当前位置:首页 >> 计算机软件及应用 >>

ABAQUS声学分析-acoustics-lecture4


Structural-Acoustic Analysis with ABAQUS

Lecture 4

深 圳 ABAQUS培 训 http://www.xncae.com 深 圳 ANSYS培 训 http://www.xncae.com 深 圳 ANSYS http://www.xn cae.co m 深 圳 ABAQUS http://www.xncae.com 深 圳 有 限 元 培 训 http://www.xncae.com ABAQUS培 训 http://www.xncae.com ANSYS培 训 http://www.xncae.com

Coupled Structural-Acoustic Analysis

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .2

Overview
? Introduction ? Near-Field and Far-Field Effects ? Fully Coupled Analysis ? Sequentially Coupled Analysis ? Acoustic-to-Structural Submodeling ? Coupled Acoustic-Structural Substructures ? Boundary Impedances ? Creating ASI elements on geometry ? Creating ASI elements on orphan meshes

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

Introduction

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .4

Introduction
? Structural-acoustic coupling – If the acoustic medium adjoins a structure, structural-acoustic coupling occurs at the interface. – The pressure field in the acoustic medium creates a normal surface traction on the structure. – The acceleration field in the structure creates the natural forcing term at the fluid boundary. ? Recall that volumetric acceleration is the conjugate of acoustic pressure in an acoustic analysis. Volumetric acceleration is what you apply as a concentrated load in an acoustic analysis.

– Generically, the acoustic and structural fields must be solved for simultaneously.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .5

Introduction
? Simplifications – In air the forces on structures caused by the air are usually weak. – In such a case, rather than performing a coupled analysis, you might model the effect of the structure on the acoustic fluid using boundary conditions or loads on the acoustic model. – The value of acoustic pressure can be specified directly (*BOUNDARY in an input file or use the ABAQUS/CAE Load module). ? This includes the case of complicated boundary pressure fields computed in a previous structural analysis – see ?Sequentially Coupled Analysis‘ below. – A concentrated volumetric acceleration can be specified (*CLOAD in an input file or use the ABAQUS/CAE Load module). – A distributed volumetric acceleration can be specified using the *INCIDENT WAVE options. ? Requires the use of the Keywords Editor in ABAQUS/CAE.
Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .6

Introduction
? Interface impedances – The structural-acoustic interface can have an impedance, Z, of its own. – This means that the relationship between the structural motion and the acoustic pressure need not be continuous:

1 ? m ? u f ) ? ? ? p. ? n ? (u ? ? ?Z?
? Used to include easily the effects of thin interface layers, such as carpet on the floor of a car, or the absorptive acoustic coating of a submarine.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

Near-Field and Far-Field Effects

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .8

Near-Field and Far-Field Effects
? Near and far fields

Air

Far field

Near field

Vibrating machine

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .9

Near-Field and Far-Field Effects
? Near field – The region within one wavelength of the interface is generally considered the near field. ? Near-field region shrinks with increasing frequency. – The near-field solution tends to be complicated. ? Includes ―evanescent‖ effects (effects that fade quickly). – In the near field the mesh has a strong effect on accuracy. – The element size on both sides of the interface is governed by the medium that requires the finer mesh.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .10

Near-Field and Far-Field Effects
? Far field – Beyond one wavelength the complexities of the near field diminish. – The near-field mesh has limited effect on far-field results. ? Whether or not the near-field mesh is refined often does not strongly affect the results away from the interface. – The mesh in the far field needs to be appropriate only for the material and the simulation requirements, as discussed in Lecture 3. – Unlike in static problems, in acoustic simulations the far field is oscillatory, not constant. ? The far-field mesh still needs to be fine enough to capture these waves.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .11

Near-Field and Far-Field Effects

Speaker with finely meshed air (left) and coarsely meshed air (right)

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

Fully Coupled Analysis

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .13

Fully Coupled Analysis
? When is fully coupled analysis appropriate? – Fully coupled analysis is the most general approach to structural-acoustic problems. – All problems can be solved appropriately using the fully coupled approach. – Makes no assumptions about which direction has the strongest coupling effects.

? Structural deformation ? Acoustic pressure
– A drawback of coupled analysis is that it can be unnecessarily expensive for large problems where the acoustic pressure has little effect on the structure.

? In these cases sequentially coupled analysis can be more efficient (discussed in the next section).

