bluuebunny/crossref_metadata_2025 huggingface dataset:
When cats need to see to step accurately?
Authors: Volgushev Maxim , Nguyen Celina T. , Iyer Gautam S. , Beloozerova Irina N.
Published: November 2021

Locomotion on complex terrains often requires vision. However, how vision serves locomotion is not well understood. Here, we asked when visual information necessary for accurate stepping is collected and how its acquisition relates to the step cycle. In cats of both sexes, we showed that a brief (200–400 ms) interruption of visual input can rapidly influence cat's walking along a horizontal ladder. Depending on the phase within the step cycle, a 200 ms period of darkness could be tolerated fully without any changes to the strides or could lead to minor increases of stride duration. The effects of 300–400 ms of visual input denial, which typically prolonged stances and/or swings, also depended on the phase of the darkness onset. The increase of the duration of strides was always shorter than the duration of darkness. We conclude that visual information for planning a swing is collected starting from the middle of the preceding stance until the beginning of the current swing. For a stance (and/or a swing of the other paw), visual information is collected starting from the end of the previous stance and until the middle of the current stance. Acquisition of visual information during these windows is not uniform but depends on the phase of the step cycle. Notably, both the extension of these windows and their non‐homogeneity are closely related to the pattern of gaze behaviour in cats, described previously. This new knowledge will help to guide research and understanding of neuronal mechanisms of visuomotor integration and modulation of visual function by strides during locomotion.

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Key points

Cats, like humans, rely on vision to navigate in complex environments.

In cats walking along a horizontally placed ladder, we show that visual information required for accurate stepping is collected in a non‐uniform manner throughout the stride cycle.

Brief denial of visual input during a swing prolongs the next stance of that forelimb. Denial of visual input during a stance prolongs this stance, as well as the next swing and stance. Denial during the first half of a stance has a greater effect than during the second half.

The phase dependence of the use of vision for accurate stepping and the pattern of affected swings and stances are closely related to the previously described pattern of gaze behaviour in cats.

This new knowledge opens new perspectives for research into neuronal mechanisms of visuomotor coordination and visual function during walking and for understanding related disorders.
Integrally-Stiffened Composite Damage Tolerance Evaluated by Computational Simulation
Authors: Chamis Christos C. , Minnetyan Levon
Published: November 2021

An integrally stiffened graphite/epoxy composite rotorcraft structure is evaluated via computational simulation. A computer code that scales up constituent micromechanics level material properties to the structure level and accounts for all possible failure modes is used for the simulation of composite degradation under loading. Damage initiation, growth, accumulation, and propagation to fracture are included in the simulation. Design implications with regard to defect and damage tolerance of integrally stiffened composite structures are examined. A procedure is outlined regarding the use of this type of information for setting quality acceptance criteria, design allowables, damage tolerance, and retirement-for-cause criteria.
A Box Beam Testbed Structure for Evaluating Elastic Tailoring With Composites
Authors: Rehfield Lawrence W.
Published: November 2021

Elastic tailoring refers to the use of composite materials to create structures with passive self-deformation control. These structures often exhibit globally coupled modes of deformation which are unusual. Examples are bend-twist and extension-twist in beam-like structures. Illustrations are presented which show that tailored configurations must be examined with care. If the structure is optimized for a particular mode of behavior, such as bend-twist or extension-twist, and is subjected to secondary loads of an unanticipated type, unwanted or unexpected behaviors may result which can significantly alter response. Situations such as this may be avoided by choosing configurations free of undesirable elastic couplings. One such configuration is the box beam model advocated as a testbed in the present paper.
On the Role of the Shell Theory in Analyzing the Sensitivity of Laminated Cylindrical Shells to Imperfection
Authors: Sheinman Izhak , Goldfeld Yiska
Published: November 2021

Due to the importance of the imperfection sensitivity behavior of laminated cylindrical shells, an investigation of the accuracy of three different shell theories, namely: Donnell’s, Sanders’ and Timoshenko’s is carried out. The results show that the adopted theory plays an important role in terms of the characteristic and level of sensitivity.
Delamination Effects in Circular Sandwich Plates With Laminated Faces of General Layup and a “Soft” Core
Authors: Rabinovitch Oded , Frostig Yeoshua
Published: November 2021

The present study is concerned with the behavior of delaminated circular sandwich plates with a compressible “soft” core and composite laminated face sheets of general layup. The analysis follows the concepts of the High-Order Sandwich Plate Theory and employs the variational principle of virtual work for the derivation of the field equations of the fully bonded and delaminated regions. In the penny shaped disbonded region, the delaminated faces can slip horizontally with respect one to another, yet they may be in contact and resist vertical normal compressive stresses. The compressible core is considered using the 3D theory of elasticity and the lamination theory is employed for the modeling of the composite laminated face sheets. The formulation yields coordinate-dependent constitutive relations and governing equations and the solution procedure adopts the Galerkin method in the circumferential direction and the multiple-points shooting method in the radial direction. Numerical results regarding a typical delaminated sandwich plate are presented in terms of deformations and stresses. The results reveal the effect of the anisotropic laminated face sheets on the response of the structure and the influence of the delamination on the overall and, especially, the localized behavior of the plate.
Damping in Unidirectional and Cross-Ply Ceramic Matrix Composites With Matrix Cracks
Authors: Birman Victor , Byrd Larry W.
Published: November 2021

