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6DOF Solver and 1DOF 6DOF Solver and 1DOF 6DOF Solver and 1DOF UDF6DOF Solver and 1DOF UDF
www.fluentusers.comAdvanced Dynamic Mesh TrainingFLUENT v6.3 January 2008
6 DOF Solver – Introduction
S f h l d ib d ti ifi d thSo far, we have only used prescribed motion – we specified the location or velocity of the object using the in-cylinder tool or a profile.Now we would like to move the object as a result of the aerodynamic forces and moments acting together with other forces such as the forceforces and moments acting together with other forces, such as the force due to gravity, thrust forces, or ejector forces (i.e., forces used to initially push objects away from an airplane or rocket, to avoid collisions). The motion and the flow field are thus coupled, and we
ll hi l d icall this coupled motion.Store separationStage separation
Fluent provides a 6DOF solver that computes the trajectory of anFluent provides a 6DOF solver that computes the trajectory of an object based on the aerodynamic forces/moments, gravitational force, and ejector forces. Fluent also provides a 1DOF UDF for 1 degree of freedom coupled
Fluent also provides a 1DOF UDF for 1 degree of freedom coupled flow
Fluent User Services Center
www.fluentusers.comAdvanced Dynamic Mesh TrainingFLUENT v6.3 January 2008
6 DOF UDF – Theory
U d fi l t i th lUser defines several parameters in the panelGravitational forceInitial conditions including CG location, CG orientation, CG linear velocity, and CG angular velocityvelocity, and CG angular velocity
User also defines the following parameters in a UDF. A UDF is used so that they can be a function of time
Mass and momentum of inertia. Ejector forces (optional)
Fluent will compute the aerodynamic forces and momentsBased on the force balance (aerodynamic, gravity, and ejector forces), compute the translational acceleration, then integrate to calculate the translational velocity. Based on the moments, compute the angular acceleration, then integrate to calculate the angular velocity.Compute the new CG location and Euler angles
www.fluentusers.comAdvanced Dynamic Mesh TrainingFLUENT v6.3 January 2008
Example 1 – Mesh Motion
E i ithEven in cases with coupled motion, it is wise to preview the mesh motion before performing p gthe calculations.In this case, start without initializing, and the object
ill i l d d hwill simply drop under the influence of gravity and/or external forces.Observe the effect ofObserve the effect of dynamic mesh parameters (spring constant, size function, maximum
www.fluentusers.comAdvanced Dynamic Mesh TrainingFLUENT v6.3 January 2008
Example 1 – Animation
Th fi hThe figure shows pressure contours corresponding to a freestream Machfreestream Mach number of 0.8 Note how the object has drifted aft and how itdrifted aft, and how it goes forward at the beginning due to ejector forceforceThis problem exists as a tutorial.
www.fluentusers.comAdvanced Dynamic Mesh TrainingFLUENT v6.3 January 2008
Example 2 – 3D Store Separation
St d dStore dropped from a delta wing (NACA 64A010) at Mach 1.2.Ejector forces dominate for a short time.All-tet mesh.Smoothing. remeshing with i f tisize function.
www.fluentusers.comAdvanced Dynamic Mesh TrainingFLUENT v6.3 January 2008
Example 2 – Muzzle Brake
P j il iProjectile moving inside and out of a barrel.I i i l h i hInitial patch in the chamber drives the motion.U d fi d lUser-defined real gas law (Abel-Nobel Equation of State).L iLayering.Tutorial exists.
www.fluentusers.comAdvanced Dynamic Mesh TrainingFLUENT v6.3 January 2008
Example 2 – Results
I i i l h i Fi l di i h iInitial patch in the chamber drives the motion of the 50 kg
Final condition at shot exit
of the 50 kg bullet/piston.User-defined real gas law (Abelgas law (Abel-Nobel Equation of State).Very goodVery good agreement (red and green data) all the way to
www.fluentusers.comAdvanced Dynamic Mesh TrainingFLUENT v6.3 January 2008
6 DOF Coupled Motion – Tips
E i i h l d i i i i i h hEven in cases with coupled motion, it is wise to preview the mesh motion before carrying out the flow calculations (which can be expensive).
S ti d ith t i iti l li / l l it dSometimes you can proceed without initial linear/angular velocity, and observe a linear motion in the direction of the gravity vector.Other times, it may be useful to provide an initial condition in order to impart initial translational and/or rotational velocity componentsimpart initial translational and/or rotational velocity components.It is usually better (but more expensive) to compute a steady solution in order to obtain an initial distribution of pressures and shear stresses.
After convergence, switch to the unsteady solver and hook the UDF.g yDuring the preview, the object will move based on the forces that resulted from the steady calculation. The resulting motion usually involves both translation and rotation.
www.fluentusers.comAdvanced Dynamic Mesh TrainingFLUENT v6.3 January 2008
6 DOF Coupled Motion – Tutorial
A hi i d h d f 6DOF i lAt this time we recommend that you do on of our 6DOF tutorials2D Store Separation – Air Drop of a Rescue Pod3D Store Separation – Delta Wing