2015 Symposium Abstracts - Mechanical Engineering

ME-01    Dynamic Modeling And Optimal Control Of Continuous Flow Microbial Fuel Cells

Authors: Ali Abul; Xiaobo Tan

Abstract: Even though there are many parameters affecting the power output of microbial fuel cells (MFCs) in certain systems, batch or continuous flow, in this work we focus on the effect of substrate flow rate on the voltage output. First, a dynamic model is presented for a continuous flow membraneless MFC. This model includes the substrate consumption dynamics based on Monod kinetics. The input for the control model is the dilution rate while the output is voltage output. The voltage output is written in terms of state variables, which are the substrate consumption and the biomass production. Such a model will facilitate the analysis and optimal control of the MFC. We will also describe our ongoing effort in building an MFC prototype, which will be used in experimental validation of the modeling and control approaches.

 

ME-02    Dynamics Of Horizontal Axis Wind Turbines

Authors: Gizem Acar; Brian F. Feeny

Abstract: The aim of this project is to deepen our understanding in horizontal axis wind turbine dynamics. Wind turbines are under dynamic loading due to varying wind speed, cyclic changes in tangential and normal components of gravitational force, and tower shadowing. These dynamic loadings may contribute to failures. To find the loading on the rotor and the gearbox, the parts that are most susceptible to failure, blade dynamics are investigated first. A pre-twisted beam with a varying cross-section is used to model the blades. The beam is assumed to be under bend-bend-twist coupled deformation. To find the natural frequencies and the mode shapes of the blade, energy methods are used. First, potential and kinetic energy expressions are formulated. Then, using an assumed modes method, energies are expressed in terms of generalized assumed modal coordinates. Applying Lagrange’s method, the equations of motion for a single blade are found. A modal analysis is then performed on the linearized equations to find the natural frequencies and the mode shapes. The method is applied to existing turbine blades, and the results are found to be consistent with those provided in the literature. The next stage of the project involves the dynamics of three blades coupled through the rotor. Parametric excitation due to gravity and the centrifugal effects are to be investigated.

This work was supported in part by National Science Foundation-Grant:CMMI-1335177

 

ME-03    Dispersion Relationship Using Complex Decomposition Methods

Authors: Rickey Alfred Caldwell, Jr.; Brian Feeny

Abstract: Understanding traveling waves is important in structural mechanics, geophysics, biomedicine, and material science. The goal of this research is to extract the parameters of traveling waves propagating in one direction through an elastic beam. A harmonic traveling wave has the form y(x,t) = sin(kx - wt), where k and w are the wavenumber (rad/m) and frequency (rad/s). A semi-infinite Euler-Bernoulli beam is realized in the laboratory using a thin beam suspended at one end by an elastic cord, and buried in sand at the other. The sand absorbs the waves and arrests reflections to the extent that they were not detectable. The beam was sensed with evenly spaced accelerometers along the centerline of the unburied portion of the beam. An impact at the free end generated waves with components at multiple frequencies. As the waves traveled down the beam the higher frequency waves traveled at a higher velocity as predicated by the dispersion relationship w = a k^2, where a = (EI/(rho A))^(1/2), where E, I, A, and rho are the Young's modulus, area moment of inertia, area, and density of the material and its cross section. Three complex decomposition methods were applied to extract the dispersion relationship. The complex orthogonal decomposition (COD) extracted complex wave modes, from which wave numbers were estimated, and the associated modal strength. Modal coordinates were computed to obtain frequency information. Smooth complex orthogonal decomposition (SCOD) extracted complex wave modes, from which wave numbers were estimated, and the modal frequencies. A spatial smooth complex orthogonal decomposition (SCODx) is in development. From the extracted information, the parameter a was estimated as 6.44 m^2/s from COD and 6.72 from SCOD, compared to the theoretical value from the model of a = 6.55 m^2/s. An estimate from SCODx is forthcoming.