The paper elucidates the methods of estimating damping in ceramic matrix composites (CMC) with matrix cracks. Unidirectional composites with bridging matrix cracks and cross-ply laminates with tunneling cracks in transverse layers and bridging cracks in longitudinal layers are considered. It is shown that bridging matrix cracks may dramatically increase damping in unidirectional CMC due to a dissipation of energy along damaged sections of the fiber-matrix interface (interfacial friction). Such friction is absent in the case of tunneling cracks in transverse layers of cross-ply laminates where the changes in damping due to a degradation of the stiffness remain small. However, damping in cross-ply laminates abruptly increases if bridging cracks appear in the longitudinal layers.
Dynamics of Composite Structures With Multiple Delaminations
Authors: Lestari W. , Lou H. , Hanagud S.
Published: November 2021

The objective of this paper is to explore if changes in the structural dynamic response and structural dynamic characteristics can be used to identify the existence, location and magnitude of defects like a delamination or an impact damage, at the macroscale level, before they can grow to their critical sizes. Specifically dynamic response of composite structures, with delamination defects, is discussed in this paper. The experimental analysis is performed to capture the effects of nonlinearities on the dynamic response of a beam with multiple delaminations. To describe the opening and closing mode of the delaminated segments of the beam during the vibration, an analysis is performed by using a model with piecewise spring. Then, the nonlinear dynamic response is calculated.
Failure Prediction of Graphite/Epoxy Laminates With Induced Intermittent Surge in Applied Load During Fatigue
Authors: Kedlaya Diwakar N. , Pelegri Assimina A.
Published: November 2021

An analytical model, backed by numerical simulation, describing the behavior of the energy release rate of composite laminates subjected to fatigue overloads is presented. The model establishes that accumulation of damage due to intermittent surge in applied load reduces the energy release rate, G, of the material. Thus, in the case of cyclic loading with overloads, it is essential to model the failure using a damage growth law that incorporates the damage accumulation due to the overloads. The results obtained in this study, have no restrictive assumptions regarding the specimen or the delamination thickness, T and h respectively, and are presented over varying mode-mixity and h/T ratios.
Effects of Interfacial Roughness, Oxide Film Thickness and Heterogeneous Bond Coat Microstructure on Spallation Mechanism in Plasma-Sprayed TBCs
Authors: Pindera Marek-Jerzy , Aboudi Jacob , Arnold Steven M.
Published: November 2021

A major failure mechanism in plasma-sprayed thermal barrier coatings is spallation of the top coat due to the top/bond coat thermal expansion mismatch concomitant with deposition-induced interfacial roughness, oxide film growth and creep-induced normal stress reversal at the rough interface’s crest. Reduction of the thermal expansion mismatch through the use of heterogeneous bond coats has been suggested to increase coating durability. This approach is examined using the higher-order theory for functionally graded materials. Specifically, combined effects of a graded bond coat microstructure and oxide film thickness on the crack-tip stress field in the vicinity of a rough top/bond coat interface are investigated during furnace-type thermal cycling in the presence of a local horizontal delamination situated within the homogeneous top coat at the rough interface’s crest. The analysis, which accounts for the creep/relaxation effects within the individual constituents, is conducted in two distinct ways. In the first approach, the bond coat’s heterogeneous microstructure is fully taken into account while in the second approach the bond coat’s microstructure is homogenized. The feasibility of using graded bond coat microstructures to reduce horizontal delamination driving forces is critically examined and the limitations of the homogenization-based approach are highlighted.
Prediction of Remaining Life Time Based on Measurements of Stress for Thermal Barrier Coatings
Authors: Jordan E. H. , Xie W. , Gell M. , Xie L. , Tu F. , Pattipati K. R. , Willett P. , Sohn Y. H.
Published: November 2021

Non-destructive determination of the remaining life of coatings of gas turbine parts is highly desirable. The present paper describes early attempts to prove the feasibility of doing this based on the optical measurement of the stress in the oxide that attaches the coating to the metal component. Both regression methods and neural network methods are compared and it was found that the neural network approach was superior for the case where multiple signal features were present. All methods provide useful predictions for the idealized case considered. Challenges presented by more complicated thermal cycles are discussed briefly.
Behavior of Composite Materials Under Impact: Strain Rate Effects, Damage, and Plasticity
Authors: Abrate Serge
Published: November 2021

Composite materials are often subjected to low velocity impacts, ballistic impacts, or crash impacts. In order to analyze such events, realistic model of the material behavior must be used to capture phenomena no included in linear elastic models. Nonlinear behavior occurs when a unidirectional lamina is loaded in the transverse direction or in shear when the matrix material deforms plastically. The stiffness and strength of composite materials at high strain rates is often very different from what is measured in quasi-static tests. In addition, different types of damage are introduced during impart: matrix cracks, delaminations, fiber failures, fiber-matrix debonding. The introduction of this damage will affect the subsequent behavior of the material.

