Transverse heat transfer coefficient in the dual channel ITER TF CICCs Part II. Analysis of transient temperature responses observed during a heat slug propagation experiment

A heat slug propagation experiment in the final design dual channel ITER TF CICC was performed in the SULTAN test facility at EPFL-CRPP in Villigen PSI. We analyzed the data resulting from this experiment to determine the equivalent transverse heat transfer coefficient h_BC between the bundle and the central channel of this cable. In the data analysis we used methods based on the analytical solutions of a problem of transient heat transfer in a dual-channel cable, similar to Renard et al. (2006) and Bottura et al. (2006). The observed experimental and other limits related to these methods are identified and possible modifications proposed. One result from our analysis is that the h_BC values obtained with different methods differ by up to a factor of 2. We have also observed that the uncertainties of h_BC in both methods considered are much larger than those reported earlier.     

Three-dimensional Green’s functions for a steady point heat source in a functionally graded half-space and some related problems

Three-dimensional Green’s functions are derived for a steady point heat source in a functionally graded half-space where the thermal conductivity varies exponentially along an arbitrary direction. We first introduce an auxiliary function which satisfies an inhomogeneous Helmholtz equation. Then by virtue of the image method which was first proposed by Sommerfeld for the homogeneous half-space Green’s function of a steady point heat source, we arrive at an explicit expression for this function. Finally with this auxiliary function, we derive the three-dimensional Green’s functions due to a steady point heat source in a functionally graded half-space. Also investigated in this paper are the temperature field induced by a point heat source moving at a constant speed in a functionally graded full-space; the electric potential due to a static point electric charge in a dielectric full-space with electric field gradient effects; and the two-dimensional time-harmonic dynamic Green’s function for homogeneous and functionally graded materials with strain gradient effects.     

An efficient finite element procedure for analyzing three‐phase porous media based on the relaxed Picard method

Effective simulation of the solid‐liquid‐gas coupling effect in unsaturated porous media is of great significance in many diverse areas. Because of the strongly nonlinear characteristics of the fully coupled formulations for the three‐phase porous media, an effective numerical solution scheme, such as the finite element method with an efficient iterative algorithm, has to be employed. In this paper, an efficient finite element procedure based on the adaptive relaxed Picard method is developed for analyzing the coupled solid‐liquid‐gas interactions in porous media. The coupled model and the finite element analysis procedure are implemented into a computer code PorousH2M, and the proposed procedure is validated through comparing the numerical simulations with the experimental benchmarks. It is shown that the adaptive relaxed Picard method has salient advantage over the traditional one with respect to both the efficiency and the robustness, especially for the case of relatively large time step sizes. Compared with the Newton‐Raphson scheme, the Picard method successfully avoids the unphysical ‘spurious unloading’ phenomenon under the plastic deformation condition, although the latter shows a better convergence rate. The proposed procedure provides an important reference for analyzing the fully coupled problems related to the multi‐phase, multi‐field coupling in porous media. Copyright © 2014 John Wiley & Sons, Ltd.     

基于变分渐近法预测饱和多孔介质流固耦合性能的细观力学模型

饱和岩土类多孔材料内固、液相不同属性产生的各向异性和多孔微结构的不均匀性使得材料的细观力学特性计算变得十分复杂。为准确预测岩土类材料的有效弹性性能和细观应力-应变场,基于Biot多孔弹性介质理论,建立可描述岩土类多孔材料固液相运动的能量泛函和相应的多孔弹性本构关系;利用细、宏观尺度比作为小参数将能量变分泛函渐近扩展为系列近似泛函;以场变量波动函数为未知量,通过解决近似泛函的最小化问题(驻值问题)得到波动函数的解析解,从而建立逼近物理和工程真实性的细观力学模型,并通过有限元技术得以数值实现。多孔介质材料细观力学特性算例表明:与经典均匀化理论(将液体类比为具有较高泊松比的固体材料)相比,基于变分渐近均匀化细观模型预测的多孔介质材料细观力学特性更精确,尤其是能准确重构多孔微结构内局部应力-应变场分布,为损伤破坏、局部断裂分析奠定了坚实基础。      

Higher‐resolution convection schemes for flow in porous media on highly distorted unstructured grids

