Studying solutions for the fatigue of the FAST cable-net structure caused by the process of changing shape

The Five-hundred-meter Aperture Spherical Radio Telescope （FAST） is supported by a cable-net structure, whose change in shape leads to a stress range of approximately 500 MPa. This stress range is more than twice the standard recom- mended value. The cable-net structure is thus the most critical and fragile part of the FAST reflector system. In this study, we first search for a more appropriate deforma- tion strategy that reduces the stress amplitude generated by the process of changing shape. Second, we roughly estimate the tracking trajectory of the telescope during its service life, and conduct an extensive numerical investigation to assess the require- ments for fatigue resistance. Finally, we develop a new type of steel cable system that satisfies the cable requirements for construction of FAST.

Effect of Fast Neutron Irradiation on Amylose Content and Amylopectin Structure of Thailand Rice Cultivar Jao Hom Nin

[Objective]The aim was to research the effect of fast neutron irradiation on amylose content and amylopectin structure.[Method] The amylose content and amylopectin structure of the M4 plants of Thailand rice cultivar Jao Hom Nin irradiated with fast neutron at 13 Gy were evaluated and analyzed in this paper.[Result]The results showed that amylose content of rice could be changed by fast neutron irradiation,many rice mutants with reduced amylose content and many others with enhanced amylose content even some mutants with amylose content near to waxy rice could be isolated,but fast neutron irradiation almost had no effect on amylopectin structure of the samples.[Conclusion]The study provided a basis for breeding rice cultivar with different amylose content in order to meet with the taste hobby of different people and the further processing of diverse rice products via the irradiation of fast neutron.

500m口径射电望远镜(FAST)索网结构风致破坏概率评估

大跨空间索网结构风敏感性突出,极易遭受风荷载影响。针对目前缺乏此类结构抗风性能评估方法的问题,以大跨空间索网结构FAST为例,提出一种基于实测风场数据的风致破坏概率分析方法。采集1971年~2020年结构所处地区的大量实测风速数据,通过概率分布拟合建立场地的风灾危险性模型。建立FAST的精细化有限元分析模型并模拟风荷载时程输入,采用非线性动力时程分析对结构的风振反应进行计算,基于概率性需求模型绘制易损性曲线。最后,结合得出的风灾危险性和结构易损性,计算得出FAST结构在所处场地实际风灾环境中的破坏概率。研究表明:该地极限风速为17m/s,风速在0~10m/s的概率最大;在120°、210°和300°风向角下,下拉索均为易损构件,210°风向角上吸风对索网结构最不利;在最不利风向角下,结构达到轻微破坏、中等破坏和严重破坏的总破坏概率分别为1.8359×10^(-4)、1.1499×10^(-5)和1.3202×10^(-6)。

Chemical interaction motivated structure design of layered metal carbonate hydroxide/MXene composites for fast and durable lithium ion storage

Rational architecture design has turned out to be an effective strategy in improving the electrochemical performance of electrode materials for batteries.However,an elaborate structure that could simultaneously endow active materials with promoted reaction reversibility,accelerated kinetic and restricted volume change still remains a huge challenge.Herein,a novel chemical interaction motivated structure design strategy has been proposed,and a chemically bonded Co(CO_(3))_(0.5)OH·0.11 H_(2)O@MXene(CoCH@MXene)layered-composite was fabricated for the first time.In such a composite,the chemical interaction between Co^(2+)and MXene drives the growth of smaller-sized CoCH crystals and the subsequent formation of interwoven CoCH wires sandwiched in-between MXene nanosheets.This unique layered structure not only encourages charge transfer for faster reaction dynamics,but buffers the volume change of CoCH during lithiation-delithiation process,owing to the confined crystal growth between conductive MXene layers with the help of chemical bonding.Besides,the sandwiched interwoven CoCH wires also prevent the stacking of MXene layers,further conducive to the electrochemical performance of the composite.As a result,the as-prepared CoCH@MXene anode demonstrates a high reversible capacity(903.1 mAh g^(-1)at 100 mA g^(-1))and excellent cycling stability(maintains 733.6 mAh g^(-1)at1000 mA g^(-1)after 500 cycles)for lithium ion batteries.This work highlights a novel concept of layerby-layer chemical interaction motivated architecture design for futuristic high performance electrode materials in energy storage systems.

