爆破型和聚能型装药水下爆炸载荷特性

Blasting and shaped charges are the main forms of underwater weapons,and their near-field underwater explosions(UNDEX)can severely damage structures.Therefore,it is of great importance to study underwater explosive load characteristics of different forms of charges.The full physical process of a typical underwater explosion of a sphere/column blasting charge and a shaped charge was simulated using the Eulerian method.The loading characteristics of the underwater blast shock wave and bubble,as well as the projectile,were studied.The results show that the shock wave loads of spherical,cylindrical,and polygonal charges propagate outward in spherical,ellipsoidal–spherical and ellipsoidal–spherical wavefronts,respectively.When the shock wave reaches 16 times the distance-to-diameter ratio,its surface is approximately spherical.In addition,in the shaped charge underwater explosion,the shaped charge liner cover absorbs 30°–90°of the shock wave energy and some of the bubble energy to form a high-speed shaped penetrator.Spherical,ellipsoidal,and ellipsoidal bubbles are generated by underwater explosions of spherical,cylindrical,and shaped charges,respectively.The obtained results provide a reference for evaluating the power of underwater weapons.

Parallel Computing of the Underwater Explosion Cavitation Effects on Full-scale Ship Structures

象装载的冲击波和水泡脉搏一样，成穴也在对的表面轮船和另外的近表面的海洋的结构的动态反应上有很重要的影响在水下爆炸装载。在这份报纸，在 ABAQUS 嵌入的声学结构的联合方法被采用做数字分析在水下爆炸考虑成穴。体积成穴区域和本地成穴区域的形状被获得，并且他们在对分析结果的好同意。再装的持续时间比一个冲击波的若干次长。最后，单个计算和一艘照原尺寸的轮船的动态回答上的成穴效果的平行计算被介绍，它证明那再装由成穴引起了是非可忽略的。所有这些结果在理解是有用的在水下爆炸成穴效果。

Analytical and Experimental Study of Free Vibration of Beams Carrying Multiple Masses and Springs

The structures in engineering can be simplified into elastic beams with concentrated masses and elastic spring supports. Studying the law of vibration of the beams can be a help in guiding its design and avoiding resonance. Based on the Laplace transform method, the mode shape functions and the frequency equations of the beams in the typical boundary conditions are derived. A cantilever beam with a lumped mass and a spring is selected to obtain its natural frequencies and mode shape functions. An experiment was conducted in order to get the modal parameters of the beam based on the NExT-ERA method. By comparing the analytical and experimental results, the effects of the locations of the mass and spring on the modal parameter are discussed. The variation of the natural frequencies was obtained with the changing stiffness coefficient and mass coefficient, respectively. The findings provide a reference for the vibration analysis methods and the lumped parameters layout design of elastic beams used in engineering.

Calculation of the Added Mass of a Liquid Tank's Bulkheads

The added mass coefficient and the water level index formulas for the same-phase and anti-phase vibration of rectangular liquid tanks' bulkheads were derived based on dry mode theory. Three fluid-structure interaction numerical methods including Fluid FEM and Fluid BEM were used in this case. The comparison of numerical and theoretical results by the present method shows that ANSYS/Fluid80 is more credible, the NASTRAN/Virtual Mass Method is more suitable for engineering calculations and results of the same-phase vibration by the present method is more accurate.

Optimal Control of a Beam with Discontinuously Distributed Piezoelectric Sensors and Actuators

因为它的轻重量，宽带，和能适应的性质，聪明的材料广泛地在灵活结构的活跃颤动控制(AVC ) 被使用了。基于一一阶砍变丑理论由联合电、机械的操作， 4 节点有为概括排水量的自由的 24 度和自由的一电的潜在的度的四边的压电的合成元素每压电的层被导出。有不连续地分布式的压电的传感器和致动器的一根横梁的动态特征被介绍。一个线性二次的管理者(LQR ) 反馈控制器被设计用高度在州的空间压制横梁的颤动精确直接(HPD ) 集成方法。

基于CFD的斜航船舶浮态数值预报

目前涉及斜航船舶的数值模拟计算鲜有在模拟过程中考虑到船舶浮态的影响,然而浮态变化对水动力数值计算精度的影响是不容忽视的。基于此,文章以系列60船斜航运动(傅汝德数Fr=0.316,斜航角β=10°)为算例,采用重叠网格技术处理斜航船的大幅运动问题,通过耦合求解船舶六自由度运动方程和流体流动方程的方法,计算出了斜航船的升沉量、纵倾和横倾角度。结果显示,考虑浮态的数值预报结果与爱荷华大学的试验数据相比误差基本控制在10%以内,体现出该数值计算预报方法具有较强的工程实用性。

三维水翼升力线理论(英文)

