bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Nanoparticle Aggregates Using Bayesian Inference via Light Scattering Experiments
Authors: Eriçok Ozan Burak , Ertürk Hakan
Published: February 2017

Controlling the properties of the nanostructures requires use of proper characterization methods. There are many techniques available such as microscopy, time-resolved laser-induced-incandescence or light scattering methods that can be used for characterization of nanostructures. While direct observation such as microscopy is possible for some applications, the indirect characterization is carried out through measurements of structures’ emission or scattering behavior as in the laser-induced-incandescence and light scattering methods. Characterization of soot aggregates is well studied and is often classified as an inverse problem that can be formulated as a parameter estimation problem, where parameters defining the aggregate such as average size and number of nanoparticles are estimated. Estimations based on the scattering behavior can be questionable unless these parameters are directly observed by other methods. Instead of presenting a single estimate, Bayesian credible intervals would be a better option when indirect methods such as light scattering are used. The objective of this work is to investigate the strengths and weaknesses of the Bayesian approach based on numerical light scattering experiments considering soot aggregates as an example. Light scattering behavior of the soot aggregates is obtained with discrete dipole approximation, considering unpolarized light.
Unsteady Heat Transfer Around Low Aspect Ratio Cylinders in an Array
Authors: Siroka Shawn , Shallcross Melissa , Lynch Stephen
Published: February 2017

Cylindrical pins, often called pin fins, are used to create turbulence and promote convective heat transfer within many devices, ranging from computer heat sinks to the trailing edge of jet engine turbine blades. Previous experiments have measured the time-averaged heat transfer over a single pin as well as the flow fields around the pin. However, in this study, focus is placed on the instantaneous heat flux around the centerline of a low aspect-ratio pin within an array. Time-mean and unsteady convective heat flux are measured around the circumference of an isothermal heated test pin via a microsensor located at the surface. The pin is positioned at various locations within a staggered array in a large-scale wind tunnel. Reynolds numbers from 3,000 to 50,000, based on pin diameter and maximum velocity between pins, are tested with a streamwise spacing of 1.73 diameters between rows, a spanwise spacing of 2 diameters, and a pin height of 1 diameter. The time-averaged and standard deviation of convective heat flux around the pin is higher over most of the pin surface for pins in downstream row positions of an array relative to the first row pin, except in the wake which has similar levels for all rows. For a given pin position in the array, as the Reynolds number increases, the point of minimum heat transfer moves circumferentially upstream on the pin fin, corresponding to earlier transition of the pin boundary layer. Also, for a given Reynolds number, the minimum heat transfer point on the pin circumference moves upstream for pins further into the array, due to the high turbulence levels within the array which cause early transition. For a single pin row with no downstream pins, heat transfer fluctuations are very high on the backside of the pin due to the significant unsteadiness in the pin wake, but heat transfer fluctuations are suppressed for a pin with downstream rows due to the confining effects of the close spacing. The results from this study can be used to design pin-fin arrays that take advantage of unsteadiness and increase overall convective heat transfer for various industry components.
Formation and Penetration of Vortex Ring on Drop Coalescence
Authors: Deka Hiranya , Biswas Gautam , Dalal Amaresh
Published: February 2017

Numerical simulations are performed using coupled level-set and volume of fluid (CLSVOF) method to capture the formation and propagation of a vortex ring when a drop coalesces at the interface of a pool of same liquid and a lighter liquid resting above it. A Vortex ring is generated near the interface on coalescence of a drop. Subsequently the vortex ring propagates into the liquid pool. The propagation of a vortex ring and its dependence on the shape as well as impact velocity of the drop are investigated in this work.
A Survey of Approaches for Fault Diagnosis in Axial Piston Pumps
Authors: Maradey Lázaro Jessica Gissella , Borrás Pinilla Carlos , Roa Prada Sebastian
Published: February 2017

Axial piston variable displacement pumps (VDAP) are the heart of every hydraulic system, and are they commonly used in the industry for its high capacity, efficiency (volume and total), and good performance in the handling of high pressures and speeds. Faults are usually associated with wear and leakage processes, which cause significant decreases in performance.

This paper discusses about the advantages to implement a Condition-based Maintenance (CBM) and the use of techniques of fault diagnosis in axial variable displacement piston pumps (VDAP), as they are: Neural Networks (NN), Support Vector Machine (SVM) and Fuzzy Logic (FL) and other hybrid models.