The effect of hydrothermal pretreatment on the structure and fast pyrolysis behaviors of Sheng Li lignite

The structure and composition of coal determine its fast pyrolysis characteristics,and the study of the relationship between them can play an important role in the efficient and clean utilization of coal.So,in this work,hydrothermal pretreatment was used to artificially change the structure and composition of Sheng Li(SL)lignite,which was used to investigate the influence of structural changes on pyrolysis.The physicochemical structure and composition of samples were characterized by X-ray diffraction,specific surface area and porosity analyzer,solid-state 13C nuclear magnetic resonance,Fourier transform infrared spectroscopy,and elemental analyzer.Pyrolysis experiments were carried out in a powderparticle fluidized bed reactor,and the distribution and composition of the pyrolysis products were analyzed.The gasification activity of char was investigated by thermogravimetric analysis with a CO_(2) atmosphere.The results show that hydrothermal pretreatment(HTP)can destroy the cross-linking structure of SL lignite,and affect its aromaticity,pore structure,functional group,and carbon structure to change the distribution and composition of pyrolysis products of SL lignite,especially the composition of tar.Finally,the structure–activity relationship between the structure,composition,and pyrolysis characteristics of coal was comprehensively studied.

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 Low-Memory-Requiring and Fast Approach to Cluster Large-Scale Decoy Protein Structures

This work demonstrates the so-called PCAC (Protein principal Component Analysis Clustering) method, which clusters large-scale decoy protein structures in protein structure prediction based on principal component analysis (PCA), is an ultra-fast and low-memory-requiring clustering method. It can be two orders of magnitude faster than the commonlyused pairwise rmsd-clustering (pRMSD) when enormous of decoys are involved. Instead of N(N – 1)/2 least-square fitting of rmsd calculations and N2 memory units to store the pairwise rmsd values in pRMSD, PCAC only requires N rmsd calculations and N × P memory storage, where N is the number of structures to be clustered and P is the number of preserved eigenvectors. Furthermore, PCAC based on the covariance Cartesian matrix generates essentially the identical result as that from the reference rmsd-clustering (rRMSD). From a test of 41 protein decoy sets, when the eigenvectors that contribute a total of 90% eigenvalues are preserved, PCAC method reproduces the results of near-native selections from rRMSD.

Fast SSED-MoM /FEM Analysis for Electromagnetic Scattering of Large-Scale Periodic Dielectric Structures

A hybrid method combining simplified sub-entire domain basis function method of moment with finite element method( SSED-MoM /FEM) is accelerated for electromagnetic( EM) scattering analysis of large-scale periodic structures.The unknowns are reduced sharply with non-uniform mesh in FEM. The computational complexity of the hybrid method is dramatically declined by applying conjugate gradient-fast Fourier transform( CG-FFT) to the integral equations of both electric field and magnetic field. The efficiency is further improved by using OpenMP technique. Numerical results demonstrate that the SSED-MoM /FEM method can be accelerated for more than three thousand times with large-scale periodic structures.

Extraction of mode shapes of beam-like structures from the dynamic response of a moving mass

This paper proposes an approach to extract the mode shapes of beam-like structures from the dynamic response of a moving mass. When a mass passes through a beam containing several artificially installed humps, its vertical acceleration can be recorded. After applying fast Fourier transformation to the dynamic response, one can extract the mode shapes of the beam. The surface roughness was neglected compared to the humps and its adverse effect on the extraction was reduced. The passing mass performs as both “exciter” and “massage receiver”;therefore, this method requires only one single accelerometer, making it more convenient and time saving in practice. Moreover, to estimate the possible error in extracting mode shapes, a wavenumber domain filtering technique is used to reconstruct the general profiles of mode shapes. Experimental validation of this approach in laboratory scale was conducted. The experimental results show that the proposed method performs well in extracting lower order mode shapes. It should also be noted that the passing mass can not have a very high velocity (e.g. 80 mm/s), otherwise the mass may jump and separate from the beam, and the proposed method may fail to identify mode shapes.

