几何形状对气垫升力的影响研究

One of the crucial and challenging issues for researchers is presenting an appropriate approach to evaluate the aerodynamic characteristics of air cushion vehicles(ACVs)in terms of system design parameters.One of these issues includes introducing a suitable approach to analyze the effect of geometric shapes on the aerodynamic characteristics of ACVs.The main novelty of this paper lies in presenting an innovative method to study the geometric shape effect on air cushion lift force,which has not been investigated thus far.Moreover,this paper introduces a new approximate mathematical formula for calculating the air cushion lift force in terms of parameters,including the air gap,lateral gaps,air inlet velocity,and scaling factor for the first time.Thus,we calculate the aerodynamic lift force applied to nine different shapes of the air cushions used in the ACVs in the present paper through the ANSYS Fluent software.The geometrical shapes studied in this paper are rectangular,square,equilateral triangle,circular,elliptic shapes,and four other combined shapes,including circle-rectangle,circle-square,hexagonal,and fillet square.Results showed that the cushion with a circular pattern produces the highest lift force among other geometric shapes with the same conditions.The increase in the cushion lift force can be attributed to the fillet with a square shape and its increasing radius compared with the square shape.

Hydrodynamic Analysis and Shape Optimization for Vertical Axisymmetric Wave Energy Converters

The absorber is known to be vertical axisymmetric for a single-point wave energy converter （WEC）. The shape of the wetted surface usually has a great influence on the absorber＇s hydrodynamic characteristics which are closely linked with the wave power conversion ability. For complex wetted surface, the hydrodynamic coefficients have been predicted traditionally by hydrodynamic software based on the BEM. However, for a systematic study of various parameters and geometries, they are too multifarious to generate so many models and data grids. This paper examines a semi-analytical method of decomposing the complex axisyrnmetric boundary into several ring-shaped and stepped surfaces based on the boundary discretization method （BDM） which overcomes the previous difficulties. In such case, by using the linear wave theory based on eigenfunction expansion matching method, the expressions of velocity potential in each domain, the added mass, radiation damping and wave excitation forces of the oscillating absorbers are obtained. The good astringency of the hydrodynamic coefficients and wave forces are obtained for various geometries when the discrete number reaches a certain value. The captured wave power for a same given draught and displacement for various geometries are calculated and compared. Numerical results show that the geometrical shape has great effect on the wave conversion performance of the absorber. For absorbers with the same outer radius and draught or displacement, the cylindrical type shows fantastic wave energy conversion ability at some given frequencies, while in the random sea wave, the parabolic and conical ones have better stabilization and applicability in wave power conversion.

SVM for Constellation Shaped 8QAM PON System

Nonlinearity impairments and distortions have been bothering the bandwidth constrained passive optical network(PON)system for a long time and limiting the develop-ment of capacity in the PON system.Unlike other works concentrating on the exploration of the complex equalization algorithm,we investigate the potential of constellation shap-ing joint support vector machine(SVM)classification scheme.At the transmitter side,the 8 quadrature amplitude modulation(8QAM)constellation is shaped into three designs to mitigate the influence of noise and distortions in the PON channel.On the receiver side,simple multi-class linear SVM classifiers are utilized to replace complex equalization methods.Simulation results show that with the bandwidth of 25 GHz and overall bitrate of 50 Gbit/s,at 10 dBm input optical power of a 20 km standard single mode fiber(SSMF),and under a hard-decision forward error correction(FEC)threshold,transmission can be realized by employing Circular(4,4)shaped 8QAM joint SVM classifier at the maximal power budget of 37.5 dB.

Non-Uniform APSK Optimization for BICM Systems

Traditional Amplitude Phase Shift Keying （APSK） consists of rings with points uniformly spaced. By giving up this uniform-spacing feature, we propose an APSK optimization method based on the uniform APSK with Gray labeling （Gray-APSK）. The aim of the optimization is to maximize the Generalized Mutual Information （GMI） of Bit-Interleaved Coded Modulation （BICM） for the targeted code rate and channel. We show that our optimized non-uniform APSK could offer further performance gain compared with the conventional uniform Gray-APSK and considerably outperforms the traditional quadrature amplitude modulation at the targeted SNR and channel.

Shape optimization design of a heaving buoy of wave energy converter based on fully parametric modeling and CFD method

The hydrodynamic shape of the heaving buoy is an important factor of the motion response in waves and thus concerns the energy conversion efficiency for the point absorbers(PAs).The current experience-based designs are time consuming and not very efficient,hence,faster and smarter methods are desirable.An automated optimization method based on a fully parametric modeling method and computational fluid dynamics(CFD),is proposed in this paper.Using this method,a benchmark buoy is screen designed and then optimized by maximizing the heave motion response.The geometry is described parametrically and deformed by means of the free-form deformation(FFD)method.During the optimization process,the expansion factor of control points is the basis for the variations.A combination of the Sobol and the non-dominated sorting genetic algorithm II(NSGA-II)is used to search for the solutions.After several iterations,the heaving buoy shape with optimal heave motion response is obtained.The analyses show that the heave motion response has increased 55.3%after optimization.The developed methodology is valid and seems to be a promising way to design a novel buoy that can significantly improve the wave energy conversion efficiency of the PAs in future.