The study of frictional properties of human skin is important for medical research, skin care products and textile exploi- tation. In order to investigate the influence of normal load and sliding speed on the friction...The study of frictional properties of human skin is important for medical research, skin care products and textile exploi- tation. In order to investigate the influence of normal load and sliding speed on the frictional properties of skin and its possible mechanism, tests were carded out on a multi-specimen friction tester. When the normal load increases from 0.1 N to 0.9 N, normal displacement and the friction coefficient of skin increase. The friction coefficient is dependent on the load, indicating that both adhesion and deformation contribute to the friction behaviour. The deformation friction was interpreted using the plough model of friction. When sliding speed increases from 0.5 mm·s^-1 to 4 mm·s^-1, the friction coefficient increases and ＂stick-slip＂ phenomena increase, indicating that hysteretic friction contributes to the friction. The hysteretic friction was in- terpreted using schematic of energy translation during the rigid spherical probe sliding on the soft skin surface, which provides an explanation for the influence of the sliding speed on the frictional characteristics of the skin.展开更多
High-speed friction and wear behaviors of bulk Ti3SiC2 sliding drily against low carbon steel were investigated. Tests were carried out using a block-on-disk type tester with normal pressures ranging from 0.1 to 0.8 M...High-speed friction and wear behaviors of bulk Ti3SiC2 sliding drily against low carbon steel were investigated. Tests were carried out using a block-on-disk type tester with normal pressures ranging from 0.1 to 0.8 MPa and several sliding speeds from 20 to 60 m/s. The results show that, in the case of sliding speeds of 2040 m/s, the friction coefficient exhibits a decreasing tendency with increasing the normal pressure after an increment in the smaller pressure range, and the worn quantity of Ti3SiC2 exhibits a nearly linear increase with increasing the normal pressure. However, when the sliding speed is up to 60 m/s, the friction coefficient exhibits a monotonous increase and the worn quantity exhibits a quadric increase with increasing the normal pressure. These speed-dependent and pressure-dependent behaviors are attributed to the antifriction effects of a frictionally generated oxide film covering the friction surface of Ti3SiC2, and a balance between the generating rate and the removing （wearing） rate of the film.展开更多
It is shown that an impulsive force acting on a particle perpendicular to its velocity vector cannot change its direction of motion without increasing its kinetic energy. If the particle’s kinetic energy is to remain...It is shown that an impulsive force acting on a particle perpendicular to its velocity vector cannot change its direction of motion without increasing its kinetic energy. If the particle’s kinetic energy is to remain unchanged, the impulsive force must have a component in the direction opposite to the direction of motion. This situation is also realized in the case of a continuous force acting perpendicular to the velocity vector of the particle, when the particle's motion is viewed as a sequence of infinitesimal steps.展开更多
Purpose: A novel image-based method for speed of sound (SoS) estimation is proposed and experimentally validated on a tissue-mimicking ultrasound phantom and normal human liver in vivo using linear and curved array tr...Purpose: A novel image-based method for speed of sound (SoS) estimation is proposed and experimentally validated on a tissue-mimicking ultrasound phantom and normal human liver in vivo using linear and curved array transducers. Methods: When the beamforming SoS settings are adjusted to match the real tissue’s SoS, the ultrasound image at regions of interest will be in focus and the image quality will be optimal. Based on this principle, both a tissue-mimicking ultrasound phantom and normal human liver in vivo were used in this study. Ultrasound image was acquired using different SoS settings in beamforming channels ranging from 1420 m/sec to 1600 m/sec. Two regions of interest (ROIs) were selected. One was in a fully developed speckle region, while the other contained specular reflectors. We evaluated the image quality of these two ROIs in images acquired at different SoS settings in beamforming channels by using the normalized autocorrelation function (ACF) of the image data. The values of the normalized ACF at a specific lag as a function of the SoS setting were computed. Subsequently, the soft tissue’s SoS was determined from the SoS setting at the minimum value of the normalized ACF. Results: The value of the ACF as a function of the SoS setting can be computed for phantom and human liver images. SoS in soft tissue can be determined from the SoS setting at the minimum value of the normalized ACF. The estimation results show that the SoS of the tissue-mimicking phantom is 1460 m/sec, which is consistent with the phantom manufacturer’s specification, and the SoS of the normal human liver is 1540 m/sec, which is within the range of the SoS in a healthy human liver in vivo. Conclusion: Soft tissue’s SoS can be determined by analyzing the normalized ACF of ultrasound images. The method is based on searching for a minimum of the normalized ACF of ultrasound image data with a specific lag among different SoS settings in beamforming channels.展开更多
