Orthogonal expansion of ground motion and PDEM-based seismic response analysis of nonlinear structures

This paper introduces an orthogonal expansion method for general stochastic processes. In the method, a normalized orthogonal function of time variable t is first introduced to carry out the decomposition of a stochastic process and then a correlated matrix decomposition technique, which transforms a correlated random vector into a vector of standard uncorrelated random variables, is used to complete a double orthogonal decomposition of the stochastic processes. Considering the relationship between the Hartley transform and Fourier transform of a real-valued function, it is suggested that the first orthogonal expansion in the above process is carried out using the Hartley basis function instead of the trigonometric basis function in practical applications. The seismic ground motion is investigated using the above method. In order to capture the main probabilistic characteristics of the seismic ground motion, it is proposed to directly carry out the orthogonal expansion of the seismic displacements. The case study shows that the proposed method is feasible to represent the seismic ground motion with only a few random variables. In the second part of the paper, the probability density evolution method （PDEM） is employed to study the stochastic response of nonlinear structures subjected to earthquake excitations. In the PDEM, a completely uncoupled one-dimensional partial differential equation, the generalized density evolution equation, plays a central role in governing the stochastic seismic responses of the nonlinear structure. The solution to this equation will yield the instantaneous probability density function of the responses. Computational algorithms to solve the probability density evolution equation are described. An example, which deals with a nonlinear frame structure subjected to stochastic ground motions, is illustrated to validate the above approach.

Joint Non-Orthogonal Multiple Access (NOMA) & Walsh-Hadamard Transform: Enhancing the Receiver Performance

Non-orthogonal multiple access(NOMA) is a new access method to achieve high performance gains in terms of capacity and throughput, so it is currently under consideration as one of the candidates for fifth generation(5 G) technologies. NOMA utilizes power domain in order to superimpose signals of multiple users in a single transmitted signal. This creates a lot of interference at the receive side. Although the use of successive interference cancellation(SIC) technique reduces the interference, but to further improve the receiver performance, in this paper, we have proposed a joint Walsh-Hadamard transform(WHT) and NOMA approach for achieving better performance gains than the conventional NOMA. WHT is a well-known code used in communication systems and is used as an orthogonal variable spreading factor(OVSF) in communication systems. Application of WHT to NOMA results in low bit error rate(BER) and high throughput performance for both low and high channel gain users. Further, it also reduces peak to average power ratio(PAPR) of the user signal. The results are discussed in terms of comparison between the conventionalNOMA and the proposed technique, which shows that it offers high performance gains in terms of low BER at different SNR levels, reduced PAPR, high user throughput performance and better spectral efficiency.

Unconventional Hamilton-type variational principles for nonlinear elastodynamics of orthogonal cable-net structures

According to the basic idea of classical yin-yang complementarity and modem dual-complementarity, in a simple and unified new way proposed by Luo, the unconventional Hamilton-type variational principles for geometrically nonlinear elastodynamics of orthogonal cable-net structures are established systematically, which can fully characterize the initial-boundary-value problem of this kind of dynamics. An ifnportant integral relation is made, which can be considered as the generalized principle of virtual work for geometrically nonlinear dynamics of orthogonal cable-net structures in mechanics. Based on such relationship, it is possible not only to obtain the principle of virtual work for geometrically nonlinear dynamics of orthogonal cable-net structures, but also to derive systematically the complementary functionals for five-field, four-field, three-field and two-field unconventional Hamilton-type variational principles, and the functional for the unconventional Hamilton-type variational principle in phase space and the potential energy functional for one-field unconventional Hamilton-type variational principle for geometrically nonlinear elastodynamics of orthogonal cable-net structures by the generalized Legendre transformation given in this paper, Furthermore, the intrinsic relationship among various principles can be explained clearly with this approach.

