bluuebunny/crossref_metadata_2025 huggingface dataset:
A Fast Analytic Method to Calculate the Dynamic Response of Railways Sleepers
Authors: Tran L.-H. , Hoang T. , Duhamel D. , Foret G. , Messad S. , Loaec A.
Published: July 2018

Existing analytical models for railway tracks consider only one rail supported by a continuous foundation or periodic concentrated supports (called the periodically supported beam). This paper presents an analytical model for a railway track which includes two rails connected by sleepers. By considering the sleepers as Euler–Bernoulli beams resting on a Kelvin–Voigt foundation, we can obtain a dynamic equation for a sleeper subjected to the reaction forces of the rails. Then, by using the relation between the rail forces and displacements from the periodically supported beam model, we can calculate the sleeper responses with the help of Green's function. The numerical applications show that the sleeper is in flexion where the displacement at the middle of the sleeper is greater than those at the rail seats. Moreover, the deformed shape of the sleeper is nonsymmetric when the loads on the two rails are different. The model result agrees well with measurements performed using instrumented sleeper in situ
Flow Visualization of Axisymmetric Impinging Jet on a Concave Surface
Authors: Shin Dong Hwan , Kim Yeonghwan , Kim Jin Sub , Kang Do Won , Sohn Jeong Lak , Lee Jungho
Published: July 2018

Flow visualization was performed to give a physical insight with vortical structures of an axisymmetric impinging jet on a concave surface. High-speed imaging was employed to get clear images with a laser light sheet illumination. An axisymmetric jet is issued into quasi-ambient air through a straight pipe nozzle with fully-developed velocity profile. A regular vertical pattern of an axisymmetric jet was observed with different flow entrainment rate. While an impinged jet turns to convert a wall jet along a concave surface, the flow interaction between the large-scale toroidal vortex and the concave surface was observed in the transition between the stagnation and wall jet zone. The ring-shaped wall eddies induced from a pair of toroidal vortices were also appeared to diverge into the radial direction along the concave surface. As the jet Reynolds number increases, small-scale vortices can be developed to a large-scale toroidal vortex. The location in which a large-scale toroidal vortex strikes is generally identical to the location where the secondary peak in heat transfer occurs. The frequency of large scale toroidal vortex on concave surface is found to be nearly similar as that of wall jet on flat surface. As the nozzle-to-target spacing (L/D) increases, it becomes shorter due to the loss of jet momentum. The flow behavior of axisymmetric impinging jet on a concave surface can be helpful to design the internal passage cooling for gas turbine blade.
Nucleate Boiling Comparison between Teflon-Coated Plain Copper and Cu-HTCMC in Water
Authors: Jun Seongchul , Kim Jin Sub , Lee Jungho , You Seung M.
Published: July 2018

The hydrophobic, Teflon-coated surfaces on plain copper and Cu-HTCMC (High temperature Thermally Conductive Microporous Coating) compared on pool boiling heat transfer of water. The HTCMC was created by sintering of copper powders with the average particle size of 67 µm and about 300 µm coating thickness that showed a good boiling heat transfer and the CHF enhancement from the previous study at saturation of water [1]. The Teflon-coated surfaces were created by coating of Amorphous Fluoroplastic (AF) 2400 resin on both plain copper and Cu-HTCMC. The static angles of both surfaces showed hydrophobic as about 120-130°. The departure bubble sizes created by merged bubbles of both surfaces are comparable as about 7 mm at 5 kW/m2 and the sizes are increased as heat flux increases. However, unlike to the plain surface, the smaller bubbles on Cu-HTCMC are not observed at the heat flux of 5 kW/m2 because the number of nucleation sites created in the porous structure are huge smaller bubbles are merged as soon as they grow from pores. As heat flux reaches the surfaces are covered by vapor film and reached the critical heat flux (CHF) at much lower heat fluxes compared to hydrophilic surfaces but the CHF values of Teflon-coated Cu-HTCMC is 640 kW/m2 and the value is more than tenfold higher than that of Teflon-coated plain copper.
The Application of Downhole Vibration Factor in Drilling Tool Reliability Big Data Analytics—A Review
Authors: Ren Yali , Wang Ning , Jiang Jinwei , Zhu Junxiao , Song Gangbing , Chen Xuemin
Published: July 2018

In the challenging downhole environment, drilling tools are normally subject to high temperature, severe vibration, and other harsh operation conditions. The drilling activities generate massive field data, namely field reliability big data (FRBD), which includes downhole operation, environment, failure, degradation, and dynamic data. Field reliability big data has large size, high variety, and extreme complexity. FRBD presents abundant opportunities and great challenges for drilling tool reliability analytics. Consequently, as one of the key factors to affect drilling tool reliability, the downhole vibration factor plays an essential role in the reliability analytics based on FRBD. This paper reviews the important parameters of downhole drilling operations, examines the mode, physical and reliability impact of downhole vibration, and presents the features of reliability big data analytics. Specifically, this paper explores the application of vibration factor in reliability big data analytics covering tool lifetime/failure prediction, prognostics/diagnostics, condition monitoring (CM), and maintenance planning and optimization. Furthermore, the authors highlight the future research about how to better apply the downhole vibration factor in reliability big data analytics to further improve tool reliability and optimize maintenance planning.
Interaction Model for “Shelled Particles” and Small-Strain Modulus of Granular Materials
Authors: Zhou Shun-hua , Guo Peijun , Stolle Dieter F. E.
Published: July 2018

