bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of epicardial adipose tissue in cardiac biology: classic concepts and emerging roles
Authors: Antonopoulos Alexios S. , Antoniades Charalambos
Published: February 2017

Classic concepts about the role of epicardial adipose tissue (EpAT) in heart physiology include its role in cardiac metabolism, mechanical protection of coronaries, innervation and possibly cryoprotection of the heart too. Nevertheless, recent evidence has revealed that epicardial adipose tissue regulates multiple aspects of cardiac biology including myocardial redox state, intracellular Ca2+ cycling, the electrophysiological and contractile properties of cardiomyocytes, cardiac fibrosis as well as coronary atherosclerosis progression. Moreover, it is now understood that the communication between EpAT and the heart is regulated by complex bidirectional pathways, since not only do adipokines regulate cardiac function, but also the heart affects EpAT biology via paracrine ‘reverse’ signalling. Such complex interactions as well as epicardial fat accumulation as a consequence of cardiac disease and epicardium to adipocyte differentiation should be taken into account by the clinical studies investigating EpAT as a risk marker and its potential as a therapeutic target against cardiovascular disease. Further in‐depth exploration of the molecular mechanisms regulating the cross‐talk between the heart and EpAT is expected to enhance our understanding regarding the role of the latter in cardiac physiology and relevant disease mechanisms.

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Perinatal nicotine exposure impairs the maturation of glutamatergic inputs in the auditory brainstem
Authors: Baumann Veronika J. , Koch Ursula
Published: February 2017

Key points

Chronic perinatal nicotine exposure causes abnormal auditory brainstem responses and auditory processing deficits in children and animal models.

The effect of perinatal nicotine exposure on synaptic maturation in the auditory brainstem was investigated in granule cells in the ventral nucleus of the lateral lemniscus, which receive a single calyx‐like input from the cochlear nucleus.

Perinatal nicotine exposure caused a massive reduction in the amplitude of the excitatory input current.

This caused a profound decrease in the number and temporal precision of spikes in these neurons.

Perinatal nicotine exposure delayed the developmental downregulation of functional nicotinic acetylcholine receptors on these neurons.

Maternal smoking causes chronic nicotine exposure during early development and results in auditory processing deficits including delayed speech development and learning difficulties. Using a mouse model of chronic, perinatal nicotine exposure we explored to what extent synaptic inputs to granule cells in the ventral nucleus of the lateral lemniscus are affected by developmental nicotine treatment. These neurons receive one large calyx‐like input from octopus cells in the cochlear nucleus and play a role in sound pattern analysis, including speech sounds. In addition, they exhibit high levels of α7 nicotinic acetylcholine receptors, especially during early development. Our whole‐cell patch‐clamp experiments show that perinatal nicotine exposure causes a profound reduction in synaptic input amplitude. In contrast, the number of inputs innervating each neuron and synaptic release properties of this calyx‐like synapse remained unaltered. Spike number and spiking precision in response to synaptic stimulation were greatly diminished, especially for later stimuli during a stimulus train. Moreover, chronic nicotine exposure delayed the developmental downregulation of functional nicotinic acetylcholine receptors on these neurons, indicating a direct action of nicotine in this brain area. This presumably direct effect of perinatal nicotine exposure on synaptic maturation in the auditory brainstem might be one of the underlying causes for auditory processing difficulties in children of heavy smoking mothers.
Development of Standardized Material Testing Protocols for Prosthetic Liners
Authors: Cagle John C. , Reinhall Per G. , Hafner Brian J. , Sanders Joan E.
Published: February 2017

A set of protocols was created to characterize prosthetic liners across six clinically relevant material properties. Properties included compressive elasticity, shear elasticity, tensile elasticity, volumetric elasticity, coefficient of friction (CoF), and thermal conductivity. Eighteen prosthetic liners representing the diverse range of commercial products were evaluated to create test procedures that maximized repeatability, minimized error, and provided clinically meaningful results. Shear and tensile elasticity test designs were augmented with finite element analysis (FEA) to optimize specimen geometries. Results showed that because of the wide range of available liner products, the compressive elasticity and tensile elasticity tests required two test maxima; samples were tested until they met either a strain-based or a stress-based maximum, whichever was reached first. The shear and tensile elasticity tests required that no cyclic conditioning be conducted because of limited endurance of the mounting adhesive with some liner materials. The coefficient of friction test was based on dynamic coefficient of friction, as it proved to be a more reliable measurement than static coefficient of friction. The volumetric elasticity test required that air be released beneath samples in the test chamber before testing. The thermal conductivity test best reflected the clinical environment when thermal grease was omitted and when liner samples were placed under pressure consistent with load bearing conditions. The developed procedures provide a standardized approach for evaluating liner products in the prosthetics industry. Test results can be used to improve clinical selection of liners for individual patients and guide development of new liner products.
On the Efficiency Alteration Mechanisms Due to Cavitation in Kaplan Turbines
Authors: Leguizamón Sebastián , Ségoufin Claire , Hai-Trieu Phan , Avellan François
Published: February 2017