Many different approaches have been taken to account for the effects of strain rate, plasticity and damage on the mechanical behavior of composite materials. The objective of this paper is to assess current knowledge in this area, review and compare models used to describe the stress-strain behavior and predict failure of such materials. Continuum mechanics approaches are used to describe the behavior of laminas with different types of damage, and to model the behavior of interfaces between plies. Phenomenological plasticity models account for the nonlinear effects under transverse and shear loads. Some of these models are shown to be similar even though they were derived by very different approaches. Many accurate analyses of composite structures under impact assume linear elastic behavior and do not considered the complicating effects discussed here. The applicability of the different models for material behavior is also discussed in terms of selecting an appropriate model for analyzing a particular impact.
The Audi Space Frame on the A2: A New Body Concept in Aluminum for Superior Crashworthiness
Authors: Christlein Jens , Maar Eric
Published: November 2021

Vehicle concepts of the future will have to satisfy such contradictory requirements as high body rigidity and maximum safety in all driving situations, coupled with minimum weight. With this in mind, at the 1997 Frankfurt Motor Show Audi presented the Al2 study vehicle, a car which makes ultra-low fuel consumption possible thanks to its new overall technical concept based on extremely low-weight Audi Space Frame (ASF) techniques and innovative engines, but is a multi-purpose four-door vehicle despite its compact exterior dimensions. This study model was developed into a production-ready vehicle within a very short space of time: the Audi A2, which made its début at the Frankfurt Motor Show in September 1999. Only with the aid of simulation techniques it was possible to bring such a novel body concept to production maturity within such a short space of time. The following paper describes the technical highlights of the ASF body on the Audi A2.
Validation of FMVSS201 Featureless Headform Finite Element Model for Rotational Acceleration
Authors: Barbat Saeed D.
Published: November 2021

This paper demonstrates an application of the nine linear accelerometer scheme, proposed by (Padgaonkar et al., 1975), to the development and validation of a finite element model of a deformable featureless headform for rotational accelerations. Steps and procedures involved in the development and calibration of the model are also described. A set of tri-axial accelerometers was mounted at the headform center of gravity, C.G., which is located at the origin of the local coordinate axes of the headform. Three bi-axial accelerometers were also mounted at the front, left, and top of the headform’s aluminum skull and on the local coordinate axes of the physical headform. Nine linear accelerations were measured at the headform in drop tests against a rigid plate at impact speeds of 2.68, 4.0, 5.36, and 6.71 m/s (6, 9, 12, and 15 mph). The rotational accelerations of the headform were then calculated from the nine linear acceleration measurements. In the finite element (FE) model of the featureless deformable headform, a visco-elastic material law, available in the non-linear dynamic explicit code PAM-CRASH, was used to simulate the vinyl skin response during impact. The constitutive parameters of the headform’s skin material were calibrated through comparison of the headform drop simulations at various impact speeds with the corresponding tests. Headform responses, such as, resultant acceleration time histories at the headform C.G. and the rotational acceleration time histories obtained from the FE predictions of the headform responses during the drop tests simulations correlated very well with those obtained from experiments. Validation of the headform model for rotational accelerations provided higher level of confidence in the prediction capability of the model when used for interior head impact simulations with vehicle upper interior as specified by the Federal Motor Vehicle Safety Standard FMVSS 201.
Application of Topological Optimization Techniques to Automotive Front Structure Design
Authors: Mayer Robert R.
Published: November 2021

An application of topological optimization techniques to automotive front structure design was considered, for the case of crashworthiness performance. An earlier developed topological optimization technique was used by first deriving an optimality criteria. To develop an optimality criteria, a functional relationship was developed between microstructure design variables, and both strain energy and volume, for shell element structures. Its previous application was the location of holes to lighten a rear longitudinal rail. The present application applies this theory to the actual layout of automotive front structure. The nonlinear code, LS-DYNA, was used for the simulations.

