Extract the Most from Engineering Simulations

 


 

Everyone wishes that engineering consultants were free, which just can’t happen.  Short of that, DMS aims to provide the best value out of each engineering project.  As the consultant, I hate to see projects where my client tried to save a few dollars, and in the process lost the chance to double or triple the value of their project.  When you pay for engineering, would you prefer to get three answers instead of just one.  Today we discuss four engineering tasks where you can maximize your value.  Extract every last drop of knowledge from your engineering project.

1.0 3D Model

Many clients show incredulity about paying for a digital 3D model of their ship . . . until they see the first images.  With this, we can show bridge layout, cabin spaces, and exterior shots of the ship, all rendered with believable detail.  You experience the look and feel of your vessel after only committing a fraction of the final build cost.  It sits there in clear digital detail on your screen.  Spin around and fly through to see each angle and detail.  3D models generate the wow factor and energize everyone to finish the project.

But a 3D model extends beyond mere aesthetic uses.  It becomes the central linchpin when designing a new ship.  As ships become more complex, 2D drawings fail to capture all the interactions.  A 3D model allows us to quickly examine multiple angles and check between interferences of different systems.  We can explore all the structural connections. (Figure 1‑1) We may even submit the 3D model to some class societies as part of the drawing package, saving 15-25% on drafting time. [1]

Example of 3D Modeled Tug for ABS Review

Figure 1-1: Example of 3D Modeled Tug for ABS Review [1]

To truly maximize your value, combine the 3D model with finite element analysis (FEA) or computational fluid dynamics (CFD).  The first stage of those projects requires development of a 3D model.  With a little foresight, the engineer can combine two models into one and really maximize the value.

2.0 Computational Fluid Dynamics

Many clients first imagine a laundry list of conditions to test in their CFD project.  But after discovering the cost for CFD, they quickly shrink that list down to just one or two cases.  (One case = one speed, wave direction, etc.)  True, CFD is not cheap.  But don’t assume that skimping on cases reduces the cost significantly.  Between 50-80% of the cost in a CFD project resides with constructing the CFD model.  A typical model construction consists of several tasks:

  1. Create 3D geometry
  2. Create initial mesh
  3. Setup simulation physics
  4. Debug simulation and create stable first run
  5. Perform mesh independence study
    1. Convergence checks (Identify correct mesh settings)

By the time a CFD model begins the prescribed production runs, the CFD engineer already ran the model five to seven times for validation and debugging.  This development effort is necessary to ensure a reliable and accurate CFD model; otherwise you just have colorful garbage.  Reducing your scope of work can’t reduce these initial costs.

Rather than reducing cost, maximize the value of your analysis.  Invest in more CFD cases to investigate further details.  Don’t have a large budget?  DMS can provide several options to reduce the cost of each run.  The costs behind a production CFD run involve more than just computer time:

  1. Labor time: run and debug simulation
  2. Cost of computing resources
  3. Labor time for post processing raw data into human readable results
  4. Labor time to comment and incorporate results into final report

To maximize your value here, focus on reducing the last two elements from each CFD case.  Maybe your only need one measurement from the raw data of each CFD case.  That requires far less labor than generating five pictures, 3 graphs, and six numbers from each run.

Another alternative: add five supplemental cases that are not essential to the project, and specify that the engineer does not need to comment on them in the final report.  Look for opportunities to maximize the knowledge from your CFD project and minimize labor cost.

3.0 Damage Stability Analysis

Damage stability analysis requires an engineer to examine the vessel in various damaged conditions and check that it still complies with stability regulations.  This ensures the vessel has suitable survivability, even with the hull punctured.  The downside is the labor intensity for this type of analysis.  The only way to be sure about safety in a damaged condition is to check every scenario of damaged tanks and compartments.  Don’t try to save money by reducing the number of cases or limiting the analysis to damage on only one side of the vessel.