A Non-orthogonal STFC-OFDM on Frequency-Selective Fading Channels

A new non-orthogonal space-time-frequency code (STFC) was proposed. In conjunction with orthogonal frequency-division multiplexing (OFDM), it is appropriate for the application on frequency-selective fading channels. On the basis of the existing non-orthogonal STC, frequency diversity is studied and a new non-orthogonal STFC is further designed. Monte-Carlo simulations show that the non-orthogonal STFC-OFDM has the advantage of large diversity order, high bandwidth efficiency and better BER performance when compared with the orthogonal STC/STFC-OFDM and non-orthogonal STC-OFDM systems.

Modeling Approach and Analysis of the Structural Parameters of an Inductively Coupled Plasma Etcher Based on a Regression Orthogonal Design

The geometry of an inductively coupled plasma （ICP） etcher is usually considered to be an important factor for determining both plasma and process uniformity over a large wafer. During the past few decades, these parameters were determined by the ＂trial and error＂ method, resulting in wastes of time and funds. In this paper, a new approach of regression orthogonal design with plasma simulation experiments is proposed to investigate the sensitivity of the structural parameters on the uniformity of plasma characteristics. The tool for simulating plasma is CFD-ACE＋, which is commercial multi-physical modeling software that has been proven to be accurate for plasma simulation. The simulated experimental results are analyzed to get a regression equation on three structural parameters. Through this equation, engineers can compute the uniformity of the electron number density rapidly without modeling by CFD-ACE＋. An optimization performed at the end produces good results.

Optimization of the Water-Cooled Structure for the Divertor Plates in EAST Based on an Orthogonal Theory

An orthogoual experimental scheme was designed for optimizing a water-cooled structure of the divertor plate. There were three influencing factors： the radius R of the water- cooled pipe, and the pipe spacing L1 and L3. The influence rule of different factors on the cooling effect and thermal stress of the plate were studied, for which the influence rank was respectively R 〉 L1 〉 L3 and L3 〉 R 〉 L1. The highest temperature value decreased when R and L1 increased~ and the maximum thermal stress value dropped when R, L1 and L3 increased. The final optimized results can be summarized as： R equals 6 mm or 7 mm, L1 equals 19 mm, and L3 equals 20 mm. Compared with the initial design, the highest temperature value had a small decline~ and the maximum thermal stress value dropped by 19~ to 24~. So it was not ideal to improve the cooling effect by optimizing the geometry sizes of the water-cooled structure, even worse than increasing the flow speed, but it was very effective for dropping the maximum thermal stress value. The orthogoaal experimental method reduces the number of experiments by 80%, and thus it is feasible and effective to optimize the water-cooled structure of the divertor plate with the orthogonal theory.

An Orthogonal Least Squares Based Approach to FIR Designs

This paper is concerned with the application of forward Orthogonal Least Squares (OLS) algorithm to the design of Finite Impulse Response (FIR) filters. The focus of this study is a new FIR filter design procedure and to compare this with traditional methods known as the fir2() routine provided by MATLAB.

Labyrinth Seal Design Optimization Based on Quadratic Regression Orthogonal Experiment

The influence of labyrinth seal structure parameters and their interaction on the characteristics of leakage amount are numerically investigated by conducting a quadratic regression orthogonal experiment. To determine the optimal structure parameters of the steam seal for minimizing the leakage amount, a reliable regression equation that does not lack of fit is established. The flow characteristics of the fluid in the labyrinth seal are analyzed in detail. Results show that the leakage amount is greatly influenced by seal cavity depth, convex platform height, seal tooth thickness, and tooth tip clearance, with the tip clearance having the most significant effect. The interaction among the four items exerts a certain impact on the leakage amount. The proposed regression equation exhibits a good significance and does not lack of fit. After optimization, the labyrinth seal demonstrates increased entropy and energy dissipation at the tip of the seal tooth, as well as decreased speed and inertia effect in the cavity, suggesting that the resistance leakage performance of the optimized labyrinth seal is improved.

