Reduced Expanding Load Method for Simulation-Based Structural System Reliability Analysis

The current situation and difficulties of the structural system reliability analysis are mentioned. Then on the basis of Monte Carlo method and computer simulation, a new analysis method reduced expanding load method (RELM) is presented, which can be used to solve structural reliability problems effectively and conveniently. In this method, the uncertainties of loads, structural material properties and dimensions can be fully considered. If the statistic parameters of stochastic variables are known, by using this method, the probability of failure can be estimated rather accurately. In contrast with traditional approaches,RELM method gives a much better understanding of structural failure frequency and its reliability index β is more meaningful.To illustrate this new idea, a specific example is given.

Effects of Loading Methods on the Color,Phenolic and Antioxidant Properties of Cured Tobacco Leaves

[Objective] To investigate the effects of different loading methods on tobacco leaf quality.[Method] With tobacco comb,tobacco clamp,and tobacco basket,color,phenolic compounds and their antioxidant capacity of flue-cured tobacco leaves were studied.[Result] The results showed that L＊,a＊ and b＊ values of tobacco leaves packaged by tobacco clamp and comb were higher than those of tobacco basket and no significant differences were found beween values of a＊ and b＊,however,between L＊ and h values,remarkable differences existed among three loading methods.Total phenolic content and chlorogenic acid content of tobacco leaves loaded by tobacco comb kept the highest,followed by smoke clamp and tobacco basket （P＜0.05）.On the other hand,rutin content showed little differences among treatments.The order of the antioxidant properties,such as DPPH free radical scavenging activity and reducing powder,of tobacco leaves by different loading methods was tobacco comb ＞ tobacco clamp ＞ loose basket and a positive relationship was found of antioxiang property with total phenolic content and chlorogenic acid content.[Conclusion] In view of tobacco leaves quality and antioxidant property,loading method with tobacco comb proved to be a better choice.

Additional Vogt Coefficients and Improved Trial Load Method for Arch Dams

In recent years,the perceivable difference in observed and computed deflections for arch dams suggests the necessity to consider the side-load action of the hydrostatic pressure on reservoir basin(HPRB).In this paper,two additional Vogt coefficients with regard to the normal and angular deflections of arch dam foundation due to the action of HPRB are firstly elaborated,then an algorithm of the improved trial load method(ITLM)taking into account of conventional(six)and additional(two)Vogt coefficients is implemented.The elastic finite element method is employed as the bench mark in the verification of the improved method,which confirms that a better prediction of dam deflections and their gradient related stresses for arch dams may be provided by the ITLM taking into account of HPRB action.

A Precision-Positioning Method for a High-Acceleration Low-Load Mechanism Based on Optimal Spatial and Temporal Distribution of Inertial Energy

High-speed and precision positioning are fundamental requirements for high-acceleration low-load mechanisms in integrated circuit （IC） packaging equipment. In this paper, we derive the transient nonlinear dynamicresponse equations of high-acceleration mechanisms, which reveal that stiffness, frequency, damping, and driving frequency are the primary factors. Therefore, we propose a new structural optimization and velocity-planning method for the precision positioning of a high-acceleration mechanism based on optimal spatial and temporal distribution of inertial energy. For structural optimization, we first reviewed the commonly flexible multibody dynamic optimization using equivalent static loads method （ESLM）, and then we selected the modified ESLM for optimal spatial distribution of inertial energy; hence, not only the stiffness but also the inertia and frequency of the real modal shapes are considered. For velocity planning, we developed a new velocity-planning method based on nonlinear dynamic-response optimization with varying motion conditions. Our method was verified on a high-acceleration die bonder. The amplitude of residual vibration could be decreased by more than 20% via structural optimization and the positioning time could be reduced by more than 40% via asymmetric variable velocity planning. This method provides an effective theoretical support for the precision positioning of high-acceleration low-load mechanisms.

