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moving sphere in fluid domain.

    • disha
      Subscriber
      i am simulating a object in fluid region which moves due to fluid forces acting on it only .i have tried to create in 2D, two cases are happening with me when i did not boolean the object ,it created the shadow of sphere in the fluid region which is acting as stationary sphere . and when i did the boolean of the object out of fluid region , it is giving me negative cell volume by sphere movement out of the plane and values of inertia tensor becomes zero. please help me . thank youn
    • Ashish Khemka
      Ansys Employee
      Hi @disha, ,nnPlease refer to the following link:nn

      HelloI have a simple 2D problem of a pipe in which a sphere is placed in the middle (see figure). I want to simulate the motion of the sphere due to the fluid flowing through the pipe. The pipe has 1 inlet in which the velocity is prescribed as 0.30 m/s and 1 outlet where the pressure gauge is set to 0. The flow is laminar. The sphere has a 0.5 mm diameter, which gives a 6.54e-11 m3 in volume. Since the sphere material has a density of 5200 kg/m3, that gives a mass of 3.40e-7 kg. https://us.v-cdn.net/6032193/uploads/0VDFY9QJTD17/steady-calculated.pngI use the 6DOF for the particle with just One DOF translation in the X direction and the 3.40e-7 kg for the mass. For the mesh methods: smoothing with local cell with default parameters and sizing remeshing interval=1; sizing function ON with rate and variation = 0. You can check all this definitions in the pictures below.https://us.v-cdn.net/6032193/uploads/RR2ZYYVDT52J/mesh-methods.pnghttps://us.v-cdn.net/6032193/uploads/9JSADTX6VNCW/mesh-methods.pngFirst I tried the simulation using Air as the fluid ( density=1.225 kg/m3 and viscosity=1.7894e-05 kg/m-s). The solution converges in Steady state and I used this as my initialization for the Transient simulation, where I used a time step=0.0002 s, 20 iterations/time step and 20 time steps. This solves fine and I can see the circle move through the mesh (see picture below)https://us.v-cdn.net/6032193/uploads/I7G6P1E82DR4/particle-air.jpgThe problem arises when I change the fluid from Air to Water (density=998.2 kg/m3 and viscosity=0.001003 kg/m-s). The reports on the Drag force and the integral of pressure on the particle/circle go to unreasonable values and the mesh fails to update giving the "Negative cell volume". Also, the circle moves backwards...I tried changing the time step to 1e-8 (which is unreasonable small) and it also fails with the same problem (see mesh picture below).https://us.v-cdn.net/6032193/uploads/WOYE8YAWZBK1/mesh-fail.pngSo, what is the problem here? Is the mass of the circle wrong, since it's 2D, should I use a "2D mass" ? In all the 2D tutorials I see, they seem to use the "real" mass for the moving object. What settings should I look at to prevent the simulation to fail? I tried something with Solution Stabilization for the dynamic zona and Implicit Update, but wasn't successful. Any help?Thanks in advance!https://forum.ansys.com/discussion/24673/2d-negative-cell-volume-when-change-fluid-from-air-to-water

      nRegards,nAshish Khemkan
    • disha
      Subscriber
      thanks for your help sir.n
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