A transport-equation-based homogeneous cavitation model previously assessed and validated against experimental data is used to investigate and explain the efficiency alteration mechanisms in Kaplan turbines. On the one hand, it is shown that the efficiency increase is caused by a decrease in energy dissipation due to a decreased turbulence production driven by a drop in fluid density associated with the cavitation region. This region also entails an increase in torque, caused by the modification of the pressure distribution throughout the blade, which saturates on the suction side. On the other hand, the efficiency drop is shown to be driven by a sharp increase in turbulence production at the trailing edge. An analysis of the pressure coefficient distribution explains such behavior as being a direct consequence of the pressure-altering cavitation region reaching the trailing edge. Finally, even though the efficiency alteration behavior is very sensitive to the dominant cavitation type, it is demonstrated that the governing mechanisms are invariant to it.
Two Objective and Independent Fracture Parameters for Interface Cracks
Authors: Zhao Jia-Min , Wang He-Ling , Liu Bin
Published: February 2017

Due to the oscillatory singular stress field around a crack tip, interface fracture has some peculiar features. This paper is focused on two of them. One can be reflected by a proposed paradox that geometrically similar structures with interface cracks under similar loadings may have different failure behaviors. The other one is that the existing fracture parameters of the oscillatory singular stress field, such as a complex stress intensity factor, exhibit some nonobjectivity because their phase angle depends on an arbitrarily chosen length. In this paper, two objective and independent fracture parameters are proposed which can fully characterize the stress field near the crack tip. One parameter represents the stress intensity with classical unit of stress intensity factors. It is interesting to find that the loading mode can be characterized by a length as the other parameter, which can properly reflect the phase of the stress oscillation with respect to the distance to the crack tip. This is quite different from other crack tip fields in which the loading mode is usually expressed by a phase angle. The corresponding failure criterion for interface cracks does not include any arbitrarily chosen quantity and, therefore, is convenient for comparing and accumulating experimental results, even existing ones. The non-self-similarity of the stress field near an interface crack tip is also interpreted, which is the major reason leading to many differences between the interfacial fracture and the fracture in homogenous materials.
Occurrence of Dry-Out Phenomenon in an Auto Refrigerant Cascade Refrigerator Operating With Zeotropic Mixtures
Authors: Gurudath Nayak H. , Venkatarathnam G.
Published: February 2017

Auto refrigerant cascade (ARC) refrigerators are used extensively in the semiconductor manufacturing industry to provide refrigeration in the temperature range of 80–150 K. The performance of the ARC refrigerator depends on the mixture composition, operating pressures, etc. ARC refrigerators employ one or more liquid–vapor phase separators to separate the compressor lubricating oil and the condensed high boiling components and return to the compressor at an intermediate temperature to prevent freezing of the compressor lubricating oil and high boilers at low temperatures. However, dry-out of the phase separator can occur at some conditions. The phase separator dry-out phenomenon in ARC refrigerators has been studied experimentally with different mixtures and operating temperatures, the results of which are reported in this paper. The results of the studies show that the temperature difference between the streams at the cold end of the first heat exchanger can be used to reliably predict the dry-out of the phase separator.
Thermal Management Issues in Operational Data Centers: Computational Fluid Dynamics Analysis and Experimental Study
Authors: Fakhim Babak , Nagarathinam Srinarayana , Armfield Steven W. , Behnia Masud
Published: February 2017

The increase in the number of data centers in the last decade, combined with higher power density racks, has led to a significant increase in the associated total electricity consumption, which is compounded by cooling inefficiencies. Issues, such as hot air recirculation in the data center room environment, provide substantial challenges in thermal manageability. Three operational data centers have been studied to identify the cooling issues. Field measurements of temperature were obtained and were compared to numerical simulations to evaluate the overall thermal behavior of the data centers and to identify the thermal issues.
Characterization of a Commercial Synthetic Jet Actuator for Air Quality Applications
Authors: Abarr Miles , Mauney Denise , Hertzberg Jean , Montoya Lupita D.
Published: February 2017

In this study, a commercial electromagnetic synthetic jet actuator (SJA) was characterized to determine its flow patterns and sphere of influence within a room. Its axisymmetry was also evaluated. The objective of this research is to explore the potential application of this commercial SJA for indoor air quality (IAQ) control and its limitations for such application. A small fan of similar size was also partially characterized. Results showed that the SJA is axisymmetric, and it uses a small power input to impact the airflow over 1 m from the jet exit. Further, while the SJA showed less flow output than the fan in this study, it had significantly greater dynamic pressure per unit power. This feature could be potentially useful for indoor air quality control applications.
A Study of the Effect of Various Recess Shapes on Hybrid Journal Bearing Performance Using Computational Fluid Dynamics and Response Surface Method
Authors: Fu Gen , Untaroiu Alexandrina
Published: February 2017