Fabrication, Mechanical and Dielectric Characterization of 3D Orthogonal Woven Basalt Reinforced Thermoplastic Polyimide Composites

The 3D orthogonal woven basalt fiber reinforced polyimide (PI) composites were fabricated and characterized in this study. The PI film was firstly prepared to determine PI processing parameters. Fourier transform infrared (FTIR) analysis showed that 300°C was the suitable imidization temperature. Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) results showed relatively good thermal properties of the PI film. In the fabrication of composites, the multi-step impregnation method was applied. The bending properties of 3 mm-thick composite showed increasing trend in all and the second-time impregnated composite had much higher value than the first-time impregnated composite. Moreover, the bending fracture mode photos showed obvious creases except for the first-time impregnated materials, which agreed well with the bending property values. The dielectric constants for the composites were complex because they had not regular value following the mixing rule of the composites, which was mainly due to the interfacial polarization and other effects in the fabrication processing.

Proper orthogonal decomposition analysis of coherent motions in a turbulent annular jet

A three-dimensional incompressible annular jet is simulated by the large eddy simulation(LES)method at a Reynolds number Re=8500.The time-averaged velocity field shows an asymmetric wake behind the central bluff-body although the flow geometry is symmetric.The proper orthogonal decomposition(POD)analysis of the velocity fluctuation vectors is conducted to study the flow dynamics of the wake flow.The distribution of turbulent kinetic energy across the three-dimensional POD modes shows that the first four eigenmodes each capture more than 1%of the turbulent kinetic energy,and hence their impact on the wake dynamics is studied.The results demonstrate that the asymmetric mean flow in the near-field of the annular jet is related to the first two POD modes which correspond to a radial shift of the stagnation point.The modes 3 and 4 involve the stretching or squeezing effects of the recirculation region in the radial direction.In addition,the spatial structure of these four POD eigenmodes also shows the counter-rotating vortices in the streamwise direction downstream of the flow reversal region.

3D Woven Structures and Their Weave Design with Changing Cross-section on Warp and Weft Direction

With 3D orthogonal and pseudo-orthogonal weaves, woven sructures with lengthwise and widthwise changing cross section on one side or both sides of the structure can be constructed. The weave formation and the looming draft creation are discussed in this paper which can be used as references to manufacture woven preforms with changing cross sections.

LINEAR ACTIVE STRUCTURES AND MODES (Ⅱ) —DISCRETE SYSTEMS AND BEAMS

The basic concepts about the active structures and some attributes of the modes were presented in paper “Liner Active Structures and Modes]( I) ". The characteristics of the active discrete systems and active beams were discussed, especially, the stability of the active structures and the orthogonality of the eigenvectors. The notes about modes were portrayed by a model of a seven-storeyed building with sensors and actuators. The concept of the adjoint active structure was extended from the discrete systems to the beams that were the representations of the continuous structures. Two types of beams with different placements of the measuring and actuating systems were discussed in detail. One is the beam with the discrete sensors and actuators, and the other is the beam with distributed sensor and actuator function. The orthogonality conditions were derived with the modal shapes of the active beam and its adjoint active beam. An example shows that the variation of eigenvalues with feedback amplitude for the homo-configuration and non-homo-configuration active structures.

基于正交试验的民用飞机抗爆结构参数敏感性分析

最小风险炸弹位置(LRBL)结构是放置飞机上可疑爆炸物的装置,探究结构尺寸和炸药位置对其抗爆性能的影响程度可为其改进设计提供参考。基于正交试验设计与数值模拟相结合的方法,以LRBL结构各危险部位的最大应变和变形为评价指标,分别运用极差分析法和方差分析法对LRBL结构的罐体壁厚、底盖厚度、连接凸台厚度、剪切销直径和炸药位置5个影响因素开展参数敏感性分析。结果表明:在200 g炸药当量的工况下,各因素对LRBL结构的抗爆性能的影响显著程度从大到小为炸药位置、罐体壁厚、底盖厚度、凸台厚度和剪切销直径;结合评价指标综合分析得到各个因素最优水平下的LRBL结构设计方案。

