bluuebunny/crossref_metadata_2025 huggingface dataset:
Degradation of Hydrophobic Surface Coatings Under Water Exposure
Authors: Trapuzzano Matthew A. , Guldiken Rasim , Tejada-Martínez Andrés , Crane Nathan B.
Published: January 2019

Many important processes depend on the wetting of liquids on surfaces. Wetting is commonly controlled through material selection, coatings, and/or surface texture, however these means are sensitive to environmental conditions. Some “hydrophobic” fluoropolymer coatings are sensitive to extended water exposure as evidenced by declining contact angles and increasing contact angle hysteresis. Understanding degradation of these coatings is critical to processes that employ them. To accomplish this, contact angle measurements were taken before, during, and after slides coated with FluoroSyl 3750 or Cytop were submerged in water, or vibrated while covered in water. Both methods demonstrated similar changes in advancing contact angle though vibration increased degradation rates significantly. However, it does not simply accelerate the process as different trends are apparent in receding contact angles. The FluoroSyl 3750 showed no clear degradation under either condition. Surface profilometry did not detect any surface morphology differences that might cause contact angle change.
Validation of a Finite Element Model of the Mechanical Performance of Surgical Knots of Varying Topology
Authors: Qwam Alden Arz Y. , Geeslin Andrew G. , Gustafson Peter A.
Published: January 2019

Background: Knot tying is considered a basic surgical skill, however, there is no consensus on the best technique. Suture breakage and slippage are failure modes during surgical repair and are related to stress concentrations which cannot be easily established with physical testing. Few computational models exist that describe the effect of knot topology on the failure mechanism. The purpose of this study was to implement the finite element method to analyze the mechanical behavior of surgical sutures according to number of throws and to validate the model against experiments.

Methods: Experiments and models of monofilament and multifilament sutures were conducted. Multiple throw knots were tested to failure in a laboratory setting and with corresponding finite element models. Gross loads were compared when the knot reached a localized material yield stress in the model or when failure occurred in laboratory tests that have the same suture topology.

Results: The results of laboratory tests and corresponding finite element models of single throw knots were compared and found to be well correlated and consistent with existing literature in strength prediction and failure location. Moreover, single throw knots have reduced failure strengths relative to non-knotted suture approximately by 120 N for both monofilament and multifilament sutures, respectively.

Clinical Relevance: This paper describes a model which can describe the initial failure process leading to knot failure. In addition, the model can evaluate the effect of knot topology on the mechanics of surgical suture. Numerically, no assessment has been completed of knot security (i.e., how likely the knot is to untie), therefore, clinical recommendations are premature. In the future, the results may provide a framework for choosing the suture and knot types for soft tissue repairs.
A Stochastic Finite Element Method for Simulating Trabecular Bone
Authors: Alrafeek Saif , Jastifer James R. , Gustafson Peter A.
Published: January 2019

Background: Although trabecular bone is highly porous heterogeneous composite, most studies use homogenized continuum finite element (FE) approaches to model trabecular bone. Such models neglect the porous nature of the tissue. When microstructural models are desired, the use of continuum elements may require costly CT/MRI imaging and detailed meshing. The purpose of this study is to demonstrate an approach that simulates trabecular bone with less dependency on medical images while capturing of porosity.

Methods: A stochastic structural FE model was created representing the trabecular micro-architecture as beam elements. Beam orientation, length and connectivity were stochastically determined by random placement of nodes and meshing the resulting Voronoi diagram. Boundary conditions were applied on the structure to attain normalized axial and shear strain. Also, apparent mechanical properties, apparent densities and anisotropy ratio’s were calculated from the model output.

Results: The number of generated nodes within the model and cross sectional area of the random beams were observed as parameters that affect model outcome. Trabecular bone apparent density was found highly correlated to beams cross sectional area rather than the generated number of nodes. Similarly, Young’s moduli and shear moduli were dependent on beams cross sectional area. For example, a (0.015 mm2) increase in beam cross section area can produce (175 MPa, 30 MPa and 0.55 g/cm3) increases in Young’s moduli, shear moduli and apparent density, respectively.

Clinical Relevance: The proposed finite element technique provides a stochastically accurate structural representation of trabecular tissue and its reaction to applied loads. It incorporates several advantages of high fidelity methods but at lower cost and requiring only clinical imaging. Therefore, the approach may be useful for patient specific musculo-skeletal biomechanical models (e.g. osteoporosis, osteoarthritis, joint replacement and implants interface).
Escalator Risk and Assessment of Safety Review
Authors: Bress Thomas , Kennedy Eugenia , Kupkovits Robert
Published: January 2019

