Interview with Dr Ian McLuckie of AIES Ltd part II

Interview with Dr Ian McLuckie of AIES Ltd part I Does your software give a possibility to build geometry in its own environment?

Dr Ian McLuckie :Yes, we do not need CAD, as we build solid models in a truly unique manner. We build geometry and solids by joining and manipulating “finite objects” which is the solid and mesh fused, hence the name. It’s a bit like joining Lego together. We can build 2D, axisymmetric and 3D through a combination of operations. These can be saved in a library for future use in other applications.

Our unique solid modelling method builds hex mesh automatically and automatically builds geometric attributes or parameters. Only one person is needed to build the solid, the mesh and the parameters in a single environment. See examples of some of the geometry built in question 3. Could you describe a process of creating analysis by AIESL software?

Dr Ian McLuckie :Yes I will give you two examples.

Firstly using EngineDesigner to carry out tribology calculations on the piston to liner interface, and secondly using SystemDesigner to build a universal joint (Hooke’s joint) and carrying out a modal analysis and also a simple steady state torque analysis.

a) Tribology analysis of a piston and liner

The analysis of the piston to liner interface bearing involves multi-physics analyses.

Firstly we calculate the liner distortion due to assembly, carrying out a clamping calculation of the head, gasket and block. Secondly one needs to have carried out combustion simulations, cycle simulations and a conjugate heat transfer analysis to calculate the temperatures of the piston and liner over the cycle.

 As the piston is reciprocating we normally take the cycle averaged temperatures of the piston and liner at a speed and engine load point.  Thus we carry out the calculations at a number of loads and speeds.  We then calculate the thermal deformation of the piston and the liner. Normally the piston has a geometry that compensates for the thermal deformation coming from the combustion process.

Also the piston thrust and anti- thrust faces have designed and optimised crowned profiles to allow for its pivoting at the pin as it moves up and down in the liner. This is to optimise the lubrication process and to ensure scuffing does not result.

In the calculations we have to allow for the shape of the piston and the shape of the liner.  The liner shape includes effects of assembly (bolting), manufacturing, and thermal deformation.

The piston has the effect of manufacturing and thermal deformation. When we carry out an EHD analysis it also includes the effects of the piston and liner elasticity. The diagrams below show the relevant input deformation data required.  This data is calculated prior to using our tribology solvers.

The type of results the analysis outputs is similar to that from our bearing solver outputs. The user can output 3D animations of the piston and liner tribology over the cycle of simulation. This gives 3D plots of the pressure on the liner, the 3D pressure moving with the piston and isometric views showing both sides of the piston and liner simultaneously. Our software also outputs animations of piston secondary motion, trajectory and tilt over the cycle. Our software also outputs system results such as pressure, friction and MOFT over the whole cycle, as below.

a) Using SystemDesigner to build a universal joint and carrying out a modal analysis and a simple steady state torque analysis.

We build the model in our patented solid modelling software SystemDesigner. We open up the Object Builder module where we can build finite object assemblies and also objects. We start, like any good engineer by sketching what we want to achieve on a piece of paper.  We begin by choosing the finite objects that build the structure, and save them in the user area for future reference, during the building process.

We need to build a top and bottom knuckle, four bearing bushes and a spider.  We are not going to put too much detail in initially as this is a concept design. You can easily build alternative better optimised objects later on, and for example incorporate needle roller bearings and circlips if need be. We build half the top knuckle by connecting finite objects together, and scaling the geometry to a size that we are interested in.

We then join both halves to form a finished knuckle as shown below. We copy the top knuckle and save as a bottom knuckle.  Top knuckle is shown on LHS and bottom knuckle on the RHS.

Next we need to build a spider. This is done in the same manner as the knuckle by connecting finite objects together to form a closed object with an outline. See the spider object below.

You can see that it is built like a cross and has four journals coloured yellow. The RHS image shows the closed outline of the spider. I have deliberately chosen this spider shape so you can consider how to improve its design.

The next objects (solids) to build are the bearings. We need four in total so we build them in the same manner as the previous objects. But we build the bearing object for this example by using one finite object and revolving it as a closed 360 degree solid with an outline, see images below.

Once we have built the objects and saved them in the library, we can then build the universal joint system model. For this we close object builder and now open system builder.

This means we can now connect all the objects together by positioning and connecting the top and bottom knuckles, spider and the four bearings in the assembly.

You can see from the assembly of the universal joint that it contains lots of different colours, these colours simply relate to where the finite objects originated from.

Once you are happy with your model it is very easy to change your object or assembly colour.  The next images show the colour changes of the universal joint. You have a 256 colour pallet to choose from.

Once we have built the assembly we can then set up loads and boundary conditions of the model, in SystemDesigner and System Builder module. For this example we are going to consider doing a free-free modal analysis and a steady state torque analysis.

The model was output from SystemDesigner for modal analysis by a proprietary FE package. Inspection of the model shows there will be 8 rigid body modes, 3 global translations, 3 global rotations and 2 local rotations about the spider.

The first flexible mode will be number 9 as shown in the flexible modes and mode shapes below.

It can be seen from the flexible modes of Mode 9 to Mode 14 that the frequencies aren’t very high. If we wanted to assess the design in terms of system performance we would want to calculate a critical speed map. This is done by varying support flexibility and recalculating the modal frequencies at each stiffness. This shows which modes are sensitive to support stiffness or remain constant and hence insentive. For example modes like pure torsion and pure axial translation remain constant.

We can also calculate a Campbell Diagram or an interference diagram to look at forcing frequencies corresponding to critical speeds. This is all carried out early in the design stage and before we do a MBD with our tribology codes and flexible bodies.

The next images show the results of carrying out a steady state torque analysis. The LHS model shows the assembly and BC. The RHS model shows the VM stress results.

It shows we need to improve the spider design as was envisaged earlier in the discussions. What is the biggest advantage of your software?

answear in part III


About AIES Ltd

logoHave worked for and with GEC-Altshom, AEA technology, Federal Mogul Research, AVL, Rolls-Royce, Cummins, Goodrich, ITP, Babcock and Romax. Projects include predictive and experimental methods on whole engine projects, gas turbine dynamics, pump dynamics, transmission systems, turbocharger dynamics, generator and motor dynamics and locomotive drive trains.

From news concepts through to solving in sevice problems.

FEA, FEM, CAE, CAE software, Finite Element Method, CFD, engineering, AIES


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