Vibrating-Sliding Motion of Caisson Breakwaters Under Various Breaking Wave Impact Forces

Sliding is one of the principal failure types of caisson breakwaters and is an essential content of stability examination in caisson breakwater design. Herein, the mass-spring-dashpot model of caisson-base system is used to simulate the vibrating-sliding motion of the caisson under various types of breaking wave impact forces, i.e., single peak impact force, double peak impact force, and shock-damping oscillation impact force. The effects of various breaking wave impacts and the sliding motion on the dynamic response behaviors of caisson breakwaters are investigated and the calculation of relevant system parameters is discussed. It is shown that the dynamic responses of the caisson are significantly different under different types of breaking wave impact forces even when the amplitudes of impact forces are equal. The amplitude of dynamic response of the caisson is lower under single peak impact excitation than that under double peak impact or shock-damping oscillation impact excitation. Though the displacement of the caisson is large due to sliding, the rotation, the sliding force and the overturning moment of the caisson are significantly reduced.

Simulation of Wave Impact on Three-Dimensional Horizontal Plate Based on SPH Method

An improved three-dimensional incompressible smooth particle hydrodynamics(ISPH)model is developed to simulate the impact of regular wave on a horizontal plate.The improvement is the employment of a corrective function to enhance angular momentum conservation in a particle-based calculation.And a new estimation method is proposed to predict the pressure on the horizontal plate.Then,the model simulates the variation characteristics of impact pressures generated by regular wave slamming.The main features of velocity field and pressure field near the plate are presented.The present numerical model can be used to study wave impact load on the horizontal plate.

Comparative Study of Different SPH Schemes on Simulating Violent Water Wave Impact Flows

Free surface flows are of significant interest in Computational Fluid Dynamics（CFD）. However, violent water wave impact simulation especially when free surface breaks or impacts on solid wall can be a big challenge for many CFD techniques. Smoothed Particle Hydrodynamics（SPH） has been reported as a robust and reliable method for simulating violent free surface flows. Weakly compressible SPH（WCSPH） uses an equation of state with a large sound speed, and the results of the WCSPH can induce a noisy pressure field and spurious oscillation of pressure in time history for wave impact problem simulation. As a remedy, the truly incompressible SPH（ISPH） technique was introduced, which uses a pressure Poisson equation to calculate the pressure. Although the pressure distribution in the whole field obtained by ISPH is smooth, the stability of the techniques is still an open discussion. In this paper, a new free surface identification scheme and solid boundary handling method are introduced to improve the accuracy of ISPH. This modified ISPH is used to study dam breaking flow and violent tank sloshing flows. On the comparative study of WCSPH and ISPH, the accuracy and efficiency are assessed and the results are compared with the experimental data.

Classification and Comparison of Wave Impact Modes on Semi-Submersibles

Semi-submersibles for offshore oil exploration and exploitation often suffer from severe wave impacts in extreme ocean environments.Owing to the complex wave interactions among structural components of semi-submersibles,in-depth analyses on the characteristics of wave impact events are of significance for both industry and academia.An experimental study was carried out to investigate the local wave impact loads on a semi-submersible,with focus on understanding the wave impacts by identifying typical impact modes.Quantitative criteria are proposed to classify major wave impacts on the semi-submersible into six modes and two types.The results show that the classification is reasonable and provides valuable information for studying wave impacts on semi-submersibles.The incident wave characteristics at the fore column of the semi-submersible have important influence on the wave impact mode.The fore-column dominating wave impacts exert the most intense loads on the fore column and feature well-developed breaking waves or slightly breaking waves at the fore column.However,the aft-column dominating wave impacts exert the most intense loads on the aft column or the deck bottom and feature non-breaking waves at the fore column.Energy loss during the fore-column impact weakens the impact severity on the aft column in the fore-column dominating wave impacts.The shoaling effect of the submerged pontoon and different motion configurations of the platform result in higher occurrence rate of the aft-column dominating wave impacts.Different impact modes are also distinguished by different spatial distributions of wave impact loads.

Modelling Solitary Waves and Its Impact on Coastal Houses with SPH Method

The interaction between solid structures and free-surface flows is investigated in this study. A Smoothed Particle Hy- drodynamics （SPH） model is used in the investigation and is verified against analytical solutions and experimental obser- vations. The main aim is to examine the effectiveness of a tsunami-resistant house design by predicting the wave loads on it. To achieve this, the solitary wave generation and ran-up are studied first. The solitary wave is generated by allowing a heavily weighted block to penetrate into a tank of water at one end, and the near-shore seabed is modelled by an inclined section with a constant slope. Then, the SPH model is applied to simulate the three-dimensional flows around different types of houses under the action of a solitary wave. It has been found that the tsunami-resistant house design reduces the impact force by a factor of three.

