Numerical analysis of multicomponent responses of surface-hole transient electromagnetic method

We calculate the multicomponent responses of surface-hole transient electromagnetic method. The methods and models are unsuitable as geoelectric models of conductive surrounding rocks because they are based on regular local targets. We also propose a calculation and analysis scheme based on numerical simulations of the subsurface transient electromagnetic fields. In the modeling of the electromagnetic fields, the forward modeling simulations are performed by using the finite-difference time-domain method and the discrete image method, which combines the Gaver–Stehfest inverse Laplace transform with the Prony method to solve the initial electromagnetic fields. The precision in the iterative computations is ensured by using the transmission boundary conditions. For the response analysis, we customize geoelectric models consisting of near-borehole targets and conductive wall rocks and implement forward modeling simulations. The observed electric fields are converted into induced electromotive force responses using multicomponent observation devices. By comparing the transient electric fields and multicomponent responses under different conditions, we suggest that the multicomponent-induced electromotive force responses are related to the horizontal and vertical gradient variations of the transient electric field at different times. The characteristics of the response are determined by the varying the subsurface transient electromagnetic fields, i.e., diffusion, attenuation and distortion, under different conditions as well as the electromagnetic fields at the observation positions. The calculation and analysis scheme of the response consider the surrounding rocks and the anomalous field of the local targets. It therefore can account for the geological data better than conventional transient field response analysis of local targets.

A study on the discrete image method for calculation of transient electromagnetic fields in geological media

We conducted a study on the numerical calculation and response analysis of a transient electromagnetic field generated by a ground source in geological media. One solution method, the traditional discrete image method, involves complex operation, and its digital filtering algorithm requires a large number of calculations. To solve these problems, we proposed an improved discrete image method, where the following are realized： the real number of the electromagnetic field solution based on the Gaver-Stehfest algorithm for approximate inversion, the exponential approximation of the objective kernel function using the Prony method, the transient electromagnetic field according to discrete image theory, and closed-form solution of the approximate coefficients. To verify the method, we tentatively calculated the transient electromagnetic field in a homogeneous model and compared it with the results obtained from the Hankel transform digital filtering method. The results show that the method has considerable accuracy and good applicability. We then used this method to calculate the transient electromagnetic field generated by a ground magnetic dipole source in a typical geoelectric model and analyzed the horizontal component response of the induced magnetic field obtained from the ＂ground excitation-stratum measurement method. We reached the conclusion that the horizontal component response of a transient field is related to the geoelectric structure, observation time, spatial location, and others. The horizontal component response of the induced magnetic field reflects the eddy current field distribution and its vertical gradient variation. During the detection of abnormal objects, positions with a zero or comparatively large offset were selected for the drill- hole measurements or a comparatively long observation delay was adopted to reduce the influence of the ambient field on the survey results. The discrete image method and forward calculation results in this paper can be used as references for relevant research.

Time Domain Simulation of Transient Responses of Very Large Floating Structures Under Unsteady External Loads

A time domain finite element method （FEM） for the analysis of transient elastic response of a very large floating structure （VLFS） subjected to arbitrary time-dependent external loads is presented. This method is developed directly in time domain and the hydrodynamic problem is formulated based on linear, inviscid and slightly compressible fluid theory and the structural response is analyzed on the thin plate assumption. The time domain finite element procedure herein is validated by comparing numerical results with available experimental data. Finally, the transient elastic response of a pontoon-type VLFS under the landing of an airplane is computed by the proposed time domain FEM. The time histories of the applied force and the position and velocity of an airplane during landing are modeled with data from a Boeing 747-400 jumbo jet.

Transient Hydroelastic Response of VLFS by FEM with Impedance Boundary Conditions in Time Domain

A time-dependent finite element method (FEM) is developed to analyze the transient hydroelastic responses of very large floating structures (VLFS) subjected to dynamic loads. The hydrodynamic problem is formulated based on the linear theory of fluid and the structural response is analyzed based on the thin plate theory. The FEM truncates the unbounded fluid domain by introducing an artificial boundary surface, thus defining a finite computational domain. At this boundary surface an impedance boundary conditions are applied so that no wave reflections occur. In the proposed scheme, all of the procedures are processed directly in time domain, which is efficient for nonlinear analyses of structure floating on unbounded fluid. Numerical results indicate acceptable accuracy of the proposed method.

