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incomplete cut

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defining elements on both sides

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beam
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beam crossing the section   
defined section

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elements used to define the section

Figure 4.1.3–3 Invalid section definitions.   
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distributed
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face defined ng element 1

face defined ng element 2   
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concentrated
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Figure 4.1.3–4 Total force in the section.

if the same surface is defined first using element 1 and then using element 2, different answers for the total force will be obtained. In a similar way the effects of any distributed body fluxes (heat, electrical, etc.) prescribed in the identified elements are not included.

• Depending on which side of the surface is used to define the section, different answers will be obtained in analyses similar to the case illustrated in Figure 4.1.3–4(b). Assuming a quasi-static analysis with the concentrated loads shown in the figure being the only active loads, a zero total force is reported if the surface is defined using element 1 and a nonzero force equal to the sum of the concentrated loads is obtained if the surface is defined using element 2.

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# Total energy output

You can output the total energy of the model or of a specific element set to the output database. Energy output is available only as history output. Energy output requests are not available for the following procedures:

• “Eigenvalue buckling prediction,” Section 6.2.3   
• “Natural frequency extraction,” Section 6.3.5   
• “Complex eigenvalue extraction,” Section 6.3.6

# Selecting the energy output variables

The energy variables that can be written to the output database are defined in the “Total energy output quantities” section of “Abaqus/Standard output variable identifiers,” Section 4.2.1; “Abaqus/Explicit output variable identifiers,” Section 4.2.2; and “Abaqus/CFD output variable identifiers,” Section 4.2.3.

Input File Usage: \*ENERGY OUTPUT

list of output variables

Abaqus/CAE Usage: Step module: history output request editor: Select from list below

# Selecting the element set for which total energy output is required

You can specify the element set for which total energy output is being requested. In this case the energies are summed for all the elements in the specified set. You cannot specify an element set for the following procedures:

• “Transient modal dynamic analysis,” Section 6.3.7   
• “Mode-based steady-state dynamic analysis,” Section 6.3.8   
• “Response spectrum analysis,” Section 6.3.10   
• “Random response analysis,” Section 6.3.11

The following energies are not available as element set quantities: ALLCCDW, ALLCCE, ALLCCEN, ALLCCET, ALLCCSD, ALLCCSDN, ALLCCSDT, ALLFC, ALLFD, ALLKL, ALLQB, ALLWK, and ETOTAL.

If you do not specify an element set, the total energies for the whole model will be output. If total energy output for both the whole model and for different element sets is desired, the energy output requests must be repeated: once without a specified element set to request energy output for the whole model and once for each specified element set.

Input File Usage: \*ENERGY OUTPUT, ELSET=element\_set\_name

Abaqus/CAE Usage: Step module: history output request editor: Domain: Set: set\_name

# Controlling the output frequency

The frequency of energy output is controlled as described above in “Controlling the output frequency.”

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# Requesting preselected output

You can request the preselected, procedure-specific energy output variables described in Table 4.1.3–1. In this case you can specify additional variables as part of the output request.

Alternatively, you can request all energy variables applicable to the current procedure and material type. In this case any additional variables you specify are ignored.

<table><tr><td>Input File Usage:</td><td>Use the following option to request the preselected energy output variables:*ENERGY OUTPUT, VARIABLE=PRESELECTUse the following option to request all applicable energy output variables:*ENERGY OUTPUT, VARIABLE=ALL</td></tr></table>

Abaqus/CAE Usage: Step module: history output request editor: Preselected defaults or All

# Sensor definition in Abaqus/Standard and Abaqus/Explicit

For nodal, connector element, and some whole surface contact output variables, history output requests can be used to define sensors. Sensors are named entities that are intended to be used to model physical sensors such as the total force or displacement of a hydraulic piston, the motion of a given point on a structure, or the acceleration as measured by an accelerometer. Sensor values can be fed back into the model to produce actuation that is a function of the sensed quantity thus allowing for modeling of control engineering aspects of your system.

