MENG 472 Projects - 2016

In MENG 472b, students work on independent projects that cover a wide range of topics, from traditional mechanical engineering topics (e.g., mechanical device design, fluid flow, and materials analysis) to interdisciplinary topics at the interface between mechanical engineering and other branches of engineering such as biomedical, chemical, electrical, or environmental engineering. Under the supervision of faculty advisers, students investigate physical phenomena through experimental measurement and/or numerical simulation, and they design and construct functioning prototypes to solve engineering problems. The majority of the faculty advisers come from within the mechanical engineering department, with the remaining advisers distributed across the University (and occasionally outside the University). Funding for projects is generously provided by the Yale SEAS Dean's Office and, in some cases, through the faculty advisers. The students were asked to write the following short summaries two-thirds of the way through the semester, when they still had a few weeks to go on their projects.


Basic Research


Synthesis flexibility of copper oxide nanoparticles

Bolun Liu
Adviser: Professor Lisa Pfefferle, Chemical and Environmental Engineering

Our current research follows from work done at the Catalytic Combustion Lab, when a need for a broader understanding of synthesis techniques for copper oxide nanostructures arose. We are using a three-level fractional factorial design to explore the possible parameter space around one particular synthesis method that has been successful in the past. We have chosen to base our research on a wet synthesis technique involving copper nitrate and sodium hydroxide. Many of our synthesis procedures are promising. We produce nanosheets, nanowires, and nanoparticles, do not require lengthy low-temperature post-annealing to remove insolvable chemicals, and do not require as slow a filtering process. Our co-solvents, sodium chloride and ethanol, are low-cost, environmentally friendly, and have an impact on nanostructure, although the nature of the relationship is an ongoing investigation. We have also found that the bounds for the synthesis technique are between 0% and 20% by mass for ethanol, and between 0.5 and 0.005 molar for sodium hydroxide. Although this research is ongoing, we have successfully determined some of the bounds in which successful nanostructure synthesis lies, and proven that a variety of nanostructures can be produced, as shown in the image.



Hydrographic structure and circulation of Pacific winter water on the Chukchi Sea shelf in late spring

Astrid Pacini
Adviser: Dr. Robert Pickart, Woods Hole Oceanographic Institution

Pacific water crosses the Chukchi Sea shelf, located between Alaska and Russia, and delivers nutrients to the Arctic Ocean. This study looks at the dynamics behind the density structure of the water column during May and June 2014 in an effort to understand how these nutrients are being transported northward and are being upwelled from the seafloor to the zone of light penetration for primary productivity. We have found that the water column is primarily composed of two mixed layers separated by a density interface, and that if ice (see image) is generated according to a -150 Watt/m2 flux, enough brine is rejected into the top mixed layer to overturn the water column in a matter of 0.5-40 hours, depending on the level stratification between the mixed layers and the size of the top mixed layer. This overturning brings nutrients from the seafloor into the zone of light penetration, thus ensuring that, from a convective perspective, the water column of the Chukchi Sea is poised for phytoplankton blooms. Now it is crucial to perform atmospheric and ice concentration analyses in order to understand whether the shelf is advectively poised for these blooms.



Combining the scanning tunneling microscope probe with the atomic force microscope tuning fork

Taha Ramazanoğlu
Adviser: Professor Udo Schwarz, Mechanical Engineering and Materials Science

Getting a better understanding of the microstructure of materials that defines their characteristics requires the ability to observe the interactions at the atomic resolution. Combining the scanning tunneling microscope and the atomic force microscope enables us to merge their advantages into one solution. Modifying the atomic force microscope’s tuning fork that is used to detect the physical topology of materials by placing a voltage-carrying probe on it, we are able to implement the scanning tunneling microscope’s ability to detect the positions of individual atoms. The external wire solution to apply the bias voltage, as seen in the picture, is currently used in the lab but was not found satisfactory due to the damping effect of the wire on the tuning fork. We are now depositing a film of epoxy on the tuning fork to first insulate it, and then a layer of gold to carry the voltage to the probe. We are expecting the attenuation on the natural frequency of the tuning fork due to the additional mass to be much less compared to the external wire solution, and we have designed a vise mechanism that holds the tuning fork during the depositions to improve the quality and repeatability of the processes.