STEADY STATE RESPONSE ANALYSIS ON HELICAL SPRING IMPACTED BY SHORT WAVE

The wave transmission character of helical spring is applied to establish 2-DOF model of impacted vehicle on the wave impact theory. Considering the concrete structure of helical spring, corresponding responses under different impact frequency of the vehicle are imitated. The reason why the vehicle floor overresponds in some special frequency fields is explored based on analyzing the responses. When the impactions are in low frequency, the change of the spring has not been considered, but this does not affect the results. Because the transmission characters of velocity and acceleration are unanimous in helical spring, the responses characters of velocity and acceleration arc also unanimous, the only difference is the magnitude, which can make use of acceleration responses to analyse velocity responses.

Modeling on the shock wave in spheres hypervelocity impact on flat plates

In hypervelocity impacts of projectiles into thin flat targets,shock initiation and interaction dominate the responses of projectiles and targets,and especially dominate the features of the debris cloud.To estimate the geometric features of the wave front during the first complete propagation in the sphericalprojectile,the Geometric Propagation Model(GPM)is built in this paper to describe the geometry of the shock wave front,which proposes an ellipse contour as a function of time and equivalent speed.The GPM identifies the geometric features of the wave front as a function of time and impact velocity successfully.Combined with the GPM and SPH simulation,the shock pressure distribution and attenuation in the spherical-projectile have been obtained.Meanwhile,the attenuation of shock pressure and speed are presented as a function of impact velocity,respectively,and a method for obtaining the equivalent speed of the shock wave is proposed by the GPM.The GPM may be applicable to hypervelocity events involving any monolithic materials as long as the equivalent speed could be supplied from numerical simulation.The GPM proposed in this paper and the corresponding shock wave analysis provide a new insight into the processes of the quantitative analysis of the initiation of the debris cloud.

Impact Pressure of Incident Regular Waves and Irregular Waves on the Subface of Open-Piled Structures

This paper presents the results of comparison of impact pressures on open-plied structures induced by regular waves and irregular waves in a laboratory channel. Regular waves with wave heights ranging from 0.1～0.2 m and periods ranging from 1.0～2.0 s are tested. The target spectrum for the irregular wave is JONSWAP spectrum. Irregular waves with significant wave heights in the range of 0.10～0.25 m and peak periods in the range of 1.0～2.0 s are tested. The relative clearance s/H 1/3(H) is between -0.1 and 0.4, s being the subface level of structure model above the still water level. Time series of impact pressure are analyzed to indicate whether the property of impact pressures induced by the regular wave significantly deviates from that by the irregular wave. The distribution of the impact pressure along the underside of the structure is compared for different types of incident waves. The effects of wave parameters, structure dimension and structure clearance on the impact pressure are also discussed.

Clinical application of plasma shock wave lithotripsy in treating impacted stones in the bile duct system

瞄准：为了验证血浆冲击波的安全和功效，在碎裂的碎石术(PSWL ) 在胆汁管系统影响了石头。方法：从 1988 年 9 月到 2005 年 4 月，有影响石头的 67 个病人(26 个男人和 41 个女人) 与试管经历了各种各样的胆汁的操作(或 T 试管) 排水。在胆管造影术在操作以后发现的胆汁管系统的残余和影响石头被 PSWL 和 choledochofiberscopy 碎裂。201 块影响石头的一个总数被为 PSWL 的每脉搏在 2-3 J 将电压放在 2.5-3.5 kV，和能排出量的 PSWL 碎裂。然后，碎裂的石头被 choledochofiberscopy 提取。PSWL 的安全和功效被观察在期间并且在过程以后。结果：在胆汁管系统的 201 块影响石头(99.0%) 中的 199 个成功地用 PSWL 被碎裂并且由 choledochofiberscopy 提取了。为病人的石头清理率是 97%(65/67 ) 。十个病人在腹部的恰好上面的象限感到了温和疼痛，并且能容忍它很好。十一个病人有从胆汁管的粘膜流血的小数量。流血在生理盐水灌溉的 2 min 以内自发地短暂、停止。没有重要复杂并发症在期间并且在过程以后。结论: PSWL 是一个安全、有效的方法因为碎裂在胆汁管系统影响了石头。

A DAMAGE ACCUMULATING MODELING OF FAILURE WAVES IN GLASS UNDER HIGH VELOCITY IMPACT

The failure wave phenomenon was interpreted in glass media under the high velocity impact with the stress levels below the Hugoniot elastic limit. In view of the plate impact experimental observations a damage-accumulating model predominated by the deviatoric stress impulse was proposed while Heaviside function was adopted in the damage-accumulating model to describe the failure delay in the interior of Materials. Features of the failure layer and propagation mechanism as well as their dynamic characteristics were further presented. The reduction in failure wave propagation speed is pointed out as the reflected rarefaction waves reflect again from the failure layer boundary.

