bluuebunny/crossref_metadata_2025 huggingface dataset:
Defining Cyber Security and Cyber Security Risk within a Multidisciplinary Context using Expert Elicitation
Authors: Cains Mariana G. , Flora Liberty , Taber Danica , King Zoe , Henshel Diane S.
Published: February 2021

It is important to have and use standardized terminology and develop a comprehensive common understanding of what is meant by cyber security and cyber security risk given the multidisciplinary nature of cyber security and the pervasiveness of cyber security concerns throughout society. Using expert elicitation methods, collaborating cyber researchers from multiple disciplines and two sectors (academia, government–military) were individually interviewed and asked to define cyber security and cyber security risk. Data‐driven thematic analysis was used to identify the most salient themes within each definition, sector, and cyber expert group as a whole with results compared to current standards definitions. Network analysis was employed to visualize the interconnection of salient themes within and across sectors and disciplines. When examined as a whole group, “context‐driven,” “resilient system functionality,” and “maintenance of CIA (confidentiality, integrity, availability)” were the most salient themes and influential network nodes for the definition of cyber security, while “impacts of CIA vulnerabilities,” “probabilities of outcomes,” and “context‐driven” were the most salient themes for cyber security risk. We used this expert elicitation process to develop comprehensive definitions of cyber security (cybersecurity) and cyber security risk that encompass the contextual frameworks of all the disciplines represented in the collaboration and explicitly incorporates human factors as significant cyber security risk factors.
Clinical characteristics and predictors of mortality in patients with melioidosis: the Kapit experience
Authors: Toh Valerie , Tee Sui Poh , Lee Shen‐Han
Published: February 2021

Objectives

Melioidosis, caused by Burkholderia pseudomallei, is prevalent in rural areas of Malaysia. The aim of this study is to delineate the epidemiology and predictors of mortality from melioidosis in Kapit district, Sarawak.

Methods

For this retrospective study of patients with culture‐confirmed melioidosis admitted to Kapit Hospital, Sarawak, Malaysia, between July 2016 and July 2019, epidemiological, clinical and microbiological data were obtained. Univariate and multivariate logistic regression analyses were used to determine predictors of mortality.

Results

Seventy three patients met inclusion criteria. Diabetes mellitus (28.8%) and hypertension (27.4%) were primary co‐morbidities. Clinical spectrum of melioidosis ranged from bacteraemia (64.4%), pneumonia (61.6%) and internal organ abscesses (49.3%) to localised soft tissue (21.9%) and joint abscesses (6.9%). Mortality rate was 12.3%. Bacteraemia and pneumonia were significantly associated with septic shock, whereas patients with soft tissue abscesses tended to present with a milder form of melioidosis without septic shock. Septic shock, mechanical ventilation, intensive care unit admission, serum urea, creatinine, bicarbonate, albumin and aspartate transaminase were all significantly associated with increased mortality on univariate analysis (all P < 0.05). Multivariate analysis revealed that low serum bicarbonate (P = 0.004, OR 0.64, 95% CI 0.48‐0.87) and albumin (P = 0.031, OR 0.73, 95% CI 0.54–0.97) could be associated with a higher mortality.

Conclusion

Melioidosis remains a fatal infection and commonly presents with septic shock, in the form of bacteraemia and pneumonia. Two routine clinical parameters, serum bicarbonate and serum albumin, may have important prognostic implications in septicaemic melioidosis.
Memoria colectiva en el video universitario colombiano
Authors:   Pontificia Universidad Javeriana, Urbanczyk María
Published: February 2021

Este libro analiza cómo se construyen memorias del país a través de las narrativas audiovisuales universitarias en Colombia. El estudio de este tipo de producción permite acceder a una multiplicidad de interpretaciones de realidades vividas e imaginadas que tienen que ver con la alteridad étnica, la intergeneracionalidad, el conflicto armado y la conciencia ambiental. Al cuestionar en sus relatos los imaginarios sociales instituidos, los jóvenes trazan las pistas para afrontar y construir el futuro de manera distinta, a partir de la resignificación de las memorias colectivas y de las relaciones sociales. Por lo tanto, se invita al lector a reflexionar sobre la realización audiovisual universitaria como una acción política de los universitarios dirigida a diseñar lo deseable, a partir de la recuperación del tejido social afectado durante años por el conflicto armado y de la reconstrucción de historias que incluyan lo excluido, cuenten lo silenciado y revelen lo oculto.
On the Basis for Stumble Recovery Strategy Selection in Healthy Adults
Authors: Eveld Maura E. , King Shane T. , Vailati Leo G. , Zelik Karl E. , Goldfarb Michael
Published: February 2021

