Impedance Analytical Method of Wave Run-up and Reflection from A Slotted-Wall Caisson Breakwater

An impedance analytical method （IAM） is developed to study the interaction of plane water wave with a slotted-wall caisson breakwater. The non-linear boundary condition at the slotted-wall is expressed in terms of flow resistance. A set of algebraic expressions are obtained for free surface elevation inside and outside chamber, and reflection coefficient. The prediction of the reflection coefficients shows that the relative widths of the chamber inducing the minimum reflection coefficient for a slotted-wall caisson breakwater are in a range of 0.10～0.20, which are smaller than that （0.15～0.25） for a perforated-wall caisson breakwater. The reflection coefficients and free surface elevation obtained by the present model are compared with that of laboratory experiments carried out by previous researchers.

A Calculation Method for Incidence and Reflection of Irregular Waves Along Seawalls

Some researches have been made in this aspect. In the method by Walton Jr.(1992), incident waves are supposed to be the overlapping result of M component waves with different frequencies which may take different directions, the direction of incident waves should be available in advance, but in fact the direction of incident waves is not available. In our study, incident waves are supposed to be composed of M overlapping component waves with different frequencies, and different frequencies have different directions. Based on the irregular wave reflection theory, the calculation formulas of wave direction, complex amplitude of incident waves, and complex amplitude of reflected waves in surface which are composed of component waves are derived by means of discrete Fourier transform. Then, the frequency spectra of incident waves and reflected waves and the reflection coefficient of waves with corresponding frequencies are obtained. Verification of the method and the calculation results from in-situ measured data indicate that the method is reliable and highly accurate.

Comparative Analysis of Application of Seismic Wave Reflection Method in Advanced Geological Prediction

Seismic wave reflection method is an advanced geophysical detection method in tunnel geological prediction.It is more sensitive and effective in detecting geological anomalies such as fault fracture zone and karst.In order to verify the prediction efficacy and accuracy of the seismic wave reflection method with different instruments and equipment(tunnel geological prediction[TGP]/tunnel seismic prediction[TSP])and different vibration modes(hammering,explosives),a comparison test was carried out in Jinping Tunnel.The test results showed that the time-consumption of the hammering source was short,which can greatly reduce the impact on the construction site;different vibration sources methods of seismic wave reflection can predict the unfavorable geological sections accurately.

Wave reflection, transmission and harmonics due to different submerged structures

Comparisons of wave reflection, transmission and harmonics due to different types of sub merged structures are investigated by a numerical method, the boundary-fitted coordinate (BFC) method. The types of submerged structures include a submerged horizontal plate, submerged breakwa ters (rectangular and trapezoidal) and a step-type structure (topography). First, the BFC method is ver ified by comparing the computed results with the experimental data, including wave surface elevations, reflected and transmitted wave heights, and amplitudes of higher harmonics, showing that the method is a reasonable one to predict wave deformations due to the submerged structures. Secondly, the wave sur face elevations and the higher harmonics over different submerged structures are compared. Thirdly, re flected and transmitted waves due to different submerged structures are investigated.

Estimating Directional Distribution for Co-Existent Field of Incident and Reflected Waves

In the nearshore, the wave field contains reflected and incident waves in which there is correlation between their phases due to the effect of reflection by some obstacles. Based on the extended eigenvector method (EEV) derived by Guan et al., a modified method (MEEV) is proposed as a general and practical approach to estimating directional spectra for the co-existent field of incident and reflected waves and a formula is given for direct calculation of the reflection coefficient. The results of numerical simulations show that MEEV is superior to EEV in resolution power, and the computed reflection coefficient agrees well with the real value within a certain range of incident angle.

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.

Modelling of Random Waves over Submerged Breakwatersand Its Application to Reflection Estimation

Reflection and transmission of random waves from submerged ohstacles under various conditions are investigated in this study by means of the boundary element method. The algorithm is based on the Lagrangian description with finite difference adopted for the approximation of time derivative. The accuracy of the model is confirmed by a previous study of the transmission of irregular waves in a water tank without any obstacle, under which sets of submerged breakwaters are located. To reduce the effect of reflection from the wall, a sponge zone is employed at the other end of the flume as an artificial absorbing beach. The power spectrum of Bretschneider-Mitsuyasu type defined by significant wave height, H1/3, and period, T1/3, is employed for the condition of incident waves chosen for the generation of irregular waves. Time histofies of water elevations are measured with numerous pseudo wave gages on the free water surface. With reference to the method for the estimation of irregular incident and reflected waves in random sea presented by Goda and Suzuki （1976）, the dissipation efficiency of the breakwaters is investigated. Gauges in different positions are tested for their suitability for the estimation of reflection coefficients for irregular waves. The present results demonstrate the effectiveness of the estimation of reflection coefficient for random waves, and indicate the feasibility of the numerical model.

