An important analysis capability provided by PipeLay is the program facility for automatic iteration on model configuration to satisfy pre-defined installation criteria. This facility is available for all analysis stages with the exception of restarts. You use the Criteria tab to define the criteria for each stage, and to tell PipeLay what parameter you want the program to vary to satisfy that criterion. A typical example is when you want to specify the tension at a tensioner on the vessel, and that you want PipeLay to find the pipeline configuration for this tension value by moving a seabed connection point on the seabed. You define this criterion in terms of a tension range with maximum and minimum values. When this analysis stage runs, PipeLay automatically varies the position of the connection point on the seabed until such time as the tension at the vessel falls within the range you specify.
The specification of criteria for any static analysis stage is optional. Note also that it is possible to specify more than one criterion for a particular stage. If you do specify multiple criteria then the criteria are prioritised according to the order in which you defined them. For example, you might first specify a tension criterion and then a bending stress criterion for a particular stage. PipeLay first tries to satisfy the tension criterion by varying the parameter you nominate. Once the tension criterion is satisfied, the program then proceeds to iterate on bending stress. From then on, at each iteration step, PipeLay monitors both the tension and bending stress. During an iteration to satisfy bending stress, if the limits for tension are violated, the analysis returns to iterating on the tension. In this manner, the program attempts to find an appropriate configuration to satisfy all of the installation criteria.
The design and operation of the Criteria tab is similar to that of the Parameters tab. The tab contains three sections as follows:
▪The upper section of the tab contains the Stage drop-down list, where you select the stage for which you want to define criteria. The Stage drop-down list displays a list of all of the stages you defined in the Installation Stages tab.
▪The middle section of the tab is where you specify most of the criterion data. This section is divided into two columns; the Criteria column and the Iterate On column. You use the drop-down lists and buttons in the Criteria column to define the criterion you want PipeLay to satisfy, the location in the model where you want the criterion satisfied, and the actual value you want to achieve. You use the Iterate On column to define how you want PipeLay to satisfy your criterion, either by moving a connection point, varying the length of a component or modifying the water depth.
▪The bottom section of the tab contains a list where a summary of your specification is provided. There are six buttons to enable you to perform various operations on the list items; Add, Remove, Remove All, Update, Import and Export. The first four buttons function in the exactly the same way as they do on the Installation Stages and Parameters tabs. For more information, please see the section entitled ‘Stage List’. Import and Export enables the user to modify criteria using scripts or within an application such as Microsoft Excel and then import them. For more information, see the section below on Exporting and Importing Criteria.
The Criteria drop-down list displays all of the installation criteria provided by PipeLay, as follows:
Depending on the criterion you choose, some or all of the remaining Type, Comp Name and Location drop-down lists may be disabled. The Values button is always enabled and the corresponding input dialog depends on the selected criterion.
You use the options in the Iterate On column of the Criteria tab to tell PipeLay what you want the program to vary to satisfy the criterion you define in the Criteria column. The Type drop-down list, as shown in the figure below, contains the following options:
You use the Name drop-down list to choose a parameter in your model appropriate to the parameter Type you nominate.
For Fixed Connection Point, Vessel Position and Seabed Connection Point you use the Vector and User Vector drop-down lists to define the direction along which you want PipeLay to move the connection point or vessel. These options are disabled for Component Length and Water Depth. The Tolerance - Define button is enabled for all of the iteration parameters and is used to define data relating to how PipeLay iterates to satisfy the criterion you have defined.
An additional article provides information on the Criteria Tab Best Practice.
Exporting criteria creates a CSV file with fourteen columns. The columns are as follows:
Stage Number, Criteria Type, Component Type, Criteria Component, Criteria Location, Criteria Minimum, Criteria Maximum, Iterate on Type, Iterate on Component, Iterate on Axis, Iterate on - Max Iterations, Iterate on - Min Adjustment, Iterate on - Max Adjustment, Iterate on - Multi-Pass
If an export is performed when no criteria are defined, a CSV file will be generated with just the header information which can then be used as a template for importing.
The image below shows the content of the criteria tab exported from Example 3.
Example 3 Criteria exported and shown in Excel
1.Importing a criteria file overwrites the existing criteria so always ensure you have a backup of the criteria before performing an import.
2.If there is an error in the criteria file, the criteria list will be cleared.
3.When editing data in Excel, precision of large or small numbers may be altered when exporting or importing data. Ensure you change the format of cells to maintain the desired precision.