Time-domain dynamic constitutive model suitable for mucky soil site seismic response

Soil nonlinear behavior displays noticeable effects on the site seismic response.This study proposes a new functional expression of the skeleton curve to replace the hyperbolic skeleton curve.By integrating shear modulus and combining the dynamic skeleton curve and the damping degradation coefficient,the constitutive equation of the logarithmic dynamic skeleton can be obtained,which considers the damping effect in a soil dynamics problem.Based on the finite difference method and the multi-transmitting boundary condition,a 1D site seismic response analysis program called Soilresp1D has been developed herein and used to analyze the time-domain seismic response in three types of sites.At the same time,this study also provides numerical simulation results based on the hyperbolic constitutive model and the equivalent linear method.The results verify the rationality of the new soil dynamic constitutive model.It can analyze the mucky soil site nonlinear seismic response,reflecting the deformation characteristics and damping effect of the silty soil.The hysteresis loop area is more extensive,and the residual strain is evident.

Time-Domain Analysis of Body Freedom Flutter Based on 6DOF Equation

The reduced weight and improved efficiency of modern aeronautical structures result in a decreasing separation of frequency ranges of rigid and elastic modes.Particularly,a high-aspect-ratio flexible flying wing is prone to body freedomflutter(BFF),which is a result of coupling of the rigid body short-periodmodewith 1st wing bendingmode.Accurate prediction of the BFF characteristics is helpful to reflect the attitude changes of the vehicle intuitively and design the active flutter suppression control law.Instead of using the rigid body mode,this work simulates the rigid bodymotion of the model by using the six-degree-of-freedom(6DOF)equation.A dynamicmesh generation strategy particularly suitable for BFF simulation of free flying aircraft is developed.An accurate Computational Fluid Dynamics/Computational Structural Dynamics/six-degree-of-freedom equation(CFD/CSD/6DOF)-based BFF prediction method is proposed.Firstly,the time-domain CFD/CSD method is used to calculate the static equilibrium state of the model.Based on this state,the CFD/CSD/6DOF equation is solved in time domain to evaluate the structural response of themodel.Then combinedwith the variable stiffnessmethod,the critical flutter point of the model is obtained.This method is applied to the BFF calculation of a flyingwing model.The calculation results of the BFF characteristics of the model agree well with those fromthe modalmethod andNastran software.Finally,the method is used to analyze the influence factors of BFF.The analysis results show that the flutter speed can be improved by either releasing plunge constraint or moving the center ofmass forward or increasing the pitch inertia.

An Improved Time-Domain Inverse Technique for Localization and Quantifcation of Rotating Sound Sources

The time-domain inverse technique based on the time-domain rotating equivalent source method has been proposed to localize and quantify rotating sound sources. However, this technique encounters two problems to be addressed: one is the time-consuming process of solving the transcendental equation at each time step, and the other is the difculty of controlling the instability problem due to the time-varying transfer matrix. In view of that, an improved technique is proposed in this paper to resolve these two problems. In the improved technique, a de-Dopplerization method in the time-domain rotating reference frame is frst applied to eliminate the Doppler efect caused by the source rotation in the measured pressure signals, and then the restored pressure signals without the Doppler efect are used as the inputs of the time-domain stationary equivalent source method to locate and quantify sound sources. Compared with the original technique, the improved technique can avoid solving the transcendental equation at each time step, and facilitate the treatment of the instability problem because the transfer matrix does not change with time. Numerical simulation and experimental results show that the improved technique can eliminate the Doppler efect efectively, and then localize and quantify the rotating nonstationary or broadband sources accurately. The results also demonstrate that the improved technique can guarantee a more stable reconstruction and compute more efciently than the original one.

Integrated system of traditional THz time-domain spectroscopy and asynchronous optical sampling

Terahertz time-domain spectroscopy(THz-TDS)system,as a new means of spectral analysis and detection,plays an increasingly pivotal role in basic scientific research.However,owing to the long scanning time of the traditional THz-TDS system and the complex control of the asynchronous optical scanning(ASOPS)system,which requires frequent calibration,we combine traditional THz-TDS and ASOPS systems to form a composite system and propose an all-fiber trigger signal generation method based on the time overlapping interference signal generated by the collinear motion of two laser pulses.Finally,the time-domain and frequency-domain spectra are obtained by using two independent systems in the integrated systems.It is found that the full width at half maximum(FWHM)of the time-domain spectra and the spectral width of the frequency-domain spectra are almost the same,but the sampling speed of the ASOPS system is significantly faster than that of the traditional THz-TDS system,which conduces to the study of the transient characteristics of substances.

