A Multi-Domain Boundary Element Method to Analyze the Reflection and Transmission of Oblique Waves From Double Porous Thin Walls

In the present paper, we examine the performance of an efficient type of wave-absorbing porous marine structure under the attack of regular oblique waves by using a Multi-Domain Boundary Element Method(MDBEM). The structure consists of two perforated vertical thin barriers creating what can be called a wave absorbing chamber system. The barriers are surface piercing, thereby eliminating wave overtopping. The problem of the interaction of obliquely incident linear waves upon a pair of perforated barriers is first formulated in the context of linear diffraction theory. The resulting boundary integral equation, which is matched with far-field solutions presented in terms of analytical series with unknown coefficients, as well as the appropriate boundary conditions at the free surface, seabed, and barriers, is then solved numerically using MDBEM. Dissipation of the wave energy due to the presence of the perforated barriers is represented by a simple yet effective relation in terms of the porosity parameter appropriate for thin perforated walls. The results are presented in terms of reflection and transmission coefficients. The effects of the incident wave angles, relative water depths, porosities, depths of the walls, and other major parameters of interest are explored.

Antireflection Coating for Solar Cells Based on Graded-Index Materials

The conversion of sunlight into electricity via photovoltaics presents tremendous opportunities for the generation of renewable energy. However, solar cells still face several challenges and limitations to further reduce manufacturing costs and increase module efficiency. Photon management is paramount to increase the efficiency of the mainstream silicon-based cell and always includes a suitable antireflection coating (ARC) structure to decrease the reflectance (R) at the top surface. We propose a novel triple-layer anti-reflective coating (TLAR) consisting of three layers sandwiched between the upper cover (glass) and the substrate (silicon). The inner three layers are graded refractive index material (GIM) as an active layer, titanium dioxide (TiO2), and zinc sulfide (ZnS), respectively. The optical properties of the TLAR have been investigated using the transfer matrix method (TMM). The results of using GIM as the active medium lead to the reflection decaying to the minimum value, and the transmittance reaching the maximum values at a specific wavelength range. The proposed triple-layer anti-reflective coating (TLAR) structure presents a promising solution for enhancing the efficiency of solar cells. Its unique design and utilization of graded refractive index material (GIM) as the active layer make it a novel and innovative approach that holds great potential for advancing solar cell technology.

The analytical transfer matrix method for quantum reflection

In this paper, the analytical transfer matrix method （ATMM） is applied to study the properties of quantum reflection in three systems： a sech2 barrier, a ramp potential and an inverse harmonic oscillator. Our results agree with those obtained by Landau and Lifshitz [Landau L D and Lifshitz E M 1977 Quantum Mechanics （Non-relativistic Theory） （New York： Pergamon）], which proves that ATMM is a simple and effective method for quantum reflection.

波流耦合影响下分层海床隧道周围砂土渗流孔压及液化分析

目前针对波浪作用下海底盾构隧道周围渗流场的既有理论研究一般将衬砌考虑为不透水介质,较少考虑隧道衬砌的渗透性,尤其是较少考虑波浪与海流共同作用对隧道的影响。此外,既有理论一般将海床视为均质且各向同性工况,忽略了实际情况下分层海床的影响。首先,基于波流共同作用下的海床表面的动力边界条件,采用传递-反射矩阵法得到波流共同作用下自由分层海床的孔压响应;其次,采用镜像法建立了由于隧道存在引起的砂土摄动压力控制方程,并利用砂土与衬砌间渗流连续条件获得了该方程的Fourier级数展开解析解;接着,采用叠加原理得到了波流共同作用下分层海床中隧道周围砂土的渗流压力响应及液化判定解答。最后,将理论解析解与数值结果及已有的试验结果进行对比,获得了较好的一致性。此外,针对海床渗透性和隧道衬砌渗透性进行了影响因素分析。结果表明:海流顺流会增大海床中的孔压和液化程度,逆流会减小海床中的孔压并抑制海床的液化,且流速相同时海床对逆流响应的相对差异总体上也大于顺流;当分层海床上层渗透系数较大时(k+s>1×10^(-2)m/s),海床整体孔压较大,且第一次分层处孔压变化明显;当隧道衬砌渗透系数较小时(k+l<1×10^(-6)m/s),隧道对超静孔隙水压在海床内传播“阻挡”效应明显。

REFLECTION/TRANSMISSION CHARACTERISTICS OF A DISCONTINUOUS GALERKIN METHOD FOR MAXWELL'S EQUATIONS IN DISPERSIVE INHOMOGENEOUS MEDIA

In this paper, we analyze the transmission and reflection properties of a high order discontinuous Galerkin method for dispersive Maxwell＇s equations, originally proposed by Lu et al. [J. Comput. Phys. 200 （2004）, pp. 549-580]. We study the reflection and transmission properties of the numerical method for up to second-order polynomial elements for one- and two-dimensional Maxwell＇s equations with rectangular meshes. High order accuracy has been shown for reflection and transmission coefficients near material interfaces.