Load Reduction Test Method of Similarity Theory and BP Neural Networks of Large Cranes

Static load tests are an important means of supervising and detecting a crane＇s lift capacity. Due to space restrictions, however, there are difficulties and potential danger when testing large bridge cranes. To solve the loading problems of large-tonnage cranes during testing, an equivalency test is proposed based on the similarity theory and BP neural networks. The maximum stress and displacement of a large bridge crane is tested in small loads, combined with the training neural network of a similar structure crane through stress and displacement data which is collected by a physics simulation progressively loaded to a static load test load within the material scope of work. The maximum stress and displacement of a crane under a static load test load can be predicted through the relationship of stress, displacement, and load. By measuring the stress and displacement of small tonnage weights, the stress and displacement of large loads can be predicted, such as the maximum load capacity, which is 1.25 times the rated capacity. Experimental study shows that the load reduction test method can reflect the lift capacity of large bridge cranes. The load shedding predictive analysis for Sanxia 1200 t bridge crane test data indicates that when the load is 1.25 times the rated lifting capacity, the predicted displacement and actual displacement error is zero. The method solves the problem that lifting capacities are difficult to obtain and testing accidents are easily possible when 1.25 times related weight loads are tested for large tonnage cranes.

Force Control Compensation Method with Variable Load Stiffness and Damping of the Hydraulic Drive Unit Force Control System

Each joint of hydraulic drive quadruped robot is driven by the hydraulic drive unit（HDU）, and the contacting between the robot foot end and the ground is complex and variable, which increases the difficulty of force control inevitably. In the recent years, although many scholars researched some control methods such as disturbance rejection control, parameter self-adaptive control, impedance control and so on, to improve the force control performance of HDU, the robustness of the force control still needs improving. Therefore, how to simulate the complex and variable load characteristics of the environment structure and how to ensure HDU having excellent force control performance with the complex and variable load characteristics are key issues to be solved in this paper. The force control system mathematic model of HDU is established by the mechanism modeling method, and the theoretical models of a novel force control compensation method and a load characteristics simulation method under different environment structures are derived, considering the dynamic characteristics of the load stiffness and the load damping under different environment structures. Then, simulation effects of the variable load stiffness and load damping under the step and sinusoidal load force are analyzed experimentally on the HDU force control performance test platform, which provides the foundation for the force control compensation experiment research. In addition, the optimized PID control parameters are designed to make the HDU have better force control performance with suitable load stiffness and load damping, under which the force control compensation method is introduced, and the robustness of the force control system with several constant load characteristics and the variable load characteristics respectively are comparatively analyzed by experiment. The research results indicate that if the load characteristics are known, the force control compensation method presented in this paper has positive compensation effects on the load characteristics variation, i.e., this method decreases the effects of the load characteristics variation on the force control performance and enhances the force control system robustness with the constant PID parameters, thereby, the online PID parameters tuning control method which is complex needs not be adopted. All the above research provides theoretical and experimental foundation for the force control method of the quadruped robot joints with high robustness.

Slope stability analysis under seismic load by vector sum analysis method

The vibration characteristics and dynamic responses of rock and soil under seismic load can be estimated with dynamic finite element method （DFEM）. Combining with the DFEM, the vector sum analysis method （VSAM） is employed in seismic stability analysis of a slope in this paper. Different from other conventional methods, the VSAM is proposed based on the vector characteristic of force and current stress state of the slope. The dynamic stress state of the slope at any moment under seismic load can he obtained by the DFEM, thus the factor of safety of the slope at any moment during earthquake can be easily obtained with the VSAM in consideration of the DFEM. Then, the global stability of the slope can be estimated on the basis of time-history curve of factor of safety and reliability theory. The VSAM is applied to a homogeneous slope under seismic load. The factor of safety of the slope is 1.30 under gravity only and the dynamic factor of safety under seismic load is 1.21. The calculating results show that the dynamic characteristics and stability state of the slope with input ground motion can be actually analyzed. It is believed that the VSAM is a feasible and practical approach to estimate the dynamic stability of slopes under seismic load.

Grouping response method for equivalent static wind loads based on a modified LRC method

Wind loading is one of the most important loads for controlling the design of large-span roof structures. Equivalent static wind loads, which can generally aim at determining a specific response, are widely used by structural designers. A method for equivalent static wind loads applicable to multi-responses is proposed in this paper. A modified load- response-correlation （LRC） method corresponding to a particular peak response is presented, and the similarity algorithm implemented for the group response is described. The main idea of the algorithm is that two responses can be put into one group if the value of one response is close to that of the other response, when the structure is subjected to equivalent static wind loads aiming at the other response. Based on the modified LRC, the grouping response method is put forward to construct equivalent static wind loading. This technique can simultaneously reproduce peak responses for some grouped responses. To verify its computational accuracy, the method is applied to an actual large-span roof structure. Calculation results show that when the similarity of responses in the same group is high, equivalent static wind loads with high accuracy and reasonable magnitude of equivalent static wind distribution can be achieved.