The results of this investigation provide guidelines for the selection of the most suitable technique to prevent faults in VDAP in order to help reducing down time, increase productivity and competitiveness of companies that requires the use of fluid power systems by enabling the implementation of a non-intrusive fault diagnosis management system, which must be reliable, economical and easily accessible to the industry.
Development of the Reliability-Risk Modeling Framework for Ranking Conceptual Designs
Authors: D’Angelo Anthony
Published: February 2017

A critical component of Systems Engineering (SE) is to conduct a thorough Risk Analysis. This paper introduces a novel hybrid approach to develop a Reliability-Risk modeling technique that will be able to rank Conceptual Designs as a function of Reliability. A traditional SE approach is used to identify all success modes associated with the development of a complex system. Also, the Advanced Development, Design, Integration & Evaluation, Production, and Operation & Support that make up the major phases of a Systems Engineering model will define the Holographic Reliability Design Space.

Requirements of the System under development are captured through the implementation of the Integration Definition Function Modeling (IDEF0) technique. The IDEF0 method is defined in Federal Information Processing Standard Publications (FIPS PUBS 183) [1]. Using the developed IDEF0 model allows the function of each component to be identified, the proper reliability model to be chosen, and completion of a reliability-based analysis.

Upon completion of calculating the reliability, for each criterion, the use of a Multi-Criteria Decision System (MCDS) is required to rank the conceptual designs in terms of reliability. A MCDS was developed to analyze the conflicting objects inherent during the design and integration of any complex system.

The model developed herein was used to analyze 5 Packaging Conceptual designs being considered to become part of the military Supply Chain. After completion of the analysis, the new and innovative Packaging Designs were ranked based on reliabilities associated with design, test, integration, manufacturing, and incorporation into the existing Supply Chain. The results of the rankings were then presented to the ultimate decision makers for final approval.
Non-Linear Modeling of Ocean Current Turbine Blades Under Large Deflection
Authors: Suzuki Takuya , Mahfuz Hassan
Published: February 2017

This paper presents a non-linear modeling approach for large-scale ocean current turbine (OCT) blades. During the operation, OCT blades are subjected to a hydrodynamic load that has fluid density 800 times higher than that of air. The fluid load on OCT blades are sufficient to cause large deflection; therefore, a method that couples the blade’s deflection and the hydrodynamic load is required. For this purpose, we developed a non-linear model for turbine blades based on blade element momentum (BEM) theory. The newly developed method considers interplay between blade’s deflection and the hydrodynamic load. In addition, geometric non-linearity is also considered in the analysis, which provides a more accurate prediction of the structural response.

For validation purposes, the developed method and a set of existing National Renewable Energy Laboratory (NREL) codes were used to calculate the deflection of the OCT blade. A comparison of flap-wise and edge-wise deflections given by both methods were determined and the results showed a good correlation between the two methods. This comparison was made only for small deflection since NREL codes cannot account for large deflection.

In the next step, to investigate the effect of non-linearity, both linear and non-linear analyses were performed for a large-scale OCT blade where deflection was indeed large. In this study, we analyzed a flexible blade made of E-glass/epoxy composite. The difference in deflection was about 11% for the flexible blade since the fluid-structure interaction was significant as the blade deflection was large.
Quantifying the Linearity of the Fluid Dynamics for Noncontacting Annular Seals
Authors: Watson Cori , Paudel Wisher , Wood Houston G. , Weaver Brian K.
Published: February 2017

Non-contacting annular seals are used in turbomachinery to reduce the leakage of working fluid. The leakage is caused by a pressure differential across the seal and is reduced through textures cut into the surface of the seal. Three common types of non-contacting annular seals are labyrinth seals, hole-pattern seals, and helical groove seals. Labyrinth seals have circumferentially cut grooves as their surface texture. Helical groove seals have continuously cut grooves following a helical path along the surface. Hole-pattern seals have holes patterned across the surface. Each surface texture causes different flow patterns and sealing mechanisms.

These non-contacting annular seals can have textures cut across the surface of the rotor, the surface of the stator, or both. The goal of this study is to determine the degree to which the flow of seals with textures on both surfaces can be viewed as the superposition of the flow for a seal with the rotor surface textured and a smooth stator combined with the flow for a seal with the stator surface textured and a smooth rotor. To accomplish this goal, simulations were run in ANSYS CFX for each seal type and configuration for a variety of rotor speeds and pressure ratios to compare superimposed solutions to standard 3D solutions.

The ability to superimpose solutions to a differential equation — and therefore a fluid dynamics system — is determined by the linearity of the differential equation. By comparing the superimposed solution with the standard solution, this study will quantify the degree of non-linearity in the system. The degree of divergence away from linearity will be compared against the rotor speed and pressure ratio, which are proportional to the Reynold’s number. The Navier-Stokes equation contains a non-linear inertial force term. The relative significance of the inertia forces is predicted by the Reynold’s number so a strong correlation is expected between the Reynold’s number and the agreement between the flow found by superposition and the flow found by the actual seal model.

