bluuebunny/crossref_metadata_2025 huggingface dataset:
Muscle and tendon lengthening behaviour of the medial gastrocnemius during ankle joint rotation in children with cerebral palsy
Authors: Kalkman Barbara M. , Bar‐On Lynn , Cenni Francesco , Maganaris Constantinos N. , Bass Alfie , Holmes Gill , Desloovere Kaat , Barton Gabor J. , O'Brien Thomas D.
Published: August 2018

New Findings

What is the central question of this study?

Which structures of the medial gastrocnemius muscle–tendon unit contribute to its lengthening during joint rotation and thus receive the stretching stimulus?

What is the main finding and its importance?

We show, for the first time, that muscle and tendon lengthen in a different manner in children with cerebral palsy compared with typically developing children during a similar amount of muscle–tendon unit lengthening or joint rotation. This indicates possible differences in mechanical muscle and tendon properties attributable to cerebral palsy, which are not evident by assessment of muscle function at the level of a joint.

Children with cerebral palsy (CP) commonly present with reduced ankle range of motion (ROM) attributable, in part, to changes in mechanical properties of the muscle–tendon unit (MTU). Detailed information about how muscle and tendon interact to contribute to joint rotation is currently lacking but might provide essential information to explain the limited effectiveness of stretching interventions in children with CP. The purpose of this study was to quantify which structures contribute to MTU lengthening and thus receive the stretch during passive ankle joint rotation. Fifteen children with CP (age, in mean ± SD, 11.4 ± 3 years) and 16 typically developing (TD) children (age, in mean ± SD, 10.2 ± 3 years) participated. Ultrasound was combined with motion tracking, joint torque and EMG to record fascicle, muscle and tendon lengthening of the medial gastrocnemius during passive ankle joint rotations over the full ROM and a common ROM. In children with CP, relative to MTU lengthening, muscle and fascicles lengthened less (CP, 50.4% of MTU lengthening; TD, 63% of MTU lengthening; P < 0.04) and tendon lengthened more (CP, 49.6% of MTU lengthening; TD, 37% of MTU lengthening; P < 0.01) regardless of the ROM studied. Differences between groups in the amount of lengthening of the underlying structures during a similar amount of joint rotation and MTU displacement indicate possible differences in tissue mechanical properties attributable to CP, which are not evident by assessment at the level of a joint. These factors should be considered when assessing and treating muscle function in children with CP, for example during stretching exercises, because the muscle might not receive much of the applied lengthening stimulus.
Numerical Investigations of an Axial Exhaust Diffuser Coupling the Last Stage of a Generic Gas Turbine
Authors: Mihailowitsch Marius , Schatz Markus , Vogt Damian M.
Published: August 2018

It is well known that the last stage of a turbine and the subsequent diffuser should be viewed at and designed as a coupled system rather than as single standalone components. The turbine outlet flow imposes the inlet conditions to the diffuser, whereas the recovered dynamic pressure in the diffuser directly controls the turbine back pressure. With changing operating point, the turbine outflow can vary significantly. This results consequently in large variations of the diffuser performance. A major role in the coupled system of turbine and diffuser can be attributed to the tip leakage flow. While it is desirable to minimize the tip leakage with regard to the turbine, a higher leakage mass flow can often be beneficial for the diffuser performance. As there is currently a trend toward aggressive and hence shorter diffusers which are particularly prone to separation, the question arises where the optimum for this tradeoff problem lies. To investigate the performance in the coupled turbine/diffuser system, a generic last stage with shrouded rotor and axial exhaust diffuser has been designed. The components are representative for heavy duty stationary gas turbine applications. Results are presented for three different operating points representing part-load (PL), design-load (DL), and over-load (OL) condition. Three different seal gap widths are taken into account to control the leakage flow. The results indicate that an operating point-dependent optimum gap width can be found for the coupled system efficiency, whereas the maximum turbine performance is always achieved with a minimum gap width.
Torsional Friction Behavior of Contact Interface Between PEEK and CoCrMo in Calf Serum
Authors: Liu Dongliang , Wang Qingliang , Zhang Dekun , Wang Jian , Zhang Xiao
Published: August 2018

