Numerical Study of the Vibrations of Beams with Variable Stiffness under Impulsive or Harmonic Loading

The behavior of beams with variable stiffness subjected to the action of variable loadings (impulse or harmonic) is analyzed in this paper using the successive approximation method. This successive approximation method is a technique for numerical integration of partial differential equations involving both the space and time, with well-known initial conditions on time and boundary conditions on the space. This technique, although having been applied to beams with constant stiffness, is new for the case of beams with variable stiffness, and it aims to use a quadratic parabola (in time) to approximate the solutions of the differential equations of dynamics. The spatial part is studied using the successive approximation method of the partial differential equations obtained, in order to transform them into a system of time-dependent ordinary differential equations. Thus, the integration algorithm using this technique is established and applied to examples of beams with variable stiffness, under variable loading, and with the different cases of supports chosen in the literature. We have thus calculated the cases of beams with constant or variable rigidity with articulated or embedded supports, subjected to the action of an instantaneous impulse and harmonic loads distributed over its entire length. In order to justify the robustness of the successive approximation method considered in this work, an example of an articulated beam with constant stiffness subjected to a distributed harmonic load was calculated analytically, and the results obtained compared to those found numerically for various steps (spatial h and temporal τ ¯ ) of calculus, and the difference between the values obtained by the two methods was small. For example for ( h=1/8 , τ ¯ =1/ 64 ), the difference between these values is 17%.

Variable damping forces caused by electromagnetic energy harvesting with an adjustable load

A novel variable damper using an adjustable energy harvesting structure is proposed for semi-active vibration systems. The fluid flowing in a hydraulic cylinder is employed to drive an electromagnetic generator for harvesting vibration energy, which on the other hand, leads to a damping effect of the hydraulic damper. To make the damping force variable, an adjustable resistor is adopted to tune the capability of energy harvesting. The present approach is validated by both theoretical analysis and experimental evaluation. When connected with different resistance loads, the prototype damper has different equivalent damping coefficients ranging from 3. 987 × 104 to 2. 488 × 105 N· s/m. The results show that the damping force of the damper is variable in response to the adjustable load for the vibration energy harvesting.

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.

Novel Models and Algorithms of Load Balancing for Variable-structured Collaborative Simulation under HLA/RTI

High level architecture(HLA) is the open standard in the collaborative simulation field. Scholars have been paying close attention to theoretical research on and engineering applications of collaborative simulation based on HLA/RTI, which extends HLA in various aspects like functionality and efficiency. However, related study on the load balancing problem of HLA collaborative simulation is insufficient. Without load balancing, collaborative simulation under HLA/RTI may encounter performance reduction or even fatal errors. In this paper, load balancing is further divided into static problems and dynamic problems. A multi-objective model is established and the randomness of model parameters is taken into consideration for static load balancing, which makes the model more credible. The Monte Carlo based optimization algorithm(MCOA) is excogitated to gain static load balance. For dynamic load balancing, a new type of dynamic load balancing problem is put forward with regards to the variable-structured collaborative simulation under HLA/RTI. In order to minimize the influence against the running collaborative simulation, the ordinal optimization based algorithm(OOA) is devised to shorten the optimization time. Furthermore, the two algorithms are adopted in simulation experiments of different scenarios, which demonstrate their effectiveness and efficiency. An engineering experiment about collaborative simulation under HLA/RTI of high speed electricity multiple units(EMU) is also conducted to indentify credibility of the proposed models and supportive utility of MCOA and OOA to practical engineering systems. The proposed research ensures compatibility of traditional HLA, enhances the ability for assigning simulation loads onto computing units both statically and dynamically, improves the performance of collaborative simulation system and makes full use of the hardware resources.

SIMPLE SHAKEDOWN OF STRUCTURES UNDER VARIABLE MULTI-LOADINGS

The shakedown analysis of structures under variable multi-loadings is considered, and the corresponding simple shakedown condition is presented in this paper. Distribution of fixed stresses field is given, and the self-equilibrium of fixed stresses field is analyzed. Elastic shakedown and plastic shakedown conditions are presented based on the fixed stresses field. The theorem is convenient to evaluate the shakedown limit of structures under cyclical variable multiloadings through solving positive scalar fields and fixed stresses field factors at a series of dangerous positions of the structure, and tedious computations are avoided. Finally the theorem is applied to a thick-walled cylindrical tube under variable pressure and temperature, and the rolling contact problem. The results are in good agreement with some computational results.

