Posted by Jordan Kennedy on December 18, 2017
I begin my introduction at the end.
Final Project: Fluid Flume (ie. Gold Fish Race Track) with Depth Sensing and Flow Velocity Sensing
Motivation: The final project build supports my thesis research. I am conducting a series of experiments to observe hydraulically driven jamming of high aspect ratio granular media. Or simply, I am creating log jams and then characterizing them.
What Does my Fluid Flume Do?: I have two fluid flumes that circulate water by means of a pump. The desings of each are quite different. The smaller flume, which is being presented at the final exam, is a circular flume that flows water around. The larger flume is linear and flows water from an inlet resiviour through a channel to an outlet resivour. Both are closed systems that are connected through hosing.
I spent the majority of this semester building my larger flume. However, due to its size, weight, and my continued wish to use it for my research, I am bringing the smaller flume to the final in its place.
This is my larger flume built during the semester.
This is the smaller flume that I built before the class but is much easier to transport.
Shown below is one of my early jamming experiments in an earilier iteration of my flume design.
The flow sensor and depth sensor are completely unnecessary to the function of my flume. However, I am using the fluid flume to caibrate my sensors so that I might deploy them in the field the other component of my thesis work. My depth sensor, through capacitance, will give me water depth. My flow sensor, also through capacitance, will give me velocity.
Previous Work: The concept of moving objects through human made water channels is far from a new concept. Although it would be difficult to pin down , irrigation canals have been dated as far back as 4000 BC in Mesopotamia.
For studying experimental fluid dynamics, the use of fluid flumes is common in many research and teaching settings. Designs for fluid flumes vary widely as many of them are built for a specific set of experiments and often are built in-house.
What I designed Unsurpisingly, my first iteration of my design was terrible. The second iteration was also terrible, but slightly less so.
And so on and so forth…
I’ve lost count of how many iteration each of these designs went through, but here are my most recent designs.
Bill of Materials
Doesn’t look like much but does need to be water tight. This is not trivial.
I accomplished this using the CNC and etching 1/8” a track into 1/4” acrylic sheet.
The etch design looked a lot like this.
FYI - Acrylic is a foolish thing to try and machine but I got really lucky it and didn’t fast fracture on me.
I was then able to cut the walls of my tank (also acrylic, still foolish material to use) and bend them with liberal amounts of heat over a long and slow bending process.
Bending looked like this.
After I bend my walls, I was able to fit them into their track. I then sealed on both sides of the wall with silicone.
The final project looked like this and works very well.
What Questions Were Answered?:
The most pressing question for my project is if I can adequately control water depth and water velocity it a high enough degree that I can easily control my experimental setup. Right now, I can get water to flow but I am lacking any tight controls.
Evaluation Metrics My first level of evaluation metrics are can my flume flow water without leaking.
Second level of metrics are how tightly can I control flow. How much control do I have over depth?
After running my large tank once, I need to revisit the design on the input and output of tank. I am generating edge effects that are not ideal for my experiment at the end of my tank.
My final project will be a fluid flume.
A fluid flume is a human made channel with the intent of transferring water. They generally move water from point A to point B. They can be made from metal, wood, or stone.
My fluid flume is meant to be used in an experimental lab setting. It will cycle water by means of a pump. It will need to be optically clear, mechanically strong, and water tight. My top material candiates are arcryllic, glass, and polycarbonate.
Here is my design.
Previous Build of my own Design: Problem - Curvature induces turbulance.
Pump (purchase part)
Inlet Pipe (3/4” diameter)
Outlet Pipe (3/4” diamter)
Inlet Valve (Custom Design)
Outlet Valve (Custom Design)
The following are fabrication techniques used to make my fluid flume and are assossicated with each week. This does not represent the order or timeline in which components were built or assembled for my final project. Instead they related to the specific skill learned in each week. Some skills were more utilized than others. Some fabrication techniques were not used at all in my final design but will be need to be implemented at a later date for my own thesis work.
I laser cut 3 pieces of 1/4” blue tinted optically clear acryllic for my inlet resivour.
I wanted an optically clear piece so that I could troubleshoot any issues that may arise during the operation of the flume.
The tinted blue are my three laser cut pieces in the image below.
One of the most understated and important weeks of the course and to the build of my final project.
This week I made a programmer that would make all of my electronics come alive.
While my final project did not require any 3D Scanning (at least, not yet. I may need that for my data analysis in the future), I did 3D print an inlet valve. This inlet valve consists of an array of 7 in. long 1/4 in. dia channels to train the direction of water flow. This piece can be found printed specifically for the smaller fluid flume.
This valve is to be attached to my smaller tank.
Although I did not appreciate it at the time of building, variations from the “Hello World” board have been critically in programming and designing my depth and velocity sensors.
