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The interface processes the following load types:
Initial Temperatures : applied to parts or sets, expanded to nodes. Gravity Loading : applied to whole model. Centrifugal Loading : applied to the whole model. Concentrated Force : applied to parts or sets, expanded to nodes. Uniformly Distributed : applied to parts or sets, expanded to elements or extrapolated to nodes. Hydrostatic : applied to parts or sets, expanded to elements or extrapolated to nodes. Prescribed Displacements : applied to parts or sets, expanded to nodes. Surface Flux : applied to parts or sets, expanded to elements. Forced convection : applied to parts or sets, expanded to elements. Prescribed Temperatures : applied to parts or sets, expanded to nodes.
All loads of the same type, with the exception of initial temperatures, are sorted
and grouped in ascending order of loadcase number. A loading summary is written to
the input deck prior to any load data using type 41 cards with a loadcase number and
blank load fields thus:
00
00 LOADING SUMMARY FOLLOWS:
00
00 THERE ARE 2 LOADCASES, THEY ARE:
41 1 LOAD CASE 1
41 2 LOAD CASE 2
00
For all loads types, the actual load values (be it per unit depth, area, or circumference) must be expressed in the correct manner by the user. For example, the interface does not attempt any interpretation of load values per unit thickness; it simply transfers the load value to the BERSAFE deck. The user should consult the element definition sections of BERSAFE volumes 2 and/or 4 for detailed information.
A temperature load is applied to a part or set using the command 'PROPERTY LOADS TEMPERATURE ...'. A temperature and a temperature difference may be applied. If the temperature difference is positive or zero, initial temperatures will be created, if the temperature difference is negative prescribed temperatures will be produced (see later). For initial temperatures the interface applies the desired temperature loads to each node in the model using the last two fields of the type 25 cards along with the nodal coordinates.The FEMGEN load case identifier is disgarded in the interface because the BERSAFE deck does not support it. For nodes on the boundary between two parts with different temperatures, the temperature assigned will be that of the last temperature load to be defined.
Centrifugal and gravity loads are applied to the whole model using the command 'PROPERTY LOADS GRAVITY ...'. Centrifugal and Gravitational loads are expressed on type 41 cards. For Centrifugal loads, the two point axis definition is not supported by BERSAFE and this information is disgarded in the interface. Care must be taken to ensure that the centrifugal or gravitational load values are consistent with the units defined on the material properties cards, and that the model is correctly orientated with respect to the BERSAFE default rotational axis. For a model having both centrifugal and gravitational loads, the interface will produce to type 41 cards. The user must then edit the input deck and merge the information on the two into a single card .
Concentrated loads are applied to a part or set using the command 'PROPERTY LOADS FORCE ...'. Concentrated forces and moments are expressed on type 51 cards. Loads are applied relative to the global coordinate system at all nodes in the part or set in a single cartesian direction. Point loads which do not act along one of the cartesian axes must be split up into X, Y, and Z components and entered as three separate loads.
Uniformly distributed loads are applied to a part or set using the command 'PROPERTY LOADS PRESSURE ...'. The load will have a value, a direction (global FX, FY, FZ, MX ,MY ,MZ or normal to the element face/edge), and be applied to a certain face/edge of a group of elements. Distributed moments are not detailed in the FEMGEN/FEMVIEW user manual but it does seem possible to define them using load directions 4, 5, and 6 in FEMGEN, and to interpret them in the interface. This facility is untested and not supported, but should work in the same way as uniformly distributed forces.
Uniformly distributed loads will either be expressed as an elemental block loading using a single type 51 card and a number of type 52 cards, or as a group of equivalent nodal loads on a number of type 51 cards. Extrapolation to nodal equivalent loads will be performed where a distributed shear load (ie not normal to element face/edge) has been applied (no BERSAFE element supports this load type).
