Flexcom 8.10.2 |
 
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Flexcom 8.10.2 |
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The following faults are present in Flexcom 8.10.2. More detailed information on each fault is provided in the following sections.
No |
Issue |
Severity |
1 |
Hydrostatic pressure and slug flow |
Critical |
2 |
Run-time statistics for rotational velocity and acceleration |
Minor |
3 |
Orientation of pipe-in-pipe connections |
Minor |
4 |
Database revision number |
Minor |
5 |
Line meshing for repeating sub-sections |
Minor |
6 |
Job execution service fails to start analysis process on Windows 10 due to limited user account privileges |
Minor |
7 |
Job execution service fails to start analysis process due to blocked port |
Minor |
8 |
Analysis job appears paused if Flexcom project is located on a mapped network drive |
Minor |
9 |
Sliding Pipe-in-Pipe Connections |
Major |
10 |
Use of equations in the *P-y keyword |
Minor |
11 |
RAO conversions from WAMIT |
Minor |
12 |
AVI Studio unaware of nodal displacement scaling option |
Minor |
13 |
Keyword editor very slow for models which contain a large number of lines |
Minor |
14 |
Information messages relate specifically to nodes and elements even if a model has been constructed with Lines |
Minor |
15 |
Network licensing client app issues warning messages about unlicensed modules |
Minor |
16 |
Equivalent nodes in pipe-in-pipe models |
Major |
17 |
User-Defined Wave Spectrum in Frequency Domain |
Minor |
•Related Topics: Hydrostatic Pressure, Slug Flow, Buoyancy Forces
•Description: This issue could possibly be viewed as a software improvement rather than a program fault, in the sense that the software behaviour is consistent with the program documentation. However, given its potential significance for engineering design, it is being categorised as a critical issue in order to raise awareness amongst the Flexcom user community. This issue is quite specific, so a detailed explanation is provided in the following bullet points.
▪The hydrostatic pressure differential due to slugs (e.g. gas) is usually relatively minor when compared with the hydrostatic pressure associated with the typically heavier surrounding internal fluid (e.g. oil). In situations where slugs are relatively short in length, any inaccuracy in the current numerical modelling approach is minimal. For longer slugs however, the inaccuracy in hydrostatic pressure, particularly for non-horizontal elements, can lead to incorrect buoyancy forces being modelled by Flexcom.
▪Let’s consider an extreme case for illustrative purposes. Imagine you are modelling a vertical pipe which is supported at one end using a fixed boundary condition. When the pipe is full of internal fluid, the weight of the fluid is correctly modelled, and the reaction force at the support location is consistent with expectations. Now imagine that a very long slug is passed through the pipe – sufficiently long that the pipe becomes fully filled with slug material. In this case, the weight of material within the pipe remains consistent with the fluid density rather than the slug density. Naturally the reaction force at the support location is incorrect.
▪The hydrostatic pressure within an element is based on the internal fluid definition and any local changes in hydrostatic pressure caused by the presence of slug flow is neglected by Flexcom 8.10.2 (and all previous versions). The program operation is consistent with expectations, as the software documentation clearly states that… “It is important to note that the hydrostatic pressure term is computed solely on the basis of the internal fluid definition and is unaffected by presence of any slug flow. It would not be numerically feasible for Flexcom to attempt to compute and sum up local variations in hydrostatic pressure in consecutive elements for different fluid densities and different elevations”.
▪The gravitational and inertial forces for an element containing fluid or slug are modelled correctly in Flexcom 8.10.2. For any element which is either partially or wholly filled with a slug, the number of integration points for that particular element is temporarily increased to the maximum number (which is equal to 10, assuming the user is not already using this number). The composition of the internal fluid is then determined on an integration point-by-point basis – each integration point is assumed to govern a section of the element in the region of that point. This ensures that the composition of the entrained fluid is accurately quantified, which means that relatively long elements may still be used without compromising the accuracy of the slug flow model.
