bluuebunny/crossref_metadata_2025 huggingface dataset:
Impacts of Dilution on Hydrogen Combustion Characteristics and NOx Emissions
Authors: Resende Pedro , Afonso Alexandre , Pinho Carlos , Ayoobi Mohsen
Published: January 2018

Combustion characteristics at small scales have been studied continuously due to the potential applications in portable power devices. It is known that heat release impacts at small scales result in different flame behavior as compared to conventional scales. The impacts of geometry, stoichiometry, flow rates, wall temperatures, etc. are widely studied in literature. However, dilution impacts still need to be further studied due to its important role on controlling the flame behavior and subsequent pollutants emissions at these scales. In this work, premixed hydrogen/air combustion is simulated at an axis-symmetric micro channel (with diameter D = 0.8mm and length L = 10mm), where detailed chemical kinetics are implemented in simulations (32 species and 173 reactions). The heat transfer on the wall is considered by imposing a hyperbolic temperature profile on the wall, where the wall temperature increases from 300 K at the inlet to 1300 K at the outlet. With this setup, a range of equivalence ratios including a typical fuel-lean regime (ϕ = 0.7), stoichiometric regime (ϕ = 1.0) and and two cases at an ultra-rich regime (ϕ = 2.0 and ϕ = 3.0) are investigated. For each equivalence ratio, excess dilution (using N2) is introduced to the mixture and its impact is compared with other cases. With that, the impacts of dilution variations on the combustion characteristics of premixed hydrogen/air are investigated for different equivalence ratios. More specifically, several incidents such as flame dynamics, flame stabilization, extinctions and NOx emissions are studied for the aforementioned operating conditions.
Mechanical Behavior of Bio-Inspired Wavy Adhesive Bonding Under Shear
Authors: Nash Richard , Pruyn Timothy , Chaput Heather , Li Yaning
Published: January 2018

Inspired by biological suture joints with wavy morphology, wavy adhesive joints were designed and the shear resistance of the designs were explored via finite element (FE) simulations. The influences of waviness and material properties of the layer on the mechanical behaviors of the adhesive joints were quantified. Both adhesive and cohesive failure mechanisms were explored: (1) delamination along the interface between the softer layer and the harder substrates, and (2) layer material failure.

In the FE models, both cohesive interaction and ductile damage mechanics models were used to capture the two failure mechanisms. The effects of Young’s modulus and damage evolution parameters on the force-displacement relation were studied. Both failure mechanisms were observed by varying the material properties in the adhesive layer. It was found that, the stiffness, strength and the failure mechanisms of the wavy adhesive joints are largely dependent on the geometry and material properties of the layer.
Effect of Progressive Aging on the Viscoelastic Material Functions of Asphalt Concrete and its Binder
Authors: Rahman A. S. M. Asifur , Faisal Hasan M. , Tarefder Rafiqul A.
Published: January 2018

In this study, field collected loose asphalt-aggregate mixtures were used to prepare cylindrical asphalt concrete specimen using a Superpave gyratory compactor and samples were subjected to four levels of aging. Unaged and aged samples were then tested for complex modulus, relaxation modulus, and creep compliance in the laboratory at different temperatures and loading conditions. To determine broadband characteristics, mastercurves of related viscoelastic material functions were determined by applying time-temperature superposition principle. A comparison study showed that increasing levels of aging have significant effect on viscoelastic functions of asphalt concrete. In addition, liquid asphalt binder corresponding to the asphalt-aggregate mixture was tested for complex shear modulus at various levels of aged conditions, using a dynamic shear rheometer. Results showed that even though the binder shear modulus increases significantly with aging, asphalt concrete modulus does not necessarily show similar increment.
Evaluation of Fatigue Life of Asphalt Concrete From Dynamic Modulus Test
Authors: Hasan Md Mehedi , Faisal Hasan M. , Bairgi Biswajit K. , Rahman A. S. M. , Tarefder Rafiqul
Published: January 2018

Asphalt concrete’s dynamic modulus (|E*|) is one of the key input parameters for structural design of flexible pavement according to the Mechanistic Empirical Pavement Design Guide (MEPDG). Till this day, pavement industry uses |E*| to predict pavement performance whether the material is hot mix asphalt (HMA) or warm mx asphalt or Reclaimed Asphalt Pavement (RAP) mixed HMA. However, it is necessary to investigate the correlation of |E*| with laboratory performance testing. In this study, laboratory dynamic modulus test was conducted on four different asphalt concrete mixtures collected from different construction sites in the state of New Mexico and mastercurves were obtained to evaluate dynamic modulus (|E*|) for a wide range of frequency. In addition, fatigue performance of these mixtures was predicted from the mastercurves and compared with the laboratory fatigue performance testing. Fatigue performance of these mixtures was evaluated from the four point beam fatigue test. The laboratory results show a good agreement with the predicted value from mastercurves. It is also observed from this study that the fatigue life of the asphalt concrete materials decreases with increase in |E*| value.
3D Printed Carbon Nanotube Array Interface for In Vivo Drug Delivery
Authors: McGee James K. , Kubrin Koby , Ahmed Adeel , Schrlau Michael G.
Published: January 2018