Polyether ether ketone (PEEK) and its composites are recognized as alternative bearing materials for use in arthroplasty because of their excellent mechanical properties. In this paper, torsional friction tests of PEEK against the CoCrMo alloy, simulating the contact mode between the prosthesis tibia and femur, were carried out under a 25% calf serum solution in a Leeds Prosim knee simulator. The torsional friction behavior of PEEK against the CoCrMo alloy was investigated under various normal loads (1000 N, 1600 N and 2200 N), torsional angular displacement amplitudes (±1 deg, ±3 deg, and ±5 deg), and the number of cycles (7500, 15,000, and 30,000). The torsional friction characteristics and damage mechanism are discussed. The results show that PEEK exhibited low friction coefficient under the different conditions. With increases in the torsional angle and normal load, three types of torque/angular displacement amplitude (T–θ) curves (i.e., linear, parallelogram, and elliptical loops) were observed and analyzed during the process of torsional friction. With the increase of the torsional angle, the coefficient of friction decreases. And the contact states change from the partial slip regime to the slip regime. The greater the torsional angle displacement, the more severe the damage to the PEEK surface. With an increase in the normal load, the wear scars increased. The wear depth is deepened and the width is widened, and the wear gradually becomes serious with an increase in the load. The small load is more likely to cause damage to the central area of PEEK, and the larger load causes more serious damage to the marginal region. The central and marginal regions of the PEEK sample have different wear characteristics. The worn surfaces of the central regions were characterized by convex ridges resulting from plastic deformation, while curved ploughs and fatigue peeling appeared in the marginal region. The wear mechanism of PEEK in the central region is plastic deformation, while fatigue wear and abrasive wear mainly appeared in the marginal region.
Study on the Performance of a Curved Fresnel Solar Concentrated System With Seasonal Underground Heat Storage for the Greenhouse Application
Authors: Li Zhiyong , Ma Xinglong , Zhao Yunsheng , Zheng Hongfei
Published: August 2018

A solar heating system in greenhouse driven by Fresnel lens concentrator is built in this study. This system uses a soil thermal storage for greenhouse to supply heat in the absence of sunlight, ensuring the safety of the growth of crops. The structure and working principle of the device are introduced in this paper. The underground soil temperature was tested, compared with the indoor and outdoor temperature. The experimental testing result is given. A research shows that when the heating pipe buried 1.65 m underground, the time of heat transfer to the ground is about 5 days. The overall temperature rise of the soil is about 4 °C. In the condition of the coldest weather without additional energy supplement, the greenhouse's temperature is guaranteed above 8 °C, which can ensure the minimum temperature requirements of crop growth. According to the structural parameters of the existing system, the simulation of underground soil heat transfer and heat storage performance was carried out. Then, the temperature curves of different buried depths of the tube are given. The soil temperature steady time in different pipe-buried depths of heat storage temperature is theoretically calculated. It is proved that, to achieve the seasonal thermal storage in this system, the buried depth of the pipe should be over 2.5 m.
Investigations of a Dehumidifier in a Solar-Assisted Liquid Desiccant Demonstration Plant
Authors: Jaradat Mustafa , Fleig Daniel , Vajen Klaus , Jordan Ulrike
Published: August 2018

A solar-assisted liquid desiccant demonstration plant was built and experimentally evaluated. Humidity of the air, density of the desiccant, and all relevant mass flow rates and temperatures were measured at each inlet and outlet position. Adiabatic dehumidification experiments were performed in different seasons of the year under various ambient air conditions. The moisture removal rate m˙v, the mass balance factor κm, and the absorber effectiveness, εabs, were evaluated. An aqueous solution of LiCl was used as liquid desiccant with an initial mass fraction of about 0.4 kgLiCl/kgsol. The mass flow rate of the air through the absorber was about 1100 kg/h. The experimental results showed a reduction in the air humidity ratio in the range of 1.3–4.3 g/kg accompanied with an increase in the air temperature in the range of 3–8.5 K, depending on the inlet and operating conditions. For the air to desiccant mass flow ratio of 82, a mass fraction spread of 5.7% points in the desiccant and a volumetric energy storage capacity of 430 MJ/m3 were achieved. By operating the desiccant pump in an intermittent mode, a mass fraction spread of about 13% points in the desiccant and an energy storage capacity of about 900 MJ/m3 were reached. In addition, the experimental results were compared with results from a numerical model. The numerical model overestimates the heat and mass transfer because it assumes ideal surface wetting and uniform distribution of the circulated fluids.
Data-Driven Predesign Tool for Small-Scale Centrifugal Compressor in Refrigeration
Authors: Violette Mounier , Cyril Picard , Jürg Schiffmann
Published: August 2018