The elastic modulus of a granular assembly composed of spherical particles in Hertzian contact usually has a scaling law with the mean effective pressure p as K∼G∼p1/3. Laboratory test results, however, reveal that the value of the exponent is generally around 1/2 for most sands and gravels, but it is much higher for reclaimed asphalt concrete composed of particles coated by a thin layer of asphalt binder and even approaching unity for aggregates consisting of crushed stone. By assuming that a particle is coated with a thin soft deteriorated layer, an energy-based simple approach is proposed for thin-coating contact problems. Based on the features of the surface layer, the normal contact stiffness between two spheres varies with the contact force following kn∼Fnm and m∈[1/3,  1], with m=1/3 for Hertzian contact, m=1/2 soft thin-coating contact, m=2/3 for incompressible soft thin-coating, and m=1 for spheres with rough surfaces. Correspondingly, the elastic modulus of a random granular packing is proportional to pm with m∈[1/3,  1].
Impact of the Lattice Angle on the Effective Properties of the Octet-Truss Lattice Structure
Authors: Abdelhamid Mohamed , Czekanski Aleksander
Published: July 2018

Cellular materials are found extensively in nature, such as wood, honeycomb, butterfly wings, and foam-like structures like trabecular bone and sponge. This class of materials proves to be structurally efficient by combining low weight with superior mechanical properties. Recent studies have shown that there are coupling relations between the mechanical properties of cellular materials and their relative density. Due to its favorable stretching‐dominated behavior, continuum models of the octet‐truss were developed to describe its effective mechanical properties. However, previous studies were only performed for the cubic symmetry case, where the lattice angle θ=45 deg. In this work, we study the impact of the lattice angle on the effective properties of the octet-truss: namely, the relative density, effective stiffness, and effective strength. The relative density formula is extended to account for different lattice angles up to a higher-order of approximation. Tensor transformations are utilized to obtain relations of the effective elastic and shear moduli, and Poisson's ratio at different lattice angles. Analytical formulas are developed to obtain the loading direction and value of the maximum and minimum specific elastic moduli at different lattice angles. In addition, tridimensional polar representations of the macroscopic strength of the octet‐truss are analyzed for different lattice angles. Finally, collapse surfaces for plastic yielding and elastic buckling are investigated for different loading combinations at different lattice angles. It has been found that lattice angles lower than 45 deg result in higher maximum values of specific effective elastic moduli, shear moduli, and strength.
Numerical Simulations of Natural Convective Heat Transfer in Vertical Concentric and Eccentric Annular Channels
Authors: Busedra A. A. , Tavoularis S.
Published: July 2018

Natural convective heat transfer in a concentric and a highly eccentric, vertical, open ended, annular channel has been investigated numerically. The inner to outer diameter ratio was 0.61, and the height to hydraulic diameter ratio was 18:1. Three heating modes were considered, all having uniform heat flux applied to one or both of the two walls, while the unheated wall was kept adiabatic. The wall temperature distribution, mass flow rate, and midchannel Nusselt number for the case with both walls heated were found to be in excellent agreement with available experimental results. For the same heating conditions, the heat transfer rate in the concentric annular channel was found to be greater than that in the highly eccentric channel, while the mass flow rate was higher in the eccentric channel. A novel finding for the eccentric channel was that the location of maximum velocity was intermediate between the narrow and wide gaps. Another novel observation, which was attributed to radiation effects, was that the fluid temperature in the wide gap region was lower than that of an adiabatic wall. The paper contains additional observations that would be of interest to designers of systems containing annular channels.
Discussion: “Homogeneous–Heterogeneous Reactions in Boundary-Layer Flow of a Nanofluid Near the Forward Stagnation Point of a Cylinder” (Zhao, Q., Xu, H., and Tao, L., 2017, ASME J. Heat Transfer, 139(3), p. 034502)
Authors: Pantokratoras Asterios
Published: July 2018

The present discussion concerns some doubtful results included in the discussed paper.
Multivariable Proportional-Integral-Derivative Controller Tuning Via Linear Matrix Inequalities Based on Minimizing the Nonconvexity of Linearized Bilinear Matrix Inequalities
Authors: Merrikh-Bayat Farshad
Published: July 2018