You can use sensors in user subroutine UAMP or VUAMP to define a customized amplitude that is a function of sensor values at the end of the previous increment as shown in “VUAMP,” Section 1.2.9 of the Abaqus User Subroutines Reference Guide, and illustrated in the example in “Crank mechanism,” Section 4.1.2 of the Abaqus Example Problems Guide. Alternatively, you can use sensor values in a co-simulation analysis with the logical modeling program Dymola. Abaqus exports sensor information to Dymola and imports computed actuation information; i.e., the current amplitude value of an amplitude function (see “Structural-to-logical co-simulation,” Section 17.4.1). In these cases the amplitude function can be used to actuate any Abaqus feature that can reference an amplitude, such as concentrated loads, boundary conditions, connector motion/load, distributed pressure, and material properties via field variables.

A sensor must be uniquely associated with a particular scalar output variable (U1, CTF3, etc.) and can be defined using history output requests by following some simple rules. The sensor name is specified in the history output definition, and one and only one nodal output, element output, or whole surface request can be specified for each sensor definition. For whole surface contact or contact pair output requests only the magnitude and the center of the total force due to contact pressure are supported (CFNM and XN). Since the named sensor must point to a unique real number at a given time, the node set or element set used in the definition must contain only one member. Moreover, regardless of the userspecified output frequency, sensors are computed at every increment during the analysis. However, they are written to the output database according to the user-specified frequency.

Input File Usage: Use the following options to specify a sensor definition using element output:

\*OUTPUT, HISTORY, SENSOR, NAME=name

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\*ELEMENT OUTPUT

element output variable

Use the following options to specify a sensor definition using nodal output:

\*OUTPUT, HISTORY, SENSOR, NAME=name

\*NODE OUTPUT

nodal output variable

Use the following options to specify a sensor definition using contact output:

\*OUTPUT, HISTORY, SENSOR, NAME=name

\*CONTACT OUTPUT

contact or contact pair output variable (CFNM and XN)

Abaqus/CAE Usage: Step module: history output request editor: Domain: Set: name, toggle on Include sensor when available

# Filtering output and operating on output in Abaqus/Explicit

You can pre-filter element and nodal field output and element, nodal, contact, integrated, and fastener interaction history output before it is written to the output database. You can also operate on filtered or unfiltered (raw) output data to extract the maximum, minimum, or absolute maximum of the output variables over time. In addition, you can set a limit value for the output variables, and you can stop the analysis at the time this limit is reached. For field output the time at which the maximum, minimum, and absolute maximum were reached or the time when the limit was reached is output by default for each output variable.

If you filter a field output request that includes many output variables and applies to the entire model, the memory requirements and the running time will both increase. For common output requests consisting of a few element output variables and a few nodal output variables the memory requirements and the running time will not increase substantially.

# Defining a low-pass Infinite Impulse Response digital filter

You can define three types of low-pass Infinite Impulse Response filters as part of the model definition. Typical magnitude curves for analog type filters are presented in Figure 4.1.3–5, where $\Omega _ { c }$ represents the normalized cutoff frequency, which is the ratio of the cutoff frequency to the sampling frequency (the sampling frequency is the inverse of the time increment). The Butterworth filter is very common; its response in the pass band is known as maximally flat. The Type I Chebyshev filter has a sharper transition between the pass band and the stop band, but it has a ripple in the pass band. The Type II Chebyshev filter also has a sharper transition between the pass band and the stop band than a Butterworth filter of the same order, but it has a ripple in the stop band. The higher the order of the filter, the narrower the transition band. However, the computational cost increases as the order increases. In addition, for high-order filters the phase lag, which is the time delay between the filtered and unfiltered signal, may become significant. For most applications filter orders of two or four are sufficiently accurate.

To define a Butterworth filter, you must specify the cutoff frequency, $f _ { c }$ , and the filter order, N. Since the implementation of the filters is done using cascades of second-order sections, Abaqus expects

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| transition band | Butterworth | Type I Chebyshev | Type II Chebyshev |
| --------------- | ----------- | ---------------- | ----------------- |
| passband        | 1           | 1/√(1+ε²)         | 1/A               |
| Ωc              | 1           | 1                | 1/A               |
| stopband        | 1           | 1                | 1/A               |
</details>

Figure 4.1.3–5 Typical magnitude curves for low-pass filters.

an even number for the filter order. If you specify an odd number for the order, the order will be increased internally to the next even number. The default value for the order is two, and the highest order that can be prescribed is twenty. For the Chebyshev filters you must also specify an additional parameter, the ripple factor. The ripple factor is equal to for a Type I Chebyshev filter and is equal to $1 / A$ for a Type II Chebyshev filter (see Figure 4.1.3–5).