Hybrid bearings are mostly used in high-speed and load situations due to their better stability and loading capacity. They are typically designed with recess grooves to enhance both static and dynamic performance of the bearing. Previous theoretical studies on the influence of the recess geometrical shapes often utilize the Reynolds equation method. The aim of this paper is to analytically study the influence of various recess geometrical shapes on hybrid journal bearings. A three-dimensional (3D) computational fluid dynamics (CFD) model of a hybrid journal bearing is built, and a new method of response surface model is employed to determine the equilibrium position of the rotor. Based on the response surface model, an optimization scheme is used to search around the equilibrium position to get an accurate solution. The current analysis includes the geometries of rectangular, circular, triangular, elliptical, and annular shaped recesses. All these different shapes are studied assuming the same operating conditions, and static properties are used as the indices of the bearing performance. This study proposes a new design process using a CFD method with the ability of calculating the equilibrium position. The flow rate, fluid film thickness, and recess flow pattern are analyzed for various recess shapes. The CFD model is validated by published experimental data. The results show that the response surface model method is fast and robust in determining the rotor equilibrium position, even though a 3D-CFD model is utilized. The results suggest that recess shape is a dominant factor in hybrid bearing design.
A Cooperative Co-Evolutionary Algorithm for Large-Scale Process Planning With Energy Consideration
Authors: Tao Fei , Bi Luning , Zuo Ying , Nee A. Y. C.
Published: February 2017

Process planning can be an effective way to improve the energy efficiency of production processes. Aimed at reducing both energy consumption and processing time (PT), a comprehensive approach that considers feature sequencing, process selection, and physical resources allocation simultaneously is established in this paper. As the number of decision variables increase, process planning becomes a large-scale problem, and it is difficult to be addressed by simply employing a regular meta-heuristic algorithm. A cooperative co-evolutionary algorithm, which hybridizes the artificial bee colony algorithm (ABCA) and Tabu search (TS), is therefore proposed. In addition, in the proposed algorithm, a novel representation method is designed to generate feasible process plans under complex precedence. Compared with some widely used algorithms, the proposed algorithm is proven to have a good performance for handling large-scale process planning in terms of maximizing energy efficiency and production times.
PTFE and MoS2 Additives for Mineral Oil Film Formation in EHL Point Contacts
Authors: Gyimah Glenn Kwabena , Guo Zhongning , Huang Ping , Jiang Shuzhen , Barber Gary C.
Published: February 2017

Lubricant film-forming viscosity index improvers blended with commercial engine oil have been developed and studied by using optical interferometry. The influence of the viscosity index improvers (PTFE and MoS2) mixed with oil were experimentally studied and compared with engine oil without the index improvers as the baseline. The effect of the viscosity index improvers on lubricant film thickness, contact pressure and rolling speed for the case of a steel ball loaded on a flat glass surface in point contact condition was investigated. An optical interferometry technique which utilized a monochromatic two-beam interferometry light source, a microscope and a high-speed video recording device was used for the investigation. Hamrock and Dawson calculations for EHL film thickness were also used for comparative analysis. The lubricants used were commercial SAE #30 engine oil and PTFE and MoS2 mixed with commercial SAE #30 engine oil. The oil viscosities ranged from 0.0109 Pa.s to 0.255 Pa.s. The rolling speed and the loads were varied between 0.189 m/s to 0.641 m/s and 1 N to 2.6 N respectively. The lubricant film thickness stability at the point of contact between the steel ball and the glass disc was investigated for both steady and rolling state conditions. The viscosity index improvers were found to have a significant effect on the film thickness behavior under pure rolling point contact conditions.
Comparisons of Bending Stiffness of 3D Printed Samples of Different Materials
Authors: Ahmed Mahbub , Islam Md. R. , Vanhoose Justin , Hewavitharana Lionel , Stanich Aaron , Hossain Mohammad
Published: February 2017

3D printing technology has become more affordable than ever before. Today 3D printers are not only used for making prototypes but are also being used to make good quality 3D parts for different purposes. A wide variety of filament materials are used in the market. Finding bending stiffness of different plastic filaments is the particular interest in the current study. The purpose of the project is to investigate the bending stiffness of different 3D printed beam samples. A series of samples for performing bending tests were designed using a solid modeling tool. These samples were printed with four different plastic filaments on a 3D printer in the engineering Lab of Southern Arkansas University. The samples were tested for flexural stiffness (bending) using a materials testing system. A popular 3-point bending test was conducted for this purpose. The force vs. deflection data was obtained to obtain the flexural stiffness of the beam samples. The results were discussed in detail in the result section of this paper.
Optimized Design of Wastewater Disinfection Reactors Based on an Artificial Neural Network Metamodel
Authors: Wei Wangshu , Haas Charles N. , Farouk Bakhtier
Published: February 2017