Biomechanics Research


Contribution of the transverse arch to foot stiffness

Lucia Korpas
Adviser: Professor Madhusudhan Venkadesan, Mechanical Engineering and Materials Science

We are investigating how compression of the transverse arch, along the width of the foot, affects overall foot stiffness (i.e., resistance to deformation under load). The windlass mechanism, in which flexing the toes upward induces an increase in the arch height, is used to load the foot. We have designed and built a platform, as shown in the image, to raise the toes while reducing the effect of friction on the observed change in arch height. During data collection, we are tracking the movement of the top of the arch as the toes are raised for two conditions for each subject: the arch compressed by wrapping athletic tape around the midfoot, and the uncompressed arch. We have currently collected data from two subjects. Preliminary results indicate that an increase in the strain on the tape decreases the height to which the arch can rise for a given toe angle, which implies an increase of the stiffness of the foot. We will collect foot deformation data from several other subjects to confirm this result. Ultimately, we hope to compare our results against an existing theoretical model.



Body orientation stability during two-legged jumping

Alexander Lee
Adviser: Professor Madhusudhan Venkadesan, Mechanical Engineering and Materials Science

In two-legged jumping, a person’s body provides shear and moment forces to compensate for differences in vertical force provided by the legs. The purpose of this project was to determine the effects of shear and moment forces, applied at the feet, upon body orientation stability during two-legged jumping. We collected velocity data at 200 times a second at 16 points on a mechanical jumper using three Vicon T20-S motion-tracking cameras and analyzed this data in Matlab to calculate the angular and linear momentum as a function of applied force. We varied the force application to the jumper’s legs to find the relationship between force and momentum for our jumper. We anticipate finding that both types of forces contribute to body orientation stability but that shear forces contribute more heavily than moment forces. Our final results will be presented in the form of a figure that plots the angular momentum against the linear momentum for all four combinations of force: shear, moment, both, and none. Our results have the potential to impact the field of robotics and further collective understanding of biological two-legged jumping. Moving forward, we recommend further investigation of the effect of moment and shear forces upon biological subjects.



Modeling muscle mechanics for mathematical analysis

Betsy Li
Adviser: Professor Madhusudhan Venkadesan, Mechanical Engineering and Materials Science

The Yale Biomechanics and Control Lab is interested in the mechanics of how muscles actuate and is designing an apparatus that demonstrates a simplistic model of how myosin retracts and lengthens actin to analyze the mechanics on a simplistic level. Designing the model began with research on the fundamentals of muscle theory and how the myosin and actin interact with each other, and on bi-stable mechanisms that would form the basis of the myosin’s movement. Progress thus far has produced a design that uses electromagnetism to actuate a myosin model into one of two states formed by a geometric structure capable of bi-stable positions. The mechanical design of the muscle actuation is made to appropriately represent muscle movement, and allows measures of error that will decrease as the mathematical model becomes more complex. Conclusions of the design phase include thermoforming a soft, plastic dome attached with a strong neodymium magnet at the apex of the geometry. The part will act as the myosin and an electromagnetic frame will actuate the dome into one of its two possible stable states. The proposed design will serve as a prototype to demonstrate a representable movement to later refine and determine a mathematical model.



Estimation of bone surface curvatures

Xuan-Truc Nguyen
Adviser: Professor Madhusudhan Venkadesan, Mechanical Engineering and Materials Science

Paleontologists and anthropologists will often use the shape of bones to determine their function and how they interacted with neighboring bones. However, there is currently no mathematically rigorous method of analyzing bones. In order to quantitatively characterize bone shape, we are using non-uniform rational B-splines (NURBS) to fit the bone surfaces to functions. We used VGStudio MAX (a CT visualization and analysis software) to extract surface data in the form of point clouds from high-resolution CT scans of fossils. We are using MATLAB to generate the NURBS functions to smooth our data and to perform analysis on both generated test surfaces with known curvatures and arbitrary bone surfaces. We will use these functions to calculate surface curvatures of various bones, which will allow us to compare bones within and across species. We hope to achieve a new general method of quantitatively characterizing bone shapes, and particularly curvatures.