Domestic scale heat pumps and air conditioners are mainly driven by volumetric compressors. Yet the use of reduced scale centrifugal compressors is reconsidered due to their high efficiency and power density. The design procedure of centrifugal compressors starts with predesign tools based on the Cordier line. However, the optimality of the obtained predesign, which is the starting point of a complex and iterative process, is not guaranteed, especially for small-scale compressors operating with refrigerants. This paper proposes a data-driven predesign tool tailored for small-scale centrifugal compressors used in refrigeration applications. The predesign model is generated using an experimentally validated one-dimensional (1D) code which evaluates the compressor performance as a function of its detailed geometry and operating conditions. Using a symbolic regression tool, a reduced order model that predicts the performance of a given compressor geometry has been built. The proposed predesign model offers an alternative to the existing tools by providing a higher level of detail and flexibility. Particularly, the model includes the effect of the pressure ratio, the blade height ratio, and the shroud to tip radius ratio. The analysis of the centrifugal compressor losses allows identifying the underlying phenomena that shape the new isentropic efficiency contours. Compared to the validated 1D code, the new predesign model yields deviations below 4% on the isentropic efficiency, while running 1500 times faster. The new predesign model is, therefore, of significant interest when the compressor is part of an integrated system design process.
On the Role of Fluid–Structure Interaction on Structural Loading by Pressure Waves in Air
Authors: Gauch Hannes L. , Montomoli Francesco , Tagarielli Vito L.
Published: August 2018

This study investigates the significance of fluid–structure interaction (FSI) effects on structural response to pressure wave and shock wave loading. Finite element (FE) simulations and one-dimensional (1D) analytical models are used to compare the responses of simple structures in presence and absence of FSI. Results are provided in nondimensional form and allow rapid estimation of the significance of FSI. The cases of a square elastic plate in bending and a square rigid-perfectly plastic plate undergoing membrane stretching are discussed in detail. We deduce simple formulae to identify scenarios in which effects of FSI can be neglected.
Experimental Study of Water Flow and Heat Transfer in Silicon Micro-Pin-Fin Heat Sinks
Authors: Xu Fayao , Wu Huiying
Published: August 2018

An experimental study is performed to investigate water flow and heat transfer characteristics in silicon micro-pin-fin heat sinks with various pin–fin configurations and a conventional microchannel, with a length of 25 mm, a width of 2.4 mm, and a height of 0.11 mm. The micro-pin-fin heat sinks have different fin arrangements, fin shapes, and fin pitches. The results show that the micro-pin-fin heat sinks have the better overall thermal-hydraulic performance including the heat transfer enhancement and the pressure drop penalty compared to the conventional microchannel. A parametric study is carried out to investigate the effects of various pin-fin configurations on the flow and heat transfer characteristics. The linear relationship between fRe and Re is found for the water flow through the micro-pin-fin heat sinks for the first time. A new friction factor correlation is further developed based on the linear relationship between fRe and Re. Taking the effects of the various pin-fin configurations on the Nusselt number into consideration, a new Nusselt number correlation is also developed. The new correlations of friction factor and Nusselt number predict the experimental data well. An infrared thermo-imaging system was used to measure the temperature field of water heat transfer in the micro-pin-fin heat sinks and the conventional microchannel. The infrared thermo-images show the more uniform temperature profile in the transverse direction for the micro-pin-fin heat sinks than that for the conventional microchannel, which indicates the better heat transfer performance of the former than the latter. The dominant mechanism of heat transfer enhancement caused by the micro-pin-fins is the hydrodynamic effects, including fluid disturbance as well as the breakage and re-initialization of the thermal boundary layer near the wall of the heat sinks.
Effect of Rounded Corners on Heat Transfer and Fluid Flow Through Triangular Duct
Authors: Kumar Rajneesh , Kumar Anoop , Goel Varun
Published: August 2018