 

ME-04    Multiscale Analysis Of Micro-Scale Stresses At The Laminate Free Edge And Influence Of The Interlaminar Microstructure

Authors: Christopher Cater; Xinran Xiao; Robert K. Goldberg

Abstract: In composite laminates, the property mismatches between plies of varying orientations results in stress gradients at the free edges of the composites and are a significant driver of delamination failure. The free edge effect has been well understood at the laminate or meso-scale. The influence of the microstructure on free edge cracking, however, is less known. A two-scale multiscale finite element (FE) approach was utilized to model the micro-scale stresses near the laminate free edge. An IM7/8552 carbon fiber composite with a laminate stacking of [25/-25/90]S, known to be vulnerable to free edge initiated failure, was investigated. Two free edge investigations were performed using the multiscale approach. First, the influence of the micro-scale interlaminar thickness between 90 degree plies on the formation of pre-cracking during manufacturing, as a result of thermal free edge stresses, was explored. The results found a correlation between matrix rich interlaminar regions and higher free edge micro-scale stresses. Second, an investigation of mechanical tensile loading on the composite at the 90 degree ply interfaces found the local free edge micro-scale stresses were not strongly influenced by interlaminar thickness. The conclusions from the analysis are supported by experimental evidence from literature which found higher pre-cracking at 90 ply interfaces and relative insensitivity of pre-cracks to the development of transverse cracks.

This work was supported in part by NASA NRA

 

ME-05    Improving Structural Integrity With Boron-Based Additives For 3D Printed 420 Stainless Steel

Authors: Truong Do; Shenli Pei; Aleksandr Vartanian; Patrick Kwon

Abstract: This study explores the possibility of attaining fully dense stainless steel (SS) 420 parts with a powder-based 3D printing (3DP) method by sintering, instead of following the standard protocol of bronze infiltration. Possible ingredients that can be added to improve the densification are explored, as a small addition of ingredients (sintering aids) enhances densification and improves the final structural integrity of a metal base powder. Boron based sintering aids, Boron (B), Boron Nitride (BN) and Boron Carbide (B4C), were experimented in this study. The contents of each sintering aid ranging between 0 wt% to 1.5 wt% was added to the SS420 powder with an average powder size of 30μm. Parts produced by powder-based 3DP were sintered at various temperatures between 1150°C to 1350°C. Each sintered sample was analyzed in terms of the final density attained, the amount of ingredient mixed, the sintering temperature and the distortion after sintering. Samples with 0.5 wt% B sintered at 1350°C for 6 hours yielded 93% relative density and also retained a minimum distortion. Additionally, the study further explored the possibility of mixing two different particle sizes of SS420 power (~30μm and ~6μm) with the sintering aids in order to further increase the density attained.

 

ME-06    Identification And Comparison Of Finger Forces Over Ranges Of Motions Between Healthy And Reduced Hand Functionality Participants

Authors: Joshua Drost; Sam Leitkam; Tamara Reid Bush

Abstract: Diagnosing the amount of hand function lost due to injury, arthritis, or nerve damage is currently task-based and subjective to the clinician. Recently, work has modeled the differences in kinematic finger space between hands with and without reduced functionality due to arthritis; however, the forces that each finger can produce at each posture are not included in this kinematic model. Both motion and forces associated with each finger posture are necessary to generate a comprehensive hand model for clinical use. The goal of this work was to map forces associated with the index finger at different positions and orientations within the kinematic fingertip workspace of participants with and without reduced hand functionality.Twelve participants without any reported injury or arthritis, termed “Healthy”, and fifteen participants with doctor diagnosed arthritis, termed “Arthritic”, were included in this study. In-plane tests (no adduction or abduction of the finger) measured force differences related to flexion and extension and out-of-plane tests measured force differences related to abduction/adduction. Using a two-way ANOVA, several significant differences were identified in the finger forces. Overall, the forces of Arthritic participants were less than those of Healthy participants. In both groups, maximum forces were lower with abduction (left) and increased with adduction (right). Also, models overlaying these force data with the kinematic space were successfully developed. With the combination of motions and forces, subject specific models will be robust tools for clinical assessment of the hand and fingers.

 

ME-07    Comparing The Flexural Modulus Of High Modulus Carbon Fibers In Randomly Oriented Thermoplastic Composites

Authors: Martin Ducote; Alfred Loos

Abstract: The objective of this investigation was to compare the flexural properties of high-modulus carbon fiber in two different thermoplastic composite systems. With increased pressure from government regulations and consumers to create lighter, more fuel-efficient cars, the automotive industry has long been looking toward composite materials. Thermoplastics offer the strength and toughness required for many applications as well as the promise of reduced cycle times over thermosetting resins. In this study, a papermaking process was used to randomly and uniformly disperse matrix and reinforcement fibers in a non-woven, fabric-like mat, which could then be molded into square composite panels. Multiple composite systems were created, pairing a high-modulus carbon fiber along with a thermoplastic Nylon 6,6 or PEEK to produce the composite plates at different fiber volume fractions. Test blanks were then cut from these panels and subjected to visual inspection and flexural strength testing. Insights were then drawn from the comparisons giving specific attention to fiber-matrix bonding and overall strength properties. As a secondary objective, this papermaking process was evaluated as a viable production method for consistent, randomly oriented composite material.