Towards extreme fast charging of 4.6 V LiCoO_(2) via mitigating high-voltage kinetic hindrance

High-voltage LiCoO_(2)(LCO) is an attractive cathode for ultra-high energy density lithium-ion batteries(LIBs) in the 3 C markets.However,the sluggish lithium-ion diffusion at high voltage significantly hampers its rate capability.Herein,combining experiments with density functional theory(DFT) calculations,we demonstrate that the kinetic limitations can be mitigated by a facial Mg^(2+)+Gd^(3+)co-doping method.The as-prepared LCO shows significantly enhanced Li-ion diffusion mobility at high voltage,making more homogenous Li-ion de/intercalation at a high-rate charge/discharge process.The homogeneity enables the structural stability of LCO at a high-rate current density,inhibiting stress accumulation and irreversible phase transition.When used in combination with a Li metal anode,the doped LCO shows an extreme fast charging(XFC) capability,with a superior high capacity of 193.1 mAh g^(-1)even at the current density of 20 C and high-rate capacity retention of 91.3% after 100 cycles at 5 C.This work provides a new insight to prepare XFC high-voltage LCO cathode materials.

MATRIX ALGEBRA ALGORITHM OF STRUCTURE RANDOM RESPONSE NUMERICAL CHARACTERISTICS

A new algorithm of structure random response numerical characteristics, namedas matrix algebra algorithm of structure analysis is presented. Using the algorithm, structurerandom response numerical characteristics can easily be got by directly solving linear matrixequations rather than structure motion differential equations. Moreover, in order to solve thecorresponding linear matrix equations, the numerical integration fast algorithm is presented. Thenaccording to the results, dynamic design and life-span estimation can be done. Besides, the newalgorithm can solve non-proportion damp structure response.

ANALYSIS OF OPEN MICROSTRIP STRUCTURES BY USING DIAKOPTIC METHOD OF LINES COMBINED WITH PERIODIC BOUNDARY CONDITIONS

This paper presents the analysis of open microstrip structures by using diakoptic method of lines (ML) combined with periodic boundary conditions (PBC). The parameters of microstrip patch are obtained from patch current excited by plane wave. Impedance matrix elements are computed by using fast Fourier transform(FFT), and reduced equation is solved by using diakoptic technique. Consequently, the computing time is reduced significantly. The convergence property of simulating open structure by using PBC and the comparison of the computer time between using PBC and usual absorbing boundary condition (ABC) show the validity of the method proposed in this paper. Finally, the resonant frequency of a microstrip patch is computed. The numerical results obtained are in good agreement with those published.

THE EFFECTS OF PLASMA-INDUCED GRAFT COPOLYMERIZATION WITH ACRYLIC ACID ON THE STRUCTURE AND DYEING PROPERTIES OF MULBERRY SILK

The effects of plasma-induced graft copolymerization with acrylic acid (AAc) on the structure and dyeing properties of mulberry silk are investigated. Through the transmission infrared spectroscopy(IR) , attenuated total reflection infrared spectroscopy(ATR-IR) and X-ray photoelectron spectroscopy(XPS) studies, changes of the surface structure and composition are observed. The results show that plasma-induced graft copolymerization has a different meehanism from that of chemical graft copolymerization. The plasma graft copolymerization brings AAc branch polymers into the surface of silk through the initiation of some kinds of oxygen and nitrogen groups created by plasma. That is just the reason that the dyeing ability and color fastness of plasma-grafted silk for cationic dyestuff increase and its mechanical properties have not been changed significantly.

A SEMI-ANALYTICAL AND SEMI-NUMERICAL METHOD FOR SOLVING 2-D SOUND-STRUCTURE INTERACTION PROBLEMS

Based on the transfer matrix method and the virtual source simulation technique, this paper proposes a novel semi-analytical and semi-numerical method for solving 2-D sound- structure interaction problems under a harmonic excitation.Within any integration segment, as long as its length is small enough,along the circumferential curvilinear coordinate,the non- homogeneous matrix differential equation of an elastic ring of complex geometrical shape can be rewritten in terms of the homogeneous one by the method of extended homogeneous capacity proposed in this paper.For the exterior fluid domain,the multi-circular virtual source simulation technique is adopted.The source density distributed on each virtual circular curve may be ex- panded as the Fourier's series.Combining with the inverse fast Fourier transformation,a higher accuracy and efficiency method for solving 2-D exterior Helmholtz's problems is presented in this paper.In the aspect of solution to the coupling equations,the state vectors of elastic ring induced by the given harmonic excitation and generalized forces of coefficients of the Fourier series can be obtained respectively by using a high precision integration scheme combined with the method of extended homogeneous capacity put forward in this paper.According to the superposition princi- ple and compatibility conditions at the interface between the elastic ring and fluid,the algebraic equation of system can be directly constructed by using the least square approximation.Examples of acoustic radiation from two typical fluid-loaded elastic rings under a harmonic concentrated force are presented.Numerical results show that the method proposed is more efficient than the mixed FE-BE method in common use.