Escalators are common mechanical vertical transportation systems that move an estimated 245 million people daily in the U.S. on the more than 33,000 escalators [1]. It has been estimated that about 10,000 escalator-related injuries per year result in an emergency department treatment in the U.S. [2]. A study of escalator injuries published in 2001 concluded that injuries were primarily the result of falls or entrapment at the bottom or top of an escalator or between a moving stair and escalator sidewall [3]. Regarding sidewall entrapment, the 2000 edition of the ASME A17.1, “Safety Code for Elevators and Escalators,” introduced periodic tests for both new and existing escalators to evaluate the potential for sidewall entrapment [4]. The development history of the step/skirt performance index is presented and current requirements in the ASME A17.1 and A17.2, “Guide for Inspection of Elevators, Escalators and Moving Walkways,” codes regarding the index are reviewed. Injury data from the U.S. Consumer Product Safety Commission (CPSC) for escalator riders are analyzed from the timeframe of 1998 to 2017 to seek trends in escalator entrapments during the time period between the introduction of the index and the present.
Pedestrian Collision Responses Using Legform Impactor Subsystem and Full-Sized Pedestrian Model on Different Workbenches
Authors: Mohammed Obaidur Rahman , Memon Shabbir , Lankarani Hamid M.
Published: January 2019

Car-pedestrian collision fatalities have been reported for a significant number of roadside accidents around the world. In order to reduce the lower extremity injuries in car-pedestrian collisions, it is important to determine the impact forces on the pedestrian and conditions that the car frontal side impacts on the lower extremities of the pedestrian. The Working Group 17 (WG17) of the European Enhanced Vehicle-safety Committee (EEVC) has developed a legform subsystem impactor and procedure for assessing pedestrian collisions and potential injuries. This research describes a methodology for the evaluation of the legform impactor kinematics after a collision utilizing finite element (FE) models of the legform and cars and comparing the simulation results with the ones from a multi-body legform model as well as a 50th percentile male human pedestrian model responses.

Two approaches are carried out in the process. First, the collision strike simulations with the FE model using an FE lower legform is considered and validated against the EVVC/WG17 regulation criteria. Secondly, the collision strike simulations with a multi-body legform and an ellipsoidal multi-body car model are conducted to compare the responses from the FE model and the multi-body model. The results from the impact simulations of FE legform and the multi-body legform are also compared with the ones from a full-size pedestrian model at constant speeds. All the models and simulation in this are using the LS-DYNA nonlinear FE code, while the multibody legform, car, and full-sized pedestrian models are developed and evaluated in MADYMO.

The results from this study demonstrate the differences between the subsystem legform and the full-size pedestrian responses as well as suitability of various FE and multibody models related to pedestrian impact responses. Different workbenches comparisons with finite model and ellipsoidal models gives more better correlation to this research.
Visualisation and Detection of Road Traffic Events Using Complex Event Processing
Authors: Figueiras Paulo , Antunes Hugo , Guerreiro Guilherme , Costa Ruben , Jardim-Gonçalves Ricardo
Published: January 2019

In the recent decades, we have witnessed an increase in the number of vehicles using the road infrastructure, resulting in an increased overload of the road network. To mitigate such problems, caused by the increasing number of vehicles and increasing the efficiency and safety of transport systems has been integrated applications of advanced technology, denominated Intelligent Transport Systems (ITS). However, one problem still unsolved in current road networks is the automatic identification of road events such as accidents or traffic jams, being inhibitor to efficient road management. In order to mitigate this problematic, this paper proposes the development of a technological platform able to detect anomalies (abnormal traffic events) to typical road network status and categorize such anomalies. The proposed work, adopts a complex event processing (CEP) engine able to monitor streams of events and detect specified patterns of events in real time. Data is collectively collected and analysed in real-time from loop sensors deployed in Slovenian highways and national roads, providing traffic flows. This prototype will work with a large number of data, being used to process all data, complex event processing tools. All the data used to validate the present study is based on the Slovenian road network. This work has been carried out in the context of the OPTIMUM Project, funded by the H2020 European Research Framework Program.
Array Jet Impingement Onto High Porosity Thin Metal Foams at Zero Jet-to-Foam Spacing
Authors: Singh Prashant , Zhang Mingyang , Pandit Jaideep , Mahajan Roop L.
Published: January 2019

Metal foams enhance heat transfer rates by providing significant increase in wetted surface area and by thermal dispersion caused by flow mixing induced by the tortuous flow paths. Further, jet impingement is also an effective method of enhancing local convective heat transfer rates. In the present study, we have carried out an experimental investigation to study the combined effect of the two thermal performance-enhancement mechanisms. To this end, we conducted a set of experiments to determine convective heat transfer rates by impinging an array of jets onto thin metal foams attached on a uniformly heated smooth aluminum plate simulating a high heat-dissipating chip. The metal foams used were high porosity aluminum foams (ε∼0.94–0.96) with pore densities of 5 ppi, 10 ppi and 20 ppi (ppi: pores per inch) with thicknesses of 19 mm, 12.7 mm and 6.35 mm, respectively. With the jet-to-foam distance (z/d) set to zero, we conducted experiments with values of jet-to-jet spacing (x/d = y/d) of 2, 3 and 5. The jet plate featured an array of 5 × 5 cylindrical jet-issuing nozzles. The normalized jet-to-jet distance was varied by changing the jet diameter and keeping the jet center-to-center distance constant. Steady state heat transfer and pressure drop experiments were carried out for Reynolds number (based on jet diameter) ranging from 2500 to 10000. We have found that array impingement on thin foams leads to a significant enhancement in heat transfer compared to normal impingement over smooth surfaces. The gain in heat transfer was greatest for the 20 ppi foam (∼2.3 to 2.8 times that for the plain surface smooth target). However, this enhancement came at a significant increase of about 2.85 times in the plenum static pressure. With the pressure drop penalty taken into consideration, the x/d = 3 jet plate for the 20 ppi foam and x/d = 2 jet plate for the 10 ppi foam were found to be the most efficient cooling designs amongst the 18 cooling designs investigated in the present study.
Systematic Study of the Effect of Non-Uniform Seal Stiffness on the Contact Stress in Flat-Faced Soft-Seated Spring Operated Pressure Relief Valves
Authors: Schimanowski Alex , Seibel Arthur , Schlattmann Josef
Published: January 2019