High-precision solution to the moving load problem using an improved spectral element method

In this paper, the spectral element method(SEM)is improved to solve the moving load problem. In this method, a structure with uniform geometry and material properties is considered as a spectral element, which means that the element number and the degree of freedom can be reduced significantly. Based on the variational method and the Laplace transform theory, the spectral stiffness matrix and the equivalent nodal force of the beam-column element are established. The static Green function is employed to deduce the improved function. The proposed method is applied to two typical engineering practices—the one-span bridge and the horizontal jib of the tower crane. The results have revealed the following. First, the new method can yield extremely high-precision results of the dynamic deflection, the bending moment and the shear force in the moving load problem.In most cases, the relative errors are smaller than 1%. Second, by comparing with the finite element method, one can obtain the highly accurate results using the improved SEM with smaller element numbers. Moreover, the method can be widely used for statically determinate as well as statically indeterminate structures. Third, the dynamic deflection of the twin-lift jib decreases with the increase in the moving load speed, whereas the curvature of the deflection increases.Finally, the dynamic deflection, the bending moment and the shear force of the jib will all increase as the magnitude of the moving load increases.

A Review of the Calculation Methods of Lifting Capacity in Wind Loads on Ocean Platforms

Wind load is a control load that affects the safety of structures in the design of ocean platforms. It has not only direct and powerful effects that may cause structure resonance but also has indirect effects causing waves or currents in the ocean. By analyzing the domestic and international norms, this study presents a review of calculation methods of wind load on ocean platforms, which belongs to large-scale non-entity structure used in the open sea while surrounding wind has no fixed direction. Current computations according to the norms are not accurate, which even not takes the force of the wind against the surface perpendicular to the structure into consideration. Additionally, this study also introduces and compares the lift model of platforms based on different theories, such as vortex-excitation and vibration, engineering structure dynamics, gas flow pressure theory, analyzing their applicability, advantages, and disadvantages. This paper analyzes the limitations and applicable conditions of the existing calculation method itself, such as the lift model is suitable for the existence of stable vortex wake;the calculation method of the structural dynamics of marine engineering must be combined with the wind tunnel test and consider the mistakes caused by the position relationship;the numerical simulation method is accurate but tedious. This study provides an insight into the calculation methods of lift in designing ocean platforms, including the finite element method for simulating fluid force and updating formulas in Chinese norms.

Test Method for Refractoriness Under Load of Refractory Products(Non-differential,with Rising Temperature)

This standard specifies the definitions, theory, apparatus, specimens, procedures, test results and disposal, test error and report of test method for refractoriness under load of refractory products （non-differential, with rising temperature）.

Improved Data Processing of Loading Spectrum for Applications of Rainflow Counting Method

The rainflow counting method is a reasonable cyclecounting procedure for fatigue life calculation and simulation testing of structures.It defines cycles as closed stress /strain hysteresis loops.Application of the rainflow counting method requires a data processing of the loading spectrum,which consists of the elimination of non-peak value data points,load time histories adjustment and loop extraction.In the data processing of the loading spectrum,if a stress point is neither the peak nor the valley,it will be identified and eliminated from the loading spectrum.Generally,the loading process is idealized as a single peak-valley straight line.But in actually,there are polylines or nearly straight lines between peaks and valleys which can't be ignored.Therefore,in the process of eliminating such data points,it will produce error in method itself.To reduce the error produced by the traditional method itself,a new method which can well simplify the polylines in data processing of loading spectrum is proposed in this paper.Comparing with the original approximation method,the proposed method has higher precision.

Finding the buckling load of non-uniform columns using the iteration perturbation method

The aim of this study is to calculate the critical load of variable inertia columns. The example studied in this paper can be used as a paradigm for other non-uniform columns. The wavelength of equivalent vibratory system is used to calculate the critical load of the trigonometrically varied inertia column. In doing so, the equilibrium equation of the column is theoretically studied using the perturbation method. Accuracy of the calculated results is evaluated by comparing the solution with numerical results. Effect of improving the initial guess on the solution accuracy is investigated. Effects of varying parameters of the trigonometrically varied inertia and the uniformly tapered columns on their stability behavior are studied. Finally, using the so-called ＂perfectibility＂ parameter, two design goals, i.e., being lightweight and being strong, are studied for the discussed columns.