 

ME-08    Experiments And Modeling Of A Controlled Turbulent Jet Ignition System For Internal Combustion Engine

Authors: Masumeh Gholamisheeri; Elisa Toulson

Abstract: Pre-chamber combustion systems are advanced ignition systems which are under investigation in order to replace current automotive ignition systems. In the last several decades various pre-chamber combustion systems have been produced and investigated to increase efficiency and reduce pollutants through lean, low temperature combustion. Turbulent jet ignition (TJI) is composed of a pre-chamber and a main chamber connected with a single/multiple orifice(s). The combustion occurs first in the pre-chamber where the fuel injector and the spark plug are located and then is directed into the main chamber via the orifice. Orifice geometry is critical as it determines the mixing quality of the air-fuel mixture and the turbulent structures generated in the main chamber. Hence, it has a great influence on the quality of combustion and flame propagation. The main focus of the present research is to investigate the performance of TJI system both numerically and experimentally by changing a range of various parameters such as nozzle shape and the number of injectors (fuel, air or both) in the pre-chamber. Investigation of the effectiveness of alternative fuels, such as propane, on efficiency and lean limit extension is another priority. Generally, it was found that the jet ignition system provides faster burn rates due to the distributed ignition sites and higher level of dilution (lean burn). In addition, jet ignition systems also enable higher compression ratio and higher engine efficiency compared to SI engines.

 

ME-09    Influence Of An Asymmetric Trajectory On The Forces And Flow Structure Of An Airfoil Pitching At High Reduced Frequency

Authors: P. Hammer; A. Naguib; M. Koochesfahani

Abstract: Previous experimental work has shown that non-sinusoidal oscillation of a pitching airfoil can greatly alter the vortical flow structure in the wake. The current study focuses on characterizing the corresponding changes in the resulting loads on the airfoil and how they might be connected to the wake structure. High-order computations are carried out using the FDL3DI solver developed at the Air Force Research Laboratory. It is observed that the introduction of asymmetry produces a non-zero average lift. However, the behavior of the average lift depends strongly on both the amount of asymmetry and the pitching reduced frequency. Decomposition of the lift shows that the average lift comes primarily from the vortex lift component. It is found vortex lift generated during the pitch-down increases in relation to the pitch-up vortex lift as the reduced frequency increases.

This work was supported in part by AFSOR Grant No. FA9550-10-1-0342

 

ME-10    Design And Development Of A Wirelessly Charged Robotic Fish

Authors: Hussein Hasan; Xiaobo Tan

Abstract: In the past two decades, robotic fish have received significant interest due to their various perceived applications. Designing robotic fish is a very challenging task, partly due to the delicate need of waterproofing. In addition, one needs to optimize the hydrodynamic performance while accommodating the constraints on size, cost, and feasibility of manufacturing. In this work a robotic fish with wireless charging capability is designed and prototyped. The robot is equipped with wireless communication for data transmission and remote control. Integrated on this robot are inertia measurement unit (IMU), temperature sensor, and power measurement unit. The body is 3D-printed and propelled by a pair of pectoral fins and a caudal fin, all actuated with servomotors. The developed robotic fish will be used for research on modeling and control of robotic fish, as well as for education and outreach including museum exhibits.

This work was supported in part by National Science Foundation (NSF)

 

ME-11    Numerical Simulation Of A Charged Particle In A Charged Rotating Tubular Membrane