基于正交试验的泡沫混凝土导热性能和孔结构研究

以硫铝酸盐水泥、粉煤灰为胶凝材料,采用正交试验法研究了发泡剂、减水剂、增稠剂对于泡沫混凝土导热性能的影响并确定最优组合。制备5组不同密度(300、400、500、700、900 kg/m^(3))泡沫混凝土,采用Photoshop图像处理软件对各组样品截面图进行二值化处理,并利用Image-Pro Plus软件对孔隙率、圆度值和孔径分布等孔结构特性进行分析。结果表明,影响泡沫混凝土导热系数的各因素主次顺序为增稠剂、发泡剂、减水剂。泡沫混凝土的密度与孔隙率呈负相关,相关系数R^(2)为0.91;密度越大,圆度值为1的孔隙占比越大。不同密度等级泡沫混凝土的孔径分布近似服从对数正态分布,孔径主要集中于200μm,且大孔径比例随着密度的增大而逐渐降低。

通井规携屑性能研究结构及参数优化

针对一体化井筒准备作业中岩屑通过通井规效果差,导致通井规携屑能力低的问题,以携屑能力为性能指标,采用正交试验法对通井规进行结构优化设计,得到了最优结构参数:过流道深度6 mm、过流道螺旋角度80°、过流道宽度40 mm、扶正套锥角11°;同时以最优结构参数对通井规作业参数进行优选,优选出最佳作业参数:循环排量1.1 m^(3)/min、转速60 r/min。研究结果表明,对通井规结构参数优化和作业参数优选,提高了通井规携屑能力,为通井规结构参数和工况参数的优化研究提供了参考,具有指导和借鉴意义。

碳纤维树脂基复合材料回转体的网格结构优化研究

针对复杂回转体的网格结构参数进行优化,以最大载荷质量比为优化目标,筋条几何参数及数量为设计变量,ABAQUS有限元屈曲分析为手段,确定模型结构承载效率的评价指标,进行单因素分析。其中,纵筋数量、纵筋宽度、筋条高度3种因素对模型承载效率影响较为显著。环筋数量与环筋宽度对模型承载效率的影响显著性较低,并结合实际制造条件分析得出用于正交试验的因素范围。利用数理上的正交性原理设计了L16(45)正交表与适用于复杂网格结构的正交试验方案。通过数值模拟,得到16组试验结果,并对试验结果进行极差分析。发现各因素对目标值影响程度的排序均为:纵筋宽度>筋条高度>纵筋数量>环筋数量>环筋宽度,并得出最优参数组合。最后对最优参数组合进行试验验证,找出使用最优参数组合的回转体所能承受最大载荷的理论值与实际值之间的差异,并分析差异出现的原因。

大直径偏心型文丘里施肥器优化设计与试验

为改善现有大直径文丘里施肥器的吸肥性能,对其进行结构优化设计.基于大直径对称型文丘里施肥器(M型),对其改造设计为偏心型文丘里施肥器(P型).采用正交设计方法,应用数值模拟技术,以吸肥效率为评价指标确定P型文丘里施肥器最优结构参数组合,并对2种施肥器进行试验测试和数值模拟对比分析.结果表明最优结构参数组合为喉管进口直径17 mm、扩散角3°、喉管出口直径20 mm、喉管凹槽宽度4 mm、喉管直线段长度16.6 mm、喉管凹槽直径27 mm、收缩角23.5°.通过试验测试对比分析,经结构优化后的P型施肥器较M型施肥器的最大吸肥流量提高了21.4%;在进口压力为0.25 MPa时,最大吸肥浓度提升了约30.7%,最大吸肥效率提升了约13.9%.流场分析表明,相较于M型施肥器,在相同的压差条件下,P型施肥器更不容易产生空化,并且P型文丘里施肥器流态更加稳定,能量损失更小.可见优化后的偏心型文丘里施肥器能提高吸肥性能.

