A time integration method for analysis of dynamic systems using domain decomposition technique

This paper presents a precise and stable time integration method for dynamic analysis of vibration or multibody systems A total system is divided into several subsystems and then responses are calculated separately, while the coupling effect is treated equivalently as constant force during time steps By using iterative procedure to improve equivalent coupling forces, a precise and stable solution is obtained Some examples such as a seismic response and multibody analyses were carried out to demonstrate its usefulness

     

汽轮发电机组叶片—轴耦合系统动力响应问题研究

为了深入研究汽轮发电机组叶片弯振和轴扭振在外界扰动下的耦合振动响应问题 ,提出了阻抗匹配法。该法可以用来分析具有任意多个叶片数目的叶片—轴耦合系统动力响应问题 ,可以计算耦合系统稳态或瞬态响应。研究结果表明叶片弯曲振动和轴扭转振动之间具有很强的耦合性。耦合系统中叶片弯振固有频率降低而轴扭转固有频率增大 ,在外界扰动作用下两者会同时被激发出来 ,叶片根部所承受的力和力矩在短时间内有可能会达到一个比较大的峰值 ,从而影响到叶片的安全稳定运行     

阶跃载荷下气体轴承-转子系统瞬态特性流固耦合分析

以气体轴承-转子系统为研究对象,基于流固耦合法,对系统在铣削过程中受到阶跃载荷瞬间转子位移动态响应、气膜流场压力变化等瞬态特性进行研究。研究结果表明：在流固耦合作用下,转子最终达到稳定平衡状态,在不同阶跃载荷下,转子均出现偏心倾斜,转子末端及刀头处出现振荡过程;阶跃载荷越大,系统超调量、上升时间、转子偏斜位移越大,而超调时间变小;与稳态阶跃载荷相比,矩形阶跃载荷下系统因预载荷导致超调量减小,稳定时间缩短;矩形阶跃载荷超调时刻的压力变化较小且高压区域波动平稳,有利于提高转子瞬态响应特性。     

Improvement of dynamic response in an impact absorber by frictional elements

A novel device that uses friction between one or more pairs of elastic conical rings to dissipate the energy from an impacting body is presented. The device consists of one moving and one stationary cylinders coupled to each other using two pairs of conical rings and a spring. The spring is used to restore the system to its original configuration after the impact. The dynamic response of the system to the impact forces during impact events is analysed numerically and experimentally. The effects of several governing parameters, such as the mass ratio between the cylinders, the duration of the transient response of the device, the magnitude of the rest zone of the moving element and the peak impact force are investigated. The proposed system is applicable in sequential impact scenarios, in which remarkable improvements were observed over traditional solid-rod impact absorbers. The present study may serve as a guide for the design of improved damping devices for impact applications.     

Development of Calculation Software for Automotive Side Swing Door Closing Energy

The existing research of the automotive side swing door closing energy is mainly conducted by measuring the closing energy and the closing angle via tests and simulations.In these tests,the door closing velocity and initial door closing angle are usually not taken into consideration,so the accuracy of the test data cannot be ensured,and,meanwhile,simulations require a great deal of manpower and time.Moreover,frequent tests would give rise to the increasing research and development costs.In this paper,in response to the deficiencies of these current methods,the complicated door closing process is decomposed into the closing processes of different subsystems of door,which includes weather strip seal,air-binding effect,door weight,hinge,check-link and latch.Mathematical models of those subsystems are established according to their working principles during the door closing process.In addition to the theoretical research,an Excel-based software using Visual Basic Application programming language is developed to realize the mathematical models,which aims to calculate the energy consumption of the subsystems.The energy consumption of different subsystems of a production vehicle door is measured to verify the accuracy of the calculation software developed.The proposed research provides not only the theoretical basis for the future door closing energy research,but also an interactive method and system,effectively improving the quality and efficiency of vehicle door design.     