Healthy adults employ one of three primary strategies to recover from stumble perturbations—elevating, lowering, or delayed lowering. The basis upon which each recovery strategy is selected is not known. Though strategy selection is often associated with swing percentage at which the perturbation occurs, swing percentage does not fully predict strategy selection; it is not a physical quantity; and it is not strictly a real-time measurement. The objective of this work is to better describe the basis of strategy selection in healthy individuals during stumble events, and in particular to identify a set of real-time measurable, physical quantities that better predict stumble recovery strategy selection, relative to swing percentage. To do this, data from a prior seven-participant stumble experiment were reanalyzed. A set of biomechanical measurements at/after the perturbation were taken and considered in a two-stage classification structure to find the set of measurements (i.e., features) that best explained the strategy selection process. For Stage 1 (decision between initially elevating or lowering of the leg), the proposed model correctly predicted 99.0% of the strategies used, compared to 93.6% with swing percentage. For Stage 2 (decision between elevating or delayed lowering of the leg), the model correctly predicted 94.0% of the strategies used, compared to 85.6% with swing percentage. This model uses dynamic factors of the human body to predict strategy with substantially improved accuracy relative to swing percentage, giving potential insight into human physiology as well as potentially better informing the design of fall-prevention interventions.
Micro Solder Joint Reliability and Warpage Investigations of Extremely Thin Double-Layered Stacked-Chip Packaging
Authors: Lee Chang-Chun , Kao Kuo-Shu , Liu Hou-Chun , Hsieh Chia-Ping , Chang Tao-Chih
Published: February 2021

To overcome the limited operational speed for nanoscaled transistors, scaling electronic devices to small and thin packaging and high-density arrangements have become the technological mainstream in designing versatile packaging architectures. Among these, a promising candidate is a three-dimensional integrated circuit (3D-IC) package due to its excellent capability of heterogeneous integration. However, sequential reliability is a troublesome concern given the complex packaging structure, especially for the assembly of microsolder joints. To address this issue, we propose a double-layered, thin stacked chip package under the application of temperature cycling load. The packaging warpage and creep impact of SnAg microsolder joints on their fatigue lifespan are examined separately. Nonlinear material/geometry finite element analysis (FEA) is used on important designed factors, including the elastic modulus of underfill, chip thickness, and the radius and pitch of through silicon via (TSV). The simulated results indicate that the best fatigue lifetime of SnAg microsolder joint can be achieved at 10 μm of each chip thickness, 230 μm and 5 μm for TSV pitch and radius within the examined designed extent. Moreover, a hard underfill material requires consideration when the mounted chips thicken. Consequently, reliability significantly improves by dispersing thermomechanical stress/strain of the SnAg microjoints to neighboring underfill and related packaging components, especially for large TSV array spacing.
Custom Three-Dimensional-Printed CPAP Mask Development, Preliminary Comfort and Fit Evaluation
Authors: Ma Zhichao , Hyde Philip , Drinnan Michael , Munguia Javier
Published: February 2021

Obstructive sleep apnea (OSA) is an acute breathing disorder, which causes soft tissue inside the throat to collapse, thus blocking the airways while sleeping. This syndrome is usually treated by the supply of pressurized air delivered by a pump, which is connected to the patient via mouth and/or nose using a mask as an interface. While most of the literature on OSA is focused on the pressure pump and the therapy conditions (pressure, humidity, velocity, etc.) there has been an increased interest in the mask/interface as a key contributing factor to the treatment's effectiveness. Mask-related issues such as skin damage, allergic reactions, or air leaking due to poor fit can deter OSA patients from following this treatment. This study presents a preliminary evaluation of customized mask designs, which are tailored to specific wearer's facial contours. The development process includes the use of three-dimensional scanning/modeling/printing as an integrated workflow. Individual facial features have been digitally acquired and used to generate a custom device, which conforms to predefined facial landmarks of interest, which delimit the mask contour. A trial study was undertaken by recruiting two healthy volunteers for the fit and comfort evaluation of custom mask designs using a randomized fit test with a series of three-dimensional (3D) printed versus commercial standard mask. Results indicate that custom masks exhibit a higher level of comfort compared to conventional continuous positive airway pressure (CPAP) masks particularly on fit, contact pressure and comfort.
Axisymmetric Thermal Stresses of a Piezoelectric Poroelastic Circular Solid Plate
Authors: Abjadi Ali , Jabbari Mohsen , Khorshidvand Ahmad Reza
Published: February 2021

This paper presents the steady-state thermoelasticity solution for a circular solid plate is made of an undrained porous piezoelectric hexagonal material symmetry of class 6 mm. The porosities of the plate vary through the thickness; thus, material properties, except Poisson's ratio, are assumed as exponential functions of axial variable z in cylindrical coordinates. Having axisymmetric general form, external thermal and electrical loads are acted on the plate and the piezothermoelastic behavior of the plate is investigated. Using a full analytical method based on Bessel Fourier's series and separation of variables, the governing partial differential equations are derived. A formulation is given for the displacements, electric potential, thermal stresses, and electric displacements resulting from prescribed the general form of thermal, mechanical, and electric boundary conditions. Finally, the application of the derived formulas is illustrated by an example for a cadmium selenide solid, the results of which are presented graphically. Also, the effects of material property indexes, the porosity, and Skempton coefficients are discussed on the displacements, thermal stresses, electrical potential function, and electric displacements.
Thermal Analysis of a Solar Hybrid Dehydrator Designed for Uniform Multi-Product Drying
Authors: Munir Anjum , Mahmood Farhat , Amjad Waseem , Ahmad Syed Amjad
Published: February 2021