Numerical Simulation of Wave Interaction with Perforated Caisson Breakwaters

The volume of fluid (VOF) method is presented to determine the reflection coefficient of and the total horizontal wave force on perforated caisson breakwaters. The present numerical model is compared with a linear analytic solution obtained by Sahoo et al. (2000). Also this model is verified with the authors′ laboratory data. It is found that the numerical model is in good agreement with the regression equations obtained from the experimental data. The present numerical method is further discussed to relate porosity, the relative wave absorbing chamber depth, the reflection coefficient of perforated caissons and the total horizontal force on them.

Millimeter-Wave Absorption Properties of Thin Wave Absorber in Free Space with New Porous Carbon Material

In this paper, we focus on PHYTOPOROUS, a porous carbon material made entirely from plant-based ingredients, as a new broadband-wave absorber material that acts in the millimeter wave band. We created prototypes of thin rubber-sheet wave absorbers that contain porous carbon (PHYTOPOROUS) made from rice chaff and soybean hulls, which are both agricultural residue products that are generated in large quantities. We investigated the permittivity and reflectance characteristics of this material using the free-space time-domain method. The thin rubber-sheet wave absorber that contained PHYTOPOROUS made from soybean hulls exhibited a frequency band that was approximately 18 GHz wide and centered at 90 GHz. The return loss for this material was greater than −20 dB. This demonstrates that the material provides nearly constant reflection absorption over a wide frequency band.

Effect of High-Frequency Electric Field on Propagation of Electrostatic Wave in a Non-Uniform Relativistic Plasma Waveguide

The effect of a high frequency （HF） electric field on the propagation of electrostatic wave in a 2D non-uniform relativistic plasma waveguide is investigated. A variable separation method is applied to the two-fluid plasma model. An analytical study of the reflection of electrostatic wave propagation along a magnetized non-uniform relativistic plasma slab subjected to an intense HF electric field is presented and compared with the case of a non relativistic plasma. It is found that, when the frequency of the incident wave is close to the relativistic electron plasma frequency, the plasma is less reflective due to the presence of both an HF field and the effect of relativistic electrons. On the other hand, for a low-frequency incident wave the reflection coefficient is directly proportional to the amplitude of the HF field. Also, it is shown that the relativistic electron plasma leads to a decrease in the value of reflection coefficient in comparison with the case of the non relativistic plasma.

Scaled Boundary Finite Element Analysis of Wave Passing A Submerged Breakwater

The scaled boundary finite element method （SBFEM） is a novel semi-analytical technique combining the advantage of the finite element method （FEM） and the boundary element method （BEM） with its unique properties. In this paper, the SBFEM is used for computing wave passing submerged breakwaters, and the reflection coeffcient and transmission coefficient are given for the case of wave passing by a rectangular submerged breakwater, a rigid submerged barrier breakwater and a trapezium submerged breakwater in a constant water depth. The results are compared with the analytical solution and experimental results. Good agreement is obtained. Through comparison with the results using the dual boundary element method （DBEM）, it is found that the SBFEM can obtain higher accuracy with fewer elements. Many submerged breakwaters with different dimensions are computed by the SBFEM, and the changing character of the reflection coeffcient and the transmission coefficient are given in the current study.

浅层地震反射波法及地质雷达法在地下防空洞探测的应用研究

由于早期人防工程相关资料的缺失,形成若干盲区。本文采用浅层地震反射波法及地质雷达法对浙江宁波地区的地下防空洞盲区进行定位探测,分析其满水和抽水后状态下进行无损检测的可行性。结果表明,结合两种方法的应用可基本实现对防空洞埋深定位探测,抽干水后状态下的反射信号更为清晰。在现场勘测应用时,应减少环境干扰,优选测试分析参数并验证结果。

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。

瞬变电磁法和地震反射波法在不良地质洞段超前地质预报中的应用

物探方法是超前地质预报的主要手段,通过不良地质体与围岩物性参数差异,及时发现和预测地质条件的变化。较完整一完整围岩岩体物性参数与不良地质体物性参数存在较明显差异,有利于分辨出不良地质体;但是在地质条件差洞段的不良地质体与围岩岩体物性参数差异极小,不利于分辨出不良地质体,使得岩体质量情况和地质灾害风险预报难度极大。本次采用瞬变电磁法与地震反射波法的综合物探法,在滇中引水工程大理Ⅱ段Ⅴ_(特)类岩体开展专项超前地质预报工作,主要利用岩体视电阻率、应力梯度、纵波波速、横波波速等参数对未开挖段岩体质量和可能存在的地质灾害风险进行预测。创造性地通过“日进尺”这一指标间接对开挖岩体破碎程度进行评价,经对比,预报成果中符合长度占实际开挖过程中问题段长度的85.1%,预报结果与开挖成果较为吻合;此外,对坍塌失稳段、突泥涌水段也有明显反映,为该方法组合在不良地质洞段超前地质预报中的应用提供了借鉴。