Example of a Damage Case

Figure 3-1: Example of a Damage Case

 

The real labor originates from constructing the damage stability model.  Stability analysis requires a model of the vessel.  Most of these are proprietary models, and we can’t just import the geometry from another program like Rhino 3D.  To make matters worse, normal stability models don’t typically include the internal compartmentation (all the bits that we need to damage for a damage stability analysis).  For a complicated vessel, this may require modeling 50 – 150 individual compartments.  And then the engineer develops the different damage cases, often a manual operation.

But after developing the stability model, the analysis process accelerates.  Most stability software includes automation options to rapidly iterate through all the damage cases.

Most of the options for damage stability get stipulated by regulations, and you don’t have any options to reduce engineering costs.  Even worse, if the analysis gets abridged, the engineer can not report any definitive conclusions.  Cutting back does not help.  Instead, can we get anything more from this beyond regulatory compliance?  Dive deeper and expose the rationale behind the results.

Ask for Maximum VCG curves from each damage case.  Expose the weak points on your vessel.  This may even uncover options to improve performance.  Perhaps your ship was limited by a single bad damage case.  Some small changes could improve everything.  Adding a few small tanks below decks may vastly expand the cargo capacity above deck.  Tackled creatively, damage stability analysis becomes an opportunity for growth.

4.0 Fatigue FEA

Finite element analysis (FEA) for fatigue holds great potential:  both to improve vessel life and to incur a high engineering cost.  Fatigue FEA really involves two analyses combined.

  1. Use FEA to determine the stress range at various critical points in the structure.
  2. Perform fatigue analysis to determine the expected life of each point.

Unfortunately, the ocean makes things complicated.  Most of the stress cycles on a ship derive from either machinery vibrations or ocean waves.  The ocean waves generate a wide array of stress ranges.  To reduce engineering costs here, focus on the type of fatigue analysis.  Full spectral fatigue requires a detailed history of the vessel operating region and records of the weather.  We need to reproduce the various wave spectra for the life of the vessel and predict fatigue performance for all those cases.  Very labor intensive.

A simpler option is the simplified fatigue assessment.  Rather than generate each wave from past history, this creates an assumed distribution of waves based on a few critical numbers.  Same results, a little less accuracy, with a lot less labor.  This method doesn’t work for all case situations, but it makes a great cost saver when applicable.

Maybe you don’t need every point analyzed.  A typical fatigue FEA identifies dozens of potential fatigue sites.  But some are more important than others.  Work with the engineer to select only a few sites for full fatigue life predictions.  The remaining sites just get noted for inspections.  This focuses the maintenance and still improves your efficiency.  But at a lower engineering cost, and everyone wins.

5.0 Conclusion

We all want to feel good about paying for engineering analysis.  Sometimes the best answer drives us to maximize value, rather than minimize cost.  Engineering is not a commodity; some tasks have minimum costs to ensure safety and reliable results.  In those cases, you do better to go beyond basic safety and search for enhancements.  Many times, the key to satisfactory engineering projects lies in asking for more, not less.

6.0 References

[1]American Bureau of Shipping, “ABS and Crowley Pilot Validates 3D Modeling Techniques to Meet Class Requirements,” American Bureau of Shipping, 2018 23 Aug. [Online]. Available: https://ww2.eagle.org/en/news/press-room/abs-and-crowley-pilot-validates-3d-techniques-to-meet-class-requirements.html. [Accessed 22 Oct 2018].
[2]VesselView, “Vessel View – 3D Animation Studio – Yacht 3D Trailer,” YouTube, 10 Oct. 2011. [Online]. Available: https://www.youtube.com/watch?v=Os9zYb18QoU. [Accessed 29 Oct 2018].
[3]Wikipedia Authors, “CFD Simulation Showing Vorticity Isosurfaces Behind Propeller,” Wikimedia Commons, 22 May 2011. [Online]. Available: https://commons.wikimedia.org/wiki/File:CFD_simulation_showing_vorticity_isosurfaces_behind_propeller.png. [Accessed 29 Oct 2018].
[4]Vard Marine, “Finite Element Analysis,” Vard Marine, 2018. [Online]. Available: https://vardmarine.com/vessel-design-process/advanced-analysis/fea/. [Accessed 29 Oct 2018].