▪Buoyancy forces are modelled in Flexcom using a summation of all the pressure forces acting on a particular element. In the case of a horizontally aligned element, the pressure forces acting on the element end faces cancel each other out so there is no net horizontal force. This means that for a horizontal element, whether it contains fluid or slug or a mixture of both, the buoyancy forces are modelled correctly. In the case of a vertically aligned element, the pressure forces acting on the element faces produce a net vertical force. Where the element is filled with fluid, the pressure differential correctly simulates the weight of entrained fluid. However, if the element is slug filled (or partially filled), the effective weight modelled is incorrect as it remains consistent with the surrounding fluid. In the case of an element of arbitrary orientation, the degree of inaccuracy is related to its angular orientation with respect to the horizontal plane.
•Workaround: No feasible workaround exists.
•Related Topics: Database Files
•Description: If you request the storage of run-time statistics via the *DATABASE CONTENT keyword, any subsequent results for nodal rotational velocity and acceleration will be incorrect. Specifically, the values are presented in terms of radians (e.g. radians/sec) but they are labelled as degrees (e.g. degrees/sec).
•Workaround: You can manually apply a scale factor to convert from radians to degrees, or simply suppress the storage of run-time statistics and allow the post-processor to compute the required statistics.
•Related Topics: Pipe-in-Pipe Contact Modelling
•Description: The orientation of a pipe-in-pipe connection may be computed incorrectly if the primary node forms part of an element which does not belong to the primary element set. A situation where this might occur would be one where a vertical outer pipe, containing a vertical inner pipe, is also connected to a horizontal pipe via a T-piece fitting. When determining the local orientation for a pipe-in-pipe connection, Flexcom searches for an element which contains the primary node. As soon as it finds such an element, it assumes this to be the primary element, even if there are other more suitable elements. Although the problem is generally quite rare, it has the potential to dramatically alter a model, and would not be immediately obvious to a Flexcom user.
•Workaround: You can avoid the problem by ensuring that the primary elements (i.e. the vertical pipe in the hypothetical case mentioned above) are defined before any additional elements (i.e. the horizontal pipe). Feel free to contact us should you have any concerns about a particular model you are working on.
•Related Topics: Motion Database File Structure, Database Access Routines, VBA, Excel-Add-in
•Description: All database files created by Flexcom are marked with a database revision number. This is a unique identifier which denotes the contents and storage format of the database file. When a new software release adds new information to the database file, the database revision number is incremented. This ensure that any user-defined custom post-processing routines remain compatible with database files created by different versions of Flexcom. When Flexcom 8.10 was released, the motion database file was extended to include vessel velocity and acceleration terms. Due to an oversight however, the database revision number was not incremented accordingly. In theory, this means that any DBM files created by Flexcom 8.10.1 and Flexcom 8.10.2 are incompatible with user-defined custom post-processing routines. In practical terms however, you are unlikely to encounter this fault, as it only manifests itself when then vessel velocities and accelerations (parameter No.20) are explicitly requested for storage under the *DATABASE CONTENT keyword.
•Workaround: No action is required unless you have explicitly set the Vessel Velocity and Acceleration storage option to Yes, in which case you should reset it to No.
•Related Topics: Meshing Algorithm, Modelling Repeating Sub-Sections
•Description: If you are modelling a line which is composed of repeating sub-sections, the mesh density generated by the software may not be entirely consistent with expectations. Specifically, if you explicitly specify a Min. Element Length at End for any section, Flexcom inadvertently overwrites the Min. Element Length at Start for the next section with this value. The issue is very minor, and it is highly unlikely to be even noticed the vast majority of users.
•Workaround: Leave all the inputs for Min. Element Length at End blank, in which case they will default to the corresponding Min. Element Length at Start values. In practical terms, both inputs are likely to be very similar (if not identical) in the vast majority of cases.
•Related Topics: Job Execution Service
•Description: The execution service fails to start on a Windows 10 operating system if the Local Service account does not have full access to the “ServiceProfiles\LocalService” in the Windows installation folder. This happens because all services running under the Local Service account are required to store their configuration files in that folder.