气象要素与潜在林火风险关联性研究

为探究川西南地区复杂气候与森林火灾之间的关联性,以四川省凉山彝族自治州木里藏族自治县(以下简称“四川省凉山州木里县”)为例,通过局部规模的气象异常值变化,分析了各气象要素与森林火灾的潜在联系性。再通过FWI与FFDI,分析木里县历史火险变化,验证了其与木里县森林火灾的关联性。结果表明:森林火灾发生前后气压、气温、湿度、风速、蒸发量出现不同周期的连续增加(或衰减)。同时,木里县森林火险指数FWI与FFDI呈现出年际震荡且逐渐增大的趋势,且木里县林火频数与FWI的年均相关系数(46.9%)、月均相关系数(80.7%)均大于FFDI(年相关系数38.7%、月相关系数53.1%)。此外,林火风险值出现极端异常还与同期(或同年)发生的气候事件密切相关。因此,气候异常事件所导致的持续高温、低湿、多风的气象条件是森林火险等级快速升高或重大森林火灾事故的本质原因之一。

加拿大森林火险气候指数系统(FWI)的原理及应用

森林火险等级预报系统对预测预报森林火灾十分重要。加拿大森林火险等级系统(CFFDRS)是当前世界上发展最完善、应用最广泛的系统之一,是世界上唯一能适应从区域到全球任何尺度的系统,加拿大森林火险气候指数(FWI)系统是CFFDRS的重要组成部分。加拿大火险气候指数系统以时滞-平衡含水率理论为基础,通过天气条件的变化计算可燃物含水率的变化,然后根据不同位置或大小的可燃物含水率划分森林潜在火险等级。从FWI的发展状况、基本结构、程序,以及优点和局限性作了简单的描述,并讨论了如何在基于FWI技术的基础上发展中国的森林火险等级系统。

江西南昌典型林分地表死可燃物含水率预测——方法优选与FWI适用性分析

亚热带针阔混交林是我国南方重要的植被类型，森林火灾发生次数多。对该植被类型的典型可燃物含水率将有助于提高火险预报的准确性。以位于该区域内的南昌市茶园山林场5种典型林分地表死可燃物为研究对象，通过对其含水率的连续观测，分析了死可燃物含水率与气象因子的关系。采用气象要素、FWI因子和两者的结果，区分不同含水率范围，分别建立的各可燃物3种预测模型。结果表明：研究地区防火期内可燃物含水率从11．8％到276．6％，只有1／4的时间低于35％，具备发生森林火灾的条件，其余的时间燃烧性都很低，平均火险不高。但最小含水率已低到10％左右，具备发生大火的潜在可能性。3种预测方法中，FWI模型误差最大，气象要素回归模型和混合模型误差相似，考虑到简单方便，该地区的含水率预测可以采用气象要素回归法。含水率小于35％时，模型MAE2．25％～4．67％，平均3．73％；MRE11．14％～23．73％，平均18．63％。含水率〉35％时，模型MAE6．34％～18．33％，平均8．63‰MRE10．49％～18．16％，平均14．43％。在全范围含水率时，模型MAE7．46％～16．43％，平均10．51％；MRE18．78％～23．64％，平均20．99％。FWI指标与研究地区可燃物含水率关系密切，也可以用于含水率预测和火险预报，如果考虑全国统一的预报模型，对于该地区，FWI系统是适用的，但为提高预测的准确性，应进行进一步的修正。

PC-based artif icial neural network inversion for airborne time-domain electromagnetic data

