This mobile storage tank is evaluated using plate elements in a linear elastic stress analysis.  The mesh is hand created.  That is, each line is created manually by either direct entry or copy and pasting.  Algor, in their results tab, for plate elements, has a direct evaluation of membrane stress intensity (Pm) and membrane plus bending stress intensity (Pm+Pb), which are used against ASME Code allowables.  The maximum tresca stress intensity value found using the probe search in Algor is used to evaluate for fatigue.  The Algor maximum value tag could also be used to identify this highest stress intensity value.

A different mobile tank was analyzed for structural strength of the floor and reinforcement beams.  Again, the mesh was entirely hand made and maximum stress intensities were evaluated against Pm and Pm+Pb Code criteria.  Loading was only applied to the floor in this analysis.

A heat exchanger is evaulated for maixmum stress intensities in the shell adjacent to the tubesheet-to-shell juncture.  Various nodal cross section points are investigated.  The above image shows the location and the seven data points used to calculate the linearized stress intensities.  Typically, at a minimum, three elements across the cross-section are required to properly capture bending stresses; however, mid-nodes are used instead for this purpose.

Non-Linear Stress Analysis-Plastic Collapse With Mechanical Event Simulation - Accounting for material non-linearality means accounting for the material stress-strain curve properties outside of a purely linear elastic range.  There are different ways of accounting for this non-linearality.  Either a straight line hardening coeffient can be used to approximate the material hardening effect, or curve data can be used to provide a truer means of matching the actual stress-strain curve profile. A hardening coefficient essentially creates two straight lines to represent the material curve, one for the linear elastic portion and the other to represent the non-linear portion of the curve.  Curve data is based on a set up data points of stress versus strain, which will eventually create a multitude of straight line between these data points.  Thus, the more data sets, the more representative it will be of the real curve.  Next, in the non-linear analysis, the FE analysis can consider geometry changes, which is where much of the added time in a non-linear analysis comes from because a stiffness matrix is recalculated at each step.  A step is dependent upon user data input as to how often this matrix should be recalculated.  With non-linear analysis, there is also consideration for small and large displacements.  For example, a long plastic object will have large displacements. Thus, large displacement theory is necessary to get proper results. Mechanical Event Simulation (MES) allows for actual motion which can lead to impact, inertial effects, and more realistic surface-to-surface effects.  The following are two examples of SMPES's work involving non-linear FEA with MES:

A medical device company contact asked to evaluate one of their VBR in conjunction with a plate and screw system.  SMPES used non-linear plastic collapse (material curve data) FEA with MES to evaluate this design.  A spinal column was modeled to implant the VBR and then to attach the plate screws.  MES is used along with a displacement plot to determine unstable deformation, which indicates plastic collapse.  The model is also used to capture peak stresses for evaluating fatigue.

A three chamber pressure vessel tower was completely modeled to evaluate 1) if the vessel could be lifted in one piece from the ground up, and 2) to calculate the loads on the tangential nozzles due to hurricane winds.  A mechanical event simulation was performed to study the stress intensities of the shells during lifting.  During the lift siginificant yielding was determined and the thus it was deemd that the tower needed to be lifted in at least two pieces.  A second mechanical event simulation was performed to capture loading on the top two tangential nozzles.  Hand calculations were used, using standard formulas for cylinders, to determine the wind load and wind vortice frequency on the tower.  These loads and frequency of loading were prescribed in the setup over several cycles.  Embedded graphs associated with the tangential nozzle base nodal points are used to graph the variable X, Y, and Z loading of the nozzle.  Using the graphs, the frequency of the load peaks is also used to calculate the various directional natural frequencies of the piping system associated with that nozzle.  When observing movie clips of the pipes swaying in the wind, the differences between the wind vortice forcing frequency and piping natural frequency is readily observed.  This model is made using Algor's PV Designer, in conjunction with the use of added beam, pipe, and shell elements.  Beam elements are used for the structural supports.  Shell elements are used for the platforms.  The final tangential nozzle loads determined from this MES where used in the design model created in the PVElite software package.

Computation Fluid Dynamics (CFD) - Fluid analysis is performed using CFD.  Fluid velocity and/or pressure profiles can be generated by analyzing effects of differential pressure, prescribed velocities, and fan curves.  CFD requires an immense amount of setup and patience in order to acquire results.  Much of the setup process requires obtaining a suitable mesh that accurately depicts the model without resulting in localized flow constraints.  The Algor software automatically applies zero flow velocity constraints at fluid walls; however, how the flow is ramped up, what the convergence tolerances are, and how to handle turbulence are the primary adjustment factors.  Computational time can be lengthy indeed.

A thermal by-pass tee is evaluated for maximum allowable stresses.  CFD is used to determine flow velocities of the gas stream during steady-state flow, valve opening, and valve closing conditions.  The velocity profile results from this CFD is used to automatically calculate internal convection coefficients in a thermal analysis.  The image above shows the velocity and flow profile results for the selected stream-line locations for the valve opening condition.

CFD is performed to study the flow characteristics of a vertical heat exchanger baffle and bustle configuration.  This heat exchanger has a history of tube end cracking. The CFD results showed a stagnant location where the flows diverged in different directions to the exit bustle system.  Investigation showed that this was the primary area of tube-to-tubesheet joint cracking.  The boiler feedwater on the shell side is heated by a tubeside exothermic reaction, which generates steam on the shell side. This steam collects in a bubble at the area of stagnation causing a localized thermal hot spot on the top tubesheet.  The CFD also showed that the exit nozzle side of the bustle created a strong flow pattern on that side of the bustle, but only minimal flow on the opposite side, thereby causing uneven bottomside heat convection coefficients and resultantly uneven temperatures along the entire tubesheet.  This uneven temperature of the tubesheet leads to higher tubesheet bending stresses.