How do I model a subcritical flow with FLOW3D?
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I want to model a subcritical flowin FLOW3D. When the height of the lower boundary is greater than of the upper boundary the water will enter the downstream boundary of the computational region. As a result of my assumptions is destroyed. Please help me 
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Why height of downstream is not more than height of upstream? if y2>y1 then flow3d enter water of downstream boundary condition. y2=height of downstream y1=height of upstream i want y2>y1 and flow direction is upstream > downstream but after Run flow direction is downstream > upstream 
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Why height of downstream is not more than height of upstream? if y2>y1 then flow3d enter water of downstream boundary condition. y2=height of downstream y1=height of upstream i want y2>y1 and flow direction is upstream > downstream but after Run flow direction is downstream > upstream 
FLOW3D is a transient solver. You are using assumptions of steadystate graduallyvaried flow. The only way to model this kind of situation is to include the control structure that causes the downstream free surface elevation to be higher than the upstream elevation. That is, you must model the contraction, critical transition structure, or bed elevation change explicitly, instead of assuming that by setting h2 > h1 you can force FLOW3D to assume that the flow is steady/graduallyvaried.

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