Peracetic acid (PAA) is an emerging disinfectant for the treatment of wastewater. While it would be possible to optimize the design of this system using computational fluid dynamics (CFD), the computational intensity would be high. As an alternative, we show that an Artificial Neutral Network (ANN) based metamodel can approximate the CFD solutions over an 11 dimensional performance space (dimensions, hydraulic characteristics, and chemical kinetics). By sampling the design space using a quasi-random sampling technique, a series of CFD simulations of disinfection characteristics of PAA in a wastewater treatment reactor are carried out. After a training process using 40 different CFD runs are completed, the ANN developed can be used to achieve an optimized design of wastewater treatment facilities with minimal total cost and acceptable disinfection performance efficiency.
Reducing Wear Debris and Increasing Lower-Limb Amputees’ Comfort by Optimizing Prosthetic Socket Design Using Local Contact Pressure Relief and Implementing Appropriate Holes
Authors: Nehme Gabi , Dib Micheline
Published: February 2017

Maintaining a comfortable fit in prosthetic socket for trans-tibial amputees (TTA) using design of experiment (DOE) and finite element model (FEM) to implement relief areas and holes in socket structure are important goals to help ensure better pressure distributions and successful rehabilitation. Design and fit of socket rely on patient acceptance and comfort. Sixteen sockets designed with different levels of reliefs and holes were investigated by Finite Element Model (FEM) and Design of Experiment (DOE) for flexibility and pressure distribution using ultra high molecular weight polyethylene (UHMWPE) and polyamide 6 (PA6) or Duraform then compared to conventional socket without any compliance.

The purpose of this study was to assess performance of sockets with compliant features integrated into the socket wall to relieve in-socket pressure, increase flexibility and patient comfort during transtibial amputee gait. Reducing thickness at designated areas and hole implementation between the Patellar Tendon (PT) and Distal Tibia (DT) would decrease stiffness and increase prosthesis range of motion where flexibility is needed without compromising mechanical efficiency and the structural integrity of the socket. Different materials sockets 3 of each obtained by FEM/DOE analysis were manufactured and used by six amputees of the same age groups to measure the level of comfort and check the worn surfaces using scanning electron microscopy (SEM) and amputee performances after one year of usage. SEM and optical images were compared. The calculated stiffness of the two compliant sockets with holes are much less than the conventional sockets; they were more comfortable and showed significant decrease in wear debris over the course of the trial period.
Two-Phase Heat Transfer in a Wall-Driven Cubical Heat Sink
Authors: Molki Majid
Published: February 2017

Turbulent heat transfer for flow of water-air mixture driven by moving walls in a cubical heat sink is investigated. One wall is maintained at an elevated temperature, while the vertical walls are at a low temperature. The cubical enclosure functions as a heat sink using water-air mixture with no phase change. Different arrangements for wall motion are considered, which include 1 to 4 moving walls. As the number of moving walls increases, the flow and heat transfer become more complex. In general, the flow reveals complex and multi-scale structures with an unsteady and evolving nature. The larger structure of the flow is resolved using Large Eddy Simulation, while the sub-grid scales are captured by the dynamic k-equation eddy-viscosity model. The focus of this work is on thermal field and heat transfer as affected by the complex flow field generated by multiple moving walls. The results indicate that the Nusselt number for the heat sink varies from 5202.8 to 7356.1, depending on the number of moving walls. Contours of fluid temperature, liquid volume fraction, local and average values of Nusselt number are among the results presented in this paper.
Modeling and Numerical Simulation of Flow Resistance Characteristics in Slowly-Varying Rectangular Cross-Section Microchannel
Authors: Teng Shen , Jiong Wang , Dong Sun , Yafeng Liu , Zhouyu Tian
Published: February 2017

In this paper, flow characteristics in slowly-varying rectangular microchannels with different aspect ratios and Re numbers ranging from 7 to 200 are investigated. The obtained simulation results are compared with theoretics values based on the Bernoulli equations. The results show that the simulation results just hold an average discrepancy of 10% with the theoretical calculation value whichis presents a good accord. All the research of microchannel, the Poiseuille number of the flow is inconstant within the range of Re number, except when the contract angle is small where Poiseuille number is essentially unchanged.
Finite Element Analysis of an Under-Actuated Robotic Device for Knee Loading Applications
Authors: Korupolu Sandeep , Anwar Sohel , Yokota Hiroki , Chien Stanley
Published: February 2017

Knee loading is one form of joint loading modalities, which potentially provides a therapeutic regimen to stimulate bone formation and prevent degradation of joint tissues [1]. Healing of knee injuries is sensitive to many environmental stimuli. Since mechanical stimuli are crucial for the growth, development, and maintenance of articular cartilage and bone, we have developed an innovative robotic knee loading device to achieve this goal [2]. This device induces mechanical loading to stimulate articular cartilage and bone, and it potentially reduces the healing time of injuries such as bone fractures. The robotic device, described in this study, is an improved version over previous joint loading devices [1], in which loads are applied at specific points with non-uniform loading around the knee joint. In this paper, finite element analysis (FEA) of this robotic device has been presented that includes static structural analysis and modal frequencies of the device for two different material configurations used in the design. The study shows that the design with ABS plastic material offers the desired margin of safety while reducing the weight and cost.
Development of an Active Curved Beam Model Using a Moving Frame Method
Authors: Murakami Hidenori
Published: February 2017

In order to develop an active large-deformation beam model for slender, flexible or soft robots, the d’Alembert principle of virtual work is derived for three-dimensional elastic solids from Hamilton’s principle. This derivation is accomplished by refining the definition of the Cauchy stress tensor as a vector-valued 2-form to exploit advanced geometrical operations available for differential forms.