The development of gene therapies, small molecules and nanoparticle-based therapeutics in pharmacology have prompted the need for parenteral administration as they possess limited bioactivity, low stability, high specificity and potency. The ability to directly deliver drugs to a specific area offers the capability of minimized required drug quantity, localization of exposure, and limited systemic side effects. Currently, there is no standard for the creation of implantable devices to monitor health status and provide therapeutic treatment. We explored the applications and uses for carbon nanotube based arrays for in vivo drug delivery, specifically as an implantable reusable mode of delivery. The increased availability of 3D printing allows for not only the rapid and reproducible fabrication of designs, but also the ability to incorporate these carbon nanotube arrays in ways that are not feasible using traditional machining methods. These techniques offer the means to design and fabricate a reservoir on carbon nanotube arrays to create a loadable reservoir that can regulate flow, dispensing cargo for mass cellular injection. This research focuses primarily on the development of an attachable drug reservoir for these devices and looks to explore the possibilities of designing reservoirs made out of biocompatible 3D printed materials such as plastics, alloys, or bioceramics. We explored several routes, including a rigid and semi-rigid, as well as how each design impacted the flow through the membrane.
Thermal Transport in a Crossflow Jet Subject to a Very Strong Favorable Pressure Gradient
Authors: Quinones Carlos , Araya Guillermo , Chen Yi
Published: January 2018

Incompressible jets transversely issuing into a spatially-developing turbulent boundary layer is one of the most challenging and crucial types of three dimensional flows due to its fluid-dynamic complexity and technological applications; for instance, film cooling of turbine blades, chimney plumes, fuel injection, etc. In this investigation, Direct Numerical Simulation (DNS) of a jet in a crossflow under different streamwise pressure gradients (zero and favorable pressure gradient, hereafter ZPG and FPG) is performed. The goal is to accurately model the interaction between the wall-normal laminar jet with the incoming spatially-developing turbulent boundary layer in order to elucidate the physics behind the thermal coherent structures in crossflow jets at different streamwise pressure gradients (ZPG vs. FPG) and low velocity ratios (∼ 0.5). The analysis is done by prescribing accurate turbulent information (instantaneous velocity and temperature) at the inlet of a computational domain for simulations of spatially-developing turbulent boundary layers. The methodology is based on the Dynamic Multiscale Approach (DMA) by Araya et al. (JFM, Vol. 670, pp. 581–605, 2011). The major effect of strong FPG on crossflow jets has been identified as a damping process of the counter-rotating vortex pair system (CVP).
Numerical Investigation of the Influence of Different Work Distributions on the Performance of Axial Fans for Automotive Cooling Applications
Authors: Epple Philipp , Porzelt Alexander , Gast Stefan
Published: January 2018

In this work the influence of different radial work distributions on the performance of low pressure axial fans for automotive cooling purposes was investigated. The general standard solution in the design of axial fans is to assume constant work distribution (free vortex design). This also leads to a constant meridional flow velocity and thus makes the calculations for the design rather simple. To fulfill the constant work assumption, however, a high swirl component of the absolute outlet flow velocity results near the hub. Assuming the incoming airflow to be swirl-free, this means that the flow near the hub must be strongly deflected, leading to a very high blade load in this area and to very long chords. Thus, the assumption of constant radial work distribution leads to a high risk of flow separation near the hub, especially for low pressure cooling fans, where a small hub to shroud diameter ratio is needed in order to achieve higher flow rates.

Furthermore, in fan applications, often the total-to-static pressure and total-to-static efficiency are the relevant design parameters, and not the total-to-total pressure and the total-to-total efficiency. In order to address these issues, linear and parabolic non-constant work distributions were investigated. These distributions were parametrized and for each work distribution a series of designs was created with the airfoil theory method. These designs were computed with the commercial Navier-Stokes-Solver STAR CCM+ and the results were analyzed in detail. As an application example a series of fans for a Formula Student racing cars cooling applications was developed.

With this method, it was possible to achieve smaller hub to shroud diameter ratios, higher flow rates and better total-to-static efficiencies. The result was a new series of fans with improved cooling properties for automotive applications. These new fans, the design method and the results are presented in detail in this work.
Experimental Characterization of Thermal Shock Resistance of Refractories Reinforced by Silicon-Carbide and Zirconia Particles
Authors: Makarian Kamran , Santhanam Sridhar , Wing Zachary N.
Published: January 2018

Zirconia and Silicon-carbide based castable composites are both known to be reliable, high-temperature refractory materials, capable of withstanding damage caused by thermal shock. There exists a growing body of literature regarding micro-scale as well as macro-scale properties of each aforementioned type. In the present work, we have investigated these refractory castables using different volume fractions of ZrO2 and SiC particles and have made a comparison between their thermal shock responses. Equivalent homogeneous material properties including elastic modulus, crushing strength and modulus of rupture (MOR) are determined experimentally, and thermal shock experiments at 900°C are conducted to determine the effect of the compositions on the propensity of these castables to survive thermal shock. The experimental findings were compared to predictions made by thermal shock indices and the two were in good agreements. Applying thermal shock cycle in all cases showed a drop in strength and elastic modulus of the material.
Study of a Woman Athlete’s Knee to Prevent Valgus
Authors: Mohacsi Paulette , Piccorelli Lorraine , Watroba Kathryn , Weiss Daniel , Saboori Parisa , Toscano Lisa
Published: January 2018