Boiling heat transfer-based temperature rise characteristics of automotive permanent magnet synchronous motors at peak operating conditions

Using two-phase flow boiling heat transfer theory, the RPI subcooling boiling heat transfer model was established to study the temperature rise characteristics of the permanent magnet synchronous motor (PMSM) of electric vehicles under peak operating conditions, and the effects of coolant inlet temperature, altitude and inlet flow rate on the motor temperature rise were analyzed. The results showed that: the temperature rise characteristics of the motor are closer to the test results when boiling heat transfer is considered after the motor is warmed up, so the effect of boiling heat transfer of the cooling system should be considered when studying the temperature rise characteristics of the motor; The temperature rise characteristic of the motor increases with the increase of coolant inlet temperature at peak working condition. The short time required for the motor winding to reach 150 °C indicates that the motor temperature rises quickly. In the plateau environment, the temperature growth rate of the motor at peak working conditions increases with the increase of cooling water inlet temperature, while the motor temperature decreases with the decrease of atmospheric pressure. Thus, due to the boiling heat transfer phenomenon of cooling water two-phase flow, the temperature rise characteristic of the motor at high altitude is better than that in plain area.

     

Incompressible and Analytical Study on an Out-Pump Type Complex Thrust Gas Bearing

ABSTRACT

The structure of an out-pump type thrust gas bearing was described, and an analytical model was developed under completely incompressible condition. The objectives were to investigate the coupling between aerodynamics and aerostatics in a complex thrust gas bearing and to improve the performance of the bearing. The model showed that the load-carrying capacity had five parts to it and that apparently there were pressure coupling and structure coupling between aerodynamics and aerostatics. The surface feature function was identically positive: it increased the load-carrying capacity greatly. There was also no limit regarding the pressure ratio—when the pressure ratio was 0, the load-carrying capacity increased to about 25%.

     

黏性流体环境中压电宏纤维致动柔性结构的流固耦合振动特性及试验

柔性结构与周围流体的耦合作用机制广泛应用于仿生机器人、水下航行器、精密仪器及生命医疗等领域。具有驱动变形大、防水性好且柔韧性好的压电宏纤维（Macro fiber composite,MFC）致动器是水下柔性结构变形控制的首选。建立MFC内部致动弯矩和水动力载荷共同作用下柔性结构的流固耦合动力学模型。对粘贴MFC致动器的柔性结构特征截面进行计算流体动力学（Computational fluid dynamics,CFD）分析,得到不同振动特征频率下柔性结构周围流场、压力分布及所受水动力载荷,分别拟合得到MFC致动柔性结构水动力函数的实部和虚部表达式。结果表明柔性结构水动力载荷的附加质量和阻尼效应都随着振动频率的增加而减小。在等振动特征频率下,MFC致动梁结构水动力函数的实部大于匀质等截面梁的实部;在高振动频率下其水动力函数虚部同样大于匀质等截面梁。试验测试了MFC致动柔性结构的水下振动特性,试验所得MFC激励下柔性结构末端稳定振动的幅频特性和相频特性与建立的耦合动力模型相吻合,证实了所建立MFC致动柔性结构的水动力函数及流固耦合振动模型的有效性。     

Numerical and experimental investigation on electromechanical aileron actuation system with joint clearance

A closed-loop coupling model at the system-level is developed to analyze the effects of joint clearance on the dynamic responses of electromechanical aileron actuation system. The proposed model considers the coupling effects between the electromechanical actuator (EMA) control performance and dynamic characteristics of linkage mechanism with joint clearance. Besides, the experiments are conducted in a test rig, which verifies the effectiveness of the proposed closed-loop coupling model. The nonlinear contact force model and modified Coulomb friction model are adopted in the joint clearance of the linkage mechanism, and the influences of clearance size on the dynamic behaviors of electromechanical aileron actuation system are studied. The numerical and experimental results indicate that the novel closed-loop coupling model, considering the EMA control performance and dynamics of linkage mechanism with joint clearance at the same time, is an effective model to predict the dynamic characteristics of electromechanical aileron actuation with joint clearance, which provides a practical method to analyze the dynamic performance of electromechanical coupling multibody systems with joint clearance.

     

Collaborative simulation method with spatiotemporal synchronization process control

When designing a complex mechatronics system, such as high speed trains, it is relatively difficult to effectively simulate the entire system’s dynamic behaviors because it involves multi-disciplinary subsystems. Currently, a most practical approach for multi-disciplinary simulation is interface based coupling simulation method, but it faces a twofold challenge: spatial and time unsynchronizations among multi-directional coupling simulation of subsystems. A new collaborative simulation method with spatiotemporal synchronization process control is proposed for coupling simulating a given complex mechatronics system across multiple subsystems on different platforms. The method consists of 1) a coupler-based coupling mechanisms to define the interfacing and interaction mechanisms among subsystems, and 2) a simulation process control algorithm to realize the coupling simulation in a spatiotemporal synchronized manner. The test results from a case study show that the proposed method 1) can certainly be used to simulate the sub-systems interactions under different simulation conditions in an engineering system, and 2) effectively supports multi-directional coupling simulation among multi-disciplinary subsystems. This method has been successfully applied in China high speed train design and development processes, demonstrating that it can be applied in a wide range of engineering systems design and simulation with improved efficiency and effectiveness.     