The other application of this research is to the computational modeling of annular seals. Annular seals can be computationally demanding and time consuming to model. This is especially true for seals with texture on both surfaces where millions of finite volumes may be needed in the simulation in order to find a convergent solution. For rotor speeds with strong agreement between the actual flow and the superimposed flow, superposition can be applied to perform faster simulations of seals with texture on both surfaces.
A Finite Element Model to Predict the Part Strength of Fused Deposition Modeling Printed Parts
Authors: Velivela Vivek , Gurunathan Saravana Kumar
Published: February 2017

This paper aims at creating a computational finite element model, which will be used for prediction of deformation and failure of specimen under static loads for specimens prepared using FDM based 3D printers with different raster fill patterns and density. The work is divided as follows: a) understanding heterogeneity in specimen printed using FDM; b) conducting strength testing experiments to estimate stiffness and failure corresponding to particular infill configuration; c) creating and validating computational finite element model of FDM printed specimen with various raster fill pattern and density. In this work, the computational model of FDM parts is created as a multi-layered composite model. The computational model generated in this work can be used to estimate the deformation of a specimen printed using FDM process under a specific load condition. This model can further be used within an optimization framework to maximize part strength for a part with any geometry by suitably selecting part orientation and slicing parameters for a given service load condition.
Analytical Solutions of a First-Order Quadratic Nonlinear System With Parametrical and Periodical Excitation
Authors: Zhou Guopeng , Luo Albert C. J. , Zhou Naiding , Liang Feng
Published: February 2017

In this paper, a quadratic nonlinear dynamical system with two periodic excitation forces is discussed. Analytical period-1 motions of such dynamical system are obtained by using generalized harmonic balance method. Stability analysis is carried out via eigenvalues analysis. To verify approximate analytical solutions, numerical simulations are completed to compare analytic and numerical solutions of the dynamical system, the approximate precision is guaranteed with appropriate harmonic balance terms. More harmonic terms should be employed to guarantee good approximation of periodic motions if excitation frequency is small. Furthermore, infinite harmonic balance terms must be introduced for chaotic systems.
Frequency Response of Electrostatically Actuated MEMS Resonators Under Superharmonic Resonance Using MMS
Authors: Caruntu Dumitru I. , Reyes Christian
Published: February 2017

This work investigates the voltage response of superharmonic resonance of second order of electrostatically actuated Micro-Electro-Mechanical Systems (MEMS) resonator cantilevers. The results of this work can be used for mass sensors design. The MEMS device consists of MEMS resonator cantilever over a parallel ground plate (electrode) under Alternating Current (AC) voltage. The AC voltage is of frequency near one fourth of the natural frequency of the resonator which leads to the superharmonic resonance of second order. The AC voltage produces an electrostatic force in the category of hard excitations, i.e. for small voltages the resonance is not present while for large voltages resonance occurs and bifurcation points are born. This solution is then used in the first-order problem to find the voltage-amplitude response of the structure. The influences of frequency and damping on the response are investigated. This work opens the door of using smaller AC frequencies for MEMS resonator sensors. The frequency response of the superharmonic resonance of the structure is investigated using the method of multiple scales (MMS).
A Preliminary Study: The Effects of Personal Motivation on Design Quality
Authors: Mountain Philip , Carini Robert M. , Bohm Matt R. , Riggs Marie
Published: February 2017

The ultimate goal of most design projects or endeavors should be to create a product with high quality as it typically leads to higher customer satisfaction and brand retention. Product design teams are usually comprised of a group of engineers with varying backgrounds, personalities, and motivational drives. This paper presents an initial study on how motivation of individuals affects the quality of their resulting designs. The ultimate goal of this research is to identify factors — such as motivational factors — that may prove useful to forming the most effective design teams. Initial data for this study stems from a senior level capstone design course in a mechanical engineering program and takes the form of a design quality assessment; and one survey instrument that assesses the 6 distinguishing qualities of serious leisure, and in particular, its motivations and benefits. Design quality is measured by a group of engineering faculty and industry representatives utilizing a proposed design quality rubric which scrutinizes factors such as customer satisfaction, manufacturability, and product fit and finish. Motivational factors are measured using the Serious Leisure Inventory and Measure (SLIM) short form, a 9-point Likert style questionnaire. The goal of this research is to identify teaming strategies such that a group of designers will achieve the level of design quality desired of a specific product or project. Findings in this study indicate that teams, comprised of individuals largely motivated toward design-focused leisure, or conversely demotivated by personal aspects, tend to realize better design quality outcomes.
Optimal Sinusoidal Cellular Structures for Energy Absorption
Authors: Jiang Yunyao , Li Yaning
Published: February 2017

In this investigation, the elastic mechanical properties of the sinusoidal cellular structures were first explored via analytical models. The analytical analysis showed that for linear elastic materials, the amplitude-to-wavelength ratio of the sinusoidal structures is a key geometric parameter to determine the deformation mechanisms. To further evaluate the influences of the geometric nonlinearity, a set of finite element simulations were performed for sinusoidal structures with the same density but various amplitude-to-wavelength ratios. It was found that the optimal amplitude-to-wavelength ratio for the maximum energy absorption corresponds to the transition between symmetric to asymmetric deformation mechanisms.

