Interaction of Irregular Waves with Vertical Breakwater and Characteristics of Secondary Wave Generated by Overtopping

This study investigated the interaction between irregular waves and vertical breakwater.The main goal was to determine the wave force on the breakwater for different depths,along with the evolution of the secondary wave generated by overtopping.The open source code DualSPHysics was used in the simulation.Wavelet transform was employed to remove the acoustic components from the weakly compressible smoothed particle hydrodynamics pressure solution.The results of the experiments and simulations showed that although the wave height at the low water level(case 2 was smaller than that at the high water level(case 1,the horizontal and uplifting force of case 2 was higher than that of case 1.In case 2,a large impact pressure occurred because of the plunging wave and wave breaking effects.As the water level was close to the breakwater top in case 1,the secondary wave generated by overtopping was studied.Results indicated that wave and breakwater interactions transfer wave energy from the leading wave component to higher harmonics.Two main harmonics were identified in the secondary wave.The first harmonic was the incident peak frequency,which was still the dominant component.During the wave propagation behind the breakwater,the frequencies of harmonics remained unchanged,but the amplitude of the first harmonic showed an obvious change.Under the same wave condition,the first and second harmonics did not change with depth.

四参数正弦曲线拟合的快速算法

对四参数正弦拟合软件运行时间进行了研究,提出一种软件拟合时间的定量评价方法,对序列长度、序列所含信号周波数、正弦波形幅度、相位、直流分量,以及A/D位数等不同因素条件,给四参数正弦曲线拟合所用时间的影响进行了定量评价,获得了拟合时间随各个因素而变化的规律。针对影响软件运行时间的主要因素,提出了以减少拟合序列长度为手段,进而降低拟合所用时间的快速拟合方法。它们是直接序列截取法和二次抽样法。并在一组实验上验证了所述方法的有效性与可行性,获得了二次抽样法优于直接截取法的明确结论。所述方法可用于四参数正弦拟合的快速运算。

高载能超声骨刀的优化设计与性能评估

针对超声骨刀在手术过程中切割效率低和产生骨组织热损伤的问题,设计了具有二级放大结构的高载能超声骨刀。基于驻波理论的等效长度法,结合有限元仿真对其二级放大结构进行设计和优化,测试了其振动性能并进行了骨切割试验。结果表明:具有二级放大结构的超声骨刀的谐振频率为23306 Hz,振幅为140μm,骨切割表面平整且无损伤,满足临床手术需求。

基于气泡统一方程的声场双气泡耦合作用研究

针对声致空化现象中双气泡相互作用力展开了研究。本文基于气泡动力学的基本理论,将气泡统一方程应用到声场中双气泡的耦合作用研究中,建立了可用于计算声场中多气泡耦合的理论模型,并以此研究了不同类型的声场中双气泡次Bjerknes力的变化趋势。研究结果表明:在声压幅值较小的行进波声场中,对于非线性脉动的双气泡,其相互作用现象不仅与声场参数相关,还会受到双气泡初始体积比的影响。若固定其中一个气泡的初始体积,同时改变另一个气泡的初始体积,则双气泡间第1周期内的次Bjerknes力会在初始体积相等时达到第1个极值,随后呈现周期性的起伏,并在总体上呈增大趋势;而双气泡相互作用在声压幅值较大的行进波声场中会随初始半径比的增大持续增强,且周期性的起伏现象并不明显。在驻波声场中靠近波节的位置也能观测到这一现象。此外,本文还探究了非线性振动的双气泡在具有相同频率、不同声压幅值的组合波声场中的耦合效应。本文的研究可为声场中双气泡相互耦合作用以及气泡群动力学相关应用提供理论基础。

光子带隙光纤背向散射次波建模及实验验证

光子带隙光纤有着独特的结构形式、传输介质和导光机制,这使其具有传统光纤无法比拟的优点,是未来光纤陀螺的理想选择。但光子带隙光纤粗糙的纤芯内壁导致其产生强烈的背向散射次波,会使光子带隙光纤陀螺产生额外的非互易误差。为了定量分析光子带隙光纤背向散射次波强度大小,论文基于电偶极子辐射理论建立了一种简单的光子带隙光纤背向散射次波理论模型。通过聚焦离子束微纳加工法和原子力显微镜测量得到了准确的纤芯内壁表面形貌功率谱密度,进而计算得到HC-1550-02型光子带隙光纤背向散射系数理论值为2.61×10^(-9)/mm。通过光频域背向反射散射仪得到HC-1550-02型光子带隙光纤背向散射系数测量值为~1.82×10^(-9)/mm,初步验证了背向散射次波模型的正确性,为背向散射次波抑制技术研究奠定了基础。