Model Based Tuning of a Non Linear Spherical Tank Process with Time Delay

Abstract

A 40 liter spherical tank with varying time delay was subjected to open loop analysis using a step response technique with sodium chloride solution as tracer. The experimental data was adequately represented by a first order plus dead time (FOPDT) model with an error of less than five percent. These model parameters were used to generate Smith Predictor controller, IMC controller, and IMC PID controller using MATLAB. For closed loop control of the process based on rise time, settling time, overshoot, peaktime, decay ratio, and ISE, it was found that the IMCPID controller is better suited for this process.     

破拆机器人负载敏感系统多臂复合动作能量回收研究

 破拆机器人臂系负载敏感系统具有功率自适应节能降耗、结构紧凑等特点,应用十分广泛。然而负载敏感系统中负载敏感泵流量压力仅与系统最大负载相适应,导致多臂复合动作时小负载回路上压力补偿阀能量损失较大。为进一步降低能耗,利用液压马达回收小负载回路压力补偿阀的能量损失,并带动液压泵将回收能量储存在蓄能器中,蓄能器回收能量通过扭矩耦合的方式回馈至主泵实现能量回收。通过AMESim建模仿真结果表明,增加能量回收系统可使复合动作能量回收利用率提升20%以上,系统阶跃响应与未安装能量回收的系统响应基本一致,且速度振荡减小改善了瞬态响应。     

Design and performance of a pulse transformer based on Fe-based nanocrystalline core

A dry-type pulse transformer based on Fe-based nanocrystalline core with a load of 0.88 nF, output voltage of more than 65 kV, and winding ratio of 46 is designed and constructed. The dynamic characteristics of Fe-based nanocrystalline core under the impulse with the pulse width of several microseconds were studied. The pulse width and incremental flux density have an important effect on the pulse permeability, so the pulse permeability is measured under a certain pulse width and incremental flux density. The minimal volume of the toroidal pulse transformer core is determined by the coupling coefficient, the capacitors of the resonant charging circuit, incremental flux density, and pulse permeability. The factors of the charging time, ratio, and energy transmission efficiency in the resonant charging circuit based on magnetic core-type pulse transformer are analyzed. Experimental results of the pulse transformer are in good agreement with the theoretical calculation. When the primary capacitor is 3.17 μF and charge voltage is 1.8 kV, a voltage across the secondary capacitor of 0.88 nF with peak value of 68.5 kV, rise time (10%-90%) of 1.80 μs is obtained.     

Multilevel solution for thermal elastohydrodynamic lubrication of rolling/sliding circular contacts

A fast multigrid approach is presented for the analysis of thermal elastohydrodynamic lubrication (EHL) under rolling/sliding circular contacts at high loads and high slip ratios with low computing time on a personal computer. This fast solver combines directiteration, multigrid, Newton-Raphson, Gauss-Seidel iteration, and multilevel multi-integration methods into one working environment that can reduce the computational complexity from O(n³ to O(nlnn) for the thermal EHL problem under rolling/sliding circular contacts. Since the couped Reynolds and energy equations are simultaneously solved by the Newton-Raphson scheme, the iteration for the convergence solution is less than those of the classical approach. Results show that thermal effects on the pressure profile and film thickness are significant for a wide range of loads, speeds and slip ratios. The maximum midfilm and surface temperature rise in the Hertzian contact region increases with increasing slip ratio, dimensionless speed, and load. The minimum film thickness decreases with increasing load and slip ratio, and decreasing dimensionless speed.     

Multi-objective collaborative optimization using linear physical programming with dynamic weight

The multi-objective collaborative optimization problem with multi-objective subsystems has a bi-level optimization architecture, that consists of the system and subsystem levels. Combining the multi-objective optimization algorithm with a bi-level optimization structure can obtain a satisfactory solution. Given that the preference-based algorithm requires minimal running time, the Linear physical programming (LPP) method, one of the typical preference-based algorithms, is adopted. Considering that setting the preference values for the incompatibility function is difficult, the weighted incompatibility function is added to the piecewise linear function of the LPP model. An expression of dynamic weight is also presented according to the inconsistency among the subsystems, which is caused by the sharing and auxiliary variables relative to the different subsystems. Using an engineering example, this study reveals that the interdisciplinary consistency is satisfactory when the dynamic weight is used in the LPP model, which thereby demonstrates the effectiveness of the presented method.

