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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Energy–depth relationship in a rectangular channel ： ウィキペディア英語版 Energy–depth relationship in a rectangular channel In open channel flow, specific energy (E) is the energy length, or head, relative to the channel bottom. Specific energy is expressed in terms of kinetic energy, and potential energy, and internal energy. The Bernoulli equation, which originates from a control volume analysis, is used to describe specific energy relationships in fluid dynamics. The form of Bernoulli’s equation discussed here assumes the flow is incompressible and steady. The three energy components in Bernoulli's equation are elevation, pressure and velocity. However, since with open channel flow, the water surface is open to the atmosphere, the pressure term between two points has the same value and is therefore ignored. Thus, if the specific energy and the velocity of the flow in the channel are known, the depth of flow can be determined. This relationship can be used to calculate changes in depth upstream or downstream of changes in the channel such as steps, constrictions, or control structures. It is also the fundamental relationship used in the Standard Step Method to calculate how the depth of a flow changes over a reach from the energy gained or lost due to the slope of the channel. ==Introduction== With the pressure term neglected, energy exists in two forms, potential and kinetic. Assuming all the fluid particles are moving at the same velocity, the general expression for kinetic energy applies (KE = ½mv2). This general expression can be written in terms of kinetic energy per unit weight of fluid, :$\backslash frac\}\; =\; \backslash fracmv^2\}\; =\; \backslash frac\backslash bigl(\backslash rho\; V\backslash bigr)v^2\}$           (1) : The kinetic energy, in feet, is represented as the velocity head, :$\backslash mathit=\backslash frac$          (2) The fluid particles also have potential energy, which is associated with the fluid elevation above an arbitrary datum. For a fluid of weight (ρg) at a height y above the established datum, the potential energy is wy. Thus, the potential energy per unit weight of fluid can be expressed as simply the height above the datum, :$\backslash frac\; =\; y$          (3) Combining the energy terms for kinetic and potential energies along with influences due to pressure and headloss, results in the following equation: :$\backslash frac+y\_1+\backslash frac-h\_f\; =\; \backslash frac+y\_2+\backslash frac$           (4) : As the fluid moves downstream, energy is lost due to friction. These losses can be due to channel bed roughness, channel constrictions, and other flow structures. Energy loss due to friction is neglected in this analysis. Equation 4 evaluates the flow at two locations: point 1 (upstream) and point 2 (downstream). As mentioned previously, the pressure at locations 1 and 2 both equal atmospheric pressure in open-channel flow, therefore the pressure terms cancel out. Headloss due to friction is also neglected when determining specific energy; therefore this term disappears as well. After these cancelations, the equation becomes, :$\backslash frac+y\_1\; =\; \backslash frac+y\_2$           (5) and the total specific energy at any point in the system is, :$E\; =\; \backslash frac+y$           (6) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Energy–depth relationship in a rectangular channel」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.