From the three-dimensional principle of virtual work, both the beam principle of virtual work and beam equations of motion with consistent boundary conditions are derived, adopting the kinematic assumption of rigid cross-sections of a deforming beam. In the derivation of the beam model, Élie Cartan’s moving frame method is utilized. The resulting large-deformation beam equations apply to both passive and active beams. The beam equations are validated with the previously reported results expressed in vector form.

To transform passive beams to active beams, constitutive relations for internal actuation are presented in rate-form. Then, the resulting three-dimensional beam models are reduced to an active planar beam model. Finally, to illustrate the deformation due to internal actuation, an active Timoshenko-beam model is derived by linearizing the nonlinear planar equations. For an active, simply-supported Timoshenko-beam, the analytical solution is presented.
Flow and Combustion Characteristics of Annular Advanced Vortex Combustor
Authors: Deng Yangbo , Zheng Luohan , Su Fengmin , Ma Chenshuo
Published: February 2017

To provide an optimized configuration of an annular advanced vortex combustor (AVC), a combined experimental and computational study was carried out about the flow characteristics of an AVC in a rectangular channel under the non-reacting flow condition. A detailed analysis was carried out about the flow through the AVC in a rectangular channel. On this basis, annular AVC model burning hydrogen was designed and consisted of an annular channel which was circumferentially arranged 18 pairs of blunt bodies between two cylinders. A numerical simulation study was conducted to provide understanding of the combustion characteristics of the annular AVC model. The results show: (1) By placing after-bodies, the wake shedding vortex of the flow behind fore-bodies can be effectively controlled and the resistance of the flow can be reduced in a rectangular channel; (2) The injection in the cavities reduces the drag effect depth of the shear layer on the flow in the cavities so that the vortex cores of the main vortexes shift outward the cavity in the AVC in a rectangular channel; (3) With the spacing between fore-body and after body increasing, the state of the main flow is basically kept unchanged and the drag effect of the shear layer on the flow in the cavities is enhanced in the AVC in a rectangular channel; (5) A reasonable configuration of an annular AVC can sustain steady combustion, and keep a low emission level, as the equivalence ratio of the premixed hydrogen and air is between 0.5 and 0.65. (6) Comparing the annular AVC with injection to that without injection, the vortex structures with injection are more symmetrical, the combustions are more stable, and the temperature distributions are more homogeneous. (7) The vortex structure in the annular AVC is almost not changed and the temperature distribution at the outlet alters into less uniformity with injection angle increasing.
Buckling Load Maximization of Composite Laminates Using Particle Swarm Optimization With Various Constraints
Authors: Kim Tae-Uk
Published: February 2017

The stacking sequence of composite laminates is designed to have maximum buckling load using the particle swarm optimization (PSO) algorithm. The original PSO algorithm is modified to handle the discrete ply angles and the constraints such as stiffness and 4-ply contiguity requirements. For this, the augmented Lagrange multiplier (ALM) method is incorporated into the PSO algorithm. For the verification of the algorithm, the benchmarking problems are solved and the results are compared with the ones from the genetic algorithm or the analytic solutions. And then the laminates under in-plane compressive loadings are optimized for maximum buckling load considering the various constraints. The numerical results show that the algorithm finds the optimum with relatively small number of iterations with satisfying the constraints explicitly. Considering its advantage of derivative-free and simple procedures, the proposed algorithm can be applied to more complex models coupled with finite element analysis and various constraints.
The Effect of Processes Parameters on the Abrasive Wear Resistance of Boronized AISI 1050 Steel
Authors: Boztepe Mete Han , Bayramoglu Melih
Published: February 2017

Boronizing is one of the thermochemical surface treatment processes which is extensively used to obtain excellent mechanical properties such as high strength, very high hardness, good toughness and fracture toughness. In this study, AISI 1050 steel specimens have been subjected to pack boronizing process by using Ekabor 2 powder within the stainless steel seal container. The experiments were carried out at temperatures of 800 °C, 850 °C and 900 °C for 3, 6 and 9 hours to investigate the effect of these parameters on the wear resistance of boronized specimens. Pin-on-Disk wear testing is used to characterize wear properties of boronized specimens. Wear tests were performed at dry conditions under constant load of 30 N by using 220 mesh size Al2O3 abrasive paper. Different rotating speeds of the pin-on disk were selected as 300, 600, 900, 1200, 1500 revolutions for each of the test specimens. After the abrasive tests, weight losses of the specimens were measured to determine the abrasive wear resistance of boronized specimens. The results were also compared with unboronized and conventional hardened AISI 1050 steel specimens respectively.
The Structure and Mechanical Properties of Aluminum Cellular Metal With Periodic Cubic Cells
Authors: Dang Xiaobing , Du Ruxu , He Kai , Zuo Qiyang
Published: February 2017