     

Incompressible and Analytical Study on a Basic Model of a Complex Journal Gas Bearing

ABSTRACT

A basic analytical model of a hybrid journal gas bearing was set up completely for investigating the coupling between aerodynamics and aerostatics in a hybrid gas bearing under incompressible conditions, and for further improving its performance, under incompressible conditions. In this analytical model, the load-carrying capacity function is composed of five items. Apparently, there are pressure coupling and structure coupling between aerodynamics and aerostatics and when the groove distribution coefficient is 0.36, it is approximately maximum. However, this type of hybrid gas bearing structure can not be used when the pressure ratio is less than 1.

     

Efficiency characteristics of piezostack pump for linear actuators

A piezostack pump for linear actuators is presented and studied in terms of mechanical energy efficiency (MEE), energy conversion efficiency (ECE) and design method. MEE is defined as the ratio of the output mechanical energy to that converted from input electrical energy, and ECE is the ratio of output mechanical energy to input electrical energy. The analysis results show that both MEE and ECE decrease with the increase of stiffness of the chamber diaphragm (k _s), which is a function of the radius ratio (rigid disk radius to chamber radius). There is respective optimal external load (F _c) for them to achieve peak value for a given piezostack with blocked force (F _b) and stiffness (k _a). The optimal force ratio (F _c/F _b) is a constant of 0.5 for maximum MEE, and between 0.57 and 0.5 for maximum ECE. Considering the deflection of the pump chamber and dynamic response of the piezostack, the stiffness ratio (k _s/k _a) should be limited between 0.3 and 1, and the relative radius ratio is between 0.7 and 0.8. With the increase of the radius ratio in the range, the maximal MEE decreases from 0.38 to 0.25, and the peak ECE decreases from 0.20 to 0.14.     

COUPLING OF NON-LINEAR SUBSTRUCTURES USING VARIABLE MODAL PARAMETERS

This paper presents a general methodology for the coupling analysis of systems with relatively weak non-linearities by assuming that the response remains harmonic under harmonic excitation. Standard coupling methods and their current shortcomings were discussed first. Two ways of obtaining non-linear modal parameter variations, namely profile constructing and parameter extracting, were presented next. The profile constructing method uses the system's spatial data directly, while the parameter extracting method is based on a non-linear modal analysis of measured response data. Through numerical test cases, it was shown that both methods yielded virtually identical results. An iterative algorithm for the coupling of non-linear subsystems was presented in a form compatible with profile building. A six-degree-of-freedom system with cubic stiffness non-linearity was chosen for a detailed numerical study. Two subsystems, one linear and the other non-linear, were coupled to obtain the modal parameter variations of the coupled system. Using the non-linear modal parameters, the response of the coupled system was predicted at various force levels and the findings were checked via direct simulations using the harmonic balance method. Finally, the methodology was validated by coupling experimentally derived non-linear modal models of two substructures. As for the numerical study, the response of the coupled non-linear structure was predicted at various force levels and the findings were checked against direct measurements. Very good agreement was obtained in all cases studied.     

Experimental investigations on combustion characteristics of a swirl-stabilized premixed burner

Experimental investigations have been conducted to understand the combustion characteristics of a swirl-stabilized double-cone pre-mixed burner used for industrial gas turbines for power generation. NOx and CO emissions, extinction limit, combustion noise, pressure loss, and wall temperature distributions were measured for various operating conditions. Results show that NOx emissions are decreased with increasing air/fuel ratio or decreasing air load unless the air load is too small. CO emissions are also decreased with increasing air/fuel ratio, leading to a positive correlation between NOx and CO emissions. Flame extinction limit is reduced with increasing air flow rate as the flow residence time is reduced. Combustion noise has its peak amplitude at the frequencies of 150 or 300 Hz, which are considered to be the resonance frequencies of the longitudinal mode of the combustor. The noise level at the peak frequency is maximized when the flame is considered to be located near the burner exit. Pressure loss is decreased with the A/F ratio as the flame moves downstream out of the burner.