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==== V-funnel simulation ====
=== Test setup and Geometry ===

V-funnel problem is one of the first problem, that was modeled. It is focused on boundary condition influence. In it's easiest form is modeled in 2D. The geometry is shown at figure below. Characteristic time can be defined for V-funnel simulation. It is the time between opening the gate and the moment, when it is posible to look through the gate.   

{{:tailorcrete:examples:v_funnel_geometry.png?200|}}

=== Computational Model ===
Scheme of two-dimensional computational model is shown on the picture below. The whole problem is modeled as a two-phase flow problem. Since the fluids (concrete and air)  are immiscible, problem can be resolved finding position of the interface between both fluids in each time step. This is done using Level Set Method [1]. On the picture is also specification of boundary condition. The whole domain is decomposed into two regions. Initially, in the first region is air modeled as a newtonian fluid. In the second region is concrete, considered as a Bingham fluid. Parameters are therefore 
  *yield stress 60 Pa 
  *plastic viscosity 20 Pa*s. 
So called "Slip with friction" boundary condition was used on walls, when tangential component of the velocity is proportional to the tangential component of the stress tensor.

{{:tailorcrete:examples:v_funnel_mesh_bc.png?200|}} 

On the next picture is mesh used for simulation. It is devided into two parts. Lower part is finer to improve accuracy of the flow near the neck. The mesh contains 2907 nodes and 5567 elements. It is solved using linear triangular elements (linear both in velocity and pressure field). Since that element is not satisfying LBB condition, PSPG stabilization is used for preventing oscilations in pressure field. SUPG stabilization improving accuracy in connection with non-linear convective term is also used. For further information, see [2]. 

{{:tailorcrete:v-funnel_geometry.png?200|}}

The link below contains input file of V-funnel simulation for OOFEM program. It is a text file containing specifications about geometry (mesh), physics (constitutive model) and numerical solver.

{{:tailorcrete:examples:v_funnel_tau60_mu20_oofem.in|}}

Description of input file can be found here: [[tailorcrete:input_file_description|Input File Description]]


=== Results ===
On the video below, motion of concrete-air interface is shown. The characteristic "V-funnel time" (the time from opening the gate at the bottom to the moment when it is possible to look through the gate) is aproximately 2s.

{{:tailorcrete:examples:v_funnel_tau60_mu20.avi|}}