An observation of various automotive front structural topologies, sometimes called structural layouts or architectures, reveals that many different design approaches are possible. In order to numerically assess the optimum layout the design space available for front structure design is built up from layers of shell elements, and the method of constructing these models using LS-INGRID is discussed. Some of these elements are deleted at each optimization iteration, resulting in a design concept. The design concept is interpreted as a number of structural load paths, and a unique design was then identified.
Engineering Across Borders: Educational Practices for Improving the Effectiveness of Globally Distributed Engineering Design Teams
Authors: David Kenneth , Lloyd John R.
Published: November 2021

Globalization of engineering design teams occurs both in industry and also in the engineering classroom. Strategic needs for operating multi-site operations and inter-organizational alliances call for more effective boundary-spanning partnerships: inter-divisional, inter-organizational, and often, multi-country partnerships. This paper reports a multi-discipline research study — involving engineering, anthropology and telecommunications elements — on global engineering design teams. US engineering students from mechanical, chemical, and electrical engineering worked together with counterparts from China and the Netherlands. The students learned advanced telecommunication media and transcultural communication skills needed to carry out the tri-continental design project. They used an active learning process called transcultural incident reporting that focuses on cultural and power issues that must be managed in order to accomplish high quality design. The engineers’ reports show a gain in understanding of the cultural and power issues that affect boundary-spanning project performance.
A New Approach to Teaching a Mechanical Systems Design Course
Authors: Jouaneh Musa
Published: November 2021

This paper discusses a new approach to teaching a senior-level mechanical systems design course at the University of Rhode Island. The MCE401 class was split into 9 teams, each with four students. Team members were selected to complement their learning styles. To each team, additional 4 students from the URI Business school were added. In the Fall semester, each team selected one of several different, product-oriented design projects or proposed their own project topic subject to certain requirements. The students were asked to perform a patent search, to critique related products, to prepare a marketing study, to propose a design of this product, and to realize their design using a 3-D solid-modeling software. At the end of the Fall semester, groups competed for funding for activities in the following Spring term that included building prototypes of their design, formulating business plans for commercialization, and applying for patent protection. The new proposed format gave students better understanding and exposure to the entrepreneurial process of product design and innovation.
Rapid Simulation of Preloaded Bolted Assemblies for Slewing Bearings
Authors: Leray Dimitri , Daidié Alain , Combes Bertrand
Published: November 2021

Fatigue failure is a common problem with bolted joints. Preloading can often offer great advantage, in that it reduces the intensity of the alternative part of strains. Although it is more and more usual to carry out very precise finite element calculations, it should be highlighted that the error arising from simulations or experiments may be surprisingly great when looking at supplements of strain, i.e. alternative strain.

That is one of the reasons why designing preloaded bolted joints requires great care, and sometimes turns out to be impractical.

A partnership has been established for several years with a group of industrial manufacturers and users of slewing bearings. The objective is to model a parameterised bolt-assembled slewing bearing system and to develop a simulation tool that

• allows us to check resistance of the bolts for maximum load as well as fatigue load

• runs much faster than a three-dimensional simulation in order to enable us to compare multiple configurations, in order to be used in early design stages.
Equilibrium Elasto-Hydrodynamic Analysis in Wafer Slicing Process Using Wiresaw
Authors: Zhu Liqun , Kao Imin
Published: November 2021

An improved elasto-hydrodynamic (EHD) model of wiresaw slicing process is summarized in this paper which incorporates the equation of equilibrium for the motion of the wire. Parametric studies are conducted, which encompass different cases in the wiresaw slicing process. Based on the results, we examine the effects of wire bow angle on the EHD properties and the slicing mechanism of wiresaw process. The simulation results provide insights to the wiresaw slicing mechanism, and suggest ways to facilitate the experimental study for industry wiresaw slicing.
A Methodology for Evaluating the Mechanical Reliability of Alternatives to Tin-Lead Solder Electronic Interconnection Systems (Focus on Electrically Conductive Adhesives)
Authors: Rafanelli Anthony J.
Published: November 2021

A methodology for evaluating suitable alternative materials to traditional tin-lead solder, as an electronic component interconnection media, is presented. This methodology was developed as part of prior research that addressed the mechanical reliability of alternative materials using approaches and methods, which were traditionally unique to tin-lead, solder.

The original research included evaluation and subsequent tabulation of basic mechanical, fatigue, creep, and fracture mechanics properties. Basic mechanical data was acquired either through the literature or laboratory test. Fatigue data was limited to thermal shock/cycling. Creep data consisted of observing material behavior under temperature and thermo-mechanical loads. The fracture mechanics study features the validation and subsequent use of the J-Integral as applied to solder and electrically conductive adhesives (ECAs).

This paper suggests a framework for establishing a methodology for evaluating mechanical reliability of electronic interconnection media based on the acquired materials data.
Finite Element Modeling of Processes in Optoelectronic Alignment
Authors: Ting Ben , Manno Vincent P.
Published: November 2021

