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Pure Rocket Science or also Applicable for Engineers in Everyday Working Life?

Analyzing motions doesn’t sound that difficult at first sight. But taking a detailed look at this engineering technology, it can become quite tricky. So, what does one need to bring with him to correctly do the job of Motion Analysis? In this blog we want you to get a better understanding of simulation techniques, especially Multibody Dynamic Simulations. Therefore, we show you some differences of various simulation techniques, describe some wording issues, and help you get a feeling for the knowledge you need to start your simulation career.  

What is Motion Analysis?

Before you can start any new software, technique, or even sports activity, it’s best to inform yourself beforehand about it. So, before you start applying Motion Analysis, here are some facts about this method. 

Multibody Simulation, Multibody Dynamics Simulation, Multibody Dynamics or Motion Analysis after all?

First of all, let’s answer the question, what do you do when you analyze motion? You calculate and analyze motions of systems consisting of several rigid or flexible parts. You can also say you virtually simulate multibody systems, their movements, constraints and boundaries. For this calculation and analysis you may find some different wording definitions in literature, but also in practical application. This might be confusing for newbies but also experienced engineers. Sometimes you hear or read Multibody Dynamics (MBD), sometimes it’s Multibody Simulation (MBS), sometimes Multibody System Dynamics or Multibody Dynamics Simulation. So, what is the difference? Nothing. It’s the same technology but with different preferred wording. They all talk about the already described analysis of motion of your system consisting of multiple parts.  

One could also say, with Multibody Dynamic Simulation you can bring digital mechanical systems to life. In other words, this means, for example, that a CAD assembly with fully defined kinematics is enriched with forces like gravity, springs, or actuators and sensors like distance, velocity, angle, or acceleration. Then its forward dynamics is analyzed. Forward dynamics means that starting from a given initial condition, the states like positions, angles, or velocities of all bodies involved are calculated as a result over time. 

With these results you can then for example

  • animate your mechanical system just like with an CAD-integrated kinematic solver, but with much more detail and realistic motion based on physical laws 
  • postprocess any (internal) quantity within your system. Body and Joint positions, forces in joints or your additional force elements, etc. 
  • examine the performance of a system

Where and When do I Apply Motion Analysis?

Multibody Systems can be found in nearly every object, movement, system in your business but also your private life. As we provide software solutions for companies, mostly mechanical engineering companies, here is a typical application of Motion Analysis in the automotive industry: 

Imagine you get in or out of a car, first you must open the door. Here, you already have a multibody system in action, without really recognizing it. The door hinge allows you to smoothly close and open your door. This little object, consisting of several parts, and their movements, constraints and limits were calculated, simulated and analyzed earlier during the development of the door hinge.  

Multibody Dynamics Simulation of a door hinge used in common cars

Asking our CEO Stefan, when he knows whether to apply Motion Analysis, the solution in his answer seems to be quite easy: “A former colleague of mine once claimed: Well, it’s quite simple where Multibody Dynamics (MBD) is important: Whenever m times q” (mass times acceleration) is large, the use of MBD can be beneficial, and that’s about it.”  

In other words, when a system with high inertia is in motion, even at low speeds, or a system that moves quickly, e.g. vibrations, even with low inertia, knowledge of the dynamics is crucial. This can help getting answers to important questions like:  

  • Is my actuator appropriate for operating my system as I intended? 
  • Where do I get loads for detailed structural Finite Element Analysis (FEA)? 
  • Which loads and cycle counts should I consider when dimensioning standard parts like roller bearings, screws, joint heads, etc.? 
  • Are there any collisions of parts during the operation of my system? 
Typical Industries and Application Fields of Motion Analysis

What other Simulation Techniques are there for Other Applications?

As there are various scenarios, systems, requirements, and applications of products, there are also different questions engineers must answer during product development. As there are different solutions for different problems and scenarios, there are also various techniques to help engineers answer those questions.  

Let’s take some situation in the same domain as Multibody Dynamics is applied, but as a more detailed analysis on body-level – Solid Mechanics. Here we have e.g. the deformation of a body, where you use different forces acting on different areas of a solid body to simulate the body’s degree of deformation. Also, the simulation of stresses and strains on a solid body is to be named here. Investigating different physical domains, you can also simulate wind, fluids or thermic effects and combustion, and even electromagnetism as well as alternative designs and system performance in logistics under various conditions with the help of Finite Element Method (FEM), Computational Fluid Dynamics (CFD), Discrete Element Method (DEM), or Discrete Event Simulation (DES). Sure, some of you have at least heard of them or already applied one of them.  

Analyzing and understanding non-existing or inaccessible systems with FEM
Analyzing fluids and heat, flow and thermodynamics, aiding in system optimization or performance evaluation with CFD
Simulating and analyzing sand, particles or fluids with the aid of DEM
Investigating scenarios, alternative designs, and and system performance under various condistions with DES

What Education Level does One Need to correctly Apply Motion Analysis

Also here, the answer seems quite simple. As multibody systems and their movements are usually very complex, having your A-levels or completed your apprenticeship probably won’t do the job. At least not with the common tools, which are designed for experts and only lead to meaningful results with an academic background. Tedious tasks such as assigning inertial data in the correct coordinate and unit system or applying transformations to bodies and joints are necessary here. However, it is not always that simple to understand and correctly apply them. We at principia MBS have this academic background and are determined to contribute our knowledge and guide users through this process.  

So What do We Know about Motion Analysis and the Knwoledge Required?

You see, there are many possible applications for Motion Analysis as Multibody Systems appear in quite a lot of situations and scenarios in everyday life. When you have to or can apply MBD is also an easy decision, one could say, so that’s maybe not the point where your level of education must be for a PhD. Further, you will gather more and more knowledge the more you use MBD tools and do it alongside your other daily business. Also, relevant technical terms you will internalize quickly. But, as soon as it comes to interpretation of the results, relevant knowledge on a certain level of education is crucial. But, with basic technical knowledge, like your A-levels or a professional apprenticeship, you can gain this know-how by attending training.  

With this blog article we just scratched the surface, but there is way more to learn about these techniques. For your applications you don’t need to know everything about every technique. So, for any more or detailed information about Motion Analysis feel free to drop us a message at any time.

… and stay tuned for more principia MBS 

About the author

Sebastian Sammer

UI/UX Lead

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