A minimum traveltime ray tracing global algorithm on a triangular net for propagating plane waves

To address the problem of subdividing inflexible rectangular grid models and their poor definition of velocity interfaces,we propose a complex structure triangular net for a minimum traveltime ray tracing global algorithm.Our procedure is：（1） Subdivide a triangle grid based on the Delaunay triangular subdivision criterion and the relationships of the points,lines,and the surfaces in the subdividing area.（2） Define the topology relationships and related concepts of triangular unit ray tracing.（3） The source point and wave arrival points at any time compose the propagating plane wave and the minimum traveltime and secondary source positions are calculated during the plane wave propagation.We adopt the hyperbolic approximation global algorithm for secondary source retrieving.（4） By minimum traveltime ray tracing,collect the path from receiver to source points with the neighborhood point＇s traveltime and the direction of the secondary source.Numerical simulation examples are given to test the algorithm.The results show that the triangular net ray tracing method demonstrates model subdivision flexibility,precise velocity discontinuity interfaces,and accurate computations.

脆性梁弯曲断裂所激发的弯曲波

脆性细长结构在弯曲载荷作用下突然断裂,可能导致断裂点附近出现二次断裂。传统的Euler-Bernoulli梁理论难以描述突加载荷或突卸载荷所导致的波动现象,而Timoshenko梁中的弯曲波速度为有限值,具有一个内禀特征时间,因此基于Timoshenko梁理论来分析弹性梁的弯曲断裂问题。使用Timoshenko梁理论,结合一个包含断裂能的脆性内聚力弯曲断裂模型,建立一维弯曲波传播问题的初边值问题,采用特征线方法求解3种边界条件下半无限长梁中卸载弯曲波的传播问题;进一步分析了断裂能对断裂时间以及峰值弯矩的影响,然后通过数值计算给出这3种情况下梁的动力学响应过程。研究结果表明:处于纯弯曲状态的梁一旦发生瞬时断裂,二次断裂发生点距离初次断裂点的最短距离为梁截面回转半径的5倍,因为该距离以内的弯矩不会出现过冲;最有可能发生二次断裂的位置与无量纲断裂能和无量纲开裂角度有关,在距离初始断裂点17.7个特征长度的位置会产生幅值达到1.67倍初始弯矩的峰值弯矩;较大的断裂能将延长断裂时间,导致弯矩峰值点位置偏远,相应的峰值载荷也降低。

发动机活塞敲击下的整机动力学响应分析及优化

抑制活塞二次运动产生的敲击噪声是发动机NVH控制的重要内容。以某款两缸四冲程发动机为研究对象,考虑活塞和缸套工作变形及其接触特性,建立整机刚柔耦合动力学模型,探究活塞敲击激励下的整机振动与噪声响应;以活塞间隙、活塞销偏置及活塞质心位置为设计变量,活塞动能和摩擦损失为优化目标进行多目标优化设计。结果表明活塞敲击激励主要影响机体上侧部分,气缸盖罩振动噪声明显;优化后多个转速下的活塞敲击动能、摩擦损失以及机体振动和噪声均有所改善,其中6000 r/min下的活塞敲击动能比优化前降低31.1%;气缸盖罩顶部辐射噪声减小量最大为4.8%。

允许越浪斜坡式防波堤顶高程优化研究

基于南海应急抢险打捞保障基地工程对允许越浪斜坡式防波堤顶高程进行优化,在保证不恶化港内泊稳条件、码头结构和防波堤结构安全的前提下,最大限度降低堤顶高程以达到降低工程投资的目的。通过波浪断面物理模型试验模拟堤后次生波并与波浪数学模型推算的绕射波进行叠加,计算不同堤顶高程对应码头结构所受的波浪力,并通过有限元软件分析码头结构的安全性,同时通过波浪断面物理模型试验验证防波堤结构的稳定性。结果表明:对于码头和防波堤采用分离式布置的工程,防波堤防护要求可适当降低。堤顶高程按设计高水位+2 a一遇H13%基本不越浪控制,防波堤和码头结构安全可靠。

少数民族乡镇中学开展电磁波发射与接收实验的探索

先进的物理技术及其应用实验是展现物理魅力和激发学生兴趣的重要手段,然而少数民族地区的乡镇中学由于客观原因,一些先进物理技术的实验没有条件开展或开展效果不好,就如何利用生活低成本资源,设计电磁波发射与接收实验进行了探索和研究,结果表明设计该实验能有效激发学生学习物理的兴趣,并且能增强学生的动手能力和解决问题的能力,对少数民族地区乡镇中学如何开展现代物理实验具有借鉴意义.