NONLINEAR STABILITY OF TRUNCATED SHALLOW SPHERICALSHELL WITH VARIABLE THICKNESS UNDERUNIFORMLY DISTRIBUTED LOAD

In this paper, to begin with. the nonlinear differential equations of a truncaled shallow spherical shell with variable thickness under uniformal distributed load are linearized by step-by-step loading method. The linear differential equations can be solved by spline collocanon method. Critical loads have been obtained accordingly.

Reliability of Life Calculation Laws for Materials under Variable Amplitude Loading

For many years, researchers have been looking for a reliable law that will take into account the type of loading, the mechanical characteristics of the material, the geometric configuration in the determination of the service life of mechanical parts. The service life of structures at risk (automotive, aeronautics, among others.) in service, subjected to variable solicitations in time, are random for a same type of loading. This article proposes to highlight the influence of this variation in service life on the reliability of structures by a probabilistic approach. The characteristics of the proposed law are satisfactory compared to the classical laws because it takes into account the parameters of the classical laws (Weibull law) and the dispersions of the lifetimes of a same material.

Evaluation of a Pulse Width Modulated Bypass Nozzle for the Development of a Variable Load Residential Oil Burner

Due to the need for energy conservation in buildings and the simultaneous benefit of cost savings, the development of a low firing rate load modulating residential oil burner is very desirable. One of the two main requirements of such a burner is the development of a burner nozzle that is able to maintain the particle size distribution of the fuel spray in the desirable (small) size range for efficient and stable combustion. The other being the ability to vary the air flow rate and air distribution around the fuel nozzle in the burner for optimal combustion at the current fuel firing rate. In this paper, which deals with the first requirement, we show that by using pulse width modulation in the bypass channel of a commercial off-the-shelf bypass nozzle, this objective can be met. Here we present results of spray patterns and particle size distribution for a range of fuel firing rates. The results show that a desirable fuel spray pattern can be maintained over a fuel firing rate turndown ratio (Maximum Fuel Flow Rate/Minimum Fuel Flow Rate) of 3.7. Thus here we successfully demonstrate the ability to electronically vary the fuel firing rate by more than a factor of 3 while simultaneously maintaining good atomization.

LARGE DEFLECTION PROBLEM OF CIRCULAR PLATES WITH VARIABLE THICKNESS UNDER THE ACTION OF COMBINED LOADS

By using the modified iteration method of large deflection theory of plates with variable thichness[1], we solve the problem of circular plates with variable thickness subjected to combined loads under the boundary conditions of the clamped edges and get comparatively more accurate second-order approximate analytical solution. If the results of this paper are degraded into the special cases, the results coinciding with those of papers [1,2] can be obtained. In this paper, the characteristic curves are plotted and some comparisons are made. The results of this paper are satisfactory.

Research on Energy Saving Technology of Load Sensitive Variable Steering System for Vehicles

In view of the large energy loss problem in the traditional full hydraulic steering system,a scheme of replacing the ordinary pump with the priority valve with the load sensitive variable pump is proposed to make the variable pump provide the corresponding flow rate according to the needs of the steering system to achieve the purpose of energy saving.Through the establishment of the system AMESim simulation model,the data comparison shows that the energy loss of the load sensitive variable steering system is significantly reduced relative to the traditional full hydraulic steering system.

Determination of Dynamic Load Condition of Aircraft Carrier based on Multivariable Distribution of Flight Parameters

In order to solve the design problem of dynamic load of a carrier-based aircraft,according to the relevant criteria of national military standards,eight key flight parameters of the dynamic load conditions for the aircraft carrier were selected.Based on the multivariable distribution data of landing flight parameters obtained from flight test,the distribution form and range limitation of each flight parameter were determined by using the probability distribution of each flight parameter and the spatial relationship among variables.Furthermore,100000 sets of data were constructed to simulate the landing condition of aircraft in the form of random number.After the envelope is screened by multivariable joint probability distribution,the boundary conditions were compared and merged,and finally the dynamic load conditions were obtained.In this paper,a set of dynamic load condition design method based on the aircraft requirements is constructed,which systematically covers all kinds of situations that occur in the process of aircraft landing,and improves the conventional design process of aircraft dynamic load.