The extrapolation to equivalent nodal loads is performed in the following manner. The area/length of each element edge/face is calculated, and multiplied by the pressure load to give a total force per element. The area calculation for element faces is performed by splitting the face up into a group of triangular flat plates, calculating the area of each and then summing to get the total face area. For highly curved shells this area calculation may be slightly inaccurate. The total force is then split up into equivalent nodal loads according to the scheme detailed on page 21 of BERSAFE volume 2, and a direction applied (global X, Y, Z). The interface then checks each node to see if a local coordinate system has been applied there. Where a local system is found, a transformation is applied to the load to skew it into the local X, Y, or Z directions.
Where more than one local system has been applied at a node, the system used for the transformation will be the one which was applied first in FEMGEN. This is also the one which will appear on type 24 cards (local nodal coordinate systems). A case may arise where a local nodal system intrudes onto the edge of a loaded part which does not have a local system attached to it, and the user does not want the nodal loads skewed. There is currently no simple way around this problem, and the user should be aware that it exists.
The interface will not be able to generate an equivalent BERSAFE load under the following conditions:
Under these circumstances the interface issues a warning, changes the load direction to global Z as a guess, and extrapolates the load to equivalent nodal loads. For cases where the above loading conditions are required, the user should change the load direction to 1, 2, or 3, and additionally (if the load is not in these global directions) attach a suitable local nodal coordinate system to skew the resulting equivalent nodal loads around into the correct directions.
The interface is also unable to interpret line loads along the edges of brick elements (the interface will issue a warning indicating that it cannot determine the element loaded face and ignore that particular load). To get around this problem the user should place some beam elements along the edge to be loaded. If the these elements are given a very small cross-section and assigned some appropriately 'floppy' material properties, the analysis will not be significantly affected. The user can remove these elements from the BERSAFE deck prior to analysis to be absolutely sure.
These loads are applied using a sub-command under the 'PROPERTY LOADS PRESSURE' command (see FEMGEN/FEMVIEW User Manual) and the pressure on the model varies linearly in one direction defined by two points. The interface interprets these loads in a very similar manner to uniformly distributed loads. The differences are as follows:
The interface calculates the pressure load for every element, assigning a value according to the postition of the element face/edge centroid relative to the two points defining the hydrostatic load. The element face/edge centroid is calculated as the mean of the coordinates of the nodes on the face/edge. The load is then applied to the individual element face/edge or split up into equivalent nodal loads as per Uniformly Distributed Loads above
Prescribed Deflections may be applied to a part or set using the command 'PROPERTY LOADS DISPLACE ...'. A deflection value and direction (global X,Y, or Z) may be assigned. Again, prescribed moments are possible but not tested or supported (see uniformly distributed loads). Prescribed deflections are expressed using type 71 cards with one card per node per prescribed deflection. Prescribed deflections are always expressed in the global cartesian system, but will be affected by local axis system definitions on previous type 24 cards.
The interface does not check whether a local axis system is active on the same parts as a prescribed deflection. It is thus up to the user to ensure that any local axis system definitions do not have any undesired interractions with any prescribed dislpacement definitions.
Surface Flux and Forced Convection loads may be applied to a part or set using the command 'PROPERTY LOADS HEAT ...'. These loads are interpreted as block loadings on the faces/edges of groups of elements using type 63 and 65 cards. In FEMGEN two real values may be assigned; ALPHA (heat transfer coefficient), and TEMP (heat source temperature). The interface interprets these values differently to enable two types of thermal load to be produced. If ALPHA is positive, the interface will produce a surface flux load where the surface flux is ALPHA. If ALPHA is negative, the interface will produce a forced convection heat transfer load where the heat transfer coefficient is +ALPHA, and the ambient temperature is TEMP.
A temperature load is applied to a part or set using the command 'PROPERTY LOADS TEMPERATURE ...'. A temperature and a temperature difference may be applied. If the temperature difference is positive or zero, initial temperatures will be created (see earlier), if the temperature difference is negative prescribed temperatures will be produced. For prescribed temperatures the temperature is applied to all nodes on the part or set using a type 75 card with nodes packed into blocks of 15 on each card. The FEMGEN load case identifier and the temperature difference are discarded.
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