FLUID243
2D 4-Node Acoustic Fluid
FLUID243 Element Description
FLUID243 is a lower order 2D 4-node element that exhibits linear pressure behavior. Use it for modeling acoustic phenomena in the fluid medium and the interface in fluid-structure interaction problems.
For more information on acoustic element usage, see Elements for Acoustic Analysis.
FLUID243 Input Data
The geometry, node locations, and coordinate system for this element are shown in Figure 243.1: FLUID243 Geometry. The element is defined by 4 nodes, a reference pressure, and the isotropic material properties.
A summary of the element input is given in "FLUID243 Input Summary". For more details, see Acoustic Element Input. A general description of element input is given in Element Input.
FLUID243 Input Summary
- Nodes
I, J, K, L
- Degrees of Freedom
UX, UY, PRES if KEYOPT(2) = 0 or 8 PRES if KEYOPT(2) = 1 or 9 ENKE if KEYOPT(2) = 4 VX, VY, PRES, ENKE if KEYOPT(4) = 3 or 4 - Real Constants
PREF -- Reference pressure PSREF -- Reference static pressure - Material Properties
- Surface Loads
Fluid-structure interface (FSI) flag; impedance (IMPD); normal speed or normal acceleration (SHLD); sloshing surface (FREE); equivalent source surface (MXWF); Robin boundary surface (INF); absorption coefficient (ATTN); port (PORT); rigid wall (RIGW); permeability (PERM):
face 1 (I-J), face 2 (J-K), face 3 (K-L), face 4 (L-I) - Body Loads
Mass source, mass rate, or power source (MASS); static pressure (SPRE); impedance (IMPD); temperature (TEMP); velocity or acceleration (VELO); interior port (PORT); Floquet periodic boundary condition (FPBC)
- Special Features
- KEYOPT(1)
Specific algorithm options:
- 0 --
FSI present in the model (unsymmetric element matrices) (default)
- 2 --
FSIs present in the model for full harmonic analysis (symmetric element matrix)
- 3 --
Deactivate the diagonalization of the damping matrix in a diffusion analysis
- 4 --
Activate the velocity potential formulation in a transient analysis
- KEYOPT(2)
Acoustic element types:
- 0 --
Coupled acoustic element with FSIs
- 1 --
Uncoupled acoustic element without FSIs
- 4 --
Diffusion element for room acoustics
- 8 --
Coupled nonlinear acoustic element
- 9 --
Uncoupled nonlinear acoustic element
- KEYOPT(3)
Specify 2D axisymmetric model:
- 0 --
2D plane model (default)
- 1 --
2D axisymmetric model
- KEYOPT(4)
Perfectly matched layers (PML) or irregular perfectly matched layers (IPML) absorbing condition:
- 0 --
Do not include any PML or IPML absorbing condition
- 1 --
Include PML absorbing condition in a modal or harmonic analysis (Modal analysis is invalid with the axisymmetric option)
- 2 --
Include IPML absorbing condition in a modal or harmonic analysis (This option is invalid with the axisymmetric option)
- 3 --
Include PML absorbing condition in a transient analysis (This option is invalid with the axisymmetric option)
- 4 --
Include IPML absorbing condition in a transient analysis (This option is invalid with the axisymmetric option)
- KEYOPT(5)
Acoustic element morphing control:
- 0 --
Element can be morphed during the structural static solution
- 1 --
Element will not be morphed during the structural static solution
- KEYOPT(6)
Fluid property control:
- 0 --
Compressible fluid
- 1 --
Incompressible fluid
FLUID243 Output Data
The solution output associated with the elements consists of the following:
Nodal degree of freedom included in the overall nodal solution.
Nodal sound pressure level (SPL) and A-weighted SPL.
Nodal velocity is included in the element corner node solution and accessed via standard output commands with
Item= PG (for example, PRNSOL, PLVECT, PRESOL, and PLESOL).Nodal energy density flux for room acoustics is included in the element corner node solution and accessed via standard output commands with
Item= PG (for example, PRNSOL, PLVECT, PRESOL, and PLESOL).Nodal sound intensity is included in the element corner node solution and accessed via standard output commands with
Item= SNDI (for example, PRNSOL, PLVECT, PRESOL, and PLESOL).Additional element output as shown in Table 243.1: FLUID243 Element Output Definitions.
A general description of solution output is given in Solution Output. See the Basic Analysis Guide for ways to view results.
The Element Output Definitions table uses the following notation:
A colon (:) in the Name column indicates that the item can be accessed by the Component Name method (ETABLE, ESOL). The O column indicates the availability of the items in the file jobname.out. The R column indicates the availability of the items in the results file.
In either the O or R columns, “Y” indicates that the item is always available, a letter or number refers to a table footnote that describes when the item is conditionally available, and “-” indicates that the item is not available.
Table 243.1: FLUID243 Element Output Definitions
| Name | Definition | O | R |
|---|---|---|---|
| EL | Element Number | Y | Y |
| NODES | I, J, K, L | Y | Y |
| MAT | Material number | Y | Y |
| VOLU: | Volume | Y | Y |
| XC, YC, ZC | Location where results are reported | Y | 1 |
| TEMP | T(I), T(J), …, T(L) | Y | Y |
| PRESSURE |
Average pressure or Average acoustic energy density in room acoustics | Y | Y |
| PG(X, Y, Z, SUM) |
Velocity components and vector sum or Energy density flux components and vector sum for room acoustics | Y | Y |
| PL2 | Square of the L2 norm of pressure over element volume | 2 | 2 |
| DENSRE | Real part of complex effective density | 2 | 2 |
| DENSIM | Imaginary part of complex effective density | 3 | 3 |
| SONCRE | Real part of complex effective sound velocity | 2 | 2 |
| SONCIM | Imaginary part of complex effective sound velocity | 3 | 3 |
| POUT | Output sound power | 2 | 2 |
| PINC | Input sound power | 2 | 2 |
| KENE | Acoustic kinetic energy | Y | Y |
| MENE | Acoustic potential energy | Y | Y |
Table 243.2: FLUID243 Element Item and Sequence Numbers lists output available through the ETABLE command using the Sequence Number method. See The General Postprocessor (POST1) in the Basic Analysis Guide and The Item and Sequence Number Table of this reference for more information. The following notation is used in Table 243.2: FLUID243 Element Item and Sequence Numbers:
- Name
output quantity as defined in the Table 243.1: FLUID243 Element Output Definitions
- Item
predetermined Item label for ETABLE command
- E
sequence number for single-valued or constant element data
FLUID243 Assumptions and Restrictions
The element must not have a zero volume.
The element nodes can be numbered either as shown in Figure 243.1: FLUID243 Geometry or may have faces IJ and KL interchanged. All elements must have 4 nodes. A triangle-shaped element can be formed by defining duplicate K and L nodes. (See Degenerated Shape Elements.)
The element may not be twisted such that it has two separate volumes. Such a case typically occurs when the element nodes are not in the correct sequence.
The acoustic pressure in the fluid medium is determined by the wave equation with the following assumptions:
The acoustic pressure is considered to be the excess pressure from the mean pressure.
Analyses are limited to relatively small acoustic pressures so that the changes in density are small compared with the mean density.
The mean flow effect is not valid for this element. Therefore, the VMEN and UFOR body load labels (BF command) are not applicable.
The boundary layer impedance model is not valid for this element. Therefore, the BLI surface load label (SF command) is not applicable.
Viscous-thermal acoustics is not valid for this element. Therefore, the following surface load and body load labels are not applicable:
Poroelastic acoustics is not valid for this element.
The lumped mass matrix formulation (LUMPM,ON) is not valid for this element.