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Tolpa Technical Services, LLC of Hempstead, Texas, has used ALGOR FEA software to analyze industrial equipment such as pressure vessels, rotating machines, structural skids and piping systems for clients mainly in the offshore oil and gas compression industries. |
Applying FEA to Offshore and Gas Compression Structures
Tolpa has been involved with the integration of FEA software and 3-D modeling applications for design, detailing and numerical control (NC) manufacturing with dimensional control for more than 25 years. "I first performed computer-aided stress analysis in 1979," she recalled, "when I wrote custom applications on a Commodore 64 as part of my master's thesis." Tolpa has used many commercial FEA and piping analysis systems including SAP, TRIFLEX, T-Pipe, Nu-Pipe, ADLPipe and CAESAR. "We had been using CADRE Pro to import AutoCAD 3-D CAD models for beam and plate analysis. The need to perform code checks drove us to look into buying ALGOR."
TTS purchased ALGOR FEA and PipePak piping design and analysis software in November 2005. "The ALGOR account manager worked with us to structure a payment arrangement that fit our needs, which sealed the deal," said Tolpa. "So, it was flexibility in commercial licensing that got us started using ALGOR software. But, it's the quality of the support that keeps us as a customer."
TTS often uses ALGOR's customer support services including an individually assigned technical support representative from ALGOR's staff of P.E.- and E.I.T.-certified application engineers. "Having a dedicated support engineer is much better than being served next-in-queue from a pool of representatives and always talking to someone different," said Tolpa. "Over time, our support engineer has learned our business and now knows what we know and what we need. He can direct and advise us. The SUS (Software Updates and Support) subscription is the most affordable engineering support you can buy -- it's priceless."
ALGOR's customer support team has helped TTS achieve innovation in its engineering design work. "We developed a custom method for fatigue analysis of FPSO (Floating Production, Storage and Offloading) gas compressor skids," said Tolpa. "Our support engineer showed us how to put together all the stress load components in one analysis so we could find the maximum stress. This technique along with the ability to calculate the peak velocity responses for rotating machines were the most significant technical breakthroughs that we've accomplished using ALGOR. The customer support team helped us execute our vision and extend our capability."
Tolpa described TTS' typical use of ALGOR software by noting, "Stress analysis of piping systems is our core application; but, we've also expanded our usage to include nonlinear stress, linear dynamics and MES (Mechanical Event Simulation)." The following examples illustrate how TTS has used ALGOR software for offshore and gas compression applications.
Analyzing a Compressor Discharge Bottle
For one typical application, TTS used ALGOR's PV/Designer modeling extender to construct a plate-type model of a compressor discharge bottle and pulsation damper. "Using PV/Designer's modeling wizard for pressure vessels, we built the bottle with its three inlets and single outlet flange in approximately 30 minutes," said Tolpa.
The bottle was subjected to an 800 psi internal pressure and to nodal forces and moments at the center of the outlet flange. "Beam elements were added to the outlet flange in FEMPRO® (ALGOR's easy-to-use, single user interface) to provide the center point for the nodal loads."
A linear static stress analysis was performed to determine the stress distribution. "The analysis results allowed us to optimize the placement of supports for choke tubes passing through the bottle's elliptical heads. Pulsation bottles are sized to reduce the frequency response to the acoustic standing waves inside the pressure vessel."
Tolpa Technical Services, LLC used ALGOR's PV/Designer software to construct this plate-type model of a compressor discharge bottle (pulsation damper/filter). A linear static stress analysis was run to determine stresses due to internal pressure and outlet flange loads. |
Analyzing a Compressor-and-Motor Base
TTS performed linear dynamic analyses of a base frame that supports a gas compressor and its drive motor. "This type of support skid can require anti-vibration media underneath a machine," explained Tolpa. "A well-designed skid is important because it allows the machine to run quieter and last longer by limiting the amplitude of displacements and thus reducing fatigue effects."
TTS first performed a Modal with Load Stiffening analysis to determine natural frequencies. The modal results were then used in a Frequency Response analysis with load curves representing lateral, unbalanced, trip-level, rotating machine forces to calculate the shaking forces and peak velocities. "The idea here was to subject the base to excitations at the natural frequencies as well as at the principal vibration frequencies of the motor-compressor system in order to ensure that the operating stress levels were acceptable." The analysis results confirmed the anti-vibration performance of the skid design.
TTS performed a Modal with Load Stiffening analysis of a base frame that supports a compressor and its drive motor. The modal results were then used in a Frequency Response analysis to determine the displacement magnitude and calculate the shaking forces and peak velocities at the compressor and motor supports. |
Evaluating a Horizontal Tank on Saddles
TTS used ALGOR's MES software to determine peak and residual stresses in a saddle-mounted horizontal tank assembly. "The saddle supports were unusually tall," observed Tolpa, "such that, when the assembly was shipped by rail, the very high transportation loads were a concern."
PV/Designer was used to generate a model of the cylindrical tank and then additional plate elements (for the saddles) were added in FEMPRO. High transportation loads were represented by components of acceleration simultaneously acting in three different directions.
"We applied the loads in steps, searching for yielding in the supports. The MES results showed how much permanent deformation can occur, important to the manufacturer because, sometimes inexpensive repairs are a better investment than exceptionally heavy and stiff supports."
TTS used ALGOR MES to determine peak and residual stresses in this saddle-mounted horizontal tank assembly due to very high transportation loads when shipped by rail. |
Simulating Local Reinforcement at a Lifting Point
TTS used MES to determine the amount of local reinforcement needed at a structure’s lifting point. "The structure was typical of the kind of equipment bases or frame weldments that we deal with," said Tolpa. "We worked iteratively by adding plate elements as reinforcement on the bottom, front or back and then performing the simulation and examining the results to see what effect it had. The goal was to have the final displacement match the initial displacement – that is, no significant permanent deformation." In the final design, stress levels were controlled while the residual displacement, following a lifting cycle, was reduced to a negligible level.
TTS used MES to determine the amount of local reinforcement needed at this structure’s lifting point. Stress levels were controlled while the residual displacement, following a lifting cycle, was reduced to a negligible level. In this display, the ALGOR FEA model shows result contours of displacement magnitude as well as the displaced shape. |
Future Plans for ALGOR FEA
Tolpa plans to continue using ALGOR software for upcoming TTS projects. "In the future, we would like to incorporate two- and three-dimensional fluid flow analysis for prediction of definitive acoustic and flow-induced vibration in piping systems."
Tina Tolpa, principal engineer and owner of TTS, has used ALGOR FEA software to analyze numerous product designs for her company's engineering consulting work. |
Hubertina (Tina) Tolpa, P.Eng., earned a B.S. degree in Engineering at the University of Toronto and an M.S. degree in Mechanical Engineering at the University of Waterloo. She worked in the nuclear and heavy petrochemical fields before founding Tolpa Technical Services, LLC. For more information about TTS, visit www.tolpatechnical.com.
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