液压与气压传动外文翻译.doc

论文出处：《Hydraulics and Pneumatics Transmission》 Fulid and Hydraulic system The history of hydraulic power is a long one, dating from man’s prehistoric efforts to harness the energy in the world around him. The only source readily available were the water and the wind—two free and moving streams. The watermill, the first hydraulic motor, was an early invention. One is pictured on a mosatic at the Great Palace in Byzantium, dating from the early fifth century. The mill had been built by the Romans. But the first record of a watermill goes back even further, to around 100BC, and the origins may indeed have been much earlier. The domestication of grain began some 5000 years before and some enterprising farmer is bound to have become tired of pounding or grinding the grain by hand. Perhaps, in fact, the inventor were some farmer’s wives. Since the often drew the heavy jobs. Fluid is a substance which may flow; that is, its constituent particles may continuously change their positions relative to one another. Moreover, it offers no lasting resistance to the displacement, however great, of one layer over another. This means that, if the fluid is at rest, no shear force (that is a force tangential to the surface on which it acts) can exist in it. Fluid may be classified as Newtonian or non--Newtonian. In Newtonian fluid there is a linear relation between the magnitude of applied shear stresses and the resulting rate of angular deformation. In non—Newtonian fluid there is a nonlinear relation between the magnitude of applied shear stress and the rate of angular deformation. The flow of fluids may be classified in many ways, such as steady or non steady, rotational or irrotational, compressible or incompressible, and viscous or no viscous. All hydraulic systems depend on Pascal’s law, such as steady or pipeexerts equal force on all of the surfaces of the container. In actual hydraulic systems, Pascal’s law defines the basis of results which are obtained from the sy