Custom Postprocessing

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Custom Postprocessing

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The Custom Postprocessing component allows you to obtain customised results from analyses in addition to those automatically generated by PipeLay.

custom_postprocessing

You specify a Custom Postprocessing component for individual stages of an analysis via the Installation Stages tab on the Analysis component. This allows you to select the appropriate Custom Postprocessing component from a list of all those defined in the project file.

The Custom Postprocessing component has two modes of operation the first of which relates to the scenario where no Model component has been selected at the top of the component view. This mode of operation allows you to specify additional postprocessing by direct reference to the finite element model of the pipeline, which is generated by PipeLay. For this reason, a certain level of familiarity with how PipeLay generates the finite element model is required when it comes to using the component in this mode. The 'Nodes, Elements & Element Sets' section provides information on how to become familiar with the finite element model of the pipeline.

The second mode of operation corresponds to the case where a particular Model component has been associated with the Custom Postprocessing. This operational mode has the same postprocessing capabilities as the first one, but differs in that postprocessing requests are not made in terms of nodes, elements and element sets. Instead you can designate locations on various components by specifying the component name and by identifying the location on that component through the specification of a suitable length along the component. The 'Output Categories' section provides more information on the related inputs for this mode of operation.

 

Nodes, Elements & Element Sets

In general, the specification of data in PipeLay makes no reference to the standard finite element concepts of nodes, elements and element sets. The user interface takes full responsibility for the task of converting your input data to a finite element model.

To allow complete generality, however, the Custom Postprocessing component can directly reference nodes, elements and element sets. To use this facility, you must ensure that no Model component is assigned to the Custom Postprocessing and you must also be familiar with the finite element model that PipeLay generates. The best way to achieve this familiarity is by direct examination of the finite element model.

There are two ways to do this. The first is through the use of the Dynamic Display Module while the second is through examination of the PipeLay Analysis Specification File, which is the input file for the analysis engine. Whichever means you choose, you must first run an analysis of the pipeline at least once – a static analysis will suffice.

To view the model in the Dynamic Display, open the animation file using the button provided on the Results tab of the Analysis component. PipeLay generates a Dynamic Display file for each stage of your analysis. Use the Options | Show Node Numbers and the Options | Show Element Numbers menu items to toggle the display of node and element numbers. Using these facilities, you can determine the node and element numbers corresponding to particular locations on the pipeline.

While the Dynamic Display is a quick and convenient way to examine the model, it does not give comprehensive information on element sets, which is frequently useful when specifying custom postprocessing. To find this information, you must look at the analysis specification file.

The analysis specification file can be found in the top-level results directory for the analysis (this is the directory opened by pressing the Open Results Directory button on the Results tab of the Analysis component). By default it is called analysis.pas. Double-clicking on this file will run the analysis in a command window, so to view it you should open it in a standard text editor.

Internally, the file is split into several sections, each headed by a line whose first character is a dollar sign ($). The section of most interest, that containing the definition of the finite element model, is the model section, which follows the line $MODEL.

This section contains the definition of the nodes, elements and element sets under the keywords *NODE, *ELEMENT and *ELEMENT SETS respectively. This format will be familiar to users of other Wood Group analytical programs and will not be elaborated upon here. By examining the analysis specification file in this way, you can not only determine the node and element numbers corresponding to particular locations on the pipeline, but you can also determine the element sets that correspond to particular sections of the pipeline.

Having determined the nodes, elements or element sets of interest you can define element sets by selecting the Element Sets button in the Define section of the Custom Postprocessing component. This will open the Define Element Sets dialog.

Please note that making changes to the PipeLay project can alter the composition of the generated finite element model. If you change components in the project, you should re-examine the model before performing custom postprocessing.

 

Output Categories

The Custom Postprocessing component allows output in four basic categories – namely Snapshot, Timetrace, Spectrum, and Statistics. Additional facilities are available to define Element Sets and to define plot settings. Note that the define Element Sets feature is only available with the first mode of operation. The following is a summary of each of the output categories.

1.Snapshot

A snapshot is a plot of the distribution of a particular parameter throughout the structure (or a part of the structure that you specify) either at the end of a static analysis or at a particular time during a dynamic analysis. PipeLay has five snapshot options, namely:

Motion: The distribution of the motion in a global degree of freedom (DOF).

Force: A restoring force, stress or strain.

Structure: A plot of the actual structure configuration at a particular time.

Reaction: Support reactions in the local support axis system.

Separation: Support separations in the local support axis system.

2.Timetrace

A timetrace is a time history of the variation of a particular parameter throughout a dynamic analysis. You can request timetrace output under six headings, as follows.

Kinematic: The motion, velocity or acceleration of a node (first mode) or point on a selected component (second mode) in a global DOF.

Force: A restoring force, stress or strain at a location on an element (first mode) or at a point on a selected component (second).

Reaction: The reaction at a restrained node (first mode) or at a selected connection point (second mode) in a global DOF. The reaction at a support in a local DOF can also be requested in the case of the second mode of operation.

Wave Elevation: The wave elevation at Y=Z=0.

Time Step: The analysis time-step.

Separation: The motion, velocity or acceleration of the separation at a selected support in a local DOF. Axial motion, velocity and acceleration timetrace plots for Zero-Gap O-Supports can be requested by specifying DOF 3 and selecting the Tensioner as location. This timetrace type is only available for the second operational mode when a Model component is assigned to the Custom Postprocessing.

3.Spectrum

The results of a random sea dynamic analysis are usually presented in terms of response spectra, for which PipeLay has four options:

Motion: A spectrum of  motion.

Force: A spectrum of  force.

Reaction: A spectrum of  reaction.

Elevation: The wave elevation at Y=Z=0.

This last option is useful for comparison with the target spectrum, which is the theoretical spectrum corresponding to the parameters you specified using the Wave component. The spectrum calculated from the PipeLay wave elevation trace is referred to as the realised spectrum. The Options button is used in specifying a number of parameters common to the calculation of all response spectra, such as the number of ensembles to be used, the start time, and the time step. Further details are contained in the corresponding Data Inputs article.

4.Statistics

This option is available for dynamic analyses. You can request response statistics of:

Motion: A max/min envelope, plot of mean value, or plot of standard deviation of motion in a global degree of freedom (DOF).

Force: A max/min envelope, plot of mean value, or plot of standard deviation of a restoring force, stress or strain.

Reaction: A max/min envelope, plot of mean value, or plot of standard deviation of support reactions in the local support orientation.

Separation: A max/min envelope, plot of mean value, or plot of standard deviation of support separations in the local support orientation.