针对无叶风扇气动噪声过大的问题,开展基于CST(Class Function/Shape Function Transformation,CST)参数化方法的柯恩达面气动噪声敏感性分析。首先,以NACA0012翼型及样条曲线构造柯恩达面,建立无叶风扇的风圈截面及三维模型。然后,通...针对无叶风扇气动噪声过大的问题,开展基于CST(Class Function/Shape Function Transformation,CST)参数化方法的柯恩达面气动噪声敏感性分析。首先,以NACA0012翼型及样条曲线构造柯恩达面,建立无叶风扇的风圈截面及三维模型。然后,通过数值模拟分析柯恩达面处的流动情况及气动噪声,并通过试验验证数值计算的准确性。最后,建立柯恩达面参数化模型,并以气动噪声为目标响应,采用Sobol法与Kriging代理模型相结合的方法,计算参数化模型中Bernstein多项式系数的一阶灵敏度系数和总灵敏度系数,找出对气动噪声影响较大的参数。结果表明,影响柯恩达面处气动噪声的主要因素依次为风圈截面的厚度、前缘半径、后缘厚度。展开更多
Based on features of dimension variation propagation in multi-station assembly processes,a new quality evaluation model of assembly processes is established. Firstly,the error source of multi-station assembly system i...Based on features of dimension variation propagation in multi-station assembly processes,a new quality evaluation model of assembly processes is established. Firstly,the error source of multi-station assembly system is analyzed,the relationship of dimension variation propagation in multi-station assembly processes is studied and the state equation for variation propagation is constructed too. Then,the feature parameters which influence variation propagation and accumulation in multi-station assembly processes are found to evaluate quality characteristic of the assembly system. Through the derivation of equation on dimension variation propagation,station coefficient matrices which are combined and conversed to determine the max eigenvalue are educed. The max eigenvalue is multiplied by the weight coefficient to establish the quality evaluation model in multi-station assembly processes. Furthermore,assembly variation indexes are proposed to judge of the assembly technology process. Finally,through the practical example,the application of the model and assembly variation indexes are presented.展开更多
Head actuator arm assembly (HAA) is the most important mechanical component of a mobile hard disk drive (HDD) and its shock dynamic response is a principal index of vibration resistance. In this paper,a finite element...Head actuator arm assembly (HAA) is the most important mechanical component of a mobile hard disk drive (HDD) and its shock dynamic response is a principal index of vibration resistance. In this paper,a finite element (FE) model is firstly developed in ANSYS of 2.5 inch (1 inch=25.4 mm) mobile hard disk. This model includes actuator arm,voice coil motor (VCM) and pivot bearing. The various step modal of HAA is calculated by FE model. Then the actuator arm vibration behavior is simulated with LS-DYNA procedure. The influence of pulse waveform,pulse amplitude and pulse width on the shock response of the relative displacement of the head actuator arm assembly is studied.展开更多
Background The diagnosis of liver fibrosis is a difficult task at any time using conventional clinical imaging.Intravoxel incoherent motion （IVIM） can be used to investigate both diffusion and perfusion changes in t...Background The diagnosis of liver fibrosis is a difficult task at any time using conventional clinical imaging.Intravoxel incoherent motion （IVIM） can be used to investigate both diffusion and perfusion changes in tissues.This study was designed to determine the value of IVIM in the diagnosis and staging of liver fibrosis.Methods IVIM examinations were performed on a GE 3.0T MR scanner in 25 patients with liver fibrosis and 25 healthy volunteers as the control group.Patients with liver fibrosis diagnosis were confirmed by pathology and staged on a scale of F0-4.The standard ADC values and the values of a biexponential model （slow ADC （Dslow）,fast ADC （Dfast） and fraction of fast ADC （FF）） were measured in three liver regions per person.The mean standard ADC values,Dslow values,Dfast values and FF values from the study group were compared among the right posterior hepatic lobe,right anterior hepatic lobe and medial segment of the left lobe.Receiver Operating Characteristic （ROC） curves and independent-samples t-tests were used to calculate the mean standard ADC values,Dslow values,Dfast values and FF values from the study group and the control group.Spearman rho correlation analysis was used for the stage of liver fibrosis.The liver fibrosis stages between the groups F0-1 and F2-4,the groups F0-2 and F3-4 were compared.Results Among the liver fibrosis,there was no significant difference in the mean standard ADC values,Dslow values,Dfast values,and FF values obtained from the right posterior hepatic lobe,right anterior hepatic lobe and medial segment of the left lobe.Using ROC analysis,the Area Under the Curve （AUC） values of standard ADC,Dslow,Dfast,FF were all between 0.7 to 0.9.The mean standard ADC values,Dslow values,Dfast values and FF values of the liver in the study group were significantly lower than the values in the control group （P ＜0.05）.As the stage of the fibrosis increased,the values decreased by Spearman rho correlation analysis.The mean values （standard ADC,Dslow,Dfast,and FF） of liver fibrosis stages between the groups F0-1 and F2-4,the groups F0-2 and F3-4 showed significant differences （P＜0.05）.Conclusions IVIM can reflect the conditions of perfusion and diffusion in liver fibrosis and thus distinguish between normal liver and liver fibrosis.The IVIM technique may serve as a valuable tool for detecting and characterizing liver fibrosis,and monitoring its progression in a noninvasive manner.展开更多