For semiconductor lasers, fiber and optical source alignment is crucial for maintaining high optical transfer efficiency. Traditional optoelectronic manufacturing, production of butterfly packages for example, involves laser welding of fiber mountings followed by a tedious realignment procedure to reverse thermally-induced distortions. An alternate technique, laser hammering, entails manipulation of the fiber to light alignment through deformation of the fiber housing with high precision laser beams. A detailed understanding of the material and mechanical behavior, characteristics, and dynamic response is vital to successfully apply an efficient controller that can choose an optimal weld pattern based on a light to fiber misalignment. Modeling provides an effective means to determine an optimal fiber alignment control technique. Modeling is difficult due to the dynamic thermal-mechanical coupling of these processes. This paper presents the preliminary results of a series of parametric studies regarding thermal-mechanical coupling models employed in finite element analysis in order to assess the behavior and dynamic response of representative materials and geometries under various boundary conditions. Fiber ferrule and ferrule housing dimensions affect resistance to bending and torsion, which in turn governs the magnitude of the displacement field. The models are then applied to geometries typical of alignment fixtures used in laser diode packages. The effects of laser energy deposition location and resolution as well as assumed boundary and initial conditions are also discussed. Convection and the small variations in ferule geometry do not have a strong effect on the overall response.
Constitutive-Related Instabilities in Pipe Flow of a Viscoelastic Fluid
Authors: Alves Manuel A. , Pinho Fernando T. , Oliveira Paulo J.
Published: November 2021

The analytical solution for the steady-state flow in a pipe of viscoelastic fluids obeying the complete Phan-Thien-Tanner constitutive equation with a linear stress coefficient is derived. The results include the radial profiles of all relevant stresses, of the axial velocity and of the viscosity. The pipe flow is found to be unstable when the pressure gradient exceeds a critical value determined by a maximum shear rate at the wall. Expressions are also given for the viscometric viscosity and the first and second normal stress difference coefficients, as a function of the shear rate, in steady plane shear flow. For this case, and in line with similar results for the Johnson-Segalman model, the shear stress was found not to be a monotonically increasing function of the shear rate as strong shear-thinning sets in. A new finding is that the critical condition for the maximum shear stress in the simple-shear case is related to the condition for existence of steady-state solution in the pipe flow case. While this may seem evident “a priori” since the pipe flow is a viscometric flow, it is formally demonstrated.
Numerical Study of Mold Filling Dynamics in “Cold-Box” Sand Coremaking Process
Authors: Bakhtiyarov Sayavur I. , Overfelt Ruel A.
Published: November 2021

In this paper we present the results of the numerical simulations of sand core shooting process using the CFD package FLOW-3D. The simulations are based on a two-fluid flow approach. The computation results are compared to experimental data obtained earlier.
CFD Simulations of Flow Dynamics in Porous Media of Variable Permeability Arranged in Series
Authors: Bakhtiyarov Sayavur I. , Siginer Dennis A.
Published: November 2021

In this paper we present the results of the CFD simulations of the viscous fluid flow in two porous media of different permeability and same porosity arranged in series. FLOW-3D software package (Flow-Simulations, Inc.) has been used to predict flow velocity distributions and pressure losses when Newtonian fluid flows through the non-homogenous porous medium. The results of simulations are compared to those obtained experimentally earlier.
Steady Secondary Flows of Phan-Thien-Tanner Fluids in Pipes of Complex Shapes
Authors: Letelier Mario F. , Olguín Mauricio A. , Siginer Dennis A.
Published: November 2021

Some kinematic and dynamic characteristics of secondary flows in straight tubes are explored for the case where the flow is laminar steady, the fluid is described by the modified Phan-Thien-Tanner model of viscoelastic fluids, and the tube cross-section shape varies through a wide range of configurations. This analysis is aimed at providing information about the transport capacity of secondary flows. Viscoelastic fluids have been observed to enhance heat transfer in pipe flow due to the transversal motion generated in non-circular pipes.

In order to improve the design of heat exchangers it is necessary to understand how some basic variables, such as pipe geometry determine the structure of the corresponding secondary flows. In this paper it is investigated the kinematics and dynamic of some secondary flows for pipe shapes that generate different flows structures.
Full Simulation of Natural Waves in Falling Films
Authors: de Korte Edwin , Kok Jim B. W. , van der Meer Theo H.
Published: November 2021

The two dimensional Navier Stokes equations have been solved for a falling film flow, i.e. a laminar flow running down a vertical wall driven by gravity. The aim of this research is to describe the onset of natural waves by using full simulation of the Navier-Stokes equations. In order to find the natural wave the flow velocity at the the inlet boundary (top horizontal plane) is perturbed.

With the boundary condition described above the fastest growing wave is triggered for a range of Reynolds numbers in the laminar wavy range. The wave numbers and velocities agree with results based on Orr-Sommerfeld theory reported by Pierson & Whitaker [7] for Re = 5.90 and Re = 11.8. For Re = 23.5 a different wavelength triggered than the one predicted by linear stability analysis. However the wavespeeds are in reasonable agreement with each other. A complete understanding for this phenomenon is not found yet.