Selected designs were fabricated via a 3D printer (Objet, Connex 260). Mechanical experiments under quasi-static uniaxial compression and cyclic compression were performed on the 3D printed specimens. Finite element (FE) simulations with both linear elastic and nonlinear hyperelastic material models were performed and compared with the experiments. The 3D-printed sinusoidal structures were shown to be re-configurable under cyclic loading.
Numerical Simulation of Non-Isothermal Two-Phase Flow in a Pipeline Using the Flux-Corrected Transport Method
Authors: Sondermann Carina N. , Patricio Rodrigo A. C. , Figueiredo Aline B. , Baptista Renan M. , Rachid Felipe B. F. , Bodstein Gustavo C. R.
Published: February 2017

Two phase flows occur in many engineering problems, especially in the nuclear, gas and petroleum industries. In oil and gas applications, specifically, a mixture of oil and natural gas is transported in pipelines from offshore platforms to the continent. The prediction of how the flow behaves in time as it moves along the pipe is extremely important, mainly during the pipeline design stage or regular operation. This paper presents simulations for stratified gas-liquid two-phase flow in a horizontal pipeline that is subject to the temperature gradients that exist in the bottom of the ocean, and the resulting heat transfer process that may lead to wax formation and deposition. A one-dimensional two-fluid mathematical model was employed that includes conservation equations of mass and momentum for each fluid and one energy equation for the mixture of liquid and gas. The problem was formulated as an initial-boundary value problem of the hyperbolic type and it was solved using the Flux Corrected Transport (FCT) numerical method, which is second-order accurate in space, coupled with an explicit discretization in time that is first-order accurate. The FCT method is appropriate to solve problems characterized by hyperbolic equations that may contain discontinuities and shock waves, and it presents small dispersive effects. The results showed excellent accuracy results when compared to commercial software widely used in the oil and gas industry.
Magnesium and Calcium-Containing Scaffolds for Bone Tissue Regeneration
Authors: Adhikari Udhab , Rijal Nava P. , Khanal Shalil , Pai Devdas , Sankar Jagannathan , Bhattarai Narayan
Published: February 2017

Bone is a living tissue that constantly remodels and adapts to the stresses imposed upon it. Bone disorders are of growing concern as the median age of our population rises. Healing and recovery from fractures requires bone cells to have a 3-dimensional (3D) structural base, or scaffold, to grow out from. In addition to providing mechanical support, the scaffold, an extracellular matrix (ECM) assembly, enables the transport of nutrients and oxygen in and removal of waste materials from cells that are growing into new tissue. In this research, a 3D scaffold was synthesized with chitosan (CS), carboxymethyl chitosan (CMC), calcium phosphate monobasic and magnesium oxide (MgO). CS is a positiviely-charged natural bioactive polymer. It is combined with its negatively-charged derivative, CMC, to form a complex scaffold. Magnesium phosphate biocement (MgP), formed by reacting calcium phosphate monobasic and MgO, was incorporated into CMC solution before adding CS solution. Scaffolds were prepared by casting, freezing and lyophilization. The scaffolds were characterized in terms of pore microstructures, surface topography, water uptake and retention abilities, and crystal structure. The results show that the developed scaffolds exhibit highly interconnected pores and present the ideal pore size range (100–300 μm) to be morphometrically suitable for the proposed bone tissue engineering applications. These scaffolds not only mimic the nanostructured architecture and the chemical composition of natural bone tissue matrices but also serve as a source for soluble ions of magnesium (Mg++) and calcium (Ca++) that are favorable to osteoblast cells. The scaffolds thus provide a desirable microenvironment to facilitate biomineralization. These observations provide a new effective approach for preparing scaffold materials suitable for bone tissue engineering.
Nonlinear Characterization of Heart Rate Variability in Normal Sinus Rhythm, Atrial Fibrillation and Congestive Heart Failure
Authors: Zaidi Syed Hassan , Akhtar Imran , Majeed Syed Imran , Zaidi Tahir , Khalid Muhammad Saif Ullah
Published: February 2017