For my final project, I heavily depended upon the CNC for cutting my polycarbonate sheets. All of my polycarbonated used in this project was cut using a CNC.
My 2’x2’ outlet resivour was cut using a shopbot. My 8’ x 3’ containment resivour was cut on the Zune in the Harvard University Graduate School of Design since the largest CNCs on campus reside in their machine shop.
Building Outer Containment
For my inlet resivour, I used the small CNC to machine StarBoard. This material was left over from the previous section of “How to Make Almost Anything.” Given the large quantity of it, I cut 8 unique pieces for my inlet resivour assembly.
Shown below is a sluice gate for my inlet.
Show is one of my many cuts on the shopbot.
Inlet Valve: I have been practicing different inlet values for my final project. Following is my most current design.
Taking the Hello World Board, I added an additional input and an additional output from the ATTiny 44. Each lead to a metal pad in order to generate a capacitance reading.
For this week, I created a block to use in my fluid flume to nucleate the formation of jams. This is done by means two triangle blocks to create a neck in the flow.
I would like to add sticks (ie. toothpicks) to my resivour at a constant rate. I was inspired by rotary toothpick dispensors that I have commonly encountered in restaurants.
Using Neil’s DC Motor Board and DC Motor Code, I modified it for my purpose. I added a button and a resistor to the DC Board. I modifying the code such that, when I pressed a button, my motor increased in rotation speed. I also made the motor uni-directional so that it rotated in one direction.
I then added a wooden dowel to the end of the motor and etched in a pocket to pick up toothpicks.
As it rotates, toothpicks will be deposited into the flume.
My role as part of the Harvard Shop Team was to build a frame for our machine in the woodshop. I made good use of this new skill in the design and build of my frame for my fluid flume.
Using four 2”x3”x8’ wood beams, I cut a frame using a saw. Big Thank You to Rob for helping me cut the wood in the machine shop and showing me the best techniques to drill.
My input device for my final project is are capacitive sensing pads used to give me information about water depth. This is tied into embedded programming (ie. the Hello World Board).
I also had to make my capacitive nodes. For future use I will need to make something more robost. However, for proof of concept, I took two copper sheets, connect a wire to each, and covered with clear packaging tape as an insulator. They worked really well given how cheaply they were constructed. I’m very impressed with this technique and I will continue to make good use of it.
My capacitive sensors are below.
Although the resolution could be vastly improved, my capacitance sensors can tell when they are in and out of water.
Networking and communications were not implemented into my final project.
Future use for Networking for my final project: I would like my sensor to be able to communicate with my phone or some other external device so that I don’t have to manually pull data from each of the depth and velocity sensors in the field. For this I would need to implement the use of bluetooth.
I have no composites as part of my final project.
Future use of composites for my fluid flume: My flume leaks down onto the wood base. I would like to create a tapered composite at the outlet to prevent water from running along the base of my flume.
Assembly My fluid flume must be leak free. Dripping water in a scientific lab is a considerable safety hazard. In order to make a seal on my tanks, I used dichloromethane, which is a solvent for polycrabonate. Dichloromethane must be used in a well-ventilated (fume hood) in full PPE. I used a lab jacket, face mask, gloves, and eye wear to distribute dichloromethane that the junction of the polycarbonate parts, arcryllic parts, and starboard material. Once each of these joints was sufficiently stiff (I gave it 24 hours), I would seal on both sides of the connecting seams with silicone. I distributed silicone with a chaulking gun. I then finished the seams with a chaulking kit. I allowed the silicone to cure for 12 hours before it came in contact with water.
For all of my hose fittings, I used gaskets and a wrench to produce a tight seal. I did not use glue for a permenant hold.
Troubleshooting I tested out my flume a day later than I anticipated because of water leaks that I found within the resivour. I spend a day patching up holes in my flume bed before circulating water through.
I checked for leaks in my outlet reseviour.
My inlet resivour leaks. This will need to patched for continued use of project.
Also, I need a BIGGER pump to achieve the flow rates I want. For this I will likely need different hosing/piping. However, using a garden hose and a garden pump was a good first guess approximation for the fluid flume to ensure everything works well enough.
Frankly, I wish I could have spent more time developing and perfecting my sensors. The mechanical part of my final project was quite involved and required a lot of machine time. Also, I was under pressure to get my flume finished. In the long run, however, I think developing better sensors to deploy in streambeds would have helped me out much more.
Overall, I am happy with the class. Sometimes it was a wild whirlwind of trying to catch up and butchering code. I am happy with the Teaching staff who made all of our maching possible. I am also happy with my class section. Everybody in my section was fantastic. There always seemed to be somebody who knew exactly what was going on and was more than willing to help.