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Bài tập thủy lực - chương 4

Tham khảo tài liệu 'bài tập thủy lực - chương 4', khoa học tự nhiên, vật lý phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | A vortex ring The complex three-dimensional structure of a smoke ring is indicated in this cross-sectional view. Smoke in air. Photograph courtesy of R. H. Magarvey and C. S. MacLatchy Ref. 4. .4 Fluid Kinematics Kinematics involves position velocity and acceleration not force. In the previous three chapters we have defined some basic properties of fluids and have considered various situations involving fluids that are either at rest or are moving in a rather elementary manner. In general fluids have a well-known tendency to move or flow. It is very difficult to tie down a fluid and restrain it from moving. The slightest of shear stresses will cause the fluid to move. Similarly an appropriate imbalance of normal stresses pressure will cause fluid motion. In this chapter we will discuss various aspects of fluid motion without being concerned with the actual forces necessary to produce the motion. That is we will consider the kinematics of the motion the velocity and acceleration of the fluid and the description and visualization of its motion. The analysis of the specific forces necessary to produce the motion the dynamics of the motion will be discussed in detail in the following chapters. A wide variety of useful information can be gained from a thorough understanding of fluid kinematics. Such an understanding of how to describe and observe fluid motion is an essential step to the complete understanding of fluid dynamics. We have all observed fascinating fluid motions like those associated with the smoke emerging from a chimney or the flow of the atmosphere as indicated by the motion of clouds. The motion of waves on a lake or the mixing of paint in a bucket provide other common although quite different examples of flow visualization. Considerable insight into these fluid motions can be gained by considering the kinematics of such flows without being concerned with the specific force that drives them. 4.1 The Velocity Field In general fluids flow. That is there is