This paper highlights the application of methods and techniques from nonlinear analysis to illustrate their far superior capability in revealing complex cardiac dynamics under various physiological and pathological states. The purpose is to augment conventional (time and frequency based) heart rate variability analysis, and to extract significant prognostic and clinically relevant information for risk stratification and improved diagnosis. In this work, several nonlinear indices are estimated for RR intervals based time series data acquired for Healthy Sinus Rhythm (HSR) and Congestive Heart Failure (CHF), as the two groups represent different cases of Normal Sinus Rhythm (NSR). In addition to this, nonlinear algorithms are also applied to investigate the internal dynamics of Atrial Fibrillation (AFib). Application of nonlinear tools in normal and diseased cardiovascular states manifest their strong ability to support clinical decision support systems and highlights the internal complex properties of physiological time series data such as complexity, irregularity, determinism and recurrence trends in cardiovascular regulation mechanisms.
Thermal Performance of Parabolic Trough Collector for Cooling Applications in Residential Buildings in UAE
Authors: Ghaith Fadi A. , Razzaq Haseeb-ul-Hassan
Published: February 2017

This paper addresses the potential of integrating Parabolic Trough Collectors (PTC) with a double-effect absorption chiller for the purpose of space cooling in residential buildings. The proposed model was designed such to provide a continuous cooling while in the absence of sun, the bio-mass heater was used as an auxiliary heating source. In this study, the thermal performance was investigated and a feasibility study was conducted in order to assess the system’s economic and environmental impacts. The obtained model was implemented on a case study represented by a four-floored residential building based in Dubai with a net cooling load requirement of 366 kW. The obtained results from the numerical simulation were analyzed to identify the optimum configuration in terms of feasibility and potential savings. It was found that a hybrid system with 40% solar contribution is the optimum solution compared to other alternatives. The proposed system achieved Annual Energy Consumption savings (AEC) of about 556061 kWh and a reduction by 69% in the annual operating costs. Moreover; the system reduced the Carbon-dioxide emissions by 344 tons/year. The payback period of the proposed system was found to be 2.42 years only.
Electro-Mechanical Impedance Measurements in an Imitated Low Earth Orbit Radiation Environment
Authors: Anderson Mary L. , Daniel Joshua D. , Zagrai Andrei N. , Westpfahl David J.
Published: February 2017

Piezoelectric sensors are used in many structural health monitoring (SHM) methods to interrogate the condition of the structure to which the sensors are affixed or imbedded. Among SHM methods utilizing thin wafer piezoelectric sensors (PWAS), electro-mechanical impedance monitoring is seen as a promising approach to assess structural condition in the vicinity of a sensor. Using the converse and direct piezoelectric effects, this health monitoring method utilizes mechanical actuation and electric voltage to determine the impedance signature of the structure. If there is damage to the structure, there will be a change in the impedance signature. It is important to discern between actual damage and environmental effects on the piezoelectric ceramic sensors and the structure. If structural health monitoring is to be implemented in space structures on orbit, it is imperative to determine the effects of the extreme space environment on piezoelectric sensors and the structures to which they are affixed. The space environment comprises extreme temperatures, vacuum, atomic oxygen, microgravity, micro-meteoroids and debris, and significant amounts of radiation. Radiation in space comes from three sources: solar events, background cosmic radiation, and trapped particles in the Van Allen Belts. Radiation exposure to structures on orbit will vary significantly depending on the duration of the flight and the altitude and inclination of the orbit. In this contribution, the effect of gamma radiation on piezoelectric ceramic sensors and space grade aluminum is investigated for equivalent gamma radiation exposure to 3-months, six-months, and 1-year on Low Earth Orbit (LEO).

An experiment was conducted at White Sands Missile Range, Gamma Radiation Facility using Cobalt-60 as the source of radiation. A free PWAS and a PWAS bonded to a small aluminum beam were exposed to increasing levels of gamma radiation. Impedance data were collected for both sensors after each radiation exposure. The total radiation absorbed dose was 200 kRad (Si) by the end of the experiment. The results show that piezoelectric ceramic material is affected by gamma radiation. Over the course of increasing exposure levels to Cobalt-60, the impedance frequency of the free sensor increased with each absorbed dose. The impedance measurements of the sensor bonded to the aluminum beam reflects structural and sensor’s impedance. The data for this sensor show an increase in impedance amplitude with each level of absorbed dose. The mechanism at work in these impedance changes is suggested and future experimental work is identified. A survey of previous results of radiation exposure of piezoelectric ceramic sensors and aluminum alloys is presented and are compared to previous studies.
Effect of Truck-Trailer Gap on Boat-Tail Performance of a Heavy Vehicle: A Numerical Approach
Authors: Tashmatova Chinara , Nazarinia Mehdi
Published: February 2017

