FULL-SCALE MOTIONS OF A LARGE HIGH-SPEED CATAMARAN: THE INFLUENCE OF WAVE ENVIRONMENT, SPEED AND RIDE CONTROL SYSTEM

To assess the behaviour of large high-speed catamarans in severe seas, extensive full-scale trials were conducted by the U.S. Navy on an INCAT Tasmania built vessel in the North Sea and North Atlantic region. Systematic testing was done for different speeds, sea states and ride control settings at different headings. Collected data has been used to characterise the ship’s motions and seakeeping performance with respect to wave environment, vessel speed and ride control system. Motion response amplitude operators were derived and compared with results from a two-dimensional Green function time-domain strip theory seakeeping prediction method. An increase of motion response with increasing vessel speed and a decrease with the vessel moving from head to beam seas was found. In higher sea states and headings ahead of beam seas an increasing influence of the centre bow on pitch motion damping was found. Significant motion RAO reduction was also found when the ride control system was active. Its effectiveness increased at higher speeds and contributed to heave and pitch motion RAO reduction. Predicted motion magnitudes with the time domain seakeeping code were consistent with the measured motion responses, but maximum heave was predicted at a rather higher frequency than was evident in the trials.

Propeller Speed Control System on Autonomous Quadcopter with Variations in Load Fulcrum Point

The need for unmanned vehicles is increasingly needed in certain conditions, such as distribution of disaster supply, distribution of medicines, distribution of vaccines in the affected areas in pandemic situations. The various types of goods to be distributed require a different fulcrum. This research implemented PID control for the quadcopter balance control system to achieve stability during hovering. PID control is used to achieve a certain setpoint to produce the required PWM output for the propeller to reach a speed that can fly the quadcopter tilted until it reaches a steady state. Tests were carried out on the roll and pitch motion of the quadcopter by providing a load. The results show that PID control can be implemented for the quadcopter balance control system during hovering by determining the PID constants for each roll and pitch motion with the constanta of Kp = 0.15, Kd = 0.108, and Ki = 0.05. The quadcopter takes 3 – 6 seconds to return to the 0 degree setpoint when it is loaded.

Realisation of pitch-rotational torque wrench in two-beam optical tweezers

3D Pitch (out-of-plane) rotational motion has been generated in spherical particles by maneuvering the laser spots of holographic optical tweezers. However, since the spherical particles, which are required to minimise drag are perfectly isotropic, a controllable torque cannot be applied with it. It remains free to spin about any axis even after moving the tweezers beams. It is here that we trap birefringent particles of about 3 $\mu$m diameter in two tweezers beams and then change the depth of one of the beam foci controllably to generate a pitch rotational torque-wrench and avoid the free spinning of the particle. We also detect the rotation with newly developed pitch motion detection technique and apply controlled torques on the particle.

Conceptual Design and Hydrodynamic Performance of a Modular Hybrid Floating Foundation

The comprehensive utilization of offshore renewable energies is an effective way to solve the intermittency and variability of power supply. This paper aims to present a hybrid floating system (HFS) based on a modular buoyancy-distributed floating foundation (BDFF) that can be equipped with a horizontal-axis wind turbine, solar panels, and wave energy converters (WEC). A simplified test model with a Froude scale ratio of 1/10 is employed to perform the experiments in a deep-water basin to validate the numerical results computed from the code program ANSYS AQWA based on the potential flow theory. The Response Amplitude Operators (RAOs) under regular waves are compared to evaluate the hydrodynamic performance. There is a good agreement in the surge, pitch, and heave RAOs for experiments and the numerical simulation, with a maximum of 6.45 degrees per meter for the pitch motion. Furthermore, the mooring tensions in the time domain are analyzed under different wave conditions.The tension RAOs from simulations are slightly higher than those from measurements with a maximum value at the period of 3.416 s. The mooring line on the windward side has a more considerable mooring tension that is far less than the allowable tensile strength, especially under the wave height of 2 m and the wave period of 2.873 s. The influence of loaded weight representing solar panels is weak, and the impact of winds is acceptable, as the platform deviates 1.3 degrees from the equilibrium state under the test wind speed. Eventually, the effect of irregular waves on the HFS is presented with the critical parameters of mooring tension and pitch motion. The results show that the HFS has a good motion performance.