A Receiver Structure for Frequency-Flat Time-Varying Rayleigh Channels and Performance Analysis

This paper proposes a wavelet based receiver structure for frequency-flat time-varying Rayleigh channels, consisting of a receiver front-end followed by a Maximum A-Posteriori (MAP) detector. Discretization of the received continuous time signal using filter banks is an essential stage in the front-end part, where the Fast Haar Transform (FHT) is used to reduce complexity. Analysis of our receiver over slow-fading channels shows that it is optimal for certain modulation schemes. By comparison with literature, it is shown that over such channels our receiver can achieve optimal performance for Time-Orthogonal modulation. Computed and Monte-Carlo simulated performance results over fast time-varying Rayleigh fading channels show that with Minimum Shift Keying (MSK), our receiver using four basis functions (filters) lowers the error floor by more than one order of magnitude with respect to other techniques of comparable complexity. Orthogonal Frequency Shift Keying (FSK) can achieve the same performance as Time-Orthogonal modulation for the slow-fading case, but suffers some degradation over fast-fading channels where it exhibits an error floor. Compared to MSK, however, Orthogonal FSK provides better performance.

“三改联动”下高中压内缸适应灵活运行改造探讨

为实现“双碳”目标和构建新型电力系统,高中压内缸如何适应灵活性运行成为现役煤电高中压合缸机组“三改联动”时重点关注内容之一。文章通过对高中压内缸结构要素组合、典型结构方案、结合电厂实际运行情况和相应结构有限元分析,得出高中压进汽部分分开的内缸结构作为适应灵活性运行优选结构,并对现役机组高中压内缸改造方案进行探讨。

FAST反射面支承结构整体索网方案研究

采用整体索网作为大射电望远镜(FAST)反射面的支承结构,通过对四边形、凯威特型和短程线型三种整体索网方案的研究、对比,认为短程线型网格是一种合理的较优方案;分别对提出的刚性、半刚性和柔性三种子结构方案进行分析研究,论证该刚性方案的可行性,初步论证半刚性方案的可行性,同时对柔性方案提出改进建议。

深层煤层气水平井安全钻井技术

针对吐哈盆地深层煤层气的勘探,前期以直井试采为主,水平井的钻井技术仍处于探索阶段。由于该区块属于高陡斜坡区、煤系地层发育,导致直井段井斜易超标、煤系地层的井眼井壁易失稳、水平井井段的轨迹难以控制及固井质量差等问题,文章通过分析高陡斜坡区提速限制因素,引入自动垂钻系统,形成直井段防斜打快技术,解决了高陡斜坡区防斜和大钻压快速钻进的矛盾;分析煤层井壁失稳机理,开展浸泡实验,优选了胺基有机盐钻井液体系,提高抑制性和封堵固结井壁性能,强化了煤系地层井壁稳定;结合深层煤层三压力剖面预测数据优化井身结构及轨迹控制,设计防卡PDC钻头和钻具组合,配套强抑制、强封堵性胺基有机盐钻井液,实现了煤层水平段安全延伸;强化钻井参数,应用岩屑清洁工具和个性化通井钻具组合,提高了井眼清洁效率;优化套管选型、扶正器配置及水泥浆体系,保障了固井质量。该系列技术为实现吐哈盆地深层煤层气水平井安全高效钻探奠定了基础。

国家天文台500m口径球面射电望远镜(FAST)钢结构工程施工技术

介绍了国家天文台500m口径球面射电望远镜(FAST)钢结构的结构特点、钢结构安装施工方案、施工的关键技术和设备,特别是对圈梁结构的安装技术作了详细阐述。其倒扣式曲线轨道滑移系统解决了高空无法满铺轨道的技术难题,多功能平板车的运用同时解决了高空运输、高空滑移和高空吊装的难题,获得了良好的经济效益。现场施工结果表明:钢结构的施工方案和各项技术是合理可行的。

FAST背架结构选型及优化

背架结构是巨型射电望远镜(FAST)反射面支承系统中的一个重要组成部分,其性能直接影响整个系统的精度和造价.为了给FAST反射面结构的实际选型提供理论依据,首先针对FAST特殊功能要求,提出了背架结构保形设计方法,然后对所提出的空间网格结构、弦支结构、混合结构等多种背架结构进行了优化,从结构力学性能、加工制作工艺等多方面对其进行比较,结果表明局部双层网格结构具有自重轻、刚度好及加工制作简单的优点.