Higher‐resolution schemes are presented for convective flow approximation on highly distorted unstructured grids. The schemes are coupled with continuous full‐tensor Darcy‐flux approximations. A sequence of non‐uniform and distorted grid formulations are developed and compared for a range of unstructured meshes with variable grid spacing. The higher‐order schemes are constructed using non‐uniform grid slope limiters such that they are stable with a local maximum principle, ensuring that solutions are free of spurious oscillations. Benefits of the resulting schemes are demonstrated for classical test problems in reservoir simulation including cases with full‐tensor permeability fields. The test cases involve a range of unstructured grids with variations in grid spacing, orientation and permeability that lead to flow fields that are poorly resolved by standard simulation methods. The higher‐order formulations are shown to effectively reduce numerical diffusion, leading to improved resolution of concentration and saturation fronts. Copyright © 2008 John Wiley & Sons, Ltd.     

基于新型自复位摩擦耗能支撑的RC框架结构地震残余变形控制

基于Cu-Al-Be合金丝,研制了一种新型自复位摩擦耗能支撑,通过试验研究了该支撑的滞回性能,并利用OpenSEES平台建立了分析模型,将其应用于RC框架结构的地震残余变形控制。结果表明:摩擦力越大,该支撑耗能性能越好,但相应会增大残余位移;利用OpenSEES分析模型计算的滞回曲线与试验曲线吻合较好,表明所建立的分析模型具有良好的计算精度;在RC框架结构地震残余位移较大处布置该支撑,能够经济有效地控制结构整体的残余位移。     

基于胎面-路面摩擦自激的轮胎非线性振动建模仿真

轮胎的多边形磨损是汽车研发设计过程中迫切需要解决的问题之一。考虑轮胎接地磨擦的非线性特性,建立了悬架-轮胎-胎面系统的考虑时间延迟的两自由度动力学振动模型,研究基于自激振动理论的轮胎多边形磨损现象。通过matlab/simulink进行仿真试验,验证了汽车中高速行驶时硬自激振动现象的存在,并给出了能够引起自激振动的敏感参数及车速范围。所建立的动力学振动模型可以帮助分析悬架动力学特性对轮胎多边形磨损的影响,为减小或消除轮胎的自激振动提供了理论依据。     

基于主成分分析马氏距离的支腿控制阀健康评估

支腿控制阀的性能是影响起重机支腿系统伸缩性能的重要因素之一。为了准确的评估支腿控制阀的健康性能,提出一种支腿系统的性能衰退与健康状态的评估方法,该方法基于PCA降维与马氏距离相结合的分析模型,建立不同状态下传感器信号与关键零部件的映射关系,从而达到对起重机支腿系统性能衰退量化评估的目的。该方法应用于起重机支腿控制阀的压力信号,通过对传感器信号内蕴关系及起重机在各年份提取的特征在特征空间的相关性分析,以得到量化性能评估结果。与常见的其他方法相比,该模型能够准确地反映起重机支腿系统历年来的性能衰退趋势,具有更好的鲁棒性与泛化性。     

Topology optimization of multi-material for the heat conduction problem based on the level set method

This article presents a numerical approach of topology optimization with multiple materials for the heat conduction problem. The multiphase level set model is used to implicitly describe the geometric boundaries of material regions with different conductivities. The model of multi-material representation has no emergence of the intermediate density. The optimization objective is to construct the optimal heat conductive paths which improve the efficiency of heat transfer. The dissipation of thermal transport potential capacity is taken as the objective function. The sensitivity analysis is implemented by the adjoint variable method, which is the foundation of constructing the velocity field of the level set equation. The optimal result is gradually realized by the evolution of multi-material boundaries, and the topological changes are naturally handled during the optimization process. Finally, the numerical examples are presented to demonstrate the feasibility and validity of the proposed method for topology optimization of the heat conduction problem.     

The structural design of digital correlometers for operational correlation analysis based on sign-function analog-stochastic quantization

A fast digital algorithm for measuring correlation and cross-correlation functions is presented. The algorithm is based on the use of sign-function analog-stochastic quantization of samples of the random processes being investigated. Block diagrams of multichannel digital correlometers for operational correlation analysis are given. __________ Translated from Izmeritel’naya Tekhnika, No. 4, pp. 6–11, April, 2007.     