This paper proposes an iterative linear matrix inequality (LMI) method for tuning the parameters of multi-input multi-output (MIMO) proportional–integral–derivative (PID) controllers. The proposed method calculates the parameters of controller such that the singular values (SVs) of the sensitivity function are shaped according to the given weight function. For this purpose, first using bounded real lemma (BRL), this problem is represented as a bilinear matrix inequality (BMI) where one of the matrix variables is the variable of Lyapunov equation and the other is structured and contains the matrices of the state-space representation of the controller. This BMI is solved approximately using a novel iterative procedure which linearizes the BMI around an initial solution to arrive at an LMI. The point around which the BMI is linearized is updated automatically at each iteration and the linearized BMI has the nice property that it is obtained by minimizing the amplitude of nonconvex terms.
Effect of Structural State and Surface Finishing on Corrosion Behavior of 1.4970 Austenitic Steel at 400 and 500 °C in Flowing Pb-Bi Eutectic With Dissolved Oxygen
Authors: Tsisar Valentyn , Schroer Carsten , Wedemeyer Olaf , Skrypnik Aleksandr , Konys Jürgen
Published: July 2018

The effect of structural state (solution annealed (SA) and after 40% cold work (CW)) and surface finishing (turning, grinding, and polishing) on the corrosion behavior of austenitic 1.4970 (15-15 Ti) steel in flowing (2 m/s) Pb-Bi eutectic containing 10−7 mass% dissolved oxygen at 400 °C and 10−6 mass% O at 500 °C is investigated. At 400 °C for ∼13,000 h, the corrosion losses are minor for steel in both structural states and for surfaces finished by turning and grinding—a thin Cr-based oxide film is formed. In contrast, the polished surface showed initiation of solution-based corrosion attack with the formation of iron crystallites and preferential propagation along the grain boundaries. The depth of corrosion attack does not exceed 10 μm after ∼13,000 h. At 500 °C for 2000 h, the samples in both structural states showed general slight oxidation. Cold-worked steel underwent a severe groove-type and pit-type solution-based attack of 170 μm in maximum depth, while the SA sample showed only sporadic pit-type corrosion attack to the depth of 45 μm in maximum.
An Analytical Model for Nonhydrostatic Sheet Metal Bulging Process by Means of Polymer Melt Pressure
Authors: Farahani Saeed , Arezoodar Alireza Fallahi , Dariani Bijan Mollaei , Pilla Srikanth
Published: July 2018

In this paper, a theoretical approach to model free deformation of sheet metal via polymer injection pressure is presented. It is a general methodology that can be applied for any situation where a nonuniform pressure distribution is responsible for free deformation of sheet metal within a circular cavity. This approach is composed of two iterative approximation loops. In the outer loop, the radius of curvature at the tip of dome shape was optimized based on the boundary condition at the edge of clamped area while in the inner successive loop, principal stresses determined from plasticity theories were used to satisfy the equilibrium equations. While forming sheet metal via polymer injection is a revolutionary yet complex process, its modeling is challenging. Hence, before implementing this general approach to this process, the modeling methodology as such necessitates a simplified solution for melt flow analysis to obtain a pressure distribution encompassing the entire cavity. To evaluate the proposed model, a customized experimental setup was designed and fabricated, which allows sheet metal bulging with the plastic injection. The deformation of the AA1100-O sheet was investigated during the injection of the polypropylene–olefin compound. The comparison of the theoretical and experimental results shows that the general approach formulated here can be successfully applied to predict the surface strains and thickness distributions with maximum error of 6% while the deformed geometry remains within ±0.35 mm deviation in the final deformation stage.
Reproducibility of Experiments With Swirling Flow: Numerical Prediction With Polynomial Chaos
Authors: van Hove Alouette , Skov Lasse N. , Hinz Denis F.
Published: July 2018

Achieving good reproducibility in fluid flow experiments can be challenging, in particular in scenarios where the experimental boundary conditions are obscure. We use computational uncertainty quantification (UQ) to evaluate the influence of uncertain inflow conditions on the reproducibility of experiments with swirling flow. Using a nonintrusive polynomial chaos method in combination with a computational fluid dynamics (CFD) code, we obtain the expectation and variance of the velocity fields downstream from symmetric and asymmetric swirl disturbance generators. Our results suggest that the flow patterns downstream from the asymmetric swirl disturbance generator are more reproducible than the flow patterns downstream from the symmetric swirl disturbance generator. This confirms that the inherent breaking of symmetry eliminates instability mechanisms in the wake of the disturber, thereby creating more stable swirling patterns that make the experiments more reproducible.
Transforming Optimal Tetrahelices Between the Boerdijk–Coxeter Helix and a Planar-Faced Tetrahelix
Authors: Read Robert L.
Published: July 2018

