Week 2
June 24-28
What we did with our model this week
After leaving the silicon exposed in the air for the weekend, it already becomes solid when we came back on Monday. We put the model in the water so the PVA core would dissolve in water. The process of dissolving the PVA core is harder than I thought because it takes a long time to dissolve. To speed up the process, we had to manually try to remove the PVA core from the silicone, which is quite hard. After removing the PVA, we glued the valves in so the water can only flow in one direction in the model.
Getting the silicone model out of the acrylic box
The silicone model without the box and with the PVA core inside
Dissolving the PVA core in water
Completed model with valves in
About 4D Flow MRI
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. Unlike the usual 2D image of MRI, 4D MRI includes the magnitude of space and time. In a 4D flow MRI, we track the movement of particles in a given amount of time. By comparing two MRI images taken with a certain time interval, we get to track the movement of those particles, and then we can calculate the speed of this particle and the direction it's moving in.
About Shear Stress
Shear stress is defined as restoring force over the cross-sectional area. It measures how big the restoring force when something is being sheared. Shear strain is the ratio of the change in deformation to its original length perpendicular to the axes of the member due to shear stress. Shear modulus is defined as the ratio of shear stress to the shear strain. The shear modulus determines how hard it is to shear something into a distance.
About Wall Shear Stress
Wall shear stress is the tangential drag force produced by blood moving across the endothelial surface. It is a function of the velocity gradient of blood near the endothelial surface. Its magnitude is directly proportional to blood flow and blood viscosity and inversely proportional to the cube of the radius.
About Viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, the syrup has a higher viscosity than water. As we can see in the picture, liquids with different viscosity have different physical properties and behave differently when being poured into a container. In the second picture, it showed how shear stress is related to the viscosity of the liquid. There is a boundary plate at the top surface of the liquid, and this boundary plate in moving with a certain velocity. The velocity of the liquid flowing underneath will decrease layer by layer until it stops moving on the bottom. The viscosity is also associated with shear stress. Because of the shear stress between layers, the liquid's velocity decrease as it moves down to the boundary plate on the bottom.
About setting up the PIV experiment
One thing we did with the experiment this week is that we did the set up for the particle image velocimetry that we are going to do on our model. What we have is a big table with screw holes and we have to use the materials we have to stable everything to the table. This set up is different from what we had before. We need to raise the laser and the camera so the camera is facing down onto the model. Here's what we did:
We put concrete under the laser so the laser would be at the right hight. We stabled the laser to the table with the screw hole on the side of the laser so it won't move.
We build a "bridge" that is stabled to the table and put the high-speed camera on it. I was really worried that the bridge will not be stable enough to hold the camera but it worked just fine.
Compelte set up for the experiment with camera, model lazer and pump in their place.