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .14

Fully Coupled Analysis
? Coupling with ASI (acousticstructural interface) elements

Air

– If the structural mesh and the acoustic mesh share nodes at their interface, lining the interface with ASI elements enforces the required coupling.
– While this approach is available, but the surfacebased approach is generally recommended.
Vibrating machine

ASI elements lining machine surface

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .15

Fully Coupled Analysis
– Coupling ? Accelerations at the ASI nodes induce acoustic pressures in the acoustic mesh. ? Acoustic pressures at the ASI nodes induce accelerations in the structural mesh. – Degrees of freedom

? ASI element degrees of freedom include translations (degrees of freedom 1, 2, 3) and acoustic pressure (degree of freedom 8).
? Boundary conditions can be applied to any of these degrees of freedom at the interface.

? Local structural rotations (degrees of freedom 4, 5, 6) are not coupled.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .16

Fully Coupled Analysis
– Element normals ? ASI element normals must point into the acoustic medium. ? For user-specified two- and three-dimensional ASI elements the normal directions are implicit in the node numbering. ? For one-dimensional user-specified ASI elements the normal direction must be specified on the data line of the *INTERFACE option.

– You can specify impedances (*IMPEDANCE, *SIMPEDANCE) at the interface to include surface treatment effects.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .17

Fully Coupled Analysis
– ABAQUS/CAE and ASI elements ? ASI elements cannot be created directly in ABAQUS/CAE. However…

– A special technique using "skins" and the Keywords Editor can be employed to create ASI elements from within ABAQUS/CAE for axisymmetric and 3D geometries.
? 2D planar geometries must be addressed manually.

– If the underlying solid elements are tetrahedral, the triangular skin elements must be converted into degenerated quadrilateral elements. This may done done, e.g., with a script.
– This details of this technique will be outlined later.

? The recommended approach when using ABAQUS/CAE, however, is to use surface-based TIE constraints to enforce the coupling.
– This is discussed next. – The exception is acoustic submodeling, where ASI elements are required.
Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .18

Fully Coupled Analysis
? Surface-based interfaces – Do not require the structural and acoustic meshes to match at the interface. – The structural and acoustic meshes have separate nodes at the interface. – You define separate surfaces on the structural and acoustic meshes at the interface. ? Essentially the same approach as defining contact between two surfaces. – Can be modeled directly in ABAQUS/CAE: Create an assembly with an acoustic part and a solid part, and use TIE constraints. – The internally generated ASI elements will have the correct normal directions automatically.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .19

Fully Coupled Analysis
– Usage: You define a TIE constraint between the two surfaces using:
*TIE, NAME=tie_interaction_name1

slave surface, master surface ? Automatically couples the structural accelerations and the acoustic pressures at the interface in the same way as ASI elements. ? Acoustic pressure boundary conditions (degree of freedom 8) can be applied to nodes on the surface of the acoustic mesh. ? Translation boundary conditions (degrees of freedom 1, 2, 3) can be applied to the surface of the structural mesh.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .20

Fully Coupled Analysis
– Example: Acoustic radiation of a muffler
*TIE, NAME=MUFFLER_AIR

INT_AIR, MUFFLER_INT
OUT_AIR, MUFFLER_EXT
The material with the lower wave speed generally should be more refined and, therefore, should be the slave surface.

MUFFLER_INT: interior MUFFLER_EXT: exterior

INT_AIR

OUT_AIR (only half the surface is shown)

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .21

Fully Coupled Analysis
– Example: Truck cab analysis

CAB-INSIDE

Inside-air

*TIE, POSITION TOLERANCE=0.01, ADJUST=NO Inside-air, CAB-INSIDE

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .22

Fully Coupled Analysis
– Master and slave surfaces ? Either surface can be slave or master, but the choice affects the accuracy of the solution. – Mesh refinement depends on the wave speeds of the two materials meeting at the interface. – The material with the lower wave speed generally should be more refined and, therefore, should be the slave surface. – If solution details near the interface are important, the meshes on either side should be refined equally corresponding to the requirements of the lower wave speed material.

? In this case choice of the slave and master are arbitrary.
? Exception: Fluids coupled to both sides of a shell or beam. At least one of the surfaces of the solid must be a master surface.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

Sequentially Coupled Analysis

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .24

Sequentially Coupled Analysis
? When is sequentially coupled analysis appropriate?