The Boerdijk–Coxeter helix (BC helix, or tetrahelix) is a face-to-face stack of regular tetrahedra forming a helical column. Treating the edges of these tetrahedra as structural members creates an attractive and inherently rigid space frame, and therefore is interesting to architects, mechanical engineers, and roboticists. A formula is developed that matches the visually apparent helices forming the outer rails of the BC helix. This formula is generalized to a formula convenient to designers. Formulae for computing the parameters that give proven edge-length minimax-optimal tetrahelices are given, allowing transformation through a continuum of optimum tetrahelices of varying curvature while maximizing regularity. The endpoints of this continuum are the BC helix and a structure of zero curvature, the equitetrabeam. Only one out of three members in the system change their length to transform the structure into any point in the continuum. Numerically finding the rail angle from the equation for pitch allows optimal tetrahelices of any pitch to be designed. An interactive tool for such design and experimentation is provided. A formula for the inradius of optimal tetrahelices is given. The continuum allows a regular Tetrobot supporting a length change of less than 16% in the BC configuration to untwist into a hexapodal or n-podal robot to use standard gaits.
Minimum Base Attitude Disturbance Planning for a Space Robot During Target Capture
Authors: Hu Jingchen , Wang Tianshu
Published: July 2018

This paper presents a method to minimize the base attitude disturbance of a space robot during target capture. First, a general dynamic model of a free-floating space robot capturing a target is established using spatial operator Algebra, and a simple analytical formula for the base angular velocity change during the impact phase is obtained. Compared with the former models proposed in the literature, this model has a simpler form, a wider range of applications, and O(n) computation complexity. Second, based on the orthogonal projection matrix lemma, we propose the generalized mass Jacobian matrix (GMJM) and find that the base angular velocity change is a constant multiple of the component which the impact impulse projects to the column space of the GMJM. Third, a new concept, the base attitude disturbance ellipsoid (BADE), is proposed to express the relationship between the base attitude disturbance and the impact direction. The impact direction satisfying the minimum base attitude disturbance can be straightforwardly obtained from the BADE. In particular, for a planar space robot, we draw the useful conclusion that the impact direction unchanged base attitude must exist. Furthermore, the average axial length of the BADE is used as a measurement to illustrate the average base attitude disturbance under impact impulses from different directions. With this measurement, the desired pre-impact configuration with minimum average base attitude disturbance can be easily determined. The validity and the efficiency of this method are verified using a three-link planar space robot and a 7DOF space robot.
Output Feedback Control Surface Positioning With a High-Order Sliding Mode Controller/Estimator: An Experimental Study on a Hydraulic Flight Actuation System
Authors: Şener Kaya Ali , Zeki Bilgin Mehmet
Published: July 2018

In this paper, an output feedback sliding mode position controller/estimator scheme is proposed to control an single input single output (SISO) system subject to bounded nonlinearities and parametric uncertainties. Various works have been published addressing the theoretical effectiveness of the third-order sliding mode control (3-SMC) in terms of chattering alleviation and controller robustness. However, the application of 3-SMC with a feedback estimator to a flight actuators has not been treated explicitly. This is due to the fact that the accurate full state estimation is required since SMCs performance can be severely degraded by measurement or estimation noise. Aerodynamic control surface actuators in air vehicles mostly employ linear position controllers to achieve guidance and stability. The main focus of the paper is to experimentally demonstrate the stability and positioning performance of a third-order SMC applied to a class of system with high relative degree and bounded parametric uncertainties. The performance of the closed-loop system is also compared with a lower level SMC and classical controller to show the effectiveness of the algorithm. Realization of the proposed algorithm from an application perspective is the main target of this paper and it demonstrates that a shorter settling time and higher control action attenuation can be achieved with the proposed strategy.
Design and Experimental Validation of a Large-Displacement Constant-Force Mechanism
Authors: Li Ming , Cheng Wei
Published: July 2018

This paper presents the design and experimental validation of a passive large-displacement constant-force mechanism (CFM). Unlike previous studies, without using extra stiffness-compensation components and active control devices, the presented CFMs can utilize the interaction between the components of a cam and sliders to directly achieve the constant-force characteristic over the entire flexibly designed large displacement once the cam is advisably designed with the consideration of friction effect by using the profile curve identification method (PCIM). Corresponding to the different requirements of conventional and extreme engineering environments, two versions of the mechanism, the basic and ultra-large-displacement CFM models are proposed, respectively. The basic version is designed directly based on the PCIM, whereas the ultra-large-displacement CFM is proposed using the relay-mode action of the multistage sliders. According to the theoretical design method, we design and fabricate two corresponding CFM prototypes. Validation experiments are then conducted, and the results show that both of the prototypes can satisfy the design requirements and possess large-displacement constant-force characteristics owing to the consistency of experimental and design data. Therefore, the proposed design theory for the cam-based large-displacement CFMs is validated and the designed CFMs will have extensive applications in relevant fields for force regulation and overload protection.
Rigid Foldability of Generalized Triangle Twist Origami Pattern and Its Derived 6R Linkages
Authors: Feng Huijuan , Peng Rui , Ma Jiayao , Chen Yan
Published: July 2018

