PACPML

Bulk Data Entry Defines the properties of acoustic Adaptive Perfectly Matched Layer (APML) elements.

Format

(1)	(2)	(3)	(4)	(5)	(7)
PACPML	`PID`	`MID`	`MODINT`
	`ESBYL`	`TBYL`	`MESHG`	`MESHM`	`DBNAME`
	`EPS`	`XP`	`YP`	`ZP`
	`MFID`	`NBND`	`BNDTYP`	`ADAPF`

Example

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
PACPML	7	1	4

Definitions

Field	Contents	SI Unit Example
`PID`	Unique property identification number. No default (Integer > 0)
`MID`	Material identification number of a MAT10 material entry. No default (Integer > 0)
`MODINT`	Modified integration element formulation option. 2 0 (Default) Regular element formulation is used. 1 Modified element formulation is used.
`ESBYL`	Number of adaptively meshed elements to be present in the minimum wavelength of each frequency band. Default = 4.0 (Real)
`TBYL`	Ratio of the thickness of each PML layer to the maximum wavelength of the frequency band. Default = 1.0 (Real)
`MESHG`	Maximum Ratio between element size of a neighboring element and the size of a particular element. This option allows you to control neighboring element sizes to prevent poor meshes for PML computations. Default = 2.0 (Real)
`MESHM`	Meshing method to be chosen for adaptive meshing. TET(Default) Tetrahedral elements blank
`DBNAME`	Database file name which is used to save meshes generated during the APML process. Default = pml_DB (Character)
`EPS`	Regularization parameter for distance field computation. Default = 0.001 (Real)
`XP`, `YP`, `ZP`	Coordinates of the pole of the APML acoustic elements (defined in the basic coordinate system). Default = Center of Gravity of PML layer (Real)
`MFID`	Identification number of a MESHF Bulk Data Entry, which manually identifies the frequency bands for adaptive mesh generation. Default = Blank (Integer)
`NBND`	Number of frequency bands in the range of frequencies (from the minimum to maximum frequency in the range). Default = Blank (Integer)
`BNDTYP`	Scaling type to be used for frequency bands. 5 LIN (Default LOG ALOG
`ADAPF`	Adaptive factor for generation of frequency bands (ratio between the maximum and minimum frequency for each band). Default = 1.2 (Real)

Comments

Adaptive Perfectly Matched Layer (APML) mesh at the outer boundary of the acoustic domain ensures the following conditions are satisfied:
- Acoustic waves at the interface do not get reflected.
- Waves which pass through this layer are attenuated.
Direct and Modal Frequency Response Analysis are currently supported.
The four continuation lines in this PACPML entry allow the definition of the following characteristics:
- Line 1 – Definition and element formulation.
- Line 2 – Adaptive APML mesh generation properties.
- Line 3 – Distance field computation (determines the complex coordinate stretch direction).
- Line 4 – Defines the frequency bands.
The modified integration flag in MODINT may be turned on to reduce the dispersion error (which is the error in the computed wavelength, measured relative to the actual wavelength, for an acoustics solution).
Adaptive meshing is automatically carried out either via HyperMesh or SimLab to generate the domain of the perfectly matched layer. It may be inefficient to generate a single PML mesh for the entire frequency range, as this mesh would be constrained to handle the full range of loading frequencies (from the lowest to the highest). A single mesh which handles the complete range of frequencies may lead to a very thick PML mesh layer and at the same time, a very fine mesh. Therefore, it is a good practice to divide the frequency range for mesh generation into multiple frequency bands. Likewise, it is not an efficient practice to generate one PML mesh for every single frequency of analysis.
A single adaptive mesh is generated per frequency band.
The regularization parameter is employed along with the pole in conjunction with the gradient of the distance field to determine the direction of the complex coordinate stretch.
The order of priority for frequency band generation is MFID > (NBND+BNDTYP) > ADAPF. If none of them are input, then the default of ADAPF = 1.2 is applied.
The NBND and BNDTYP fields provide a way to determine the frequency bands based on the following:
Where:

$N$

Number of bands (NBND)

$(F_{i}, F_{i + 1}]$ where $i = 1, 2, 3, ..., N$

Frequency bands

$F_{1}$ and $F_{N + 1}$

Minimum and maximum loading frequencies
Then based on the band distribution type (BNDTYP), the frequency bands are generated as:
- Linear (BNDTYP=LIN) provides equal spacing for frequency bands.(1)
  $F_{i} = F_{1} + \frac{i - 1}{N} (F_{N + 1} - F_{1})$
- Logarithmic (BNDTYP=LOG) provides larger spacing at higher frequencies.(2)
  $F_{i} = F_{1} {(\frac{F_{N + 1}}{F_{1}})}^{(\frac{i - 1}{N})}$
- Anti-logarithmic (BNDTYP=ALOG) provides larger spacing at lower frequencies.(3)
  $F_{i} = \log 10 [10^{F_{1}} + \frac{i - 1}{N} (10^{F_{N + 1}} - 10^{F_{1}})]$
ADAPF provides an adaptive factor which defines each frequency band as:(4)
$(A D A P F^{n}, A D A P F^{n + 1}]$
Where, $n = 0, 1, 2, ...$ .