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Environmental Fluid Mechanics - Chapter 8

Hệ thống cơ khí có thể dao động nếu chuyển từ một trạng thái cân bằng là một lực lượng khôi phục lại. Một số ví dụ về các rung động như vậy được đại diện bởi búa nước trong đường ống, sóng âm, sóng trọng lực bề mặt, sóng bề mặt mao mạch, và sóng nội bộ. Lực lượng phục hồi trong những trường hợp đặc biệt có thể được tính đàn hồi ống, chất lỏng nén, trọng lực, sức căng bề mặt, hoặc lực lượng Coriolis trong trường hợp chất lỏng quay. Trong hầu hết các trường hợp. | 8 Surface Water Waves 8.1 INTRODUCTION Mechanical systems may vibrate if their displacement from a state of equilibrium is subject to a restoring force. Some examples of such vibrations are represented by water hammer in pipes sound waves surface gravity waves surface capillary waves and internal waves. The restoring force in these particular cases may be the pipe elasticity fluid compressibility gravity surface tension or Coriolis force in cases of rotating fluids. In most cases wave motions decay by viscous shear stresses unless there is a constant supply of energy to maintain the motion. Water quality issues of the marine environment as well as of lakes channels and rivers are often closely related to topics of wave formation and propagation. For example waves carry mechanical energy which can lead to the destruction of maritime structures. With regard to environmental issues wave energy leads to mixing in the water column and also along the bottom causing movement of sediments along coastlines affecting various current patterns in a water body and aiding the transport of solutes and floating materials in the environment. The present chapter discusses basic features and properties of waves in such environments focusing on surface waves. These waves on a horizontal water surface of a marine or lake environment are confined to two-dimensional propagation in the horizontal plane and are subject to a vertical external gravity restoring force. An initial presentation of the wave equation is given along with a discussion of its application to several specific issues of environmental fluid mechanics. Special attention also is given to the development and propagation of waves in open channels and rivers. Internal waves are presented in Sec. 13.2. Copyright 2001 by Marcel Dekker Inc. All Rights Reserved. 8.2 THE WAVE EQUATION Neglecting viscous and Coriolis forces the general governing equations for fluid motion are the equations of motion and mass conservation as .