This paper presents results obtained from a numerical investigation of various configurations of gap clearances for a truck model equipped with boat-tails. ANSYS FLUENT V14.5 was used to examine the flow around the vehicle and to obtain the drag coefficient reductions at a range of yaw angles of 0° to 20°. The vehicle had a streamlined front end and was scaled to 12% of a full size truck with no tractor-trailer gap modeled. The computational domain was calculated at Reynolds number of approximately 8 × 105. The numerical data obtained from the investigation yielded a best configuration of the boat-tail which produced maximum of 10% drag reduction at 0° yaw angle when compared to the baseline model. The optimum boat-tail angles are also determined to be in the range of 15° to 20° for both 0° and 10° yaw angles.
Nonlinear Reduced-Order Models for Aerodynamic Lift of Oscillating Airfoils
Authors: Khalid Muhammad Saif Ullah , Akhtar Imran
Published: February 2017

For the present study, setting Strouhal Number as the control parameter, we perform numerical simulations for the flow over oscillating NACA-0012 airfoil at Reynolds Number 103. Temporal profiles of the unsteady lift, and their respective spectra clearly indicate the solution to be a period-1 attractor for low Strouhal numbers. This study reveals that aerodynamic forces produced by the oscillating airfoils are independent of the initial kinematic conditions that proves existence of the limit cycle. Frequencies present in the oscillating lift force are composed of the fundamental harmonics, and its odd harmonics. Using these numerical simulations, we observe the shedding frequencies nearly equal to the excitation frequencies in all the cases. Hence, considering it as a primary resonance case, we model the unsteady lift force through a modified van der Pol oscillator. Using the method of multiple scales and spectral analysis of the steady-state CFD solutions, we estimate the frequencies and the damping terms in the reduced-order model. We prove the applicability of this model to all the planar motions of airfoil; heaving, pitching and flapping. With the increasing Strouhal number, the nonlinear damping terms for all types of motion approach similar magnitudes. Another important aspect in one of the currently-proposed model is capturing the time-averaged value of the aero-dynamic lift force.
Role of Particle Size to Channel Thickness Ratio on Performance of Nanofluids in Micro-Channels
Authors: Smith Sonya T. , Mosleh Mohsen , Shirvani Khosro A.
Published: February 2017

Experimental and numerical investigations were conducted to explore the viability of single-phase nanofluids for microchannel cooling. The experiments were conducted with water/ethylene glycol-based nanofluids to investigate the thermal conductivity enhancement. In the numerical analysis, micro-channels ranged in width from 40 μm to 90 μm with the fixed channel height were considered.

Thermal conductivity enhancements of nearly 14% at particle concentration of 0.1% by weight was observed in the experiments. Numerical predictions suggest that design variables (particle size and channel aspect ratio) and thermo-physical properties of the nanofluid have a significant effect on the thermal performance of micro-channel heat sinks. It was shown that at fixed Reynold number, reduction of channel width reduces the hydraulic pressure loss and the heat transfer coefficient, and utilizing nanofluids increases these parameters.
Multi Parameter Estimation in an Induced Draft Cooling Tower Using Genetic Algorithm
Authors: Singh Kuljeet , Das Ranjan
Published: February 2017

Considering the need of performance control in engineering systems, this work presents a methodology to predict the controlling variables to control the performance of an induced draft cooling tower. At first, the set of experiments have been conducted with the variation of mass flow rate of water and air under identical ambient conditions. The experimental data for temperatures at different locations has been collected using data acquisition system (by National Instruments) in conjunction with LABVIEW™. Thereafter, relevant 3rd order empirical correlations of range and approach have been developed using the experimental readings. Depending upon the pertinent requirement, it is required to operate the cooling tower at certain combination of mass flow rate of water and air to fulfill the required output. Based upon the user requirement, the correlations are further employed to construct relevant constraint functions using the least square technique. In order to meet a desired performance (say either a given range, approach or optimum operation) of the cooling tower, the retrieval of design variables (water and air flow rates) has been carried out using an inverse optimization methodology to ensure minimum power consumption. The Genetic Algorithm (GA) is used as an optimization algorithm that minimizes the objective function along with given constraint. The optimization algorithm simultaneously predicts the possible combination of mass flow rate of water and air (control or design variables) in order to meet the given requirement. Further, the methodology avoids multiple combinations of controlling variables that satisfies a particular requirement. Therefore, the user can select an optimum combination that results in minimum power consumption. Moreover, if the cost involved in the cooling tower is considered, it is directly proportional to the range (difference between water inlet and outlet temperatures), whereas, at the same time, the cost is inversely proportional to the approach (difference between outlet water temperature and inlet air wet bulb temperature). In many applications like HVAC (heating, ventilating and air conditioning), chillers, cold storage plants and many more, lower cooling water temperature (at system inlet) is preferable in order to enhance the system efficiency. On the other hand, lower water outlet temperature from the cooling tower for a given water inlet temperature (at tower inlet) means either high range of the tower or low approach, consequently increasing the tower operating cost. Therefore, in order to save the cost involved in cooling tower operation, a compromise between the range and the approach has to be maintained to achieve an optimum performance. So, this method can be also used to predict the optimum operating parameters ensuring the possible optimum performance from the cooling tower under a given set of operating conditions.
Transient Characterization of Data Center Racks
Authors: Fulpagare Yogesh , Joshi Yogendra , Bhargav Atul
Published: February 2017