As a light-weight material with high stiffness and strength, cellular metal has attracted a lot of attentions in the past two decades. In this paper, the structure and mechanical properties of aluminum cellular metal with periodic cubic cells are studied. The aluminum cellular metal is fabricated by sheet metal stamping and simple adhesion. Two sizes of specimens with cell sizes of 3mm and 5mm are fabricated. Their relative density and mechanical properties are tested by means of experiments. The results show that the cubic-cell cellular metal has high and predictable strength and hence, can be used for many practical applications.
Modeling of Lamb Wave Propagation in Beam-Like Structures via Wavelet Finite Element Method
Authors: Zuo Hao , Chen Xuefeng , Yang Zhibo , Yang Laihao
Published: February 2017

Beam-like structure is known as one of crucial engineering structures in practical application of aerospace, vessel, civil and machinery. The damages have a great influence on machine performance and may cause a serious threat for security of mechanical structures and systems. Thus it is very significant to identify the damage of beam-like structures for security of mechanical structures and systems. This paper presents a novel application of wavelet finite element method (WFEM) in Lamb wave propagation of beam-like structures. The WFEM, adopting excellent B-spline wavelet on interval (BSWI) basis as approximating functions, has been verified to possess some superiorities for structural dynamic analysis and damage detection. The motion equations of Lamb wave propagation are derived according to Hamilton’s principle and two-dimensional wavelet-based element is constructed by adopting BSWI scaling functions. The damage, which is modeled as open crack with duplicate nodes, is considered in beam-like structures and corresponding damage model is also added in proposed wavelet finite element model. Then central difference method in time domain is employed for wave propagation simulation. Firstly, the validity and accuracy of proposed WFEM are demonstrated on a beam-like structure without crack by comparing with traditional finite element method (FEM) using 2D plane element. What’s more, the obtained velocities of fundamental S0 and A0 mode waves are also compared with Lamb theoretical results to verify the validity and accuracy of proposed model once more. Then the wave propagation in beam-like structures with crack are performed and the process and interaction between Lamb wave and damage are analyzed and discussed in detail. The reflected mode wave and converted mode wave for incident wave interacting with crack are also observed in wave motion snapshots. In summary, this paper presents an accurate but simple and effective numerical method for wave propagation of beam-like structures.
Identification of Fragments in a Meshfree Peridynamic Simulation
Authors: Littlewood David , Silling Stewart , Demmie Paul
Published: February 2017

The peridynamic theory of solid mechanics provides a natural framework for modeling constitutive response and simulating dynamic crack propagation, pervasive damage, and fragmentation. In the case of a fragmenting body, the principal quantities of interest include the number of fragments, and the masses and velocities of the fragments. We present a method for identifying individual fragments in a peridynamic simulation. We restrict ourselves to the meshfree approach of Silling and Askari, in which nodal volumes are used to discretize the computational domain. Nodal volumes, which are connected by peridynamic bonds, may separate as a result of material damage and form groups that represent fragments. Nodes within each fragment have similar velocities and their collective motion resembles that of a rigid body. The identification of fragments is achieved through inspection of the peridynamic bonds, established at the onset of the simulation, and the evolving damage value associated with each bond. An iterative approach allows for the identification of isolated groups of nodal volumes by traversing the network of bonds present in a body. The process of identifying fragments may be carried out at specified times during the simulation, revealing the progression of damage and the creation of fragments. Incorporating the fragment identification algorithm directly within the simulation code avoids the need to write bond data to disk, which is often prohibitively expensive. Results are recorded using fragment identification numbers. The identification number for each fragment is stored at each node within the fragment and written to disk, allowing for any number of post-processing operations, for example the construction of cumulative distribution functions for quantities of interest. Care is taken with regard to very small clusters of isolated nodes, including individual nodes for which all bonds have failed. Small clusters of nodes may be treated as tiny fragments, or may be omitted from the fragment identification process. The fragment identification algorithm is demonstrated using the Sierra/SolidMechanics analysis code. It is applied to a simulation of pervasive damage resulting from a spherical projectile impacting a brittle disk, and to a simulation of fragmentation of an expanding ductile ring.
Robotic Gripper for Payload Capture in Low Earth Orbit
Authors: Genta Giancarlo , Dolci Marco
Published: February 2017

