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.

General Response Surface Reliability Analysis for Fuzzy-Random Uncertainty both in Basic Variables and in State Variables

A general response surface（RS） method is presented for reliability analysis of complex structure/mechanism with fuzzy-random uncertainty both in basic variables and in failure state variables. On the basis of equivalent transformation from fuzzy basic variable to random basic variable, the fuzziness and randomness in the basic variables are considered simultaneously in the presented general RS method. Once the fuzzy basic variables are transformed into the random basic variables, the conventional RS method is employed to establish the general RS for the complex structure/mechanism with implicit limit state equation by finite element numerical simulation. Furthermore, the general failure probability is defined according to the probability formula for fuzzy-random event by taking the fuzziness and randomness in the failure-safety state into consideration, and an appropriate fuzzy operator is adopted to calculate the general failure probability for the complex structure/mechanism with multiple implicit failure modes. Finally, a general reliability analysis of an elastic linkage mechanism is introduced to illustrate the present method.

Reliability analysis for aeroengine turbine disc fatigue life with multiple random variables based on distributed collaborative response surface method

The fatigue life of aeroengine turbine disc presents great dispersion due to the randomness of the basic variables,such as applied load,working temperature,geometrical dimensions and material properties.In order to ameliorate reliability analysis efficiency without loss of reliability,the distributed collaborative response surface method(DCRSM) was proposed,and its basic theories were established in this work.Considering the failure dependency among the failure modes,the distributed response surface was constructed to establish the relationship between the failure mode and the relevant random variables.Then,the failure modes were considered as the random variables of system response to obtain the distributed collaborative response surface model based on structure failure criterion.Finally,the given turbine disc structure was employed to illustrate the feasibility and validity of the presented method.Through the comparison of DCRSM,Monte Carlo method(MCM) and the traditional response surface method(RSM),the results show that the computational precision for DCRSM is more consistent with MCM than RSM,while DCRSM needs far less computing time than MCM and RSM under the same simulation conditions.Thus,DCRSM is demonstrated to be a feasible and valid approach for improving the computational efficiency of reliability analysis for aeroengine turbine disc fatigue life with multiple random variables,and has great potential value for the complicated mechanical structure with multi-component and multi-failure mode.

CALCULATING RESPONSE SPECTRAL MOMENTS BY COMPLEX MODAL ANALYSIS

Response spectral moments are useful for system reliability analysis.Usually,spectral mo- ments are calculated by the frequency domain method.Based on the time domain modal analysis of random vibrations,the authors present a new method for calculating response spectral moments through response correlation functions.The method can be applied to both classical and non-classical damping cases and to three kinds of random excitations,i.e.,white noise,band-limited white noise, and filtered white noise.

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 thermo-mechanical analysis for bimorph soft robot based on thermally responsive liquid crystal elastomers

Thermally responsive liquid crystal elastomers (LCEs) hold great promise in applications of soft robots and actuators because of the induced size and shape change with temperature. Experiments have successfully demonstrated that the LCE based bimorphs can be effective soft robots once integrated with soft sensors and thermal actuators. Here, we present an analytical transient thermo-mechanical model for a bimorph structure based soft robot, which consists of a strip of LCE and a thermal inert polymer actuated by an ultra-thin stretchable open-mesh shaped heater to mimic the unique locomotion behaviors of an inchworm. The coupled mechanical and thermal analysis based on the thermo-mechanical theory is carried out to underpin the transient bending behavior, and a systematic understanding is therefore achieved. The key analytical results reveal that the thickness and the modulus ratio of the LCE and the inert polymer layer dominate the transient bending deformation. The analytical results will not only render fundamental understanding of the actuation of bimorph structures, but also facilitate the rational design of soft robotics.

Reliability analysis of slopes considering spatial variability of soil properties based on efficiently identified representative slip surfaces

Slope reliability analysis considering inherent spatial variability(ISV)of soil properties is timeconsuming when response surface method(RSM)is used,because of the"curse of dimensionality".This paper proposes an effective method for identification of representative slip surfaces(RSSs)of slopes with spatially varied soils within the framework of limit equilibrium method(LEM),which utilizes an adaptive K-means clustering approach.Then,an improved slope reliability analysis based on the RSSs and RSM considering soil spatial variability,in perspective of computation efficiency,is established.The detailed implementation procedure of the proposed method is well documented,and the ability of the method in identifying RSSs and estimating reliability is investigated via three slope examples.Results show that the proposed method can automatically identify the RSSs of slope with only one evaluation of the conventional deterministic slope stability model.The RSSs are invariant with the statistics of soil properties,which allows parametric studies that are often required in slope reliability analysis to be efficiently achieved with ease.It is also found that the proposed method provides comparable values of factor of safety(FS)and probability of failure(Pf)of slopes with those obtained from direct analysis and lite rature.