Traditionally, airborne time-domain electromagnetic （ATEM） data are inverted to derive the earth model by iteration. However, the data are often highly correlated among channels and consequently cause ill-posed and over-determined problems in the inversion. The correlation complicates the mapping relation between the ATEM data and the earth parameters and thus increases the inversion complexity. To obviate this, we adopt principal component analysis to transform ATEM data into orthogonal principal components （PCs） to reduce the correlations and the data dimensionality and simultaneously suppress the unrelated noise. In this paper, we use an artificial neural network （ANN） to approach the PCs mapping relation with the earth model parameters, avoiding the calculation of Jacobian derivatives. The PC-based ANN algorithm is applied to synthetic data for layered models compared with data-based ANN for airborne time-domain electromagnetic inversion. The results demonstrate the PC-based ANN advantages of simpler network structure, less training steps, and better inversion results over data-based ANN, especially for contaminated data. Furthermore, the PC-based ANN algorithm effectiveness is examined by the inversion of the pseudo 2D model and comparison with data-based ANN and Zhody＇s methods. The results indicate that PC-based ANN inversion can achieve a better agreement with the true model and also proved that PC-based ANN is feasible to invert large ATEM datasets.

Solution and Analysis of Chatter Stability for End Milling in the Time-domain

In this paper, the instantaneous undeformed chip thickness is modeled to include the dynamic modulation caused by the tool vibration while the dynamic regenerative effects are taken into account. The numerical method is used to solve the differential equations goveming the dynamics of the milling system. Several chatter detection criteria are applied synthetically to the simulated signals and the stability diagram is obtained in time-domain. The simulation results in time-domain show a good agreement with the analytical prediction, which is validated by the cutting experiments. By simulating the chatter stability lobes in the time-domain and analyzing the influences of different spindle speeds on the vibration amplitudes of the tool under a Fixed chip-load condition, conclusions could be drawn as follows： In rough milling, higher machining efficiency can be achieved by selecting a spindle speed corresponding to the axial depth of cut in accordance with the simulated chatter stability lobes, and in Fmish milling, lower surface roughness can be achieved by selecting a spindle speed well beyond the resonant frequency of machining system.

基于无线传感网的森林火灾FWI系统分析

林火的高发性和破坏性决定了林火防控的重要性,无线传感器网络技术的兴起和发展为现代林业火灾预警预报的实现提供了机遇。加拿大森林火险气候指数(Fire Weather Index,FWI)系统是以时滞-平衡含水率理论为基础,通过天气条件的变化计算地面可燃物含水率的情况,根据地表到地下不同层次的可燃物含水率划分森林潜在火险等级。笔者分析研究了FWI系统的原理,并以南京市为参照验证了FWI系统的分析结果,希望在基于FWI系统的基础上发展中国的森林火险等级预警系统。

Comparison of the time-domain electromagnetic field from an infinitesimal point charge and dipole source

An electromagnetic field is generated through the accelerating movement of two equal but opposite charges of a single dipole. An electromagnetic field can also be generated by a time-varying infinitesimal point charge. In this study, a comparison between the electromagnetic fields of an infinitesimal point charge and a dipole has been presented. First, the time-domain potential function of a point source in a 3D conductive medium is derived. Then the electric and magnetic fields in a 3D homogeneous lossless space are derived via the relation between the potential and field. The field differences between the infinitesimal point charge and the dipole in the step-off time, far-source, and near-source zones are analyzed, and the accuracy of the solutions from these sources is investigated. It is also shown that the field of the infinitesimal point charge in the near-source zone is different from that of the dipole, whereas the far-source zone fields of these two sources are identical. The comparison of real and simulated data shows that the infinitesimal point charge represents the real source better than the divole source.

Numerical modeling of the 2D time-domain transient electromagnetic secondary field of the line source of the current excitation

To effectively minimize the electromagnetic field response in the total field solution, we propose a numerical modeling method for the two-dimensional （2D） time- domain transient electromagnetic secondary field of the line source based on the DuFort- Frankel finite-difference method. In the proposed method, we included the treatment of the earth-air boundary conductivity, calculated the normalized partial derivative of the induced electromotive force （Emf）, and determined the forward time step. By extending upward the earth-air interface to the air grid nodes and the zero-value boundary conditions, not only we have a method that is more efficient but also simpler than the total field solution. We computed and analyzed the homogeneous half-space model and the fiat layered model with high precision--the maximum relative error is less than 0.01% between our method and the analytical method--and the solution speed is roughly three times faster than the total-field solution. Lastly, we used the model of a thin body embedded in a homogeneous half-space at different delay times to depict the downward and upward spreading characteristics of the induced eddy current, and the physical interaction processes between the electromagnetic field and the underground low-resistivity body.