The consensus to a study phase for an IXV (Intermediate eXperimental Vehicle) successor, a preoperational vehicle called PRIDE (Programme for Reusable In-orbit Demonstrator in Europe), has been recently enlarged, as approved during last EU Ministerial Council. One of the main project task consists in developing PRIDE to conduct on orbit servicing activity with no docking. PRIDE would be provided with a robotic manipulator system (arm and gripper) able to transfer payloads, such as scientific payloads, from low Earth orbiting platforms to PRIDE payload bay. The platform is a part of a space tug designed to move small satellites and other payloads from Low Earth Orbits (LEO) to Geostationary orbit (GEO) and viceversa. A study on this robotic technology is here presented. This research is carried out by Politecnico di Torino and Thales Alenia Space Italy (Grasping Manipulator Design), and by Thales Alenia Space Italy and Amet (PRIDE Robotics System Design). The system configuration of the robotic manipulator is first described in terms of volumes and masses. The assumed housing payload bay requirements in terms of volume (<100 l) and mass (<50 kg) combined with the required overall arm dimensions (4 m length), as defined following the stated mission scenario, and mass of the payload (5–30 kg) force to developing an innovative robotic manipulator with the task-oriented end effector. It results in a 7 degree-of-freedom arm to ensure a high degree of dexterity and a dedicate end-effector designed to grasp the payload interface. The gripper concept here developed consists in a multi-finger hand able to lock both translational and rotational payload degrees of freedom through an innovative under actuation strategy to limit its mass and volume. While in the literature in usual actuation architectures, underactuated systems have been realized where the first (nearest) phalanx closure led afterwards to the closure of the second (distal) one using the loading of a torsional springs and mechanical linkages, this system presents a new underactuation strategy. In this case the distal phalanx closes before the nearest one, allowing to grasp the handle side and limiting the handle length and volume. This concept will allow the distal phalanx to move independently from the nearest one. A configuration study on the payload handle interface has also been performed. Moreover, trade-off studies, computer aided design models, multibody and structural analysis of the whole system are shown to prove its feasibility. Finally, the concept of system control architecture, organized in three main blocks is defined: the Control Overall System Block, the Control Arm Block and the Control Robotic Hand Block.
Exoskeleton Wrist Design Using Composite Visualization Methods
Authors: James Thomas D. , Carignan Craig R.
Published: February 2017

The design process is examined for retrofitting a robotic arm exoskeleton with a three-axis wrist for enhanced teleoperation. Exoskeleton wrist design is particularly challenging due to the need to incorporate three actuated joints into a compact volume, while maintaining a large range of motion. The design process was greatly facilitated by the development of a new visualization method which enabled the designer to examine the interactions between the exoskeleton and its operator in the same virtual workspace. This allowed the designer to evaluate the exoskeleton’s range of motion and ergonomic properties, while also adding task visualization functionality. Future applications of the exoskeleton in telepresence will also be discussed.
Investigation of the Effect of Vortex Generation on Heat Transfer Enhancement in Horizontal Channel Flow
Authors: Morjan Saleh , Jawad Badih A. , Liu Liping , Yee Kingman , Fernandez Vernon
Published: February 2017

In this experimental work, a flow field test system was installed to investigate the impact of vortex generators on the flow structure and heat transfer of air flow in a horizontal channel. Three different configurations of vortex generators, a small single delta winglet pair, a large single delta winglet pair, and two delta winglet pairs developed in a V-formation array were fitted vertically on an aluminum plate and tested in a small wind path system of open circuit with horizontal test section of dimensions 70 mm (width) × 35 mm (height) × 1600 mm (length). An axial AC fan was used to supply the flow of air through the test section. The air flow was cooling the flat plate which had embedded electric heating constructed as a layered structure. Temperature distributions along the heated plate were measured using thermocouples to obtain the Nusselt numbers. The effect of three different attack angles, 15°, 30°, and 45° of the selected VGs were investigated in this work. The experimental results showed that under the tested Reynolds number of 10145, the presence of vortex generators had considerable effect on temperature distribution, pressure drop and heat transfer augmentation in the channel flow. Compared with the plain channel; the heat transfer rate was enhanced by (31.9% – 51.0%), (30.8% – 53.7 %), and (18.2 % – 36.2%) while the pressure drop increased by (1.8% – 11.0%), (4.5% – 35.4%), and (6.0 % – 30.0%) with the small single delta winglet pair, the large single delta winglet pair, and two pairs deployed in a V-formation array, respectively.
Atomistically Informed Method of Cells Based Multiscale Approach for Analysis of CFRP Composites
Authors: Rai Ashwin , Subramanian Nithya , Chattopadhyay Aditi
Published: February 2017

In this paper a multiscale-modeling framework is presented wherein fundamental damage information at the atomic level is coupled with a sectional micromechanics model for the nonlinear and damage analysis of carbon fiber reinforced polymer (CFRP) composites. Damage information in the polymer matrix originating from the atomic scale, as investigated using molecular dynamics (MD) simulations, is transferred to the continuum length scale using a continuum damage mechanics approach with a physical damage evolution equation. Such a framework is shown to be computationally efficient for the linear and damage analysis of CFRP composites and reasonably accurate when compared to experimental data and verified models in literature. Furthermore, material uncertainty, such as curing degree variation in polymers, can be computationally calculated leading to a computational stochastic analysis of the CFRP composites. Thus, such a framework can be used to investigate the damage mechanics of ply level CFRP components at the nano, micro and macro length scales.
Analysis of Singular Stress Fields at 3D Piezoelectric Bonded Joints Using a Conservative Integral
Authors: Luangarpa Chonlada , Koguchi Hideo
Published: February 2017

