VIBRO_2_MODAL_simulations-ACTRAN 模态频响分析理论
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• • Lower case op2, .bdf or .dat
Copyright Free Field Technologies
6
Fluid / Structure Coupling
When a cavity and a structure are involved, they can be coupled Cavity and structure meshes are always considered as incompatible The fluid/structure coupling is set through the COUPLING data block: STRUCTURE and CAVITY keyword must be present The surface over which the coupling occurs can be specified in two ways:
2
Copyright Free Field Technologies
Introduction
The modal frequency response is a computation procedure which is used to compute the response of a (acoustic or vibro-acoustic system) to a specific excitation using modal coordinates. This sequence performs a modal superposition at the specified frequencies . It requires a modal basis for the structure (in vacuo) and the cavity (rigid wall) to be available. The modal bases can be either computed with:
Vibro-Acoustic Modal Frequency Responses
ACTRAN Training – VIBRO
Copyright Free Field Technologies
Outline
Introduction General Structure of the Input File Modal Models Damping Boundary Conditions Launching Fluid/Structure Coupling Integration in ACTRAN/VI
Acoustic Damping
A global damping can be added to the cavity Use keyword GLOBAL_DAMPING 0.01 An imaginary part is added to the speed of sound (c.η). This parameter can be linked to the “PARAM GFL” used in Nastran according to the following relation (GFLvalue = 2.η).
⇒
4
Copyright Free Field Technologies
General Structure of the Input File
The input file can be seen as :
A list of references to several external existing meshes (structure, cavity, output points,…) A list of parameters definition for the computation (BCs, frequency range,…)
a mesh of the model a modal basis of the model
BEGIN CAVITY_MODEL FILENAME_RADICAL cavity/cavity FIRST_MODE_INDEX 0 NUMBER_OF_MODES 229 GLOBAL_DAMPING 0.05 MASS_UNIT 1000. LENGTH_UNIT 0.001 END CAVITY_MODEL BEGIN STRUCTURE_MODEL FILENAME_RADICAL struct/plate FIRST_MODE_INDEX 0 NUMBER_OF_MODES 145 GLOBAL_DAMPING 0.01 MASS_UNIT 1000. LENGTH_UNIT 0.001 END STRUCTURE_MODEL
Structure Cavity
The fluid-structure coupling coefficients are computed prior (-e
MODAL_COUPLING)
The final solution is obtained by the modal solver (--executionsequence= MODAL_SOLVER) : the following system of equation is solved at each frequency
7
Copyright Free Field Technologies
Damping
Structural Damping:
A global damping can be added to the structure Use keyword GLOBAL_DAMPING 0.01 Same damping as “PARAM G” in NASTRAN
A PID of 2D elements included in the cavity model file
BEGIN COUPLING 2 STRUCTURE CAVITY 1 END COUPLING 2
See detailed presentation on the fluid/structure coupling
Random
• Diffuse Sound Field • Turbulent Boundary Layer • Delta Correlated Excitation
The following boundary condition can be applied on the cavity
Spherical Source (Determinist) Acoustic Velocity
Structure modal damping
A modal damping can be applied to the structure by specifying an OP4 files (exported from NASTRAN) OP4 File specified by MODAL_DAMPING_FILE containing the requested modal damping coefficients
Define the frequency range
Define the boundary conditions
Define the output parameters
5
Copyright Free Field Technologies
Modal Models (1)
The modal model is characterized by
9
Copyright Free Field Technologies
Only the radical of is specified
Both modes and mesh files must have the same radical (ex: plate.bdf & plate.op2) Extension must be correctly defined to ensure a correct format recognition:
8
Copyright Free Field Technologies
Boundary Conditions Available
The following boundary conditions can be applied on the structure Determinist
• • • • • • Solid Acceleration Solid Velocity Solid Displacement Point Force Node Force Surface Load
ACTRAN (Modal Extraction calculation procedure) ANSYS NASTRAN (SOL 103)
A modal frequency response is activated through the main ACTRAN_MODAL data block. Remark : not all the boundary conditions are compatible with a modal frequency response analysis.
3
Copyright Free Field Technologies
System of Equations
The preliminary modal extractions provide the modes and the mass and stiffness matrices in the modal space
BEGIN ACTRAN_MODAL
Main data block: ACTRAN_MODAL Define the structure or cavity modal model through the STRUCTURE_MODEL or CAVITY_MODEL data block
BEGIN STRUCTURE_MODEL FILENAME_RADICAL structure FIRST_MODE_INDEX 0 NUMBER_OF_MODES 146 END STRUCTURE_MODEL BEGIN FREQUENCY_DOMAIN 10.0 5.0 1500.0 END FREQUENCY_DOMAIN BEGIN DIFFUSE_FIELD SOUND_SPEED 340.0 REFERENCE_PSD 1 STRUCTURE 2 END DIFFUSE_FIELD BEGIN OUTPUT_FRF output.plt END OUTPUT_FRF END ACTRAN_MODAL
The FILENAME_RADICAL defines the radical of files containing the finite element mesh and the modal basis Following formats are supported:
Modal Basis NASTRAN OP2 (*.op2) ANSYS RST (*.rst) ACTRAN OP2 (*.op2) Mesh NASTRAN BDF (*.bdf) ANSYS RST (*.rst) ACTRAN DAT (*.dat)
The external surface mesh defined by SURFACE_FILE. An optional list of PIDs can be specified to reduce the coupling to some domain of the mesh)
BEGIN COUPLING 1 STRUCTURE CAVITY SURFACE_FILE coupling_surface.dat 13 END COUPLING 1
Copyright Free Field Technologies
6
Fluid / Structure Coupling
When a cavity and a structure are involved, they can be coupled Cavity and structure meshes are always considered as incompatible The fluid/structure coupling is set through the COUPLING data block: STRUCTURE and CAVITY keyword must be present The surface over which the coupling occurs can be specified in two ways:
2
Copyright Free Field Technologies
Introduction
The modal frequency response is a computation procedure which is used to compute the response of a (acoustic or vibro-acoustic system) to a specific excitation using modal coordinates. This sequence performs a modal superposition at the specified frequencies . It requires a modal basis for the structure (in vacuo) and the cavity (rigid wall) to be available. The modal bases can be either computed with:
Vibro-Acoustic Modal Frequency Responses
ACTRAN Training – VIBRO
Copyright Free Field Technologies
Outline
Introduction General Structure of the Input File Modal Models Damping Boundary Conditions Launching Fluid/Structure Coupling Integration in ACTRAN/VI
Acoustic Damping
A global damping can be added to the cavity Use keyword GLOBAL_DAMPING 0.01 An imaginary part is added to the speed of sound (c.η). This parameter can be linked to the “PARAM GFL” used in Nastran according to the following relation (GFLvalue = 2.η).
