Specification of conditions at boundary nodes (Input Table)
Through the input data table ENDPTS (ENDPOINTS) the conditions at the boundary nodes of the pipeline configuration considered are specified. If the pipeline is one continuous line without branches, only the first and last node of the configuration are boundary nodes.
Most common situation is a connected pipeline. This connecting pipeline is considered to extend over an infinite long distance in the direction of the boundary element of the specified pipeline. Pipe and soil properties are equal to those at the boundary elements. This applies to pressure and temperature as well in case of an OPEN connection. In case of a CLOSED connection pressure and temperature in the connecting pipeline are assumed to be zero. An imaginary valve at the boundary node takes care of the pressure and temperature jump. (see also tables PRESS and TEMP) In case there is no connecting pipeline, the boundary node may be rigidly attached to a fixed structure or may remain a free end.
In the CLOSED state pressure is reacted by the end of the pipe, in the OPEN and FREE state the content of the pipe is pouring out with a theoretical flow reaction force exerted on the pipe end (in case of pressure).
The FIXED boundary condition is interpreted as a 'rigid' connection, i.e. all displacement components are zero. In case of a FIXED boundary condition an external support is not allowed.
The combination of a closed endpoint and INFIN pipeline usually is not a recommended situation, as loading changes at the model boundary may negatively impact the calculations and/or the results.
If the pipeline has branches specified in table CONNECT (and possibly TEECONF in case of Tee's), each end point of a branch - not connected to a point of the pipeline model - is considered to be a boundary node for which a condition has to be specified in this table ENDPTS.
The imaginary valve is closed and the internal pressure is counteracted by the valve. In the case of a connecting INFIN pipeline this pipeline is pressureless. In case of a temperature loading, the temperature difference is stopped by the valve as well. Any connecting INFIN pipeline is without temperature load in that case.
The imaginary valve is open and both the internal pressure and the temperature difference are continued into the connected INFIN pipeline.
Example: A both ends fixed beam and a status Open and Closed respectively. As a result of the internal pressure the extension of the diameter results in a contraction of the pipe-beam in axial direction due to the Poisson effect.
In case of an "open" ended pipe-beam the contraction of the pipe will be counteracted by the endpoint fixed supports, resulting in "tensile" reaction forces.
In case of a "closed" ended pipe-beam the contraction of the pipe is more than compensated by the pressure forces acting on the "closed valves", resulting in a elongation of the pipe-beam. This elongation is counteracted by the endpoint fixed supports, resulting in "compressive" reaction forces.
In a model where the pipe-beam is not counteracted by fixed endpoint supports, the contraction and elongation work out in displacements of the free endpoint.
H330112, last changed: 11/4/2020