Turbulent flow heat transfer and friction penalty in triangular cross-sectional duct is studied in the present paper. The sharp corners of the duct are modified by converting it into circular shape. Five different models were designed and fabricated. Heat transfer through all the models was investigated and compared conventional triangular duct under similar conditions. The curvature radius of rounded corners for different models was kept constant (0.33 times the duct height). The numerical simulations were also performed and the obtained result validated with the experimental findings and close match observed between them. The velocity and temperature distribution is analyzed at particular location in the different models. Because of rounded corners, higher velocity is observed inside the duct (except corners) compared to conventional duct. Considerable increase in Nusselt number is seen in model-5, model-4, model-3, and model-2 by 191%, 41%, 19%, and 8% in comparison to model-1, respectively, at higher Reynolds number (i.e., 17,500). But, frictional penalty through the model-5, model-4, model-3, and model-2 increased by 287%, 54%, 18%, and 12%, respectively, in comparison to model-1 at lower Reynolds number (i.e., 3600).
Identification of a Lathe Spindle Dynamics Using Extended Inverse Receptance Coupling
Authors: Jasiewicz Marcin , Powałka Bartosz
Published: August 2018

In order to ensure machining stability, it is essential to properly determine the dynamic properties of machine tool–workpiece system. Experimental modal analysis provides good results; however, due to high time consumption, in some cases, its use is not practically justified. Then, a receptance coupling method can be used, that allows for the synthesis of the experimental models of the machine tool components and analytical models of the workpiece. However, a significant disadvantage of this method is the need for the experimental identification of the rotational degrees-of-freedom, fully defining dynamic properties of the spindle. This paper presents an improved method based on inverse receptance coupling, which enables effective identification of the spindle dynamics with the properties of the joint. Then, a measurement procedure and results of the experimental validation are presented.
Sequential Control of Multichannel On–Off Valves for Linear Flow Characteristics Via Averaging Pulse Width Modulation Without Flow Meter: An Application for Pneumatic Valves
Authors: Pawananont Kanchit , Leephakpreeda Thananchai
Published: August 2018

Control of on–off valves for linear flow characteristics is a challenging design problem due to nonlinearity of valve mechanism and fluidic properties under various operating conditions. In this study, averaging pulse width modulation (PWM) is proposed as a control valve signal by implementing PWM with predetermined duty period so that overflow at the open position and underflow at the closed position are divided proportionately around desired mean flow rates during entire cycle periods. Multichannels in a parallel pattern are implemented to yield linear flow characteristics with higher resolution than a single channel. With pressure and temperature measurements, the volumetric flow rate is determined by an empirical model of flow characteristics across flow control valves at given operating conditions. The experimental results on achieving the desired volumetric flow rate of air under actual flow conditions without a flow meter are presented for viability of the proposed methodology in practical uses.
Starting Poiseuille Flow in a Circular Tube With Two Immiscible Fluids
Authors: Ng Chiu-On , Wang C. Y.
Published: August 2018

Starting flow due to a suddenly applied pressure gradient in a circular tube containing two immiscible fluids is solved using eigenfunction expansions. The orthogonality of the eigenfunctions is developed for the first time for circular composite regions. The problem, which is pertinent to flow lubricated by a less viscous near-wall fluid, depends on the ratio of the radius of the core region to that of the tube, and the ratios of dynamic and kinematic viscosities of the two fluids. In general, a higher lubricating effect will lead to a longer time for the starting transient to die out. The time development of velocity profile and slip length are examined for the starting flows of whole blood enveloped by plasma and water enveloped by air in a circular duct. Owing to a sharp contrast in viscosity, the starting transient duration for water/air flow can be ten times longer than that of blood/plasma flow. Also, the slip length exhibits a singularity in the course of the start-up. For blood with a thin plasma skimming layer, the singularity occurs very early, and hence for the most part of the start-up, the slip length is nearly a constant. For water lubricated by air of finite thickness, the singularity may occur at a time that is comparable to the transient duration of the start-up, and hence, an unsteady slip length has to be considered in this case.
Experimental Investigation of Residual Ultimate Strength of Damaged Metallic Pipelines
Authors: Cai Jie , Jiang Xiaoli , Lodewijks Gabriel , Pei Zhiyong , Zhu Ling
Published: August 2018