Influence of suspension parameter for derailment analysis of a full railway vehicle model cruising on a curved track

The main intention of this research work is to study the derailment response of high speed railway vehicle (HSRV) cruising on a curved track. In previous research work, lower degree of freedom (DOF) has been considered for the derailment analysis which may not give more accurate results. Hence, a 31 DOF bondgraph model of HSRV has been developed which consist of carbody, two truck frames and two selfsame wheelsets for each truck frame. Vertical, lateral, roll, yaw and pitch motion are considered for carbody and bogie and except pitch motion all the other motion are considered for wheelsets. Non-linearities in terms of heuristic nonlinear creep model and flange contact has been employed to simulate the derailment response at high speed. The effect of vehicle speed running on a curved track was investigated for derailment quotient. The main aim of present research work to evaluate derailment quotient at the speed range of 150 kmph to 600 kmph for hard and soft suspension parameter. Derailment quotient has been calculated for both linear and nonlinear creep models and it is seen that DQ for linear model has a lower value compare to non linear creep. The major advantages of the proposed model are that, the presented model can actively predict the derailment of a railway vehicle, and also precisely determine the nonlinear critical hunting speeds.

Dynamic Hull Vane – A Solution for active Pitch Motion Reduction and Resistance Reduction of ships

The Dynamic Hull Vane® is an actively controlled version of the Hull Vane®, a patented energy-saving and seakeeping device which consists of a submerged wing mounted on the aft ship. The Hull Vane is positioned in the upward flow aft of the ship, to develop forward thrust and reduce the stern wave. Naiad Dynamics US Inc, is a supplier of ride control systems and has worked with Hull Vane BV to develop the Dynamic Hull Vane®. By enabling the Hull Vane® to rotate, it can produce variable lift forces which when suitably controlled can reduce the pitching motions of a vessel in a seaway. This paper describes some of the research carried out on the AMECRC series 13, a generic fast displacement hull.

An Experimental Analysis of Active Pitch Control for an Assault Amphibious Vehicle Considering Waterjet-Hydrofoil Interaction Effect

The present study aims to reduce the pitch motion of an assault amphibious vehicle system in seaways by waterjet impeller revolution rate control. A series of seakeeping tests were performed in a towing tank with a 1/4.5-scale model. This vehicle is manufactured as a box-shaped hull, and since an appendage that generates lift force is attached, the amount of change in pitch motion is large according to the forward speed. For pitch motion reduction, the impeller revolution rate and resultant pitch moment were controlled through a proportional-integral-derivative controller. Improvements in seakeeping performance were examined in both regular and irregular conditions by the model tests in terms of root mean square of pitch motion. The tuned controller decreased pitch motion by more than 60%.

Beneficial wake-capture effect for forward propulsion with a restrained wing-pitch motion of a butterfly

Unlike other insects, a butterfly uses a small amplitude of the wing-pitch motion for flight. From an analysis of the dynamics of real flying butterflies, we show that the restrained amplitude of the wing-pitch motion enhances the wake-capture effect so as to enhance forward propulsion. A numerical simulation refined with experimental data shows that, for a small amplitude of the wing-pitch motion, the shed vortex generated in the downstroke induces air in the wake region to flow towards the wings. This condition enables a butterfly to capture an induced flow and to acquire an additional forward propulsion, which accounts for more than 47% of the thrust generation. When the amplitude of the wing-pitch motion exceeds 45°, the flow induced by the shed vortex drifts away from the wings; it attenuates the wake-capture effect and causes the butterfly to lose a part of its forward propulsion. Our results provide one essential aerodynamic feature for a butterfly to adopt a small amplitude of the wing-pitch motion to enhance the wake-capture effect and forward propulsion. This work clarifies the variation of the flow field correlated with the wing-pitch motion, which is useful in the design of wing kinematics of a micro-aerial vehicle.

Optimal design of the vehicle mechatronic ISD suspension system using the structure-immittance approach

There are three types of two-terminal mechanical elements, namely the inerter, the spring, and the damper in the vehicle ISD suspension system, and how to design the suspension structure has drawn much attention in automotive engineering fields. Due to the advantage of using the external electrical network to simulate the corresponding mechanical impedance output, a ball-screw mechatronic inerter is adopted in the optimal design procedure in this paper. A half vehicle dynamic model considering the vehicle body vertical motion and pitch motion is established, and the optimal design methodology of the vehicle mechatronic ISD suspension is proposed by using the structure-immittance approach to ensure the simplicity of the suspension structures. The dynamic performance indexes constraints are taken into account, and the optimal structures are discussed in detail. Numerical simulations results show that, the dynamic performance indexes, namely the RMS (root-mean square) of the vehicle body vertical acceleration and the RMS of the pitch motion acceleration of the mechatronic ISD suspensions can be reduced by 31% and 35% without constraints, and 18% and 15% with constraints by comparing to the passive suspension system. The structure-immittance approach can be easily adopted in the vehicle suspension structural design, and the research fruits will provide a new thought for the application of the inerter element in automotive engineering.