Spring operated pressure relief valves (SOPRVs) are essential components of technical systems. As parts of safety systems, they protect people and the environment from technological hazards. Their ability to open at a predefined pressure is considered the most important feature. The reliability of this function depends on numerous operational and design factors.

In this paper, we examine the effects of design measures on the mechanical loads in seat seals of SOPRVs. In particular, we evaluate the applicability of the principle of non-uniform system stiffness in order to systematically control the mechanical loads in seat seals for an exemplary case of a flat faced soft seated SOPRV. We systematically vary design parameters and accurately estimate the contact stresses as well as the set pressure by performing non-linear finite element analyses. We focus on the quasi-static case of a closed seal, since dynamic effects of the opening and closing processes are not within the scope of this work. In our contribution, we show that the application of these design measures can significantly influence both the initial contact stresses and the set pressure at a constant spring force. In particular, the effects of the taper angle are analyzed and discussed.
Methods of Mass-Flow Characterization of Water-Glycol Mixtures Through Micro/Nano-Channels
Authors: Lee John , Huang Po-Hao
Published: January 2019

The design of a novel micro-propulsion system for small satellites of the nano-satellites class (1–10kg) that is low-cost, non-toxic, non-flammable, and no-pressurized at launch conditions is currently being developed at the University of Arkansas. The goal of the present micro-propulsion system is to achieve milli-Newton thrust levels with specific impulses on the order of 100s. The proposed propellant is the water-propylene glycol. However, little data is available for its fluid and thermal characteristics at the gaseous state, nor the evolution of similar mixtures through micro/nano-channels. This paper will present experimental methods of measuring the mass flow rate of the water-glycol mixtures through micro/nano-channels. A MEMS fluidic chamber fabricated with a nano-channel is used to quantify the mass flow through optical tracking of liquid interfaces confined in the chamber. The dimensions of the channels are designed with the purpose to act as a passive throttling valve that prevent liquid-phase fluids from entering into the nozzle in order to achieve a simple water-based cold-gas propulsion system.
Enhanced Heat Transfer in Radial Heat Sinks for LED Lamps
Authors: Cano-Banda Fernando , Gallardo-Gutierrez Ana , Garcia-Gonzalez Jesus , Hernandez-Guerrero Abel , Luviano-Ortiz Luis
Published: January 2019

A radial design of a passive heat sink for cooling LED illumination devices is analyzed numerically in order to identify the geometric shape that promotes better heat dissipation rates. Natural convection with the surrounding is considered during the operation of the heat sink. Due to the fact that natural convection is the main mechanism of heat transfer, the shape of the heat sink has a high influence in the heat dissipated. An analysis of the influence of different parameters of a heat sink is conducted in the presented study.

The radial heat sink under analysis consists in a flat disc with rectangular fins on it, and the fins are distributed with a radial longitudinal orientation in a circular row arrangement. The number of rows can vary but there is a constant relation of two times the number of fins between the number of fins in an inner row and the next outer row. In order to find a correct configuration to improve the dissipation of heat, parameters like the number of fins, the length of the fins and the separation between fins are studied.

The average Nusselt number and thermal resistance for each geometric configuration are compared. The output analysis provides the best shape for a maximum heat transfer.
Large-Eddy Simulation of Offshore Wind Farms for Power Prediction
Authors: Sandusky Micah , DeLeon Rey , Senocak Inanc
Published: January 2019

Offshore wind turbines are mega structures that span a critical section of the lowest part of atmospheric boundary layer while experiencing significant wind shear. A detailed knowledge of the wind field through a wind farm as part of the atmospheric boundary layer is essential to design efficient farm layouts and estimate power production for grid integration. To address these needs, we present a micro-scale wind prediction model based on a large-eddy simulation paradigm. We consider actuator disk models with and without rotation to simulate the influence of turbines on the wind field and apply our computational capability to the well-known Horns Rev offshore wind farm in Denmark to estimate power production. Instead of using manufacturers power curve to estimate power production, we propose an alternative approach based on the control volume analysis of kinetic energy conservation around turbines.
Development and Analysis of Robotic Arms for Humanoid Melo
Authors: Shen He , Rojas Salvador , Molina Eduardo , Moxo Galicia Francisco , Li Ni
Published: January 2019