Postural hand synergies during Bharatnatyam dance

Lucinda Peng
Adviser: Professor Madhusudhan Venkadesan, Mechanical Engineering and Materials Science

The aim of this project is to explore whether the human hand has more independence of control over individual joints than current research indicates. This independence of control is measured by postural hand synergies, which is the idea that the joints are linked neurologically, so that they move proportionally rather than independently. To assess the independence of joint movement, participants will shape their hands into many hand postures from Bharatnatyam dance, which focuses on hand gestures, one of which is shown in the image. The position of the markers on the hand will be measured to obtain joint angles. We are studying postural hand synergies by using a motion capture system, and have modified the existing hand model to analyze the joint angles. The preexisting model used by the motion capture system overly simplifies the hand. Our model more accurately measures the movement of the hand by tracking the position of the bone under the pinky separately from the three bones under the middle three fingers, and defining each finger segment as a reference frame instead of a line so that joint movement can be broken into forward/backward and side to side components, flexion and ab/adduction respectively.



Unraveling the significance of the tenodesis effect for human throwing

Petter Wehlin
Adviser: Professor Madhusudhan Venkadesan, Mechanical Engineering and Materials Science

The biomechanics of human throwing are yet to be fully understood. However, in the Yale Biomechanics and Control Lab we have developed a hypothesis that might answer the question about what enables humans’ unique throwing abilities. The centerpiece of our hypothesis is the tenodesis effect, which is a mechanical coupling between the wrist angle and the opening angles of a person’s fingers. To test our proposition we have built a model of the human arm, which incorporates the tenodesis effect, and tested its throwing capabilities. We found that we faced three main obstacles that prevented us from measuring the arm’s full throwing potential. The obstacles were: deflection of our projectile caused by the shape of the finger, suboptimal opening angle of the finger caused by incorrect lengths and elastic moduli of the tendons, and excessive oscillations caused by an underdamped response. We are currently addressing these obstacles by redesigning the finger, and by using a mathematical model to optimize the static and dynamic characteristics of the throwing arm. We will then be able to measure the full throwing potential of our model and compare it to other throwing mechanisms, to ultimately prove or disprove our hypothesis about human throwing.




Design


Implementation of continuous waves in surf park design

Katherine Berry
Advisers: Professor Jan Schroers and Dr. Larry Wilen, Mechanical Engineering and Materials Science

Existing surf parks suffer from an inability to provide consistent, long-lasting waves in a variety of styles to the surfing community. These shortcomings inhibit the entrance of surfing into major athletic events, and more generally do not provide a realistic, workable environment for surfers at a range of skill levels. In order to address these needs, our team is investigating the feasibility of an annular park design, which we believe will produce longer-running waves. Additionally, the interchangeable base of our design allows us to test how different underwater curvatures provoke different wave breaks. The main work until this point has been determining the best structure and material setup for a testing model. The model has recently been completed, as shown in the figure, and a range of base inserts machined for preliminary tests. Our final design consideration concerns the wave-generating apparatus. The current generator is a flexible stand-in that will allow us to test the optimal states of properties such as size, angle, and speed, before the development of a more streamlined model. A better-designed surf park will not only increase the utility to the surfing community, it will also provide greater visibility for the sport, making surf-related business endeavors more lucrative.



SEARCH Center air quality monitor

Jonathan Chang, Genevieve Fowler, Mieke Scherpbier, and Patrick Wilczynski
Adviser: Professor Drew Gentner, Chemical and Environmental Engineering

The SEARCH Center air quality monitors are two different monitor designs, one stationary and one portable, which contain sensors to collect research grade data of common air pollutants. Both monitors measure temperature, humidity, particulate matter, nitrogen oxides, carbon monoxide, methane, ozone, and carbon dioxide. The stationary monitor includes an additional sulfur dioxide sensor. The design is separated into two subsystems: the physical housing and the electronics.

The physical housing of both monitors is constructed from a combination of acrylic and ABS plastic. The airtight and waterproof outer casing was constructed out of laser cut acrylic, glued together, and sealed with silicone sealant. Adhesive-backed copper foil was then added to the internal surface to provide electromagnetic shielding for the electronics. The internal airflow manifold components, which form an airtight chamber that houses the sensors, were 3D printed out of ABS plastic.