基于全波形反演速度约束的叠后地震反演方法

对于井数较少或者沉积相变化较快的地层,利用测井曲线建立的反演低频模型难以控制反演弹性参数的空间变化趋势。据此笔者发展了基于FWI速度约束的叠后地震反演方法,该方法充分利用了FWI速度的真三维信息,据此得到反演弹性参数的空间变化趋势。对于叠后地震反演所需要的纵波阻抗低频模型,提出了基于测井岩石物理拟合关系将FWI速度转换为FWI纵波阻抗的方法。另外,针对FWI纵波阻抗和测井纵波阻抗存在一定差异的问题,提出了FWI纵波阻抗均值校正方法,据此可得到较为准确的纵波阻抗低频模型。单井和实际工区应用表明,纵波阻抗反演结果和井上结果匹配性较高,因此笔者提出的基于FWI速度约束的叠后地震反演方法较为有效,可为储层预测提供较为有利的技术支持。

Dynamic Coupling Analysis of Semisubmersible Platform Float-over Method for Docking Case

In this paper,the multi-body coupled dynamic characteristics of a semisubmersible platform and an HYSY 229 barge were investigated.First,coupled hydrodynamic analysis of the HYSY 229 barge and the semisubmersible platform was performed.Relevant hydrodynamic parameters were obtained using the retardation function method of three-dimensional frequency-domain potential flow theory.The results of the hydrodynamic analysis were highly consistent with the test findings,verifying the accuracy of the multifloating hydrodynamic coupling analysis,and key hydrodynamic parameters were solved for different water depths and the coupling effect.According to the obtained results,the hydrodynamic influence was the largest in shallow waters when the coupling effect was considered.Furthermore,the coupled motion equation combined with viscous damping,fender system,and mooring system was established,and the hydrodynamics,floating body motion,and dynamic response of the fender system were analyzed.Motion analysis revealed good agreement among the surge,sway,and yaw motions of the two floating bodies.However,when the wave period reached 10 s,the motion of the two floating bodies showed severe shock,and a relative motion was also observed.Therefore,excessive constraints should be added between the two floating bodies during construction to ensure construction safety.The numerical analysis and model test results of the semisubmersible platform and HYSY 229 barge at a water depth of 42 m and sea conditions of 0°,45°,and 90° were in good agreement,and the error was less than 5%.The maximum movement of the HYSY 229 barge reached 2.61 m in the sway direction,whereas that of the semisubmersible platform was 2.11 m.During construction,excessive constraints should be added between the two floating bodies to limit their relative movement and ensure construction safety.

Spatial sensitivity to absorption changes for various near-infrared spectroscopy methods:A compendium review

This compendium review focuses on the spatial distribution of sensitivity to localized absorption changes in optically diffuse media,particularly for measurements relevant to near-infrared spectroscopy.The three temporal domains,continuous wave,frequency domain,and time domain,each obtain different optical data types whose changes may be related to effective homogeneous changes in the absorption coefficient.Sensitivity is the relationship between a localized perturbation and the recovered effective homogeneous absorption change.Therefore,spatial sensitivity maps representing the perturbation location can be generated for the numerous optical data types in the three temporal domains.The review first presents a history of the past 30 years of work investigating this sensitivity in optically diffuse media.These works are experimental and theoretical,presenting one-,two-,and three-dimensional sensitivity maps for different Near-Infrared Spectroscopy methods,domains,and data types.Following this history,we present a compendium of sensitivity maps organized by temporal domain and then data type.This compendium provides a valuable tool to compare the spatial sensitivity of various measurement methods and parameters in one document.Methods for one to generate these maps are provided in Appendix A,including the code.This historical review and comprehensive sensitivity map compendium provides a single source researchers may use to visualize,investigate,compare,and generate sensitivity to localized absorption change maps.