Prandtl’s lifting line theory was generalized to the lifting problem of a three-dimensional hydrofoil in the presence of a free surface. Similar to the classical lifting theory, the singularity distribution method was utilized to solve two-dimensional lifting problems for the hydrofoil beneath the free surface at the air-water interface, and a lifting line theory was developed to correct three-dimensional effects of the hydrofoil with a large aspect ratio. Differing from the classical lifting theory, the main focus was on finding the three-dimensional Green function of the free surface induced by the steady motion of a system of horseshoe vortices under the free surface. Finally, numerical examples were given to show the relationship between the lift coefficient and submergence Froude numbers for 2-D and 3-D hydrofoils. If the submergence Froude number is small free surface effect will be significant registered as the increase of lift coefficient. The validity of these approaches was examined in comparison with the results calculated by other methods.

Flow Separation and Vortex Dynamics in Waves Propagating over A Submerged Quartercircular Breakwater

The interactions of cnoidal waves with a submerged quartercircular breakwater are investigated by a ReynoldsAveraged Navier–Stokes(RANS) flow solver with a Volume of Fluid(VOF) surface capturing scheme(RANSVOF) model. The vertical variation of the instantaneous velocity indicates that flow separation occurs at the boundary layer near the breakwater. The temporal evolution of the velocity and vorticity fields demonstrates vortex generation and shedding around the submerged quartercircular breakwater due to the flow separation. An empirical relationship between the vortex intensity and a few hydrodynamic parameters is proposed based on parametric analysis. In addition, the instantaneous and time-averaged vorticity fields reveal a pair of vortices of opposite signs at the breakwater which are expected to have significant effect on sediment entrainment, suspension, and transportation,therefore, scour on the leeside of the breakwater.

三体船构型水动力性能试验研究

This paper presents experimental results on configuration hydrodynamics.Three models are used in the model tests,which are typical of hard,round,and soft chines.Although specific values are different,the influence patterns are similar in the three ship models.A set of different outrigger positions is investigated in calm water and regular waves.A variety of interesting phenomena are observed,among which the splash resistance is the dominant component for a trimaran at high speeds(with Froude number Fr>0.6).If two small outriggers are placed inside Kelvin’s wave systems of the main hull,a strong splash appears,resulting in a significant resistance increase.Moreover,short and long waves cannot be neglected,for they may excite the motions of much smaller outriggers.This condition leads to non-vanishing heaving at high-frequency and non-normalized pitches at low frequencies.Based on the tests,three spectra of optimum configurations for resistance,longitudinal motions,and transverse motions are presented.These results reveal the optimum configurations of a trimaran hull in terms of hydrodynamic performance,thus providing a very powerful tool for optimum design of trimaran ships.

基于浸没边界-多相格子玻尔兹曼通量法的圆柱体出入水时自由液面形态的数值模拟

In this work,the deformation of free interface during water entry and exit of a circular cylinder is investigated numerically by using the two-dimensional(2D)immersed boundary-multiphase lattice Boltzmann flux solver(IB-MLBFS).The fluid domain is discretized by finite volume discretization,and the flux on the grid interface is evaluated by lattice Boltzmann equations.Both the implicit velocity correction and the surface flux correction are implemented by using the immersed boundary-method to consider the fluid-structure interaction and the contact interface between the multiphase fluids and the structure.First,the water entry of a circular cylinder is simulated and the results are compared with the experiment,which considered the length-diameter ratio of the circular cylinder.The reliability of 2D simulation is verified and the deformation of the free interface is well investigated.Afterward,the water exit of a circular cylinder with constant velocity is simulated,which is less researched.In addition,the results show the advantage of present IB-MLBFS to some extent.Finally,the water exit and re-entry of a circular cylinder are presented,and the results present the complex deformation of the free interface and the dynamic response of the moving structure.Based on the numerical results,the free interface of the multiphase fluids is well captured,and the contact interface on the boundary of the moving structure is accurately presented by the IB-MLBFS.

Numerical research on slamming characteristics of aircraft landing on water

In order to investigate the impact characteristic of an aircraft landing on water,a computational fluid dynamics(CFD)simulation is conducted to explore the slamming characteristics of the NACA TN 2929 A model.The flow around the model is solved by using Reynolds-averaged Navier-Stokes equations with the shear stress transport(SST)k—ωturbulence model,based on finite volume method(FVM).The free surface is captured by using the volume of fluid(VOF)method,and the aircraft impact process is realized with help of overset mesh technology.Then,the effects of horizontal and vertical velocities and initial pitch angle on the slamming load,attitude change,impact pressure and flow field evolution are investigated.The results reveal that the horizontal velocity has a considerable influence on whether the aircraft’s horizontal tail hits the water,and further affects the maximum vertical load as well as the maximum pitch angle throughout the impact process.The vertical velocity determines the slamming load before the horizontal tail strikes the water,while the horizontal velocity has a significant effect on the load after the horizontal tail hits the water.A smaller initial pitch angle results in not only a heavier slamming load but also a more dramatic change of the posture after the aircraft impacts the water.The impact pressure of the aircraft is maximized at the junction of the approaching surface of the fuselage and the free surface.In some cases,the pressure is also concentrated on the undersurface of the horizontal tail.