Authors: Sina Jahangiri Mamouri; Volodymyr V. Tarabara; André Bénard

Abstract: Cross flow filtration (CFF) is a common membrane separation process which has broad applications in food industry, biotechnology, chemical industry and recycling technologies. For instance, membranes are widely used for liquid-liquid separation processes such as oil-water separation. However, a major challenge in this method of separation is fouling. It can dramatically decrease the permeate flux and therefore shorten the membrane life and its efficiency. Membrane fouling can be treated by increasing the shear on the membrane’s surface. In this regard, induction of swirl in a stationary membrane was shown to be significantly beneficial. Another treatment to improve membrane efficiency, is to repel droplets/particles from the surface of membrane using a repulsive electric force. For this purpose, the surface of the membrane is coated with Polyelectrolyte Multilayers (PEM) with a surface potential, and droplets/particles are induced to have the same electric charge. Polyelectrolyte multilayers are thin films manufactured by layer-by-layer (LbL) deposition, which can maintain a charged surface with a small uncertainty. In this work, a numerical simulation of motion of a charged solid droplet within an axially rotating charged tubular membrane is investigated. The particle and the inner surface of the tubular membrane are assumed to be positively charged. It is expected that the increase in the shear stress due to the rotation of membrane on one hand, and the repelling force between the charged membrane and the particle on the other hand, improve the separation efficiency of the membrane.

 

ME-12    The Effect Of Temperature On The Tensile Deformation Behavior Of A Beta Titanium Alloy, An In-Situ SEM Study

Authors: Vahid Khademi; Carl J. Boehlert

Abstract: Beta titanium alloys are becoming more and more attractive for medical and structural applications due to their good formability, high strength, and good fracture toughness. However, some beta alloys tend to exhibit microstructural instabilities and transformations at intermediate temperatures. In this study, rolled sheets of Ti-13Cr-1Fe-3Al, which is a low-cost B-type alloy, were studied. In-situ SEM tensile tests were conducted to investigate the effect of temperature on the mechanical behavior between room temperature and 450 C. Electron Backscatter Diffraction and slip trace analysis showed that the active slip systems at RT and 200 C had relatively high Schmid factors. However, at 400 and 450 C, this trend was not observed. This was due to the omega-phase transformation which will be discussed. Overall, this work highlights the stability of this alloy at intermediate temperatures along with the deformation mechanisms as a function of temperature and microstructure.

 

ME-13    Asymmetric Post-Flutter Oscillations Of A Cantilever Due To A Dynamic Follower Force

Authors: Vahid Zamani; Ehsan Kharazmi; Ranjan Mukherjee

Abstract: For elastic systems with an end-load, instability can occur through divergence or flutter. The type of instability depends on the load. When the load is conservative, instability can occur through divergence whereas for non-conservative load, flutter instability can occur. Follower force is a common example of a non-conservative end load. It has been shown in the literature that for the case of follower force, increasing the load above a critical value can make the system unstable through flutter. In this study, the behavior of a cantilever beam subjected to a follower force has been investigated where the direction of the force follows the slope of the tip of the beam and the magnitude of the force is comprised of "static" and "dynamic" terms. The "static" term is a constant term and the "dynamic" term is a term that varies linearly with the slope of the tip of the beam. The Ritz-Galerkin method is used to obtain a finite degree-of-freedom model of the system; this model has a quadratic nonlinearity due to the slope-dependent magnitude of the follower force. After introducing modal damping, the dynamics of the system is investigated using the method of multiple scales. Our results, which are verified through numerical simulations, indicate that in the presence of damping, stability is maintained for a follower force of constant magnitude larger than the critical load. More importantly, the addition of the slope-dependent term in the magnitude of the follower force does not cause instability; instead, it results in asymmetric oscillations. Such behavior of the cantilever is expected due to the asymmetric nature of the force.

 

ME-14    Experimental Method To Quantify Residual Limb Displacement Within A Prosthetic Socket

Authors: Amy L. Lenz; Katie A. Johnson; Tamara Reid Bush

Abstract: In prosthetics, many clinical practices are subjective in nature. When an amputee presents with a pressure ulcer on their residual limb the exact cause or etiology is often unknown. Previous research has attempted to address bone motion relative to the socket because assessing tissue motion is difficult to capture due to the opaque nature of the device. The current research study presents the development of a novel method to measure residual limb motion beneath the surface of a prosthetic socket using motion capture technology. Twenty-two retro-reflective thin-disc markers were placed beneath a clear transparent test socket. Using a 12 camera Vicon system, the location of all 22 markers was recorded relative to markers placed on the outside of the socket and pylon. Data collection included a test setup with a replica of a patient’s leg interfaced with a standard gel liner pin suspension system. Distances between markers were measured with a digital caliper. These values were compared to the inter marker distances captured with the motion capture system when the residual limb replica was placed into the test socket. Dynamic trials were then collected of by vertically displacing the limb and capturing marker movement patterns relative to the device. Results of inter marker distances (+/- 0.25mm) were within error tolerances of the motion analysis system, confirming the ability to accurately capture limb motion within a socket. These results encourage this novel methodology to be applied to amputee patients during walking to empirically assess the distribution of deformation within the socket.