Dynamic probabilistic analysis of stress and deformation for bladed disk assemblies of aeroengine

In order to describe and control the stress distribution and total deformation of bladed disk assemblies used in the aeroengine, a highly efficient and precise method of probabilistic analysis which is called extremum response surface method(ERSM) is produced based on the previous deterministic analysis results with the finite element model(FEM). In this work, many key nonlinear factors, such as the dynamic feature of the temperature load, the centrifugal force and the boundary conditions, are taken into consideration for the model. The changing patterns with time of bladed disk assemblies about stress distribution and total deformation are obtained during the deterministic analysis, and at the same time, the largest deformation and stress nodes of bladed disk assemblies are found and taken as input target of probabilistic analysis in a scientific and reasonable way. Not only their reliability, historical sample, extreme response surface(ERS) and the cumulative probability distribution function but also their sensitivity and effect probability are obtained. Main factors affecting stress distribution and total deformation of bladed disk assemblies are investigated through the sensitivity analysis of the model. Finally, compared with the response surface method(RSM) and the Monte Carlo simulation(MCS), the results show that this new approach is effective.

Modal Correlation Based Analysis on Dynamic Characters of a Commercial Semi-Trailer's Chassis Frames

In order to evaluate two different schemes＇ structural dynamic characters, dynamic response analysis of a commercial truck＇s main chassis frames is carried out. On the basis of correlation study between the tested and calculated modal results, the assembled frames＇ finite element analysis （FEA） models with sufficient precision are built up. Random response analysis in frequency domain is carried out with these FEA models, RMS values of yon Mises and main principle stresses of these two frames are obtained. It shows that the analysis resuits of the distributing tendency and concrete value ranges are coincident very well with test results. And from the results, it could be concluded that frames of scheme A endures relative better loading conditions and should be adopted as the final scheme.

Stochastic Finite Element Analysis of Plate and Shell Construction

The response of random plate and shell construction is analyzed with the stochastic finite element method (SFEM). Random material properties and geometric dimensions of construction are involved in this paper. A simplified isoparametric local average model is used to describe the random field. Numerical results of the examples indicate that the approach presented herein is an economical and efficient solution for such an analysis compared with Monte Carlo simulation (MCS).

炎症、代谢物与骨质疏松症

背景:多项研究表明炎症、代谢物与骨质疏松症之间存在密切关系,但炎症相关蛋白与骨质疏松症之间是否存在遗传因果效应以及代谢物是否在其中发挥中介效应尚不清楚。目的:采用孟德尔随机化方法研究了炎症相关蛋白和骨质疏松症的因果关系以及血浆代谢物在该关系中的中介作用。方法:利用全基因组关联研究(GWAS)的汇总数据,骨质疏松症数据来Fengenn数据库,炎症相关蛋白和血浆代谢物的数据来自己发表的研究。评估暴露与结局之间的关联性主要是反方差加权方法,通过双向孟德尔随机化分析探索炎症相关蛋白与骨质疏松症之间的因果关系,并通过两步孟德尔随机化分析发现潜在的发挥中介作用的血浆代谢物。随后进行敏感性分析以进一步验证结果的稳健性。采用Cochran’s Q检验评估研究结果的异质性。通过MR-Egger截距法和MR-PRESSO法进行水平多效性评估。结果与结论:(1)通过初步双向孟德尔随机化分析,鉴定出5种与骨质疏松症有正向因果关系且没有反向因果关系的炎症相关蛋白;其中神经鞘胚素(OR=0.895,95%CI:0.819-0.979,P=0.015)与骨质疏松症呈负相关,而趋化因子(C-X-C基序)配体1(OR=1.100,95%CI:1.002-1.209,P=0.046)。趋化因子(C-X-C基序)配体11(OR=1.150,95%CI:1.043-1.268,P=0.005)、白细胞介素17 C(OR=1.087,95%CI:1.004-1.176,P=0.040)、肿瘤坏死因子样凋亡微弱诱导因子(OR=1.108,95%CI:1.002-1.226,P=0.046)与骨质疏松症呈正相关;敏感性分析显示,这些因果效应都没有异质性和多效性。(2)文章还进行了两步孟德尔随机化分析发现潜在的中介血浆代谢物:1-棕榈酰gpc(16∶0)增加了神经鞘胚素对骨质疏松症的负向作用,5α-雄甾烷-3α,17β-单硫酸二醇会增加趋化因子(C-X-C基序)配体1、趋化因子(C-X-C基序)配体11介导的骨质疏松症风险性;Α-酮戊二酸与琥珀酸比值会导致趋化因子(C-X-C基序)配体11、白细胞介素17 C介导的骨质疏松症风险性增加;亚精胺、脯氨酸与反式-4-羟脯氨酸比值导致趋化因子(C-X-C基序)配体11介导的骨质疏松症风险性增加;12,13-二羟基十八碳烯酸会导致白细胞介素17 C介导的骨质疏松症风险性增加;胡椒碱代谢物C_(16)H_(19)NO_(3)(3)的硫酸盐水平、腺苷3′,5′-环单磷酸腺苷会导致肿瘤坏死因子样凋亡微弱诱导因子介导的骨质疏松症风险性增加。(3)上述数据证实,部分炎症相关蛋白可以影响骨质疏松症的风险,这种作用是正向和负向的,并且其中一部分作用由血浆代谢物介导,这为未来探究骨质疏松症的发生发展机制提供了新的认知。