PROGRESSIVE FRACTURE MODELING OF THE FAILURE WAVE IN IMPACTED GLASS

The failure wave has been observed propagating in glass under impact loading since 1991. It is a continuous fracture zone which may be associated with the damage accumulation process during the propagation of shock waves. A progressive fracture model was proposed to describe the failure wave formation and propagation in shocked glass considering its heterogeneous meso-structures. The original and. nucleated microcracks will expand along the pores and other defects with concomitant dilation when shock loading is below the Hugoniot Elastic Limit. The governing equation of the failure wave is characterized by inelastic bulk strain with material damage and fracture. And the inelastic bulk strain consists of dilatant strain from nucleation and expansion of microcracks and condensed strain from the collapse of the original pores. Numerical simulation of the free surface velocity was performed and found in good agreement with planar impact experiments on K9 glass at China Academy of Engineering Physics. And the longitudinal, lateral and shear stress histories upon the arrival of the failure wave were predicted, which present the diminished shear strength and lost spall strength in the failed layer.

Global structure stability of impact-induced tensile waves in phase-transforming materials

The global structure stability of the impact-induced tensile waves mentioned by Huang （Huang, S. J. Impact-induced tensile waves in a kind of phase-transforming materials. IMA Journal of Applied Mathematics, 76, 847-858 （2011）） is considered. By introducing Riemann invariants, the governing equations of motion are reduced into a 2 ~ 2 diagonally strictly hyperbolic system. Then, with the aid of the theory on the typical free boundary problem and maximally dissipative kinetics, the global structure stability of the impact-induced tensile waves propagating in a phase-transforming material is proved.

PROGRESSIVE FRAGMENT MODELING OF FAILURE WAVE IN CERAMICS UNDER PLANAR IMPACT LOADING

Polycrystalline ceramics have heterogeneous meso-structures which result in high singularity in stress distribution. Based on this, a progressive fragment model was proposed which describes the failure wave formation and propagation in shocked ceramics. The governing equation of the failure wave was characterized by inelastic bulk strain with material damage and fracture. And the inelastic bulk strain consists of dilatant strain from nucleation and expansion of microcracks and condensed strain from collapse of original pores. Numerical simulation of the free surface velocity was performed in good agreement with planar impact experiments on 92.93% aluminas at China Academy of Engineering Physics. And the longitudinal, lateral and shear stress histories upon the arrival of the failure wave were predicted, which present the diminished shear strength and lost spall strength in the failed layer.

雷电冲击下土体应力及弹塑性界面时程分析

雷电作为自然界一种极端天气的表现形式,常给地基、地面、高耸建筑等造成严重破坏。工程防雷措施依赖于土体雷电冲击特性。现阶段,研究人员大多从电气工程角度探究雷电冲击土体造成的危害,但因学科间的差异与局限,雷电作用下岩土工程与电气工程的交叉融合方面的研究十分欠缺。本文构建土体雷电冲击模型,基于电弧通道能量平衡方程计算雷电放电产生的冲击波压力,将冲击波压力作为外加荷载作用在土体中,并通过修正Mohr-Coulomb屈服准则考虑动荷载下土体应变硬化,利用土体的理想锁定状态方程(Idealized Locked Equation of State)和动态扩孔方法考虑冲击波非稳态加载,探究雷电冲击下土体的弹塑性界面及应力时程变化规律。研究表明:在雷电冲击下,土体应力随时间变化呈现先陡增后迅速衰减的趋势,应力突变点表明土体此时正处于弹塑性交界面;在应力突变点之前,土体附加应力趋于0,处于弹性状态。任一时刻下,随着逐渐远离雷电冲击点,土体应力呈现迅速衰减的趋势,应力发生突变骤降表明此处土体正处于弹塑性交界面;在突变点之后土体附加应力趋于0,处于弹性状态。土体压缩系数对土体的弹塑性界面变化具有显著影响,随着压缩指标增大,土体塑性区半径逐渐减小;随着土体黏聚力逐渐增大,土体塑性区半径逐渐减小;增大土体弹性模量可以增大土体塑性区半径,但变化幅度相对较小;电流波形对土体塑性区中的应力会产生较大影响,而对土体弹性区影响较小。

海洋结构物波浪砰击的数值研究综述

波浪砰击是发生在波浪与结构物之间的一种强非线性相互作用,其载荷通常具有峰值大、作用时间短的特点.近年来,海上极端环境导致海洋结构物经常遭受严重的波浪砰击,造成生命和财产损失,从而使得波浪砰击问题备受重视.对于复杂的砰击过程,理论分析和模型实验仅能给出砰击载荷的简化解析解及有限的砰击流场信息,数值模拟逐渐成为研究波浪砰击问题的有效手段.目前,国内外学者已经对海洋结构物的波浪砰击载荷特性、砰击作用过程及其影响因素等问题开展了大量的数值研究,并获得了许多重要的研究结论.针对海洋结构物波浪砰击的数值研究进展、现有方法及重要结论进行综述,为波浪砰击数值模拟的进一步研究提供有益参考.