No checks are performed to ensure that the cutoff frequency is appropriate; for example, Abaqus does not check that only the noise of the signal is eliminated. You need to know the range of the physical frequencies that are expected in the solution, and you must prescribe a cutoff frequency greater than these frequencies. In addition, the cutoff frequency should be less than half the sampling frequency; otherwise, no filtering is performed. Abaqus internally remaps (using a quadratic interpolation) the output raw data so that the filtering can satisfy the constant time-increment (sampling) requirement.

You must assign each filter definition a name that can be used to refer to the filter from an output request.

Input File Usage: Use one of the following options to define a filter:

\*FILTER, NAME=filter\_name, TYPE=BUTTERWORTH

\*FILTER, NAME=filter\_name, TYPE=CHEBYS1

\*FILTER, NAME=filter\_name, TYPE=CHEBYS2

Abaqus/CAE Usage: Step module: Tools→Filter→Create: Name: filter\_name; Butterworth, Type I Chebyshev, or Type II Chebyshev

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# Start-up conditions for the filter

By default, the values of the variables at time zero (zero increment) are used as the initial conditions (or start-up conditions); however, you can change this initial value.

Input File Usage: Use the following option to use the default initial conditions:

```python
*FILTER, NAME=filter_name, TYPE=filter_type, START CONDITION=DC
Use the following option to specify the initial variable values:
*FILTER, NAME=filter_name, TYPE=filter_type,
START CONDITION=USER DEFINED 
```

Abaqus/CAE Usage: You cannot specify the initial variable values in Abaqus/CAE.

# Filtering using the low-pass Infinite Impulse Response filters

To pre-filter element, nodal, contact, or integrated history output or element and nodal field output based on one of the low-pass Infinite Impulse Response filters that you defined, you refer to this filter by name from the output request.

Input File Usage: Use the following option to apply a filter to an output request:

```gitattributes
*OUTPUT, FILTER=filter_name 
```

Abaqus/CAE Usage: Step module: field or history output request editor: Apply filter: filter\_name

# Filtering the output based on the time interval

For history output you can request that Abaqus/Explicit create an antialiasing filter that is internally based on the time interval specified in the output request. The cutoff frequency is set internally to one-sixth of the time frequency (the time frequency is the inverse of the time interval, t, used for history output). If no time intervals are specified, the default number of history output intervals is used to create the cutoff frequency of the filter. You can also use antialiasing filters for a field output request, but in this case the cutoff frequency is set to one-sixth of a time frequency corresponding to two hundred time intervals per step if less than two hundred field frames are requested. If more than two hundred field frames are requested, the cutoff frequency is set to one-sixth of the requested time frequency. The antialiasing filter is a second-order Butterworth type and a filter definition is not required.

Abaqus/Explicit does not check whether the specified time interval for history output provides an appropriate cutoff frequency to build the internal filter. You should know approximately how many data points are required to describe your history curve (or signal) accurately, and Abaqus/Explicit will give you the most physical (un-aliased) representation of the signal for that number of points. Similarly for field output Abaqus/Explicit does not check whether the cutoff corresponding to two hundred sampling intervals or more (if you request more than two hundred frames) is appropriate for your analysis. If a lower (or higher) cutoff frequency is needed, you should define the filter in the model data.

# Filtering field output or history output written at time intervals

You can apply a filter to a field output request or a history output request written at intervals of time in your analysis.

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<table><tr><td>Input File Usage:</td><td>Use one of the following options:*OUTPUT, FIELD, FILTER=ANTIALIASING, TIME INTERVAL=t*OUTPUT, HISTORY, FILTER=ANTIALIASING, TIME INTERVAL=t</td></tr></table>

<table><tr><td>Abaqus/CAE Usage:</td><td>Step module: field or history output request editor: Frequency: Every x units of time: t, Apply filter: Antialiasing</td></tr></table>

Filtering field output written at evenly spaced intervals of time

You can apply a filter to a field output request written at evenly spaced time intervals in your analysis.