ELASTIC MODULUS REDUCTION METHOD FOR LIMIT LOAD EVALUATION OF FRAME STRUCTURES

A new strategy for elastic modulus adjustment is proposed based on the element bearing ratio （EBR）,and the elastic modulus reduction method （EMRM） is proposed for limit load evaluation of frame structures. The EBR is defined employing the generalized yield criterion,and the reference EBR is determined by introducing the extrema and the degree of uniformity of EBR in the structure. The elastic modulus in the element with an EBR greater than the reference one is reduced based on the linear elastic finite element analysis and the equilibrium of strain energy. The lower-bound of limit-loads of frame structures are analyzed and the numerical example demonstrates the flexibility,accuracy and effciency of the proposed method.

微种植体支抗加力方式对上颌前突患者关闭拔牙间隙后颌面部软、硬组织影响的研究

目的:探讨微种植体支抗加力方式对上颌前突患者关闭拔牙间隙后颌面部软、硬组织的影响。方法:选取2020年4月-2023年6月在上海交通大学医学院附属第九人民医院口腔外科、口腔颅颌面科收治的156例上颌前突患者作为研究对象。所有患者均需拔除上颌双侧第一前磨牙并使用微种植体支抗内收上前牙,采用随机数字表法将患者分入A组(予以短牵引钩和直接支抗法,n=52例)、B组(予以长牵引钩和直接支抗法,n=52例)和C组(予以短牵引钩和间接支抗法,n=52例)关闭拔牙间隙。比较三组治疗前后颌面部软硬组织变化。结果:关闭间隙前,三组患者颅颌软组织、硬组织指标比较差异无统计学意义(P>0.05),但B组鼻根点与上、下齿槽座点三者连线的夹角(ANB)大于A组、C组(P<0.05)。关闭间隙后,三组患者蝶鞍点与鼻根点,上齿槽座点三者连线的夹角(SNA)、蝶鞍点与鼻根点,下齿槽座点三者连线的夹角(SNB)、下颌平面角(SN-MP)、上中切牙内收量(U1-SN)、鼻唇角、牙冠舌向移动量(U1c-Sv)、覆盖、上颌第一磨牙近中颊尖点、近中根尖点压低量(U6c-H、U6r-H)变化值比较差异无统计学意义(P>0.05),ANB、颌平面角(SN-OP)、上颌第一磨牙内收量(U6-SN)、牙根舌向移动量(U1r-Sv)、上中切牙切缘点、牙根尖点压低量(U1c-H、U1r-H)、上颌第一磨牙近中颊尖点、近中根尖点与Sv距离(U6c-Sv、U6r-Sv)、上颌第一磨牙近中颊尖点、近中根尖点压低量(U6c-H、U6r-H)、覆(牙合)变化值比较差异有统计学意义(P<0.05);且B组ANB、Ls-E线变化值大于C组(P<0.05),A组SN-OP、U6-SN、U1c-Sv变化值大于C组(P<0.05);B组U1r-Sv、U1c-H变化值大于A组、C组,且C组大于A组(P<0.05);B组U1r-H变化值大于A组、C组,且A组大于C组(P<0.05);C组U6c-Sv变化值大于B组(P<0.05);A组U6c-H、U6r-H变化值大于B组(P<0.05);B组覆(牙合)变化值大于A组、C组(P<0.05)。结论:三种不同的微种植体支抗加力方式用于上颌前突患者均具有较好的支抗效果,可改善上颌硬组织的形态,并引起相应软组织的改变。其中,短牵引钩配合直接支抗法能明显压低磨牙、使冠远中倾斜,且(牙合)平面顺时针旋转;长牵引钩配合直接支抗法可获得更好的前牙控根移动和压低效果,且对上前牙垂直向改变效果也较好,有益于覆(牙合)控制,与短牵引钩配合间接支抗法均可获得较好的滑动内收力,稳定(牙合)平面。