•Workaround: Ask your local IT personnel to grant full access rights to the %Windows%\ServiceProfiles\LocalService folder for the Local Service account.
•Related Topics: Job Execution Service
•Description: If port 8000 is locked by another application, the execution service fails to initialise fully, which in turn means that the finite element engine fails to start. From a user perspective, it appears that there is a connectivity issue between user interface and the execution service (i.e. traffic light icon appears red). The service will be shown as running in Windows Task Manager, but in the System Application Log a message will appear stating that the service failed to start. If Debug Logging is enabled in Flexcom, a communication exception will be recorded, stating that port 8000 is being used by another application.
•Workaround: Resolve the conflict by closing the other application, freeing up port 8000 for use by Flexcom.
•Related Topics: Analysis Jobs
•Description: If you are running a Flexcom project over a mapped drive, any new analysis jobs will appear paused in the Analysis Status View. You may see an error relating to low disk space, but this is misleading. A sample project on a mapped drive might appear in Windows Explorer as follows… U:\Flexcom\Project.fcproj. The same project stated with the full network path might appear as follows… \\Server Name\Drive Name\Folder Name\Flexcom\Project.fcproj.
•Workaround: Use the full network path when opening the Flexcom project, rather than the mapped drive location.
•Related Topics: Sliding Connections
•Description: Sliding pipe-in-pipe connections may be set-up incorrectly by Flexcom 8.10.1 and Flexcom 8.10.2. The algorithm which selects the appropriate secondary node from the user-specified secondary pipe set no longer functions correctly following a restructuring process undertaken during the development of Flexcom 8.10.1. This fault relates only to models with both sliding pipe-in-pipe connections and pipe-in-pipe sections. Specifically, inactive pipe-in-pipe connections (e.g. if an inner pipe is being inserted into an outer pipe, many of the connections will be initially inactive) do not become active subsequently to reflect changes in the physical configuration which occur due to relative sliding (e.g. when the inner pipe is fully inserted and contained within the outer pipe) if the sliding element set referenced under the *PIP CONNECTION keyword is also defined as an inner pipe-in-pipe section under the *PIP SECTION keyword. If you are modelling a sliding pipe-in-pipe scenario, it is strongly advised that you perform some spot-checks on the connected node pairs using the *PRINT keyword.
•Workaround: If you create a duplicate element set, this will allow you to reference different element set names in the *PIP SECTION and *PIP CONNECTION keywords, and thereby avoid the software fault. The sample keyword inputs below provide an illustrative example. Strictly speaking, this fault could be classified as 'minor' given that a feasible workaround exists (consistent with the fault severity definitions provided above). However, given its potential significance for engineering design, it is being categorised as a 'major' issue in order to raise awareness amongst the Flexcom user community.
C Create a duplicate element set for the inner pipe
*ELEMENT SETS
SET=InnerPipeHydrodynamics
SUBSET=InnerPipe
C Reference the duplicate inner pipe element set in the *PIP SECTION keyword
*PIP SECTION
OUTER=OuterPipe, INNER=InnerPipeHydrodynamics
C Reference the original inner pipe set in the *PIP CONNECTION keyword
*PIP CONNECTION
GEN={OuterPipe_Start}, {OuterPipe__End}, 1, SET=InnerPipe, CURVE=PowerLaw
•Related Topics: *P-y, Parameters, Equations
•Description: If you reference pre-defined parameters or use equations when defining the *P-y keyword, the pre-processor fails to process the relevant data and simply passes character expressions to the finite element engine to which they appear meaningless. For example, if you specify a depth term of ‘DEPTH==[Mudline-10]’, where the mudline is located at X=0, then the pre-processor should evaluate the expression and pass ‘DEPTH=-10’ to the analysis engine. Instead it simply passes ‘DEPTH==[Mudline-10]’, and this is interpreted as ‘DEPTH=0’ by the analysis engine which is incapable of processing the equation.
•Workaround: Do not use pre-defined parameters or use equations when defining the *P-y keyword. Always specify variables explicitly in numerical form.