Thermal analysis was performed for a vertical cabinet solar hybrid dryer having a salient feature of the perforated sheet along its entire height to achieve uniform drying. The dryer was integrated with a solar collector and gas burner for a hybrid heating source. Experiments were performed using tomato at 55 °C with solar, gas, and dual (solar-gas) heating sources. Energy analysis showed that rates of energy utilization were found in ranges of 2.7–12.5 kW (dual), 3–13 kW (gas), and 2.9–12 kW (solar), and energy ratios were 13–56% (dual), 14–58% (gas), and 12–50% (solar). Exergy analysis showed that exergy losses were 2.1–5.0 kJ/kg (dual), 2.1–5.3 kJ/kg (gas), and 1.5–4.2 kJ/kg (solar) while exergy efficiencies found 33–70% (dual), 30–75% (gas), and 20–69% (solar). Based on higher values of exergetic factor and improvement potential rate (IP), it was found that optimization of heating source especially those consisting solar collector and heat exchanger (IP 1.93 kW) is required. The specific energies for the removal of product moisture and to dry the product were found 2.42, 2.72, 2.58 MJ/kg of water and 18.8, 21.2, 20.15 MJ/kg dried product for drying processes conducted under solar, gas, and dual (solar-gas) heating sources, respectively. For design optimization, a complete algorithm has been prepared for complete drying systems in terms of available energy and losses.
Analysis of Thermal Creep Effects on Fluid Flow and Heat Transfer in a Microchannel Gas Heating
Authors: Ramadan K. M. , Kamil Mohammed , Tlili I. , Qisieh O.
Published: February 2021

Thermal creep effects on fluid flow and heat transfer in a microchannel gas flow at low velocities are studied numerically. The continuity and Navier–Stokes equations in vorticity–stream function form, coupled with the energy equation, are solved, considering the thermal creep effect due to the longitudinal temperature gradient along the channel wall in addition to the combined effects of viscous dissipation, pressure work, axial conduction, shear work, and nonequilibrium conditions at the gas–wall interface. The governing equations are also solved without thermal creep, and comparisons between the two solutions are presented to evaluate the thermal creep effect on the flow field in the slip flow regime at relatively low Reynolds numbers. The results presented show that the thermal creep effect on both velocity and temperature fields become more significant as the Reynolds number decreases. Thermal creep effect on the velocity field also extends a longer distance downstream the channel as the Reynolds number decreases, hence increasing the hydrodynamics entrance length. Thermal creep can cause high positive velocity gradients at the upper channel wall for gas heating and hence reverse the flow rotation in the fluid layers adjacent to the wall. Thermal creep also results in a higher gas temperature in the developing region and higher heat exchange between the fluid and the channel wall in the entrance region. Thermal creep effect on heat exchange between the gas and the channel wall becomes more significant as the Knudsen number decreases.
Quaternion-Based Control of Acrobatic Quadrotor With Trajectory Following
Authors: Liu Haowen , Yang Bingen
Published: February 2021

For an unmanned aerial vehicle (UAV), its navigation in terrains can be quite challenging. To reach the destination within the required time, the maneuver of the quadrotor must behave aggressively. During this aggressive maneuvering, the quadrotor can experience singularities in the yaw-direction rotation. Thus, it is essentially important to develop a mathematical model and control method that can avoid singularities while enabling such an aggressive maneuver. In our previous effort, we demonstrated a vertical loop aggressive maneuver performed by a quadrotor UAV, which utilizes the controlled loop path following (CLPF) method. As found in this work, conventional modeling and tracking control method may not be good enough if specific requirements, such as fast coasting speed and sharp turns, are imposed. The numerical simulation by singularity-free modeling and the CLPF method enables a quadrotor to be operated in aggressive maneuverability with features like automatic flipping and precise trajectory following. The current research extends the maneuverability of a quadrotor by using a different and more capable control approach. More complex trajectories are used to test this new control method.

