INISTRS

Bulk Data Entry Defines initial stress values and settings for elements in nonlinear analysis.

Format


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INISTRS	`ID`	`ETYPE`	`CIDA`

The following continuation line(s) are optional when ETYPE = SHELL. They can be used to define the sections where initial stress values are applied and they need to be given before the continuation lines starting with EORS.


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	`SECT`	`NSEC`	`SEC1`	`SEC2`	`SEC3`	etc.

The following continuation lines are used to define initial stress values for an element or a set of elements. They are mandatory and can be repeated as required.


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	`EORS`	`EID`/`ESETID`	`CIDB`
	`VALUE`	`STRS1`	`STRS2`	`STRS3`	etc.

When ETYPE = SHELL and the SECT line is given, each VALUE line defines initial stress for a shell section; and so, for any shell element (with EID) or shell element set (with ESETID), the number of VALUE lines must be NSEC.

Alternate Format (Initial Stress from H3D file)


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INISTRS	`ID`			`ASSIGN`	`SUBID`
	`EORS`	`EID1`/ `ESETID1`	`EID2`/ `ESETID2`	`EID3`/ `ESETID3`	`EID4`/ `ESETID4`	`EID5`/ `ESETID5`	`EID6`/ `ESETID6`	`EID7`/ `ESETID7`
		`EID8`/ `ESETID`	etc.	etc.

Alternate Format (Initial Stress from external results LS-DYNA .k file)


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INISTRS	`ID`			`ASSIGN`				`MAP`
	`EORS`	`EID1`/ `ESETID1`	`EID2`/ `ESETID2`	`EID3`/ `ESETID3`	`EID4`/ `ESETID4`	`EID5`/ `ESETID5`	`EID6`/ `ESETID6`	`EID7`/ `ESETID7`
		`EID8`/ `ESETID`	etc.	etc.

The following optional continuation line is available if initial stress results from the external file (.H3D or .k file) are to be relocated.


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	`RELOC`	`RTYPE`	`PA1`	`PA2`	`PA3`	`PB1`	`PB2`	`PB3`

The following optional continuation line can be used to specify the unit system of the external file. The units can either be defined using field 3 (that is, SI/CGS/MPA/BG) or by specifying units in fields 4, 5, 6 and 7. When fields 3 to 7 are all specified, only field 3 is considered and the following fields are ignored.


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	`UNITS`	`SI`/`CGS`/`MPA`/`BG`	`MASS`	`FORCE`	`LENGTH`	`TIME`

Note: When the UNITS continuation line is defined and the length unit of the external H3D model differs from the current model’s length unit, the external H3D model is scaled to match the current model. In such cases, the RELOC continuation line must also be defined along with the UNITS continuation line. Defining these fields is not mandatory unless model scaling is required. If these entries are not specified, the default unit system is used.

Example 1


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INISTRS	7
	`ELEM`	1001
	`VALUE`	3.5e4	-1.5e3	0.0	3.0e3	0.0	2.0e3
	`ESET`	200
	`VALUE`	3.0e4	-1.5e3	0.0	3.0e3	0.0	2.0e3

Example 2


(1)	(2)	(3)	(4)	(5)
INISTRS	8	SHELL	-1
	`SECT`	2
	`ELEM`	101
	`VALUE`	3.5e4	0.0	0.0
	`VALUE`	-3.5e4	0.0	0.0
	`ELEM`	102
	`VALUE`	3.0e4	0.0	0.0
	`VALUE`	-3.0e4	0.0	0.0

Example 3 (Alternate Format – Stress from H3D file)


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INISTRS	7			19	3
	`ELEM`	1001	2002	3003

Example 4 (Alternate Format – Stress from H3D file)


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INISTRS	8			29	6
	`ESET`	2	5	9
	`ESET`	9	19	29

Example 5 (Alternate Format – Stress from LS-DYNA .k file)


(1)	(2)	(3)	(4)	(5)
INISTRS	9			25
	`ESET`	2	5	9
	`ESET`	9	19	29

Example 6 (Specify Units of the External File)


