Case Study

Fluid Flow And Interface Definition Case Study

Fluid Flow and Interface Definition


  • Design requirements for the linear actuator were not known
  • Syringe model provided required information to specify a capable linear actuator

We were asked to evaluate the robustness of a linear actuator that extruded drug from a syringe. The demands on the linear actuator were poorly understood – i.e. we did not know how much force the linear actuator needed to provide and how that force varied with variation in inputs.  By modeling the syringe and using what was known about the drug’s characteristics we were able to develop a syringe model that provided the nominal and limits of the force required and used that in a Monte Carlo simulation.  Some of the inputs were empirically derived (e.g. plunger friction). 

Summary: Determine input requirements for an autoinjector (force to move plunger in syringe)


  • Understand independent inputs and their variability
    • Some empirical inputs determined by low-level testing e.g., plunger break-loose and glide force


  • Built analytical model and ran Monte Carlo simulation (50,000 virtual syringes)
  • Identified requirements for robust actuator

Key Takeaways

  • Modeling enables clear identification of quantitative requirements
  • Without a Monte Carlo simulation we would have likely ended up with a system that was under-designed – i.e., met nominal requirements – or over-designed – i.e., met worst case requirements.
  • With the rigorous model and Monte Carlo simulation we have an appropriately robust system that is a good compromise between requirements and capability.
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