In this paper, a quadrotor is used to demonstrate the capability of the proposed control method in delivering an aggressive and singularity-free maneuver. A quaternion-based mathematical model of the quadrotor is derived to avoid the singularities of rotation during the aggressive maneuvers. At the same time, a new control method, namely the full quaternion differential flatness (FQDF) method, is developed for quadrotors to combat the requirement of a fast maneuver in three-dimensional space. The FQDF method, which makes use of full quaternion modeling and differential flatness, enables the quadrotor to react to the reference trajectory timely and to exhibit aggressive rotation without any singularity. Also, the singularities resulting from the heading direction can be resolved by a new algorithm. The FQDF method is compared with the reference literature’s methods and is tested in different trajectories from the ones in the previous studies. The numerical simulation demonstrates the aggressive maneuverability and computational efficiency of the proposed control method.
Parametric Resonance of a Beam Structure Induced by Groups of Oscillators in Periodic Movement
Authors: Gao Hao , Yang Bingen
Published: February 2021

Flexible structures carrying moving subsystems have various engineering applications, including cable transport, fast transit systems, and weapon systems. In some applications, the vibration of the supporting structure induced by successively moving subsystems can become significant and develop into parametric resonance. In study of the parametric resonance caused by moving subsystems, a conventional approach is to model subsystems as moving concentrated external loads, which leads to traditional resonance due to periodic excitation. In this paper, with consideration of the inertia effect and flexible coupling of subsystems, parametric resonance of a beam structure induced by groups of oscillators moving over it is investigated. Through a special formulation of sequential state equations, dynamic stability of the beam structure is predicted by eigenvalues of a time-domain mapping matrix. From numerical simulation, it shows that apart from the speed of oscillators that directly determines the characteristic period, the inertia and stiffness of the oscillators can also alter the parametric resonance conditions. This phenomenon cannot be captured with the conventional moving load assumption.
A Perspective on Tribology and Design
Authors: Suh Nam Pyo
Published: February 2021

Tribology — the science and engineering of friction, wear, and lubrication — enables the design of engineered systems with moving parts to achieve its intended functions. Many systems are so well designed already that they work as expected without requiring much attention, most of the time. However, when a system fails because of tribological problems, we may have a major disaster that may bring down the entire system, such as vehicles, engines, machinery, and even factories. Fortunately, the field of tribology has so far advanced, though often empirically, that many systems usually perform well. For instance, commercial airplanes are airborne for days without maintenance; windmills in the middle of the sea produce electricity for years; the tires of automobiles now last much longer than they used to, and machine tools make products for many months with minimal maintenance. Yet, there are still many unsolved tribology problems that require solutions. The ultimate goal of a tribological system is a life-time operation without any failure.

The quality of design determines the performance of tribological systems. Tribological failures of the system may be avoided through rational and creative design. In that sense, there is a symbiotic relationship between tribology and design. Many tribology problems encountered are often the result of poor system design. By properly designing the tribological system, potential failures caused by friction and wear can be avoided or minimized. Continuous testing of poorly designed tribological systems, which occurs in some cases, can be costly and with no noticeable improvements in the system performance. Since well-designed products yield immense benefits, the creation of tribological systems based on rational design should be pursued. The biggest source of tribological problems is the coupling of the functional requirements (FRs) that are introduced in the early stages of design. Attempts should be made to eliminate coupled tribological systems to improve their performance.
Reduced Order Model for Efficient Engineering Analysis
Authors: Zhong Allan X. , Zhang Haoyue
Published: February 2021

Engineering analysis of complex structures or mechanical systems typically involves contact with multiple components, large deformation, and material nonlinearity, which requires the application of nonlinear finite element methods. Despite the advancement of commercial software for finite element analysis (FEA), nonlinear FEA of a multi-component mechanical assembly will take hours to days, and even weeks to complete. It is highly desired to develop a reduced-order model for a family of complex structures that can reduce an original problems’ complexity and degree of freedom but has a reasonably small discrepancy with the full model and significantly reduces the computation time.

The typical approach to construct a reduced model includes 1) the response surface method via numerical design of experiments and, 2) the simplified physics approach. In this paper, it is proposed to develop a reduced model through the combination of simplified physics, dimensional analysis [1], and numerical design of experiments. The approach is applied to the construction of a reduced model for the analysis of a downhole plug [2]. The developed reduced model is verified by full-scale FEA models and validated through physical tests. The reduced model is implemented in a spreadsheet and takes only seconds to complete a calculation in contrast to hours using a full FEA model, enabling engineers’ quick evaluation of the corresponding designs.
Biomechanical Analysis of the Sensitivity of Brain Tissue Responses to FE Head Models in the Study of Impact-Induced TBI
Authors: Moghaddam Hesam S. , Rezaei Asghar , Ziejewski Mariusz , Karami Ghodrat
Published: February 2021

A numerical investigation is conducted on the injury-related biomechanical parameters of the human head under blunt impacts. The objective of this research is twofold; first to understand the role of the employed finite element (FE) head model — with its specific components, shape, size, material properties, and mesh size — in predicting tissue responses of the brain, and second to investigate the fidelity of pressure response in validating FE head models. Accordingly, two independently established and validated FE head models are impacted in two directions under two impact severities and their predicted responses in terms of intracranial pressure (ICP) and shear stress are compared. The coup-counter ICP peak values are less sensitive to head model, mesh size, and the brain material. In all cases, maximum ICPs occur on the outer surface, vanishing linearly toward the center of the brain. Hence, it is concluded that different head models may simply reproduce the results of ICP variations due to impact. Shear stress prediction, however, is mainly affected by the head model, direction and severity of impact, and the brain material.
Medium Frequency Vibration Analysis of Beam Structures Modeled by the Timoshenko Beam Theory
Authors: Zhang Yichi , Yang Bingen
Published: February 2021

