FLUID221

3D 10-Node Acoustic Fluid

FLUID221 Element Description

FLUID221 is a higher order 3D 10-node element that exhibits quadratic 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.

Figure 221.1: FLUID221 Geometry

FLUID221 Input Data

The geometry, node locations, and coordinate system for this element are shown in Figure 221.1: FLUID221 Geometry. The element is defined by 10 nodes, a reference pressure, and the isotropic material properties.

A summary of the element input is given in "FLUID221 Input Summary". For more details, see Acoustic Element Input. A general description of element input is given in Element Input.

FLUID221 Input Summary

Nodes

I, J, K, L, M, N, O, P, Q, R

Degrees of Freedom

UX, UY, UZ, PRES if KEYOPT(2) = 0 or 8

PRES if KEYOPT(2) = 1 or 9

ENKE if KEYOPT(2) = 4

VX, VY, VZ, UX, UY, UZ, TEMP, PRES if KEYOPT(2) = 5

VX, VY, VZ, TEMP, PRES if KEYOPT(2) = 6

UX, UY, UZ, PRES if KEYOPT(2) = 7

VX, VY, VZ, PRES, ENKE if KEYOPT(4) = 3 or 4

Real Constants

PREF -- Reference pressure

PSREF -- Reference static pressure

Material Properties

DENS, SONC, VISC, KXX, C, CVH, BVIS, EX, GXY, BETA, SDIF (MP command)

PERF, AFDM (TB command)

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); viscous-thermal boundary layer (BLI); port (PORT); rigid wall (RIGW); viscous impedance (VIMP); thermal impedance (TIMP); pressure (PRES); heat flux (CONV); permeability (PERM):

face 1 (J-I-K), face 2 (I-J-L), face 3 (J-K-L), face 4 (K-I-L)

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); mean flow velocity (VMEN); force potential (UFOR); shear force (SFOR); volumetric heat source (HFLW)

Special Features

Linear perturbation

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 FSI
1 --: Uncoupled acoustic element without FSI
4 --: Diffusion element for room acoustics
5 --: Coupled viscous-thermal acoustic element with FSI
6 --: Uncoupled viscous-thermal acoustic element without FSI
7 --: Poroelastic element for poroelastic acoustics
8 --: Coupled nonlinear acoustic element
9 --: Uncoupled nonlinear acoustic element

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
2 --: Include IPML absorbing condition in a modal or harmonic analysis
3 --: Include PML absorbing condition in a transient analysis
4 --: Include IPML absorbing condition in a transient analysis

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

FLUID221 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 221.1: FLUID221 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 221.1: FLUID221 Element Output Definitions

Name	Definition	O	R
EL	Element Number	Y	Y
NODES	I, J, K, L, M, N, O, P, Q, R	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(R)	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 (not available for viscous-thermal acoustics) 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

Available only at centroid as a *GET item.
Output only if ANTYPE,HARMIC or MODAL, and invalid with SET,,,,AMPL or 3.
Available only for equivalent fluid model, and invalid with SET,,,,AMPL or 3.

Table 221.2: FLUID221 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 221.2: FLUID221 Element Item and Sequence Numbers:

Name: output quantity as defined in the Table 221.1: FLUID221 Element Output Definitions
Item: predetermined Item label for ETABLE command
E: sequence number for single-valued or constant element data

Table 221.2: FLUID221 Element Item and Sequence Numbers

Output Quantity Name	ETABLE and ESOL Command Input
Output Quantity Name	Item	E
PGX	SMISC	1
PGY	SMISC	2
PGZ	SMISC	3
PL2	SMISC	4
DENSRE	SMISC	5
DENSIM	SMISC	6
SONCRE	SMISC	7
SONCIM	SMISC	8
POUT	SMISC	9
PINC	SMISC	10
PRESSURE	NMISC	1
PGSUM	NMISC	2

FLUID221 Assumptions and Restrictions

The element must not have a zero volume.
The element nodes should be numbered as shown in Figure 221.1: FLUID221 Geometry. All elements must have 10 nodes
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 lumped mass matrix formulation (LUMPM,ON) is not valid for this element.

FLUID221 Product Restrictions

There are no product-specific restrictions for this element.