•Related Topics: RAO Conversions, *VESSEL,INTEGRATED, *RAO
•Description: When converting RAO data from WAMIT to Flexcom, Flexcom incorrectly converts the RAOs for the rotational degrees of freedom (yaw, roll and pitch). Rotational RAOs from WAMIT have units of radians per metre/foot, but the Flexcom conversion fails to take this into account and imports the coefficients as degrees per metre/foot, with performing the necessary adjustment.
•Workaround: Manually convert the RAO data from WAMIT to Flexcom.
•Related Topics: AVI Studio, Scale Nodal Displacements
•Description: The AVI studio does not store any user-defined settings for nodal displacement scaling in the Model View. Hence all videos created with the AVI studio display real-life displacement values which remain unscaled.
•Workaround: No workaround exists, but the issue is not very important.
•Related Topics: Keyword Editor, Line Generation Report, Lines
•Description: The Line Generation Report is slowing down the Keyword Editor unnecessarily. If your model contains a lot of lines, this report contains quite a lot of information which must be computed and presented by the Flexcom user interface. However, this information only needs to be computed when the Line Generation Report is being displayed. The window is normally switched off as typically you will not be interested in such a level of detail. It is hidden by default when the software is first run and remains hidden unless you have explicitly enabled it. In Flexcom 8.10.2 and earlier versions, the user interface computes this information at all times, regardless of whether it is required or not, and this is placing an unnecessary burden on resources.
•Workaround: Rather than using the keyword editor in the normal fashion, use the 'Open as Text Document' option, or simply use any standard text editor software.
•Related Topics: Running Analyses, Lines
•Description: Lines are a relatively recent addition to Flexcom which have proven very popular with software users. They provide an automatic mesh creation facility so that the user need not concern themselves with any particular node and element numbering scheme (as would have been the case in earlier versions of the software). Behind the scenes, Flexcom translates the user-defined lines into the fundamental building blocks of nodes, elements and cables. However, any error or warning messages issued by the program, typically during the pre-processing stage, still relate specifically to nodes and elements, which makes it awkward for a user to quickly understand the source of any problem relating to input data.
•Workaround: Examine the Line Generation Report or the Model View to relate the node and element numbers back to the lines from which they are derived.
•Related Topics: Network Licensing Client
•Description: If you are using a network license, the Network Licensing Client app continually pops into the foreground, alerting you about unlicensed software modules, regardless of whether or not the module is required for your current simulation. For example, if you are running a standard Flexcom simulation, the client app can issue a warning such as “You do not currently have a network license for Flexcom Wind”.
•Workaround: No workaround is necessary as the warning messages may simply be ignored.
•Related Topics: Sliding Connections
•Description: As noted in Hydrodynamic Forces, drag forces and hydrodynamic inertia on inner pipe-in-pipe elements are modelled as terms on the left hand side of the equations of motion, capturing the required coupling between the outer node’s velocity/acceleration and the inner node loading. In Flexcom 8.10.1 and 8.10.2, token connections of zero stiffness are automatically inserted by the software where inner nodes have no physical connection (i.e. no contact stiffness) to the outer pipe. In situations where the outer and inner pipes have been connected using Equivalent Nodes, these additional connections can lead to unexpected behaviour in the finite element solution.
•Workaround: The problem can be avoided by redefining the element sets listed under *PIP SECTION to ensure that any equivalenced nodes do not form part of the section definitions. Strictly speaking, this fault could be classified as 'minor' given that a feasible workaround exists (consistent with the fault severity definitions provided above). However, given its potential significance for engineering design, it is being categorised as a 'major' issue in order to raise awareness amongst the Flexcom user community.
•Related Topics: User-Defined Wave Spectrum, Frequency Domain Analysis
•Description: If you apply a user-defined wave spectrum in a frequency domain simulation, an internal error can occur within the program and the application may terminate without issuing any explanation.
•Workaround: Use one of the standard wave spectrum definitions instead, or perform a time domain simulation with the original user-defined spectrum.