⇒
4
Copyright Free Field Technologies
General Structure of the Input File
The input file can be seen as :
A list of references to several external existing meshes (structure, cavity, output points,…) A list of parameters definition for the computation (BCs, frequency range,…)
a mesh of the model a modal basis of the model
BEGIN CAVITY_MODEL FILENAME_RADICAL cavity/cavity FIRST_MODE_INDEX 0 NUMBER_OF_MODES 229 GLOBAL_DAMPING 0.05 MASS_UNIT 1000. LENGTH_UNIT 0.001 END CAVITY_MODEL BEGIN STRUCTURE_MODEL FILENAME_RADICAL struct/plate FIRST_MODE_INDEX 0 NUMBER_OF_MODES 145 GLOBAL_DAMPING 0.01 MASS_UNIT 1000. LENGTH_UNIT 0.001 END STRUCTURE_MODEL
Structure Cavity
The fluid-structure coupling coefficients are computed prior (-e
MODAL_COUPLING)
The final solution is obtained by the modal solver (--executionsequence= MODAL_SOLVER) : the following system of equation is solved at each frequency
7
Copyright Free Field Technologies
Damping
Structural Damping:
A global damping can be added to the structure Use keyword GLOBAL_DAMPING 0.01 Same damping as “PARAM G” in NASTRAN
A PID of 2D elements included in the cavity model file
BEGIN COUPLING 2 STRUCTURE CAVITY 1 END COUPLING 2
See detailed presentation on the fluid/structure coupling
Random
• Diffuse Sound Field • Turbulent Boundary Layer • Delta Correlated Excitation
The following boundary condition can be applied on the cavity
Spherical Source (Determinist) Acoustic Velocity
Structure modal damping
A modal damping can be applied to the structure by specifying an OP4 files (exported from NASTRAN) OP4 File specified by MODAL_DAMPING_FILE containing the requested modal damping coefficients
Define the frequency range
Define the boundary conditions
Define the output parameters
5
Copyright Free Field Technologies
Modal Models (1)
The modal model is characterized by
9
Copyright Free Field Technologies
Only the radical of is specified
Both modes and mesh files must have the same radical (ex: plate.bdf & plate.op2) Extension must be correctly defined to ensure a correct format recognition:
8
Copyright Free Field Technologies
Boundary Conditions Available
The following boundary conditions can be applied on the structure Determinist
• • • • • • Solid Acceleration Solid Velocity Solid Displacement Point Force Node Force Surface Load
ACTRAN (Modal Extraction calculation procedure) ANSYS NASTRAN (SOL 103)
A modal frequency response is activated through the main ACTRAN_MODAL data block. Remark : not all the boundary conditions are compatible with a modal frequency response analysis.
3
Copyright Free Field Technologies
System of Equations
The preliminary modal extractions provide the modes and the mass and stiffness matrices in the modal space
BEGIN ACTRAN_MODAL
Main data block: ACTRAN_MODAL Define the structure or cavity modal model through the STRUCTURE_MODEL or CAVITY_MODEL data block
BEGIN STRUCTURE_MODEL FILENAME_RADICAL structure FIRST_MODE_INDEX 0 NUMBER_OF_MODES 146 END STRUCTURE_MODEL BEGIN FREQUENCY_DOMAIN 10.0 5.0 1500.0 END FREQUENCY_DOMAIN BEGIN DIFFUSE_FIELD SOUND_SPEED 340.0 REFERENCE_PSD 1 STRUCTURE 2 END DIFFUSE_FIELD BEGIN OUTPUT_FRF output.plt END OUTPUT_FRF END ACTRAN_MODAL
The FILENAME_RADICAL defines the radical of files containing the finite element mesh and the modal basis Following formats are supported:
Modal Basis NASTRAN OP2 (*.op2) ANSYS RST (*.rst) ACTRAN OP2 (*.op2) Mesh NASTRAN BDF (*.bdf) ANSYS RST (*.rst) ACTRAN DAT (*.dat)
The external surface mesh defined by SURFACE_FILE. An optional list of PIDs can be specified to reduce the coupling to some domain of the mesh)
BEGIN COUPLING 1 STRUCTURE CAVITY SURFACE_FILE coupling_surface.dat 13 END COUPLING 1