To improve the vibration isolation performance of suspensions,various new structural forms of suspensions have been proposed.However,there is uncertainty in these new structure suspensions,so the deterministic researc...To improve the vibration isolation performance of suspensions,various new structural forms of suspensions have been proposed.However,there is uncertainty in these new structure suspensions,so the deterministic research cannot refect the performance of the suspension under actual operating conditions.In this paper,a quasi-zero stifness isolator is used in automotive suspensions to form a new suspension−quasi-zero stifness air suspension(QZSAS).Due to the strong nonlinearity and structural complexity of quasi-zero stifness suspensions,changes in structural parameters may cause dramatic changes in suspension performance,so it is of practical importance to study the efect of structural parameter uncertainty on the suspension performance.In order to solve this problem,three suspension structural parameters d_(0),L_(0) and Pc_(0) are selected as random variables,and the polynomial chaos expansion(PCE)theory is used to solve the suspension performance parameters.The sensitivity of the performance parameters to diferent structural parameters was discussed and analyzed in the frequency domain.Furthermore,a multi-objective optimization of the structural parameters d_(0),L_(0) and Pc_(0) of QZSAS was performed with the mean and variance of the root-mean-square(RMS)acceleration values as the optimization objectives.The optimization results show that there is an improvement of about 8%−1_(0)%in the mean value and about 4_(0)%−55%in the standard deviation of acceleration(RMS)values.This paper verifes the feasibility of the PCE method for solving the uncertainty problem of complex nonlinear systems,which provide a reference for the future structural design and optimization of such suspension systems.展开更多
In order to solve the problem of weak stifness of the existing fully decoupled parallel mechanism, a new synthesis method of fully decoupled three translational (3T) parallel mechanisms (PMs) with closed-loop units an...In order to solve the problem of weak stifness of the existing fully decoupled parallel mechanism, a new synthesis method of fully decoupled three translational (3T) parallel mechanisms (PMs) with closed-loop units and high stifness is proposed based on screw theory. Firstly, a new criterion for the full decoupled of PMs is presented that the reciprocal product of the transmission wrench screw matrix and the output twist screw matrix of PMs is a diagonal matrix, and all elements on the main diagonal are nonzero constants. The forms of the transmission wrench screws are determined by the criterion. Secondly, the forms of the actuated and unactuated screws can be obtained according to their relationships with the transmission wrench screws. The basic decoupled limbs are generated by combination of the above actuated and unactuated screws. Finally, a closed-loop units construction method is investigated to apply the decoupled mechanisms in a better way on the high stifness occasion. The closed-loop units are constructed in the basic decoupled limbs to generate a high-stifness fully decoupled 3T PM. Kinematic and stifness analyses show that the Jacobian matrix is a diagonal matrix, and the stifness is obviously higher than that of the coupling mechanisms, which verifes the correctness of the proposed synthesis method. The mechanism synthesized by this method has a good application prospect in vehicle durability test platform.展开更多
Owing to the relatively low stiffness of the slide and the considerable deformation under support force,the fluid–structure interaction(FSI)phenomenon in aerostatic slides is generally pronounced.This phenomenon affe...Owing to the relatively low stiffness of the slide and the considerable deformation under support force,the fluid–structure interaction(FSI)phenomenon in aerostatic slides is generally pronounced.This phenomenon affects the performance of static pressure slides,particularly those with high load-carrying capacity and low stiffness.However,most existing methods for analyzing the efect of FSI on the stiffness of static pressure slides are iterative and computationally expensive.To address this issue,a novel direct method is proposed for evaluating the stiffness of static pressure slides while considering FSI.This method can quickly and precisely obtain numerical solutions.Furthermore,the accuracy of the proposed method is validated through experiments.Based on the developed FSI model,the efects of normal force and flm thickness on the normal stiffness of aerostatic slides are also investigated.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.51875256)Open Platform Fund of Hunan Institute of Technology of China(Grant No.KFA20009)Hong Kong,Macao and Taiwan Science and Technology Cooperation Project in Jiangsu Province of China(Grant No.BZ2020050)。
文摘To improve the vibration isolation performance of suspensions,various new structural forms of suspensions have been proposed.However,there is uncertainty in these new structure suspensions,so the deterministic research cannot refect the performance of the suspension under actual operating conditions.In this paper,a quasi-zero stifness isolator is used in automotive suspensions to form a new suspension−quasi-zero stifness air suspension(QZSAS).Due to the strong nonlinearity and structural complexity of quasi-zero stifness suspensions,changes in structural parameters may cause dramatic changes in suspension performance,so it is of practical importance to study the efect of structural parameter uncertainty on the suspension performance.In order to solve this problem,three suspension structural parameters d_(0),L_(0) and Pc_(0) are selected as random variables,and the polynomial chaos expansion(PCE)theory is used to solve the suspension performance parameters.The sensitivity of the performance parameters to diferent structural parameters was discussed and analyzed in the frequency domain.Furthermore,a multi-objective optimization of the structural parameters d_(0),L_(0) and Pc_(0) of QZSAS was performed with the mean and variance of the root-mean-square(RMS)acceleration values as the optimization objectives.The optimization results show that there is an improvement of about 8%−1_(0)%in the mean value and about 4_(0)%−55%in the standard deviation of acceleration(RMS)values.This paper verifes the feasibility of the PCE method for solving the uncertainty problem of complex nonlinear systems,which provide a reference for the future structural design and optimization of such suspension systems.