After the introduction of Title IX, a federal law prohibiting discrimination based on gender, the number of women involved in high school and collegiate level sports has significantly increased. Increasing the number of female athletes has a direct correlation with the amount of injuries experienced by these women. One of the most common injuries to female athletes is a sprain or a tear in the Anterior Cruciate Ligament (ACL) located in the knee. The ACL is one of the main components in the stabilization of the knee. A strain or tear to the ACL causes everyday life to be impacted significantly. ACL injuries are not only debilitating, but are expensive and have long term effects including arthritis.

Women have an increased chance of injuring their ACL for three main reasons: anatomical, hormonal, and biomedical. Statistically, women have wider hips and weaker inner thigh muscles than men. Additionally, women experience changes in hormonal imbalance which contributes to their cyclic changes in ligament strength. Lastly, knees can experience a bio-medical condition known as valgus. The presence of extreme valgus typically indicates a high risk of future ACL injury due to the increased stress on the ligament. Due to these factors, this study involved designing three prophylactic braces to be used as part of a training program to help strengthen the muscles surrounding the knee.
Development of Upper Extremity Finite Element Model for Elderly Female: Validated Against Dynamic Loading Conditions
Authors: Hammad Anand , Kalra Anil , Khandelwal Prashant , Jin Xin , Yang King H.
Published: January 2018

Injuries to the upper extremities that are caused by dynamic impacts in crashes, including contact with internal instrument panels, has been a major concern, especially for smaller female occupants, and the problem worsens with increasing age due to reduced strength of the bones. From the analysis of 1988–2010 CDS unweighted data, it was found that risk of AIS ≥ 2 level for the arm was 58.2±20.6 percent higher in females than males, and the injury risk for a 75-year-old female occupant relative to a 21-year-old subjected to a similar physical insult was 4.2 times higher. Although injuries to upper extremities are typically not fatal, they can have long-term effects on overall quality of life. Therefore, it is important to minimize risks of injuries related to upper extremities, especially for elderly females, who are most at risk.

Current anthropomorphic surrogates, like crash-test dummies, cannot be directly used to study injury limits, as these dummies were developed mainly to represent the younger population. The current study is focused on the development of a finite element (FE) model representing the upper extremity of an elderly female. This can be further used to analyze the injury mechanisms and tolerance limits for this vulnerable population. The FE mesh was developed through Computer Tomography (CT) scanned images of an elderly female cadaver, and the data included for validation of the developed model were taken from the experimental studies published in scientific literature, but only the data directly representing elderly females were used. It was found that the developed model could predict fractures in the long bones of elderly female specimens and could be further used for analyzing injury tolerances for this population. Further, it was determined that the developed segmental model could be integrated with the whole body FE model of the elderly female.
3D Printed Composites With Continuous Carbon Fiber Reinforcements
Authors: N. Sarvestani Ali , van de Werken Nekoda , Khanbolouki Pouria , Tehrani Mehran
Published: January 2018

Additively manufactured polymers can be reinforced with high-performance reinforcements such as carbon fibers. Printed thermoplastics with embedded continuous carbon fibers are up to two orders of magnitude stronger and stiffer than high-grade 3D printed polymers. In this work, the mechanical response of such 3D printed carbon fiber specimens is evaluated. While the precursor carbon fiber reinforced filaments achieve a stiffness of 50GPa and strength 700MPa, mechanical properties of their printed parts are highly affected by printed carbon fiber curvatures. In this work, the structure of 3D printed parts was examined, and some design rules for 3D printing with continuous carbon fibers are suggested. Moreover, failure mechanisms in these samples are discussed and correlated to the micro-structure of the composites and the carbon fiber configuration.
Numerical Simulations of Thermal Transport in Random Porous Materials and Powder Systems Using the Smoothed Particle Hydrodynamics Method
Authors: Shah Deepak , Volkov Alexey N.
Published: January 2018

A numerical method to solve thermal transport problems in powder bed systems and porous materials with finite thermal contact conductance at interfaces between individual powder particles or grains is developed based on the Smoothed Particle Hydrodynamics approach. The developed method is applied to study the effective thermal conductivity of two-dimensional random powder bed systems with binary distribution of powder particles radii. The effects of particle size distribution parameters, density parameter, and effective interface area between particles on the effective thermal conductivity are studied. It is found that at finite Biot number, which characterizes the ratio of the interfacial conductance to the conductance of the bulk powder material, the effective thermal conductivity of porous samples increases with increasing fraction of particles of larger size.
Inflow Conditions and Heat Transfer From Suddenly Expanding Annular Pseudoplastic Flows
Authors: Hammad Khaled J.
Published: January 2018