Vibration analysis of complex structures at medium frequencies plays an important role in automotive engineering. Flexible beam structures modeled by the classical Euler-Bernoulli beam theory have been widely used in many engineering problems. A kinematic hypothesis in the Euler-Bernoulli beam theory is that plane sections of a beam normal to its neutral axis remain normal when the beam experiences bending deformation, which neglects the shear deformation of the beam. However, as observed by researchers, the shear deformation of a beam component becomes noticeable in high-frequency vibrations. In this sense, the Timoshenko beam theory, which describes both bending deformation and shear deformation, may be more suitable for medium-frequency vibration analysis of beam structures.

This paper presents an analytical method for medium-frequency vibration analysis of beam structures, with components modeled by the Timoshenko beam theory. The proposed method is developed based on the augmented Distributed Transfer Function Method (DTFM), which has been shown to be useful in various vibration problems. The proposed method models a Timoshenko beam structure by a spatial state-space formulation in the s-domain, without any discretization. With the state-space formulation, the frequency response of a beam structure, in any frequency region (from low to very high frequencies), can be obtained in an exact and analytical form. One advantage of the proposed method is that the local information of a beam structure, such as displacements, bending moment and shear force at any location, can be directly obtained from the space-state formulation, which otherwise would be very difficult with energy-based methods. The medium-frequency analysis by the augmented DTFM is validated with the FEA in numerical examples, where the efficiency and accuracy of the proposed method is present. Also, the effects of shear deformation on the dynamic behaviors of a beam structure at medium frequencies are illustrated through comparison of the Timoshenko beam theory and the Euler-Bernoulli beam theory.
A Proposed Method for Generating Lifetime Failure Data for Manufacturing Equipment: Validation With Bearings
Authors: Wescoat Ethan , Mears Laine
Published: February 2021

Digitization of manufacturing allows modeling and diagnosis of equipment failure, but training such systems is difficult without observations of failed states. This paper presents a method whereby failure data, from the baseline to the destruction case, is methodically generated to train machine health models. Creating failure classifiers and predictive models of manufacturing equipment suffer from two problems: training-data accuracy and data representation of lifetime machine failure modes of both components and systems. The Purposeful Failure Method aims to generate defect training data at both the component and system level, from initial defect to final destruction. Bearings are a validation case and are monitored from a healthy baseline state to a maximum-damage state by applying artificial damage. Bearings are used for validating the method, due to prior knowledge of failure progression, as well as their prevalent use. The generated data were analyzed to see if they matched expected failure phenomena. Preliminary results with the Purposeful Failure Method show promise for generating failure data for machine health models; continued work on validating the method on other components is justified.
Crash Analysis and Characterization of Bio Organic Fillers in the BFRP/Epoxy Composites
Authors: Velukkudi Santhanam Senthil Kumar , Sukumar Pullayikodi Srinil , Sampath Prakash , Doraiswamy Viswanathan , Manickam Dhanashekar
Published: February 2021

Basalt fiber/polymer composites have extensive applications in automotive, aerospace, defense, and sports goods. Addition of ash fillers has enhanced the properties of the composite material. Two types of bio-ash fillers namely, rice husk ash (RHA) and coconut fiber ash (CFA) particles were used. Ashes obtained from rice husk and coconut fiber are a good source of silica which when heated at higher temperature make them good fillers. Hand lay-up technique was used to fabricate composites in rectangular column shapes.

Characterization study of ash particles incorporated polymer composites were made by subjecting it to X-ray diffraction (XRD) measurement. The presence of filler particles reduces the voids ratio and enhances the strength of the composites. The load vs. displacement relations of the composite specimens were obtained from low velocity compression tests. Crashworthiness parameters like maximum force, average force and energy absorption were derived from the compression test results. Properties of plain basalt fiber composites were compared with that of BFRP/Epoxy composites with RHA and CFA fillers incorporated composites. The conclusion drawn from the test results was that the addition of ash filler particles in the composite have an improvement in crashworthiness of BFRP/Epoxy composite.
Developing a Thermally Actuated Soft Robot for Finger Rehabilitation
Authors: Taylor Mark , Westra Kees , Han Yen-Lin
Published: February 2021

As more Americans suffered from mobility impairments, rehabilitation becomes more and more important. Using robots for rehabilitation could potentially lower the barriers of rehabilitation for patients in need and increase the effectiveness of rehabilitation. This paper presented a proof-of-concept soft robot that could be used for finger rehabilitation. This soft robot can bend with heat-induced actuation without many external components. In this soft robot design, a phase changing material (PCM) is sealed in reservoirs inside an elastomer structure. As heat applied, the PCM begins to change phase from solid to liquid and the pressure inside the sealed reservoirs increases and “pushes” the elastomer structure to a different shape to create a “movement” of the robot. Depending on the locations of the reservoirs and methods the heat applied, the movements of the soft robot can be controlled with precision. Preliminary results successfully demonstrated a basic bending motion of this soft robot that mimics the human finger movement.
Effect of Thickness on Tube Deformation Mechanics During Low Pressure Tube Hydroforming Process Sequence Variation
Authors: Nikhare Chetan P.
Published: February 2021