光催化技术在纺织领域的研究及应用进展

太阳能光催化技术因环保、低成本的特点备受研究者青睐,将光催化技术应用于纺织领域的研究已取得一定的成果。半导体光催化剂在光辐照下吸收光子能量并激发出具有强氧化还原能力的活性自由基,以此分解有机污染物。综述光催化材料的常用载体以及其在纺织品上的负载方法,归纳其赋予纺织品的特殊功能。研究表明,光催化材料处理纺织印染废水具有很好的应用前景;经过光催化剂整理的织物可获得自清洁、抗菌以及防紫外线的功能,减少纺织品的洗涤次数,有效保护人体皮肤健康;将光催化剂负载于纤维或织物上有效提升其可回收利用性。

静水外压下纤维缠绕复合材料圆柱厚壳的稳定性研究

针对静水外压下纤维缠绕复合材料圆柱厚壳的临界屈曲载荷理论预报,本文基于Sander非线性壳体理论,结合圆柱壳变形几何方程以及纤维缠绕层的本构关系,推导出静水外压下纤维缠绕复合材料圆柱厚壳的屈曲控制方程;通过求解控制方程提出一种适用于静水外压下复合材料圆柱厚壳临界屈曲压力预报的解析方法;基于有限元模型对不同缠绕形式和缠绕角下的壳体临界屈曲压力进行对比计算,验证解析方法的准确性;基于解析方法,研究复合材料圆柱厚壳关键几何参数及材料设计对临界屈曲压力的影响。

参数耦合下风力发电机叶片机械颤振检测研究

受气候、风速等因素影响,会使风力发电机叶片的运行条件发生较大变化,增加了颤振检测的难度。为此,该文提出参数耦合下风力发电机叶片机械颤振检测方法。建立风力发电机叶片结构模型,推导结构动力学方程,并利用优化后的参数耦合算法对其求解,获取非稳态气动载荷,通过动力学模型反馈得到叶片的结构响应和振动情况;构建非稳态气动降阶模型,采用能量法分析叶片的结构响应与气动载荷的时域或频域,计算能量交换角度,确定叶片的颤振程度,实现颤振检测。实验结果表明,该方法气动阻尼系数计算结果准确、检测正确率高、计算时间短。

舰载飞机着舰撞击载荷实测技术研究

针对国内飞机起落架载荷测量中普遍存在的静标动测问题,从理论和机理上分析了静标定的应变法实测动态载荷存在问题的原因。同时,考虑到舰载飞机因定点着舰方式遭受严重的动态载荷,重点研究了舰载飞机着舰撞击载荷的静标动测问题。通过动态落震试验模拟飞机着舰过程,根据测力平台的实测载荷分析,获取了应变法实测载荷精度受动态影响的程度,提出一种改进的惯性修正方法,即:通过落震试验数据辨识质量矩阵,通过辨识的质量矩阵和实测加速度修正应变法的实测载荷。试验结果表明,改进的惯性修正方法进一步提高了垂向载荷的测量精度,显著提高了航向和侧向载荷的实测精度。

考虑节点刚度随机性的焊接钢筋部品变形计算方法研究

为量化钢筋部品刚度,从受力机理角度出发,基于试验和理论分析,提出考虑刚度随机性的焊接钢筋部品变形计算方法。从受力机理的角度提出三向转动刚度独立力学求解模型,考虑钢筋直径的影响,设计了105组T形焊接钢筋试件及两类加载固定试验装置,开展分级加载试验;在此基础上,考虑焊接节点转动刚度随机性,提出基于蒙特卡洛随机抽样的焊接钢筋部品变形计算方法,并分别开展了6个焊接钢筋网片和6个钢筋块体试验进行验证。结果表明:钢筋焊接节点刚度与钢筋直径有关,当焊接条件相同时,钢筋直径越大,焊接节点刚度越大;同一钢筋直径组合的焊接节点转动刚度基本符合正态分布,3个方向的转动刚度R x>R z>R y;钢筋焊接节点刚度与焊接节点断面面积基本呈线性关系;竖筋和横筋连接节点刚度对钢筋部品变形影响显著,所采用的节点刚度取值方法计算的焊接钢筋部品变形偏差均在10%以内,与传统刚接和铰接方法相比,变形计算精度大幅提高,变形计算方法合理。