– When the normal surface traction exerted on the structure created by the acoustic fluid is negligible compared to the other forces on the structure.
? Example: Vibrating machine radiates sound to the air, but the reaction pressure of the air on the machine may be insignificant to the analysis.
Machine vibrating in a room

Air

Vibrating machine

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .25

Sequentially Coupled Analysis
? Sequentially coupled analysis – In these cases the structural analysis can be performed first (uncoupled from the fluid). – The acoustic analysis follows, driven by the structure at the interface. – Solving the problem in two distinct analyses decouples the solution. – The decoupling reduces computational cost, especially for large problems.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .26

Sequentially Coupled Analysis
? Submodeling – Submodeling is the approach used to drive the acoustic analysis with the results of the structural analysis. – The term submodeling refers to the technique of using a coarse global solution to drive a refined local analysis. In acoustics we use the same technique, although the application is different.

? The first analysis—which includes the structure—supplies the global model.
? The second analysis—which includes an acoustic fluid—supplies the submodel.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .27

Sequentially Coupled Analysis
? Global model – This analysis includes the structure. – Example: In the case of the vibrating machine the global model contains the machine only.

Global model: vibrating machine only

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .28

Sequentially Coupled Analysis
– Example: Acoustic Radiation of a Muffler

? The global model contains the interior air of the muffler and the muffler structure.
? The two domains are coupled using TIE constraints. ? The relevant material properties and boundary conditions used in the fully-coupled analysis model are also used in this model. ? A single step invoking the direct steady-state dynamics procedure is used.
Shell model of the muffler

Acoustic model of the internal air

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .29

Sequentially Coupled Analysis
– The displacement results of the global analysis must be saved to the output database (.odb) or results (.fil) file at the structural-acoustic interface. – Examples: ? Vibrating machine analysis: The nodes at the interface are the exterior nodes of the machine. ? Muffler analysis: The nodes at the interface are all nodes on the muffler shell structure.
*NSET, NSET=muffler :
*OUTPUT, FIELD *NODE OUTPUT, NSET=muffler U,
Copyright 2005 ABAQUS, Inc.

For .fil file output use: *NODE FILE, NSET=muffler U,

Structural-Acoustic Analysis with ABAQUS

L4 .30

Sequentially Coupled Analysis
? Submodel – In the submodel analysis only the acoustic domain is modeled. – The interface with the location of the structural model (modeled in the previous, global analysis) is lined with ASI elements. ? The surface-based approach is not available to drive a sequentially coupled analysis.

? A technique to create ASI elements from within ABAQUS/CAE will be described later.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .31

Sequentially Coupled Analysis
– The mesh of the acoustic fluid need not match the mesh of the structure in the previous, global analysis.

? The submodeling capability interpolates structural displacements saved from the global, structural analysis and applies them to the driven nodes in the submodel analysis.

Submodel (acoustic and ASI elements)

Global model (solid or structural elements)

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .32

Sequentially Coupled Analysis
– Example (cont'd) ? In submodel analysis:
*NSET, NSET=muffler **driven nodes must be on the ASI *SUBMODEL, EXTERIOR TOLERANCE=0.05 muffler *BOUNDARY, SUBMODEL, STEP=1 muffler, 1, 3

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .33

Sequentially Coupled Analysis
? Execution procedure for submodel analysis:
abaqus job=submodel job name globalmodel=global job name (with either .odb or .fil extension)

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .34

Sequentially Coupled Analysis
Fully coupled analysis
Excitation frequency 170 Hz

Sequentially coupled analysis

Acoustic pressure in internal air Global model

Induced displacements in muffler body

Acoustic pressure in external air CPU time: 465 sec (NT)
Copyright 2005 ABAQUS, Inc.

Submodel

CPU time: 60 + 88 = 148 sec (NT)

Structural-Acoustic Analysis with ABAQUS

L4 .35

Sequentially Coupled Analysis
– Is sequential analysis appropriate? ? If sequential analysis is appropriate for a given problem, the effect of the global model on the submodel is nearly the same as the effect of the structure on the acoustic fluid in a fully coupled single analysis. ? In the case of the muffler analysis the peak pressure in the fully and sequentially coupled results differs by approximately 10%.