A rapid increase in fuel consumption has been seen due to a sudden increase in the usage of automotive vehicles. This results in an increase in air pollution. Due to which a stricter regulation applied by the federal government to decrease air pollution. To escape from the pollution penalty innovations are been pushed. The industry has been looking at many innovative manufacturing processes like electric assisted manufacturing, single point incremental forming, high-speed forming, and many. All these innovative processes promise more uniform deformation and increases formability in the part. One such process is tube hydroforming for tubular parts. Tube hydroforming is the successful manufacturing process to create a variety of shapes using fluid pressure. The fluid medium can be water with preventive additives, oil, or viscous liquid. In this process, the tube was filled with the fluid medium and further pressurized to deform to various shapes. Tube hydroforming is categorized into three types: high pressure, pressure sequencing and low-pressure tube hydroforming. Ferrous and non-ferrous metals are formed using these processes. Due to uniform thinning in the formed part, the parts can be lower weight and thus proven to be the technology to create light-weight parts for automotive and aerospace industries to increase the fuel economy. Tube hydroforming has gained popularity due to its many advantages such as part consolidation, quality of the formed part and the possibility of unique shapes with indents or angles. This paper focuses on low-pressure tube hydroforming. In low-pressure tube hydroforming, during the closing of the die the tube is marginally pressurized to a fixed volume. The previous study which was published in IMECE2019 was focused on investigating the deformation mechanics of the tube due to variation in the process sequence during low-pressure tube hydroforming. In the second part of this research focus on how the thickness of the tube affect the deformation mechanics in the variation of the process sequence during low-pressure tube hydroforming. The circular tube was formed in a square shape. The four sides of die edges were considered as individual edges and the motion of these edges will be varied to achieve the final shape. The deformation mechanics in each condition was presented and analyzed. The relative thickness and strain distribution were studied. The change of tube profile pattern from the start to the end of the process were presented and compared. It was found that the deformation mechanics was mostly influenced by the variation of movement by punch and die side with no internal pressure case. The buckling in the tube wall also depended on which side of the die moves to deform the tube.
A Numerical Study of Laminar and Intermittently Turbulent Boundary Layer on an Oscillating Flat Plate Using Pseudo-Compressible RANS Model
Authors: Srivastava Shivank , Taravella Brandon M. , Akyuzlu Kazim M.
Published: February 2021

A numerical study was conducted to study the unsteady characteristics of incompressible boundary layer flows over an oscillating flat plate under laminar and intermittently turbulent flow conditions using pseudo-compressible Reynolds Averaged Navier-Stokes (RANS) model. The numerical study is carried out using an in-house code and a commercial CFD package (Fluent). Two equation (k-ε) turbulence closure model, modified near the wall, is used along with RANS equations to simulate intermittently turbulent flows. Fully Explicit-Finite Difference technique (FEFD) is employed to solve the governing differential equations. For validation purposes, the velocity fields predicted by the in-house code and commercial CFD package are compared to the one given by analytical solution to Stokes’ second problem for an oscillating flat plate. Numerical experiments were conducted for unsteady cases for Stokes’ Reynolds number corresponding to laminar and intermittently turbulent flows, respectively. Time dependent velocity profiles, shear stress distribution, turbulence properties during the accelerating and decelerating stages of oscillations are predicted. The above predictions are then compared to ones predicted by commercial CFD code. The velocity magnitudes predicted by the in-house code and commercial CFD code are within acceptable range for laminar and intermittently turbulent flow conditions.
A Finite-Element Based Framework for Transient Rotor Dynamic Simulations
Authors: Rajagopal Anurag , Mandal Dilip K.
Published: February 2021

Transient simulations play a key role in the analysis and subsequent design of structural components with one or more rotating parts. A framework is proposed to this effect, centered around the finite-element solver OptiStruct, consisting of a time integration scheme built on the Newmark family with an appropriate adaptive time-step control. The process accounts for a computationally efficient handling of nonlinearities that might arise through bearings and casings. This solution is detailed starting from the governing equations for transient rotor dynamics to the nuances of the time marching scheme, and this process is applied to a test case from which conclusions are drawn that might be of interest to practicing engineers. These conclusions include insights into enforced motion, operation at or near critical speeds, rotor damping and contact. This work is aimed at producing a user-friendly and robust tool and process for the practicing engineer to perform complex rotor dynamic analysis.
Unreinforced Flat Oval Duct Deformation Testing and Modeling
Authors: Paruchuri Avinash , Liu Jane , Idem Stephen
Published: February 2021

