FEM Loads

Click on FEM Loads item in the Navigation Window to display a table with applied loads.

Tank Loads created in Femap is not possible to edit in SDC Verifier. The Loads which can be edited are marked with in the Editable column.

The loads with only applied force/moment on nodes can be converted to Multi Nodal Forces (it is possible to edit few loads at once).

The following types of loads can be created in SDC Verifier:

To create a Fem Load execute Model - FEM Loads - Type from the main menu. Alternatively, use the FEM Loads context menu.

Wind

Wind Load - wind pressure (height dependent) applied to the selection.

Warning:

Wind can be applied to the bar, beam, curved beam, plate and solid (only topology brick) elements.

To Add Wind execute Model - FEM Loads - Wind from the main menu. Alternatively, use FEM Loads context menu or a toolbar icon.

To create it the following parameters should be defined:

  • Vertical Direction - the height uses the vertical direction to calculate pressure for the elements (in the global rectangular coordinate system);
  • Direction - wind direction. It is possible to select a global axis of define vector using Femap Vector dialog box;
  • Selection - elements to apply the wind (can be applied to the bar, beam, curved beam, plate, and solid (only topology brick) elements). Selection is defined using Selector Control;
  • Pressure - define pressure dependency from the height (user defines the direction of the vertical axis for height). Dependency is displayed on the chart.

Wind Altitude is presented by Coordinate and Pressure Value. Use and to add or remove points. Using and points can be moved.

Wind Altitude can be stored in the library. Press and the Title dialog will be displayed:

Wind_set_title

Press to load a profile from the library:

FemLoads_wind_altitude

To Export/Import wind altitude to XML file use and .

Drag Coefficients

Drag coefficients - used to quantify the drag or resistance of an object in a fluid environment. Press Set Drag Coefficient to define them in Y and Z directions:

FemLoads_drag_coefficients

It is possible to add coefficient for a user-defined selection or based on components/ /materials/properties/groups selections:

FemLoads_drag_coefficients_add

- preview only elements of the selected items;

- highlight all elements of the selected items;

- display a criteria plot with coefficient values of the selected items;

Press OK to create or update the wind.

Buoyancy Load

Buoyancy Load gives a possibility to create FEM Loads with pressure acting on the plate elements and force acting on the beam elements including wave parameters.

To add Buoyancy Load select Model - FEM Load - Buoyancy Load from the main menu. Alternatively, use the Fem Loads context menu or a toolbar icon.

Hydroload

The applied hydrostatic pressure at the hull of a floating ship depends on the seawater density, the gravity and the height of the water. If the water line is known the pressure will be applied according to

p = ρgh

Where p is the hydrostatic pressure, ρ is the fluid density and h is the vertical distance to the waterline.

The weight distribution of a ship and the shape of the hull will determine the depth, roll, and pitch of the ship. If the waterline is unknown, then the tool will iteratively find such waterline that there will be a vertical force balance of the upward water pressure and the downward weight. It will also find the pitch and the roll with the balance of moments of the ship. With the Newton-Raphson method, the waterline will be determined with a certain amount of iterations until the balance is found within a numerical tolerance. If the balance is found then the tool has converged and the load set is created.

In the Density field define the density of the water.

Gravity - gravitation (set by default -9.81 m/s^2);

Vertical Axis - waterline is defined for the vertical axis;

Length Axis - longitudinal axis of the ship. Convergence - is accuracy for balancing when the waterline is calculated using predefined mass.

Fdiff = Pressure_Force - Predefined_Mass * Gravity;

Fdiff^2 < 100 * Convergence and Mdiff^2 < 100 * Convergence;

Waterline can be calculated using:

  • Calculate waterline using model mass;
  • Calculate waterline using predefined mass; - the center of the gravity point should be defined.
  • Predefined Waterline.

Note: If the predefined mass option is used but mass is set to 0, then the mass of the model is used.

Pitch and Roll rotational angles (in degrees) around width and length axis respectively. For the predefined waterline option, it is possible to set pitch and roll manually. For another methods, they are calculated automatically.

Select hull of a ship using Selector Control.

Buoyancy Load automatically recognizes element faces to apply pressure but the recognition requires perfectly connected mesh. Otherwise, buoyancy can be applied to the wrong side and faces should be modified manually.

Check if the pressure is applied inside of the hull update faces for these elements.

To update faces uncheck the option Calculate Faces automatically.

