Whether you would like to model a pressure venting panel or simply measure some output parameters averaged over a defined area, you can use the pressure relief panel types in FLACS. The parameters for pressure relief panels are defined in CASD as a part of the scenario input.

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How to set up pressure relief panels

Open the Pressure relief panels section and click on Add. This will add a new panel (as shown below).

Add and Edit a panel in the pressure relief panels section in CASD

Highlight the panel entry and click on Edit or double-click on the panel entry. This opens the parameter section of the panel, enabling you to apply the settings you require. There is a long list of properties that can be defined in order to set up a pressure relief panel. These parameters are explained below.

Edit the parameters of the added panel

Give the name (optional), position, size and material of the panel. The Position is defined as Cartesian coordinates of the panel corner with lowest values in each axis. The Size of the panel is defined as a box giving dimensions in all directions; one dimension has to be zero while the other two must be positive, defining the extent of the panel. The Material of the panel is mostly used to change its colour by assigning a hue number.

Panel types

The six types of panels in CASD scenario menu are shown on the drop-down list. Double-click on the parameter to the right of the Opening pressure to be able to expand the drop-down list.

5 of the 6 panel types in FLACS; the plastic pressure relief panel must be added directly in the cs-file

The panel type on top of the list is Inactive: a passive panel that does not affect the numerical simulations in any aspect. It is only used to monitor output parameters as surface averages. The various variables that are possible to monitor are listed under Variables in the pressure relief panels parameters section in CASD.

The other types of panels are active and affect the numerical simulations according to the settings they have. In general, the active panels are expected to yield under a certain overpressure. The Unspecified and Popout panel types have a linear displacement when the panel yields. A Hinged panel has a rotational displacement when the panel yields.

An Overlay panel will keep the porosity level of the object it is applied to. The final porosity of the surface will be the initial porosity of the surface multiplied by the final porosity of the panel. For example, if an Overlay panel is applied to a surface that is 50% porous and the final porosity of the panel is 100% then the final porosity of the surface will be 50%.

The Plastic panel type is not listed in the menu in CASD. This type of panel is only used to mimic a plastic sheet that is used in experiments. It can be added by editing the scenario file (cs-file) directly.

The rest of the parameters in the pressure relief panel section are greyed out or activated depending on the type of panel you choose.

Parameters for active panels

This section lists and explains the different parameters that are available in the pressure relief panel section (only for the active panels).

Opening pressure differences

This parameter corresponds to the net pressure (difference of pressure on the two sides of panel) at which the panel starts to yield. You need to give two values in [barg], first value for the negative side and the second value for positive side. FLACS disregards the signs so only the absolute value is taken into account.

Initial and final porosity

The initial porosity corresponds to the fraction of the panel that is open at the initial phase, before the pressure difference forces the panel to yield. The final porosity corresponds to the open fraction of the panel surface when it has yielded completely. Porosity is specified as a fraction of unity, where 1 means a surface that is completely open.


This parameter is the mass per unit area of the part of the panel that is moved by overpressure and given in [kg/m2]. This parameter is only relevant for the panel types where the inertial forces are taken into account in the dynamical process when the panel yields due to pressure forces: Unspecified, Popout and Hinged. Both the Overlay and Plastic panels are assumed to be light panels and the inertia forces are neglected by FLACS.

Drag coefficient

A dimensionless drag coefficient is only needed for the Unspecified panel type. A value of 2 is pre-set by FLACS for the Popout and Hinged type.

Maximum travel distance

A maximum travel distance in [m] has to be given only for the panel type Unspecified. That is the distance from initial position after which the yielded panel does not affect the effective area porosity at the initial position of panel.

Panel sub-sizes

This field has to be defined only for panel types Popout and Hinged. The two parameters in the field are defined, for the width [m] and height [m] of sub-panel, respectively.