Unreinforced 12 in. × 23 in. (305 mm × 584 mm) galvanized steel flat oval ducts were tested to measure deformations when internal static gauge pressures were applied. The experiments were performed on spiral seam non-corrugated duct. Finite element models with discrete ring seams and an average wall thickness approach were utilized to represent the continuous spiral seam, and therein predict duct deflections at prescribed locations along the duct wall. Predicted deflections from the finite element models were tabulated and compared to experimental data. Satisfactory agreement between model predictions and test data were obtained from a non-linear finite element analysis that employed a simplified average wall thickness to characterize the spiral seam and duct wall. It is straightforward to implement the average wall thickness methodology in finite element modeling of duct deformation.
Design of a Compliant Jumping Robot With Passive Stabilizer
Authors: Hooper Joshua , Garcia Martin , Pena Paul , Tekes Ayse
Published: February 2021

This study presents the design and development of a compliant multi-link hopping mechanism actuated by a single DC motor. Two main design goals are to have a single piece designed main body for the jumping robot and a passive stabilizer to allow consecutive jumps. Mechanism consists of monolithically designed large deflecting main body incorporating the gears and initially curved flexure hinge. Due to the limitations of the design goal, revolute motion between top and bottom legs on the main body are realized by a compliant link which replaces the need of ball bearings. Also, continuous energy store and release during jumping is ensured by the same flexure hinges. Passive self-righting cage is attached to the bottom of the main body to maintain upright position both in landing and takeoff. The cage allows the center of mass to stay in the vertical plane to prevent tilting. During landing, cage absorbs the impact and allows the main body to roll to its initial configuration so that the robot can complete jumping. Mechanism parts including the cage are 3D printed using PETG. Design optimization of the body parts including the rigid legs and flexure hinges are analyzed both experimentally and analytically. Finite element analysis is performed to calculate the equivalent stiffness and natural frequency of the jumping robot and simplified mathematical model is derived using rigid body dynamics.
Numerical Study of the Pressure Drop in a Flame Arrestor Using a Porous Media Model
Authors: Farah Hoden A. , Lu Frank K. , Griffin Jim L.
Published: February 2021

A numerical study of the flow characteristics of a crimped flame arrestor element was conducted using a porous media model. The porous zone was modeled using the Forchheimer equation. The Forchheimer equation was incorporated into the governing conservation equations as a momentum sink. A small-scale crimped flame arrestor element was tested to determine the empirical coefficients in the Forchheimer equation. The numerical simulation result using this porous media model was verified using experimental data. The flow characteristics of a four-inch detonation flame arrestor with the same crimp design as the small-scale sample, was simulated using the porous media model. The numerical simulation flow data were compared against experimental values and agreed to within five percent. The method used to determine the Forchheimer coefficients and the experimental test setup are described in detail. The application of the Forchheimer equation into the governing flow equations is presented. The challenges and limitation of numerical studies in flame arrestors applications are discussed. The simplification gained by using the porous media model in flame arrestor numerical studies is presented.
Numerical Simulation of Detonation Propagation in Flame Arrestor Applications
Authors: Farah Hoden A. , Lu Frank K. , Griffin Jim L.
Published: February 2021

A detail numerical study of detonation propagation and interaction with a flame arrestor product was conducted. The simulation domain was based on the detonation flame arrestor validation test setup. The flame arrestor element was modeled as a porous zone using the Forchheimer equation. The coefficients of the Forchheimer equation were determined using experimental data. The Forchheimer equation was incorporated into the governing equations for axisymmetric reactive turbulent flow as a momentum sink. A 21-step elementary reaction mechanism with 10 species was used to model the stoichiometric oxyhydrogen detonation. Different cases of detonation propagation including inviscid, viscous adiabatic, and viscous with heat transfer and a porous zone were studied. A detail discussion of the detonation propagation and effect of the arrestor geometry, the heat transfer and the porous zone are presented. The inviscid numerical model solutions of the detonation propagation parameters are compared to one-dimensional analytical solution for verification. The viscous solutions are qualitatively compared to historical experimental data which shows very similar trend. The effect of the porous media parameters on shock transmission and re-initiation of detonation is presented.
Roller Trace Design in Multi-Pass Conventional Spinning Based on Cylindrical Part
Authors: Zixuan Li , Xuedao Shu , Bohai Ye , Jitai Wang
Published: February 2021

Conventional spinning is a kind of ancient revolving process which controls the product’s shape by roller trace design. It is also widely used in civil, military, automobile, aerospace and other fields. Unlike the power spinning process, the roller trace used in conventional spinning is complex. Both thickness uniformity and crack defects are affected by it. However, roller trace design is still based on experience without a solid theoretical basis. This paper simulated five different roller trace curves: involute curve, circular curve, Bezier curve, conchoids and line. Experiments using superalloy GH3030 were conducted in conjunction with a multi-pass conventional spinning simulation model. Blank thickness variations, mandrel and roller forces of different roller traces in the first pass are analyzed and assessed through the verification experiments. The results suggest that the curve trace parameters play a key role on the product thickness uniformity. And the distribution of Bezier and conchoid roller traces is more uniform than the other traces. The axial force of mandrel is a very important factor in the design of tool load capability. Larger roller feed ratio and proper roller traces can reduce the thinning which may avoid the cracks.
Dynamic Response Near Critical Build Heights in Ultrasonic Additive Manufacturing
Authors: Lyle Dennis M. , Gibert James M.
Published: February 2021