The increased computational and storage demand has increased the heat dissipation of servers in data centers. The flow inside the data center is highly dynamic due to various parameters such as server workload, server fan speed, tile porosity, Computer Room Air Conditioning (CRAC) air flowrates, CRAC supply & return air temperatures and data center cold & hot aisle arrangements. Data center facility level transient CFD analysis was reported in recent literature which needs weeks to accomplish the computation. Hence, such facility level simulations are difficult to achieve with good accuracy. The main contributions of this paper are transient experiments, transient CFD model & transient effects on thermal and flow field due to variation in server load of server rack inside the raised floor plenum data center.

In the current study we have developed a transient CFD model of three racks in a raised floor plenum data center room with cold and hot aisle containment based on experiments. The middle 42U (1U = 4.45 cm) rack houses four server simulators each having height of 10U. The flow tiles supply the cold air as inlet with average velocity of 1.53 m/s at 17°C. All the rack servers were modelled with 75% porosity and estimated thermal mass Each server simulator was assigned a total heat dissipation of 2500 W, with a total heat load of 10 kW per rack. The effect on rack inlet and outlet air temperatures were monitored by providing server heat loads as step & ramp inputs to the middle simulator rack. The results show that the rack level transient effects are significant and cannot be ignored.
Structural Stress Correction Methods for Linear Elastic Finite Element Analysis of Spot Welded Joints
Authors: Kang Hong-Tae , Wu Xiao
Published: February 2017

Structural stress concepts are widely used in fatigue life prediction of spot welds and seam welds in vehicle structures. For fatigue life prediction of welded joints based on the structural stress methods, it is necessary to obtain applied force ranges versus fatigue life of the welded specimens. Then, the force ranges versus fatigue life information is converted to structural stress ranges versus fatigue life (S-N) of the joints. The structural stress ranges versus the fatigue life curve of the welded specimens becomes the material fatigue property of the welded joints to predict fatigue life of joints in vehicle structures. While converting the applied load ranges to the structural stress ranges, linear elastic finite element analysis (FEA) is used. Therefore, the applied load ranges are considered as the responses of linear elastic deformation even though the load ranges consist of the linear elastic deformation and plastic deformation. As results the structural stress ranges of the welded joints are reduced in S-N curve. This study introduces simple techniques for spot welded joints to include the plastic deformation effect on the structural stress calculation without performing elastic-plastic finite element analysis. Fatigue test results of spot welded joints for lap-shear and coach peel specimens of advanced high strength steels (AHSS) and mild steels were used. The corrected structural stress methods showed better correlation with the test results.
Synthesis and Characterization of Alginate-Based Hydrogel Microbeads for Magnesium Release
Authors: Khanal Shalil , Adhikari Udhab , Rijal Nava P. , Pai Devdas , Sankar Jagannathan , Bhattarai Narayan
Published: February 2017

Magnesium injection is a suitable approach for replenishment of its ions (Mg++) during neural or tissue injury and stroke to avoids risks associated with abnormally low level of Mg++ in blood. In this study, alginate encapsulated magnesium sulfate microbeads were fabricated by the electrospraying technique for Mg++ delivery. Microbeads were evaluated for particle size and surface morphology using inverted optical microscopy and scanning electron microscopy (SEM) respectively. Average particle size of 200–500 μm for hydrated and 50–200 μm for dry beads were observed. An in vitro release study of Mg++ was performed; revealing a cumulative release of ∼50% within first 24 h. This strategy can potentially be useful for the targeted local delivery of magnesium at required concentrations and subsequently enhance the therapeutic efficacy of magnesium in treating tissue injury or stroke.
Boiling Heat Transfer From an Oscillated Water Column Through a Porous Domain: A Simplified Thermodynamic Analysis
Authors: Sayar Ersin
Published: February 2017