A consistent approach for fluid-structure-contact interaction based on a porous flow model for rough surface contact

Simulation approaches for fluid-structure-contact interaction, especially if requested to be consistent even down to the real contact scenarios, belong to the most challenging and still unsolved problems in computational mechanics. The main challenges are 2-fold—one is to have a correct physical model for this scenario, and the other is to have a numerical method that is capable of working and being consistent down to a zero gap. Moreover, when analyzing such challenging setups of fluid-structure interaction, which include contact of submersed solid components, it gets obvious that the influence of surface roughness effects is essential for a physical consistent modeling of such configurations. To capture this system behavior, we present a continuum mechanical model that is able to include the effects of the surface microstructure in a fluid-structure-contact interaction framework. An averaged representation for the mixture of fluid and solid on the rough surfaces, which is of major interest for the macroscopic response of such a system, is introduced therein. The inherent coupling of the macroscopic fluid flow and the flow inside the rough surfaces, the stress exchange of all contacting solid bodies involved, and the interaction between fluid and solid are included in the construction of the model. Although the physical model is not restricted to finite element–based methods, a numerical approach with its core based on the cut finite element method, enabling topological changes of the fluid domain to solve the presented model numerically, is introduced. Such a cut finite element method–based approach is able to deal with the numerical challenges mentioned above. Different test cases give a perspective toward the potential capabilities of the presented physical model and numerical approach.     

A Solution‐Processed High‐Performance Phototransistor based on a Perovskite Composite with Chemically Modified Graphenes

Phototransistors with a structure of a nitrogen‐doped graphene quantum dots (NGQDs)–perovskite composite layer and a mildly reduced graphene oxide (mrGO) layer are fabricated through a solution‐processing method. This hybrid phototransistor exhibits broad detection range (from 365 to 940 nm), high photoresponsivity (1.92 × 10⁴ A W^?1), and rapid response to light on–off (≈10 ms). NGQDs offer an effective and fast path for electron transfer from the perovskite to the mrGO, resulting in the improvement of photocurrent and photoswitching characteristics. The high photoresponsivity can also be ascribed to a photogating effect in the device. In addition, the phototransistor shows good stability with poly(methyl methacrylate) encapsulation, and can maintain 85% of its initial performance for 20 d in ambient air.     

Modal criteria for optimizing the acoustic behaviour of a coupled fluid–structure system based on a systemic approach

This paper proposes modal criteria to represent various noise sources within a complex structure, such as an automobile. By optimizing a complex system using criteria linked to modal mass and stiffness matrices, different modes of noise propagation can be investigated separately. Several criteria are thus suggested, each related to a vibrational propagation path. Since the system is studied using modal analysis, criteria can be found based on modes associated with the structure's hollow parts, plates, and cavities. These different criteria are analysed based on the assumption of a complex vibroacoustic system. It is shown that by analysing such criteria, one can determine which part of the structure needs to be optimized. The optimization of such a system could constitute a research topic in its own right, and is beyond the scope of the present paper. Copyright © 2007 John Wiley & Sons, Ltd.     

基于AR模型的印刷机滚筒扭矩及其振动试验研究

稳定性低是国产印刷机面临的共性问题,印刷滚筒扭振是影响稳定性的关键因素之一。以印刷机压印滚筒作为研究对象,分析了压印滚筒在动力传递过程中的扭矩传递规律：滚筒扭矩因空档等原因存在突变。采用AR（自回归）模型和小波分析相结合,提出了滚筒扭振信号的后处理方法,实现了信号去噪;通过对扭矩测试和数据分析,提取出印刷滚筒的扭振前5阶固有频率65Hz、80Hz、300Hz、375Hz、400Hz;通过与传递矩阵法结果比较,验证了扭振信号处理方法的正确性。研究结果为印刷滚筒的减振与结构优化提供了依据。     

地震作用下刚体滑动位移的计算与比较——基于Coulomb摩擦模型

首先对滑动干摩擦模型的研究现状进行了系统的论述。推导了基于Coulomb摩擦模型时刚体在简谐地面运动时滑动位移的解析方程;讨论了滑动状态与粘结状态过渡时刻的求解精度对刚体与地面相对位移的影响;对基于摩擦力－位移模型和基于Coulomb摩擦模型下刚体在简谐地面运动作用下滑动位移的差异进行了对比。然后采用Newmark线性加速度法推导了基于Coulomb摩擦模型刚体在任一地震加速度作用下滑动位移的数值求解方法;对比了基于摩擦力－位移模型和基于Coulomb摩擦模型下刚体在任一地面运动作用下滑动位移的差异。     