The impact of inflow conditions on flow and heat transfer in suddenly expanding annular pipe flows of a pseudoplastic fluid is studied within the steady laminar flow regime. The equations governing conservation of mass, momentum, and energy, along with the power-law constitutive model are numerically solved using a finite-difference numerical scheme. The influence of inflow conditions, annular-nozzle-diameter-ratio, k, power-law index, n, and Prandtl numbers, is reported for: Inflow Condition = {fully-developed, uniform}; κ = {0, 0.5}; n = {1, 0.6}; Re = {50}; Pr = {1, 10, 100}. Fully-developed inflows result in larger and more intense recirculation, which leads to higher wall heat transfer rates, in comparison with uniform inflows. Substantial heat transfer augmentation, downstream the plane of expansion, is only observed for Pr = 10 and 100.
Study on Modeling About Some Forces Related to Dynamics Responses During Operation of Reciprocating Compressors
Authors: Mizobe Yu , Mori Yoshifumi , Nakamura Takenori , Saito Takashi
Published: January 2018

To avoid discontinuation during long-term continuous operation in plants, a reliable monitoring system for the state diagnosis is strongly expected. However, occurring troubles of various facilities in a plant aren’t simple. We proposed a sophisticated estimation method to diagnosis the state for reciprocating compressors. Our monitoring system uses both the measuring data in the factory and the analytical results based on the mathematical model, which can express the dynamic behavior about the reciprocating compressor. The mathematical model has multi degrees of freedom and the model parameters are identified to estimate the state change. To realize the reliable monitoring, we have to establish estimation and diagnosis method for any change of the operation state.

In this paper, we discuss a dynamic model that is able to analyze the dynamics responses of the reciprocating compressor during operation based on the measurement data. We show that the viscous damping coefficients are rather smaller than the spring constants of the parallel elements and the only behavior in the horizontal direction is affected by the damping character. To express the vertical acceleration in time history, we examine the dependency of time histories about acceleration during operation upon the crank angle and propose modified generating forces in the connecting parts.
Multi Effects Desalination-Mechanical Vapor Compression Powered by Low Temperature Supercritical Organic Rankine Cycle
Authors: Almatrafi Eydhah , Moloney Francesca , Goswami D. Y.
Published: January 2018

Availability of clean drinking water and power are two important issues in the world. In this paper, an innovative new design of multi effect desalination coupled with mechanical vapor compression (MED-MVC) powered by supercritical organic Rankine cycle utilizing a low grade solar heat source using evacuated tube collectors is analyzed. The supercritical organic Rankine cycle efficiency is about 10% at 150°C and 5MPa with R152a as the working fluid. The performance of the LT-MED-MVC was found to be better than similar systems found in the literature. The specific power consumption for MVC is lower than 1 kWh/m3 for seawater feed salinity of 42,000 ppm, 14 forward feed effects, and a recovery rate of 50%. The overall system efficiency is 7%. The impact of increasing the number of effects on the performance ratio, effect specific area, specific power consumption, solar collector area, and the system efficiency are also analyzed in this paper.
Monitoring of Respiratory Cycles Utilizing Sensors on Sleeping Mat
Authors: Dow Douglas E. , Horiguchi Yukio , Hirai Yoshiki , Hayashi Isao
Published: January 2018

Sleep apnea and other sleeping disorders impair health and quality of life. Polysomnography is the primary method for diagnosis, but involves cost and utilization of medical resources, which limit access for potential patients. The clinical environment and sensors of polysomnography hinder typical sleep patterns in many individuals, thus degrading the analysis. Sensors suitable for at-home monitoring of sleep have recently become available. At-home monitoring of sleep may improve diagnosis due to increased familiarity for sleeping and ability for multiple sleep sessions, as well as lowering the cost. However, more robust algorithms would be needed to partially compensate for the less controlled conditions and sensor systems. A mat with a grid of force sensors has become available. This study was developing a state machine algorithm to analyze the activity at multiple force sensors of a mat while the subject was lying in supine position on the mat and undertaking natural, rhythmic respiration. The algorithm monitored the subset of active sensors to detect potential respiratory cycles. The similarity of the timing of the detected cycles between different sensors was used to determine the overall pattern of respiratory activity for the subject. Reliable detection of timing for respiratory cycles would be useful for detection of sleep apnea events.
Effect of Fineness Modulus and Uniformity Coefficient on the Complex Modulus Function of Asphalt Concrete
Authors: Rahman A. S. M. Asifur , Tarefder Rafiqul A.
Published: January 2018