 

ME-15    Modeling To Predict Micro-Scale Permeability For Fiber Reinforcement In Liquid Composite Molding

Authors: Timothy Luchini; Stephen Sommerlot; Alfred Loos

Abstract: In liquid composite manufacturing, permeability is the driving process parameter for mold fills and is critical for understanding the infusion flow and pressure distribution that results. Permeability has been identified as a complex variable which can vary significantly in magnitude for similar test cases. Permeability has also been isolated at different levels because of the multi-scale nature of composite fiber reinforcement. In the micro-scale, fibers are formed into randomly aligned tows composed of thousands of fibers. A second scale, the meso-scale, considers the tow dimensions and weave parameters, but inputs a Darcy based permeability to make up for physical geometry variations. On the micro-scale, fibers are generally considered as ordered in some kind of idealized packing arrangement, for example hexagonal or square packing. This is not always realistic and defining permeability as a function of porosity alone may not be enough to achieve an accurate permeability prediction on the micro-scale. Here, we isolate the micro-scale structures of unidirectional fiber reinforcements and investigate flows across aligned fiber geometries and infusion characteristics during manufacturing. Reduced geometries are utilized to represent the fiber and matrix interactions during a liquid infusion and periodic boundary conditions are applied. The overarching goal of this research is to use numerical tools to create better understanding of composite manufacturing processes. A systematic computational approach will be utilized to understand how material packing changes the fluid flow regime during composite manufacturing, helping to select appropriate infusion parameters to produce a finished part with good properties. This approach incorporates a numerical modelling procedure to predict unidirectional permeability on the micro-scale. The results set up a baseline that compares well with analytical models as a function of fiber diameter and volume fraction. The ability of this numerical procedure goes above current analytical models because, in the future, it can take various fiber diameters, fiber count, random packing arrangements, and flow rates into account. Specific areas that analytical models lack could be investigated like the effects of a fabric that incorporates both fiberglass and carbon fiber elements. Results show that variations due to fiber packing can be identified independently of fiber volume fraction.

This work was supported in part by General Electric Aviation

 

ME-16    Stretchable Luminescent Films Of Silicon Nanocrystals

Authors: Rajib Mandal; Naomi Carlisle; Michael Bigelow; Rebecca Anthony

Abstract: Nanocrystalline silicon is widely known as an efficient and tunable optical emitter and is attracting great interest for applications such as light-emitting devices. To date, however, luminescent silicon nanocrys-tals have been used exclusively in traditional rigid devices. There is a need to investigate whether these nanocrystals can be used in flexible and stretchable devices. Here we present a study on how the optical and structural/morphological properties of plasma-synthesized silicon nanocrystals (Si NCs) change when they are deposited on stretchable substrates made from polydimethylsiloxane (PDMS). The silicon nanocrystal synthesis was performed in a nonthermal, low-pressure gas phase plasma reactor. Silicon nanocrystals were deposited directly out of the plasma into thin-film layers using inertial impaction through a slit-shaped orifice. The PDMS substrates were either relaxed or pre-stretched to several different percentages of their original length ("stretching ratio") prior to deposition. The morphologies of films deposited on both PDMS substrates and on rigid silicon wafer sub-strates were studied using SEM. Si NC Films deposited on PDMS substrates have significantly different morphology as compared to films deposited on silicon substrates. The reason behind this morphological difference is still under investigation, but is likely attributed to the difference in elastic properties of the PDMS as compared to silicon. We also measured the photoluminescence (PL) properties of Si NCs deposited on pre-stretched PDMS substrates depending on stretching ratio. Between unstretched PDMS and PDMS stretched 40% beyond its original length, the PL peak is adjusted by 80 nm. We will also present results on how the PL from Si NCs depends upon the stretch state of the PDMS substrates during measurement, demonstrating the viability of these luminescent Si NC layers for flexible electronics such as light-emitting device dis-plays and sensors.