Singular stress fields at a vertex of the interface in three-dimensional piezoelectric bonded joints are analyzed. A conservative integral based on the Betti reciprocal principle is applied for calculating the intensities of singularities. Eigenanalysis formulated using a three-dimensional finite element method (FEM) is used to calculate the order of stress singularity, angular functions of mechanical displacements, stresses, electric displacements and electric potential. A bimaterial bonded joint with three terms of singularities is investigated. In order to study the influence of mesh refinement and integral area on the accuracy of the results, two models with different element sizes and various integral areas are used. The results are compared with those obtained from conventional FEM, in which using extremely refined meshes near the singular point.
A Numerical Study of the Simultaneous Natural Convective Heat Transfer From the Upper and Lower Surfaces of a Thin Isothermal Horizontal Circular Plate
Authors: Oosthuizen Patrick H. , Kalendar Abdulrahim
Published: February 2017

Natural convective heat transfer from the top and bottom surfaces of a thin circular isothermal horizontal plate which, in general, has a centrally placed adiabatic section has been numerically investigated. The temperature of the plate surfaces is higher than the temperature of the surrounding fluid. The range of conditions considered is such that laminar, transitional, and turbulent flow occurs over the plate. The heat transfer from the upper and lower surfaces of the plate as well as the mean heat transfer rate from the entire surface of the plate have been considered. The flow has been assumed to be axisymmetric and steady. The k-epsilon turbulence model with account being taken of buoyancy force effects has been used and the solution has been obtained using the commercial CFD solver ANSYS FLUENT©. The heat transfer rate from the heated plate has been expressed in terms of a Nusselt number based on the outside plate diameter and the difference between the plate temperature and the fluid temperature far from the plate. The mean Nusselt number is dependent on the Rayleigh number, the ratio of the diameter of the inner adiabatic section to the outer plate diameter, and the Prandtl number. Results have only been obtained for a Prandtl number of 0.74, i.e., effectively the value for air. The variations of the mean Nusselt number averaged over both the upper and lower surfaces and of the mean Nusselt numbers for the upper surface and for the lower surface with Rayleigh number for various adiabatic section diameter ratios have been studied. The use of a reference length scale to allow the correlation of these mean Nusselt number-Rayleigh number variations has been investigated.
BELBIC-Sliding Mode Control of Robotic Manipulators With Uncertainties and Switching Constraints
Authors: Klecker Sophie , Plapper Peter
Published: February 2017

This paper addresses the control problem for trajectory tracking of a class of robotic manipulators presenting uncertainties and switching constraints using a biomimetic approach. Uncertainties, system-inherent as well as environmental disturbances deteriorate the performance of the system. A change in constraints between the robot’s end-effector and the environment resulting in a switched nonlinear system, undermines the stable system performance. In this work, a robust adaptive controller combining sliding mode control and BELBIC (Brain Emotional Learning-Based Intelligent Control) is suggested to remediate the expected impacts on the overall system tracking performance and stability. The controller is based on an interplay of inputs relating to environmental information through error-signals of position and sliding surfaces and of emotional signals regulating the learning rate and adapting the future behaviour based on prior experiences. The proposed control algorithm is designed to be applicable to discontinuous freeform geometries. Its stability is proven theoretically and a simulation, performed on a two-link manipulator verifies its efficacy.
Experimental Calibration of ISV Damage Model Constants for Pure Copper for High-Speed Impact Simulation
Authors: Dou Yangqing , Liu Yucheng , Whittington Wilburn , Miller Jonathan
Published: February 2017

Coefficients and constants of a microstructure-based internal state variable (ISV) plasticity damage model for pure copper have been calibrated and used for damage modeling and simulation. Experimental stress-strain curves obtained from Cu samples at different strain rate and temperature levels provide a benchmark for the calibration work. Instron quasi-static tester and split-Hopkinson pressure bar are used to obtain low-to-high strain rates. Calibration process and techniques are described in this paper. The calibrated material model is used for high-speed impact analysis to predict the impact properties of Cu. In the numerical impact scenario, a 100 mm by 100 mm Cu plate with a thickness of 10 mm will be penetrated by a 50 mm-long Ni rod with a diameter of 10mm. The thickness of 10 mm was selected for the Cu plate so that the Ni-Cu penetration through the thickness can be well observed through the simulations and the effects of the ductility of Cu on its plasticity deformation during the penetration can be displayed. Also, that thickness had been used by some researchers when investigating penetration mechanics of other materials. Therefore the penetration resistance of Cu can be compared to that of other metallic materials based on the simulation results obtained from this study. Through this study, the efficiency of this ISV model in simulating high-speed impact process is verified. Functions and roles of each of material constant in that model are also demonstrated.