There is shown that the behavior of the waves is strongly non-linear and transient. In this work is to illustrate that the wave profiles can be calculated by simply solving the Navier-Stokes equations without any prior assumptions.
The Central Roles of Fractals, Bifurcation, and Chaos in Optimal Fluid Mixing
Authors: Bondar Farshid , Taeibi-Rahni Mohammad
Published: November 2021

Mixing processes are widely used in industries and are being studied by a number of scientists; even though, a fundamental insight of the subject is still lacking. In this paper, some basic thoughts are set on the analogy between fluid mixing phenomena and fractal geometry/properties/ processes. To this end, an unstable horseshoe pattern, which leads to a continuous extending boundary with maximum stretching and folding, is created and repeated. As a result, self-similarity property along with instability is imposed throughout the region, enhancing the fluid mixing. The procedures are verified computationally using the techniques of capacity and information dimensions, which are measured as time-dependent functions. The results can be used to explore how well a fractal representation can describe fluid mixing phenomena, how fractal-like processes can optimize it, when fractal properties grow rapidly in the fluid system, and ultimately how unsteady flows are impending chaotic behavior in dynamical mixing systems when local bifurcations occur.
A Non-Intrusive Experimental Technique for Constructing Poincaré Maps in 3D Chaotically Advected Flows
Authors: Sotiropoulos Fotis , Mezić Igor , Webster Donald R.
Published: November 2021

We propose and develop the theoretical framework for a new experimental technique for constructing Poincaré maps in three-dimensional flows exhibiting chaotic advection. The technique is non-intrusive and, thus, simple to implement. Planar laser-induced fluorescence (LIF) is employed to collect a sufficiently long sequence of instantaneous light intensity fields on the plane of section of the Poincaré map (defined by the laser sheet). The chains of unmixed (regular) islands in the flow are visualized by time-averaging the instantaneous images and plotting iso-contours of the resulting mean light intensity field. A rigorous theoretical justification for this technique is derived using concepts from ergodic theory. We demonstrate the capabilities of the method by applying it to visualize the rich Lagrangian dynamics within steady vortex breakdown bubbles in a closed cylinder with a rotating bottom. The experimental results are shown to be in excellent agreement with numerical simulations.
Transient Whole Field Flow Diagnostics
Authors: Anderson Chris , Sforza Pasquale M. , Martel John
Published: November 2021

A new technique is described to perform whole field flow diagnostics in highly transient environments. A modified Hartmann sensor is used in conjunction with digital imaging to provide time-resolved imagery with inter-frame times as low as 1 μsec. Details of the approach are given and experimental data from an application to two dimensional cavity flows is provided. Applications of the instrument are then discussed including transient analysis, high altitude/low density applications, and comparison with transient CFD analysis.
Simulation of the Onset of Rotating Stall
Authors: Freitas Christopher J. , Smalley Anthony J.
Published: November 2021

This paper presents the results of a series of numerical simulations exploring the stability of fluid flow in vaneless diffusers of centrifugal compressors. Three-dimensional, time-dependent, Reynolds-averaged Navier-Stokes simulations were performed for a fixed diffuser width ratio. Effective flow angle was varied from simulation to simulation in order to predict the threshold angle at which the instability — rotating stall — is manifested and maintained. The predicted threshold angle or stability limit is in excellent agreement with experimental data. The simulations reveal a two-stall cell configuration at the threshold condition.
An Investigation of the Hydrodynamics of a Rectangular Slot, Spouted Bed
Authors: Shirvanian P. A. , Calo J. M. , Hradil G.
Published: November 2021

An Eulerian model is presented that has been developed to describe the hydrodynamics of a rectangular slot, spouted bed experimental apparatus. This study was undertaken as a part of a project focused on the development of a Spouted Bed Electrolytic Reactor (SBER) for metals recovery. The results presented here include the effects of particle loading, inlet jet velocity, and bed geometry on void fraction distributions, pressure drop, and particle recirculation rate. The simulations show that pressure drop and particle recirculation rate both increase with inlet jet velocity and particle loading. However, at some point “choking” is predicted such that the particle recirculation rate will then remain constant with increasing particle loading and inlet jet velocity.
Viscous Flows Involving a Liquid-Vapor Compound Droplet
Authors: Palaniappan D.
Published: November 2021

Exact analytical solutions for steady-state axisymmetric creeping flows in and around a compound multiphase droplet are presented. The solutions given here explain the droplet fluid interactions in uniform and nonuniform flow fields. The compound droplet has a two-sphere geometry with the two spherical surfaces (of unequal radii) intersecting orthogonally. The surface tension forces are assumed to be sufficiently large so that the interfaces have uniform curvature. The singularity solutions for the uniform and paraboloidal flows in the presence of a compound droplet are derived using the method of reflections. The exact solutions for the velocity and pressure fields in the continuous and dispersed phases are given in terms of the fundamental singularities (Green’s functions) and their derivatives. It is found that flow fields and the drag forces depend on two parameters namely, the viscosity ratio and the radii ratio. In the case of paraboloidal flows, a single or a pair of eddies is noticed in the continuous phase for various values of these parameters. The eddies changes their size and shape if the size of the droplet is altered. These observations may be useful in the study of hydrodynamic interactions of compound droplets in complex situations. It is found that the Stokes resistance is greater when the liquid volume is large compared to the vapor volume in uniform flow. It is also noticed that the maximum value of the drag in paraboloidal flow depends on the viscosity ratio and significantly on the liquid volume in the dispersed phase. The exact solutions presented here may be useful for boundary integral formulations that are based on special kernels and also in validating numerical algorithms and codes on multiphase flow and droplet-fluid interactions.
Unsteady Pressure Measurement of an Axial Fan
Authors: Xu C. , Amano R. S.
Published: November 2021