A formula is developed to estimate the total mass loss of projectile, based on the assump- tions that the peeling of molten surface layer in projectile nose is the primary cause of mass loss, and the frictional heat i...A formula is developed to estimate the total mass loss of projectile, based on the assump- tions that the peeling of molten surface layer in projectile nose is the primary cause of mass loss, and the frictional heat is totally absorbed by the projectile. Extrapolating this formula to predict the mass loss of local area of projectile, the receding displacement on projectile surface is obtained, which is vertical to the symmetry axis of projectile. Thereby, a finite difference method model is constructed to simulate the variation of projectile shape. The shape of residual projectile, depth of penetration of projectile and its mass loss obtained by calculation are found in good consistency with respective experimental data.展开更多
果蝇优化算法(Fruit Fly Optimization Algorithm)是一种群体智能算法,其灵感来源于果蝇群体觅食行为。该算法通过模拟果蝇利用敏锐的嗅觉搜索食物源及利用视觉飞向食物位置的过程,实现对优化问题解空间的高效搜索。FOA算法具有原理简...果蝇优化算法(Fruit Fly Optimization Algorithm)是一种群体智能算法,其灵感来源于果蝇群体觅食行为。该算法通过模拟果蝇利用敏锐的嗅觉搜索食物源及利用视觉飞向食物位置的过程,实现对优化问题解空间的高效搜索。FOA算法具有原理简单、易于实现、参数较少等优点,在函数优化、机器学习、图像处理、工程设计等多个领域展现出了良好的应用潜力,为解决复杂的实际优化问题提供了一种有效的新途径,然而其在收敛速度和求解精度方面仍存在一定的改进空间,二维正态分布果蝇优化算法(Fruit Fly Optimization Algorithm based on Two-Dimensional Normal Distribution,简称2D-NDFOA)是一种结合了果蝇优化算法与正态分布特性的优化策略,提高果蝇群体的全局搜索能力。展开更多
液压设备在运行过程中伴随着多域间的能量转换,尤其在变工况下呈现出非平稳性及非线性等特征,为状态监测与故障诊断带来难度。为了提高非平稳工况轴向柱塞泵故障诊断的性能,该研究提出采用既是运行参数又是状态参量的瞬时转速信号作为...液压设备在运行过程中伴随着多域间的能量转换,尤其在变工况下呈现出非平稳性及非线性等特征,为状态监测与故障诊断带来难度。为了提高非平稳工况轴向柱塞泵故障诊断的性能,该研究提出采用既是运行参数又是状态参量的瞬时转速信号作为轴向柱塞泵故障诊断的信息源。通过理论分析得出瞬时转速信号的波动成分中蕴含着元件健康状态信息。提出采用同步提取标准S变换(synchro-extracting of normal S transform,SNST)对其进行线通滤波处理。利用K-medoids方法将滤波重构后的瞬时转速波动信号角度域特征值进行聚类分析,并在机电液一体化平台上进行了变转速和变负载工况试验,实现了轴向柱塞泵配流盘在正常、轻微、严重磨损时的故障诊断。研究成果可为液压设备的运行状态监测与故障诊断提供新的方法。展开更多
基金This work was supported by the National Natural Science Foundation of China(grant No.50475164 and 50535050)by the Science Foundation of China University of Mining and Technology(grant No.2005B034).
文摘The study of frictional properties of human skin is important for medical research, skin care products and textile exploi- tation. In order to investigate the influence of normal load and sliding speed on the frictional properties of skin and its possible mechanism, tests were carded out on a multi-specimen friction tester. When the normal load increases from 0.1 N to 0.9 N, normal displacement and the friction coefficient of skin increase. The friction coefficient is dependent on the load, indicating that both adhesion and deformation contribute to the friction behaviour. The deformation friction was interpreted using the plough model of friction. When sliding speed increases from 0.5 mm·s^-1 to 4 mm·s^-1, the friction coefficient increases and ＂stick-slip＂ phenomena increase, indicating that hysteretic friction contributes to the friction. The hysteretic friction was in- terpreted using schematic of energy translation during the rigid spherical probe sliding on the soft skin surface, which provides an explanation for the influence of the sliding speed on the frictional characteristics of the skin.
基金Project(2003AA332080) supported by Hi tech Research and Development Program Project(50472045) supported by theNational Natural Science Foundation of China Project(JXJ04008) supported by the Science Developing Fund of Beijing Jiaotong Universi ty
文摘High-speed friction and wear behaviors of bulk Ti3SiC2 sliding drily against low carbon steel were investigated. Tests were carried out using a block-on-disk type tester with normal pressures ranging from 0.1 to 0.8 MPa and several sliding speeds from 20 to 60 m/s. The results show that, in the case of sliding speeds of 2040 m/s, the friction coefficient exhibits a decreasing tendency with increasing the normal pressure after an increment in the smaller pressure range, and the worn quantity of Ti3SiC2 exhibits a nearly linear increase with increasing the normal pressure. However, when the sliding speed is up to 60 m/s, the friction coefficient exhibits a monotonous increase and the worn quantity exhibits a quadric increase with increasing the normal pressure. These speed-dependent and pressure-dependent behaviors are attributed to the antifriction effects of a frictionally generated oxide film covering the friction surface of Ti3SiC2, and a balance between the generating rate and the removing （wearing） rate of the film.