Rigid origami is a restrictive form of origami that permits continuous motion between folded and unfolded states along the predetermined creases without stretching or bending of the facets. It has great potential in engineering applications, such as foldable structures that consist of rigid materials. The rigid foldability is an important characteristic of an origami pattern, which is determined by both the geometrical parameters and the mountain-valley crease (M-V) assignments. In this paper, we present a systematic method to analyze the rigid foldability and motion of the generalized triangle twist origami pattern using the kinematic equivalence between the rigid origami and the spherical linkages. All schemes of M-V assignment are derived based on the flat-foldable conditions among which rigidly foldable ones are identified. Moreover, a new type of overconstrained 6R linkage and a variation of doubly collapsible octahedral Bricard are developed by applying kirigami technique to the rigidly foldable pattern without changing its degree-of-freedom. The proposed method opens up a new way to generate spatial overconstrained linkages from the network of spherical linkages. It can be readily extended to other types of origami patterns.
Computational Fluid Dynamics Reproduction of Nonlinear Loads on a Vertical Column During Extreme Irregular Wave Events
Authors: Bachynski Erin E. , Pákozdi Csaba , Östman Anders , Stansberg Carl Trygve
Published: July 2018

Recently, a method for numerical reproduction of measured irregular wave events has been developed. The measured motion of the wave maker flaps defines the wave kinematics at the boundary of the numerical simulation in order to generate the waves. When such data are not available, the control signal of the wave maker can, instead, be generated from a given free surface elevation following the same procedure as in model tests. This procedure is applied to a model test case with extreme irregular wave events and resulting nonlinear global wave loads on a vertical cylinder, focusing on higher-order ringing excitation. The purpose of the investigation is twofold: (1) to validate the wave reconstruction procedure and (2) to validate the resulting computational fluid dynamics (CFD) ringing loads with the given waves. In order to better understand the frequency content in the CFD-generated loads, wavelet analysis as well as the response of a single degree-of-freedom (SDOF) oscillator is examined and compared with the corresponding results for the third-order wave forcing based on the MacCamy–Fuchs (MF) and Faltinsen, Newman, Vinje (FNV) formulations. The results show generally good agreement between CFD and experiment both in the waves and in the loads; discrepancies found in the loads mainly originate from corresponding uncertainties in the wave reconstruction. Wave breaking may be one source of uncertainty. The MF + FNV formulation showed reasonable prediction of the maximum responses of an SDOF oscillator, but could not capture the loads well at all of the important frequencies.
Development of a Cross-Coupled Robust Controller for a Multi-Axis Micromachining System
Authors: Karagoz Mumtazcan , Cakmakci Melih
Published: July 2018

In the current era of miniaturization for complex, ubiquitous, and energy efficient systems, micromanufacturing had become one of the most popular fields for engineering development. This paper introduces a modular robust cross-coupled controller design structure applied to a three axis micromachining system that can be extended to more axis systems and configurations. In order to develop a robust controller that can withstand the disturbances due to tool–workpiece interactions, a dynamic model of the whole system is needed. Developing control-oriented models for micromachining systems can be challenging. Using the sum of sines identification input, essential nonlinearities including the effects of assembly and slider orientation are included. Verification data show that these transfer function models represent the physical system satisfactorily while avoiding an over-fit. Using the transfer functions from the identified model, a controller structure with robust axis controllers with cross-coupled control (CCC) are developed and fine-tuned with simulations. Machining experiments are also done in order to compare the performance of the proportional-integral-derivative control design, an adaptive robust controller (ARC, both from earlier work in the literature) and the new H∞ robust controller. According to results of experiments, the new robust controller showed the best tracking and contouring performance with improved surface quality due to reduced oscillations.
An Assessment of Shock-Disturbances Interaction Considering Real Gas Effects
Authors: Hejranfar K. , Rahmani S.
Published: July 2018

In this study, a theoretical analysis is performed to assess the interaction of freestream disturbances with a plane normal shock considering real gas effects. Such effects are important in a field with high velocities and high temperatures. To perform the theoretical analysis, the downstream disturbances field is expressed as a mathematical function of the upstream one by incorporating real gas effects in the formulation. Here, the linearized one-dimensional perturbed unsteady Euler equations are used for the classification of the downstream/upstream disturbances field and the linearized one-dimensional perturbed Rankine–Hugoniot equations are applied to provide a relationship between the disturbances field of two sides of the shock. To incorporate real gas effects in the formulation, real gas relations and equilibrium air curve-fits are used in the resulting system of equations. The general formulation presented here may be simplified to derive Morkovin's formulation by the perfect gas assumption. The magnitudes of downstream disturbances field resulting from different types of upstream disturbances field (entropy wave and fast/slow acoustic waves) with the shock are expressed by appropriate analytical relations. Results for different disturbance variables are presented for a wide range of upstream Mach number considering real gas effects and compared with those of the perfect gas and some conclusions are made. The effects of the presence of body are also studied theoretically and the analytical relations for the magnitude of the pressure disturbance at the body for different types of upstream disturbances field considering real gas effects are provided and their results are presented and discussed.
Residual Stresses in Titanium Spinal Rods: Effects of Two Contouring Methods and Material Plastic Properties
Authors: Berti Francesca , La Barbera Luigi , Piovesan Agnese , Allegretti Dario , Ottardi Claudia , Villa Tomaso , Pennati Giancarlo
Published: July 2018

