![]() ![]() In hydrodynamics and sediment transport the kinematic viscosity, μ w, is often utilized. The flows resulting from water with and without viscosity are referred to as viscous and inviscid flows respectively. ![]() When a fluid has zero viscosity it called inviscid. The viscosity of liquids decreases rapidly with an increase in temperature, and the viscosity of gases increases with an increase in temperature. The unit of viscosity, accordingly, is newton -second per square metre, which is usually expressed as pascal -second in SI units. The water viscosity is a measure of the resistance to deformation at a given rate. The dimensions of dynamic viscosity are force × time ÷ area. Currently, in HEC-RAS the salinity is assumed to be 0.5 PSU. The error is less than 1.0% over the range 0 28 ∘C. The error compared to the data of Riley and Skirrow (1965) is less than 0.5% over the range (0 38 PSU and 8 24 ∘C). If the user specifies a time series of water temperature, the water density is calculated using the UNESCO (1981) equation (at standard atmospheric pressure) 2) The default water unit weight in HEC-RAS is 62.4177 lb/ft 3. The water specific weight or unit weight particles, γ w, is the density times the gravitational constant 1) There are many formulas in literature for computing the water temperature. The water density is a function a water temperature and salinity. The default water temperature in HEC-RAS is 55.4 F. These correspond to the "clear water" values without sediment. However, salinity is currently ignored in HEC-RAS. (The viscosity of water is approximately 1 cP.). These are a function of the water temperature and salinity. The practical unit of absolute viscosity is centipoise (cP), which is identical to the MKS unit mPa s. The main physical properties utilized in hydrodynamics and sediment transport are the density and viscosity. ![]()
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