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	`UNITS`	SI	KG	N	M	S

Definitions


Field	Contents	SI Unit Example
`ID`	Unique identification number. No default (Integer > 0)
`ETYPE`	Element type which initial stress is applied. Blank (Default) The initial stress is applied for a collection of solid and/or shell elements. SHELL Applying initial stress for a collection of shell elements specifically.
`CIDA`	Coordinate system identification number, or stress components flag. Blank (Default) The initial stress components are defined in material coordinate system for solids and in element coordinate system for shells. -2 Material coordinate system -1 Element coordinate system 0 Basic coordinate system Integer > 0: user-defined (prescribed) coordinate system.
`SECT`	Keyword indicating the start of continuation line(s) for the shell sections.
`NSEC`	Number of shell sections where initial stress is applied for shell elements. No default (1 ≤ Integer ≤ 6)
`SEC(i)`	Through-thickness position for the shell sections. `SEC(i)` must be either all blank or all non-blank, that is, the number of `SEC(i)` must be either `NSEC` or zero; and `SEC(i)` must be given in ascending order if all non-blank. Blank implies that the sections are located uniformly through the shell thickness, starting at the bottom surface and ending at the top surface. A Real value is the multiplier to shell thickness to get the location. -0.5 means the bottom surface of the shell element and 0.5 means the top surface. The through-thickness positive direction, pointing from the bottom surface to the top surface, is determined by the right-hand rule and the order in which the grid points are listed on the connection entry. It is same as the convention for `Z1`/`Z2` of PSHELL. <Blank, or -0.5 ≤ Real ≤ 0.5> Default = Blank
`EORS`	Flag indicating an element, or element SET is selected in the following field. ELEM (Default) Element is selected ESET Element SET is selected
`EID`/`ESETID`	Identification number of the element or element SET to which the stress values apply. No default (Integer > 0)
`CIDB`	Coordinate system identification number or stress components flag. Blank (Default) Implies that `CIDA` is used; -2, -1 or Integer ≥ 0 suppresses `CIDA`. -2 Initial stress components are defined in material coordinate system -1 Element coordinate system 0 Basic coordinate system Integer > 0: user-defined (prescribed) coordinate system.
`VALUE`	Keyword indicating the start of a continuation line for the stress components.
`STRS(i)`	Stress components 4 No default (Real)
Alternate Format Definitions (Stress from H3D file): 5
`ASSIGN`	Identification number of ASSIGN, H3DRES. When ASSIGN is specified, `SUBID` should be specified as well, and “`VALUE`” continuation line is not allowed. This field is mandatory for Alternate Format (Stress from H3D file). No default (Integer > 0)
`MAP`	Mapping control options. AUTO (Default) Initial stresses are mapped when the external file has geometry data (element and grid data). If the external file does not have geometry data, simple element ID search is conducted by assuming that the external results file also contains the same element IDs as the OptiStruct input file. When matching element IDs are not found, the job stops and an ERROR is issued. ID The simple element ID search is conducted by assuming that the external results file also contains the same element IDs as the OptiStruct results file, even if the external results file contains geometry data. This can improve performance for applying initial stresses from external files where it is known that there is geometry and element ID match. When matching element IDs are not found, the job stops and an ERROR is issued. Default = AUTO (AUTO, ID, or Blank)
`SUBID`	Subcase identification number where initial stress is applied from a H3D file. This field is mandatory for Alternate Format (Stress from H3D file). No default (Integer > 0)
`EORS`	Flag indicating an element, or element SET is selected in the following field. ELEM (Default) Element is selected ESET Element SET is selected
`EID#/ESETID#`	Identification number of the element or the element SET to which the stress values apply. No default (Integer > 0)
Alternate Format Description (Stress from external results LS-DYNA .k file): 6
`ASSIGN`	Identification number of ASSIGN,MANUF. This field is mandatory for Alternate Format (Stress from external results .k file) No default (Integer > 0)
`EORS`	Flag indicating an element, or an element SET is selected in the following field. ELEM (Default) Element is selected ESET Element SET is selected
`EID#`/`ESETID#`	Identification number of the element or the element SET to which the stress values apply. No default (Integer > 0)
Optional Continuation Line Options for Relocation:
`RELOC`	Activates the Relocation option. 7 The matching grid point ID pairs in the model and external result file are to follow.
`RTYPE`	Relocation type. MATCH (Default) The result from the external result file is relocated by using 3 pairs of matching grids in the model (`PA1`, `PA2`, `PA3`) and the external result file (`PB1`, `PB2`, `PB3`). MIRROR The result from the external result file is laterally mirrored according to the plane defined by grid points (`PB1`, `PB2`, `PB3`). Then it is relocated and mapped.
`PA1`, `PA2`, `PA3`	IDs of three non-collinear grid points in the model.
`PB1`, `PB2`, `PB3`	IDs of three non-collinear grid points in model from the external result file that are matched to corresponding grid points in the structure (`PA1`, `PA2`, `PA3`, respectively).
`UNITS`	SI International System of Units Length: Meter = m Mass: Kilogram = kg Time: Second = s Temperature: Kelvin = K Pressure: Pa CGS Centimeter-gram-second System of Units Length: Centimeter = cm Mass: Gram = g Time: Second = s Temperature: Kelvin = K Pressure: Bayre = 0.1 Pa MPA Mega Length: Millimeter = mm Mass: Tonne = tonne Time: Second = s Temperature: Kelvin = K Pressure: MPa BG British Gravitational System of Units Length: Feet = ft Mass: Slug = slug Time: Second = s Temperature: Rankine = R Pressure: lbf/ft² No default
`MASS`	Units of mass. kg (Default) Kilogram lbm Pound-mass slug Slug gram Gram ozm Ounce-mass klbm Kilo pound-mass (1000.lbm) mgg Megagram slinch 12 slugs ug Microgram ng Nanogram uston US ton mg Milligram
`FORCE`	Units of force. N (Default) Newton lbf Pound-force kgf Kilograms-force ozf Ounce-force dyne Dyne kn Kilonewton klbf Kilo pound-force (1000.lbf) mn Millinewton un Micronewton nn Nanonewton
`LENGTH`	Units of length. mm (Default) Millimeter km Kilometer m Meter cm Centimeter mi Mile ft Foot in Inch um Micrometer nm Nanometer ang Angstrom yd Yard mil Milli-inch uin Micro-inch
`TIME`	Units of time. s (Default) Seconds h Hours min Minutes ms Milliseconds us Microsecond nanosec Nanosecond d Day