The ultimate strength of metallic pipelines will be inevitably affected when they have suffered from structural damage after mechanical interference. The present experiments aim to investigate the residual ultimate bending strength of metallic pipes with structural damage based on large-scale pipe tests. Artificial damage, such as a dent, metal loss, a crack, and combinations thereof, is introduced to the pipe surface in advance. Four-point bending tests are performed to investigate the structural behavior of metallic pipes in terms of bending moment–curvature diagrams, failure modes, bending capacity, and critical bending curvatures. Test results show that the occurrence of structural damage on the pipe compression side reduces the bending capacity significantly. Only a slight effect has been observed for pipes with damage on the tensile side as long as no fracture failure appears. The possible causes that have introduced experimental errors are presented and discussed. The test data obtained in this paper can be used to further quantify damage effects on bending capacity of seamless pipes with similar D/t ratios. The comparison results in this paper can facilitate the structural integrity design as well as the maintenance of damaged pipes when mechanical interference happens during the service life of pipelines.
A Mode-Resolved Continuum Mechanics Model of Acoustic Wave Scattering From Embedded Cylinders
Authors: Unni Vineet , Feser Joseph P.
Published: August 2018

In this paper, we use continuum mechanics to develop an analytic treatment of elastic wave scattering from an embedded cylinder and show that a classic treatise on the subject contains important errors for oblique angles of incidence, which we correct. We also develop missing equations for the scattering cross section at oblique angles and study the sensitivity of the scattering cross section as a function of elastodynamic contrast mechanisms. We find that in the Mie scattering regime for oblique angles of incidence, both elastic and density contrast are important mechanisms by which scattering can be controlled, but that their effects can offset one another, similar to the theory of reflection at flat interfaces. In comparison, we find that in the Rayleigh scattering regime, elastic and density contrast are always complimentary toward increasing scattering cross section, but for sufficiently high density contrast, the scattering cross section for incident compressional and y-transverse modes is nearly independent of elastic contrast. The solution developed captures the scattering physics for all possible incident elastic wave orientations, polarizations, and wavelengths including the transition from Rayleigh to geometric scattering regimes, so long as the continuum approximation holds. The method could, for example, enable calculation of the thermal conductivity tensor from microscopic principles which requires knowledge of the scattering cross section spanning all possible incident elastic wave orientations and polarizations at thermally excited wavelengths.
Reactive Joining of Thermally and Mechanically Sensitive Materials
Authors: Rheingans Bastian , Furrer Roman , Neuenschwander Jürg , Spies Irina , Schumacher Axel , Knappmann Stephan , Jeurgens Lars P. H. , Janczak-Rusch Jolanta
Published: August 2018

Reactive joining, i.e., utilization of an exothermal reaction to locally generate the heat required for soldering or brazing, represents an emerging technology for flexible and benign joining of heat-sensitive materials, e.g., for microelectromechanical systems (MEMS) applications. However, for successful reactive joining, precise control of heat production and heat distribution is mandatory in order to avoid damaging of the components during the process. For the exemplary case of borosilicate glass, the reactive joining process for a both thermally and mechanically sensitive material is developed. Employing various nondestructive and destructive testing methods, typical problems which can occur upon reactive joining are identified, e.g., exposure of the joining zone to excessive temperatures, experience of thermal shock by the substrate due to sudden temperature increase, and generation of residual stresses in substrate and soldering zone. Utilizing the results of nondestructive and destructive testing, procedures for successful reactive joining of borosilicate glass, silicon and aluminum oxide are provided.
An Inertia-Deformability Hybrid Circulating Tumor Cell Chip: Design, Clinical Test, and Numerical Analysis
Authors: Chen Hongmei , Zhang Zhifeng
Published: August 2018

Detection and capture of circulating tumor cells (CTCs) with microfluidic chips hold significance in cancer prognosis, diagnosis, and anti-cancer treatment. The counting of CTCs provides potential tools to evaluate cancer stages as well as treatment progress. However, facing the challenge of rareness in blood, the precise enumeration of CTCs is challenging. In the present research, we designed an inertial-deformability hybrid microfluidic chip using a long spiral channel with trapezoid-circular pillars and a capture zone. To clinically validate the device, the microfluidic chip has been tested for the whole blood and lysed blood with a small number of CTCs (colorectal and nonsmall-cell lung cancer) spiked in. The capture efficiency reaches over 90% for three types of cancer cell lines at the flow rate of 1.5 mL/h. Following numerical modeling was conducted to explain the working principle and working condition (Reynolds number below 10 and Dean number around 1). This design extended the effective capture length, improved the capture efficiency, and made the CTC enumeration much easier. We believe that this hybrid chip is promising clinically in the CTCs enumeration, evaluation of cancer therapy, and pharmacological responses.
Investigating the Mechanical Properties of Biological Brain Cells With Atomic Force Microscopy
Authors: Bahwini Tariq Mohana , Zhong Yongmin , Gu Chengfan , Nasa Zeyad , Oetomo Denny
Published: August 2018