 

ME-17    Design Considerations And Estimated On-Vehicle Performance For A Compression-Couple Based Thermoelectric Generator

Authors: Nariman Mansouri; Edward Timm; Harold Schock

Abstract: Approximately 55% percent of the energy produced from conventional vehicle resources is lost due to heat losses. An efficient waste heat recovery process will undoubtedly lead to improved fuel efficiency and reduced emission of greenhouses gases. A thermoelectric generator (TEG) is one of the most viable waste heat recovery approaches being used among industries for the purpose of converting waste heat to electrical energy. With high fuel costs and increasing demand for clean energy, a solid-state thermoelectric device is an attractive choice for reducing fuel consumption. Although they are reliable energy convertors, there are several barriers that have limited their implementation into the automotive market. Cracking of the materials is found to be a major failure mechanism which affects not only structural integrity, but also the energy conversion and overall performance of the system. In this paper, cracking of the thermoelectric material as observed in performance testing is analyzed by both numerical simulations and analytical approaches. With the help of finite element (FE) analysis, the detailed distribution of stress, strain, and temperature are obtained for each design. FE based simulations show that the tensile stresses are the main reason causing radial and circumferential cracks in the thermoelectric material known as skutterudite. Based on FE and computational fluid dynamic (CFD) analysis, strategies in tensile stress reduction and failure prevention are suggested followed by the reasons to change the thermoelectric couple and generator design resulting in a reliable TEG.

This work was supported in part by Tenneco Inc, Grass Lake, MI

 

ME-18    An Exponential Hardening Model For Crystal Plasticity Modeling Of Single Crystals

Authors: Aboozar Mapar; Farhang Pourboghrat; Thomas Bieler

Abstract: Stress-strain curve of single crystals usually involves three stages. The deformation starts activation of a single slip system, there is not much dislocation interactions and therefore the hardening rate is low. The next stage is when other slip systems active and rapidly increase the hardening rate. In the third stage cross slip happens and hardening rate decreases. Classical hardening model can only capture the first part of the stress-strain curve. In this study a new hardening model is proposed that can capture the first and second stages of the deformation. This model has been evaluated for Iron and Niobium single crystals and has successfully predicted the deformation behavior of both materials.

 

ME-19    Electroosmotic Flow Through The Polymer-Coated Nanochannels

Authors: Aryan Mehboudi; Junghoon Yeom

Abstract: The electroosmosis refers to the motion of a polar media next to a charged surface, due to an external tangential electric field. The counterions are attracted by the ions of the surface. In presence of the external electric field along the wall, the counterions located adjacent to the wall move along the surface and drag the fluid particles due to the fluid’s viscosity. The produced net flow is referred to as the electroosmotic flow (EOF). Nowadays, the EOF is employed as the underlying mechanism in a large number of the micro/nano devices. However, its effects sometimes need to be controlled or even completely suppressed, particularly in those designs which are purely based on the electrophoresis mechanism. In such situations, the device’s efficiency can be adversely affected by the EOF enormously. The polymer coating technique is commonly utilized to quench the unwanted side effects of the EOF. A profound understanding of the EOF behavior through the polymer-coated channels is consequently of uttermost importance. In this poster, we are going to present some of our results which have been obtained by using the numerical simulations. As a part of an ongoing project, we utilize the dissipative particle dynamics (DPD), which is a Lagrangian mesoscpic method, in order to study the effects of the important parameters like density of grafting, solvent quality, thickness of polymer layer, etc., on the EOF behavior in terms of the overall mobility, and the velocity profile across the channel.

 

ME-20    Population Balance Method For Modeling Droplet Breakage And Coalescence In Turbulent Dispersion

Authors: Abdul Motin; André Bénard

Abstract: This paper addresses the detail mathematical modeling of droplet breakage and coalescence using the Population Balance Method (PBM). The population balance equation (PBE) represents the dynamics of droplet size distribution due to a process involving continuous interactions between individual droplets (such as coalescence and breakup). The PBM has been used to examine the time evolution of the distribution of volume fraction and Sauter mean size. An understanding of PBM in regards to the conservation of numbers and mass of dispersed droplets is also developed here. An in-house code (written in Matlab) has been used for solving the models for collision frequency, compaction force on the droplets, coalescence and breakage rates, daughter droplet distribution and the stand-alone PBE. Film drainage theory with the different regimes of droplet morphology is applied for calculating the coalescence time. Effect of the turbulent intensity and interfacial tension of oil-water mixture, volume fraction and API gravity of dispersed phase on the time evolution of size distribution of volume fraction and Sauter mean diameter are examined. The results show that, the drop-drop coalescence is dominant over the droplet breakage in pipe flow; the opposite is observed for flow through valve.

