Academia Focus Part 1

UCL Mechanical Engineering

Previously on academia focus…

In 2014, we examined how UCL students were using CATIA to design a flow rig for vascular networks to either validate Magnetic Resonance Imaging (MRI) results or highlight errors in the MRI model. The project involved processing detailed information on tumours and various liver cancers vascular networks and consequently printing representative flow model networks using 3D printers. The objective within the printing section of the project was to design an automated assembly package, to enable rapid modelling.

On a recent visit to the Mechanical Engineering department at the University, we thought it was worth revisiting how this project had progressed under the tutelage of Dr Tim Baker, a lecturer at UCL Mechanical Engineering, and explore the work of Sam Suchal, a third year Mechanical Engineering student.

UCL Mechanical Engineering uses 400 student and 35 academic licences of CATIA V5 from Dassault Systèmes. Components commonly used by the students include surface design, assembly design, mechanical design, FE analysis and modelling.

 

THE PROJECT

Why is this project important?

The ability of organs to function efficiently within the body is directly dependent on the delivery of blood. Blood supply is achieved by a complex network of blood vessels, varying in size from capillaries through to arteries. This network brings oxygenated blood within finite distances of every tissue in the body to meet the required metabolic demands. Blood fulfils these demands by carrying dissolved nutrients (e.g. oxygen) and solutes (e.g. drugs), which subsequently diffuse into the intended tissue through the vessel walls. Hence, if the network has an abnormal structure, this will result in limitations and the network will struggle to deliver blood to the organs, culminating in reduced functionality and efficiency.

To gain a quantitative insight into microvascular networks, mechanical engineering students at UCL are required to produce models – systems of straight pipes joined together in a specific 3D structure obtained by micro CT/MR scans of rat tissue corrosion casts. A computer programme is used to calculate the pressure and flow distribution at any point in this network. In order to confirm the validity of the computer’s results, prototypes of scaled-up vascular networks need to be manufactured, flowed and the resulting measurements compared to the computation outputs.

A step-by-step guide to using CATIA to produce flow prototypes…

For Sam to manufacture flow prototypes, the vascular networks needed to be translated from a simple geometrical description to a full 3D model using CATIA V5. Sam’s network was first modelled as a simple set of points joined by straight lines which would become segments, to create the underlying geometry in Generative Shape design workbench. In order to create cylindrical solids, circles were added on planes perpendicular to the segment centre line. The positions of the points (nodes) of the network and the diameters of the circles were inputted parametrically, using the Formula function in CATIA. This 3D geometry is shown below.

3d vascular guide

Using Rib function in Part design workbench, Sam then created solid cylindrical segments to form solid segments using lines and circles he had earlier created. However, this created uneven geometry at the nodes due to differences in the diameter of each segment. This was rectified by creating a solid sphere at each node with the diameter of the largest segment joining the node. The dimensions of the sphere were driven by the diameter parameter. The resulting network, shown below, represents the empty space inside the vascular network that is being modelled.

UCL Vascular diagram 2

In order to create a tubular structure, the same simple geometry was used to create the same network superimposed on the one created earlier. However, this time, the diameters were doubled. This process yielded two networks, one representing the empty space and one that represents the outer shell of the vascular network. Then, using boolean operator Remove, the small-diameter network was removed from the large diameter network to create the desired tubular structure that represents the vascular network, shown below.

UCL 3D Vascular diagram

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The Final Design

The images below show the final design and its 3D printed component.

UCL Vascular 3D

This network is used to validate the pressure distribution predicted by a computer simulation. In order to accommodate the pressure sensors, a set of mounts was added to the model.

Within CATIA, Sam came across a function called Design Table which enabled him to export all the parametrically defined dimensions (i.e. nodal cartesian coordinates and diameters) into a spreadsheet.

 

Any changes to dimensions in the spreadsheet, automatically updates the 3D model. Since all other dimensions are linked to the parametric geometry, if the user wants to make any changes (small or significant), all that he or she needs to do is adjust the spreadsheet values and everything else re-computes.

UCL 3D CATIA vascular final

Therefore a network of 104 segments, such as the one modelled above, can easily be handled.

Read more on CATIA

 

At UCL Mechanical Engineering we endeavour to push our students to design something that results in a commercially viable product and to do this we need the latest technology. We encourage hands-on, problem solving design engineering and solutions like CATIA help us deliver graduates that are more than capable of handling the day-to-day challenges of the work environment.
Dr Tim Baker, Lecturer - UCL Mechanical Engineering

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