Morphological Characteristics of Sand Waves in the Middle Taiwan Shoal Based on Multi-beam Data Analysis

A DTM map of the study area in the Taiwan Shoal was drawn based on precise and high- density data acquired in a field survey by a multi-beam sounding system （R2Sonic2024）. We identified sand waves in the study area at water depths of 13.89-49.12 m; the main sand waves had heights of 5- 25 m, lengths of 0.1-2.0 km, and crest lines 0.1-6.5 km long. The spatial distribution of the sand waves on the seabed is dense in the north and sparse in the south and the directions range between 50°-80° and 90°-135°. Between the main sand waves, secondary sand waves develop with heights of 0.1-5.0 m and lengths of 10-100 m, which are difficult to detect by satellite remote sensing. By comparing the evolution structures of the secondary and main sand waves, we identified three evolution modes of the secondary sand waves： parallel, oblique, and divergent modes according to the relative crest directions. Suitable water depth, reciprocating current speeds between 40 and 100 cm/s, and abundant sediment supply create favorable conditions for the formation of linear sand waves. Comparing the DTM maps and profiles of the June 2012 and June 2013 surveys of the same area, we found that the shape and morphology of the sand waves remained mostly unchanged under normal hydrodynamic conditions.

Investigation on the Oscillating Buoy Wave Power Device

An oscillating buoy wave power device (OD) is a device extracting wave power by an oscillating buoy. Being excited by waves, the buoy heaves up and down to convert wave energy into electricity by means of a mechanical or hydraulic device. Compared with an Oscillating Water Column (OWC) wave power device, the OD has the same capture width ratio as the OWC does, but much higher secondary conversion efficiency. Moreover, the chamber of the OWC, which is the most expensive and difficult part to be built, is not necessary for the OD, so it is easier to construct an OD. In this paper, a numerical calculation is conducted for an optimal design of the OD firstly, then a model of the device is built and, a model test is carried out in a wave tank. The results show that the total efficiency of the OD is much higher than that of the OWC and that the OD is a promising wave power device.

THEORETICAL ANALYSIS AND EXPERIMENTAL VERIFICATION ON TERNARY-WAVES METHOD TO COMPILE ACCELERATED SPECTRA

The equivalent damage calculation formulae of fatigue crack formation andgrowth are established. In order to compile the fatigue crack formation and growth accelerated loadspectra, the main wave shapes and load sequence of the actual load spectrum are kept constant, andthe carrier waves are cut off. And secondary waves are put together into new secondary waves toshorten the test time according to the equivalent damage calculation formulae respectively. Then bythe fatigue cumulative damage calculation of the fatigue crack formation and growth accelerated loadspectra, the one corresponding to the bigger damage is determined as the fatigue accelerated testload spectrum. Therefore in the test process, the fatigue accelerated test spectrum may be appliedtill fatigue failure, the engineering fatigue crack length of full-scale structure need not beinspected, and the fatigue crack formation accelerated load spectrum need not be transferred intothe fatigue crack growth accelerated load spectrum. Finally, it is verified by tests of two kinds ofspecimens that the damages of the specimens caused by the accelerated load spectra are near tothose by the actual load spectra; namely, the tested life of actual load spectra is similar to thatof accelerated load spectra. But the test time of accelerated load spectra is shortened by aboutthree-quarters that of actual load spectra. From these tests, it is also found that the fatigueaccelerated test spectrum has an advantage over FALSTAFF spectra.

PSE as applied to problems of secondary instability in supérsonic boundary layers

Parabolized stability equations （PSE） approach is used to investigate problems of secondary instability in supersonic boundary layers. The results show that the mechanism of secondary instability does work, whether the 2-D fundamental disturbance is of the first mode or second mode T-S wave. The variation of the growth rates of the 3-D sub-harmonic wave against its span-wise wave number and the amplitude of the 2-D fundamental wave is found to be similar to those found in incompressible boundary layers. But even as the amplitude of the 2-D wave is as large as the order 2%, the maximum growth rate of the 3-D sub-harmonic is still much smaller than the growth rate of the most unstable second mode 2-D T-S wave. Consequently, secondary instability is unlikely the main cause leading to transition in supersonic boundary layers.