文摘It is shown that an impulsive force acting on a particle perpendicular to its velocity vector cannot change its direction of motion without increasing its kinetic energy. If the particle’s kinetic energy is to remain unchanged, the impulsive force must have a component in the direction opposite to the direction of motion. This situation is also realized in the case of a continuous force acting perpendicular to the velocity vector of the particle, when the particle's motion is viewed as a sequence of infinitesimal steps.
文摘Purpose: A novel image-based method for speed of sound (SoS) estimation is proposed and experimentally validated on a tissue-mimicking ultrasound phantom and normal human liver in vivo using linear and curved array transducers. Methods: When the beamforming SoS settings are adjusted to match the real tissue’s SoS, the ultrasound image at regions of interest will be in focus and the image quality will be optimal. Based on this principle, both a tissue-mimicking ultrasound phantom and normal human liver in vivo were used in this study. Ultrasound image was acquired using different SoS settings in beamforming channels ranging from 1420 m/sec to 1600 m/sec. Two regions of interest (ROIs) were selected. One was in a fully developed speckle region, while the other contained specular reflectors. We evaluated the image quality of these two ROIs in images acquired at different SoS settings in beamforming channels by using the normalized autocorrelation function (ACF) of the image data. The values of the normalized ACF at a specific lag as a function of the SoS setting were computed. Subsequently, the soft tissue’s SoS was determined from the SoS setting at the minimum value of the normalized ACF. Results: The value of the ACF as a function of the SoS setting can be computed for phantom and human liver images. SoS in soft tissue can be determined from the SoS setting at the minimum value of the normalized ACF. The estimation results show that the SoS of the tissue-mimicking phantom is 1460 m/sec, which is consistent with the phantom manufacturer’s specification, and the SoS of the normal human liver is 1540 m/sec, which is within the range of the SoS in a healthy human liver in vivo. Conclusion: Soft tissue’s SoS can be determined by analyzing the normalized ACF of ultrasound images. The method is based on searching for a minimum of the normalized ACF of ultrasound image data with a specific lag among different SoS settings in beamforming channels.
基金supported by the National Natural Science Foundation of China (11172282)the Science Foundation of China Academy of Engineering Physics(2009A0201009)
文摘A formula is developed to estimate the total mass loss of projectile, based on the assump- tions that the peeling of molten surface layer in projectile nose is the primary cause of mass loss, and the frictional heat is totally absorbed by the projectile. Extrapolating this formula to predict the mass loss of local area of projectile, the receding displacement on projectile surface is obtained, which is vertical to the symmetry axis of projectile. Thereby, a finite difference method model is constructed to simulate the variation of projectile shape. The shape of residual projectile, depth of penetration of projectile and its mass loss obtained by calculation are found in good consistency with respective experimental data.
文摘果蝇优化算法(Fruit Fly Optimization Algorithm)是一种群体智能算法,其灵感来源于果蝇群体觅食行为。该算法通过模拟果蝇利用敏锐的嗅觉搜索食物源及利用视觉飞向食物位置的过程,实现对优化问题解空间的高效搜索。FOA算法具有原理简单、易于实现、参数较少等优点,在函数优化、机器学习、图像处理、工程设计等多个领域展现出了良好的应用潜力,为解决复杂的实际优化问题提供了一种有效的新途径,然而其在收敛速度和求解精度方面仍存在一定的改进空间,二维正态分布果蝇优化算法(Fruit Fly Optimization Algorithm based on Two-Dimensional Normal Distribution,简称2D-NDFOA)是一种结合了果蝇优化算法与正态分布特性的优化策略,提高果蝇群体的全局搜索能力。
文摘液压设备在运行过程中伴随着多域间的能量转换,尤其在变工况下呈现出非平稳性及非线性等特征,为状态监测与故障诊断带来难度。为了提高非平稳工况轴向柱塞泵故障诊断的性能,该研究提出采用既是运行参数又是状态参量的瞬时转速信号作为轴向柱塞泵故障诊断的信息源。通过理论分析得出瞬时转速信号的波动成分中蕴含着元件健康状态信息。提出采用同步提取标准S变换(synchro-extracting of normal S transform,SNST)对其进行线通滤波处理。利用K-medoids方法将滤波重构后的瞬时转速波动信号角度域特征值进行聚类分析,并在机电液一体化平台上进行了变转速和变负载工况试验,实现了轴向柱塞泵配流盘在正常、轻微、严重磨损时的故障诊断。研究成果可为液压设备的运行状态监测与故障诊断提供新的方法。