Different material attributes such as mix volumetrics, aggregate gradations, and binder characteristics are the factors affecting viscoelastic material functions of asphalt concrete. In this study, the effects of aggregate gradation on the complex modulus function of asphalt concrete are determined. The two distinct properties of the aggregate blend considered in this study are the fineness modulus and the uniformity coefficient. A total of 54, plant produced, asphalt concrete mixtures with asphalt binders having various performance grades and sources were collected from the manufacturing plants. The asphalt-aggregate mixtures were then compacted, cored, and sawed to cylindrical specimens. Three cylindrical specimens from each of the asphalt-aggregate mixtures were prepared and tested in the laboratory for complex or dynamic modulus. After that, average mastercurves of complex modulus and phase angle were generated by applying time-temperature superposition principle. Study showed that the complex modulus function of asphalt concrete is significantly related to the fineness modulus and uniformity coefficient of the aggregate blends used in the asphalt-aggregate mixture.
Using Discreet Models to Study Concussion and Analyze Passenger Head Response During Front-End Vehicle Collisions
Authors: Honarmandi Peyman , Khan Basil , Barakat Alaa , Gordon Douglas
Published: January 2018

Head concussion and neck injury are often induced by an accident even in a minor collision. In this study, a discrete model of masses, springs, and dampers are considered which represent the components of a vehicle-passenger system. The vehicle accounts for 5 degrees of freedom (DOF) whereas the passenger contributes an additional 5 DOF. Differential equations that express the dynamic forces and moments acting upon each mass are developed and then solved numerically using Runge-Kutta method. The results were used to validate the use of such a model to accurately represent real life crash situations. The primary responses of the model are the magnitudes of acceleration experienced by various sections of the model and their relative displacements in two-dimensional space. Analyses were conducted at varying crash velocities and also with different model configurations. It was found that the behavior of the model corresponds well to previous studies and also to what one would intuitively expect at actual collision scene.
Airborne Turbines: The Impact of Scaling on System Performance
Authors: Mohafez Mir Hamed , Goudarzi Navid
Published: January 2018

Tethered airborne wind energy systems are among emerging renewable energy technologies in recent years. These systems can harness greater power densities at higher altitudes with lower costs of installation and energy production in comparison with those from conventional ground-based energy harnessing technologies. A Buoyant Airborne Turbine (BAT) as a flying aerostat has a horizontal axis wind turbine within its shell and can elevate up to 600m. There are a number of pertinent parameters such as BAT configurations/component dimensions or its aerodynamic characteristics that impact the system total power performance. Identifying the optimum values of these parameters by conducting theoretical and computational analysis will benefit both lab- and full-scale experiments with more accurate dimensional and aerodynamic analysis.

This paper presents an analytical model for investigating the impact of a BAT system scaling and in particular the BAT shell dimensions on its power performance/coefficient. The model uses the flying conditions and BAT shell dimensions from literature to derive the system total mass as a function of BAT shell dimensions. The effect of BAT shell variations/scaling on system power coefficient and its optimum value for stable/safe system design are determined. This work provides a basis for the follow on research phases of this project that has focus on studying BAT system aerodynamic performance and its wake behavior at different scales and environmental conditions.
POD Analysis of the Impact Dynamics of the Olive Tree Branch: Nature’s Paradigm of a Complex Soft-Stiff Structural System in Biomechanics
Authors: Georgiou Ioannis T.
Published: January 2018

Geometry consistent spatio-temporal measurements of the experimental acceleration of olive tree branches were analyzed with advanced POD tools in an effort to gain knowledge on the mechanics-dynamics of this bio-mechanical structure. To pave the way for understanding the dynamics of this system, both the typical olive tree as a whole and its typical branch are approached as interacting soft-stiff continuum mechanical systems. The POD analysis reveals that the impact response is a nonlinear vibration with very fast dissipation. The POD modal amplitudes are nonlinear vibrations of continuous, broadband frequency spectrum. Initially they exhibit regular phases of nonlinear slow dissipation-and-amplification followed by irregular, fast dissipation-and-amplification phases. Sequentially applied impacts at the branch soft area results in a complete detachment of the fruit. The POD analysis reveals that this occurs because the response is highly localized in the soft area where the impact is applied and thus it transfers its momentum to the fruits. The work is supplemented with analysis of field measurements of the acceleration dynamics of orchard olive tree branches excited by harvesting devices generating combing clouds of impulsive forces aimed at detaching the olive fruit by momentum transfer.
District Heating Network Modelling for the Analysis of Low-Exergy Sources
Authors: Verda Vittorio , Guelpa Elisa
Published: January 2018

One of the main advantages of district heating system technology is the possibility of integrating multiple heat sources for domestic heating. In particular, it is often possible exploit low-exergy sources, such as waste heat recovered from industry or from renewable energy sources, that are often affected by time variation of the temperature.

A very convenient and useful opportunity for predicting and analyzing district heating network behavior is modelling. Modelling allows to quantify opportunities related to changes in DH (district heating) network design or management, before real implementation. Therefore an important point is the creation of models able to simulate network, also very large and linked to many power plants, working at variable heat production conditions (i.e. variable mass flow rates and temperatures).