低应变法与数值模拟在桩基检测中的综合应用

以某集团科研楼工程为背景,利用ABAQUS软件进行实验模拟,并将模拟结果与实际检测结果进行详细对比,主要目的是验证优化的数值模型在桩基完整性检测中的可靠性,并为工程检测提供波形参考。结果表明:建立的完整桩数值模型成功模拟了实际检测的速度时域波形,波形曲线规则且光滑,存在明显的入射波和桩底反射波,入射波与桩底反射波同相,是明显的完整桩反射波形;模拟波速数值与实际检测波速相差低于1%,高度的一致性说明采取的模拟方法贴合工程实际。同理,建立某工程扩径桩的数值模型,结果表明:扩径位置与实际位置相差5.9%,反射波波形较为平滑,有明显的入射波和桩底反射波,缺陷处有清晰的反射信号;入射波与桩底反射波同相,扩径缺陷处反射波与入射波反相,根据整体波形可以判断出缺陷类型与位置。

建筑基桩中结合反射波法有限元分析的无损检测技术研究

建筑基桩的安全性和稳定性是确保建筑物结构完整性和使用寿命的关键因素。本研究针对道路建筑基桩的无损检测问题,提出了一种基于反射波法有限元分析方法。过程中选取扭剪波作为数据收集介质,对扭剪波的传播形式进行了研究,使用ANSYS有限元软件对无损检测数值进行模拟,并使用显示求解提升准确性,之后对扭剪波在基桩内部的波速进行了修正优化,最后设计了不同基桩缺陷情况的建模参考模型。实验结果表明,研究方法在进行系统响应效率测试时,检测缩径缺陷损害涉及高度为0.5 m时的系统响应时间为约54 ms;进行有效检测高度分析时,研究方法在离析缺陷和断桩缺陷中的有效检测高度为29.9 m。说明研究方法能够有效完成对基桩的无损检测且具有较好的检测性能。

软土地基处理中PHC管桩桩身及单桩承载力试验研究

为研究软土地基PHC管桩处理效果,结合某泵站工程,通过第三方检测公司对施工单位使用PHC管桩处理后的地基进行抽验。采用低应变反射波法进行PHC管桩桩长、桩身完整性检测,并进行复合地基单桩竖向抗压承载力试验研究,从而判断PHC管桩处理后泵站软土地基中的承载力大小是否满足要求。经第三方抽检,检测结果合格,单桩完整性及复合地检测结果可以直接为本次泵站设计施工及竣工验收提供技术方法和数据借鉴。

低应变法检测工程基桩浅部缺陷的波形实例分析

结合工程现场实例,简要论述了低应变反射波检测方法的原理和工程中常见的浅部缺陷桩,并详细分析了实际检测工作中典型浅部缺陷的低应变反射波形曲线。根据实测波形资料,总结了检测工作中常见的各种浅部缺陷桩的波形特征和技术要点,为判别基桩缺陷性质提供借鉴。通过对基桩浅部异常波形曲线的详细分析,避免实际检测工作中的错判或漏判。

静载试验和低应变法对PHC管桩性能的检测

采用静载试验和低应变反射波法对PHC管桩的性能进行检测,通过抽检小比例PHC管桩进行静载试验对承载力进行检测,利用低应变反射波法对桩身完整性进行检测。结果表明:利用静载试验得出位移-荷载曲线的最大沉降量为14.78 mm,位移-对数时间曲线均较为平直发展;利用低应变反射波法检测PHC管桩桩身的完整性,其符合设计要求,可满足工程安全性要求。

低应变反射波法在桩基检测中的理论研究与实际应用

低应变发射波法可以为桩基检测提供有效的、非破坏性的评估手段,为桩基的设计和维护提供可靠的依据。本文从基本理论出发,讲述了低应变反射波法的基本原理与实际应用的意义,并结合工程实际分析了不同桩基情况下的低应变反射曲线的特征。通过分析低应变反射曲线的特征,可以对桩基问题进行初步判断,然后进一步采取适当的措施进行修复和维护。