Transient characteristics verification method for DC transformer used in flexible HVDC system

Previous studies have proposed higher requirements for the transient characteristics of a DC transformer used in a flexible high-voltage direct current(HVDC) system to achieve faster sampling speed and meet wider bandwidth requirements of the control and protection signal, and to eventually suppress the large transient fault current. In this study, a transient characteristics verification method is proposed for transient characteristics verification of a DC transformer used in a flexible HVDC system based on resampling technology and LabVIEW measurement technology after analyzing the key technology for transient characteristics verification of a DC transformer. A laboratory experiment for the transient characteristics of a full-fiber electronic DC transformer is conducted, and experimental results show that such verification method can be employed for frequency response and step response verification of a DC transformer at 10% of the rated voltage and current, and can eventually improve the screening of a DC transformer.

Transient impact responses of laminated composite cylindrical shells

The generalized ray method(GRM) has been successfully used to study the transient elastic wave transmitting in the beams,planar trusses,space frames and infinite layered media.In this letter,the GRM is extended to investigate the early short time transient responses of laminated composite cylindrical shells under impact load.By using the Laplace transformation and referring to the boundary conditions,the ray groups transmitting in the finite laminated cylindrical shells under the shock load are obtained and the transient response related to each ray group can be derived via FFT algorithm.From the numerical results,it is shown that the early short time transient accelerations of the laminated composite cylindrical shell under impact loads are very large.But the short time transient shear strain and displacement are very small.

TRANSIENT-STATE RESPONSE OF WAVE PROPAGATION IN MAGNETO-ELECTRO-ELASTIC SQUARE COLUMN

This is a continued work in studying the wave propagation in a magneto-electroelastic square column （MEESC）. Based on the analytic dispersive equation, group velocity equation and steady-state response obtained in our previous paper ＇Steady-state response of the wave propagation in a magneto-electro-elastic square column＇ published in CME, the dynamical behavior of MEESC was studied in this paper. The unlimited column is an open system. The transientstate response in the open system subjected by arbitrary external fields was derived when the propagating wave pursuing method was introduced.

A convolution-type semi-analytic DQ approach to transient response of rectangular plates

The convolution-type Gurtin variational principle is known as the only variational principle that is, from the mathematics point of view, totally equivalent to the initial value problem system. In this paper, the equation of motion of rectangular thin plates is first transformed to a new governing equation containing initial conditions by using a convolution method. A convolution-type semi-analytical DQ approach, which involves differential quadrature （DQ） approximation in the space domain and an analytical series expansion in the time domain, is proposed to obtain the transient response solution. This approach offers the same advantages as the Gurtin variational principle and, at the same time, is much simpler in calculation. Numerical results show that it is very accurate yet computationally efficient for the dynamic response of plates.

Research on Transient Response of the Rotor System with Flange Ring SFD

The state of motion of inner and outer oil films of flange ring squeeze film damper (FRSFD) is analyzed in this paper. The integral expressions of transient oil film force under fixed coordinate system are developed for segmented squeeze film using Reynolds equation. The transient vibration behaviour of the rotor supported on FHSFD under impact loading of sudden unbalance and nonlinear oil film force is simulated successfully using the finite element-Wilsonθ method. Much discussion is given on the effect of oil film clearance and flange ring stiffness on transient vibration of rotor system. The simulation results show that tile expressions of transient oil film force presented in thes paper are feasible, vibration induced by impact loading can he greatly attenuated if oil film clearance and flange ring stiffness are designed properly.

