Output Parameters |
 
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Output Parameters |
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The parameters for inclusion in the summary output file are grouped under 7 headings, namely:
(i)Nodal motions
(ii)Element restoring forces
(iii)Reactions
(iv)Restoring force envelopes
(v)Angle between two elements
(vi)Angle between an element and a vector or axis system
(vii)Seabed parameters
(viii)Pseudo-curvature and associated angle and tension
Very many of these parameters are straightforward. For example, in the case of nodal motions or reactions, you simply identify a node and a global degree of freedom. Likewise in the case of element restoring forces, you simply identify an element, a location on the element (start node, midpoint or end node), and the restoring force of interest, whether effective tension, bending moment, von Mises stress or any of the standard outputs. Force envelopes are similar except that you identify a range or set of elements, and again the restoring force of interest. Flexcom then loops over all the elements of the set and all three locations on each element in computing the response statistics. The remaining categories require further elaboration. This is provided in the following sections.
The aim of the Standard Output option is to allow you to quickly request a summary of pertinent information, without the inconvenience of explicitly requesting specific outputs. This facility automates many of the (admittedly minor) tasks which you would otherwise undertake manually. For every element set referenced, Flexcom produces outputs of effective tension, resultant bending moment and von Mises stress for that set. The element set entry is also optional, and if no element sets are listed, it is assumed that output is required for all elements (i.e. element set All). Statistical data is presented for dynamic analyses (i.e. maximum, minimum, mean and standard deviation). Note that the option is not relevant for static or quasi-static analyses. Statistics are measured over the last two wave periods for regular wave analyses, and initial transients are automatically excluded from random sea analysis postprocessing. Given that these output parameters are rarely examined in base units (e.g. effective tension is normally presented in kN or kips, rather than N or lbf), appropriate scale factors are automatically applied to the outputs.
Flexcom provides a range of outputs under the general heading of Angles. Specifically, Flexcom can calculate and output the angle between an element and i) another element, ii) a vector, and/or iii) an axis system, which can be either the global axes or a local axis system you define. These outputs are provided both here, in Summary Postprocessing, and in Database Postprocessing. Rather than describe the range of outputs in two sections of the manual, a detailed description is confined to one section only. You are referred to Angles Output for a more detailed discussion of Flexcom angles output.
Flexcom offers three options under the heading of Seabed Parameters as follows:
•Clearance. The first summary output option is the statistics of clearance (minimum and maximum distance) between this range of elements and the seabed, whether rigid or elastic, horizontal or of arbitrary bathymetry.
•Length on Seabed. The second option is to calculate the statistics of the length of riser in the element range lying on the seabed during the analysis.
•Maximum Span and Average Gap. The third option is to request outputs of maximum span and average gap. Maximum Span is defined as the maximum continuous length of pipeline that is not supported by the seabed. Average Gap is defined as the average clearance between the pipeline and the seabed within the region of the maximum span. The Average Gap is also presented over the central third of the maximum span.
In all cases, you identify a range or set of elements. All options are largely self-explanatory. Note however that in calculating the first option, Clearance, what actually happens is that for the element set you specify the program first attempts to identify “sagging” and “hogging” sections within the set. The minimum clearance calculations are then based on the sagging sections and the maximum clearance calculations on hogging sections. Where no such sections can be identified, the calculations cannot be performed, and a zero value is returned by default. Consider for example the case of a free-hanging catenary partly lying on the seabed, where seabed clearance is requested for a set of elements well above the touchdown zone. Flexcom will report zero clearance in this case, because no sagging and hogging regions are present. Although this might appear counter-intuitive the program is operating as intended.
Pseudo-curvature is a parameter used by some manufacturers and contractors in the design of bend stiffeners. The parameter is defined as follows:
(1)
where:
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is pseudo-curvature
•T is axial force or effective tension
•θ is rotation angle
Pseudo-curvature is calculated for an element and location (start, middle or end) you identify. You also specify whether you want Flexcom to use axial force or effective tension in the calculations. Finally, the rotation angle θ is the angle between the element you nominate and either another element, a vector or an axis system that you also identify.
When you add pseudo-curvature to the list of summary output parameters, the actual statistics output to the summary file are slightly different to those output for the other parameters. Specifically, Flexcom calculates and outputs:
•The maximum value of kp, and the associated values of T and θ
•The maximum value of θ, and the associated values of kp and T
•The maximum value of T, and the associated values of kp and θ
Minima and ranges are not parameters of interest with respect to pseudo-curvature. An example of pseudo-curvature output is provided later in the Summary Output File section.
•*STANDARD OUTPUT is used to quickly request a selection of commonly used outputs.
•*PARA KINEMATIC is used to request summary output of nodal motions.
•*PARA FORCE is used to request summary output of element restoring forces.
•*PARA FORCE ENVELOPE is used to request summary output of statistics of element restoring forces.
•*PARA REACTION is used to request summary output of nodal reactions.
•*PARA ANGLE AXIS is used to request summary output of the angle between an element and either a vector or an axis system.
•*PARA ANGLE ELEMENT is used to request summary output of the angle between two elements.
•*PARA ANGLE TENSION is used to request summary output of angle/tension/pseudo-curvature.
•*AXIS/VECTOR is used to define axis systems and vectors for use in postprocessing.
•*PARA SEABED is used to request summary output of statistics of parameters related to seabed contact.
•*COLLATE PLOT AXES is used to define a number of key parameters which uniquely identify a particular simulation within a load case matrix. This is a prerequisite for generating 3-dimensional Summary Collation Plots.
•*ELEMENT SETS is used to group individual elements into element sets.
•*OPTIONS is used to select a number of options relating to summary postprocessing.
•*RESTART is used to indicate that a postprocessing run is to be restarted from an analysis file of different stub name.
•*TIME is used to specify the time interval over which the summary output statistics are to be calculated.
If you would like to see an example of how some of these keywords are used in practice, refer to E01 - CALM Buoy - Simple.