机械制造及自动化专业外文翻译--机械运动和动力学.doc

英文原文:
Kinematics and dynamics of machinery
One princple aim of kinemarics is to creat the designed motions of the subject mechanical parts and then pute the positions, velocities ,and accelerations ,which those motions will creat on the parts. Since ,for most earthbound mechanical systems ,the mass remains essentially constant with time,defining the accelerations as a function of time then also defines the dynamic forces as a function of time. Stress,in turn, will be a function of both applied and inerials forces . since engineering design is charged with creating systems which will not fail during their expected service life,the goal is to keep stresses within acceptable limits for the materials chosen and the environmental conditions encountered. This obvisely requies that all system forces be defined and kept within desired limits. In mechinery , the largest forces encountered are often those due to the dynamics of the machine itself. These dynamic forces are proportional to acceletation, which brings us back to kinematics ,the foundation of mechanical design. Very basic and early decisions in the design process invovling kinematics wii prove troublesome and perform badly.
Any mechanical system can be classified according to the number of degree of freedom which it systems DOF is equal to the number of independent parameters which are needed to uniquely define its posion in space at any instant of time.
A rigid body free to move within a reference frame will ,in the general case, plex motoin, which is bination of rotation and translation. In three-dimensional space , there may be rotation about any axis and also simultaneous translation which can be resoled ponention along three axes, in a plane ,or two-dimentional space ,complex motion es bination of simultaneous along two axes in the plane. For simplicity ,we will limit our present discusstions to the case of planar motion:
Pure rotation the body pessesses one point (center of rotation)which