A Real-Time Transient Analysis of a Functionally Graded Material Plate Using Reduced-Basis Methods

Based on the hybrid numerical method (HNM) combining with a reduced-basis method (RBM), the real-time transient response of a functionally graded material (FGM) plates is obtained. The large eigenvalue problem in wavenumber domain has been solved through real-time off-line/on-line calculation. At off-line stage, a reduced-basis space is constructed in sample wavenumbers according to the solved eigenvalue problems. The matrices independent of parameters are projected onto the reduced-basis spaces. At on-line stage, the reduced eigenvalue problems of the arbitrary wavenumbers are built. Subsequently, the responses in wavenumber domain are obtained by the approximated eigen-pairs. Because of the application of RBM, the computational cost of transient displacement analysis of FGM plate is decreased significantly, while the accuracy of the solution and the physics of the structure are still retained. The efficiency and validity of the proposed method are demonstrated through a numerical example.

Transient stochastic response of quasi integerable Hamiltonian systems

The approximate transient response of quasi in- tegrable Hamiltonian systems under Gaussian white noise excitations is investigated. First, the averaged It6 equa- tions for independent motion integrals and the associated Fokker-Planck-Kolmogorov （FPK） equation governing the transient probability density of independent motion integrals of the system are derived by applying the stochastic averag- ing method for quasi integrable Hamiltonian systems. Then, approximate solution of the transient probability density of independent motion integrals is obtained by applying the Galerkin method to solve the FPK equation. The approxi- mate transient solution is expressed as a series in terms of properly selected base functions with time-dependent coeffi- cients. The transient probability densities of displacements and velocities can be derived from that of independent mo- tion integrals. Three examples are given to illustrate the ap- plication of the proposed procedure. It is shown that the re- suits for the three examples obtained by using the proposed procedure agree well with those from Monte Carlo simula- tion of the original systems.

Transient Response of the Starting Rotor System with the Fault of Pedestal Looseness

The dynamic model of a pedestal looseness rotor system is built and the dynamics of the system near the resonance region is analyzed using the KBM method. Then the asymptotic method to study a dynamic system with slow-changing parameters is used to study the starting and braking course of the system. Finally, the analytical results are proved by experiment. The results can be used in the inspecting and fault diagnosis of a rotor system of this type.

Nonlinear dynamical response of high-voltage transmission lines based on cable dropping

In order to study the dynamic response of high-voltage transmission lines under mechanical failure, a finite element model of a domestic 500-kV high-voltage transmission line system is established. The initial equilibrium condition of the coupling system model is verified by nonlinear static analysis. The transient dynamic analysis method is proposed to analyze the variation law of dynamic response under cable or insulator rupture, and the dynamic response of structural elements next to the broken span is calculated. The results show that upper crossarm cable rupture has no effect on cable tension at adjacent suspension points, but it has a significant influence on tension in the insulator and the tower component of the upper crossarm next to the broken span. The peak tension in the conductor of the upper crossarm at the suspension point exceeds the design value under insulator rupture. Insulator rupture has no effect on the tower component of the upper crossarm, but it has a significant influence on insulator tension of the upper crossarm. Insulator rupture should be taken into account in the design of overhead transmission lines. The research results can provide a theoretical basis for the design of transmission lines.

Transient reliability optimization for turbine disk radial deformation

The radial deformation design of turbine disk seriously influences the control of gas turbine high pressure turbine(HPT) blade-tip radial running clearance(BTRRC). To improve the design of BTRRC under continuous operation, the nonlinear dynamic reliability optimization of disk radial deformation was implemented based on extremum response surface method(ERSM), including ERSM-based quadratic function(QF-ERSM) and ERSM-based support vector machine of regression(SR-ERSM). The mathematical models of the two methods were established and the framework of reliability-based dynamic design optimization was developed. The numerical experiments demonstrate that the proposed optimization methods have the promising potential in reducing additional design samples and improving computational efficiency with acceptable precision, in which the SR-ERSM emerges more obviously. Through the case study, we find that disk radial deformation is reduced by about 6.5×10–5 m; δ=1.31×10–3 m is optimal for turbine disk radial deformation design and the proposed methods are verified again. The presented efforts provide an effective optimization method for the nonlinear transient design of motion structures for further research, and enrich mechanical reliability design theory.