An efficient approach for the equivalent linearization of frame structures with plastic hinges under nonstationary seismic excitations

An efficient approach is proposed for the equivalent linearization of frame structures with plastic hinges under nonstationary seismic excitations.The concentrated plastic hinges,described by the Bouc-Wen model,are assumed to occur at the two ends of a linear-elastic beam element.The auxiliary differential equations governing the plastic rotational displacements and their corresponding hysteretic displacements are replaced with linearized differential equations.Then,the two sets of equations of motion for the original nonlinear system can be reduced to an expanded-order equivalent linearized equation of motion for equivalent linear systems.To solve the equation of motion for equivalent linear systems,the nonstationary random vibration analysis is carried out based on the explicit time-domain method with high efficiency.Finally,the proposed treatment method for initial values of equivalent parameters is investigated in conjunction with parallel computing technology,which provides a new way of obtaining the equivalent linear systems at different time instants.Based on the explicit time-domain method,the key responses of interest of the converged equivalent linear system can be calculated through dimension reduction analysis with high efficiency.Numerical examples indicate that the proposed approach has high computational efficiency,and shows good applicability to weak nonlinear and medium-intensity nonlinear systems.

HF-VHF dual-channel multifunctional radio astronomy terminal system

The high frequency-very high frequency(HF-VHF)frequency band is of significant importance in astronomical observations,with applications studying various phenomena such as space weather,solar radio emissions,planetary eruptions in the solar system,pulsars,transient sources,and reionization of the early universe.This article introduces the HF-VHF frequency band multifunctional radio astronomical terminal system based on a dual-channel high-speed acquisition board with a frequency observation range of 1-250 MHz and a sampling rate of 500 Msps(Mega samples per second).The maximum quantization bit of the system is 14 bits,with a maximum time resolution of 0.1 s and a maximum spectral resolution of 16 kHz.The system combines spectral analysis of solar radio signals and recording of time-domain data of signals interfering with long baselines,and adopts a server-client separation mode to allow remote operation with separate permissions.It is used in the China-Malaysia joint astronomy project,which can carry out single-site observation of solar radio signals as well as interferometric observation of signals from multiple sites.

庆安地区地表凋落物含水率预测研究

文章以黑龙江省庆安县曙光林场典型林分为研究对象,通过野外地表凋落物含水率的连续观测,分析了地表凋落物含水率动态变化。利用曙光林场春秋两季的气象数据计算出加拿大火险气候指数系统(FWI)的湿度码,用含水率数据与气象要素和FWI湿度码分别进行回归,得到两类含水率回归模型,旨在为庆安地区森林火险预测预报提供科学参考。

底辟模糊区成像处理的关键技术

底辟带具有巨大的油气勘探潜力,但受浅层气云的影响,该领域地震资料成像品质差、构造形态不准确,对周缘含油构造潜在目标的落实带来了困难。为解决底辟模糊区成像问题,本文分析近年海上新采集资料的优势及新老资料的共性特征,提出弱信号保护的保幅处理、高精度速度建模及Q深度偏移等关键技术,形成对不同采集方案具有普适性的处理对策。采用上述方法在莺歌海盆地L工区进行实际资料的应用,得出底辟模糊区核部地震资料信噪比得到提升,有效地层清晰成像,井震相关系数比原老资料提高了38%,深度域构造与测井吻合,特别是老资料重处理的效果明显,成像质量不亚于新采集资料,验证了本方法对于底辟模糊区成像挖潜的有效性,可为后续类似领域的采集及处理提供借鉴。

Unconditionally stable Crank-Nicolson algorithm with enhanced absorption for rotationally symmetric multi-scale problems in anisotropic magnetized plasma

Large calculation error can be formed by directly employing the conventional Yee’s grid to curve surfaces.In order to alleviate such condition,unconditionally stable CrankNicolson Douglas-Gunn(CNDG)algorithm with is proposed for rotationally symmetric multi-scale problems in anisotropic magnetized plasma.Within the CNDG algorithm,an alternative scheme for the simulation of anisotropic plasma is proposed in body-of-revolution domains.Convolutional perfectly matched layer(CPML)formulation is proposed to efficiently solve the open region problems.Numerical example is carried out for the illustration of effectiveness including the efficiency,resources,and absorption.Through the results,it can be concluded that the proposed scheme shows considerable performance during the simulation.