A robotic arm is one of the most sophisticated components of a humanoid, due to its complexity in multi-degree-of-freedom actuation and sensing, size and weight constraints, and requirement for object manipulation. This paper talks about the design, development, and verification of a low-cost, light-weight robotic manipulator that can achieve anthropomorphic movements. The 5 degree-of-freedom robotic arm has a fully extended length of 31 – inches and weight of 7 - pounds. The joints of the arm were fabricated using mainly 3D printed parts using Polylactic Acid and Nylon and linked with carbon fiber tubing. The arm is actuated by 2 servo motors at the distal joint and 3 brushless DC motors at the proximal joints. All joints of the arm perform at zero backlash through harmonic gear boxes, which are also assembled mainly from 3D printed parts. The robotic arm has demonstrated a comparable performance to similar robotic arms on the market with significantly reduced cost.
Two-Wavelength Thermoreflectance and its Application in Temperature Measurement of Micro-Electronic Devices
Authors: Zhang Hongjie , Wen Sy-Bor
Published: January 2019

A two-wavelength thermoreflectance (2WTR) imaging technique is developed to conduct steady-state temperature measurement of miniature electronic devices, such as micro-scale gold resistors. Compared with traditional single wavelength thermoreflectance (TR) imaging requiring comparison of TR signals from a target under heated and unheated conditions, 2WTR method obtains temperature information from heated target under operation directly. Therefore, 2WTR is not affected by movement of a heated target due to thermal expansion. Note that thermal expansion of targets between heated and unheated conditions is a main constraint of current TR imaging of miniature targets. In addition to the low sensitivity to the target movement, the new 2WTR can provide even higher temperature resolution than single wavelength TR by appropriately selecting the adopted two wavelength to have different signs of TR coefficients. With this new TR imaging technique, we successfully measure temperature distribution of a microscale gold resistor under steady-state operation, which are challenging to be obtained by traditional single wavelength TR method.
Stereoscopic Particle Shadow Velocimetry
Authors: Harris Jeff R. , McPhail Michael , Truong Christine , Fontaine Arnold
Published: January 2019

Stereoscopic particle image velocimetry (SPIV) is a variant of particle image velocimetry (PIV) that allows for the measurement of three components of velocity along a plane in a flow field. In PIV, particles in the flow field are tracked by reflecting laser light from tracer particles into two angled cameras, allowing for the velocity field to be determined. Particle shadow velocimetry (PSV) is an inherently less expensive velocity measurement method since the method images shadows cast by particles from an LED backlight instead of scattered light from a laser. Previous studies have shown that PSV is an adequate substitute for PIV for many two-dimensional, two-component velocimetry measurements. In this work, the viability of the two-dimensional, three-component stereoscopic particle shadow velocimetry (SPSV) is demonstrated by using SPSV to examine a simple jet flow. Results obtained using SPIV are also used to provide benchmark comparison for SPSV measurements. Results show that in-plane and out-of-plane velocities measured using SPSV are comparable to those measured using SPIV.
A Comparison of the Effects of Wire Electrical Discharge Machining Parameters on the Processing of Traditionally Manufactured and Additively Manufactured 316L Stainless Steel Specimens
Authors: Bicknell Gregory , Manogharan Guha
Published: January 2019

Wire electric discharge machining (EDM) is a non-traditional machining method that has the ability to machine hard, conductive materials, with no force and high precision. This technology is used in industries, like the aerospace industry, to create precision parts used in high stress applications. Wire EDM is also commonly used in additive manufacturing (AM) applications to remove printed parts from the base-plates onto which they are printed. Numerous studies show the effects of EDM parameters, like pulse-on time, pulse-off time, and cutting voltage, on the processing of traditionally fabricated metal parts. However, very few studies identify how the parameters of wire EDM affect the processing of AM parts. This paper studies the effect of wire EDM pulse-on time, pulse-off time, and cutting voltage on the machining time, surface roughness, and hardness of additively manufactured 316L stainless steel cylinders. The effects of these wire EDM parameters are then tested on the machining time, surface roughness, and hardness of wrought 316L stainless steel cylinders. It was found that machining time of AM samples was statistically significantly lower than wrought samples and also had better surface finish and lower surface hardness.
Operational Modal Analysis and Damage Identification of Structures Undergoing Random Vibration Using a Continuously Scanning Laser Doppler Vibrometer System
Authors: Chen Da-Ming , Xu Y. F. , Zhu W. D.
Published: January 2019

A continuously scanning laser Doppler vibrometer (CSLDV) system is capable of efficient and spatially dense vibration measurements by sweeping its laser spot along a scan path assigned on a structure. This paper proposes a new operational modal analysis (OMA) method based on a data processing method for CSLDV measurements of a structure, called the lifting method, under white-noise excitation and applies a baseline-free method to identify structural damage using estimated mode shapes from the OMA method. The lifting method enables transformation of raw CSLDV measurements into measurements at individual virtual measurement points, as if the latter were made by use of an ordinary scanning laser Doppler vibrometer in a step-wise manner. It is shown that a correlation function with non-negative time delays between lifted CSLDV measurements of two virtual measurement points on a structure under white-noise excitation and its power spectrum contain modal parameters of the structure, i.e., natural frequencies, modal damping ratios and mode shapes. The modal parameters can be estimated by using a standard OMA algorithm. A major advantage of the proposed OMA method is that curvature mode shapes associated with mode shapes estimated by the method can reflect local anomaly caused by small-sized structural damage, while those estimated by other existing OMA methods that use CSLDV measurements cannot. Numerical and experimental investigations are conducted to study the OMA method and baseline-free structural damage identification method. In the experimental investigation, effects of the scan frequency of a CSLDV system on the two methods were studied. It is shown in both the numerical and experimental investigations that modal parameters can be accurately estimated by the OMA method and structural damage can be successfully identified in neighborhoods with consistently high values of curvature damage indices.
Experimental and Numerical Study on Melting of Solar Salt in a Finned Metallic Container
Authors: Costa Sol-Carolina , Mahkamov Khamid , Kenisarin Murat , Ismail Mohammad , Halimic Elvedin , Mullen David , Lynn Kevin , Werner Thomas
Published: January 2019

This work presents an experimental and numerical study of the melting and solidification processes of Solar Salt in a finned square metallic container with a constant heat flux source inside for the latent heat thermal energy storage (LHTES) for medium temperature applications. During the experiments the temperature of the PCM in several locations were recorded and used to validate results of numerical simulations that were conducted deploying the enthalpy method in Ansys FLUENT. Two prototypes of the container were tested, one with fins made of steel and the other with fins and casing made of aluminum, to compare the charging and discharging time in both configurations. The modelling results are in good agreement with experimental data for the charging of aluminum container and slightly higher deviation are found in the other cases. The validated simulation model can be used as a design tool to achieve the optimal geometry of the full scale LHTES for the required charging and discharging periods.
Individual Phonon Branch Contribution to Thermal Conductivity of 3C-SiC Using the Monte Carlo Method
Authors: Barnes Arden N. , Roberts Nick
Published: January 2019

Silicon carbide (SiC) is a useful semiconductor material due to its high thermal conductivity (λ), low reactivity, and high strength. These properties also make it an ideal nuclear fuel cladding material. Because heat transfer in SiC is dominated by phonons, there is value in understanding how different phonon branches contribute to λ. To accomplish this, it is useful to run simulations which employ fewer phonon branches than normally exist. In materials where phonons dominate heat transport, such as SiC, the Monte Carlo method as applied to phonon transport is suitable for estimating λ. This work uses the Monte Carlo method to estimate λ of 3C-SiC using four phonon branches, namely, transverse acoustic (TA), longitudinal acoustic (LA), transverse optical (TO), and longitudinal optical (LO). By adding branches into the simulation and measuring λ, the individual contributions to λ from each branch can be determined.
Cavitation Corrosions in Capillary Pulsating Heat Pipe
Authors: Cai Steve Q.
Published: January 2019

When vapor bubbles are subjected to suddenly reduced pressure or immediate subcooling, it may rapidly condense, rupture, and generate cavitation corrosions. This phenomenon often occurs behind the blade of a rapidly rotating propeller or on any surface vibrating in liquid with sufficient amplitude and acceleration. In this article, we reported cavitation and its corrosive collapse occurring in capillary tubes, called pulsating heat pipes. Visualization images of cut and opened tubes show that internal copper surface was seriously etched after a certain period of operation. Sub-millimeter etching pits are observed on the tube internal surface. Copper particles in size of a few hundred micrometers are also found in the reclaimed operating fluid. Starting from this finding, the temperature effect of performance is analyzed to understand the cavitation occurrence and collapse. Pulsating heat pipe requires a certain temperature difference between the evaporator and condenser sections, typically > 10°C, to generate continuous two-phase oscillating movements. However, during the transient startup period, this temperature difference could reach as high as 50°C. Large saturation temperature difference, associated with highly turbulent two-phase flow, drives the saturated vapor bubbles from the hot evaporation region to the subcooled environment in less than 100ms. During the rapid condensation, the accelerated shrinking vapor bubbles create interface instability, followed by forming a strong impingement jet to etch the solid pipe wall. The collapse of cavitation is associated with the generation of acoustically tinkling signals that are often heard during most of the operating pulsating heat pipe.
Determination of Mechanical Properties of Human Skull With Modal Analysis
Authors: Eslaminejad Ashkan , Hosseini-Farid Mohammad , Ramzanpour Mohammadreza , Ziejewski Mariusz , Karami Ghodrat
Published: January 2019

Traumatic brain injury (TBI) may happen due to loads at high rates. Due to the limitations in experimental approaches, computational methods can simulate and quantify mechanical properties. The experiments show that the human skull has nonlinear mechanical behavior and is significantly strain rate dependent. In this study, we implement Mooney-Rivlin nonlinear hyper and linear-elastic constitutive models to the experimental tensile data at different strain rates; 0.005, 0.1, 10, and 150 1/sec. A dried human skull including frontal, parietal, and occipital bones, was modeled by the 3D laser scanner and discretized by HyperMesh software to perform modal analysis using LS-Dyna finite element software. Using a roving hammer experimental modal analysis scheme, the frequency response function (FRF) and the first three natural frequencies of the skull will be measured. We found these natural frequencies are 496.9 Hz, 560.9 HZ, and 1246 Hz. Performing numerical modal analysis on the skull with pre-assumed linear elastic properties at high strain rate showed close natural frequencies as obtained by experiments. This study provides a new insight into a better understanding of the nonlinearity dynamical behavior of the human skull.
Force Decomposition of Medium Reynolds Number Oscillating Flow Over a Submerged Sphere
Authors: Bekkulov Aibek , Huang Shehua , Xu Ben
Published: January 2019

A variety of engineering applications involve medium Reynolds number (Re) oscillating flow around spherical objects (e.g. aerosol dispersion, microorganism motion, sedimentation of small particles, etc.), and they usually require accurate prediction of the movement of particles and the forces. Currently, the popular model of predicting forces acting on an accelerated submerged sphere was developed more than 100 years ago, but only limited to Stokes flow (Re << 1). In the 1960s, Odar and Hamilton conducted experiments and extended the model for Re number up to 64 (OH-64 law). The aim of this study is to further extend the Re number to 300 via numerical simulations using ANSYS Fluent, so that the model is more capable for more varieties of engineering applications. It is expected that the results of this study will be beneficial to advance the fundamental understanding of oscillating flow over spheres and the potential applications.
Dynamic Modeling and Control of the Hexapod Robot Using Matlab SimMechanics
Authors: Beaber Sameh I. , Zaghloul Abdelrahman S. , Kamel Mohamed A. , Hussein Wessam M.
Published: January 2019

This paper presents a detailed dynamic modeling of phantom ax12 six-legged robot using Matlab SimMechanics™. The direct and inverse kinematic analysis for each leg has been considered in order to develop an overall kinematic model of the robot. Trajectory of each leg is also considered for both swing and support phases when the robot walks with tripod gait in a straight path. Newton-Euler formulation has been utilized to determine the joint’s torque. These results were verified using SimMechanics™. Also, feet force distributions of the hexpaod are estimated via SimMechanics™, which is necessary for its control.
An Improved Non-Gaussian Statistical Theory of Rubber Elasticity for Short Chains
Authors: Morovati Vahid , Dargazany Roozbeh
Published: January 2019

The mechanical behavior of polymers has long been described by the non-Gaussian statistical model. Non-Gaussian models are generally based on the Kuhn-Grün (KG) distribution function, which itself is derived from the first order approximation of the complex Rayleigh’s exact Fourier integral distribution. The KG function has gained such a broad acceptance in the field of polymer physics that the non-Gaussian theory is often used to describe chains with various flexibility ratios. However, KG function is shown to be only relevant for long chains, with more than 40 segments. Here, we propose a new accurate approximation of the entropic force resulted from Rayleigh distribution function of non-Gaussian chains. The approximation provides an improved version of inverse Langevin function which has a limited error value with respect to the exact entropic force. The proposed function provides a significantly more accurate estimation of the distribution function than KG functions for small and medium-sized chains with less than 40 segments.
Mesoscale Material Strength Characterization for Use in Fracture Modeling
Authors: Acton Katherine , Bahmani Bahador , Abedi Reza
Published: January 2019

To accurately simulate fracture, it is necessary to account for small-scale randomness in the properties of a material. Apparent properties of Statistical Volume Elements (SVE), can be characterized below the scale of a Representative Volume Element (RVE). Apparent properties cannot be defined uniquely for an SVE, in the manner that unique effective properties can be defined for an RVE. Both constitutive behavior and material strength properties in SVE must be statistically characterized. The geometrical partitioning method can be critically important in affecting the probability distributions of mesoscale material property parameters. Here, a Voronoi tessellation based partitioning scheme is applied to generate SVE. Resulting material property distributions are compared with those from SVE generated by square partitioning. The proportional limit stress of the SVE is used to approximate SVE strength. Superposition of elastic results is used to obtain failure strength distributions from boundary conditions at variable angles of loading.
A Material Model Fitting for Recycled Polyethylene Terephthalate Implemented in the Finite Element Modelling
Authors: Mesa Vargas Diego Fernando , Vidal-Lesso Agustín , Alfaro Ayala Jorge Arturo
Published: January 2019

In this work, samples of the polyethylene terephthalate material were collected, and then tensile tests were conducted according to ASTM D-882. Three lots of samples were proposed, without sun exposure (0 months), three and six months of sun exposure where the bottles were filled with water and inclined at 45° (with respect to the horizontal), to reproduce the working conditions of a solar collector. Five experimental tests were carried out for each batch, obtaining values of force, deformation, displacement and stress. The experimental data obtained from the tests are used to fit a constituent model for the polyethylene terephthalate material, which reproduces the thermo-structural behavior in the virtual field. According to literature and characteristics of the constitutive models, three hyperelastic models were proposed: Yeoh, Mooney Rivlin and polynomial. The objective of the selection of these constitutive models is to model the material under the real thermo-structural conditions but previously a validation was carried out for each of them. Finally, after a virtual modeling process, reaction force values were collected for each constituent model which will be compared with the actual response of the uniaxial test, where maximum errors of 18% were obtained, which immediately ruled out a constituent model, while the other models handled errors of less than 5% until generating an adjustment close to 1%. The best fit was obtained with Mooney Rivlin’s five parameter hyperelastic model for polyethylene terephthalate.[1][2], [3][4]
An Optimization Model of High-Speed and High-Precision Machining Based on Model Predictive Control
Authors: Zhang Jing , Ding Jiexiong , Li Qingzhao , Ding Qicheng , Jiang Zhong , Wang Wei , Du Li
Published: January 2019

In the multi-axis high-speed and high-precision machining process, the contouring error and the feed rate of tool tip and affect the quality of machined workpiece and the processing efficiency, respectively. The faster feed motion will result in greater tracking error of each axis. The contouring error which directly affects the quality of machined part is caused by the tracking errors of the axes. Obviously, it is difficult to improve the contouring accuracy and increase the feed rate simultaneously. To this end, a novel optimization model is developed here based on the model predictive control method. First, the feed servo model of translational and rotary axes are established, and the contouring error model is afterwards constructed. Subsequently, the optimization algorithm is derived to achieve the high processing speed, and input constraints are addressed to avoid violation of the performance limitation of the drivers. In addition, contouring error constraint, which is obtained by calculating the contouring error of the processed path, is addressed to high contour accuracy. Finally, a simulation is conducted to verify the effectiveness and superiority of the proposed method.
Chemical Polishing Based Surface Finishing of 3D Printed Steel Components
Authors: Tyagi Pawan , Goulet Tobias , Chuenprateep Nitt , Stephenson Robert , Knott Rudolph , Reddick Antione , Shetty Devdas , Schlitzer Justin , Benton Cordell , Garcia-Moreno Francisco
Published: January 2019

Reducing surface roughness is critical for improving the mechanical properties of metal 3D printed components. As produced laser sintered metal 3D printed components suffer from high surface roughness. This problem is enormously big for the 3D printed components with intricate geometries involving a large internal surface area. To address this issue, we performed chemical polishing of the 3D printed 316 steel components. After 30 minutes of chemical polishing the color of 3D printed steel components’ surface became dull grey to bright lustrous. According to optical profilometer study, the surface morphology improved dramatically. The Rq roughness parameter changed from ∼8 um to ∼0.6 um. We also applied chemical polishing on cubical metal 3D printed components with internal surfaces. This surface finishing method was equally effective for the internal and external surfaces.
Physical (Steam) Activation of Post-Gasification Biochar Derived From Peach Pits
Authors: Muñoz-Hernández Andrés , Dehghan Sina , Diaz Gerardo
Published: January 2019

Activated carbon is one of the most effective materials for removing a wide range of contaminants from water, e.g., industrial and municipal wastewater. In this paper, physical (steam) activation of peach pit biochar obtained from a biomass gasification power plant is explored. Activation experiments were carried out at various temperatures, steam flow rates, and activation times. The initial biochar and activated biochar samples have been analyzed for porosity, chemical composition and surface morphology. From the porosity analyses it was determined that the raw biochar had a surface area in the order of 1 m2/g, whereas the activated samples had surface areas ranging from 379 m2/g to nearly 600 m2/g. The burn off ranged from 29 % to 56 %. Energy wise, the biochar sample processed for the shortest time with the lowest flow rate had the largest ratio of surface area-to-consumed energy.
CFD Modelling of NOx and Soot Formation in Aluminum Anode Baking Furnace
Authors: Tajik Abdul Raouf , Shamim Tariq , Ghoniem Ahmed F. , Abu Al-Rub Rashid K.
Published: January 2019

The cost and quality of aluminum produced by the reduction process are strongly dependent on heat treated (baked) carbon anodes. A typical aluminum smelter requires more than half a million tons of carbon anodes for producing one million ton of aluminum. The anode baking process is very energy intensive, approximately requires 2GJ of energy per ton of carbon anodes. Moreover, pollutant emissions such as NOx and soot formation are of major concern in the aluminum anode baking furnace. The current study aims at developing an accurate numerical platform for predicting the combustion and emissions characteristics of an anode baking furnace. The Brookes and Moss model, and the extended Zeldovich mechanism are employed to estimate soot and NOx concentration, respectively. Considering a fire group of three burner bridges, one after the other in the fire direction, combustion and emissions features of these three firing sections are interrelated in terms of oxidizer’s concentration and temperature. In the present study, considering this interconnection, the effect of diluted oxygen concentration at elevated oxidizer’s temperature (∼1200°C), which are the key features of the moderate or intense low oxygen dilution (MILD) combustion are analyzed. It is observed that by circulating some of the exhaust gases through the ABF crossovers, oxygen dilution occurs which results in higher fuel efficiency, lower pollutant emissions, and more homogeneous flow and temperature fields.
Thermo-Economic Analysis of an Integrated Supercritical CO2 Brayton Cycle and Multiple Effect Desalination Systems
Authors: Alharbi Sattam , L. Elsayed Mohamed , Chow Louis
Published: January 2019