基金Supported by National Natural Science Foundation of China(Grant No.52275032)Key Project of Hebei Provincial Natural Science Foundation of China(Grant No.E2022203077)Hebei Provincial Key Research and Development Plan of China(Grant No.202230808010057).
文摘In order to solve the problem of weak stifness of the existing fully decoupled parallel mechanism, a new synthesis method of fully decoupled three translational (3T) parallel mechanisms (PMs) with closed-loop units and high stifness is proposed based on screw theory. Firstly, a new criterion for the full decoupled of PMs is presented that the reciprocal product of the transmission wrench screw matrix and the output twist screw matrix of PMs is a diagonal matrix, and all elements on the main diagonal are nonzero constants. The forms of the transmission wrench screws are determined by the criterion. Secondly, the forms of the actuated and unactuated screws can be obtained according to their relationships with the transmission wrench screws. The basic decoupled limbs are generated by combination of the above actuated and unactuated screws. Finally, a closed-loop units construction method is investigated to apply the decoupled mechanisms in a better way on the high stifness occasion. The closed-loop units are constructed in the basic decoupled limbs to generate a high-stifness fully decoupled 3T PM. Kinematic and stifness analyses show that the Jacobian matrix is a diagonal matrix, and the stifness is obviously higher than that of the coupling mechanisms, which verifes the correctness of the proposed synthesis method. The mechanism synthesized by this method has a good application prospect in vehicle durability test platform.
基金The National Key Research and Development Program of China(2022YFB3402705)The National Natural Science Foundation of China(52105439).
文摘Owing to the relatively low stiffness of the slide and the considerable deformation under support force,the fluid–structure interaction(FSI)phenomenon in aerostatic slides is generally pronounced.This phenomenon affects the performance of static pressure slides,particularly those with high load-carrying capacity and low stiffness.However,most existing methods for analyzing the efect of FSI on the stiffness of static pressure slides are iterative and computationally expensive.To address this issue,a novel direct method is proposed for evaluating the stiffness of static pressure slides while considering FSI.This method can quickly and precisely obtain numerical solutions.Furthermore,the accuracy of the proposed method is validated through experiments.Based on the developed FSI model,the efects of normal force and flm thickness on the normal stiffness of aerostatic slides are also investigated.
文摘目的观察亚临床甲状腺功能减退症(亚临床甲减)患者血浆同型半胱氨酸(Hcy)水平及臂踝脉搏波速度(ba PWV)的变化,探讨亚临床甲减与动脉硬化的关系。方法 2013年1月-2014年6月连续入选73例未经过治疗的亚临床甲减患者,根据促甲状腺激素(TSH)水平分为A、B组,A组35例(4 m U/L<TSH<10 m U/L),B组38例(TSH≥10 m U/L)。同时选取30例健康志愿者作为对照组。所有入选者均接受Hcy及ba PWV检测。结果与对照组比较,A组TSH、Hcy、ba PWV,B组TSH、三酰甘油(TG)、低密度脂蛋白胆固醇(LDL-C)、Hcy、ba PWV均显著升高,差异有统计学意义(P<0.05);与A组比较,B组TSH、TG、LDL-C、Hcy、ba PWV均明显升高,差异有统计学意义(P<0.05)。Pearson相关分析显示,Hcy与促甲状腺激素水平呈正相关(r=0.353,P<0.01);ba PWV与促甲状腺激素水平呈正相关(r=0.416,P<0.01)。结论亚临床甲减患者血浆Hcy明显升高,外周动脉僵硬度增加,二者与TSH水平呈正相关。