THE APPROXIMATE ANALYTICAL SOLUTION FOR THE BUCKLING LOADS OF A THIN-WALLED BOX COLUMN WITH VARIABLE CROSS-SECTION

For a thin-walled box column with variable cross-section, the three governing equations for torsional-flexural buckling are ordinary differential equations of the second or fourth order with variable coefficients, so it is very difficult to solve them by means of an analytic method. In this paper, polynomials are used to approximate the geometric properties of cross-section and certain coefficients of the differential equations. Based on the energy principle and the Galerkin's method, the approximate formulas for calculating the flexural and torsional buckling loads of this kind of columns are developed respectively, and numerical examples are used to verify the correctness of the solutions obtained. The results calculated in this paper provide the basis for demonstrating the stability of thin-walled box columns with variable cross-section. This paper is of practical value.

FATIGUE RELIABILITY DESIGN AND ESTIMATION METHOD FOR VARIABLE LOADING

A method is presented for estimating fatigue reliability under variable loading, which isbased on load cycles-fatigue life interference theory as well as cumulative fatigue damageanalysis. The basic opinion is that for variable loading the increment of failure probability pro-duced by each load cycle is determined by the stress level as well as the damage state at whichthis load cycle applies Contrast to 'conditional reliability-equivalent life methodology'. this meth-od calculates the equivalent cycle numbers between different stress levels according to cumulativefatigue damage rule but not equivalent failure probability.

Numerical simulation of fatigue crack propagation in heterogeneous geomaterials under varied loads using displacement discontinuity method

Heterogeneous brittle geomaterials are highly susceptible to cyclic loads.They contain inherent flaws and cracks that grow under fatigue loads and lead to failure.This study presents a numerical model for analyzing fatigue in these materials based on the two-dimensional(2D)boundary element method and linear elastic fracture mechanics.The process is formulated by coupling the displacement discontinuity method with the incorporation technique of dissimilar regions and the governing equations of fatigue.The heterogeneous media are assumed to consist of materials with different properties,and the interfaces are assumed to be completely bonded.In addition,the domains include multiple cracks exposed to constant and variable amplitude cyclic loads.The stress intensity factor is a crucial parameter in fatigue analysis,which is determined using the displacement field around crack tips.An incremental crack growth scheme is applied to calculating the fatigue life.The growth rate values are employed to estimate the length of crack extension when there are multiple cracks.The interaction between cracks is considered,which also includes the coalescence phenomenon.Finally,various structures under different cyclic loads are examined to evaluate the accuracy of this method.The results demonstrate the efficiency of the proposed approach in modeling fatigue crack growth and life estimation.The behavior of life curves for the heterogeneous domain was as expected.These curves illustrate the breakpoints caused by utilizing discrete incremental life equations.At these points,the trend of the curves changed with the material properties and fatigue characteristics of the new material around the crack tips.

Preoperative carbohydrate load to reduce perioperative glycemic variability and improve surgical outcomes:A scoping review

The detrimental effects of both diabetes mellitus(DM)and hyperglycemia in the perioperative period are well established and have driven extensive efforts to control blood glucose concentration(BGC)in a variety of clinical settings.It is now appreciated that acute BGC spikes,hypoglycemia,and high glycemic variability(GV)lead to more endothelial dysfunction and oxidative stress than uncomplicated,chronically elevated BGC.In the perioperative setting,fasting is the primary approach to reducing the risk for pulmonary aspiration;however,prolonged fasting drives the body into a catabolic state and therefore may increase GV.Elevated GV in the perioperative period is associated with an increased risk for postoperative complications,including morbidity and mortality.These challenges pose a conundrum for the management of patients typically instructed to fast for at least 8 h before surgery.Preliminary evidence suggests that the administration of an oral preoperative carbohydrate load(PCL)to stimulate endogenous insulin production and reduce GV in the perioperative period may attenuate BGC spikes and ultimately decrease postoperative morbidity,without significantly increasing the risk of pulmonary aspiration.The aim of this scoping review is to summarize the available evidence on the impact of PCL on perioperative GV and surgical outcomes,with an emphasis on evidence pertaining to patients with DM.The clinical relevance of GV will be summarized,the relationship between GV and postoperative course will be explored,and the impact of PCL on GV and surgical outcomes will be presented.A total of 13 articles,presented in three sections,were chosen for inclusion.This scoping review concludes that the benefits of a PCL outweigh the risks in most patients,even in those with well controlled type 2 DM.The administration of a PCL might effectively minimize metabolic derangements such as GV and ultimately result in reduced postoperative morbidity and mortality,but this remains to be proven.Future efforts to standardize the content and timing of a PCL are needed.Ultimately,a rigorous data-driven consensus opinion regarding PCL administration that identifies optimal carbohydrate content,volume,and timing of ingestion should be established.