Posterior spinal fixation based on long spinal rods is the clinical gold standard for the treatment of severe deformities. Rods need to be contoured prior to implantation to fit the natural curvature of the spine. The contouring processes is known to introduce residual stresses and strains which affect the static and fatigue mechanical response of the implant, as determined through time- and cost-consuming experimental tests. Finite element (FE) models promise to provide an immediate understanding on residual stresses and strains within a contoured spinal rods and a further insight on their complex distribution. This study aims at investigating two rod contouring strategies, French bender (FB) contouring (clinical gold standard), and uniform contouring, through validated FE models. A careful characterization of the elastoplastic material response of commercial implants is led. Compared to uniform contouring, FB induces highly localized plasticizations in compression under the contouring pin with extensive lateral sections undergoing tensile residual stresses. The sensitivity analysis highlighted that the assumed postyielding properties significantly affect the numerical predictions; therefore, an accurate material characterization is recommended.
Acute Surgical Injury Alters the Tensile Properties of Thoracolumbar Fascia in a Porcine Model
Authors: Nelson-Wong Erika , Glinka Michal , Noguchi Mamiko , Langevin Helene , Badger Gary J. , Callaghan Jack P.
Published: July 2018

Recent work utilizing ultrasound imaging demonstrated that individuals with low back pain (LBP) have increased thickness and decreased mobility of the thoracolumbar fascia (TLF), an indication that the TLF may play a role in LBP. This study used a porcine injury model (microsurgically induced local injury)—shown to produce similar results to those observed in humans with LBP—to test the hypothesis that TLF mechanical properties may also be altered in patients with LBP. Perimuscular TLF tissue was harvested from the noninjured side of vertebral level L3-4 in pigs randomized into either control (n = 5) or injured (n = 5) groups. All samples were tested with a displacement-controlled biaxial testing system using the following protocol: cyclic loading/unloading and stress relaxation tests at 25%, 35%, and then 45% of their resting length. Tissue anisotropy was also explored by comparing responses to loading in longitudinal and transverse orientations. Tissues from injured pigs were found to have greater stretch–stretch ratio moduli (measure of tissue stiffness), less energy dissipation, and less stress decay compared to tissues from control pigs. Responses across these variables also depended on loading orientation. Clinical significance: these findings suggest that a focal TLF injury can produce impairments in tissue mechanical properties away from the injured area itself. This could contribute to some of the functional abnormalities observed in human LBP.
On Establishing Buckling Knockdowns for Imperfection-Sensitive Shell Structures
Authors: Gerasimidis S. , Virot E. , Hutchinson J. W. , Rubinstein S. M.
Published: July 2018

This paper investigates issues that have arisen in recent efforts to revise long-standing knockdown factors for elastic shell buckling, which are widely regarded as being overly conservative for well-constructed shells. In particular, this paper focuses on cylindrical shells under axial compression with emphasis on the role of local geometric dimple imperfections and the use of lateral force probes as surrogate imperfections. Local and global buckling loads are identified and related for the two kinds of imperfections. Buckling loads are computed for four sets of relevant boundary conditions revealing a strong dependence of the global buckling load on overall end-rotation constraint when local buckling precedes global buckling. A reasonably complete picture emerges, which should be useful for informing decisions on establishing knockdown factors. Experiments are performed using a lateral probe to study the stability landscape for a cylindrical shell with overall end rotation constrained in the first set of tests and then unconstrained in the second set of tests. The nonlinear buckling behavior of spherical shells under external pressure is also examined for both types of imperfections. The buckling behavior of spherical shells is different in a number of important respects from that of the cylindrical shells, particularly regarding the interplay between local and global buckling and the post-buckling load-carrying capacity. These behavioral differences have bearing on efforts to revise buckling design rules. The present study raises questions about the perspicacity of using probe force imperfections as surrogates for geometric dimple imperfections.
Engineered Airway Models to Study Liquid Plug Splitting at Bifurcations: Effects of Orientation and Airway Size
Authors: Copploe Antonio , Vatani Morteza , Amini Rouzbeh , Choi Jae-Won , Tavana Hossein
Published: July 2018

Delivery of biological fluids, such as surfactant solutions, into lungs is a major strategy to treat respiratory disorders including respiratory distress syndrome that is caused by insufficient or dysfunctional natural lung surfactant. The instilled solution forms liquid plugs in lung airways. The plugs propagate downstream in airways by inspired air or ventilation, continuously split at airway bifurcations to smaller daughter plugs, simultaneously lose mass from their trailing menisci, and eventually rupture. A uniform distribution of the instilled biofluid in lung airways is expected to increase the treatments success. The uniformity of distribution of instilled liquid in the lungs greatly depends on the splitting of liquid plugs between daughter airways, especially in the first few generations from which airways of different lobes of lungs emerge. To mechanistically understand this process, we developed a bioengineering approach to computationally design three-dimensional bifurcating airway models using morphometric data of human lungs, fabricate physical models, and examine dynamics of liquid plug splitting. We found that orientation of bifurcating airways has a major effect on the splitting of liquid plugs between daughter airways. Changing the relative gravitational orientation of daughter tubes with respect to the horizontal plane caused a more asymmetric splitting of liquid plugs. Increasing the propagation speed of plugs partially counteracted this effect. Using airway models of smaller dimensions reduced the asymmetry of plug splitting. This work provides a step toward developing delivery strategies for uniform distribution of therapeutic fluids in the lungs.
Augmented and Virtual Reality for Underground Facilities Management
Authors: Soria Gregorio , Ortega Alvarado L. M. , Feito Francisco R.
Published: July 2018

