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<br />(C<. VI^ <br /> <br />F'MA <br /> <br />.\ ' <br /> <br />'.r' <br /> <br />III. Fluid mechanics <br /> <br />A. Continuity <br /> <br />Q = AY (Steady flow) <br /> <br />d(Yol) = Q <br />dt in - Qout <br /> <br />(unsteady flow) <br /> <br />B. Momentum (steady) <br /> <br />F +" +F +F = pQ(Y2-Yl) <br />t p q a <br /> <br />C. Energy Eq. <br /> <br />Y 2 <br />1 <br />-+ <br />2g <br /> <br />Y 2 <br />2 <br />Zl = 2g + <br /> <br />Pl <br />-.. <br />y <br /> <br />P2 <br />-+ <br />Y <br /> <br />D. Specific energy <br />'y2 <br />H = 2g .. Z <br /> <br />E. <br /> <br />Resistance to flow <br /> <br />. . i ~ <br /> <br />n = 319 (d7S) l/6 <br /> <br />(d7S in inches) <br /> <br />F. Temperature <br /> <br />G.. Flow distribution <br /> <br />5 <br /> <br />Used all the time, including sometimes <br />when it shouldn't because of timc <br />dependence. <br /> <br />Inclusion of time dependence cnables <br />evaluation of effcctiveness of <br />channel storage. <br /> <br />Useful for calculation of forces <br />imposed by the flow <br /> <br />Can calculatc loss in energy betwecn <br />different sections of the channcl. <br /> <br />Z2 + H2 <br /> <br />For steady flow cnables easy dcter- <br />mination of water surface profiles <br />for changes in channel Cross section. <br /> <br />(a) Use Water Supply paper 1849 for <br />. pictorial refcrence <br />(b) Calculate Manning's n from sediment <br />size. (coarse materials) <br />(c) Usemeasurcd hydraulic data, Q, <br />slope, channcl geometry. <br /> <br />Change in fluid viscosity is largest <br />effect. Also, water quality and growth. <br />rates of flora. <br /> <br />Need to calculate lu;.u beu. shear <br />stress, calculate aver;,J.:c velocity <br />in a vertical section. <br />