A FETI‐based domain decomposition technique for time‐dependent first‐order systems based on a DAE approach

We present a novel partitioned coupling algorithm to solve first‐order time‐dependent non‐linear problems (e.g. transient heat conduction). The spatial domain is partitioned into a set of totally disconnected subdomains. The continuity conditions at the interface are modeled using a dual Schur formulation where the Lagrange multipliers represent the interface fluxes (or the reaction forces) that are required to maintain the continuity conditions. The interface equations along with the subdomain equations lead to a system of differential algebraic equations (DAEs). For the resulting equations a numerical algorithm is developed, which includes choosing appropriate constraint stabilization techniques. The algorithm first solves for the interface Lagrange multipliers, which are subsequently used to advance the solution in the subdomains. The proposed coupling algorithm enables arbitrary numeric schemes to be coupled with different time steps (i.e. it allows subcycling) in each subdomain. This implies that existing software and numerical techniques can be used to solve each subdomain separately. The coupling algorithm can also be applied to multiple subdomains and is suitable for parallel computers. We present examples showing the feasibility of the proposed coupling algorithm. Copyright © 2008 John Wiley & Sons, Ltd.     

An anomaly detection technique based on a chi‐square statistic for detecting intrusions into information systems

An intrusion into an information system compromises its security (e.g. availability, integrity and confidentiality) through a series of events in the information system. Intrusive events often show departures (anomalies) from normal events in an information system. This paper presents an anomaly detection technique based on a chi‐square statistic. This technique builds a profile of normal events in an information system—a norm profile computes the departure of events in the recent past from the norm profile and detects a large departure as an anomaly—a likely intrusion. This technique was tested for its performance in distinguishing normal events from intrusive events in an information system. The test results demonstrated the promising performance of this technique for intrusion detection in terms of a low false alarm rate and a high detection rate. Intrusive events were detected at a very early stage. Copyright © 2001 John Wiley & Sons, Ltd.     

Reliability analysis of structures based on a probability‐uncertainty hybrid model

The traditional reliability analysis method based on probabilistic method requires probability distributions of all the uncertain parameters. However, in practical applications, the distributions of some parameters may not be precisely known due to the lack of sufficient sample data. The probabilistic theory cannot directly measure the reliability of structures with epistemic uncertainty, ie, subjective randomness and fuzziness. Hence, a hybrid reliability analysis (HRA) problem will be caused when the aleatory and epistemic uncertainties coexist in a structure. In this paper, by combining the probability theory and the uncertainty theory into a chance theory, a probability‐uncertainty hybrid model is established, and a new quantification method based on the uncertain random variables for the structural reliability is presented in order to simultaneously satisfy the duality of random variables and the subadditivity of uncertain variables; then, a reliability index is explored based on the chance expected value and variance. Besides, the formulas of the chance theory‐based reliability and reliability index are derived to uniformly assess the reliability of structures under the hybrid aleatory and epistemic uncertainties. The numerical experiments illustrate the validity of the proposed method, and the results of the proposed method can provide a more accurate assessment of the structural system under the mixed uncertainties than the ones obtained separately from the probability theory and the uncertainty theory.     

Synthesis and characterization of a new material based on porous silica—Chemically immobilized C,N-pyridylpyrazole for heavy metals adsorption

The immobilization of C,N-pyridylpyrazole on the surface of epoxy group containing silica gel phase for the formation of a newly synthesized material based on porous silica-bound C,N-pyridylpyrazole (SGPP) is described. The surface modification was characterized by ¹³C NMR of solid sample, elemental analysis and infrared spectra and was studied and evaluated by determination of the surface area using the BET equation, the adsorption and desorption capability using the isotherm of nitrogen and BJH pore sizes, respectively. The new material exhibits good thermal stability determined by thermogravimetry curves. The synthesized material was utilised in column and batch methods for separation and trace extraction of (Hg²⁺, Cd²⁺, Pb²⁺, Cu²⁺, Zn²⁺, K⁺, Na⁺ and Li⁺) and compared to results of classical liquid–liquid extraction with the unbound C,N-pyridylpyrazole compound. The grafting at the surface of silica does not affect complexing properties of the ligand and the material exhibits a high selectivity toward Hg(II).