The current system uses one printed circuit board (PCB) per sensor for the sensor itself and processing electronics. We have successfully shown changes in data output correspond as expected with changes in pollutant levels for a number of the boards, and going forward will continue to validate their functionality using our specially designed testing chamber. We will edit the design so that the data acquisition and processing electronics for all sensors sit on one PCB. The single PCB will simplify the system. Each of the sensors must be electrically connected to this board with their sensing ends in the airflow manifold at the approximate same height. The sensors can either be soldered directly to the main PCB or attached to a small raised PCB to make up for the shorter height. Sixteen bit analog-to-digital converters (ADCs) are used to convert the signal from the sensor to a digital signal. The boards have been designed so that the ADCs are as close to the sensor output as possible to minimize noise. The ADC output is communicated using I2C to the Arduino, which sits on a third PCB. This PCB also includes a battery management circuit, SD card memory slot, and a cellular data chip. As the Arduino collects the data from the ADCs, it will send it to an external server via the cell chip. This data will then be used by researchers to develop a real-time map of pollution levels across the area over which the monitors are distributed.



Simulated body for central venous catheter placement device

Jonathan Dorsch
Adviser: Professor Steven Tommasini, Orthopedics and Rehabilitation and Biomedical Engineering

Along with two undergraduates and a resident at the medical school, we are working to create a device to improve the current method of performing central venous catheter (CVC) placement. CVC placement is a surgical technique during which physicians place a small tube within the body to gain access to the venous system. In order to improve upon current prototypes of our device and to gain more useful feedback from physicians with whom we interact, we aimed to create a more realistic model to simulate the human body in a CVC placement procedure. We have been successful in planning a model which integrates both the soft tissue surrounding the target vein as well as the circulation found within the human body. Tested independent of the soft tissue portion of the simulator, the circulation system provided proper hemodynamic conditions (accurately recreates the conditions produced by the heart in a human body). The process of creating a model for simulation of the procedure has already begun to influence aspects of the design. By continuing to create and refine the simulator, we hope to improve the quality of the device which will lead to better care for patients in need of CVC placement.



Miniaturized and low-cost VOC sensor

Evan Doyle
Adviser: Professor Drew Gentner, Chemical and Environmental Engineering

This project involves designing and prototyping an air quality monitor to detect volatile organic compounds, or VOCs. The primary goal for the semester is to make a sensor that is around the size of a shoebox, which could be widely deployable due to small size and low cost. This would be approached by first using a computer-aided design program to model the components and assembly of the sensor, and then creating a physical model based on that. In order to accomplish this, we have created a Solidworks 3D computer model of a sensor 8”X8”X6” (see the image), which incorporates the necessary chemical measurement, heating, and processing elements to measure VOCs in a field setting. This model was originally designed to be built with a frame made entirely from acrylic, but due to the high temperatures reached by some components, aluminum will be used to house heating elements. Additionally, printed circuit boards have been designed to interface with the sensor components, and will be incorporated into the system when the final prototype has been built, along with a power distribution system and control computer.



Optical hemoglobin meter

Russell Egly
Adviser: Professor Douglas Rothman, Biomedical Engineering and Diagnostic Radiology

It is immensely important for people to have access to a portable, non-invasive device for measuring blood hemoglobin concentration. We designed a device that uses two light emitting diodes with a photodiode in a finger splint and a National Instruments myRio microcontroller deck to measure this concentration. The circuit hardware has been assembled and the device has been used to measure a user’s pulse. The circuit diagram shows the final layout of the device and how the diodes interface with the microcontroller and a desktop. The lights and photodiode are currently housed in a finger splint and the signal is taken through the finger sideways as this has yielded the signal with the best signal to noise ratio compared to a light signal transmitted vertically through the finger or reflected off the bone in the finger. We also found that the two wavelengths of light generate different signals and in the remaining time in the semester we will be working to correlate the ratio of these signals to actual blood hemoglobin concentration. We also implemented resistors to guarantee that the power being emitted by the lights complies with Food and Drug Administration regulations (< 3 W/cm2).