基于正交试验的硅基MEMS齿形后坐保险机构参数敏感性

为了对硅基MEMS后坐保险机构进行优化设计和性能研究,基于正交试验与有限元仿真软件相结合的方法,选择齿高、齿宽、弹簧线宽、闭锁梁宽、锁钩间距、初始距离这6个设计参数,对后坐保险机构在正常发射和勤务跌落载荷下的位移和应力的影响进行参数敏感性分析。通过极差分析与方差分析,定量地给出了后坐保险机构各参数对结构在不同冲击载荷下的影响。结果表明,齿高的影响最显著,是影响后坐保险机构位移与应力响应的最主要因素;初始距离、弹簧线宽、齿宽是影响勤务跌落最大位移的次要因素;其他因素均对正常发射与勤务跌落载荷下位移和应力不显示显著性。在相对少的试验次数中定量得出不同设计参数对硅基后坐保险机构的影响大小,对多参数双目标的硅基后坐保险机构优化提供了一定的参考。

结构参数对电连接器接触性能的影响及优化

接触电阻是直接反映电连接器接触性能的主要因素之一。为研究片簧式电连接器的公母端子过盈量、簧片片宽、簧片悬臂梁长度、簧片厚度四种结构参数对接触电阻的影响,基于赫兹接触理论建立电连接器接触电阻的理论计算模型,并利用ABAQUS对接触电阻进行仿真分析,设计了正交试验对某款电连接器四种结构参数进行优化,并得到了四种结构参数对接触电阻影响的显著性水平。试验结果表明:片簧式电连接器四种结构参数中簧片悬臂梁长度、簧片厚度对其影响更为显著;且公母端子过盈量和簧片片宽与接触电阻呈线性变化、簧片悬臂梁长度和簧片厚度与接触电阻呈抛物线变化;电连接器结构参数优化后接触电阻减小了7.52%。

油浸式变压器绕组瞬态温升降阶快速计算方法

油浸式电力变压器绕组温升监测是保证其安全稳定运行的重要手段。为了改善采用有限元方法计算油浸式电力变压器绕组瞬态温升时存在效率不高的问题,提出一种结构保留的本征正交分解(SPOD)与离散经验插值方法(DEIM)相结合的计算策略。首先,该文采用最小二乘有限元法(LSFEM)与迎风有限元法(UFEM)构建变压器绕组瞬态温升计算控制方程;其次,针对控制方程的特点,引入SPOD方法,通过将采样时间内的计算结果构成快照矩阵,建立降阶模型,降低有限元刚度矩阵的计算阶数,提高求解有限元方程的效率;然后,为了改善本征正交分解方法对于非线性问题效率提升不高的缺陷,结合DEIM算法,对有限元方程中的非线性项进行插值处理,从而减少每一时步形成总体刚度矩阵的时间,进一步提高总体计算效率。为了验证文章所提算法的精确性及高效性,根据油浸式电力变压器绕组的基本特点,建立了单分区分匝绕组传热模型,对其瞬态传热过程进行计算,结果表明:基于SPOD-DEIM的有限元降阶计算能够在保证精度的前提下有效提高计算效率,与全阶计算结果相比,流场与温度场的计算误差均不超过1.5%,且计算效率提升5.1倍。同时,为了充分说明SPOD-DEIM算法在工程应用中的价值,该文基于110 kV变压器绕组搭建了温升实验平台,建立了八分区分匝绕组数值计算模型,对算法的精度、效率及工程应用价值进行了验证及讨论,计算及实验结果表明:精度方面,降阶计算较全阶计算的瞬态全过程计算误差小于2.5%,且与实验结果相比,误差不超过5.41K;效率方面,降阶计算的全过程计算时间为54.28 h,与全阶计算相比,计算效率提升至10.57倍,与商业仿真软件Fluent相比,效率提升至6.37倍,充分说明所提算法的高效性及工程应用价值,为大型电力设备快速仿真提供新思路。