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<br />I <br />I <br />I <br />I <br />t <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />'I <br />I <br />I <br />I <br />I <br /> <br />The key parameter is the coefficient of maximum pressure fluctuation Cp,max' which is in terms of the <br />velocity head of the supercritical flow jus upstream of the jump: <br /> <br />Cp_max = P/(VN2g) <br /> <br />(2-8) <br /> <br />where: P <br />VI <br />YI <br />g <br /> <br />= Pressure deviation (fluctuation) from mean (ft), <br />= Incident velocity Gust upstream of jump (fps), <br />= Incident depth (ft), and <br />= Acceleration of gravity (ft/sed) <br /> <br />Effectively, Cp is a function of the Froude Number of the supercritical flow, The parameter varies as <br />a function of the downstream distance, X, from the beginning of the jump, <br /> <br />Table I-I presents recommended CP'maJ( positive pressure values for various structure configurations, <br />When the Froude number for the design case is lower than those indicated, the lowest value of Cp <br />indicated should be used for any quick calculations (but do not reduce values on a linear relationship), <br />The values can be tempered by reviewing the Cp graphs given in the reference, a few of which are <br />given here. Note that the graphs are not maximum values but have the mean fluctuation of pressure, <br />The standard deviation of the fluctuations are also indicated, from which the recommended Cp'""", <br />values were derived, <br /> <br />TABLE 1-1 <br />NOMINAL LIMIT OF MAXIMUM PRESSURE FLUCTUATIONS <br />(Adapted from Toso, 1986) <br /> <br />Jump <br />Condition <br /> <br />Froude Suggested <br />Number Maximum Cp <br />3,0 1.0 <br />3,8 0,7 <br />3.3 0,8" <br />5.0 0,7 <br />5,0 1.0 <br /> <br />O' Slope, Developed Inflow (boundary layer at surface) <br />30' Slope, Toe ofJump at Base of Chute" <br />30' Slope, Toe of Jump on Chute <br /> <br />30' Slope for USBR Basin II <br />30' Slope for USBR Basin III <br /> <br />"Velocity head increased by elevation difference between top of jump and basin floor. <br /> <br />Figure 1-1 illustrates positive and negative pressure fluctuations coefficient, Cp' with respect to <br />location where the jump begins at the toe, Figure 1-2 presents the positive pressure fluctuation where <br />the jump begins on the face slope, Figure 1-3 illustrates how the pressure fluctuation can vary <br />remarkably in USBR Basins II or III. <br /> <br />1-3 <br />