Input File Usage: \*OUTPUT, FIELD, FILTER=ANTIALIASING, NUMBER INTERVAL=n

Abaqus/CAE Usage: Step module: field output request editor: Frequency: Evenly spaced time intervals, Interval: n, Apply filter: Antialiasing

# Requesting maximum, minimum, or absolute maximum values for an output request

You can apply a filter to a field output request or a history output request to obtain the maximum, minimum, or absolute maximum values for each variable in the output request. The absolute maximum option enables you to obtain the largest absolute value, negative or positive, for each variable in the output request. Abaqus evaluates maximum, minimum, or absolute maximum values at every increment during the analysis and reports these values at the time given by the output interval specified in the output request. For field output requests the last output frame will contain the maximum (or absolute maximum) value and minimum value over the entire step; the intermediate frames will show the maximum, minimum, or absolute maximum value up to the frame time. An additional output variable containing the time when the maximum, minimum, or absolute maximum occurred is output automatically for each output variable requested. This time output is written by default (and it cannot be suppressed).

For field output requests Abaqus filters by default each component of tensor and vector quantities of output variable independently and provides separate maximum, minimum, or absolute maximum values for each component of the variable. You can, however, request the maximum or minimum value or apply a limit value to an invariant such as Mises stress for element output or magnitude for nodal output (see “Applying bounding values to invariants,” below).

Requesting maximum, minimum, or absolute maximum values for filtered output

You can define a low-pass digital filter that returns the maximum, minimum, or absolute maximum value for output requests to which it is applied.

<table><tr><td>Input File Usage:</td><td>Use one of the following options:</td></tr><tr><td></td><td>*FILTER, TYPE=filter_type, OPERATOR=MAX</td></tr><tr><td></td><td>*FILTER, TYPE=filter_type, OPERATOR=MIN</td></tr><tr><td></td><td>*FILTER, TYPE=filter_type, OPERATOR=ABSMAX</td></tr></table>

<table><tr><td>Abaqus/CAE Usage:</td><td>Step module: Tools→Filter→Create: Butterworth, Type I Chebyshev, or Type II Chebyshev: Determine bounding value: Maximum, Minimum, or Absolute maximum</td></tr></table>

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Requesting maximum, minimum, or absolute maximum values for unfiltered output

You can define a filter that returns the maximum, minimum, or absolute maximum value for output requests to which it is applied without performing any digital filtering of the data.

Input File Usage: Use one of the following options:
*FILTER, OPERATOR=MAX
*FILTER, OPERATOR=MIN
*FILTER, OPERATOR=ABSMA

Abaqus/CAE Usage: Step module: Tools→Filter→Create: Type: Operator: Determine bounding value: Maximum, Minimum, or Absolute maximum

# Setting an upper or lower limit on variables in an output request

You can apply a filter to a field output request or a history output request to prescribe a bounding value for the variables in the output request. If any of the variables in the output request reach a value higher than the maximum limit, lower than the minimum limit, or greater than the absolute maximum limit, Abaqus returns the limiting value. The time at which the limit was reached is output separately for each requested variable. This time output is written by default (and it cannot be suppressed).

Setting an upper limit or a lower limit for filtered output

You can define a low-pass digital filter that enforces an upper or lower bound for the variables in the output requests to which it is applied.

Input File Usage: \*FILTER, TYPE=filter\_type, OPERATOR=operator\_type, LIMIT=value

Abaqus/CAE Usage: Step module: Tools→Filter→Create: Type: Butterworth, Type I Chebyshev, or Type II Chebyshev: Determine bounding value: Maximum, Minimum, or Absolute maximum: toggle on Bounding value limit: value

Setting an upper limit or a lower limit for unfiltered output

You can define a filter that enforces an upper or lower bound for the variables in the output requests to which it is applied but that does not perform any Butterworth or Chebyshev filtering of the data.

Input File Usage: \*FILTER, OPERATOR=operator\_type, LIMIT=value

Abaqus/CAE Usage: Step module: Tools→Filter→Create: Type: Operator: Determine bounding value: Maximum, Minimum, or Absolute maximum: toggle on Bounding value limit: value

# Stopping an analysis when an output variable reaches a prescribed limit

You can apply a filter to a field output request or a history output request that stops the analysis when the value of any variable in the output request reaches a specified upper bound or lower bound.

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Stopping an analysis of filtered output when a variable reaches a prescribed limit

You can define a low-pass digital filter that stops the analysis if any of the variables in the output requests to which it is applied reach a prescribed limit.

