatic forces, but also hydrodynamic ones. MATERIALS AND METHODS: equations for determining excess pressure on the hull surface are derived based on the Cauchy-Lagrange integral, a calculation scheme for the interaction of a flat-bottomed hull with the water surface is developed. Analytical expressions for the lifting hydrodynamic force, resistance force, and hydrodynamic moment are obtained. An analysis of the stability of motion is carried out taking into account the position of the center of gravity, the magnitude of the traction force of the watercraft propeller, and the trim angle. RESULTS: it was found that at Froude numbers Fr 3.0, hydrodynamic forces provide 95-97% of maintaining the AKTT afloat. The criteria for the stability of motion are obtained: with a negative arm of the propeller force, the stability depends on the magnitude of the thrust, with a positive arm, the critical speed of motion is determined. It was found that the thickness of the "reverse jet" is proportional to the angle of attack, the resistance force has a quadratic dependence on the speed, the arm of the hydrodynamic moment is linearly dependent on the trim angle. CONCLUSIONS: the developed mathematical model allows analyzing the motion of the AKTT in the planing mode taking into account key hydrodynamic factors. The obtained results create a theoretical basis for the design of high-speed amphibious vehicles and require further experimental validation.

The control objective of the Rudder Roll Stabilization (RRS) system is to deploy the rudder, which is primarily a path controlling device, to reduce the roll motion without interference in heading of ship. To achieve the control of both roll and yaw motions, the only control input is the rudder angle and hence the RRS system is referred as a Single Input, Two Output (SITO) system. Rudder roll stabilization is insignificant at low forward speed of the ship, but can give significant control at higher speed when fast rudder movement is applied. This paper presents a closed loop state space model for accurate simulations on rudder roll stabilization in irregular seas considering the 3-degree of freedom motions, i.e., sway, roll and yaw. The computational model is developed to analyze the effect of the rudder movement on sway, roll and yaw in forward speed conditions in irregular sea conditions. The Sea State conditions are modelled as wave perturbation models using the method of shaping filter established by filtered white noise. The control system has been designed using optimal linear quadratic regulator (LQR) method. The control loop contains both the signal for the autopilot action to trigger the heading angle correction as well as the signal for rudder based roll motion control. The simulations are carried out with rudder roll control system ON and OFF mode to analyze the effect of the rudder on steering and motion stabilization. In both cases the autopilot is in active mode to correct deviations in the course heading. The simulations are analyzed for three different ship speeds in two different Seas State conditions with a low and fast rudder movement to show the efficacy of the model. The performance is evaluated and presented based on the RMS value. Since the rudder based roll motion stabilization may also result in unnecessary motions of sway and yaw, besides the desirable roll reduction, the result presents the sway-roll-yaw responses as applicable under the particular speed and Sea State conditions.

The International Maritime Organization (IMO) finalized the second-generation intact stability criteria in 2022. However, an accurate and practical numerical method for stability loss has yet to be established. Therefore, a 6 DOF numerical model is further improved based on the previous study. Firstly, the rolling motion is simulated using a seakeeping model instead of the previous maneuvering mathematical model. Secondly, the roll-restoring variation is calculated directly considering the instantaneous wet hull instead of the previous pre-calculated method. Thirdly, transferring frequency to time is used to obtain heave and pitch motions, further considering yaw angle and sway velocity. Fourthly, the dynamic forces for sway, roll, and yaw motions are calculated, further considering the effect of the speed variation. Fifthly, the 6 DOF motions are used to determine the instantaneous wet hull, and the FK force and the hydrostatic force are calculated by the body’s exact method. Finally, a new conclusion is obtained that the sway and yaw motions’ effect on the ship speed loss, the relative longitudinal wave profile by the speed loss, the rudder angles, and the accompanying rudder forces in the rolling direction are significant, and much more than their centrifugal force or coupled force in the rolling direction.

Analysis of Flettner Rotor ships in beam waves

Contemporary Velocity Prediction Programs (VPP's) consider the equilibrium of forces acting on a sailing yacht in the thrust direction and in the direction of the developed side force on canoe body and appendages. In addition, force-moment equilibrium is considered in the transverse plane of the yacht. In this way a solution is found for the three main unknowns in performance prediction, viz: boat speed, leeway angle and heel angle. The impact of helm angle on performance is herein ignored. In the velocity prediction program developed by Van Oossanen &amp; Associates, a fourth equilibrium condition is included, viz: force-moment equilibrium in the horizontal plane for the calculation of the helm angle required for the equilibrium sailing condition. In this paper a description is given of some of the main problems that need to be solved when introducing this fourth equilibrium requirement. One of these is associated with the development of accurate mathematical expressions for the calculation of rudder side force and resistance, as influenced by heel angle and the proximity of the free surface. Model tests can be utilized for obtaining insight into the physical phenomena involved in such cases. Model tests were carried out in the context of an optimization study for the design of a yacht according to the International Level Class 40 (ILC40) Rule, under the International Measurement System (IMS). The analysis of some of the results of these tests with respect to improving the mathematical model for rudder side force and resistance, is described in the paper. The effect of including this mathematical model in a VPP is demonstrated in the paper by providing the results of calculations which reveal that a variation in rudder angle causes significant speed differences. It is shown that the IMS VPP that is used to calculate the rating and speed potential of ILC40 and other IMS Class yachts, in not taking into account the significant variations in performance associated with different values of the equilibrium rudder angle (and the associated rudder side force and resistance), is not sufficiently accurate.

Autonomous vehicles can risk dangerous rollover if they corner without taking roll motion into consideration. This paper proposes a control algorithm to follow a curved road while simultaneously preventing rollover. Model predictive control is applied to minimize roll motion throughout cornering. The prediction of vehicle state is based on a four-wheel nonlinear vehicle model with roll dynamics and a tire brush model. Full braking is utilized as a control actuator to achieve an optimal balance in the trade-off between vehicle speed and roll motion. CarSim simulations show the performance of the proposed control approach and the influence of vehicle parameters on control performance.