同轴线测量材料电磁参数的改进NRW传输/反射法

研究了传统的NRW传输/反射法的半波谐振和多值性问题,给出了同轴NRW传输/反射法更加完善的改进方法和相应的不确定度分析方法。使用自动矢量网络分析仪和Φ7 mm同轴线,在100 MHz^6 GHz频率范围内对空气和Teflon进行了测量。依据改进的方法计算的复介电常数值与参考值在整个频率范围内符合得很好,证明了该改进方法能够有效地解决半波谐振和多值性问题,且计算结果与试样在同轴线中的位置以及同轴线的长度无关。

Scattering of Water Waves by Dual Symmetric Inclined Floating Porous Barriers Using the DBEM

The scattering of normally incident water waves by two surface-piercing inclined perforated barriers in water with a uniform finite depth is investigated within the framework of linear water wave theory.Considering that thin barriers are zero-thickness,a novel numerical method involving the the coupling of the dual boundary element method(DBEM)with damping layers is applied.In order to effectively damp out the reflected waves,two damping layers,instead of pseudoboundaries are implemented near the two side boundaries of the computational domain.Thus,the modified linearized free surface boundary conditions are formulated and used for solving both the ordinary boundary integral equation as well as the hypersingular boundary integral equation for degenerate boundaries.The newly developed numerical method is validated against analytical methods using the matched eigenfunction expansion method for the special case of two vertical barriers or the inclined angle to the vertical being zero.The influence of the length of the two damping layers has been discussed.Moreover,these findings are also validated against previous results for several cases.After validation,the numerical results for the reflection coefficient,transmission coefficient and dissipation coefficient are obtained by varying the inclination angle and porosity-effect parameter.The effects of both the inclination angle and the porosity on the amplitudes of wave forces acting on both the front and rear barriers are also investigated.It is found that the effect of the inclination angle mainly shifts the location of the extremal values of the reflection and the transmission coefficients.Additionally,a moderate value of the porosity-parameter is quite effective at dissipating wave energy and mitigating the wave loads on dual barriers.

混凝土板件波速测试方法及影响因素分析

利用ANSYS有限元软件模拟瞬时冲击荷载作用下,应力波在混凝土结构中的传播过程,模拟分析混凝土板在冲击荷载下的波场响应特征,从而更加直观地研究冲击后混凝土板内波的传播特性,主要从波速测试影响因素以及波速测试方法等几个方面进行研究,讨论在不同激振位置和不同冲击持续时间下对波速变化的影响,以及通过反射法、透射法和瑞利波速法来预估纵波速的方法来讨论不同方法的差异性、优缺点,并提出一套合理的纵波波速测试方法。

粘接结构波动特性的矩阵表示法及参数影响

为丰富多层复合材料界面形态检测方式,笔者构建了一种声波传播界面矩阵模型。分别用空气和水模拟粘接结构的界面为脱粘和进水状态,导出了横波入射下的多层结构中的声反射和透射系数表达式;研究了超声波与不同形态界面的相互作用,分析了入射角度对声波传播特性的影响。结果表明:当横波入射角度介于30°~40°或30°~60°之间,分别采用横波的反射系数法或透射系数法可较容易区分出完好连接、脱粘以及进水界面;除了0°、临界角和90°外,采用纵波透射系数法也较容易鉴别界面形态;无论横波入射角度为多大,采用纵波反射系数法均不能很好地区分脱粘和进水界面。该方法为实验时采用超声波检测粘接结构提供了依据。

槽波地震勘探技术在煤层地质探测中的应用

为准确掌握煤矿工作面内隐伏的中小型断层发育等地质情况,将槽波地震透射技术和槽波地震反射技术综合应用于文家坡煤矿4106工作面进行地质条件探测。通过波场和速度分析、频谱分析、频散分析,确定文家坡煤矿4106工作面内槽波的有效频段以及噪声频段;为宽频带通滤波提供可靠依据,进行宽频带通滤波后,分别进行透射能量CT成像和反射叠加成像;根据成像结果综合解释,将透射能量CT成像解释结果和反射叠加成像结果相互印证,确定文家坡煤矿4106工作面存在2个异常区、2条断层,为该工作面的安全生产作业提供了地质依据。

Applying Finite Difference Method to Simulate the Performance of a Perforated Breakwater Under Regular Waves

Using a discretized finite difference method, a numerical model was developed to study the interaction of regular waves with a perforated breakwater. Considering a non-viscous, non-rotational fluid, the governing equations of Laplacian velocity potential were developed, and specific conditions for every single boundary were defined. The final developed model was evaluated based on an existing experimental result. The evaluated model was used to simulate the condition for various wave periods from 0.6 to 2 s. The reflection coefficient and transmission coefficient of waves were examined with different breakwater porosities, wave steepnesses, and angular frequencies. The results show that the developed model can suitably present the effect of the structural and hydraulic parameters on the reflection and transmission coefficients. It was also found that with the increase in wave steepness, the reflection coefficient increased logarithmically, while the transmission coefficient decreased logarithmically.

