The Sensor menu

Figure 1. The Sensor
commands

Sensors allow the evaluation of the stress tensor, strain tensor, and warping at any point of the cross-section. These various quantities are evaluated at the end of the analysis and will be printed in the output file for all the loading cases.

Sensors can be defined in the input file by simply editing this file. To place the sensor at the appropriate location of the cross-section, the following, two-step procedure it is recommended.

  1. Select a single element of the model using the Select element command.
  2. Create a sensor for this element using the New sensor command.

To view the location of a sensor, using the View sensors command.

Sensor definition

Sensor definitions are documented in three different files.

  1. In the input file. Figure 2 illustrates the definition of sensor MyOwnSensor in the input file. The syntax for the definition of sensors is defined in the section of the user's manual detailing sensors. The input file can be edited easily: feel free to change the various parameter to define the sensor. You can also add sensors as you see fit. You will need to rerun SectionBuilder for the changes you made to the input file to be reflected in the analysis.
  2. In the output file. The definition of the sensor is echoed in the output file, as illustrated in fig. 3. The output file cannot be edited.
  3. In the html file. The definition of the sensor is echoed in the html file, as illustrated in fig. 4. The html file cannot be edited.
SENSOR_DEFINITION {
@SENSOR_NAME {SensorMyOwn} {
@OBJECT_NAME {GSolSegment1}
@SENSOR_TYPE {SB_STRESSES}
@ETA_COORDINATE {0.50, 0.50}
}
}
Figure 2. Definition of the sensor MyOwnSensor in the input file
Figure 3. Definition of sensor MyOwnSensor in the output file
Figure 4. Definition of sensor MyOwnSensor in the html file

Sensor output (Stress tensor)

Figure 5 shows the stress tensors as calculated by sensor SensorStressAtPointC2 for all the loading cases. The listing starts with the sensor definition. In this case, the name of the sensor is “SensorStressAtPointC2”. The location of the sensor is at local eta coordinates (u, v) = (0.5, 0.0) within solid element “GSolSegment1”. The position of the sensor with respect to the sectional axis system is (x1, x2, x3) = (0.0, -0.85, 1.47224). Because the sensor type is SB_STRESSES, the stress tensor has been evaluated for each of the loading cases. A total of 8 loading cases were defined for this analysis.

The components of the stress tensor are listed as follows: the axial stress component, σ11, the two transverse shear stress components, τ12 and τ13, the two in-plane stress components, σ22 and σ33, and the in-plane shear stress component, τ23.

Figure 5. The stress tensors as calculated by sensor SensorStressAtPointC2 for all the loading cases

Sensor output (Strain tensor)

Figure 6 shows the strain tensors as calculated by sensor SensorStressAtPointM1 for all the loading cases. The listing starts with the sensor definition. In this case, the name of the sensor is “SensorStressAtPointM1”. The location of the sensor is at local eta coordinates (u, v) = (0.5, 1.0) within solid element “GSolSegment2”. The position of the sensor with respect to the sectional axis system is (x1, x2, x3) = (0.0, -0.60, 1.03923). Because the sensor type is SB_STRAINS, the strain tensor has been evaluated for each of the loading cases. A total of 8 loading cases were defined for this analysis.

Figure 6. The strain tensors as calculated by sensor SensorStressAtPointC3 for all the loading cases

The components of the strain tensor are listed as follows: the axial strain component, ε11, the two transverse shear strain components, γ12 and γ13, the two in-plane strain components, ε22 and ε33, and the in-plane shear strain component, γ23.

Sensor output (Warping displacement)

Figure 7. The warping fields as calculated by sensor
MyOwnSensor for all the loading cases

Figure 7 shows the warping displacements as calculated by sensor MyOwnSensor for all the loading cases. The listing starts with the sensor definition. In this case, the name of the sensor is “MyOwnSensor”. The location of the sensor is at local eta coordinates (u, v) = (0.5, 0.25) within solid element “GSolSegment3”. The position of the sensor with respect to the sectional axis system is (x1, x2, x3) = (0.0, -1.48002, -0.538682). Because the sensor type is SB_WARPING, the warping displacement has been evaluated for each of the loading cases. A total of 8 loading cases were defined for this analysis.

The components of the warping field are listed as follows: the axial warping component, w1, and the two in-plane warping components, w2 and w3.


List sensors (Sensor→List sensors)

Sensors can be defined at any location over the cross-section. Command Sensor→List sensors lists all the sensors that have been defined in the model. Figure 8 shows a typical list of sensors.

Figure 8. List of sensors

The following information is listed for each sensor.

  • Column 1. The name of the sensor
  • Column 2. The name of the solid element for which the sensor is defined
  • Column 3. Defined the SensorType, which can take one of the following three values.
    1. If SensorType = SB_STRESSES, the sensor will evaluate the stress tensor.
    2. If SensorType = SB_STRAINS, the sensor will evaluate the strain tensor.
    3. If SensorType = SB_WARPING, the sensor will evaluate the warping displacement.
  • Column 4 and 5. List the local eta coordinates u and v within solid element “GSolSegment1”.
  • Column 6. The name of the fixed frame in which the quantities evaluated by the sensor will be resolved. By default, this frame if the sectional reference frame.

View sensors (Sensor→View sensors)

The list of sensors generated by the previous command provides a complete definition of all the sensors defined for the model. It is not easy, however, to visualize the location of the sensors from the data provided in the list. Command Sensor→View sensors locates the sensors over the cross-section, as shown in fig. 6.

Figure 6. View location of the sensors on the cross-section of a circular arc

Figure 6 shows the example of a circular arc for which ten sensors were defined. Command Sensor→View sensors toggles the display of the names of the sensors. The names of the sensors are printed in magenta and their locations are highlighted by a black circle.

Select a single element (Sensor→Select element)

Command Sensor→Select element is used to select one specific element of the model. Invoke the Select element command to enter the element selection mode, see fig. 1. Once in the element selection mode, use the mouse left button to select the desired element, see fig. 2 that shows the selected element highlighted in blue. Note the following.

  • Once an element has been selected, the element selection mode is cancelled. To select another element, invoke the Select element command again and select another element.
  • An element must be selected to access to remaining commands of the Sensor menu.
Figure 1. Invoking the Sensor→Select elementFigure 2. Selecting a single element
command for a circular arcof the circular arc

Create a sensor for one element (Sensor→New sensor)

Figure 1. Creating a sensor for the circular arc

Once an element of the model has been selected, invoking the Sensor→New sensor command creates a sensor that will save the components of the stress or strain tensor to the output file. Figure 2 shows the “create new sensor” dialog that opens once the command Create sensor is invoked.

To create the sensor, enter the following information.

  1. Type the sensor name. Select a name such as SensorMySensorName.
  2. Select the sensor type.
    1. Stress. The sensor will save the components of the stress tensor.
    2. Strain. The sensor will save the components of the strain tensor.
  3. Select the sensor location within the element. The coordinates of the point at which the components of the stress or strain tensor will be computed will be printed in the output file.

    1. Element center. A single sensor will be created at the center of the element.
    2. Element corners. Four sensors will be created, one at each corner of the element.
    3. Gauss points. Four sensors will be created, one at each Gauss point of the element. Note that the highest accuracy is obtained for this option.
    4. Mid-edges. Four sensors will be created, one at the center of each edge of the element.

Once all the data has been entered, click OK to create the sensor. The sensor will be saved in the input file. next time the cross-section is analyzed, the sensor output will be printed in the output file.