Augmented reality (AR) has experienced a breakthrough in many areas of application thanks to cheaper hardware and a strong industry commitment. In the field of management of urban facilities, this technology allows virtual access and interaction with hidden underground elements. This paper presents a new approach to enable AR in mobile devices such as Google Tango, which has specific capabilities to be used outdoors. The first objective is to provide full functionality in the life-cycle management of subsoil infrastructures through this technology. This implies not only visualization, interaction, and free navigation, but also editing, deleting, and inserting elements ubiquitously. For this, a topological data model for three-dimensional (3D) data has been designed. Another important contribution of the paper is getting exact location and orientation performed in only a few minutes, using no additional markers or hardware. This accuracy in the initial positioning, together with the device sensing, avoids the usual errors during the navigation process in AR. Similar functionality has also been implemented in a nonubiquitous way to be supported by any other device through virtual reality (VR). The tests have been performed using real data of the city of Jaén (Spain).
Modeling and Applications of a Family of Five-Degree-of-Freedom Parallel Mechanisms With Kinematic and Actuation Redundancy
Authors: Kang Long , Kim Wheekuk , Yi Byung-Ju
Published: July 2018

This paper introduces a family of statically balanced five-degree-of-freedom (5DOF) parallel mechanisms (PMs) with kinematic and actuation redundancy. Moving platforms of this family of PMs can provide 4DOF Schönflies motion. Three applications are considered in this work. The first and second applications use kinematic redundancy to avoid parallel singularities and perform an auxiliary grasping task in sequence. The third application incorporates actuation redundancy into a kinematically redundant manipulator to increase the load-carrying capacity. Screw theory was used to derive the Jacobian of the 5DOF PM with kinematic and actuation redundancy. Parallel singularities can be completely alleviated by controlling the orientation of the redundant link, thereby obtaining a large rotational workspace, and actuation redundancy increases the load-carrying capacity. Using a commercially available multibody dynamic simulator, an example of trajectory was performed to illustrate the large rotational workspace of the first and second applications and compare the Euclidean norm of the vector of actuation torque of nonredundant and redundant PMs. Three prototypes were also developed to demonstrate the output motion and static balancing property.
Oil/Water Emulsions Stabilized by Nanoparticles of Different Wettabilities
Authors: Gavrielatos Ilias , Dabirian Ramin , Mohan Ram S. , Shoham Ovadia
Published: July 2018

A state-of-the-art, portable dispersion characterization rig (P-DCR) is used to investigate the effect of nanoparticles (NP) on oil-water emulsion formation and stabilization. Spherical silica NP of different wettabilities were used to investigate their effect on separation kinetics of solid stabilized emulsions in terms of solid particle concentration, wettability, initial dispersion phase, water-cut, and shearing time. The main findings of the study include the following: NP, even at concentrations as low as 0.005% or 0.01% (by weight), can significantly increase separation time of oil/water emulsions from a few minutes to several hours or even days. The P-DCR is recommended as an effective inline tool to measure emulsion stability in the field.
Thomas/Alford Force on a Partial-Admission Turbine for the Rocket Engine Turbopump
Authors: Yada Kazuyuki , Uchiumi Masaharu , Funazaki Ken-ichi
Published: July 2018

This paper describes an imbalanced torque force, called the Thomas/Alford force, of a partial-admission turbine for the rocket engine turbopump. The Thomas/Alford force is a destabilizing force imposed on the rotor that could cause rotor dynamic instability. This, in turn, may impair stable operation of the rocket engine and trigger mission failure. Such destabilizing force should be avoided as its characteristics have not been discussed in detail. In this study, Thomas/Alford forces for typical symmetric partially open/closed nozzle patterns with an open/closed ratio are analyzed. For such an open/closed ratio, it was determined that the Thomas/Alford force varied with the whirling angle, and whether the open/closed ratio may impair stable operation and reliability of the rocket engine turbopump is contingent on avoiding such fluctuation. The reason for such fluctuation was investigated by mathematical methodology, which was then extended to determine a general rule of patterns for rocket engine designers. This rule would, thus, prove useful in the future development of a partial-admission turbine for a rocket engine turbopump.
Computational Fluid Dynamics Study of Separated Flow Over a Three-Dimensional Axisymmetric Hill
Authors: Chitta Varun , Jamal Tausif , Keith Walters D.
Published: July 2018