冲击拦阻力计算及车架结构的瞬态分析

针对采用撞击试验法来测试钢索拦阻系统的可靠性问题,这里首次基于能量法建立了轨道车拦阻动力学模型。对不同指标及不同运行速度下冲击拦阻力的变化规律进行了分析,并给出了用于描述轨道车冲击拦阻力的具体表达式。在此基础上,对不同工况下的车架进行瞬态响应分析。结果表明:在撞击初期,冲击拦阻力Fx增长迅速,当轨道车位移一定距离后,Fx增长缓慢或保持不变,直到轨道车被安全拦停;车架的前心盘以及中梁与撞击梁交界处是应力集中的区域,容易出现破坏;车架在相同撞击初速度下,使拦停距离最短的车架形变量比使最大钢索拉力值为最小的车架形变量明显要大。

车辆开闭件疲劳性能分析与验证

对某汽车车门关闭过程中产生的疲劳失效问题进行了研究。首先,对车门关闭工况下的瞬态冲击载荷进行离散化处理,通过整车和台架实验分别采集振动加速度响应信号和频率响应函数,从而利用传递路径分析(transfer path analysis, TPA)方法计算得到离散化瞬态冲击载荷。其次,将求取的瞬态冲击载荷输入至车门有限元模型中,进而获得关门工况下的应力-时间历程响应云图,进一步由疲劳损伤理论计算车门关闭工况下的疲劳寿命。最后,将基于载荷识别的疲劳分析结果、基于显式动力学的疲劳分析结果以及车门关闭工况下的疲劳实验结果进行对比验证,结论表明三者结果一致性较好,验证了该方法的合理性。

结合特征根及模态分析法的逆变器多机并网系统谐波扰动响应分析

为了从本质上解释逆变器多机并网系统受到宽频谐波扰动后的动态行为,该文理论推导特征根与系统稳态和暂态响应的解析解,进而利用单个逆变器并网的实例验证了采用特征根分析系统谐波响应的可行性。针对逆变器多机并网系统,阐明特征根与谐振模态的对应关系,使得利用模态分析方法既能解析系统内部支路对不同谐振模态的可激励性和可观测性,又能视系统为一个整体对其稳定性进行分析。最后,通过仿真与实验验证了结合特征根分析逆变器并网系统动态行为的正确性及有效性。

钻孔瞬变电磁法超前探测物理模拟试验研究

钻孔瞬变电磁法采用小型收发线圈在超前探水钻孔中发射脉冲一次场间歇观测感应“二次场”并对其进行数据处理解译,以达到探测钻孔周围含水异常体的目的。基于瞬变电磁基础理论及相似准则搭建了水槽物理模拟试验平台,采用物理模拟试验的方法分析了共轴装置钻孔轴向及径向不同距离异常体、共轴装置钻孔轴向不同角度板状异常体、共面装置钻孔径向多点探测异常体的响应特征,结果表明:当存在异常体时感应电动势升高,异常体距离越近,感应电动势越强,异常特征越明显。板状异常体在早、中期感应电动势升高,柱状、块状异常体全程均出现感应电动势升高现象。板状异常体倾角越小,感应电动势升高越明显,异常特征越明显。共面装置钻孔径向多点探测视电阻率成像结果中异常体的轮廓特征反映明显,物理模拟试验结果充分验证了方法的有效性。

巷道电性源瞬变电磁响应三维数值模拟

近年来地面电性源得到成功应用,巷道电性源瞬变电磁探测将成为热点。本文采用三维时域有限差分法,对巷道底板以及巷道与巷道之间异常体的电性源瞬变电磁响应进行了模拟。模拟结果表明:对于巷道底板异常体,受异常体表面电荷影响,电场水平分量和垂直分量在异常体表面剧烈变化,水平电场对低阻体的分辨能力较强,对高阻体的分辨能力较弱,低阻体与高阻体的垂直电场响应的符号相反;低阻体和高阻体的∂B_(y)/∂t响应在早、晚期的符号相反,低阻体响应在早期的符号为负,晚期为正,而高阻体响应在早期的符号为正,晚期为负。对于巷道与巷道之间的异常体,水平电场对低阻体的分辨能力较强,对高阻体的分辨能力较弱;高阻体模型的∂B_(z)/∂t响应曲线高于背景曲线,低阻体模型的响应曲线低于背景曲线,说明磁场∂B_(z)/∂t响应对高阻体和低阻体均有分辨能力。