Fully coupled

Sequentially coupled

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

Acoustic-to-Structural Submodeling

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .37

Acoustic-to-Structural Submodeling
– Another application of submodeling in acoustics involves situations where the structural response is of primary interest and the presence of the (heavy) fluid is required mainly for the application of the load onto the structure. ? The global model is a coupled structural-acoustic analysis ? The submodel is an uncoupled structural force-displacement analysis

? Interpolated acoustic pressures are converted to concentrated loads
? Driven nodes are specified by defining an element-based surface ? Shell surfaces can be driven on both sides by different acoustic domains

? Usage:
*SUBMODEL, ACOUSTIC TO STRUCTURE

surface_name
*BOUNDARY,SUBMODEL, STEP=n node_set, 8

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .38

Acoustic-to-Structural Submodeling
? Example: Submerged submarine – The acoustic field obtained from the global coupled analysis drives submodel structural analysis. – Detailed analysis can then be performed of critical components, e.g., for shock testing. – The method is suited for design sensitivity analysis: the fluid mesh needed only once.
Global model With fluid mesh

Submodel (exterior) - no fluid mesh

Submodel (interior)

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

Coupled Acoustic-Structural Substructures

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .40

Coupled Acoustic-Structural Substructures
– Substructures may be generated in ABAQUS/Standard from models which include acoustic elements. – The retained degrees of freedom must be displacements and rotations. – At right, a simple tire (orange) and air (blue) system forms a substructure with retained nodes.
Air Tire

Retained nodes

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .41

Coupled Acoustic-Structural Substructures
– In a static analysis involving a substructure containing acoustic elements, the results will differ from the results obtained in an equivalent static analysis without substructures. ? The acoustic-structural coupling is taken into account in the substructure (leading to hydrostatic contributions of the acoustic fluid), while the coupling is ignored in a static analysis without substructures. – Coupled acoustic-structural substructures should not be used in geometrically nonlinear analyses.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

Boundary Impedances

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .43

Boundary Impedances
? Default behavior (no boundary impedance) – The fluid particle and the structural motions are equal. – The fluid pressures act directly on the structural body. – The structural displacements/accelerations directly induce pressure gradients on the fluid. – Energy and momentum losses are zero.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .44

Boundary Impedances
? Boundary impedance (Z) – Specifies the relationship between the pressure of the acoustic medium and the normal motion at the interface:

Z?

p ? u

1 1 ? ? ?i , Z (?) c1 k1
where k1 (c1 ) is the proportionality factor between the pressure and the normal component of the surface displacement (velocity), and ? is the angular frequency.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .45

Boundary Impedances
? Nonzero boundary impedances – Provide a relationship between the pressure and the particle velocity on the acoustic fluid side of the interface. – The model is analogous to a spring and dashpot in series between the fluid medium and the structure. ? Energy dissipates in proportion to c1. ? Phase lag between velocity and pressure is in proportion to k1.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .46

Boundary Impedances
– Can model the surface effects of small-amplitude ―sloshing‖ of the liquid medium.

? Vibrations in the ―air‖ side of the interface dissipate additional energy associated with displacing the liquid against gravity.
? Boundary impedance can be used to model this effect by setting the impedance equal to the density times the gravity constant, ? g. – Can model the effect of a compressible, possibly dissipative, lining (for example, carpet) between the acoustic medium and the structure.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .47

Boundary Impedances
? Impedance properties – The impedance material properties are based on measurements of the absorbing characteristics of the structural surface. – They are applied using *IMPEDANCE PROPERTY and then *IMPEDANCE for use with ASI elements or *SIMPEDANCE for use with surface-based interfaces.

? For steady-state analysis the impedance interface properties are given as functions of frequency.
? For transient analysis the impedance interface properties are given as single values.

– Since surface impedances are not considered in a frequency extraction analysis, *FREQUENCY and *STEADY STATE DYNAMICS, SUBSPACE PROJECTION are not recommended when the interfaces have strong absorbing impedances.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .48

Boundary Impedances
– Usage: ASI-based interface ? Model data:
*ELSET, ELSET=CARPET1

element numbers
*IMPEDANCE PROPERTY, NAME=CARPET_PROP

1/k1, 1/c1, frequency 1 1/k1, 1/c1, frequency 2
...