Research of Network Transient Performance at Small Perturbations

The advisability of the use of matrix methods of equations rearrangement for the investigated system which allows writing a secular equation is considered in this article. This approach greatly simplifies the analysis of performance of transient response in complicated multi-coupled electrical system at small perturbations.

非平稳随机地震激励下多层框架-摇摆墙结构的响应分析

框架-摇摆墙是一种可有效提高建筑抗震性和韧性的组合自复位结构,为充分了解其在地震下的随机响应特性,构建多自由度框架-摇摆墙结构的简化非线性方程,并利用等效线性化,基于响应的伪谐波行为假设,构建含时变参数的等效线性动力方程;基于随机平均的原理,得出控制响应幅值概率密度函数(PDF)的时间演变形式的福克-普朗克-科尔莫哥洛夫(FPK)方程,最终得出随机响应时间相关方差的一阶微分方程;并以某教学楼一榀框架为样本构建算例模型进行验证。结果表明:近似解析方法具有优异的精确度,在保证随机响应时间相关方差准确性的前提下,相对于传统的蒙特卡罗模拟(MCS)方法可提高分析的效率;在可分离形式和不可分离形式的非平稳地震动功率谱模型的结果中,随机响应方差曲线趋势与随机地震激励的形式相关,且在分段式调制非平稳谱作用下其分段点表现出很明显的不平滑现象;不同类型的随机地震激励扰动下的结果证明了此方法优异的适用性。

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。

汽车尾气温差发电系统瞬态回收性能分析

为了预测温差发电(thermoelectric generator, TEG)系统的动态特性,基于COMSOL Multiphy-sics建立了用于求解温差发电系统温度场分布的瞬态计算流体力学(computational fluid dynamics, CFD)模型和用于研究温差发电模块瞬态响应特性的分析模型,提出了混合瞬态CFD-分析模型,并经过瞬态试验验证.结果表明:由于热惯性的影响,TEG系统的转化效率会出现一个瞬时的较高值;相较于尾气温度和质量流量的瞬态波动,热电半导体的热端温度和冷端温度会存在时滞;在美国环保局的高速公路燃油经济性测试(highway fuel economy test, HWFET)模式循环工况下,瞬态模型求解得到整个温差发电系统的平均输出功率、平均转化效率分别为35.63 W和3.40%,瞬态模型的输出电压平均误差为6.41%;该模型能够以较高的精度及较短的计算时间预测温差发电系统在瞬态热源激励下的瞬态响应特性.

一种高速A/D转换器时域重构技术研究

A/D转换器在航空航天系统中的重要元器件,随着器件转换时钟频率不断提高而其工作环境不断恶化,如何准确测试其时间参数对于全面评价A/D转换器性能特别重要。目前对于高速A/D转换器时间参数测试,主流方法是通过示波器直接测试其输出,该方法对于示波器采样速度要求比较高。文章提出一种高速A/D转换器时域重构技术,可以通过计算机数字信号处理方法来实现高速A/D转换器时间参数测试,同时避免对示波器采样速度的依赖。同时,在研究高速A/D转换器时域重构技术方法及其应用的基础上,通过了相关试验验证。