Simulation and Experimental Design of Load Adaptive Braking System on Two Wheeler

The braking quality is considered the main execution of the adaptive control framework that impacts the vehicle safety and rides solace astoundingly notably the stopping distance.This research work aims to create a pattern and design of an electromechanically adjusted lever that multiplies the applied braking force depending on the inputs given by the sensors to reduce the stopping distance of the vehicle.It is carried out using two main parts of the two-wheeler vehicle:thefirst part deals with the detection of load acting on the vehicle and identifying the required braking force to be applied,and the second part deals with the micro-controller which activates the stepper motor for varying the mechanical leverage ratio from various loads on the vehicle using two actively movable wedges.The electromechanically operated variable braking force system is developed to actuate the braking system based on the load on the motorcycle.The MATLAB simulation and experimental work are carried out for various loading(driver and pillion)conditions on a two-wheeler.The results indicate that the proposed electronically operated braking system is more effective than the conventional braking system for various loads and vehicle speeds.Specifically,the stopping distance of the vehicle is decreased significantly by about 4.9%between the con-ventional braking system and the simulated proposed system.Further,the experi-mental results show that the stopping distance is condensed by about 4.1%.The validation between simulated and experimental results revealed a great deal with the least error percentage of about 0.8%.

基于等效裂纹法的铝合金T形焊接接头疲劳寿命评估

针对焊接缺陷的多样性、复杂性及随机分散性等特征,提出一种以一组高应力疲劳试验结果作为参考点的等效裂纹法开展焊接结构的疲劳寿命研究。以疲劳试验结果作为参考,假设一个完整板中的初始裂纹等效焊接结构中的缺陷及应力集中效应,基于线弹性断裂力学和Paris公式计算等效裂纹扩展寿命作为焊接结构的疲劳失效寿命。提出基于等效裂纹法的结构疲劳寿命计算流程;开展铝合金T形焊接接头的疲劳试验以及拟合P-S-N曲线;基于T形焊接接头的焊根失效模式采用等效裂纹方法预测T形接头的计算P-S-N曲线,并与试验拟合曲线进行对比,相对误差为10%,验证了该方法的可行性与有效性;最后,通过一组变幅载荷谱疲劳试验与预测P-S-N曲线对比,相对误差均小于15%,同时也验证了该方法对于变幅载荷的适用性,实现了基于一组疲劳试验结果预测全范围T形焊接接头疲劳寿命的评估。以较少的测试和成本实现确定的疲劳寿命,简化了概率疲劳寿命的评估过程,该方法可以推广于其他焊接接头寿命评估中。

特种车辆传动主轴运行载荷实时评估方法研究

为提升履带装甲车辆综合传动装置疲劳损伤的快速计算能力及其剩余寿命的准确评估性能,提出一种满足多工况条件的传动主轴运行载荷实时评估模型.提取特种车辆典型运行工况的特征参数,并采用K均值聚类及支持向量机方法实现特种车辆典型运行工况的实时判别;构建基于卷积-长短期记忆神经网络的多工况传动主轴运行载荷实时评估模型,采用贝叶斯算法对模型中学习率、神经网络隐含层单元数等超参数进行优化,以提高传动主轴运行载荷评估的准确性;依据特种车辆典型工况下的运行数据开展模型实例验证.结果表明,在换挡工况、转向工况及爬坡工况下,模型对传动主轴运行载荷评估结果的平均绝对百分比误差分别为0.150、0.014、0.006(5°坡工况)及0.004(10°坡工况),表明了本文模型在变工况条件下综合传动装置传动主轴运行载荷评估的有效性.

基于变论域云PI的含风电负荷频率控制方法

随着风电渗透率不断提高,其不确定性严重影响了电力系统频率稳定。基于此问题,建立了含风电的互联电力系统负荷频率控制模型,其中风机通过附加下垂与虚拟惯性控制参与频率调节。在此基础上,为解决风电接入系统引起的频率波动问题,提出变论域云PI负荷频率控制策略,对云模型输入和输出论域动态调整。为避免增加控制器的复杂程度,基于函数形式设计论域的伸缩因子。最后,仿真结果表明,所设计的控制器能进一步提高云PI控制器的自适应能力,更好地处理风电不确定性对系统频率的影响。