装药弹体高空跌落冲击动态响应研究

弹药意外跌落的冲击作用,可能引发事故甚至导致弹药出现早爆而造成灾难性后果。采用LSDYNA研究了分体式装药弹体从10~35 m范围内6个不同高度垂直撞击混凝土介质的冲击响应,获得了装药弹体从不同高度冲击混凝土介质时冲击过载峰值和脉宽的变化规律、装药内部应力波的传播规律,以及混凝土地面的开坑状况。冲击过载脉宽大约为5 ms,过载峰值最大约为1000 g,装药头部主要受到压缩作用,轴向应力呈近似半正弦规律变化,其最大值为43.9 MPa。开坑数值模拟结果与实验结果吻合较好,证明了数值模拟的合理性。

顶板冲击荷载作用下锚网支护巷道变形破坏规律研究

为研究顶板冲击荷载作用下锚网支护巷道的变形破坏规律,以华亭煤矿250104运输巷为背景,采用FLAC^(3D)分析了不同冲击荷载波速、角度以及偏轴距条件下锚网支护巷道围岩的应力、变形以及塑性区变化特征。研究结果表明:顶板冲击作用下,巷道顶板及两帮岩体塑性区将向上方及两侧逐渐扩展,且其最大位移呈指数衰减式增长;随顶板冲击荷载波速增大,巷道周边岩体最大位移呈指数递增式增大;随顶板冲击荷载角度增大,巷道顶板及两帮最大位移呈“S”形增长变化,冲击角度为90°时对围岩稳定性最不利;随顶板冲击荷载偏轴距增大,巷道顶板及冲击侧帮部岩体最大位移出现先增后减的变化规律,冲击偏轴距等于5.0 m时对巷道安全威胁最大。

爆炸冲击波作用后变形机翼模态数值模拟

为研究典型机翼在爆炸冲击波作用下的毁伤效应及其损伤后的结构动力学特性,基于有限元方法,研究了爆炸当量、爆炸方位及爆炸距离等对典型机翼损伤程度的影响,并分析了机翼结构变形程度与模态的关系。研究结果表明:冲击波强度和作用位置的变化对机翼结构的损伤及模态频率会产生不同程度的影响;随着冲击波强度的增加,机翼结构越早产生变形,对应的各阶模态频率下降越大,其中,二阶频率最大减少了15.02%;爆炸点位于机翼中心正上方时,机翼的变形最大;与无损伤机翼模态固有频率相比,爆炸冲击波作用在机翼中心位置时,各阶模态频率减小幅度最大,减少幅度为8.29%~15.02%。

Experimental Investigation of Wave Slamming on An Open Structure Supported Elastically

The superstructures of marine structures supported by the elastic legs and located in the splash zone will subject to violent wave slamming and vibrate consequently during storms. A series of model tests are carried out to investigate the wave impacting on the open structures supported elastically. Three kinds of models with different natural frequencies are designed. The characteristics of the wave pressures on the three models are compared. The durations of the uplift forces and the corresponding accelerations of the structure during wave impact are analyzed simultaneously. The distributions of the peak impact pressures on the subfaces of the plates with different supporting stiffness are given. The relationship between the uplift force on the three models and the relative clearance are obtained. The spectral properties of the slamming loads on the three different structures are compared, The experimental results indicate that the behaviors of the impact pressures, the uplift forces and accelerations of the plates with small natural frequencies are obviously different from those of the plates with larger natural frequencies within the range of the experimental parameters.

中高Z元素原子、离子的电子碰撞电离与激发截面快速计算方法

中高Z元素的原子数据如碰撞电离和碰撞激发截面在聚变工程、X射线与物质相互作用等工程及研究领域有非常广泛的需求.高能量密度等离子体中存在从基态到激发态的原子和各价态离子,其碰撞电离和碰撞激发截面需要分别计算.本文以73号元素钽(Ta)为例,基于相对论性Dirac-Fock理论和扭曲波模型计算了基态Ta原子到Ta^(72+)离子在入射电子能量范围为1-150 keV的碰撞电离与碰撞激发截面,并与相关实验和理论模型符合较好.通过分析Ta的碰撞电离和碰撞激发截面数据中的规律,给出两种减少计算量的方法:对初态能级进行随机抽样、筛去贡献小的反应道,并对计算量的优化程度和误差做出评估.最终结果可在误差5%内将计算效率提高一个数量级,本文所提方法可推广至其他中高Z元素的计算.