? History data:
*IMPEDANCE CARPET1, In, CARPET_PROP

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .49

Boundary Impedances
– Usage: surface-based interface ? Model data:
*SURFACE, NAME=CARPET2

carpet element set name
*IMPEDANCE PROPERTY, NAME=CARPET_PROP

1/k1, 1/c1, frequency 1

1/k1, 1/c1, frequency 2
...

? History data:
*SIMPEDANCE

CARPET2, CARPET_PROP

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

Creating ASI elements on geometry

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .51

Creating ASI elements on geometry
? Steps for creating ASI elements on geometry from within ABAQUS/CAE 1. In the Property module, create a skin on the solid geometry. This requires: a. Creating a ―dummy‖ material. b. Creating a ―dummy‖ shell section property. c. Creating a skin.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .52

Creating ASI elements on geometry
2. Create a part-level ―skin‖ set containing the skin region. This requires using the Selection Options tool in the prompt area.

3. If the geometry is 3D, flip the normal direction of the skins so that the normal points into the solid (select Assign?Normal and click Sets in the prompt area; choose the skin set).
The color brown indicates positive side of shell region: normal points outward The color purple indicates negative side of shell region: normal points inward

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .53

Creating ASI elements on geometry
4. Set the geometric order of the skin elements to match that of the underlying solid elements (select Mesh?Element Type and click Sets in the prompt area; choose the skin set). For example, if using AC3D20 elements for the acoustic domain, use quadratic elements. The element family is irrelevant.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .54

Creating ASI elements on geometry
5. Edit the model keywords and change the element type and section property:
Old SAX1 SAX2 S3/S3R S4R STRI65 New ASI2A ASI3A ASI4* ASI4 ASI8*

S8R
*Shell section

ASI8
*Interface

*Also requires changing the element connectivity from a triangle to a degenerate quad.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .55

Creating ASI elements on geometry
6. Change the element connectivity from a triangle to a degenerated quad (if using tet elements):

Tet elements are lined with triangular skin (i.e., shell, membrane, or surface) elements. Since ABAQUS does not offer triangular ASI elements, the skin element connectivity must be converted from a triangle to a degenerate quad.
Scripting example:
*Element, type=ASI4 41232, 7, 213, 41233, 30, 7, 41234, 28, 9, :

224 224 10

: newdataline = dataline[0] + ',' \ + dataline[1] + ',' + dataline[2] + ',' \ + dataline[3] + ',' + dataline[1] + newLine :

*Element, type=ASI4 41232, 7, 213, 41233, 30, 7, 41234, 28, 9, :

224, 224, 10,

7 30 28

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .56

Creating ASI elements on geometry
– A script is available to automate the conversion of triangles into degenerated quadrilaterals.

? The script is called ws_degenASI.py; to obtain this script, use the ABAQUS fetch utility:
abaqus fetch job=ws_degenASI.py

? If you are transferring the input file from a Windows platform to a Unix platform, you must first run the script ws_fixnt.py to remove the ^M characters. – This script is also available using the ABAQUS fetch utility:
abaqus fetch job=ws_fixnt.py

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

Creating ASI elements on orphan meshes

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .58

Creating ASI elements on orphan meshes
? Steps for creating ASI elements on orphan meshes from within ABAQUS/CAE

1. In the Property module, create a skin on the orphan mesh. This requires:
a. Creating a ―dummy‖ material. b. Creating a ―dummy‖ shell section property. c. Creating a skin.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .59

Creating ASI elements on orphan meshes
2. In the Mesh module, create a new orphan mesh (select Mesh?Create Mesh Part). Return to the Property module and make the new orphan mesh part current; assign section properties to the skin region of this part. 3. If the solid elements are 3D, flip the normal direction of the skins so that the normal points into the solid (select Assign?Normal and select the region with the skins directly in the viewport; use the Selection Options tool as necessary).
The color brown indicates positive side of shell region: normal points outward The color purple indicates negative side of shell region: normal points inward

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .60

Creating ASI elements on orphan meshes
4. Replace the part instance created with the original orphan mesh with a part instance based on the new orphan mesh.

5. In the Mesh module, set the geometric order of the skin elements to match that of the underlying solid elements (select Mesh?Element Type and choose the skin region directly in the viewport; use the Selection Options tool as necessary).
For example, if using AC3D10 elements for the acoustic domain, use quadratic elements. The element family is irrelevant.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .61

Creating ASI elements on orphan meshes
6. Edit the model keywords and change the element type and section property:
Old SAX1 SAX2 S3/S3R S4R STRI65 New ASI2A ASI3A ASI4* ASI4 ASI8*

S8R
*Shell section

ASI8
*Interface

*Also requires changing the element connectivity from a triangle to a degenerate quad.

