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August 12, 2018, 19:17 
Fluid Domain moving with Rigid body

#1 
New Member
Lloyd A. Sullivan
Join Date: Jun 2018
Location: UK
Posts: 9
Rep Power: 2 
Hi there,
I'm moving a 2.5D cylinder in the xdirection with a prescribed force only (no inflow) using the 6DOF rigid body solver and have succeeded in moving the internal domain at the same rate with the correct drag coefficient. https://imgur.com/ESICfEr However, i'm currently attempting to move the entire domain (including the boundaries) so that it translates at the exact same rate as the cylinder  Thus having no mesh deformation. The no mesh deformation is very important in this problem. The main question is if this is even possible because i've had no success getting the correct drag coefficient with several different versions of inlet and boundaries conditions. Any help is extremely appreciated  I've been stuck on this problem for a good while. Best regards, Lloyd 

August 12, 2018, 19:19 

#2 
New Member
Lloyd A. Sullivan
Join Date: Jun 2018
Location: UK
Posts: 9
Rep Power: 2 
This is part of the CCL that shows the boundary conditions if it's useful.
&replace FLOW: Flow Analysis 1 ANALYSIS TYPE: Option = Transient EXTERNAL SOLVER COUPLING: Option = None END INITIAL TIME: Option = Automatic with Value Time = 0 [s] END TIME DURATION: Option = Total Time Total Time = 20 [s] END TIME STEPS: Option = Timesteps Timesteps = timestep END END DOMAIN INTERFACE: Default Fluid Fluid Interface Boundary List1 = Default Fluid Fluid Interface Side 1 Boundary List2 = Default Fluid Fluid Interface Side 2 Filter Domain List1 = Default Domain Filter Domain List2 = Default Domain Interface Region List1 = F145.109,F146.109,F147.109,F148.109 Interface Region List2 = F173.177,F174.177,F175.177,F176.177 Interface Type = Fluid Fluid INTERFACE MODELS: Option = General Connection FRAME CHANGE: Option = None END MASS AND MOMENTUM: Option = Conservative Interface Flux MOMENTUM INTERFACE MODEL: Option = None END END PITCH CHANGE: Option = None END END MESH CONNECTION: Option = Automatic END END DOMAIN: Default Domain Coord Frame = Coord 0 Domain Type = Fluid Location = B109, B177 BOUNDARY: Default Fluid Fluid Interface Side 1 Boundary Type = INTERFACE Interface Boundary = On Location = F145.109,F146.109,F147.109,F148.109 BOUNDARY CONDITIONS: MASS AND MOMENTUM: Option = Conservative Interface Flux END MESH MOTION: Option = Rigid Body Solution Rigid Body = cylinder END END END BOUNDARY: Default Fluid Fluid Interface Side 2 Boundary Type = INTERFACE Interface Boundary = On Location = F173.177,F174.177,F175.177,F176.177 BOUNDARY CONDITIONS: MASS AND MOMENTUM: Option = Conservative Interface Flux END MESH MOTION: Option = Rigid Body Solution Rigid Body = cylinder END END END BOUNDARY: cylinder surface Boundary Type = WALL Create Other Side = Off Interface Boundary = Off Location = Cylinder BOUNDARY CONDITIONS: MASS AND MOMENTUM: Option = No Slip Wall Wall Velocity Relative To = Mesh Motion END MESH MOTION: Option = Rigid Body Solution Rigid Body = cylinder END END END BOUNDARY: free walls Boundary Type = WALL Create Other Side = Off Interface Boundary = Off Location = Top,Bottom BOUNDARY CONDITIONS: MASS AND MOMENTUM: Option = Free Slip Wall END MESH MOTION: Option = Rigid Body Solution Rigid Body = cylinder END END END BOUNDARY: left Boundary Type = OPENING Interface Boundary = Off Location = Left BOUNDARY CONDITIONS: FLOW REGIME: Option = Subsonic END MASS AND MOMENTUM: Option = Cartesian Velocity Components U = 0 [m s^1] V = 0 [m s^1] W = 0 [m s^1] END MESH MOTION: Option = Rigid Body Solution Rigid Body = cylinder END END END BOUNDARY: right Boundary Type = OPENING Interface Boundary = Off Location = Right BOUNDARY CONDITIONS: FLOW DIRECTION: Option = Normal to Boundary Condition END FLOW REGIME: Option = Subsonic END MASS AND MOMENTUM: Option = Opening Pressure and Direction Relative Pressure = 0 [Pa] END MESH MOTION: Option = Rigid Body Solution Rigid Body = cylinder END END END BOUNDARY: sym Boundary Type = SYMMETRY Interface Boundary = Off Location = Back A,Back B,Front A,Front B BOUNDARY CONDITIONS: MESH MOTION: Option = Unspecified END END END DOMAIN MODELS: BUOYANCY MODEL: Option = Non Buoyant END DOMAIN MOTION: Option = Stationary END MESH DEFORMATION: Displacement Relative To = Previous Mesh Option = Regions