Numerical Study of the Secondary Circulations in Rip Current Systems

To investigate the mechanism of secondary circulations in rip current systems, and to explore the relationship between wave conditions and secondary circulation intensity, a series of numerical experiments is performed using coupled nearshore wave model and circulation model. In these experiments, the rip currents and secondary circulations generated above barred beaches with rip channels are simulated. A comparison experiment is conducted to investigate the formation and hydrodynamics of the secondary circulations. Model results indicate that the secondary circulations consist of alongshore flows driven by wave set-up near the shoreline, part of the feeder currents driven by the wave set-up over the bars, and onshore flows at the end of the rip channel driven by wave breaking and convection. The existence of the secondary circulation barely affects the rip current, but narrows and intensifies the feeder currents. Three groups of experiments of varying incident wave conditions are performed to investigate the relationship between wave conditions and secondary circulation intensity. The velocity of the alongshore flow of the secondary circulation is sensitive to the variation of the incident wave height and water depth. It is also found that the alongshore flow intensity is in direct proportion to the alongshore variation of the wave height gradient between the bars and the shoreline.

On characteristics of sheath damping near a dielectric wall with secondary electron emission

A preliminary investigation is conducted to study the characteristics of sheath damping near a dielectric wall with secondary electron emission （SEE）. Making use of the linear analysis of the sheath stability, we have found two major contributions to the sheath damping, one similar to the Landau damping in uniform plasmas and another determined by local electric field and electron density of the steady-state sheath. It indicates that in a classical sheath regime the damping in the sheath region monotonically increases towards the wall and decreases with the enhancement of SEE effect. In order to verify the theoretical analysis, sheath oscillation processes induced by an initial disturbance are simulated with a time-dependent one-dimensional （1D） sheath model. Numerical results obtained are consistent with the theoretical analysis qualitatively.

NUMERICAL STUDY FOR RESONANT TRIAD INTERACTION AND SECONDARY INSTABILITY IN TWO-DIMENSIONAL SUPERSONIC BOUNDARY LAYER

By direct numerical simulation, a supersonic boundary layer was studied to see whether the mechanism for the generation of sub-harmonic waves, similar to those for the incompressible flows, existed in the process of laminar-turbulent transition. The results showed that mechanisms of both resonant triad and secondary instability did exist. Discussions were made on whether these two mechanisms are really important in laminarturbulent transition.

Experimental Investigation on a Fixed Oscillating Water Column with an Impulse Turbine for Wave Energy Conversion

A fixed oscillating water column(OWC)-type wave energy converter consists of an air chamber,an air turbine and a generator.The energy conversion processes are the primary conversion in an air chamber and the secondary conversion of the turbine.For the practical use,it is necessary to develop a design method which can consider the incident wave motion,the motion of the internal free surface affected in the structure such as a partly submerged wall,the fluctuation of air pressure in an air chamber,and the rotation of the air turbine.At here,the authors carried out the wave tank tests using the model OWC equipped with the impulse turbine and a generator to obtain the experimental data needed to make this design method.As the result,the efficiencies of the three cases with different speed ratio between generator and turbine,and the effects of the curtain wall depth and the wave length on the energy conversion performance were clarified.

直流输电线路行波采集二次回路阻抗匹配问题研究

行波信号的准确采集是输电线路行波故障测距的基础,直流输电线路二次回路阻抗不匹配对行波采集存在负面影响。针对此问题,本文研究二次回路波阻抗不匹配的原因,分析由此导致的行波折反射问题及其对单端行波故障测距的不利影响。为解决二次回路阻抗不匹配问题,提出在二次回路传输电缆首端并联电阻的方法,并对常用的传输电缆进行实测和电磁暂态仿真,分析传输电缆的波阻抗变化范围,验证匹配电阻的行波折反射抑制效果。结果表明,本文提出的阻抗匹配方法可有效消除二次回路行波折反射现象,有助于提高单端行波故障测距的可靠性,具有良好的工程适应性。

电梯轿厢-导轨耦合作用下诱发的振动与二次噪声研究

电梯轿厢运行时,电梯井道相邻居室内会产生明显的振动与噪声,严重影响居民舒适感,降低建筑物正常使用性能。以某高层住宅为研究对象,将电梯轿厢简化为6自由度多体动力学模型,建立结构振动精细化模型,考虑轿厢、导靴和导轨之间的耦合效应,基于分离迭代法求解得到结构振动响应,通过对比实测数据验证所建模型的准确性。根据真实的客厅几何形状建立声学有限元模型,将振动模型计算得到的各面板振动速度作为声学有限元的边界条件,计算居室声场内关键点声压。并分析电梯轿厢载重、运行速度以及电梯运行楼层数等电梯运行系统参数的变化对居室内振动与二次噪声的影响。最后基于振源特性与建筑的结构特征对室内振动和噪声敏感点进行评价。结果表明:随着运行楼层和轿厢速度的增加,住户室内振动和噪声在主频段均有所增加;与井道共用的墙体噪声贡献值最大,可以通过减小该处的振动来有效降低室内的二次噪声声压级。