Performance Evaluation of Bottom-Standing Submerged Breakwaters in Regular Waves Using the Meshless Singular Boundary Method

In this paper, the improved version of the meshless singular boundary method (ISBM) is developed for analyzing the hydrodynamic performance of bottom-standing submerged breakwaters in regular normally incident waves. Both the single and dual prismatic breakwaters of rectangular and trapezoidal forms are examined. Only the impermeable breakwaters are considered in this study. The physical problem is cast in terms of the Laplace equation governing an irrotational flow and incompressible fluid motion with the appropriate mixed-type boundary conditions, and it is solved numerically using the ISBM. The numerical results are presented in terms of the hydrodynamic quantities of reflection and transmission coefficients. The values are first validated against the data of previous studies, computed, and discussed for a variety of structural conditions, including the height, width, and spacing of breakwater submergence. An excellent agreement is observed between the ISBM results and those of other methods. The breakwater width is found to feature marginal effects compared with the height. The present method is shown to accurately predict the resonant conditions at which the maximum reflection and transmission occur. The trapezoidal breakwaters are found to generally present a wide spectrum of reflections, suggesting that they would function better than the rectangular breakwaters. The dual breakwater systems are confirmed to perform much better than single structures.

Meshless Method with Domain Decomposition for Submerged Porous Breakwaters in Waves

Based on the improved version of the meshless singular boundary method(ISBM)in multi domain(MD),a numerical method is proposed in this paper to study the interaction of submerged permeable breakwaters and regular waves at normal incidence.To account for fluid flow inside the porous breakwaters,the conventional model of Sollitt and Cross for porous media is adopted.Both single and dual trapezoidal breakwaters are examined.The physical problem is formulated in the context of the linear potential wave theory.The domain decomposition method(DDM)is employed,in which the full computational domain is decomposed into separate domains,that is,the fluid domain and the domains of the breakwaters.Respectively,appropriate mixed type boundary and continuity conditions are applied for each subdomain and at the interfaces between domains.The solution is approximated in each subdomain by the ISBM.The discretized algebraic equations are combined,resulting in an overdetermined full system that is solved using a least-square solution procedure.The numerical results are presented in terms of the hydrodynamic quantities of reflection,transmission,and wave-energy dissipation.The relevance of the results of the present numerical procedure is first validated against data of previous studies,and then selected computations are discussed for various structural conditions.The proposed method is demonstrated to be highly accurate and computationally efficient.

岩石介电特性及微波加热升温规律分析

微波辅助TBM破岩是一种非常有潜力的提高硬岩隧道破岩效率的新型破岩技术。为研究常温和高温条件下岩石对微波的吸收能力,采用同轴传输/反射法测试原理设计了一套变温岩石介电特性测试系统,采用该系统对隧道施工中玄武岩、砂岩和花岗岩3种常见岩石进行了实验。结果表明:该系统能够准确地测量变温条件下岩石的介电特性,工业频率对岩石介电特性参数的影响不大,温度对岩石介电特性参数有一定的影响;常温和变温条件下,3种岩石介电常数虚部ε″和损耗正切tanθ的关系均为玄武岩>砂岩>花岗岩,3种岩石微波加热的升温规律和介电特性的规律保持一致;对岩石进行介电特性测试和升温规律分析,提前预判岩石对微波的吸收能力,可选择性地对具有良好微波破岩效果的隧道实行微波辅助机械破岩。

基于行波反射的干式空心电抗器匝间短路故障诊断方法研究

匝间短路是干式空心电抗器的主要故障类型,目前缺乏有效的离线检测手段以在投运前及时发现潜在的故障。本文基于多导体传输线理论搭建干式空心电抗器绕组的分布参数模型,模拟脉冲信号注入后的折反射过程,研究匝间短路对绕组首、末端响应信号的影响规律。在此基础上提出以响应信号绝对值的积分值构建特征波形,并从中提取特征值对绕组的匝间绝缘状态进行诊断。结果表明:本文基于波过程及多导体传输线理论提出的4组特征值法试验结果与仿真计算结果一致,通过对不同结构电抗器模型进行仿真计算,发现不同结构电抗器发生匝间短路故障时的特征值变化趋势也一致,因此上述方法可应用于不同结构电抗器匝间短路故障的诊断。研究成果可为干式空心电抗器匝间短路故障严重程度和区域定位的诊断提供指导。