of Motion Specified MESH MOTION MODEL: Option = Displacement Diffusion MESH STIFFNESS: Mesh Stiffness = 1.0 [m^5 s^1] / volcvol Option = Value END END END REFERENCE PRESSURE: Reference Pressure = 101325 [Pa] END END FLUID DEFINITION: Fluid 1 Material = Water Option = Material Library MORPHOLOGY: Option = Continuous Fluid END END FLUID MODELS: COMBUSTION MODEL: Option = None END HEAT TRANSFER MODEL: Fluid Temperature = 25 [C] Option = Isothermal END THERMAL RADIATION MODEL: Option = None END TURBULENCE MODEL: Option = Laminar END END SUBDOMAIN: Subdomain 1 Coord Frame = Coord 0 Location = B177 MESH MOTION: Option = Rigid Body Solution Rigid Body = cylinder END END SUBDOMAIN: Subdomain 2 Coord Frame = Coord 0 Location = B109 MESH MOTION: Option = Rigid Body Solution Rigid Body = cylinder END END END INITIALISATION: Option = Automatic INITIAL CONDITIONS: Velocity Type = Cartesian CARTESIAN VELOCITY COMPONENTS: Option = Automatic with Value U = 0 [m s^1] V = 0 [m s^1] W = 0 [m s^1] END STATIC PRESSURE: Option = Automatic with Value Relative Pressure = 0 [Pa] END END END OUTPUT CONTROL: MONITOR OBJECTS: Monitor Coefficient Loop Convergence = On MONITOR BALANCES: Option = Full END MONITOR FORCES: Option = Full END MONITOR PARTICLES: Option = Full END MONITOR POINT: Re Coord Frame = Coord 0 Expression Value = Reynold number Option = Expression END MONITOR POINT: cyl dis Coord Frame = rigid Expression Value = Cylinder displacment Option = Expression END MONITOR POINT: cyl vel Coord Frame = rigid Expression Value = Cylinder velocity Option = Expression END MONITOR POINT: drag coefficent Coord Frame = Coord 0 Expression Value = drag coeff Option = Expression END MONITOR POINT: force input Coord Frame = Coord 0 Expression Value = force exp Option = Expression END MONITOR POINT: lift coefficient Coord Frame = Coord 0 Expression Value = lift coeff Option = Expression END MONITOR RESIDUALS: Option = Full END MONITOR TOTALS: Option = Full END END RESULTS: File Compression Level = Default Option = Essential END TRANSIENT RESULTS: Transient Results 1 File Compression Level = Default Include Mesh = No Option = Selected Variables Output Variable Operators = All Output Variables List = Velocity OUTPUT FREQUENCY: Option = Time Interval Time Interval = timestep *3 END END END RIGID BODY: cylinder Location = Cylinder Mass = mass Rigid Body Coord Frame = Coord 0 DYNAMICS: DEGREES OF FREEDOM: ROTATIONAL DEGREES OF FREEDOM: Option = None END TRANSLATIONAL DEGREES OF FREEDOM: Option = X axis END END EXTERNAL FORCE: External Force 1 Option = Value FORCE: Option = Cartesian Components xValue = force exp*mass yValue = 0 [N] zValue = 0 [N] END END END MASS MOMENT OF INERTIA: xxValue = 0 [kg m^2] xyValue = 0 [kg m^2] xzValue = 0 [kg m^2] yyValue = 0 [kg m^2] yzValue = 0 [kg m^2] zzValue = 0 [kg m^2] END END SOLUTION UNITS: Angle Units = [rad] Length Units = [m] Mass Units = [kg] Solid Angle Units = [sr] Temperature Units = [K] Time Units = [s] END SOLVER CONTROL: ADVECTION SCHEME: Option = High Resolution END CONVERGENCE CONTROL: Maximum Number of Coefficient Loops = 10 Minimum Number of Coefficient Loops = 1 Timescale Control = Coefficient Loops END CONVERGENCE CRITERIA: Residual Target = 1.E4 Residual Type = RMS END RIGID BODY CONTROL: RIGID BODY SOLVER COUPLING CONTROL: Update Frequency = General Coupling Control INTERNAL COUPLING STEP CONTROL: Maximum Number of Coupling Iterations = 10 Minimum Number of Coupling Iterations = 1 END END END TRANSIENT SCHEME: Option = Second Order Backward Euler TIMESTEP INITIALISATION: Option = Automatic END END END END 

August 16, 2018, 03:54 

#3 
Senior Member
Join Date: Mar 2011
Location: Germany
Posts: 473
Rep Power: 14 
If i have understood it correctly then you are trying to model the movement of cylinder with particular velocity to calculate the drag coefficient?


August 17, 2018, 09:58 

#4 
New Member
Lloyd A. Sullivan
Join Date: Jun 2018
Location: UK
Posts: 9
Rep Power: 2 
Hi there,
I have been able to solve the problem just setting all the boundaries to rigid body motion and splitting the the domain into two subdomains. The boundary conditions applied were a little strange, but it obtain the same drag coefficient as the moving internal domain. Regards, Lloyd 

Tags 
mesh deformation, movable mesh, rigid body motion 
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