Waste allocation load lifter – Yale class

Jonathan Karp, Amy Rockwood, and Jordan Sabin
Adviser: Professor Corey O’Hern, Mechanical Engineering and Materials Science

The purpose of this project is to develop an improved method for collecting trash in parking lots following tailgates. Current best practices rely on manual labor, making them costly and inefficient. We aim to disrupt this paradigm by developing a semi-autonomous electro-mechanical trash collector. Below we highlight the detailed design and engineering work completed on the system to date. The device can be broken down into three distinct subsystems: (1) a collection system to pick up pieces of rubbish, (2) a compaction system to reduce the bulk volume of waste, and (3) an overarching control subsystem. The design of the collection subsystem focused on the development of a scooped conveyor belt system to allow for the semi-continuous collection of trash. Difficulty with the tendency of cylindrical objects to roll away from scoop mechanisms required the implementation of a backstop. This backstop rides along the ground and is attached to a suspension to allow for movement over uneven terrain. A significant focus was placed on the development of 1/16th inch polycarbonate scoops rigid enough to hold 4 kg of trash and yet flexible enough to bend over uneven terrain. The design of the compaction system centered on the need to exert approximately 2,000 lbf to compress trash into a solid cube. Cost considerations, and a desire for equal force distribution across the plate area, resulted in the development of a compaction system with two separate track actuators, each capable of producing 900 lbf. The compaction system also serves as a disposal mechanism, pushing compacted blocks of trash out of the hinged front panel. The forces exerted on this hinge and lock assembly drove the development of an in-house designed mechanism based on those used in dump trucks. Finally, the design of the control subsystem focused on the realization of long-range remote control, the effective control of drive and secondary motors, and the implementation of several sensor feedback loops. Long-range remote control will be implemented over radio waves. Pulse-width modulation will be utilized to allow for differential skid turning, and an array of sensors, including power resistors and string potentiometers, will provide feedback on force exerted and the volume of trash compacted. In the coming weeks, the manufacture, assembly, and integration of the systems outlined above will result in a robot capable of clearing parking lots of trash and depositing the collected waste in easily disposed of compacted blocks.



Designing a stylish and durable DSLR camera bag for everyday use

Mavila Marina Miller
Adviser: Dr. Joseph Zinter, Mechanical Engineering and Materials Science

As the number of hobby photographers increases, there is a growing need for stylish camera bags that can protect equipment against extreme weather conditions and impacts. These include withstanding extreme weather conditions, small shocks, and preventing individual camera accessories from moving around loosely. Following twenty iterations of stress tests, the best trade-off between making the bag as lightweight as possible while being sufficiently protective consists of five layers. The inner layer in touch with the camera is made of silk microfiber in order not to cause scratches on the camera. The second and fourth layers consist of a buffer sponge to protect the camera in case of a fall from up to a height of 40 inches, whereas the third layer is made up of a one-inch cotton layer. To prevent rain damage, the outer layer consists of waterproof polyurethane leather. The idea is to create fun animal bags with customizable patterns and colors for each part, such as lens, ears and body. Small clips on either side of the bag allow multiple lenses and accessories to be added on. Based on our research, the bag can be produced at a manufacturing plant with a minimum order quantity of 1000 bags.



Design, fabrication, and testing of Formula SAE vehicle dynamics

Philip Piper
Adviser: Dr. Joseph Zinter, Mechanical Engineering and Materials Science

Bulldogs Racing designs, fabricates, and races an open-wheeled race car each year to compete in the Formula SAE series of competitions. This year's car, BR16, will be all-electric with a high rear weight bias of 60% requiring a change in vehicle dynamics from Bulldogs Racing's 2013 championship vehicle. Eight inch wide rear Hoosier tires and six inch wide front Hoosier tires were chosen through extensive tire data analysis to produce maximum levels of grip and meet our weight distribution needs. The BR13 suspension design was iterated for BR16 to optimize the Hoosier tire conditions in both the front and rear of the vehicle. Additionally front and rear upright weight was cut in half from about 3.5 lbs to 1.6 and 2.0 lbs for the front and rear uprights, respectively. The front brakes were lightened by using one caliper per side instead of two through careful selection of the front master cylinder. Additionally a more rigid brake line was used to produce less line flex, and therefore a much stiffer brake pedal. Overall, the vehicle dynamics portion of BR16 will weigh considerably less than BR13, and will also produce better conditions for the Hoosier tires that are used.