This work was supported in part by CETCO Energy Services and Michigan State University

 

ME-21    Combustion And Surface Degradation Of Solid Materials

Authors: Yen Nguyen; Thomas Pence; Indrek Wichman

Abstract: The goal of this research is to quantify the effect of heating and combustion on solid material degradation. Depending on the material degradation mechanism, many different surface morphologies may result like voids, cracks. These cracks affects heat and mass transfer in both solid and gas phases, therefore combustion process. This forms a cycle combustion- solid degradation- combustion. In this presentation, some crack patterns associated with some particular heating conditions are generated. They could show period doubling behavior and tree- like behaviors depending on the stages of heating.

This work was supported in part by CVRC

 

ME-22    Blood Perfusion Responses Of Lower Legs A Study Of Venous Stasis Ulcers

Authors: Wu Pan; Joshua P. Drost; Marc D. Basson; Tamara Reid Bush

Abstract: Venous stasis ulcers are skin wounds that occur most commonly on the lower leg. Little work has been conducted to identify differences in perfusion responses (blood flow) between healthy individuals and individuals with stasis ulcers. The goal of this work was to identify differences in perfusion responses to force (both normal and shear forces) between legs with existing venous stasis ulcers and healthy legs. A total of seventy five legs were evaluated resulting in three groups: 20 legs with wounds (“wounded”), 15 non-wounded legs but from patients with leg wounds (“non-wounded”) and 40 “healthy” legs. A Laser Doppler Perfusion Monitor was used to monitor and record the blood perfusion of the skin during the entire test period. Statistically significant differences occurred between wounded legs and healthy legs during baseline, perfusion decrease under loading and reactive hyperemia. Effect size calculation suggested that statistically significant differences might be expected for higher sample sizes when comparing wounded and non-wounded legs; as well as for the comparison between non-wounded legs and healthy legs. These data show that the legs with existing venous stasis ulcers are significantly different from healthy legs whereas the non-wounded legs exhibited an intermediate trend between wounded and healthy legs. A progressive trend from healthy to non-wounded to wounded legs exists and the fact that individuals eventually develop an ulcer in the “non-wounded” leg supports the possibility that changes in force-perfusion responses could serve as predictor of ulcer formation.

 

ME-23    Multi-Objective Optimization Using Variable-Length Genomes

Authors: Matt Ryerkerk; Ron Averill; Kalyanmoy Deb; Erik Goodman

Abstract: Design optimization algorithms typically operate within a fixed-sized search space. However, there exists a class of problems where the number of design variables may not be fixed. Such problems include laminate composite design, coverage problems, and portfolio problems. Solutions for each of these problems are represented by a vector of components, such as layers in the laminate composite problem. The length of this vector can change, and the optimal length may not be known a priori. For multi-objective optimization the optimal length can vary between different regions of the Pareto-optimal front. Gradient based algorithms are ill-suited for such problems due to the changing dimensionality of the search space. Genetic algorithms (GA) are viable candidates, however the traditional operators are of little use with a variable-length genome. In literature, GA is often used for such problems, but the approaches often simplify the problem so that traditional operators can be used, or use new operators that don’t handle the variable-length genome in a respectful manner. This include simply fixing the length of the vector, including an activation flag that can remove some parts of the vector from the evaluated solution, or using a cut and splice operator. These approaches are either inefficient or incapable of fully characterizing the Pareto-optimal front. This poster demonstrates the effectiveness of GA operators that have been developed to handle a variable-length genome in a meaningful way, and compares their performance to other approaches commonly found in literature.

This work was supported in part by BEACON Center

 

ME-24    Multiscale Modeling Of Polymer Nano-Composites

Authors: Azadeh Sheidaei; Farhang Pourboghrat

Abstract: In recent years, polymer nano-composites (PNCs) have increasingly gained more attention due to their improved mechanical, barrier, thermal, optical, electrical and biodegradable properties in comparison with the conventional micro-composites or pristine polymers. With a modest addition of nanoparticles (usually less than 5wt.%), PNCs offer a wide range of improvements in moduli, strength, heat resistance, biodegradability, as well as decrease in gas permeability and flammability. Although PNCs offer enormous opportunities to design novel material systems, development of an effective numerical modeling approach to predict their properties based on their complex multi-phase and multiscale structure is still at an early stage. In this research, I have focused on establishing a computational framework to predict the mechanical properties of PNC. I have developed a microstructure inspired material model based on a statistical technique to reconstruct the microstructure of polymer nanocomposite. The model was able to successfully predict the material behavior obtained from experiment. This 3D microstructure model was later incorporated in a damage modeling problem in nanocomposite where damage initiation and damage progression have been modeled using cohesive-zone model and modified Gurson-Tvergaard-Needleman (GTN) material model.