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .62

Creating ASI elements on orphan meshes
7. Change the element connectivity from a triangle to a degenerated quad (if using tet elements):

Tet elements are lined with triangular skin (i.e., shell, membrane, or surface) elements. Since ABAQUS does not offer triangular ASI elements, the skin element connectivity must be converted from a triangle to a degenerate quad.
Scripting example:
: newdataline = + + + + : *Element, type=ASI8 41232, 213, 224, 7, 9998, 9997, 9996 41233, 7, 224, 30, 9997, 13686, 13685 41234, 9, 10, 28, 10138, 13742, 13692 : dataline[2] dataline[1] dataline[5] dataline[1] + + + + ',' \ ',' \ ',' \ newLine

dataline[0] dataline[1] dataline[3] dataline[4] dataline[6]

+ + + + +

',' ',' ',' ',' ','

\ + + + +

*Element, type=ASI8 41232, 213, 224, 7, 213, 9998, 9997, 9996, 213 41233, 7, 224, 30, 7, 9997, 13686, 13685, 7 41234, 9, 10, 28, 9, 10138, 13742, 13692, 9 :

Copyright 2005 ABAQUS, Inc.

Structural-Acoustic Analysis with ABAQUS

L4 .63

Creating ASI elements on orphan meshes
– A script is available to automate the conversion of triangles into degenerated quadrilaterals.

? The script is called ws_degenASI.py; to obtain this script, use the ABAQUS fetch utility:
abaqus fetch job=ws_degenASI.py

? If you are transferring the input file from a Windows platform to a Unix platform, you must first run the script ws_fixnt.py to remove the ^M characters. – This script is also available using the ABAQUS fetch utility:
abaqus fetch job=ws_fixnt.py

Copyright 2005 ABAQUS, Inc.


相关文章:
ABAQUS声学分析-acoustics-lecture5.ppt
ABAQUS声学分析-acoustics-lecture5_计算机软件及应用_I
ABAQUS声学分析-acoustics-lecture6.ppt
ABAQUS声学分析-acoustics-lecture6_计算机软件及应用_I
Abaqus 声学分析.doc
Abaqus 声学分析 - Abaqus 声学分析 Airmage 1. 1)
Abaqus-声学分析.doc
Abaqus-声学分析_机械/仪表_工程科技_专业资料。Abaqus 声学分析 Airmage 1. 1) 2) 3) 4) 5) 6) 7) 8) 要点 基本物理量 实例模型说明 材料属性设定 ...
Acoustic Analysis in Abaqus声学仿真_图文.pdf
ABAQUS声学分析,2011年 Acoustic Analysis in Abaqus ...change Improving Acoustic Performance Acoustics ...AC3D4 elements (inner), 73833 AC3D4 elements(...
ABAQUS声学问题-屈曲,后屈曲与ABAQUS倒塌分析_图文.ppt
ABAQUS声学问题-屈曲,后屈曲与ABAQUS倒塌分析_电力/水利_工程科技_专业资料。...Lecture 3 ? Workshop 2 ? Lecture 4 ? Workshop 3 Static Postbuckling ...
lecture4-lecture1-ABAQUS教程第四讲.pdf
lecture4-lecture1-ABAQUS教程第四讲 - ABAQUS中的多步骤分析 第四讲 Copyright 2006 ABAQUS, Inc. 概述 ? 多步骤分析 ? ABAQ...
Abaqus模块介绍.pdf
4 Abaqus/Explicit 中的自适应网格功能使之能够模拟大量的材料发生严重变形的问题, 例如金属成型的 问题。声学功能提供瞬态声固耦合分析,例如潜水艇在冲击载荷作用下...
flueng acoustics modeling_fluent 声学分析教程.ppt
4 / 45 ? Fluent Inc. 12/15/2010 Fluent User Services Center www.fluent...ABAQUS声学分析-acousti... 71页 免费 acoustics fluent simul... 暂无评价 115...
acoustics-lecture1_图文.ppt
acoustics-lecture1 - Structural-Acoustic Analysis with ABAQUS Lecture 1 Introduction Copyright...
更多相关标签: