bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling Fatigue Crack Growth in CFRP Adhesively Bonded Substrate Using XFEM
Authors: Al-Dakheel Hussain , Temitope Idris , Albinmousa Jafar , Al-Athel Khaled
Published: February 2021

Carbon fiber reinforced polymers (CFRP) are crucial for many industries due to their superior material properties. CFRPs have strength and toughness that are comparable to metals but with the advantage of possessing lighter weight and higher corrosion resistance. Typically, structural parts are joined by bolts and rivets resulting in difficulties keeping the integrity of these joints. In CFRP joints, screw holes are stress concentration sites that may develop cracks, splits and delamination. Alternatively, adhesive bonding can be used as a joining method for CFRP substrates to overcome the disadvantages bolts and rivets.

Structural parts are usually subjected to cyclic loading. Therefore, fatigue is considered as a major design tool for these parts. Finite element analysis is a powerful tool for modeling damage in components. This paper aims to simulate fatigue crack growth in adhesively bonded carbon fiber reinforced polymer (CFRP) composite substrates using a double cantilever beam (DCB) specimen.

ANSYS XFEM is utilized to simulate the crack path using the enrichment technique to assign elements to the crack path. The model calculates the stress intensity factor (SIF) based on the domain integral over the contour around the crack tip. Then, it is converted at each sub-step to the energy released rate (ERR) which includes a correction factor estimated from the cohesive zone model (CZM). The model is idealized as a 2D geometry with the nodes at the unloaded edge and the corner being constrained in the longitudinal and the tangential directions, respectively. Displacement was applied at the other end of the specimen separating the two beams in a mode I condition. Finally, the number of cycles is estimated from Paris law.

To verify the proposed model, fatigue crack growth (FCG) tests were performed on an 8-layer unidirectional CFRP laminates (HexPly T700/M21) fabricated into DCB specimens. The substrates is joined by an aerospace grade adhesive (Araldite 420). The estimated energy release rate (ERR) using the developed finite element model is within 90% or more of that determined experimentally.
Numerical Modeling of Non-Affine Viscoelastic Fluid Flow Including Viscous Dissipation Through a Square Cross-Section Duct: Heat Transfer Enhancement due to the Inertia and the Elastic Effects
Authors: Hagani Fouad , Boutaous M'hamed , Knikker Ronnie , Xin Shihe , Siginer Dennis
Published: February 2021

Non-isothermal laminar flow of a viscoelastic fluid including viscous dissipation through a square cross–section duct is analyzed. Viscoelastic stresses are described by Giesekus modele orthe Phan-Thien–Tanner model and the solvent shear stress is given by the linear Newtonian constitutive relationship. The flow through the tube is governed by the conservation equations of energy, mass, momentum associated with to one non–affine rheological model mentioned above. The mixed type of the governing system of equations (elliptic–parabolic–hyperbolic) requires coupling between discretisation methods designed for elliptic–type equations and techniques adapted to transport equations. To allow appropriate spatial discretisation of the convection terms, the system is rewritten in a quasi-linear first-order and homogeneous form without the continuity and energy equations. With the rheological models of the Giesekus type, the conformation tensor is by definition symmetrical and positive-definite, with the PTT model the hyperbolicity condition is subject to restrictions related to the rheological parameters. Based on this hyperbolicity condition, the contribution of the hyperbolic part is approximated by applying the characteristic method to extract pure advection terms which are then discretized by high ordre schemes WENO and HOUC. The algorithm thus developed makes it possible, to avoid the problems of instabilities related to the high Weissenberg number without the use of any stabilization method. Finally, a Nusselt number analysis is given as a function of inertia, elasticity, viscous dissipation, for constant solvent viscosity ratio and constant material and rheological parameters.
A Numerical Study Into the Influence of Leading Edge Tubercles on the Aerodynamic Performance of a Highly Cambered High Lift Airfoil Wing at Different Reynolds Numbers
Authors: Abdelrahman Amr , Emam Amr , Adam Ihab , Hassan Hamdy , Ookawara Shinichi , El-wardany Ahmed
Published: February 2021

Through the last two decades, many studies have demonstrated the ability of leading-edge protrusions (tubercles), inspired from the pectoral flippers of the humpback whale, to be an effective passive flow control method for the stall phase of an airfoil in some cases depending on the geometrical features and the flow regime. Nevertheless, there is a little work associated with revealing tubercles performance for the lifting surfaces with a highly cambered cross-section, used in numerous applications. The present work aims to investigate the effect of implementing leading edge tubercles on the performance of an infinite span rectangular wing with the highly cambered S1223 foil at different flow regimes. Two sets; baseline one and a modified with tubercles have been studied at Re = 0.1 × 106, 0.3 × 106 and 1.5 × 106 using computational fluid dynamics with a validated model. The numerical results demonstrated that Tubercles have the ability to entirely alter the flow structure over the airfoil, confining the separation to troughs, hence, softening the stall characteristics. However, the tubercle modification expedites the presence of the stalled flow over the suction side, lowering the stall angle for the three mentioned Reynolds numbers. While, no considerable difference occurs in lift and drag before the stall.
Three-Dimensional Concentration and Velocity Measurements of a Pulsatile Contaminant Release in a Model of Oklahoma City
Authors: Benson Michael , Chung Daniel , Fuhrman Gabriel , Helmer David , Homan Ty , Mooradian Lynne , Rhee Joshua , Elkins Christopher , Banko Andrew
Published: February 2021

Motivated by the Joint Urban 2003 field project and subsequent studies, magnetic resonance imaging (MRI) techniques were used to collect full-field measurements of three-dimensional fluid velocity and concentration across a scaled model of 2003 Oklahoma City. The study was intended to develop, test, and demonstrate a repeatable puff release with MRI compatible equipment. In order to accomplish this, a contaminant was injected through the floor of a city model in discrete puffs using a solenoid valve. Sealed to fit inside a water channel, the 1:2,206 scale city model covered the central business district of the city as it was in 2003. The main flow was fully turbulent with a Reynolds number of 36,000, while vertical puff injection occurred at a Reynolds number of 2,642. Using MRV and MRC methods, the three components of velocity and concentration were measured at more than 2 million locations for each of the 12 phases of the injection period. MRV measurements examined the fluid flow with respect to building geometry. Collected at heights corresponding to this MRV data, MRC measurements enabled the analysis of the vertical and lateral dispersion of the contaminant. Ultimately, the study demonstrated a novel MRI technique through contaminant puff release and can be used for the validation of urban contaminant dispersion models.
Numerical and Experimental Analysis of a Novel Concept for Axels Dry Braking System in Off-Road Vehicles
Authors: Milani Massimo , Montorsi Luca , Muzzioli Gabriele , Storchi Gabriele , Terzi Stefano , Rinaldi Pier Paolo , Stefani Matteo
Published: February 2021

The paper proposes a novel concept for axels dry braking system in off-road vehicles by implementing an oil recovery system in the friction plates chamber. The new system is able to remove the oil in the discs’ chamber when they are not engaged and to replenish it when the braking system is activated and the heat generated has to be dissipated. Thus, the energy losses due to the oil splashing will be significantly reduced with remarkable effects on the fuel consumption of the vehicle. Since experimental measurements are very difficult to carry out on a real system, a simplified geometry is designed and an ad-hoc test rig realized. Fast imaging techniques are used to capture the multiphase flow pattern within the friction plates chamber at different rotational speeds of the axel. The experimental results are used to validate a full 3D multi-phase CFD approach. A good agreement between the measurements and the calculations is found.

The numerical modeling is therefore employed to predict the flow distribution in the real geometry and under actual operating conditions. A modular approach is adopted for the domain subdivision in order to represent accurately the three dimensional geometrical features, while the volume of fluid approach is used to model the multi-phase flow that characterizes the component. A conjugate heat transfer model is also adopted to predict the heat transferred from the discs to the working fluid and how the fluid is dissipating the heat within the component. By means of the numerical analysis the geometry of the real system is designed in order to improve the performance of the dry braking systems both in terms of energy saving and oil cooling.
Wire Arc Additive Manufacturing (WAAM): Reviewing Technology, Mechanical Properties, Applications and Challenges
Authors: Zahid Moosa , Hai Khizar , Khan Mujtaba , Shekha Ahmed , Pervaiz Salman , Moneeb Ali Syed , Abdul-Latif Omar , Salman Muhammad
Published: February 2021

Because of the flexible nature of 3D printing and additive manufacturing technology, manufacturing sector has been revolutionized. There is a possibility to manufacture different intricate geometrics that cannot be produced through conventional processes previously. The conventional design concepts such as design for manufacture (DFM) and design for assembly (DFA) have been modified and simplified. Wire arc additive manufacturing (WAAM) has emerged as one of the leading additive manufacturing (AM) processes due to its high deposition rate and economic feasibility. A lot of progress has been made to understand and improve this process and the mechanical properties associated with the fabricated parts. It is specifically cheaper to print large-scale metallic components using WAAM. This paper gives a thorough review of the work that has been done on WAAM by comparing different technological variants of WAAM, which include Metal Inert Gas (MIG), Tungsten Inert Gas (TIG) and Plasma Arc Welding (PAW). The study also discusses the mechanical properties of the fabricated components using different metals, the defects and challenges the process faces today and how they can be reduced. In the end the study also provides overview of WAAM applications in some of the industrial sectors such as construction, automotive, and structural etc.
Development of Fiber Structures for High Performance Heat Resistant Curtains
Authors: Araujo Paulo , Teixeira José Carlos , Silveira Dionisio , Silva Elisabete , Soares Delfim , Fangueiro Raul , Vilarinho Maria Cândida
Published: February 2021

The protection of human life and goods assumes a growing concern in all forms of activities. The fire and smoke curtains have as main role to act as a physical barrier to prevent the fire from spreading between spaces as well as to staunch the smoke and heat transfer to adjacent areas. They can also be easily operated (opening and closing) causing a minimal interference with the flow of materials and humans within confines spaces, such as warehouses and industries, while providing adequate protection. Thus, there are a set of characteristics that these products must exhibit high fire protection, thermal resistance and gas impermeability.

The classification of the heat resistance, described in the European Standard BS EN 1634-1: Fire resistance and smoke control tests for door, shutter and, openable window assemblies and elements of building hardware — fire resistance tests for doors, shutters and openable windows, is the procedure that allows determining the response of a product in contributing by its decomposition to a fire to which it is exposed, being according to three criteria: (i) integrity, (ii) insulation and (iii) radiation.

Usually curtains are based on fiber-based structures which can be coated to enhance their protective capabilities. In addition, the fibrous structure can be tailored to optimize its behaviour using 2D and 3D complex architectures, with single or multiple materials.

The performance assessment of the curtains regarding the aforementioned parameters is performed resorting to several experimental procedures that are detailed in the specific standards.

The present paper reports the development of novel fibrous structures used for heat protection curtains. They are based on the various combinations of hybrid structures combining 2 or 3 different yarn materials. The tests are carried out in a purpose built oven that induces a steep temperature rate (approximately 600 °C in 5 min) on one side of the sample followed by a slower rate up to 950 °C in 60 min. The sample is placed under stress during the test in order to mimic that caused by its own weight. Thermocouples monitor the temperature on both sides of the sample and its integrity is assessed by both the occurrence of fabric rupture and smoke release due to ignition. Both the fabric integrity and the temperature on the back side of the sample are an indicator of its performance which follows the European Standard BS EN 13501-2: Fire classification of construction products and building elements. Classification using data from fire resistance tests, excluding ventilation services.

From the results one can conclude that hybrid structures, including either basalt and glass fibers, are the most suitable.
Design and Build a T-Shirt Cannon Firing Mechanism
Authors: Norvell Kyle , McClelland Michael , Ratajczak Ethan , Dong Janet
Published: February 2021

The work in this paper is a part of the T-shirt cannon automation project. The objective of the project is to develop an autonomous robot carrying cannons to automatically shoot T-shirts during the sports events at the University of Cincinnati (UC). More specifically, the T-shirt cannon will be used and driven by the UC cheerleading team and be able to automatically shoot T-shirts at the audience in the Nippert Stadium and the 5/3 Arena for football and basketball games, respectively. The design and automation of the T-shirt cannon require a significant effort and a multi-disciplinary team to complete. This paper will focus on the process of designing, building, and testing the firing mechanism for the cannon, including the determination of cannon’s firing method, barrel design and assembly, base design and barrel mounting method, pneumatic analysis, and automation and control of the firing of T-shirts. The goal of the firing mechanism is that the cannon would fire off as many T-shirts as possible with the window of a single timeout at the game.

The project starts with the preliminary research and the initial testing. During the preliminary research, the relevant safety standards/codes and previous T-shirt cannon designs were reviewed and studied. Especially the possible working with pressurized air, the material used in the design must be rated above the target firing pressure to ensure the cannon itself not explode and the air supply tank and fittings must be in good condition. During the initial testing, the site visits were conducted, the cheerleaders were interviewed, the dimensions of the stadium and the 5/3 arena were measured, and therefore the shooting distance and shooting angles were estimated. After the initial testing and preliminary research, a set of engineering characteristics were established, following by the concept design, in which the barrel assembly, the pneumatics, the firing mechanism, and the mounting method were discussed, analyzed, and determined. The barrels had two major designs, one is using a railing support system with an external tank of air to power and fire the cannon, and another one is using a chamber of air to power and fire the cannon with the barrels surrounding the air chamber itself. Two methods are analyzed and compared. The optimum one, therefore, was determined and developed. For the firing mechanism, two main designs are a spring-loaded firing mechanism that could increase the sealing capabilities of the barrels, and a tight tolerance fit that has less weight. Two designs were tested and analyzed, the optimum one was determined and built, followed by the firing mechanism testing.

This paper will describe the process of design, building, and testing the firing mechanisms of this T-shirt cannon at UC. The paper will also discuss the testing results on shooting performance.
Investigation of the Effects of Design and Process Parameters on the Mechanical Properties of Biodegradable Bone Scaffolds, Fabricated Using Pneumatic Microextrusion Process
Authors: Yu Mohan , Yeow Ye Jien , Lawrence Logan , Claudio Pier Paolo , Day James B. , Salary Roozbeh (Ross)
Published: February 2021

Pneumatic micro-extrusion (PME) is a direct-write additive manufacturing process, which has emerged as a robust, high-resolution method for the fabrication of a broad spectrum of biological tissues and organs. In the PME process, a high-pressure flow is injected into a cartridge, which contains a bioink material, resulting in pressure-driven material deposition on a free surface via a converging conical micro-capillary. In this study, PCL powder was loaded into the cartridge, maintained at 120 °C. The flow pressure was set to 550 kPa. Laminar molten PCL flow was deposited on a glass surface (steadily and uniformly kept at 45 °C), using a 200 μm nozzle. A porous, cylindrical scaffold was designed (honeycomb-filled), having a diameter and height of 10 mm and 3 mm, respectively.

To investigate the effects of the design and process parameters, a series of experiments were designed and conducted where print speed was varied at four levels in the range of 0.30–0.45 mm/s with 0.05 mm/s increments. In addition, similarly, layer height and layer width were changed at four levels in the range of 125–200 μm with 25μm increments. Finally, infill density was set at four levels in the range of 0.20–0.35 with 5% increments. As a result, 16 experimental runs were characterized, each replicated four times. Of each of the PME-fabricated samples, an image was acquired (both horizontally and vertically) using a high-resolution CCD camera. Illumination was provided by an LED ring light (being of a brightness in the range of 30,000–40,000 Lux as well as a color temperature of 6000 K). Subsequently, the acquired images were analyzed using in-house digital image processing algorithms, forwarded with the aim to characterize both the diameter and the height of the fabricated bone scaffolds. The veracity of the image-based measurements was corroborated, using offline caliper measurements. Furthermore, the compression properties of the fabricated bone scaffolds were measured using a compression testing machine; the samples were subjected to a compression load, applied with a velocity of 0.08 mm/s. Overall, the results of this study pave the way for future investigation of PME-deposited PCL scaffolds with optimal mechanical and morphological properties for incorporation of hBMSCs toward the treatment of osseous fractures and defects.
Nonlinear Vibrations of Model PWR Fuel Assemblies: Part 2 — Interpretation of Results Using Bilinear Stiffness Model
Authors: Balasubramanian Prabakaran , Ferrari Giovanni , Franchini Giulio M. , Amabili Marco , Karazis Kostas , Painter Brian
Published: February 2021

The experimental response of fuel rods with spacer grids was interpreted using a bilinear hysteresis model. Nonlinear experimental responses of two configurations of rods made out of Zirconium alloy tubes were considered in this paper: one configuration with a single beam and the second configuration with a cluster of beams (stacked in a 3 × 3 matrix formulation). These two configurations were designed to emulate part of the nuclear fuel assembly in Pressurized Water Reactors (PWR). Both configurations were supported by spacer girds at their extremities and were immersed in still water. Spacer grids are grid-like structures made out of thin Zirconium alloy sheets with 17 × 17 cells arranged in a square pattern. Spacer grids provide mechanical support and reduce flow-induced vibration of nuclear fuel rods. They also improve the heat transfer between nuclear fuel rods and the surrounding coolant. The spacer grids impose nonlinear boundary conditions to the beams at the contact points/surface. Specifically, spacer grids present bilinear hysteresis due to their inherent complexity. The bilinear hysteresis shown by spacer grids was measured in terms of force-displacement loops by testing rigid rod inserted in one of its cells. The rigid rod was then excited by external harmonic excitation with excitation frequencies ranging from 5 Hz to 50 Hz in steps of 5 Hz.

The bilinear hysteresis model, first studied by Caughey, was modified to include viscous damping and was used to interpret the experimental results. The method of slowly varying parameters was used to solve the equation of motion. First, the measured force-displacement loops of spacer grids were fitted with the numerical model described in the current analysis. Good agreement between the model response and measured loops was found, and the identified parameters allowed the characterization of the nonlinear boundary conditions imposed by spacer grids. Finally, the nonlinear responses of the two configurations under study were interpreted using the bilinear hysteresis model. Excellent agreement between numerical and experimental results was obtained for both configurations.
Experimental Investigation on the Performance Loss of Cross-Linked Polymers During Photo-Oxidative Aging
Authors: Korayem Abd-Elrahman , Mohammadi Hamid , Dargazany Roozbeh
Published: February 2021

Polymeric substances have seen an unprecedented integration in countless applications and fields of life, subjecting them to a broad range of environmental conditions, which can cause a form of damage to the structural and mechanical properties of these components known as aging. In this study we investigate the effects of the degradation of polymeric materials due to the extended exposure to sunlight, which can be simulated through controlled photo-oxidative aging using ultraviolet (UV) radiation as the main catalyst of this phenomenon. The effects on mechanical behavior and chemical properties of four polymeric materials with different mechanical characteristics was accordingly monitored throughout the study. The materials range in hardness with the polyurethane adhesive being the hardest and acting plastically, followed by an acrylic which exhibits greater hardening with time, a polyurethane sealant, which behaves in an elastomeric manner, and a silicon sealant, which is the softest of the set. Samples were prepared and subjected to UV radiation at three different temperatures namely 45, 60 and 80°C, for different aging periods ranging from 1 day for higher temperatures to 150 days for lower ones. The samples were then subjected to the Fourier transform Infrared spectroscopy (FTIR) test to monitor the change in the chemical composition of the materials along the aging durations and conditions. The materials were then subjected to mechanical testing along two modes of mechanical loading, which are a simple tension until failure and a double-cyclic test with progressively increasing strain limits after every two successful cycles until the sample reaches failure. The samples are loaded at constant strain rates throughout both tests. These tests revealed the change of behavior of our materials along the aging periods and conditions. The changes in mechanical behavior vary across each individual material depending on the aging temperature and period, with the changes ranging from hardening to softening, embrittlement or an increase in the maximum strain the material can endure before failure. A general trend would be that most materials become harder after photo-oxidation, however due to the range of temperatures in the aging conditions, thermo-oxidation, which causes softening in some of the polymers, has an increasingly notable effect at higher temperatures. A visible correlation can be noted between the change in mechanical behavior and a change in absorbance of Infrared Radiation (IR) in the FTIR spectrum, as the greater the crosslinking throughout the polymer matrix, the lower the absorbance of IR radiation due to the increased stiffness of the overall macro-molecular structure.
A Computational Fluid Dynamics (CFD) Study of Material Flow in Pneumatic Microextrusion (PME) Additive Manufacturing Process
Authors: Yeow Ye Jien , Yu Mohan , Day James B. , Salary Roozbeh (Ross)
Published: February 2021

The objective of this study is to investigate the underlying physical phenomena behind material transport in pneumatic micro-extrusion (PME) process, using a computational fluid dynamics (CFD) model. The geometry of the PME deposition head assembly (including a micro-capillary having a diameter of 200 μm) was set up in the ANSYS-Fluent environment, based on a patented design in addition to direct measurements of the dimensions of the assembly. Subsequently, the geometry was meshed using tetrahedron cells. Besides, five layers of inflation were defined with the aim to obtain an accurate solution near all wall boundaries. The transient, pressure-based Navier-Stokes algorithm (based on absolute velocity formulation) was the mathematical model of choice, used to obtain transient solutions. To account for the effects of compressibility as well as viscose heating, the energy equation (in addition to the continuity and momentum equations) was utilized in the CFD model. Furthermore, the explicit volume of fluid model (composed of two Eulerian phases) and the laminar viscose model were used to collectively establish a viscose two-phase flow model for the molten polymer (PCL) deposition in the PME process. Pressure-velocity coupling was implemented using the semi-implicit method for pressure linked equations (SIMPLE). Finally, experimental sensor data was used with the aim to: (i) define the boundary conditions (as follows), and (ii) validate the CFD model.

In this study, PCL powder was loaded into the cartridge, maintained at 120 °C, defined as the temperature of all stationery walls (with no slip condition). Pressure inlet was the type of boundary defined for the high-pressure gas flow in the PME process, set at 550 kPa. The laminar molten PCL flow was deposited on a glass substrate, steadily and uniformly kept at 45 °C, defined as the temperature of the substrate wall, moving with a speed of 0.35 mm/s. Overall, the results of this study pave the way for better understanding of the causal phenomena behind material transport and deposition in the PME process toward fabrication of bone tissue scaffolds with optimal functional properties.
3D Printed MEMS-Scale Vibration Isolators
Authors: Bond Arthur , Bottenfield Brent D. , Dean Robert N. , Adams Mark L. , Zhao Jing , Li XiaoFu , Flowers George T. , Perkins Edmon
Published: February 2021

Mechanical vibration isolation is an important element for many traditional MEMS devices, (e.g., MEMS inertial sensors and micro-optics) that are deployed in harsh environments (e.g., aerospace applications or automotive applications). Without suitable vibration isolation, environmental vibrations can potentially damage these devices. Micro-scale mechanical vibration isolators usually consist of a center proof mass pad, a suspension system, and a surrounding frame. The isolator functions as a mechanical low-pass filter that provides useful attenuation of high frequency environmental vibrations between the frame and the proof mass pad, to which the vibration sensitive device is attached. These vibration isolators are usually fabricated with either laser processing or silicon micromachining techniques. Although these traditional techniques produce high quality vibration isolators, these methods take time to develop for specific sensor applications, and the batch size is typically large. This paper has two key highlights. First, the efficacy of 3D printing as a prototyping tool for small batch MEMS sensor vibration isolation applications is considered. Twenty-five mechanical vibration isolators were tested for this investigation, using both SLA and FDM printers. The resulting test data demonstrated that the MEMS-scale 3D printed mechanical vibration isolators can be a valid option for real-world vibration isolation applications. Second, it is unclear whether the bulk material properties are valid for MEMS-scale 3D printed structures, since these bulk material properties are typically calculated using tensile tests on macro-scale dog-bone specimens. Considerable variation in vibratory system parameters was found, even when the same printer, print orientation, material, and post-processing were used.
A New Method for Performance Measurement of PPV Fans for Fire Fighting Under Realistic Conditions
Authors: Steppert Michael , Epple Philipp , Steber Michael , Gast Stefan
Published: February 2021

PPV Fans (Positive Pressure Ventilation Fans) are used in firefighting to remove smoke from a burning building, so that fire fighters can have a clear view inside the house and injured people do not have to breathe toxic smoke. This can be done by placing a PPV fan in a distance of about two meters in front of a door of the burning building. On another, carefully chosen position in the building, e. g. a window, a door or at the roof an opening has to be created, where the smoke can leave the building. The same volumetric flow rate of gas that is blown into the building by the PPV fan has to leave the building at a chosen opening. Because the gas entering the building is air and the gas leaving the building is a mixture of smoke and air, the smoke concentration in the building can be reduced.

To test the performance of such PPV fans, a test building with a door in the first floor and a window in the 3rd floor has been built. To measure the volumetric flow rate of the smoke and air mixture through the window in the 3rd floor that is leaving the building, a flow meter nozzle was designed. The design process was done using the commercial Navier Stokes solver Star CCM+, where three nozzle designs, such as a nozzle with constant velocity increase, a quarter circle nozzle and a non-curved nozzle were investigated for different volumetric flow rates. Also, a rounding at the window, where the nozzle is placed, was investigated to prevent flow detachment and shock losses at the inlet of the nozzle.

The volumetric flow rate through the nozzle can be calculated, by measuring the pressure at the nozzle wall (before the contraction) and applying Bernoulli’s law, the continuity equation and assuming atmospheric pressure at the free jet flow at the end of the nozzle. The so calculated volumetric flow rate was compared with the actual flow rate, given by the numerical CFD simulations. With these values, the nozzle specific coefficient of discharge for several volumetric flow rates has been calculated and a function fitting was done to get obtain analytical relation between pressure and volumetric flow rate.

The detailed design process of the three nozzles, the numerical results of the CFD studies and the determination of the nozzle specific coefficients of discharge are shown and discussed in detail in this work.
Effect of Air Release Agents on Performance Results of Fabric Lined Bushings
Authors: Sahay Chittaranjan , Ghosh Suhash , Mormino Mathew
Published: February 2021

A configuration of a plain (sliding) bearing system is the use of a reinforced fabric comprising a woven structure of polytetrafluoroethylene (PTFE) and other fibers integrated with a phenolic resin system used to both encapsulate the fibrous materials and provide adhesion to metallic and other substrates. This construction promotes dimensional stability and improves thermal conductivity. These PTFE linings offer exceptionally low coefficient friction. The bushing is recommended for high loads when combined with low surface speeds. These fully self-lubricating bushings offer good contamination resistance, no stick-slip and excellent cold flow resistance. This technique has shown longer life of 7 to 10 times that of standard steel-backed, bronze-sintered and PTFE overlay. Proprietary self-lubricating PTFE fibers are applied directly to the steel. This polytetrafluoroethylene is woven onsite and applied directly to the steel. The woven liner is compressible and able to absorb distortions in mating surfaces. PTFE fabrics processed with phenolic resins can entrap air within the cured fabric liner. The entrapped air has the potential to affect bearing performance by reduction of bonding area and reduction in load carrying capabilities. Air release agents can be used to limit the amount of air entrapment within the liner system.

The intent of this research is to determine what, if any, affect the addition of commercially available air release agents would have on PTFE bearing performance. Experimental wear testing at various static and dynamic bearing conditions with and without contamination (de-ice fluid), including at high temperature (325°F) were conducted on eighteen specimens. Peel strength test were also conducted. All these tests were conducted based on prevalent industry standards. Parameters of static load resistance (deflection and permanent set) and loaded torque were found to be unaffected by the use of an air release agent when compared to baseline articles manufactured without such air releasing agents. Results showed that by integration of a commercially available air release agent into the processing of a PTFE based, phenolic resin bearing liner system, one can reduce variability and help stabilize wear performance. Specimens prepared with air release agent showed improved oscillation (fatigue) test results. Further, air release agent also resulted in a 35% increase in peel strength performance when tested per industry standard methods. Contamination with de-ice fluid showed no negative performance results. While the investigations here used only one ratio of additive among all tested bearings, but other concentrations are possible. Authors would like to pursue additional studies in future to determine the amount of air release agent that can reliably be added to remove the maximum air release without affecting the overall bearing performance. By finding this, a threshold of additive can also be determined.
Efficient Residual and Matrix-Free Jacobian Evaluation for Three-Dimensional Tri-Quadratic Hexahedral Finite Elements With Nearly-Incompressible Neo-Hookean Hyperelasticity Applied to Soft Materials on Unstructured Meshes in Parallel, With PETSc and libCEED
Authors: Mehraban Arash , Brown Jed , Barra Valeria , Tufo Henry , Thompson Jeremy , Regueiro Richard
Published: February 2021

Soft materials such as rubber, elastomers, and soft biological tissues mechanically deform at large strain isochorically for all time, or during their initial transient (when a pore fluid, typically incompressible such as water, does not have time to flow out of the deforming polymer or soft tissue porous skeleton). Simulating these large isochoric deformations computationally, such as with the Finite Element Method (FEM), requires higher order (typically quadratic) interpolation functions and/or enhancements through hybrid/mixed methods to maintain stability. Lower order (linear) finite elements with hybrid/mixed formulation may not perform stably for all mechanical loading scenarios involving large isochoric deformations, whereas quadratic finite elements with or without hybrid/mixed formulation typically perform stably, especially when large bending or folding deformations are being simulated. For topology-optimization design of soft robotics, for instance, the FEM solid mechanics solver must run efficiently and stably. Stability is ensured by the higher order finite element formulation (with possible enhancement), but efficiency for higher order FEM remains a challenge. Thus, this paper addresses efficiency from the perspective of computer science algorithms and programming. The proposed efficient algorithm utilizes the Portable, Extensible Toolkit for Scientific Computation (PETSc), along with the libCEED library for efficient compiler optimized tensor-product-basis computation to demonstrate an efficient nonlinear solution algorithm. For preconditioning, a scalable p-multigrid method is presented whereby a hierarchy of levels is constructed. In contrast to classical geometric multigrid, also known as h-multigrid, each level in p-multigrid is related to a different approximation polynomial order, p, instead of the element size, h. A Chebyshev polynomial smoother is used on each multigrid level. Algebraic MultiGrid (AMG) is then applied to the assembled Q1 (linear) coarse mesh on the nodes of the quadratic Q2 (quadratic) mesh. This allows low storage that can be efficiently used to accelerate the convergence to solution. For a Neo-Hookean hyperelastic problem, we examine a residual and matrix-free Jacobian formulation of a tri-quadratic hexahedral finite element with enhancement. Efficiency estimates on AVX-2 architecture based on CPU time are provided as a comparison to similar simulation (and mesh) of isochoric large deformation hyperelasticity as applied to soft materials conducted with the commercially-available FEM software program ABAQUS. The particular problem in consideration is the simulation of an assistive device in the form of finger-bending in 3D.
Dry Reforming of Biogas to Syngas: An Eco-Friendly Renewable Fuel for I C Engines
Authors: Sabnis Sandeep P. , Seethamraju Srinivas
Published: February 2021

Biogas, a promising alternative fuel, a substitute for fossil fuels, is predominantly a mixture of methane and carbon dioxide. Both are major greenhouse gases. Methane has a long-term effect on the environment while carbon dioxide is recycled by the plants. Hence, capture and burning of biogas to consume methane as a fuel is desired both from energy and environmental outlook. The presence of a large amount of carbon dioxide in biogas, however, impairs combustion in engines resulting into slow burning and higher hydrocarbon and carbon monoxide emissions.

Dry reforming, a conversion process of biogas to synthesis gas (syngas), a mixture of hydrogen and carbon monoxide, is a catalytic process that has the potential to greatly improve biogas combustion in engines. The researchers’ focus in dry reforming, however, has been for the generation of hydrogen for fuel cells and reactants for Fischer Tropsch process in industry — this approach aims towards maximum conversion of methane and carbon dioxide. The work presented here investigates the possibility of partial conversion of biogas to harness maximum energy and reduce emissions from I.C. Engines. The published research on dry reforming of biogas has examples of high concentrations of methane in the syngas with calorific values suitable for I.C. Engine application. For example, a 50:50 v/v CH4/CO2 composition biogas has calorific value of 13.33 MJ/kg which when converted to a syngas at 550°C results in a gas with 18:42:14:26 v/v CO2/CH4/H2/CO and a calorific value of 19.96 MJ/kg). Such compositions have moderate percentage of hydrogen to act as combustion enhancer and the carbon dioxide present helps to control NOx emissions. The major contributors of energy are methane and carbon monoxide in these cases.

The dry reforming reaction is an endothermic reaction, which produces hydrogen. The side reactions that happen are the reverse water gas shift reaction, which reduces hydrogen yield and the Bouduard reaction which results in carbon deposition on the catalyst surface. The reactor conditions need to be chosen appropriately, especially the reactor temperature. Simulation of dry reforming reaction using a process simulation software (Aspen Plus) is carried out to find the extent of conversion and exit syngas composition for different biogas compositions. The endothermic heat for the reactor can be provided by the heat of the engine exhaust — therefore, an opportunity exists to use waste heat recovery from the engine exhaust. However, there is a tradeoff between the reactor temperature, syngas composition going to engine inlet and the engine exhaust heat — which is investigated in this study.
A Theoretical Study of Sensor-Artery Interaction in Noninvasive Arterial Pulse Signal Measurement Using Tactile Sensors
Authors: Roxas Roman Carlo B. , Harnish Adam T. , Johnson Dylon N. , Stewart Camrie M. , Nguyen Dieu , Osbourne Erika , Wolbert Joshua A. , Vahala Linda , Hao Zhili
Published: February 2021

This paper presents a theoretical study of sensor-artery interaction in arterial pulse signal measurement using a tactile sensor. A measured pulse signal is a combination of the true pulse signal in an artery, the arterial wall, its overlying tissue, and the sensor, under the influence of hold down pressure exerted on the sensor and motion artifact. The engineering essence of sensor-artery interaction is identified as elastic wave propagation in the overlying tissue and pulse signal transmission into the sensor at the skin surface, and different lumped-element models of sensor-artery interaction are utilized to examine how the involved factors affect a measured pulse signal. Achieving ideal sensor-artery conformity is the key for acquiring a measured pulse signal with minimum distortion. Hold-down pressure, sensor design, and overlying tissue collectively contribute to ideal sensor-artery conformity. Under ideal sensor-artery conformity, both the sensor and overlying tissue cause an increase in the measured stiffness of the arterial wall; damping and inertia of the sensor and overlying tissue also affects a measured pulse signal. The theoretical study shows the need to tailor the sensor design for different arteries and individual, and interpret estimated arterial indices with consideration of individual variations as well as instruments used.
Momentum Analysis of Vehicles With Disparate Masses
Authors: Eichaker Lauren , Eiselstein Nicholas , Buczek Sean , Panoff Stephen , Wiechel John , Guenther Dennis
Published: February 2021

It is well established that the law of conservation of momentum is applicable to all interactions between any two bodies during an impact. The law dictates that the total momentum before a collision is the same as the total momentum after the collision (for elastic collisions). This law has been accepted as a fundamental part of Newtonian physics since Newton incorporated Descartes’ work into his own. Scientists rarely question its applicability to kinematics of bodies in the non-quantum world. The law of conservation of momentum is regularly used in vehicle accident reconstruction to calculate a speed of one of the vehicles before or after the collision, assuming that the masses of the vehicles and sufficient other velocities are known. Collisions of vehicles with highly disparate masses pose an interesting dilemma. In such a collision, the speed of the higher mass vehicle will change very little in a collision with a vehicle of much smaller mass and the speed change of the smaller mass vehicle will be large. This is due to the ratio of the masses of the two vehicles which minimizes the effect of the smaller mass vehicle on the vehicle of larger mass. The lopsided nature of the speed change of this kind of collision can lead one to conclude that momentum is not applicable to collisions between vehicles of dramatically different masses. The objective of this work is to investigate the effect of dissimilar masses of vehicles on the effectiveness of momentum to accurately predict speed change. The mathematical formulation of the error associated with dissimilar mass vehicles is presented and quantified to give the reconstructionist guidance in when momentum can be used reliably and when the error resulting from the use of momentum may be larger than desired.
Numerical Simulation of Stress States in White Matter via a Continuum Model of 3D Axons Tethered to Glia
Authors: Pasupathy Parameshwaran , De Simone Robert , Pelegri Assimina A.
Published: February 2021

A new finite element approach is proposed to study the propagation of stress in axons in the central nervous system (CNS) white matter. The axons are embedded in an extra cellular matrix (ECM) and are subjected to tensile loads under purely non-affine kinematic boundary conditions. The axons and the ECM are described by the Ogden hyperelastic material model. The effect of tethering of the axons by oligodendrocytes is investigated using the finite element model. Glial cells are often thought of as the “glue” that hold the axons together. More specifically, oligodendrocytes bond multiple axons to each other and create a myelin sheath that insulates and supports axons in the brainstem. The glial cells create a scaffold that supports the axons and can potentially bind 80 axons to a single oligodendrocyte.

In this study, the microstructure of the oligodendrocyte connections to axons is modeled using a spring-dashpot approximation. The model allows for the oligodendrocytes to wrap around the outer diameter of the axons at various locations, parameterizing the number of connections, distance between connection points, and the stiffness of the connection hubs. The parameterization followed the distribution of axon-oligodendrocyte connections provided by literature data in which the values were acquired through microtome of CNS white matter. We develop two models: 1) multiple oligodendrocytes arbitrarily tethered to the nearest axons, and 2) a single oligodendrocyte tethered to all the axons at various locations. The results depict stiffening of the axons, which indicates that the oligodendrocytes do aid in the redistribution of stress. We also observe the appearance of bending stresses at inflections points along the tortuous path of the axons when subjected to tensile loading. The bending stresses appear to exhibit a cyclic variation along the length of the undulated axons. This makes the axons more susceptible to damage accumulation and fatigue. Finally, the effect of multiple axon-myelin connections in the central nervous system and the effect of the distribution of these connections in the brain tissue is further investigated at present.
Seasonal Changes in Breathing Pattern, Trunk Stabilization, and Muscular Power in Paralympic Swimmers
Authors: Cavaggioni Luca , Trecroci Athos , Formenti Damiano , Hogarth Luke , Tosin Massimiliano , Alberti Giampietro
Published: February 2021

The purpose of this study was to monitor the changes in breathing pattern, trunk muscle stabilization, and upper-body muscular power in Paralympic swimmers throughout a competitive season over three time points: October (T1), March (T2), and August (T3). Six top-level Paralympic swimmers voluntarily participated in this study. The Friedman test, the Bonferroni–Dunn multiple comparison post hoc analysis, and Kendall’sWconcordance coefficient for the measure of effect were used. A significant difference was found in the breathing pattern, trunk stability, and upper-body power variables from the T1 to T3 season (p < .05). However, no significant changes were found in the T2 season. A long-term assessment of these fitness parameters may be of practical importance for better tailoring the training programs of top-level Paralympic swimmers.