The goal of this work is to propose a novel approach which combines exergy analysis with a DH network model for evaluating the best DH operating conditions. A thermo-fluid dynamic model based on conservation equation has been adapted for the discussed aims and applied to a network involving different low-exergy heat sources with variable temperatures. An evaluation of the implementation of these sources is provided for the Turin district heating network, which is the largest network in Italy.
Design and Testing of High-Performance Mini-Channel Graphite Heat Exchangers in Thermoelectric Energy Recovery Systems
Authors: Hendricks Terry J. , Mcenerney Bryan , Drymiotis Fivos , Furst Ben , Shevade Abhibit
Published: January 2018

Recent national energy usage studies by Lawrence Livermore National Laboratory in 2015 [1] show that there is approximately 59 Quads (1015 Btu’s) of waste thermal energy throughout various industrial, residential, power generation, and transportation sectors of the U.S. economy. Thermoelectric energy recovery is one important technology for recovering this waste thermal energy in high-temperature industrial, transportation and military energy systems. Thermoelectric generator (TEG) systems in these applications require high performance hot-side and cold-side heat exchangers to provide the critical temperature differential and transfer the required thermal energy. High performance hot-side heat exchangers in these systems are often metal-based due to requirements for high-temperature operation, strength at temperature, corrosion resistance, and chemical stability. However, the generally selected metal-based hot-side heat exchangers (i.e., Inconels, Stainless Steels) suffer from low thermal conductivity, high thermal expansion, and high density, which degrades their thermal performance, leads to high thermal-expansion-driven stresses, and creates relatively high mass/high volume (i.e., low power density) TEG systems that are then difficult to fabricate and integrate into viable energy recovery systems. This paper describes the design and testing of a new, high-temperature minichannel graphite heat exchanger designed for operation up to 500°C that is a critical element of a high-power-density TEG power system for aircraft energy recovery. This high-performance graphite heat exchanger represents a new state-of-the-art standard in high-temperature heat exchangers for TEG systems, which provides higher thermal transport, less thermal expansion at operation, lower system level stresses on TE components, and a lighter weight TEG system. This new heat exchanger creates a new design paradigm in TEG system design for terrestrial energy recovery and potential NASA technology infusion into terrestrial energy system applications. This paper will present and discuss the key heat transfer, pressure drop, pumping power analyses and design tradeoffs that created this unique design. Heat transfer and pressure drop modeling was performed with both empirical models based on known heat transfer and friction factor correlations and COMSOL thermal/fluid dynamic modeling of the graphite heat exchanger structure. We will also discuss resulting thermal transport and heat fluxes predicted at the TEG interface level. Heat exchanger performance testing was performed under simulated operating conditions and correlation with test data at the anticipated operating temperature conditions will be presented and discussed.
Overview of Current Hybrid Propulsion Research and Development
Authors: Nguyen Bao , Faruqui Khulood , Robles Luis R. , Ho Johnny , Wagner Geoffrey , Surmi Jeremy , Carter Ashley , Hinz Tom , Kakish Fady , Zousel Zachariah , Matthys Kory , Piacenza Joseph
Published: January 2018

As dwindling federal funding continues to constrict the national space program, private entities have carried the torch of innovation in the aerospace industry. While the concept of hybrid rocket engines, systems where solid fuels and fluid oxidizers are used for combustion, was conceived during the mid-20th century, the aerospace industry only recently has substantially increased research and development of these engines. According to the literature, hybrids are safer and cheaper than their liquid counterparts due to the utilization of solid fuel and generally provide greater values of specific impulse, density specific impulse, and fuel energy density than traditional solid-fuel engines. This paper provides an overview of the design principles used to develop hybrid engines and discusses limitations currently faced by industry. Furthermore, development of hybrid engines to allow for both scalability and reusability are explored as private aerospace companies continue to demonstrate that reusable rockets are the future of rocket technology. With applications catering from low-payload cargo delivery to the increasing interest in space tourism and exploration, hybrid engines can provide a safer, less expensive solution than traditional and well-established engine selections. Suggestions for future design opportunities and methods are proposed and discussed to make the concept of hybrid engines a viable innovation in the future of rocketry.
Computational Simulation of Dynamic Recrystallization and Severe Deformation of AA7075 Alloy
Authors: Hernández-Rivera José Luis , Cerda Vázquez Perla Julieta , Cruz Rivera Jose de Jesús , García Zugasti Pedro de Jesús , Ramos Azpeitia Mitsuo Osvaldo
Published: January 2018

The empirical model of dynamic recrystallization (DRX) coupled with DEFORM 3D® software (based on the finite element method (FEM)) was used to predict the microstructural evolution of the AA7075 processed by four passes of equal channel angular pressing (ECAP) at 250° C. The DRX model parameters were taken from the literature. The simulation results showed that the DRX exhibited a heterogeneous distribution from the back to the frontal part of the sample and this heterogeneity markedly diminished in the fourth pass. The recrystallized volume fraction reached 50% in most of the sample in the fourth pass and the average grain size did not show significant changes, going from an initial value of 16.4 μm to 12.5 μm. This latter result was attributed to the fact that DRX occurred partially even for the last pass. Experimental testing of ECAP was conducted by using the same conditions of computational simulation. The validation of model was performed by comparison of average grain size values with those obtained experimentally by means of image analysis applied on micrographs that were acquired by means of optical microscopy (OM). Hardness and peak load values also indicated the occurrence of a partial dynamic recrystallization and recovery.
Studying the Trade-Off Between Protection and Mobility of Armored Vehicles
Authors: Kamel Hisham
Published: January 2018