Previous ultrasonic additive manufacturing (UAM) models ignore higher-order modes or do not simulate the entire weld cycle when studying the dynamics near critical height-to-width ratios. A multi-modal model was developed to study the dynamics near critical build heights. The cause for the critical height-to-width ratio is dynamic interaction between the substrate and sonotrode. As the build height approaches the critical height-width-ratio, the current model predicts a local maxima in the transverse velocity response directly under the moving load (simulated sonotrode excitation). This is validated by experimental observations from previous studies. However, the current model predicts that as the height is further increased, a maximum in the transverse velocity response occurs at a height-to-width ratio of 1.2 due to resonance of higher-order modes. This result indicates that a single mode-approximation is insufficient to describe the dynamics near critical build heights. In studying the time response for an entire weld cycle (1.5 s), the amplitude of the velocity response in the transverse direction varies greatly. This indicates that assuming a quasi-static or analyzing a short time period in a model excludes potential dynamics during an entire weld cycle (on the order of 1 s).
Investigating CRAC Flow Distributions Using an Under-Floor Wind Turbine for Data Center Efficiency
Authors: Song Zhihang , Yue Qiang
Published: February 2021

The phenomena of over-cooling commonly exist in data center thermal environment, resulting in a substantial waste of energy. Previous study has proposed a solution that implementing a wind turbine in a raised-floor data center by which the over-provisioned airflow can be utilized. The impingement of the computer room air-conditioner (CRAC) flow on the plenum walls (e.g., the floor slab) may yield key causes of the energy losses. Therefore, studying the effects of the wind turbine on the CRAC flow in the data center is necessary. Here, the data center and wind turbine were simulated and modeled using Computational Fluid Dynamics (CFD) package. In this research, the numerical measure of the pressure distributed on the floor slab was numerically measured as key observations. The positioning and axial induction factors of the wind turbine were treated as the major research parameters. The consequence illustrates that implementing a wind turbine with well-tuned axial induction factor and operating height might be capable of effectively decreasing the CRAC flow impingement and increasing the turbine power efficiency. This research may provide meaningful references for effective wind turbine applications for data center energy efficiencies.
Dynamics Analysis of Truss Deployment Mechanism With Imperfect Joint Considering Input Fluctuation
Authors: Bai Zhengfeng , Zhao Jijun , Shi Xin
Published: February 2021

Modern spacecraft usually has large deployment structure, which consisting of plenty of joints could produce undesirable dynamic responses when considering clearances in joints and driving input fluctuation. However, in the dynamic performance analysis of space deployment mechanism, the clearances and input fluctuation are always ignored. In this study, the dynamic responses of a flexible planar scissor-like truss deployment mechanism with imperfect joint considering clearance and input fluctuation are investigated using computational methodology. First, the mathematic model of clearance joint is established. The revolute clearance joint is considered as force constraint and the joint components of an imperfect joint with clearance are modeled as contact bodies. The normal contact force model of clearance joint is established using a continuous contact force model considering energy loss. The friction effect is considered using a modified Coulomb friction model. Then, the dynamics performances of the flexible planar scissor-like truss deployment mechanism with imperfect joint considering clearance and input fluctuation are presented and discussed. Different case studies for the scissor-like truss deployment mechanism with clearance are investigated considering driving input fluctuation. The simulation results show that the dynamic characteristics of the mechanism with clearance joint are changed more obviously when considering driving input fluctuation. Therefore, investigation implies that dynamics responses of the truss deployment mechanism are much worse when considering clearance joint and input fluctuation, which indicates that driving input fluctuation leads to more obvious degradation of the dynamic performance of the truss deployment mechanism with imperfect joint.
Additive Manufacturing With Ceramics
Authors: Cline Kjetil , LaFlam Andrew , Smith Logan , Nowicki Margaret , Ku Nicholas
Published: February 2021

The purpose of this project is to design a device that improves the performance of a ceramic additive manufacturing (AM) 3D printer constructed by Army Research Labs (ARL). ARL modified a standard LulzBot Taz 6 3D printer to print a ceramic slurry mixture of Boron Carbide (B4C) and Silicon Carbide (SiC) instead of plastic filament. Since these compounds are often used in body armor, ARL has been observing the effects on properties when these components are 3D printed. The current printer utilizes an auger in the print head to receive and mix the B4C and SiC slurries and extrude the combined slurry out of the print nozzle. The current design is limited in its ability to thoroughly mix the slurries during the printing process. Therefore, team Concept Creators has designed an improved auger that will increase the mixedness of the slurries, thus increasing the print quality of the composite specimen.