随机激励下斜拉索-梁参数振动模型及响应分析

为了揭示随机激励下斜拉索参数振动特性,考虑拉索几何非线性、倾角以及桥面梁的协同振动影响,建立了斜拉索-桥面梁耦合参数振动模型,利用相空间变换推导了索-梁结构耦合振动伊藤状态方程组,给出了高斯白噪声作用下索梁振动时程求解迭代格式,分析了拉索随机响应时程、频域、统计特性以及概率密度变化,并与高斯截断方法进行比较,考察了拉索阻尼比、初始张力、桥面梁的初始扰动以及随机激励强度对拉索振动的影响规律。结果表明:斜拉索振动迭代方法可有效求解随机激励下索-梁耦合参数振动时程,与传统的高斯截断方法的计算结果吻合;随机激励下,斜拉索“拍振”振幅具有明显的不确定性,斜拉索与桥面梁结构发生耦合振动时,两者之间存在能量传递现象;斜拉索随机激励位移响应均值具有非平稳瞬态特性,其位移均方差的稳定时间大于理想激励下的响应;斜拉索响应功率峰值对应的频率和功率谱密度旁瓣峰值衰减量基本一致,但斜拉索第一旁瓣峰值与主峰差值并不相同。斜拉索振动响应概率密度分布满足高斯分布形态,置信区间约为0.98,符合马尔科夫性质。随着阻尼比增大,拉索阻尼抑制效率降低;桥面梁初始扰动越大,拉索振动位移越大;拉索张力越大,拉索振动幅值呈非线性减小趋势,但张力进一步增大时,拉索振动幅值衰减趋于稳定;随机激励强度越大,拉索响应越大。

考虑套筒灌浆随机缺陷的装配式剪力墙结构可靠度评估

在装配整体式剪力墙结构中,由于套筒灌浆连接的质量具有一定的随机性,势必影响结构的竖向连接性能和结构抗震性能。根据不同缺陷程度的套筒灌浆拉拔试验,建立了一套等效套筒灌浆缺陷连接承载力模型,并基于某实际工程结构,建立了装配整体式剪力墙结构有限元模型。通过考虑灌浆缺陷的随机性,赋予连接接头相应缺陷程度的力学连接性能,来反映套筒灌浆中可能存在的缺陷。通过非线性有限元分析并结合概率密度演化方法(probability density evolution method,PDEM)进行了结构随机非线性反应分析和可靠度评估。结果表明:在动力作用下,结构非线性与随机性具有明显的耦合效应;缺陷的随机性会随着时间的推移,逐渐放大对结构响应的影响;在不同的安全域内,结构的整体可靠度将存在较大的差异。

深厚覆盖层上沥青混凝土心墙坝非平稳随机地震动响应分析

由于良好的环境适应能力沥青混凝土心墙坝是我国西南强震区深厚覆盖层场地的优选坝型,然而对于沥青混凝土心墙坝非平稳随机地震作用下的抗震安全评价研究尚有不足。采用改进的Clough-Penzien功率谱结合随机函数,充分考虑地震动频率与强度的非平稳特征,生成了一系列与反应谱拟合的非平稳随机地震动集合,以某深厚覆盖层上沥青混凝土心墙坝为例,对其坝顶水平加速度及竖向永久变形等响应的均值及变化范围等进行了统计分析及分布检验,揭示了覆盖层与坝体响应均值及变异性沿高程变化规律,并通过概率密度演化方法,展示了坝顶水平加速度概率密度沿时间的演化过程,同时对生成的55条非平稳随机地震动进行调幅,结合多条带分析法易损性分析方法开展了深厚覆盖层上沥青混凝土心墙坝非平稳随机地震动易损性分析,给出了以震陷率为破坏等级控制指标的坝体易损性曲线,为深厚覆盖层上沥青混凝土心墙坝的抗震安全评价提供了新的方法和思路。

不同中药注射液治疗糖尿病周围神经病变的网状Meta分析

目的:运用网状Meta分析不同中药注射液治疗糖尿病周围神经病变(DPN)的疗效和安全性。方法:基于PubMed、Cochrane Library、EMbase、Web of Science、国家知识基础设施数据库(CNKI)、中文科技期刊数据库(CCD)、中国学术期刊数据库(CSPD)、中国生物医学文献数据库(CBM),检索中药注射液治疗DPN的随机对照试验(RCTs),将临床总有效率作为主要结局指标,正中和腓总的感觉神经传导速度(SCV)及运动神经传导速度(MCV)、空腹血糖(FBG)及不良反应作为次要结局指标。采用Cochrane评价手册5.3风险偏倚评估工具进行质量评价及RevMan 5.4.1及Stata 17软件进行数据分析。结果:共纳入76项RCTs,包括6 108例患者,11种中药注射液。网状Meta分析结果显示,丹参多酚酸盐注射液联合西药在提高临床总有效率和改善FBG水平方面疗效最佳;苦碟子注射液联合西药在改善正中神经及腓总神经的SCV、正中神经MCV方面疗效最佳;血塞通注射液联合西药在改善腓总神经MCV方面疗效最佳;在安全性方面,中药注射液联合西药与单纯西药治疗比较差异无统计学意义。结论:中药注射液联合西药与单纯西药治疗比较可提高DPN临床疗效,且未增加不良反应的发生。