Mobility, firepower and armor protection are three conflicting design requirements in any modern armored vehicle. There is a trade-off between each couple. In this study, we focused on the conflicting relationship between protection and mobility. We characterized mobility using four measurable vehicle dynamic quantities. We surveyed the different approaches for vehicle protection. Then, we studied the effect of each protection approach on vehicle mobility. Adding V shape plates for blast protection has been extensively used in modern armored vehicles with much success. Therefore, we dedicated a detailed study using finite element analysis on a generic V shape protection plate. The study included a parametric study on the effect of V shape angle, standoff distance and material type on the protection performance of the plate. It was concluded that sharper V angles are more efficient in protection. However the V angle is governed by vehicle ground clearance. In cases of vehicles with limited ground clearances, it was concluded that fitting a V shape with any angle can provide some blast protection without sacrificing mobility. We also concluded that lighter materials than steel can be used and still provide enough protection. Finally, it is believed that a study that considers all the aforementioned parameters and their effect on vehicle mobility will help in developing more capable armored vehicles.
Rheometric Studies of Functional Polyurethane Foam Composite
Authors: Bakhtiyarov Sayavur I. , Oxley Jimmie C. , Smith James L. , Baldovi Philipp M. , Siginer Dennis A.
Published: January 2018

A rheometric characterization of the functional Polyurethane (PU) foam composite with and without solid additives (aluminum flakes) were experimentally measured using a computer controlled mechanical spectrometer (rheometer) ARES-G2. It is determined that PU composite exhibits a strong time thickening and shear thinning behavior. The rheological behavior of this composite can be described with the power-law generalized non-Newtonian fluid model. The rheometric tests showed that the PU/Al mixture exhibits thermal thickening and shear thinning behavior with the yield stress. The system can be described with the power-law generalized non-Newtonian fluid (Ostwald-de-Waele) model. The effective viscosity of PU composite increases with both the testing time (exponentially) and the solid content (polynomial) in the mixture.
Vibration Analysis of Large Silos: Modeling and Experiments
Authors: Moazed Reza , Fotouhi Reza
Published: January 2018

During the discharge of large cylindrical silos, significant vibrations, pulsations and quaking are often created. The vibrations are typically accompanied by acoustical emissions referred to as silo honking. Such noise pollution is a health and safety concern for workers at site (e.g., hearing loss due to prolonged exposure). From a structural integrity standpoint, the vibrations contribute to the fatigue failure of the load carrying members and connections and endanger the safety and integrity of the overall system. The associated forces and deflections are often further amplified due to resonance between the silo support structure and the discharge loading frequencies. In order to avoid exciting one of the silo support structure modes, researchers and engineers often employ simplified mass-spring models to predict the natural frequencies of the structure. However, these models do not always capture all of the important modes of the silo system. In this paper, a detailed finite element model is developed to predict all of the dominant modes (vertical and side-way swaying) of the system. Beam, shell, and solid elements are used to model the silo support structure, silo walls, and the potash mass, respectively. For the experimental study, several strain gauges and accelerometers were installed on a full-scale silo support structure to determine the frequency of loading during material discharge. This paper summarizes the results of the numerical and experimental study that has been performed.
Aerodynamic Flutter of Turbine Brush Seals
Authors: Borgueta Samuel J. , Bach Nicholas R. , Correia Jared J. , Egan Brendan G. J. , Horton Joshua S. , Lipsett James E. , Laoulache Raymond N.
Published: January 2018

With global energy demands continually growing and environmental impacts a major concern in power production, maximizing the efficiencies of power plants is of top priority. EthosEnergy2 has sponsored a project at the University of Massachusetts Dartmouth to study and analyze the brush seals in steam turbines in pursuit of increasing steam turbine thermodynamic efficiency. Brush seals are incorporated circumferentially around the turbine blades in their housing. The brush seals provide a very minimal clearance height that compensates for start-up rotor deviation and minimizes high-pressure steam blow-by around the edges of the blades. Brush seals minimize the clearance height between the blades and housing, which allows the turbine to produce more work. However, overtime brush seals can be damaged, greatly reducing efficiency. The seals that are repeatedly showing excessive wear and damage, occur in the high-pressure sections of steam turbines with high Reynolds numbers. The bristle breakdown is attributed to high Reynolds numbers and aerodynamic flutter.

