INERTIA RELIEF ANALYSIS

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 Hey Guys, 

Today we are talking about the Inertia of relief analysis. what is Inertia relief analysis? The inertia relief analysis is such a type of analysis in which the analysis of unconstrained bodies is done.

So what is mean of unconstrained bodies, the bodies which have not any degrees of freedom fix or all dof's are free is known as unconstrained bodies. In real practises there are various unconstrained bodies are there. For doing such types of analysis we apply the fixed support or the remote displacement but in real conditions, they are not subjected to any of the constrained motion. So for evaluating these results we have to use the Inertia relief analysis

        The procedure of Inertia Relief analysis is to balance externally applied forces so that bodies with no or partial boundary conditions remain in the equilibrium position.  Let us assume the case of an Aeroplane in cruise-

When the aeroplane is on the ground we have enough boundary conditions. When it is in the cruise the lift is produced due to wings which keeps the aeroplane in the equilibrium condition. This pressure applied would cause a rigid body motion of the aircraft (without any deformation) in the direction of the applied loading. 

        In this type of analysis, the applied load is balanced by translational and rotational accelerations which are automatically determined by the solver instead of reaction forces

consider the example, Two ships moving with some velocity in the sea. If one ship collides with the other, there will be stresses generated on both the ships despite them not being constrained so to evaluate this scenario in the software we have to  do the static analysis with the concept of inertia of relief 

The Inertia of relief concept is only used for only some conditions like

1.  Models with both 2D and 3D element types or with symmetry boundary constraints are not recommended.

2. Symmetry models are not valid for an inertia relief analysis. etc 

For understanding in more details, let's take a familiar example of A-arm in ATV vehicle in which the arm is connected to chassis and the tyre.  when we have to do the analysis of this A-arm we fixed the location of A-arm connecting to chassis or either apply the remote displacement. instead of doing this, we have to go with the inertia relief analysis so that we can evaluate results with the real-life condition.

THE MOST IMPORTANT POINT OF ALL IS THAT INERTIA RELIEF IS NOT A SUBSTITUTE FOR BOUNDARY CONDITION. IT IS MERELY AN ANALYSIS TECHNIQUE FOR ANALYZING SOME SPECIFIC CASES LIKE ROCKETS, spacecraft, AEROPLANES AND SUBMARINES. Imagine a case in which a solid body is encountered at one side and pulled at the other side. Now if the BC is removed and Inertia relief loading is applied to the body, will it produce the same effect as the BC? The answer is No, Inertia loading is not a substitute for BC’s. There is logically no way in which Inertia Loading will get to know about the BC that was removed, it could have been a pinned, an Encastre or anything.



Analysis of A-arm showing IR on-off conditions


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