An unsteady pressure measurement system was developed to measure the unsteady pressure field of an axial fan. The fan unsteady pressure fields of an inlet and outlet were obtained at three axial positions for seven-radial directions. The results showed that there is a relatively long response time for pressure drop both in inlet and outlet sections during the fan start-up. The measurements also showed that, due to the vortex shedding from the trailing edge of each fan blade, the fan outlet unsteady pressure distributions have a primary frequency related to the fan operating frequency. The time-dependent pressure measurements showed that pressure distributions of inlet and outlet during the fan start-up were severely unsteady and the main variation frequency of the pressure is much smaller than the fan rotational frequency. The pressure measurement on the fan blades showed that the pressure oscillations were mainly dominated by the vortex shedding from the fen blades. A flow visualization study was also performed to validate the flow characteristics near the blade surface. A complete set of time-dependent pressure measurements along the blade fan surfaces, fan inlet and outlet are suitable for an axial fan database for an industrial use as well as CFD code validation.
The Shutoff Head of a Centrifugal Impeller
Authors: Yedidiah S.
Published: November 2021

This paper discusses the effects of different design-parameters on the magnitude of the shutoff head of a centrifugal impeller. It shows, that the observed inconsistencies between existing theories and tests can be eliminated, by considering the angular speed of the liquid contained between the rotating shrouds and the stationary casing.
A Computational Optimization of a Laminar Flow in a Small Tube With Fenestrations
Authors: Sahin Iskender , Hovland Chris
Published: November 2021

An iterative approach by a CFD analysis was applied for optimizing the distribution of a laminar fluid flow through a small diameter tube with a closed end. The goal of the optimization was that flow rates through small discharge outlets (fenestrations) be close to uniform throughout the tube. Parameters used for the optimum design were: the pipe and fenestration hole diameters and the distribution of fenestration along the pipe, and the number of holes, among others. A numerical parameter describing the efficiency of each design was introduced and used for some comparisons.
Modelling of Hydraulic Forest Boom Tip Acceleration Control to Counterbalance the Gravitational Load Force in Horizontal Timber Cutting
Authors: Inberg Juha , Mattila Jouni , Virvalo Tapio
Published: November 2021

This paper concentrates on the forest machines, which are working in the cut-to-length method. The cutting function is an essential part of a harvester’s work in the cut-to-length method. The quality of cutting is the most significant feature of a cut. Trees should be cut without causing damage, especially end checks, to the cutting surface of wood. Nowadays end checks of logs are main problem of the cutting process. It has been observed that end checks are found in as many as 70% of the logs. The cutting damages reduce the amount of useful material and cause considerable economical loss to the sawmill and veneer industries.

The study deals with the boom lowering function, which is a potential solution to avoid cutting damages during the timber cutting process. The purpose is to momentarily counterbalance the gravitational force of a log during the cross-cut. This paper presents model derivation and analysis of the kinematics, dynamics and hydraulics of the studied forest boom. The paper also shows that the model can be used as a design tool to examine the influences of hydraulics and control system to the behaviour and performance of boom tip acceleration control in a horizontal timber cutting in future studies.
Predicting the Required Slipper Hold-Down Force Within an Axial-Piston Swash-Plate Type Hydrostatic Pump
Authors: Manring Noah D.
Published: November 2021

The objectives of this research are to determine the physical contributors that tend to separate the slippers from the swash plate within an axial-piston pump. Upon determining these contributors, the hold-down force that is required for maintaining contact between the slippers and the swash plate is determined. This force is then expressed in terms of pump design-parameters and operating conditions. Physically inspecting six industrial pumps and measuring the theoretical calculations against the a-posteriori results of successful pump designs validates the analytical results of this research. By confirming the analysis of this research, an a-priori approach is recommended for adequately specifying the required spring load for the slipper hold-down mechanism.
Effects of an Auxiliary Plate Position on Natural Convection in a Vertical Channel With Radiation
Authors: Andreozzi Assunta , Manca Oronzio , Morrone Biagio
Published: November 2021

This experimental paper analyzes the effects of auxiliary plate position along the centerline of a vertical channel on combined air natural convective and radiative heat transfer. These configurations can be found in the telecommunication systems and electronic cabinets with vertical cards.