A numerical study of passenger side airbag deployment based on arbitrary Lagrangian-eulerian method

The passenger side airbags(PAB)are usually larger than the driver airbags.Therefore,the inflator of PAB is more powerful with high mass rate.In this paper,an Arbitrary Lagrangian-Eulerian(ALE)method based computational method is developed to simulate the deployment of a PAB.The tank test is used to test the property of the inflator.Through comparison of numerical and experimental results,the ALE method is validated.Based on a failed airbag test,a smaller sub-airbag is placed inside PAB to disperse the gas flow to directions which are less damaging.By applying dynamic relaxation,the initial mesh corresponding to the experimental terms is obtained.The results indicate that the interior pressure and impact force coincide with the test data,and the method in this paper is capable of capturing airbag deploying process of the PAB module accurately.

URANS COMPUTATION OF CAVITATING FLOWS AROUND SKEWED PROPELLERS

Cavitating flows around skewed propellers are investigated numerically by means of the unsteady Reynolds Averaged Navier-Stokes （RANS） Equation method. The standard k - c turbulence and the modified Z-G-B cavitation models are employed. A measured nominal wake is used for the inlet velocity boundary condition. Predicted cavitating evolution processes and tip cavity patterns are compared with experimental observations. In addition, the influence of the skew angles on the cavitation and unsteadiness performances of propellers operating in a non-uniform wake is also studied. Results show that the modified Z-G-B cavitation model performs better to simulate the cavitating flow cases studied in this paper. Comparisons demonstrate that the skewed propeller with a skew angle of 20~ is the best choice for a given stern wake with a assigned thrust and the minimum force fluctuations.

Active control of multiscale features in wall-bounded turbulence

This study experimentally investigates the impact of a single piezoelectric(PZT)actuator on a turbulent boundary layer from a statistical viewpoint.The working conditions of the actuator include a range of frequencies and amplitudes.The streamwise velocity signals in the turbulent boundary layer flow are measured downstream of the actuator using a hot-wire anemometer.The mean velocity profiles and other basic parameters are reported.Spectra results obtained by discrete wavelet decomposition indicate that the PZT vibration primarily influences the near-wall region.The turbulent intensities at different scales suggest that the actuator redistributes the near-wall turbulent energy.The skewness and flatness distributions show that the actuator effectively alters the sweep events and reduces intermittency at smaller scales.Moreover,under the impact of the PZT actuator,the symmetry of vibration scales’velocity signals is promoted and the structural composition appears in an orderly manner.Probability distribution function results indicate that perturbation causes the fluctuations in vibration scales and smaller scales with high intensity and low intermittency.Based on the flatness factor,the bursting process is also detected.The vibrations reduce the relative intensities of the burst events,indicating that the streamwise vortices in the buffer layer experience direct interference due to the PZT control.

Numerical investigation and its application on the falling motion of freefall lifeboat

In order to improve the simulation accuracy for free-fall lifeboat in ship life-saving training system,this paper analyzes and models the motion of boat’s launching from the skid.The whole launching is divided into four phases,namely:sliding down,rotation,free fall and water entry.According to the theory of momentum and strip theory,hydrodynamic forces of the boat at water entry are calculated under the effect of waves.The method of interpolation is used for calculating the half width and added mass of cross-sections at water entry.The model is used for numerical investigation about the boat launching from skid under different conditions and applied to ship life-saving simulation training system.The following conclusions are finally obtained:(1)When the initial inclination angle is 30◦,the horizontal distance between the point of water entry of the boat and the lower end of the slide is about 7.2 m.The horizontal distance will be smaller,when the initial inclination angle increases.There is no obvious law between forward distance and waves.(2)When the initial inclination angle is 45◦,the setback may occur after the boat entering the wave.When the initial angle is 60◦,the setback occurs after the boat entering the water.(3)When the center of gravity is 1.5 m in front of the midship of the boat,the boat will turn over.

Numerical Study on Bank Effects for a Ship Sailing in Shallow Channel

A numerical study on bank effects in shallow channels is carried out by using a first-order Rankine source panel method.A container ship sailing along a vertical bank and a sloping bank at different forward speeds,different water depths and different distances between the bank and the ship hull is taken as example.The sway force and yaw moment acting on the hull are calculated and the influences of the speed,water depth and distance between the bank and ship hull on the hydrodynamic force and moment are analyzed.This study can provide insight into the bank effects,as well as to give guidance on ship manoeuvring and control in restricted waterways,which is helpful to the navigation safety.