Heat transfer in an oscillating water column in the transition regime of pool boiling to bubbly flow is investigated experimentally and theoretically. Forced oscillations are applied to water via a frequency controlled dc motor and a piston-cylinder device. Heat transfer is from the electrically heated inner surface to the reciprocating flow. The heat transfer in the oscillating fluid column is altered by using stainless steel scrap metal layers (made off open-cell discrete cells) which produces a porous medium within the system. The effective heat transfer mechanism is enhanced and it is due to the hydrodynamic mixing of the boundary layer and the core flow. In oscillating flow, the hydrodynamic lag between the core flow and the boundary layer flow is somehow significant. At low actuation frequencies and at low heat fluxes, heat transfer is restricted in the single phase flows. The transition regime of pool boiling to bubbly flow is proposed to be a remedy to the stated limitation. The contribution by the pool boiling on heat transfer appears to be the dominant mechanism for the selected low oscillation amplitudes and frequencies. Accordingly the regime is a transition from pool boiling to bubbly flow. Nucleate-bubbly flow boiling in oscillating flow is also investigated using a simplified thermodynamic analysis. According to the experimental results, bubbles induce highly efficient heat transfer mechanisms. Experimental study proved that the heater surface temperature is the dominant parameter affecting heat transfer. At greater actuation frequencies saturated nucleate pool boiling ceases to exist. Actuation frequency becomes important in that circumstances. The present investigation has possible applications in moderate sized wicked heat pipes, boilers, compact heat exchangers and steam generators.
The Recreation and Evaluation of a Human Hand Using Low-Cost Reverse Engineering and 3D Printing Systems
Authors: Jacobsen C. , Ashe E. , Noorani R.
Published: February 2017

The primary goal of this research was to evaluate the effectiveness of a low-cost reverse engineering system to recreate a physical, three-dimensional model of a human hand. In order to achieve the goal of this research, three key objectives were fulfilled: (1) the first objective was to recreate the physical model of the human hand using a low-cost experimental setup (<$5000), (2) the second objective was to assess the ability of the reverse engineered hand to perform common tasks of everyday life, and (3) the third objective was to investigate the potential biomedical applications of the reverse engineered human hand. A chosen test subject had his or her hand molded and cast into a plaster three-dimensional model that could be held steady and scanned very precisely by a NextEngine Desktop 3D Scanner. Other methods could have been employed to achieve the scanned model, but given the experimental setup and timeline a casted model was assumed to be the most appropriate method to achieve the best results. The plaster casting of the subject’s hand was scanned several times using different orientations of the model relative to the stationary 3D scanner. From these scans, a computer CAD model of the human hand was generated, modified, and 3D printed using a Makerbot Replicator 2. The printed model was evaluated by its ability to perform common every-day tasks such as picking up a cup/bottle, holding a pen/pencil, or opening/closing around an object. Several iterations of the printed human hand were evaluated in order to determine the best design for the fingers’ joints and cable-driven motion system. The first iteration of the printed hand featured a snap-in joint system. This joint design suffered from requiring a large number of individual pieces and poor tolerances of the Makerbot printer. The second iteration featured a press fit style joint system. This system was hindered by tolerances similar to the first iteration as well as plastic deformation of the printed material due to inadequate elasticity. The third and final iteration of the joint system featured a single printed assembly for which the entire prosthetic could be printed at one time. It was expected that the hand would be able to translate the rotational movement of an individual’s wrist to tension the cables of the motion system thereby closing the fingers into a first. This movement will allow the user to close the prosthetic hand around everyday objects and pick them up with relative ease. Although the possibilities of reverse engineering and 3D printing systems have greatly expanded as a result of greater affordability and increased accuracy, their applications in the biomedical field have yet to be fully explored.
Design of Experiments to Support Automated Assembly Planning
Authors: Liu Yue , Huang Weifeng , Rafibakhsh Nima , Campbell Matthew I. , Hoyle Christopher
Published: February 2017

Assembly time estimation is a key factor in evaluating the performance of the assembly process. The overall goal of this study is to develop an efficient assembly time estimation method by generating the prediction model from an experimental design. This paper proposes a way to divide an assembly operation into four actions which consist of a) part movement, b) part installation, c) secure operations, and d) subassembly rotations. The focus of this paper is to design a time estimation model for the secure operation. To model secure times, a design of experiments is applied to collect experimental data based on the physical assembly experiments performed on products that are representative of common assembly processes. The Box-Behnken design (BBD) is an experiment design to support response surface methodology to interpret and estimate a prediction model for the securing operations. The goal is to use a quadratic model, which contains squared terms and variable interactions, to study the effects of different engineering parameters of securing time. The experiment is focused on individual-operator assembly operations. Various participants perform the experiment on representative product types, including a chainsaw, a lawn mower engine, and an airplane seat. In order to optimize the assembly time with different influence factors, mathematical models were estimated by applying the stepwise regression method in MATLAB. The second-order equations representing the securing time are expressed as functions with six input parameters. The models are trained by using all combinations of required data by the BBD method and predict the hold back data within a 95% confidence interval. Overall, the results indicate that the predicted value found was in good agreement with experimental data, with an Adjusted R-Squared value of 0.769 for estimated securing time. This study also shows that the BBD could be efficiently applied for the assembly time modeling, and provides an economical way to build an assembly time model with a minimum numbers of experiments.