文摘针对无叶风扇气动噪声过大的问题,开展基于CST(Class Function/Shape Function Transformation,CST)参数化方法的柯恩达面气动噪声敏感性分析。首先,以NACA0012翼型及样条曲线构造柯恩达面,建立无叶风扇的风圈截面及三维模型。然后,通过数值模拟分析柯恩达面处的流动情况及气动噪声,并通过试验验证数值计算的准确性。最后,建立柯恩达面参数化模型,并以气动噪声为目标响应,采用Sobol法与Kriging代理模型相结合的方法,计算参数化模型中Bernstein多项式系数的一阶灵敏度系数和总灵敏度系数,找出对气动噪声影响较大的参数。结果表明,影响柯恩达面处气动噪声的主要因素依次为风圈截面的厚度、前缘半径、后缘厚度。
基金supported by the National Natural Science Foundation of China ( Grant No.50575072)Scientific Research Fund of Hunan Provincial Education Department(Grant No.07C281)
文摘Based on features of dimension variation propagation in multi-station assembly processes,a new quality evaluation model of assembly processes is established. Firstly,the error source of multi-station assembly system is analyzed,the relationship of dimension variation propagation in multi-station assembly processes is studied and the state equation for variation propagation is constructed too. Then,the feature parameters which influence variation propagation and accumulation in multi-station assembly processes are found to evaluate quality characteristic of the assembly system. Through the derivation of equation on dimension variation propagation,station coefficient matrices which are combined and conversed to determine the max eigenvalue are educed. The max eigenvalue is multiplied by the weight coefficient to establish the quality evaluation model in multi-station assembly processes. Furthermore,assembly variation indexes are proposed to judge of the assembly technology process. Finally,through the practical example,the application of the model and assembly variation indexes are presented.
基金Natural Science Foundation of China (Grant No. 50575072)Scientific Research Fund of Hunan Provincial Education Department (Grant No.07C280)
文摘Head actuator arm assembly (HAA) is the most important mechanical component of a mobile hard disk drive (HDD) and its shock dynamic response is a principal index of vibration resistance. In this paper,a finite element (FE) model is firstly developed in ANSYS of 2.5 inch (1 inch=25.4 mm) mobile hard disk. This model includes actuator arm,voice coil motor (VCM) and pivot bearing. The various step modal of HAA is calculated by FE model. Then the actuator arm vibration behavior is simulated with LS-DYNA procedure. The influence of pulse waveform,pulse amplitude and pulse width on the shock response of the relative displacement of the head actuator arm assembly is studied.
文摘Background The diagnosis of liver fibrosis is a difficult task at any time using conventional clinical imaging.Intravoxel incoherent motion （IVIM） can be used to investigate both diffusion and perfusion changes in tissues.This study was designed to determine the value of IVIM in the diagnosis and staging of liver fibrosis.Methods IVIM examinations were performed on a GE 3.0T MR scanner in 25 patients with liver fibrosis and 25 healthy volunteers as the control group.Patients with liver fibrosis diagnosis were confirmed by pathology and staged on a scale of F0-4.The standard ADC values and the values of a biexponential model （slow ADC （Dslow）,fast ADC （Dfast） and fraction of fast ADC （FF）） were measured in three liver regions per person.The mean standard ADC values,Dslow values,Dfast values and FF values from the study group were compared among the right posterior hepatic lobe,right anterior hepatic lobe and medial segment of the left lobe.Receiver Operating Characteristic （ROC） curves and independent-samples t-tests were used to calculate the mean standard ADC values,Dslow values,Dfast values and FF values from the study group and the control group.Spearman rho correlation analysis was used for the stage of liver fibrosis.The liver fibrosis stages between the groups F0-1 and F2-4,the groups F0-2 and F3-4 were compared.Results Among the liver fibrosis,there was no significant difference in the mean standard ADC values,Dslow values,Dfast values,and FF values obtained from the right posterior hepatic lobe,right anterior hepatic lobe and medial segment of the left lobe.Using ROC analysis,the Area Under the Curve （AUC） values of standard ADC,Dslow,Dfast,FF were all between 0.7 to 0.9.The mean standard ADC values,Dslow values,Dfast values and FF values of the liver in the study group were significantly lower than the values in the control group （P ＜0.05）.As the stage of the fibrosis increased,the values decreased by Spearman rho correlation analysis.The mean values （standard ADC,Dslow,Dfast,and FF） of liver fibrosis stages between the groups F0-1 and F2-4,the groups F0-2 and F3-4 showed significant differences （P＜0.05）.Conclusions IVIM can reflect the conditions of perfusion and diffusion in liver fibrosis and thus distinguish between normal liver and liver fibrosis.The IVIM technique may serve as a valuable tool for detecting and characterizing liver fibrosis,and monitoring its progression in a noninvasive manner.