 

ME-25    Direct Numerical Simulation Of Turbulence And Mixing In Highly Compressible Flows

Authors: Yifeng Tian; Farhad Jaberi; Zhaorui Li; Daniel Livescu

Abstract: The effects of normal shock waves on isotropic turbulence and scalar mixing are studied by direct numerical simulation (DNS) of fully compressible equations with high-order monotonicity-preserving and compact finite-difference numerical schemes for various flow and scalar conditions. Detailed examinations of the turbulence and scalar statistics such as the turbulent kinetic energy and scalar variance indicate that the numerical method is accurate and is able to correctly capture the shock-turbulence interactions and scalar mixing near and away from the shock even at very high Mach numbers. As expected, the shock wave increases the small-scale turbulence and the skewness and flatness of the turbulent velocity fluctuations, but the turbulent compressibility is actually decreased by the shock. The effect of shock on the turbulence was to found be strongly dependent on the pre-shock turbulence parameters such as the turbulence intensity. The enhancement of scalar mixing by the shock is also found to be dependent on the pre-shock scalar structure. The mechanisms responsible for the modification of turbulence and scalar mixing are identified by analyzing the flow structure and the transport equations for the Reynolds stress, vorticity and scalar variance inside and outside the shock zone.

This work was supported in part by Los Alamos National Laboratory

 

ME-26    Numerical Simulation Of Turbulent Jet Ignition

And Combustion In Advanced Engines

Authors: AbdoulAhad Validi; Farhad Jaberi

Abstract: The ignition and combustion of lean fuel-air mixtures by a turbulent jet flow of hot combustion products injected into various geometries are studied by high fidelity numerical models. Turbulent jet ignition (TJI) is an efficient method for starting and controlling the combustion in complex propulsion systems and engines, e.g. Rapid Compression Machines (RCM). The TJI and combustion of hydrogen and propane in various flow configurations are simulated with the direct numerical simulation (DNS) and the hybrid large eddy simulation/filtered mass density function (LES/FMDF) models. In the LES/FMDF model, the filtered form of the compressible Navier-Stokes equations are solved with a high-order finite difference scheme for the turbulent velocity and the FMDF transport equation is solved with a Lagrangian stochastic method to obtain the scalar field. The DNS and LES/FMDF data are used to study the physics of TJI and combustion for different turbulent jet igniter and gas mixture conditions. The results show the very complex and different behavior of the turbulence and the flame structure at different jet equivalence ratios.

This work was supported in part by NSF/DOE

 

ME-27    Study Of Li Diffusivity In Si Via Finite Element Analysis

Authors: Miao Wang; Xinran Xiao

Abstract: Silicon is a very promising high capacity anode material for lithium iron batteries. However, the large volume expansion during lithiation can cause rapid capacity fading during battery cycling. The volume expansion effect may be remedied through electrode design. Numerical models can greatly facilitate the design process. The numerical models require material properties of Si/LixSi. The lack of key material data has prevented the efficient use of such tools in battery design. Diffusivity of Li in Si is one of the critical material properties since it determines the Li concentration gradient, and therefore the intercalation stresses in silicon. However, the diffusivity values reported in literature range from to . In this work, finite-element-analysis (FEA) is used to study the right order of Li diffusivity in Si. By simulating the a-Si nanoparticles under lithiation of the experiments by McDowell et al.1 , the Li diffusivity is estimated at the order of for Li-rich phase and for Si-rich phase. These values are further validated by comparing lithiated thickness growth, the lithiation time with several experiments in literature, and by comparing the level of stresses generated inside the particle with the reported fracture strength of Si material.  Reference: McDowell, Matthew T., Seok Woo Lee, Justin T. Harris, Brian A. Korgel, Chongmin Wang, William D. Nix, and Yi Cui. “In Situ TEM of Two-Phase Lithiation of Amorphous Silicon Nanospheres.” Nano Letters 13, no. 2 (February 13, 2013): 758–64. doi:10.1021/nl3044508.