This paper investigates the ability of computational fluid dynamics (CFD) simulations to accurately predict the turbulent flow separating from a three-dimensional (3D) axisymmetric hill using a recently developed four-equation eddy-viscosity model (EVM). The four-equation model, denoted as k–kL–ω–v2, was developed to demonstrate physically accurate responses to flow transition, streamline curvature, and system rotation effects. The model was previously tested on several two-dimensional cases with results showing improvement in predictions when compared to other popularly available EVMs. In this paper, we present a more complex 3D application of the model. The test case is turbulent boundary layer flow with thickness δ over a hill of height 2δ mounted in an enclosed channel. The flow Reynolds number based on the hill height (ReH) is 1.3 × 105. For validation purposes, CFD simulation results obtained using the k–kL–ω–v2 model are compared with two other Reynolds-averaged Navier–Stokes (RANS) models (fully turbulent shear stress transport k–ω and transition-sensitive k–kL–ω) and with experimental data. Results obtained from the simulations in terms of mean flow statistics, pressure distribution, and turbulence characteristics are presented and discussed in detail. The results indicate that both the complex physics of flow transition and streamline curvature should be taken into account to significantly improve RANS-based CFD predictions for applications involving blunt or curved bodies in a low Re turbulent regime.
Fabrication and Wettability Analysis of Hydrophobic Stainless Steel Surfaces With Microscale Structures From Nanosecond Laser Machining
Authors: Cui Cong , Duan Xili , Collier Brandon , Poduska Kristin M.
Published: July 2018

In this work, nanosecond laser machining is used to fabricate hydrophobic 17-4 PH stainless steel surfaces with microscale and submicron structures. Four surface structures were designed, with microscale channels and pillars (100 μm pitch size) of uniform heights (100 μm) or alternating heights (between 100 μm and 50 μm). During fabrication, the high-power laser beams also created submicron features on top of the microscale ones, leading to hierarchical, multiscale surface structures. Detailed wettability analysis was conducted on the fabricated samples. Measured static contact angles of water on these surfaces are over 130 deg without any coating, compared to ∼70 deg on the original steel surface before laser machining. Slightly lower contact angle hysteresis was also observed on the laser machined surfaces. Overall, these results agree with a simple Cassie–Baxter model for wetting that assumes only fractional surface area contact between the droplet and the surface. This work demonstrates that steel surfaces machined with relatively inexpensive nanosecond laser can achieve excellent hydrophobicity even with simple microstructural designs.
Damage Detection Using Dissimilarity in Phase Space Topology of Dynamic Response of Structure Subjected to Shock Wave Loading
Authors: Pamwani Lavish , Shelke Amit
Published: July 2018

Shockwave is a high pressure and short duration pulse that induce damage and lead to progressive collapse of the structure. The shock load excites high-frequency vibrational modes and causes failure due to large deformation in the structure. Shockwave experiments were conducted by imparting repetitive localized shock loads to create progressive damage states in the structure. Two-phase novel damage detection algorithm is proposed, that quantify and segregate perturbative damage from microscale damage. The first phase performs dimension reduction and damage state segregation using principal component analysis (PCA). In the second phase, the embedding dimension was reduced through empirical mode decomposition (EMD). The embedding parameters were derived using singular system analysis (SSA) and average mutual information function (AMIF). Based, on Takens theorem and embedding parameters, the response was represented in a multidimensional phase space trajectory (PST). The dissimilarity in the multidimensional PST was used to derive the damage sensitive features (DSFs). The DSFs namely: (i) change in phase space topology (CPST) and (ii) Mahalanobis distance between phase space topology (MDPST) are evaluated to quantify progressive damage states. The DSFs are able to quantify the occurrence, magnitude, and localization of progressive damage state in the structure. The proposed algorithm is robust and efficient to detect and quantify the evolution of damage state for extreme loading scenarios.
Effects of Texture Orientation on the Mixed Thermal Elastohydrodynamic Lubrication and Fatigue Life in Point Contacts
Authors: Yan Xiao-Liang , Zhang Yu-Yan , Xie Guo-Xin , Du Xiao-Qiong , Qin Fen
Published: July 2018

Predicting the mixed thermal lubrication performance and fatigue life of point contact components becomes more and more important with the increasing demand for the load capacity of machinery. To achieve this, a deterministic mixed thermal elastohydrodynamic lubrication (TEHL) model in point contacts considering surface roughness is developed in this study. This model is capable of determining the pressure and temperature under different lubrication regimes from mixed to full-film lubrication. Then, the established model is extended to the subsurface stress and fatigue life predictions. Numerical simulations are conducted to analyze the lubrication characteristics and fatigue life for the three-dimensional (3D) sinusoidal surfaces with variable directions. Results show that increasing entraining velocity contributes to the reduction of pressure fluctuation and prolongation of fatigue life. However, the resulting temperature increases with the entraining velocity. As for the influence of lubricant viscosity, increasing it prolongs the fatigue life, especially under mixed TEHL conditions. What's more, the effect of rough surface texture feature on fatigue life has a close relationship with the lubrication regime.