新型挡板-堆石防波堤水动力特性的理论研究

为有效提高挡板式防波堤的掩护效果,同时抑制基床冲刷,本文提出了一种新型的挡板-堆石防波堤结构,并利用理论解析的方法,对其透、反射特性进行了研究。基于线性势流理论,通过多项Galerkin方法模拟垂直挡板两侧的压力差,建立边值问题,利用匹配特征函数法进行解析求解。通过结果收敛性分析和正确性验证,发现解析解收敛性良好,且与分区边界元方法的计算结果一致。基于算例分析,研究了挡板-堆石防波堤的结构参数对防波堤掩护效果的影响,为实际工程提供科学指导。

基于微波的输变电线路钢筋混凝土结构腐蚀检测

针对现有钢筋混凝土腐蚀检测方法的局限性,提出了基于微波透射法和反射法的输变电线路钢筋混凝土结构腐蚀无损检测方法;建立了矩形波导扫描钢筋混凝土基础仿真模型,分析了钢筋腐蚀前后散射参量S_(21)和S_(11)的变化规律,研究了波导工作频率对检测效果的影响,并通过开展钢筋混凝土结构微波无损检测试验,验证了仿真方法的有效性。试验结果表明,根据钢筋腐蚀前后S_(21)和S_(11)幅值的变化,可实现钢筋混凝土结构的腐蚀检测;透射检测法受频率影响较小,而反射检测法受频率影响较大,需根据腐蚀部位及尺寸合理选择波导工作频率。

基于模式和广义射线理论研究水平层状介质中面波模式的接触现象

在近地表面波勘探中,尤其对于典型沉积盆地的探测,基于观测数据得到的频率-相速度域的能谱中,通常可以观察到基阶和一阶模式的模式接触现象(Mode-kissing)。基于模式理论,频率域中面波模式对应由频散方程的根给出的一系列极点。基于广义射线理论,时空域的多径,造成了频率域中的多模。本文结合广义射线理论和简正模理论研究广义射线理论中P极和S极两个表面波极点贡献对频散曲线的影响,解释实际观测的模式接触现象。基于两层介质模型,分析下层半空间S波速度β^((2))变化时,随P极点在复射线参数平面变化,引起的基阶和一阶模式的频散曲线、本征位移和质点偏振的变化特征。研究发现,模式接触现象出现在复射线参数平面内,P极越过1/β^((2))表示的支点,基本进入简正模区域时。与该极点对应的一阶露能模式,其地表质点轨迹为顺进椭圆,但本征位移随深度的变换表现出经典表面波特征,能量主要集中在地表。

基于地震槽波透反射法的煤厚与断层联合勘探技术研究

为减少断层和煤厚变化对工作面正常生产和瓦斯治理带来的影响,对新田煤矿1901工作面进行了地震槽波透射、反射联合勘探,通过透射法CT成像和反射法共中心点叠加及时深转换等手段,取得了诸多成果,可为矿井生产和瓦斯治理提供依据。研究表明,探测距离对透射、反射槽波提取均会产生一定影响,3.4 m左右稳定煤层槽波提取有效距离最短为90~110 m;1901工作面共划分2个煤厚大于3.8 m和1个煤厚小于3 m的区域,稳定煤层会降低槽波的分辨率;F 1401-5断层和F 1401-4断层向工作面内延伸长度分别为76 m和67 m。

多层介质空间电荷测试系统的等效表征模型与信号畸变特性

以高频电力变压器等为代表的新型电力系统装备面临大容量化、紧凑型发展需求,但装备多层复合绝缘材料中的电荷积聚问题严重影响其安全稳定运行,基于电声脉冲法测试空间电荷分布有利于分析其时空演化特性,但测试系统中的复杂声波透射与反射过程直接影响多层介质的电荷结果分析。本文基于电声脉冲测试信号传递和基本传输线系统中信号传播的相似性,提出了电声脉冲系统的等效表征原理,并结合与实验测量波形的一致性模拟结果验证了模型的可靠性。进一步,基于所构建传输线模型,开展了多层绝缘介质下的电荷仿真模拟,研究表明介质及吸声材料厚度是影响多层介质电荷测量结果的关键因素。基于此,提出了适用于多层介质的电声脉冲法测量遴选标准,所提出方法可有效减少声波反射对测量结果的影响。同时,针对声阻抗匹配程度对测量结果的影响作用机制开展研究,模拟结果表明:当半导电电极与试样声阻抗不相等时,将改变界面处的声波产生系数,进而影响上电极界面侧的被测信号幅值;而当传感器与背衬吸声部分的声阻抗不相等时,则会导致所测结果中所有界面处电压波形发生畸变,出现波形展宽和拖尾的情况。本文相关工作可为多层介质电声脉冲测量实验设计与波形恢复提供相关指导。