Comments

INISTRS and ISTSADD should not have the same ID.
The INISTRS Bulk Data Entry is selected by the Subcase Information command INISTRS.
Initial stress is supported for solid elements (CHEXA, CPENTA, CPYRA and CTETRA) and shell elements (CQUAD4, CTRIA3, CQUAD8 and CTRIA6), only.
Initial stress is currently not supported for solid elements with hyperelastic material in LGDISP analysis.
For initial stress of solid elements, 6 stress components are needed for each VALUE line and they are:

STRS1

$σ$ _xx

STRS2

$σ$ _yy

STRS3

$σ$ _zz

STRS4

$σ$ _xy

STRS5

$σ$ _yz

STRS6

$σ$ _zx

Where, x, y and z are the axes in the coordinate system selected via CIDA and CIDB.
For initial stress in element or material coordinate system of shell elements, 3 stress components are needed for each VALUE line and they are:

STRS1

$σ_{11}$

STRS2

$σ_{22}$

STRS3

$σ_{12}$

Where, 1 and 2 are the first two local directions in the element or material coordinate system.
For initial stress in the basic or a prescribed coordinate system of shell elements, 6 stress components are needed for each VALUE line and they are:

STRS1

$σ$ _xx

STRS2

$σ$ _yy

STRS3

$σ$ _zz

STRS4

$σ$ _xy

STRS5

$σ$ _yz

STRS6

$σ$ _zx

Where, x, y and z are the axes in the basic or prescribed coordinate system.
Alternate Format (Stress from H3D file):
1. VALUE continuation line is not allowed for the Alternate Format when Stress is sourced from a H3D file.
2. For Shell elements, currently only the equivalent of NSEC=2 is supported (Z1 and Z2 layers) to apply the initial stress, as the number of layers where stress data is available can be identified from the H3D file.
3. Currently only H3D files output from OptiStruct and HyperForm are supported.
Alternate Format (Stress from external results LS-DYNA .k file):
1. VALUE continuation line is not allowed for the Alternate Format when Stress is sourced from .k file.
2. Currently only .k file output from LS-DYNA is supported.
Relocation continuation line:
1. The RELOC entry and its related fields define three matching grid point pairs on the model and the external result file. The result from the external file is relocated (translated and rotated, as required) such that the three non-collinear grid points PB1, PB2 and PB3 coincide with PA1, PA2, and PA3, respectively.