Input File Usage: \*FILTER, TYPE=filter\_type, OPERATOR=operator\_type, LIMIT=value, HALT

Abaqus/CAE Usage: Step module: Tools→Filter→Create: Butterworth, Type I Chebyshev, or Type II Chebyshev: Determine bounding value: Maximum, Minimum, or Absolute maximum: toggle on Bounding value limit: value: toggle on Stop analysis upon reaching limit

Stopping an analysis of unfiltered output when a variable reaches a prescribed limit

You can define a filter that does not perform any Butterworth or Chebyshev filtering of your output data and stops the analysis if any of the variables in the output requests to which it is applied reach a prescribed limit.

Input File Usage: \*FILTER, OPERATOR=operator\_type, LIMIT=value, HALT

Abaqus/CAE Usage: Step module: Tools→Filter→Create: Type: Operator: Determine bounding value: Maximum, Minimum, or Absolute maximum: toggle on Bounding value limit: value: toggle on Stop analysis upon reaching limit

# Applying bounding values to invariants

By default, each component of a tensor or vector quantity is filtered individually and the maximum, minimum, or absolute maximum value and the limiting values are reported separately for each component. You can, however, apply a filter directly to an invariant. In this case Abaqus internally monitors the invariant you specified. Abaqus still writes the components to the output database, but these components correspond to the maximum, minimum, or limiting values of the invariant. Table 4.1.3–2 shows which invariants are available for output variable categories.

Applying bounding values to invariants of filtered output

You can define a low-pass digital filter that filters the invariant.

Input File Usage: \*FILTER, TYPE=filter\_type, OPERATOR=operator\_type, LIMIT=value, INVARIANT=FIRST, SECOND, MAXP, INTERMP, or MINP

Abaqus/CAE Usage: Step module: Tools→Filter→Create: Type: Butterworth, Type I Chebyshev, or Type II Chebyshev; toggle on Bounding value limit: value: Invariant: First or Second

You cannot request maximum, intermediate, and minimum principal stresses for invariants in Abaqus/CAE.

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Table 4.1.3–2 Invariants available for output variable categories. 

<table><tr><td>Category</td><td>First invariant</td><td>Second invariant</td><td>MaxP</td><td>IntermP</td><td>MinP</td></tr><tr><td>All nodal vector output</td><td>Magnitude</td><td>-</td><td>—</td><td>—</td><td>—</td></tr><tr><td>Stress element output</td><td>Mises</td><td>Press</td><td>SP3</td><td>SP2</td><td>SP1</td></tr></table>

Applying bounding values to invariants of unfiltered output

You can define a filter that does not perform any Butterworth or Chebyshev filtering of your output data and filters the invariant.

$\begin{array} { r l r l } & { \mathrm { { l n p u t ~ F i l e ~ U s a g e : } ~ } } & & { \mathrm { { s F I L T E R , ~ O P E R A I O R = } } o p e r a t o r \_ i y p e , \ L [ \mathrm { M I T = } \nu a l u e , \mathrm { I N V A R I A N T = } } \\ & { } & & { \mathrm { F I R S T ~ o r ~ S E C O N D } } \end{array}$

Abaqus/CAE Usage: Step module: Tools→Filter→Create: Type: Operator; toggle on Bounding value limit: value: Invariant: First or Second

# Output variables available for filtering

Low-pass Infinite Impulse Response filters such as Butterworth and Chebyshev filters are intended for filtering of output variables susceptible to noise, such as accelerations and reaction forces or, to a lesser degree, stress and strain. However, digital filtering is allowed for most element and nodal output variables, and you can apply bounding values on unfiltered data for nearly all element and nodal output variables. Table 4.1.3–3 shows the set of output variables that cannot be digitally filtered but to which you can apply bounding values, and Table 4.1.3–4 shows the set of output variables for which neither digital filtering nor application of bounding values are allowed.

Table 4.1.3–3 Output variables to which bounding values can be applied but digital filtering cannot be applied. 

<table><tr><td>Category</td><td>Output variables</td></tr><tr><td>Tensors and invariants</td><td>PEEQ</td></tr><tr><td>State and field variables</td><td>TEMP, FV</td></tr><tr><td>Energy densities</td><td>ENER, SENER, PENER, CENER, VENER, DMENER</td></tr><tr><td>Additional plasticity quantities</td><td>PEQC</td></tr><tr><td>Cracking model quantities</td><td>CKSTAT</td></tr></table>