Materials


Reusable bulk metallic glass molds for small parts

Kori Baij
Adviser: Professor Jan Schroers, Mechanical Engineering and Materials Science

The manufacture of small metal parts is a process that could be streamlined by the introduction of reusable molds. Currently, small parts are only mass-produced through machining, and small bulk metallic glass parts shaped by thermoplastic formation utilize single-use silicon wafer molds. This research focuses on the factors that determine the closeness of the mold to the part we are replicating, namely the alloy of the mold material, formation environment (heat, pressure, length of time), and the size of the well holding the part. In the image, we see side-by-side two steel washers embedded in the mold material, the right in a larger well (200% of the washer’s outer diameter), and the left in a smaller one (150% of the diameter). We found that the larger apertures produced molds that formed more tightly to the part to be reproduced. The next set of trials will test enclosures that are 300% the washer’s outer diameter to test the relationship between enclosure size and the gap between mold and part. Future avenues of research include the factors involved in part release and the lifetime of such molds over many stress cycles.



Effect of thermal cycling on the fracture toughness of bulk metallic glasses

Matthew Blake Knuth
Adviser: Professor Jan Schroers, Mechanical Engineering and Materials Science

This research project is focused on investigating the effect of cyclical cooling on bulk metallic glass samples. Bulk metallic glasses are metal alloys with an amorphous microstructure. In our experiment, metallic glasses are cycled between thermal reservoirs containing liquid nitrogen and lukewarm water. We are examining the impact of 5, 50, and 500 cycles. We built a robot out of repurposed LEGO parts and electronics to reliably perform the long experiments. The three-actuator robot functions by first lowering samples on spooled string into liquid nitrogen for 1 minute, pulling them out and rolling forward 8 inches, lowering them into water for 1 minute, and then rolling back until a force sensor notifies it that it has reached its home position. The material properties of the experimental samples were tested through tensile testing. Due to different local coefficients of thermal expansion within our samples, we predict that increasing the number of thermal cycles the samples undergo will result in increased fracture toughnesses.



Strain-stiffening in random packings of entangled granular materials

Henos Musie
Adviser: Professor Eric Brown, Mechanical Engineering and Materials Science

Contrary to most materials, randomly entangled packings of non-spherical granular particles exhibit strain-stiffening behavior when subject to strain or compression. Through uniaxial tensile tests on regular U-shaped staples hooked onto each other we aim to experimentally determine the effective particle modulus, the sole hitherto undetermined input parameter used in our quantitative model, by analyzing the relationship between the torque on the corner joint of the bottom staple arm and the permanent post-experiment bend angle. We initially believed that the maximum tensile force, Fmax, was obtained immediately prior to staple separation, but have concluded that Fmax occurs right before the top staple arm starts bending. We also found that there is a significant loss in sustained force coinciding with the staples’ contact point slipping. Finally, we have defined a geometrical formula for determining the effective moment arm as a function of the attachment angle at Fmax. Upon further refinement of the formula, we have the complete set of parameters necessary to determine torque, which we can transform to effective modulus. Understanding these properties of interlocking particles could play an important role in soil mechanics and geotechnical engineering applications, allowing us to create stronger foundations for buildings and other structures.



Bulk metallic glasses in surgical needle design

Erik Tharp
Adviser: Professor Jan Schroers, Mechanical Engineering and Materials Science

The focus of this project was to explore bulk metallic glasses (BMGs) as a potential candidate material for the manufacture of surgical needles in the hopes of significantly improved needle performance. Due to their high strength and hardness, BMGs could provide a more resilient cutting tool by comparison to stainless steel needles. Our needle prototypes were modelled after a general purpose needle design produced by Medtronic and will be tested for strength via their bend moment. To determine if the properties of BMGs made for a better cutting needle, the prototypes will be tested against existing steel needles for penetrative force through a standard test medium over multiple penetrations. Testing is ongoing, but we anticipate that the needles will resist a higher load in the bend moment test and maintain consistently lower penetrative forces over the course of testing, indicating that the use of BMGs improved the resilience of the needles. These stronger prototypes that are less prone to dulling of the tip would provide solid evidence that BMGs are a promising material for use in the production of surgical needles, with particular utility in the design of ophthalmic and microsurgery needles.