A thermo-economic analysis is carried for the current integrated supercritical carbon dioxide (sCO2) Brayton cycle with both multi-effect desalination coupled with mechanical vapor compression (MED-MVC) and conventional MED system. The conventional MED system uses hot water as the heat source by recuperating the waste heat from the sCO2 cycle. The MED-MVC system uses a vapor compressor to eliminate the need to condense the water vapor in the last effect of the MED system. The advantage of the MED-MVC is the ability to recuperate part of the waste heat of the sCO2 cycle through preheating the seawater feed directed to the first effect. Forward feed configuration is selected since high feed temperature can be accommodated for the MED-MVC. On the other hand, in the case of conventional MED, high feed temperature is limited to the last effect temperature. To satisfy the demand of approximately 2,500 families, the water production capacity is 1,250 m3/day, and 20 MW of electrical power is needed. The electrical power generated from the sCO2 cycle is also used to drive the MVC unit and operate the feed, brine and distillate pumps in the MED system. Results reveal that both MED and MVC systems are capable to achieve the selected production capacity. The specific power consumption, universal performance ratio, and total water price for MED systems are 1.22 kWh/m3, 56.51 and 0.69 $/m3, respectively; whereas the MED-MVC systems are 10.22 kWh/m3, 27.35 and 0.84 $/m3, respectively. The cost of electricity is 0.029 $/kWh.
Experience of Multiple Instructors About Student Presentation Based Teaching (SPET) Approach
Authors: Tyagi Pawan , Xu Jiajun , Thompson Lara , Thomas Morris , Moore Carl , Haghani Sasan , Hampton-Garland Pamela
Published: January 2019

Many college instructors are hesitant to adopt student active teaching approaches. Student activity-based classroom teaching may require a lot of time investment in designing and conducting student activities. Also, student activities during the class period may lead to inadequate coverage of the course content mentioned in the syllabus. Incomplete course coverage and the amount of effort required on the part of an instructor for designing active teaching strategies are cited as the common hindrances in adopting active student teaching. To address these widely recognized inhibiting factors, we recently implemented a new student-active teaching approach. This approach is based on the students’ presentation and hence termed as student presentation based effective teaching (SPET). The SPET approach is designed to address the key components of effective teaching. However, to understand the efficacy of SPET for different instructors we implemented it in five courses offered during the same semester. The Learning Resource Division faculty analyzed the data and interviewed the instructors that implemented SPET. Here we present the response and insights garnered from different instructors. Participating instructors reflected their views about the advantages and challenges associated with the adaptation of SPET.
Study on Dynamic Performance of the Non-Circular Bearings Using Fourier Analysis
Authors: Tian Jiale , Yang Baisong , Yu Lie , Zhou Jian
Published: January 2019

Journal bearing is one of the most important components for supporting high speed rotating machinery such as compressors and turbo machines. In recent trends, non-circular journal bearings (lemon bearing, three-lobe bearing, four-lobe bearing, etc.), for their greater load capacity and better stability, have become a superior choice and found wide spread application. In this paper, the nonlinear oil film force is expressed using the dynamic stiffness and damping of 1st-3rd order. And the film thickness and pressure are analyzed using Fourier method, so that the corresponding harmonic components and their deeper connection can be further explored. The paper shows that the nonlinear dynamic performances are connected closely with the bearings’ profile, and lays the foundation for expressing the precise nonlinear oil film force.
Pelvic Injury Survival Analysis for a Finite Element Human Body Model Using Multiple Data Sets
Authors: Weaver Caitlin M. , Miller Anna N. , Stitzel Joel D.
Published: January 2019

Finite element (FE) computational human body models (HBMs) have gained popularity over the past several decades as human surrogates for use in blunt injury research. FE HBMs are critical for the analysis of local injury mechanisms. These metrics are challenging to measure experimentally and demonstrate an important advantage of HBMs. The objective of this study is to evaluate the injury risk predictive power of localized metrics to predict the risk of pelvic fracture in a FE HBM.

The Global Human Body Models Consortium (GHBMC) 50th percentile detailed male model (v4.3) was used for this study. Cross-sectional and cortical bone surface instrumentation was implemented in the GHBMC pelvis. Lateral impact FE simulations were performed using input data from tests performed on post mortem human subjects (PMHS). Predictive power of the FE force and strain outputs on localized fracture risk was evaluated using the receiver operator characteristic (ROC) curve analysis.

The ROC curve analysis showed moderate predictive power for the superior pubic ramus and sacrum. Additionally, cross-sectional force was compared to a range of percentile outputs of maximum principal, minimum principal, and effective cortical element strains. From this analysis it was determined that cross-sectional force was the best predictor of localized pelvic fracture.