The purpose of this research is to design a prototype and empirically model steam turbine conditions with air to map out the fluid-solid interaction, determine the modes of bristle failure, and ultimately reproduce and record bristle flutter. A pressure vessel and pressure system was designed to test linear strips of brush seals with air as the working fluid. The pressure vessel accommodates varying clearance heights to identify the correlation of clearance height and the effects on fluid flow. The system also incorporates a high-speed camera that can capture the phenomena of flutter, precisely identify the modes of failure, and record fluid-solid interaction and the interaction of the bristles with each other. Designing a prototype to empirically model this problem serves as a fundamental and critical step in understanding the fluid interaction with seals in high-pressure steam turbines and will identify brush seal modes of failure. The prototype’s ability to model steam turbine conditions and rapidly test various seal designs will facilitate better brush seal designs to be constructed and will ultimately increase the thermal efficiencies of steam turbines, aid in accommodating the increase in global energy demands, and reduce the detrimental environmental impacts of producing power. The system successfully produced and recorded brush-seal-bristle flutter while modeling high-pressure steam turbine conditions. Matching Reynolds and Euler numbers of the steam turbine stages provided the ability to scale the steam turbine to our prototype, with air as the working fluid. Brush seal breakdown was occurring in steam turbines at Reynolds numbers above 20,000. The prototype repeatedly produced brush seal flutter at Reynolds numbers above 25,000, validating the theory that brush seal breakdown is dependent predominantly on the Reynolds number.
Assembly of Methyl Coenzyme M Reductase in the Methanogenic Archaeon Methanococcus maripaludis
Authors: Lyu Zhe , Chou Chau-Wen , Shi Hao , Wang Liangliang , Ghebreab Robel , Phillips Dennis , Yan Yajun , Duin Evert C. , Whitman William B.
Published: January 2018

Methyl coenzyme M reductase (MCR) is a complex enzyme that catalyzes the final step in biological methanogenesis. To better understand its assembly, the recombinant MCR from the thermophile
Methanothermococcus okinawensis
(rMCR
ok
) was expressed in the mesophile
Methanococcus maripaludis
. The rMCR
ok
was posttranslationally modified correctly and contained McrD and the unique nickel tetrapyrrole coenzyme F
430
. Subunits of the native
M. maripaludis
(MCR
mar
) were largely absent, suggesting that the recombinant enzyme was formed by an assembly of cotranscribed subunits. Strong support for this hypothesis was obtained by expressing a chimeric operon comprising the His-tagged
mcrA
from
M. maripaludis
and the
mcrBDCG
from
M. okinawensis
in
M. maripaludis
. The His-tagged purified rMCR then contained the
M. maripaludis
McrA and the
M. okinawensis
McrBDG. The present study prompted us to form a working model for MCR assembly, which can be further tested by the heterologous expression system established here.

IMPORTANCE
Approximately 1.6% of the net primary production of plants, algae, and cyanobacteria are processed by biological methane production in anoxic environments. This accounts for about 74% of the total global methane production, up to 25% of which is consumed by anaerobic oxidation of methane (AOM). Methyl coenzyme M reductase (MCR) is the key enzyme in both methanogenesis and AOM. MCR is assembled as a dimer of two heterotrimers, where posttranslational modifications and F
430
cofactors are embedded in the active sites. However, this complex assembly process remains unknown. Here, we established a heterologous expression system for MCR to learn how MCR is assembled.
Mechanism of HIV-1 Resistance to an Electronically Constrained α-Helical Peptide Membrane Fusion Inhibitor
Authors: Wu Xiyuan , Liu Zixuan , Ding Xiaohui , Yu Danwei , Wei Huamian , Qin Bo , Zhu Yuanmei , Chong Huihui , Cui Sheng , He Yuxian
Published: January 2018

SC29EK is an electronically constrained α-helical peptide HIV-1 fusion inhibitor that is highly effective against both wild-type and enfuvirtide (T20)-resistant viruses. In this study, we focused on investigating the mechanism of HIV-1 resistance to SC29EK by two approaches. First, SC29EK-escaping HIV-1 variants were selected and characterized. Three mutant viruses, which possessed two (N43K/E49A) or three (Q39R/N43K/N126K and N43K/E49A/N126K) amino acid substitutions in the N- and C-terminal repeat regions of gp41 were identified as conferring high resistance to SC29EK and cross-resistance to the first-generation (T20 and C34) and newly designed (sifuvirtide, MT-SC29EK, and 2P23) fusion inhibitors. The resistance mutations could reduce the binding stability of SC29EK, impair viral Env-mediated cell fusion and entry, and change the conformation of the gp41 core structure. Further, we determined the crystal structure of SC29EK in complex with a target mimic peptide, which revealed the critical intra- and interhelical interactions underlying the mode of action of SC29EK and the genetic pathway to HIV-1 resistance. Taken together, the present data provide new insights into the structure and function of gp41 and the structure-activity relationship (SAR) of viral fusion inhibitors.

IMPORTANCE
T20 is the only membrane fusion inhibitor available for treatment of viral infection, but it has relatively low anti-HIV activity and genetic barriers for resistance, thus calling for new drugs blocking the viral fusion process. As an electronically constrained α-helical peptide, SC29EK is highly potent against both wild-type and T20-resistant HIV-1 strains. Here, we report the characterization of HIV-1 variants resistant to SC29EK and the crystal structure of SC29EK. The key mutations mediating high resistance to SC29EK and cross-resistance to the first and new generations of fusion inhibitors as well as the underlying mechanisms were identified. The crystal structure of SC29EK bound to a target mimic peptide further revealed its action mode and genetic pathway to inducing resistance. Hence, our data have shed new lights on the mechanisms of HIV-1 fusion and its inhibition.