The experiments are carried out by means of temperature measurements to obtain significant thermal parameters. A comparison between the different positions of the plate inside the channel is given in terms of channel wall temperatures. The results are given in terms of heated wall temperature profiles and radiative heat transfer for different thermal and geometrical parameters. Average Nusselt number as a function of the main thermal and geometrical parameters are presented and useful correlation equations are proposed. The comparison of the placement of the auxiliary plate, for high radiative heat transfer, shows that the auxiliary plate placed at the channel exit displays the lowest maximum channel wall temperatures when high Rayleigh numbers and heat flux values are considered. The configuration with this auxiliary plate placement is thoroughly examined for several h/L values and different emissivity coefficients. The channel aspect ratio, L/b, is equal to 10 and 20, the ratio of the auxiliary plate height to the channel one, h/L, 0, 0.25, 0.33 and 0.5, with emissivity coefficients of the walls equal to 0.1 and 0.9 and three different auxiliary plate positions inside the channel. The modified Rayleigh number values are in the 102–105 range.
A Neoclassical Growth Model for Population Dynamics in a Homogeneous Habitat
Authors: Vadasz Peter , Vadasz Alisa S.
Published: November 2021

A neoclassical model is proposed for the growth of cell and other populations in a homogeneous habitat. The model extends on the Logistic Growth Model (LGM) in a non-trivial way in order to address the cases where the Logistic Growth Model (LGM) fails short in recovering qualitative as well as quantitative features that appear in experimental data. These features include in some cases overshooting and oscillations, in others the existence of a “Lag Phase” at the initial growth stages, as well as an inflection point in the “In curve” of the population size. The proposed neoclassical model recovers also the Logistic Growth Curve as a special case. Comparisons of the solutions obtained from the proposed neoclassical model with experimental data confirm its quantitative validity, as well as its ability to recover a wide range of qualitative features captured in experiments.
Use of Saline Injection to Create Large Thermal Lesions During Radiofrequency Ablation Therapy: 1. Thermal Model
Authors: Curley Michael G. , Hamilton Patrick S.
Published: November 2021

Radiofrequency (RF) energy has been successfully used to treat tachycardia and liver cancer through hyperthermic ablation. However, this therapy is limited to treating small volumes because of the high current density near the RF electrode, which leads to excessive temperatures in this region.

We have developed an RF therapy that uses saline injection into the tissue surrounding the electrode to increase heat transfer in this tissue to heat significantly larger volumes. This paper shows the results of a finite difference thermal model of this therapy. Results indicate that saline-enhanced RF ablation can treat tissue volumes that are 33 times larger than those created by RF alone.
High-Speed Photographic Evaluation of Retropulsion Momentum Induced by a Laser Calculi Lithotriptor
Authors: Lee Ho , Kim Jeehyun , Choi Bernard , Teichman Joel M. H. , Welch A. J.
Published: November 2021

Since the mid-1980’s, many reports have demonstrated the clinical feasibility of fragmenting urinary and biliary calculi with high power lasers [1,2]. Several lasers such as pulsed dye, alexandrite and holmium:YAG have been successfully used as intracorporeal lithotriptors[3–5]. Calculus fragmentation is produced by the combination of direct thermal energy absorption and laser induced shock waves[5–7]. During this powerful laser-tissue interaction, the calculus is subject to a strong retropulsive momentum caused by particle ejection or laser induced shock waves[8]. If the stone cannot resist this kinetic momentum, it will recoil away from the laser delivery fiber. Then physicians must reorient the fiber to the stone for additional laser irradiation. This cumbersome process makes the procedure inconvenient and difficult and eventually prolongs the operation time. This study is designed to quantify the retropulsive momentum during pulsed laser lithotripsy.
Effect of Freezing on Cell Viability and Mechanical Strength of Bioartificial Tissues
Authors: Devireddy Ramachandra V. , Neidert Michael R. , Bischof John C. , Tranquillo Robert T.
Published: November 2021

The effect of freezing on the viability and mechanical strength of bioartificial tissues was determined under a variety of cooling conditions, with the ultimate aim of optimizing the cryopreservation process. Bioartificial tissues (i.e. tissue-equivalents or TEs) were prepared by incubating entrapped human foreskin fibroblasts in collagen gels for a period of 2 weeks. The bioartificial tissues were frozen using a controlled rate freezer at various cooling rates (0.5, 2, 5, 20, 40 and > 1000°C/min or slam freezing). The viability (< 60 min after thawing) of the fibroblasts in the bioartificial tissue was assessed using the Ethidium Homodimer (dead cells stain red) and Hoechst Give cells stain blue) assay. Uniaxial tension experiments were performed on an MTS Microbionix System (Eden Prairie, MN) to assess the post-thaw mechanical properties (Maximum Stiffness; Ultimate Tensile Stress; and Strain to Failure) of the frozen-thawed bioartificial tissue (≤ 3 hours after thawing). The results suggest that cooling rates of either 2 or 5°C/min are optimal for preserving both the cell viability and mechanical properties of the bioartificial tissues, post-freeze. Bioartificial tissues were also frozen using a directional solidification stage at 5°C/min. The post-thaw viability results are comparable in both the directionally cooled and the controlled rate freezer samples. However, the mechanical properties of the directionally cooled samples are significantly different (with a higher maximum stiffness and a lower strain to failure) than those obtained for samples frozen using a controlled rate freezer. This suggests that the directionality of ice propagation into the sample affects the measured mechanical properties.