Laserfiche WebLink
<br />Where: <br />L, = length ratio <br />A, = area ratio <br />V" = volume ratio <br />T, = time ratio <br />V, = velocity ratio <br />Q, = discharp ratio <br /> <br />Subscripts m and p refer to the model and prototype, and r is the ratio between model <br />and prototype. <br /> <br />Sediment Scaling <br /> <br />Sediment models that involve erosion of noncohesive bed material must simulate shear stress (To) <br />because the shear stress creates the drag force required to overcome the forces holding a particle <br />in place. Shear stress on a particle will fluctuate because of turbulence. Drag force and turbulence <br />are a function of Reynolds number. A model operated according to Froude scaling does not <br />necessarily simulate tractive forces and sediment erosion accurately. Sediment erosion can be <br />simulated properly by making the model and prototype dimensionless unit sediment discharge rates <br />equal (q; m = q;p). <br /> <br />The following equations define dimensionless shear stress (T"), Grain Reynolds number (R') and <br />dimensionless unit sediment discharge (q;). These equations are used to relate model and <br />prototype parameters to determine sediment erosion characteristics. <br /> <br />T' = <br /> <br />U'2 <br />go <br /> <br />r <br />(r. - r) <br /> <br />[dimensionless shear stress] <br /> <br />(8) <br /> <br />R' = <br /> <br />u'tl <br />v <br /> <br />[Grain Reynolds number] <br /> <br />(9) <br /> <br />q.$ = <br /> <br />q, <br /> <br />u'd <br /> <br />[dimensionless unit sediment discharge] <br /> <br />(10) <br /> <br />u = V fi <br /> <br />[shear velocity] <br /> <br />(11) <br /> <br />4 <br />