, Get from previous iteration current value of the displacement vector u and the Lagrange multiplier ? f

, If the gap V g (u) > V f or ? f < 0, the fluid is considered to be in inactive state and the trapped fluid element is excluded from consequent calculations

. Otherwise, if V g (u) ? V f and ? f ? 0, the fluid is in active state, then the residual vector and the tangent matrix are

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