A method based on potential theory for calculating air cavity formation of an air cavity resistance reduction ship

This research is intended to provide academic reference and design guidance for further studies to determine the most effective means to reduce a ship’s resistance through an air-cavity. On the basis of potential theory and on the assumption of an ideal and irrotational fluid, this paper drives a method for calculating air cavity formation using slender ship theory then points out the parameters directly related to the formation of air cavities and their interrelationships. Simulations showed that the formation of an air cavity is affected by cavitation number, velocity, groove geometry and groove size. When the ship’s velocity and groove structure are given, the cavitation number must be within range to form a steady air cavity. The interface between air and water forms a wave shape and could be adjusted by an air injection system.     

Decoupled self-tuning PI controller for an idling stop system applied to scooters

This paper is aimed to propose a decoupled self-tuning proportional plus integral (PI) controller with simple law for an idling stop system applied to scooters. An integrated starter generator (ISG) of the idling stop system is designed with a high efficiency permanent magnet synchronous motor (PMSM). The PMSM used as an ISG must have a high torque characteristic to ensure that the engine can be accelerated up to firing speed. A conventional and useful control algorithm named PI control is unable to handle motor current very well for dynamic load, parametric variation, and external disturbance, especially in a vehicle application. Therefore, a robust algorithm for current control in an ISG is proposed. The decoupled selftuning PI controller based on the Lyapunov stability theorem is utilized to guarantee the control performance. Numerical simulations demonstrate the effectiveness of the proposed control algorithm. Experimental results show that the engine of a 150 cm3 scooter can be cranked to reach firing speed by a ISG within 0.1?0.2 second. The proposed method is simple, robust, as well as stable for idling stop system, and can be effectively implemented.     

Efficient estimation of extreme non-linear roll motions using the first-order reliability method (FORM)

In on-board decision support systems, efficient procedures are needed for real-time estimation of the maximum ship responses to be expected within the next few hours, given online information on the sea state and user-defined ranges of possible headings and speeds. For linear responses, standard frequency domain methods can be applied. For non-linear responses, as exhibited by the roll motion, standard methods such as direct time domain simulations are not feasible due to the required computational time. However, the statistical distribution of non-linear ship responses can be estimated very accurately using the first-order reliability method (FORM), which is well known from structural reliability problems. To illustrate the proposed procedure, the roll motion was modelled by a simplified non-linear procedure taking into account non-linear hydrodynamic damping, time-varying restoring and wave excitation moments, and the heave acceleration. Resonance excitation, parametric roll, and forced roll were all included in the model, albeit with some simplifications. The result is the mean out-crossing rate of the roll angle together with the most probable wave scenarios (critical wave episodes), leading to user-specified specific maximum roll angles. The procedure is computationally very effective and can thus be applied to real-time determination of ship-specific combinations of heading and speed to be avoided in the actual sea state.     

Design Optimization of a Rear Independent Suspension for the Korean Light Tactical Vehicle

Steering and suspension handle the direction of a vehicle according to the driver’s intentions and control the disturbance from the road surface while supporting the vehicle body. The static and dynamic characteristics of two systems are critical factors for the ride comfort and the directional stability. In the layout stage, the hard points of steering and suspension systems are determined. In the next design stage, the detailed design of the system, including gearboxes, springs, shock absorbers, and control links, is carried out. While the optimal hard points of a suspension are determined at the precedent design, interference with other peripheral components should be carefully examined in the detailed design process. In the case of the design point change should be made to avoid the interference, subsequent position and shape changes of the link mechanism are required. Therefore, there is a need to examine the optimization of suspension compliance characteristics with chassis design changes and the durability performance of the modified design. This study proposes an integrated analysis method for the design optimization and the durability evaluation of such optimized design specifications of the rear independent suspension for a military vehicle.     

Underwater sonar image recognition based on gray-spatial histograms

A new gray-spatial histogram is proposed, which incorporates spatial information with gray compositions without sacrificing the robustness of traditional gray histograms. The purpose is to consider the representation role of gray compositions and spatial information simultaneously. Each entry in the gray-spatial histogram is the gray frequency and corresponding position information of images. In the experiments of sonar image recognition, the results show that the gray-spatial histogram is effective in practical use.     

Measuring and sustaining the UK maritime skills base: A review

Numerous factors over the past three decades have contributed to a major decline in the number of seagoing staff in the United Kingdom. These include shipping companies opting for other flags, as well as the profession itself becoming less and less attractive for school leavers. This decrease in numbers is not only significant for shipping companies, but also for the allied services which used to get supported from seafarers coming ashore in search of a new career. It is now recognised that changes in the maritime skills base will affect both the seagoing as well as the shore side of the industry.     

Modeling a high output marine steam generator feedwater control system which uses parallel turbine-driven feed pumps

Parallel turbine-driven feedwater pumps are needed when ships travel at high speed. In order to study marine steam generator feedwater control systems which use parallel turbine-driven feed pumps, a mathematical model of marine steam generator feedwater control system was developed which includes mathematical models of two steam generators and parallel turbine-driven feed pumps as well as mathematical models of feedwater pipes and feed regulating valves. The operating condition points of the parallel ttu-bine-driven feed pumps were calculated by the Chebyshev curve fit method. A water level controller for the steam generator and a rotary speed controller for the turbine-driven feed pumps were also included in the model. The accuracy of the mathematical models and their controllers was verified by comparing their results with those from a simulator.     

Numerical simulation of viscous liquid sloshing by moving-particle semi-implicit method

A meshless numerical simulation method, the moving-particle semi-implicit method （MPS） is presented in this paper to study the sloshing phenomenon in ocean and naval engineering. As a meshless method, MPS uses particles to replace the mesh in traditional methods, the governing equations are discretized by virtue of the relationship of particles, and the Poisson equation of pressure is solved by incomplete Cholesky conjugate gradient method （ICCG）, the free surface is tracked by the change of numerical density. A numerical experiment of viscous liquid sloshing tank was presented and compared with the result got by the difference method with the VOF, and an additional modification step was added to make the simulation more stable. The results show that the MPS method is suitable for the simulation of viscous liquid sloshing, with the advantage in arranging the particles easily, especially on some complex curved surface.     

Modelling and analysis of a gyrostat elastically attached to a vehicle

In recent studies, the dynamic response of a passenger car to a gyrostat was investigated for a series of driving manoeuvres, but the gyrostat was assumed to be rigidly supported, thus neglecting the effect of rotor precession. The aim of the present study is the modelling and investigation of the gyrostat-vehicle interaction for elastically mounted gyrostats. For this purpose, a general model describing the motion of a gyrostat elastically supported by a moving platform is derived. Emphasis is placed on the mathematical derivation, where all considerations that are necessary to arrive at the final result are included. Thus, the presented considerations and results can be easily adopted and are suitable to serve beyond their actual purpose as a reference work for other applications. The derived model is tested with the aid of vehicle dynamics simulations and the simulation results prove to be consistent with the results of the rigid attachment model, provided that the elastic approach is subjected to high-bearing stiffnesses. However, it is shown that at lower bearing stiffnesses the solutions are progressively different, since low-bearing stiffnesses enable the gyrostat to move, due to the compliance of the bearings itself, relative to the vehicle chassis with high-angular velocities.