Nano- and micro-patterning bulk metallic glass for biomedical applications

Jennie Wang
Adviser: Professor Jan Schroers, Mechanical Engineering and Materials Science

Cells have been shown to respond to patterned topographies with high aspect ratios by eliciting various morphological and behavioral responses, such as contracting and secreting certain proteins. In order to investigate cellular responses to combinations of nano- and micro-features, we thermoplastically formed platinum-based metallic glass into different geometries and hierarchies to be plated with cells and analyzed for resulting changes. By applying a compressive force and heat to a layered setup with the metallic glass and patterned templates with nano- and micro-features such that the material will flow like a liquid into the molds, we were able to form the metallic glass into these particular shapes. Both a hierarchical combination of nano- and micro-patterns, shown in the picture, as well as a gradient of upward and downward sloping regions of nanorods have been formed through this process. The effect of these topographies on cell response can provide insight about methods of patterning implants to avoid foreign body rejection. We hope to fabricate and examine the effects of other geometries such as porous surfaces to further understand the interaction between cells and patterned topographies.




Mathematical Modeling


Recursive derivations of equations of motion for kinematic chains

Jeffrey Gau
Adviser: Professor Madhusudhan Venkadesan, Mechanical Engineering and Materials Science

It can be useful to model complex mechanical systems as kinematic chains. However, solving the equations of motion for such chains can be computationally expensive. Implementing a recursive solution to this problem will allow us to develop an efficient and accurate program. Such an approach involves propagating the states of each link along the chain, thereby reducing the number of calculations required. We have already developed a program to non-recursively solve the equations of motion and conduct a sensitivity analysis on two types of kinematic chains: simple and triple pendulums. The figure shows the coordinates used to define the triple pendulum, which is fixed to the world at point O. We analyzed the first singular value of the sensitivity matrix for both systems, because these values provide a measure of the overall sensitivity of a system. Using the simple pendulum, we verified the results generated by the program against exact solutions solved algebraically. We then used the triple pendulum case to validate that the program and MATLAB’s ordinary differential equation solver can accurately calculate the sensitivity for a chaotic system. We are now in the process of implementing recursion to improve the efficiency of our program.



Creating a heat transfer model for sizing and designing thermoGreenWalls based on geographic location

Astrid Sardiñas
Advisers: Professor James Axley, Architecture and Forestry & Environmental Studies, and Professor Alexander Felson, Architecture and Forestry & Environmental Studies

The Urban Ecology and Design Laboratory is working on developing a sustainable active heat rejection technology called a thermoGreenWall system. ThermoGreenWalls reject heat through evaporation and convection like cooling towers, but resemble passive green walls in appearance and their potential environmental benefits. By utilizing weather data for the typical meteorological year from 1991 to 2005, we developed a macroscopic heat transfer model of the thermoGreenWalls based on their regional and site-specific placement. Our model shows that the thermoGreenWalls perform the worst during the summer months, while rejecting the most heat during the winter. Furthermore, the thermoGreenWalls seem to perform best in hot, dry cities like Las Vegas and Los Angeles during the summer months, followed by marine cities on the west coast like San Francisco and Portland, as shown in the figure. These heat rejection potentials allow for easy sizing of the thermoGreenWalls depending on the cooling load. Our model also showed that much higher heat rejection rates could be achieved by increasing the wind speed at the wall, and by keeping its view unobstructed to allow for long wave radiation loss. These considerations can be helpful when deciding the placement of thermoGreenWalls in order to maximize their performance.



