[Lloyd Sullivan]

Hi there,


I'm moving a 2.5D cylinder in the x-direction with a prescribed force only (no in-flow) 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

[Lloyd Sullivan]

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.E-4
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

[cfd seeker]

If i have understood it correctly then you are trying to model the movement of cylinder with particular velocity to calculate the drag coefficient?

[Lloyd Sullivan]

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