George Laird's blog

LS-DYNA: Implicit Quick-Start for Explicit Simulation Engineers

This is the 5th in a series of informal articles about one engineer’s usage of LS-DYNA to solve a variety of non-crash simulation problems. The first was on LS-DYNA: Observations on Implicit Analysis, the second was on LS-DYNA: Observations on Composite Modeling, the third was LS-DYNA: Observations on Explicit Meshing, and the fourth was LS-DYNA: Observations on Material Modeling

Most FEA work in the world is dominated by linear elastic stress and vibration analysis (implicit). The complexity varies tremendously within this realm and can be every bit as challenging as a highly nonlinear transient model (explicit). In the linear world, stress values are very sensitive to small changes in strain, and often take on even greater importance, since their values are used to verify the design margin of a structure or its fatigue life. Since the mission statements and analysis requirements between implicit and explicit analyses are different, one has to shift gears to move from one to the other. It is the focus of this short note to point out how a journeyman explicit simulation engineer can quickly and efficiently create implicit analyses from linear to nonlinear.

Where do I really start?

LS-DYNA Blast Analysis of Large Generator Housings

For more than 15 years, LS-DYNA FEA consulting services have been an integral part of Predictive Engineering. In a recent project, we investigated the blast resistance of several large generator housings. The blast pulse was determined by ConWep calculations given the TNT charges and distances from the housings.

Although LS-DYNA has several built-in methods for simulating blast loading (e.g., *LOAD_BLAST_ENHANCED and *PARTICLE_BLAST), most far-field air blast load calculations of exposed structures can be done as shown in the graphics below. Results from this investigation allowed our client to decrease the weight of their design to such an extent that analysis costs were easily recovered, and that the housings would meet all infrastructure protection requirements at the base. 

LS-DYNA Blast Analysis of Large Generator Housings 01

LS-DYNA Blast Analysis of Large Generator Housings 02

Cooling Analysis of Composite Mandrel using STAR-CCM+

STAR-CCM cooling analysisModern jet engines are getting bigger and also lighter. For example, years ago it was common to use titanium or stainless steel as blade-out containment materials. These large diameter and thick rings can now be replaced by modern carbon fiber composites; however, manufacturing large diameter composites with tight tolerances is difficult. One of the key challenges is maintaining tight tolerance during heating (curing) and cooling (mandrel removal) process. In a recent CFD project for a Tier 1 aerospace manufacturer, we used STAR CCM+ to simulate the thermal-flow process of cooling the composite mandrel down to room temperature. STAR was particularly suited for this project given its advanced polyhedral meshing technology coupled with a fast MPP thermal-flow solver (High Performance Computing (HPC)). Results in this CFD consulting project were verified against prior experience and hand calculations.
 

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