Press Plot to preview the element faces (blue = face1, red = face2):

Press Define to set Face1 for elements with the inside pressures (red color on the picture above):

Hydroload_define_faces

Reference Point is a point which is located in the center of the hull but min vertical coordinate.

It is also possible to apply buoyancy with the wave:

Wave height and length:

Wave phase:

Wave Angle:

Tank Load

Tank Load gives a possibility to create FEM Loads with pressures acting inside the tank on the plate elements.

To add Tank Load select Model - FEM Load - Tank Load from the main menu. Alternatively, use FEM Loads context menu or a toolbar icon.

Tankload

Gravity - gravitation (set by default -9.81 m/s^2).

Vertical Axis - waterline is defined for the vertical axis.

Length Axis - longitudinal axis of the ship.

Convergence - is accuracy for balancing when the waterline is calculated using predefined mass.

Fdiff = Pressure_Force - Predefined_Mass * Gravity;

Fdiff^2 < 100*Convergence;

Waterline can be calculated automatically basing on the predefined mass of tank liquid or defined manually (global coordinate). Pitch - the rotation angle around Length Axis and Roll around Width Axis.

Selection - define Tank elements.

Tank Load automatically recognizes the element faces to apply pressure, but the recognition requires a perfectly connected mesh. Otherwise, the tank load can be applied to the wrong side and faces should be modified manually.

Example: Tank with not connected mesh:

Faces are not recognized automatically and a part of the pressure is applied outside:

To update faces uncheck the option Calculate Faces automatically.

In the current example, all pressures are applied only to Face1. Press Define to set Face2 for elements with the outside pressures:

Press Plot to preview faces IDs (blue = face1, red = face2):

- displays the pressure plot of Tank Load (available only when edit Tank Load).

Snow

To create Snow execute Model - FEM Loads - Snow from the main menu. Alternatively, use the Fem Loads context menu or a toolbar icon.

Add_Snow

Snow Direction, Pressure Value, and Selection should be defined to create Snow load.

For the direction, it is possible to select the Global Axis or define vector (by pressing using Femap Vector selector).

Selection should be defined using Selector Control.

It is possible with the elements to which snow will be applied. If Show Only Selected option is chosen, then the whole model in Femap is shown and snow elements are highlighted. Otherwise, only snow elements will be displayed.

Multi Nodal Force

Multi Nodal Force load gives a possibility to apply a load with different nodes magnitudes. In addition, few loads can be created at once.

To add Nodal Force Load select Model - FEM Load - Multi Nodal Force from the main menu. Alternatively, use Fem Loads context menu.

Multinodal_Force

There are 3 ways to define nodes with forces:

  • Add empty rows to the table and fill node ids and force values manually or copy from an external source (Excel/text file). Fill the number of rows in Row Count field and press .
  • From Clipboard - add new rows to the table with data from the clipboard (it has to contain only numeric values);
  • Add with Selection - add the number of rows to the table = the amount of nodes is defined using Selector Control.

Exclude Nodes In Femap - remove nodes from the table by picking nodes in FEMAP.

To set the same value for the selected cells input value in Force field and press the Set.

Press Copy to send data from the selected cells to the clipboard.

To import data from the clipboard press Paste. All data from the clipboard will be pasted starting from the top left selected cell:

Rows in the table can be copied or removed with buttons Copy or Remove respectively.

With the help of Amount of loads group box it can be controlled how many loads will be created:

- One load for all nodes:

- Separate load for each node:

- Nodes per load (4 nodes per load in the following example):

As a result, 2 loads are created:

It is possible to group nodes manually into loads. Fill the same number in # Load column to group nodes into one load.

An invalid number and not existing nodes in the model are highlighted with red when OK is pressed.

Rows with coincident nodes are highlighted:

Execute Convert Nodal Loads to MultiNodal Forces from the Fem Loads context menu:

The list of loads that can be converted is shown. Select the loads to convert:

The selected loads that are updated:

Execute Edit MultiNodal Forces from the Fem Loads context menu:

Select the loads to edit:

The editing dialog is very similar to the creation of multimodal forces dialog:

Edit_multinodal_forces

The load Ids can be used only from the list of selected loads

Nodal Force

Nodal Forces gives a possibility to apply the force, moment, displacement or rotation loads on the selected nodes.

To add Nodal Force Load select Model - FEM Load - Nodal Force from the main menu. Alternatively, use the Fem Loads context menu.

Select nodes using Selector Control.

To apply the load select Type and the values for three directions.

Nodal_Force