Simulation of heliotropic behavior as exhibited by the common sunflower (Helianthus annuus)

Robert Loweth
Adviser: Professor Madhusudhan Venkadesan, Mechanical Engineering and Materials Science

This experiment is exploring the sun-tracking (heliotropic) abilities of sunflower sprouts. While the biological processes by which this tracking occurs are well understood, the control feedback mechanics for this sunflower system are still an open scientific question. We have devised a mathematical model for biological heliotropic control and are measuring the heliotropic response of twenty sunflower sprouts. By comparing these two approaches, we hope to determine the accuracy of our math model and prior research for describing sunflower motion. While working on our model, we have grown our own sunflowers and qualitatively confirmed that they are exhibiting heliotropic behavior as shown in the image (red lines added to emphasize orientation). Once we start quantitative measurements, we expect to find that the sunflowers track the sun at a speed substantially different than predicted by the model given the sunflower’s known geometry. These results will help illuminate the extent to which the hypothesized auxin-transport control mechanism plays a role in sunflower heliotropic behavior. We believe that these experiments have important implications for designing control systems in sun-tracking solar panels, and also for devising control systems that process noisy sensory input (such as wind in the case of the sunflower).




Numerical Modeling


Elliptic grid generation and adaptive grid refinement

Ryan Humble
Adviser: Dr. Beth Anne Bennett, Mechanical Engineering and Materials Science

Although the Navier-Stokes equations govern the behavior of many fluids, their complexity all but requires solutions to be either experimentally determined or numerically simulated. For the latter, a reasonable goal is to maximize accuracy while fixing computational cost. In that pursuit, our numerical method attempts to place a constant number of grid points, at which the governing equations are solved, within the physical domain in such a way as to minimize solution error. Our method is currently composed of two steps: a generation step which determines the grid and a solution step which uses the grid to solve the flow problem. The primary focus has been to link the two steps so that the grid depends on the flow problem and adapts to its solution. The generation step must then accept a set of input parameters, in addition to the information about the physical geometry, that will influence the generated grid; the solution step must generate a set of parameters describing the solution error at each grid point. Although not yet complete, this process, shown in the accompanying flowchart, should generate grids that are successively better adapted to the particular flow problem and therefore result in less solution error.



Modeling granular avalanching in a 2D rotating drum

Hans Kassier
Adviser: Professor Corey O'Hern, Mechanical Engineering and Materials Science

An avalanche is a sudden change in the gravitational potential energy of a granular system. Collaborators of Professor O’Hern investigated the distribution of avalanche size for a granular system in a rotating drum and found that avalanche size followed a power law distribution. We worked this semester to create a computer model that would extend these results, since time constraints limited their experiment to a single material. After constructing the model, we visualized the movement of the particles during drum rotation to check for proper particle behavior. As illustrated by the velocity distribution of the particles in the image, the model achieved mixing. To ensure consistency across trials, we required that the particles had reached equilibrium (i.e., the particles had settled) after insertion but before the drum started rotating. We therefore augmented the code to calculate kinetic energy of the system and used this to determine when the system had settled. Analysis of a dozen preliminary trials showed that the avalanche size of the model system followed a rough power law distribution. Calibration of the model will continue until our distributions match the experimental results. The model will then be used to determine the avalanche characteristics of different systems.



Development of a 3D melanoma tumor simulation

Andy Law
Adviser: Professor Corey O’Hern, Mechanical Engineering and Materials Science

This semester, we were tasked with evaluating the feasibility of developing a three-dimensional simulation for the growth of melanoma tumors, and to provide and implement a blueprint for its design. After reviewing previous literature for related models, we believe that an appropriate approach is to approximate cells using vertices and edges; this method can determine new configurations of the system following cell growth by minimizing the system’s potential energy. We have concluded that a two-dimensional model for a cell network is possible and have implemented such an approach. Using this model as a stepping stone, we have modified the two-dimensional equations to represent three-dimensional cells. At present, we have converted the code to generate three-dimensional cells, such as those in the figure below, and to compute their energy, though work is underway to minimize their energy. Due to the innovative nature of this simulation, it is recommended that more people be placed on this program to accelerate its development. We believe that this simulation can serve as a model for revolutionizing the analysis of melanoma tumors by reducing the need for biological samples from lab mice or humans and by accelerating the development of cancer treatments.