Specifying Installation Criteria
Now that you have defined all the required installation stages and their associated parameters, you may proceed to the specification of installation criteria for each stage. Move to the Criteria tab, shown in the figure below.
In the Criteria tab, installation criteria are specified for each installation stage defined on the Installation Stages tab. You can choose from a wide range of criteria, for example, bending stress, tension, departure angle, tip separation, and so on. In this example, you are going to place sagbend bending strain and tip separation criteria on the analysis. To allow the program to achieve this, you are going to allow it to automatically adjust the location of the seabed connection point at the seabed. Where multiple criteria are specified for an installation stage, as will be the case here, PipeLay prioritises them in the order they are requested. It will only attempt to satisfy later criteria when earlier criteria are already satisfied.
The Stage drop-down list provides a list of the stages defined on the Installation Stages tab. Make sure the first stage is already selected, which it should be by default. The remaining inputs on the Criteria tab are divided in two sections – installation criteria and iteration parameters. The first section allows you to specify allowable criteria (e.g. maximum tension in the pipeline), while the second section allows you to specify what parameters are adjusted (e.g. vessel position) in order to meet the specified criteria.
The Criteria drop-down list provides a list of the available installation criteria. Select Bending Strain from the list as shown in the figure below.
The Component Type drop-down list defaults to Line when the selected Criteria is a strain and so it needs to be changed to Pipe Section as we are only interested in the strains in the pipe in this line stack up. The Component Name drop-down list provides a list of all of the pipelines in the selected Model component. You have only one, Pipeline(1)_16"Pipe(1), and you should select it. The Location drop-down list is greyed out for the pipe section selection as this is a subsection of the full pipeline.
You can now define the maximum allowable value of bending strain in the pipe section, by pressing the Define button. Type in a value of 0.242% as shown in the figure below. You may leave the default value of minimum bending strain (0.0%) unchanged. Press OK to confirm and close the dialog.
Defining Maximum Allowable Bending Strain
Now that you have defined the required criteria, you may proceed to specify what parameters are adjusted in order to meet the specified criteria. The Iteration Type drop-down list provides four options Fixed Connection Point, Vessel Position, Component Length and Seabed Connection Point. Select the Seabed Connection Point option.
The Name drop-down list contains a list of all the seabed connection points currently defined in the selected Model component. There is only one, Seabed Connection, which you should select.
Next you need to specify what direction the connection point is to be moved in an attempt to satisfy the specified criteria. Given that the line in the model is completely defined in the global X-Y plane, a suitable direction to move the connection point would be horizontally along the global Y axis. With this in mind, select Global Y from the Vector drop-down list. Note that if necessary the connection point could also be moved along an arbitrary direction by setting the Vector option to User Defined and selecting an appropriate Axis System component from the User Vector drop-down list.
The Tolerance button allows you some control over the iteration procedure – e.g. maximum number of iterations – but the default values are normally sufficient. For the purposes of this example, you may ignore the Tolerance button.
Press the Add button to insert these bending strain criteria and their associated iteration parameters for Stage 1. They will appear in the list as shown in the figure below.
Stage 1 – Bending Strain Criteria
So in order to specify allowable values of tip separation for Stage 1, you follow a similar procedure:
1.Ensure 1 is selected in the Stage Number input box.
2.Specify the criteria:
•Select Tip Separation from the Criteria drop-down list.
•Select Lay Vessel(1) from the Comp Name drop-down list.
•Specify a maximum allowable tip separation of 0.9m and minimum of 0.8m using the Define button
3.Specify the parameter to iterate on:
•Select Seabed Connection Point from the Type drop-down list.
•Select Seabed Connection from the Name drop-down list.
•Select Global Y from the Vector drop-down list.
4.Click on the Add button to associate the tip separation criteria with Stage 1.
The figure below shows the criteria list with the tip separation criteria added.
Stage 1 – Tip Separation Criteria
Define identical bending strain and tip separation criteria for Stage 2. As with the parameters, the criteria for the remaining stages (3-15) will be added using the Automate Stages dialog which is discussed under the under the ‘Generate Subsequent Stages’ heading.