Characterization of cell mechanical properties plays an important role in disease diagnoses and treatments. This paper uses advanced atomic force microscopy (AFM) to measure the geometrical and mechanical properties of two different human brain normal HNC-2 and cancer U87 MG cells. Based on experimental measurement, it measures the cell deformation and indentation force to characterize cell mechanical properties. A fitting algorithm is developed to generate the force-loading curves from experimental data. An inverse Hertzian method is also established to identify Young's moduli for HNC-2 and U87 MG cells. The results demonstrate that Young's modulus of cancer cells is different from that of normal cells, which can help us to differentiate normal and cancer cells from the biomechanical viewpoint.
Fast Conjugate Heat Transfer Simulation of Long Transient Flexible Operations Using Adaptive Time Stepping
Authors: Maffulli R. , He L. , Stein P. , Marinescu G.
Published: August 2018

The emerging renewable energy market calls for more advanced prediction tools for turbine transient operations in fast startup/shutdown cycles. Reliable numerical analysis of such transient cycles is complicated by the disparity in time scales of the thermal responses in fluid and solid domains. Obtaining fully coupled time-accurate unsteady conjugate heat transfer (CHT) results under these conditions would require to march in both domains using the time-step dictated by the fluid domain: typically, several orders of magnitude smaller than the one required by the solid. This requirement has strong impact on the computational cost of the simulation as well as being potentially detrimental to the accuracy of the solution due to accumulation of round-off errors in the solid. A novel loosely coupled CHT methodology has been recently proposed, and successfully applied to both natural and forced convection cases that remove these requirements through a source-term based modeling (STM) approach of the physical time derivative terms in the relevant equations. The method has been shown to be numerically stable for very large time steps with adequate accuracy. The present effort is aimed at further exploiting the potential of the methodology through a new adaptive time stepping approach. The proposed method allows for automatic time-step adjustment based on estimating the magnitude of the truncation error of the time discretization. The developed automatic time stepping strategy is applied to natural convection cases under long (2000 s) transients: relevant to the prediction of turbine thermal loads during fast startups/shutdowns. The results of the method are compared with fully coupled unsteady simulations showing comparable accuracy with a significant reduction of the computational costs.
Contact of Rough Surfaces in Ankle Implants Under Combined Normal and Twist Loading
Authors: Hodaei Mohammad , Farhang Kambiz
Published: August 2018

The medical application of implant replacements to remedy the pain in joints has necessitated a comprehensive study of wear due to contact of implant surfaces. Excessive wear can lead to toxicity and other implant associated medical issues such as patient discomfort and decreased mobility. Since implant wear is the result of contact between surfaces of tibia and talus implant, it is important to establish a model that can address implant surface contact mechanics with roughness effects. In this research, a statistical contact model is developed for the interaction of tibia and talus including normal and lateral contact in which surface roughness effects are included. The model accounts for the elastic–plastic interaction of the implant surface with roughness. For this purpose, tibia and talus implants are considered as macroscopic surfaces containing micron-scale roughness. Approximate equations are obtained that relate the contact force to the mean surface separation explicitly. Closed-form equations are obtained for hysteretic energy loss in implant using the approximate equations. Such a function can serve as a very useful tool for implant designers and manufacturers. Natural frequencies of both adduction-abduction and planter-dorsiflexion rotations are obtained using nonlinear vibration analyses.
Effects of Asymmetry on Thermoacoustic Modes in Annular Combustors: A Higher-Order Perturbation Study
Authors: Mensah Georg A. , Magri Luca , Orchini Alessandro , Moeck Jonas P.
Published: August 2018

Gas-turbine combustion chambers typically consist of nominally identical sectors arranged in a rotationally symmetric pattern. However, in practice, the geometry is not perfectly symmetric. This may be due to design decisions, such as placing dampers in an azimuthally nonuniform fashion, or to uncertainties in the design parameters, which break the rotational symmetry of the combustion chamber. The question is whether these deviations from symmetry have impact on the thermoacoustic-stability calculation. The paper addresses this question by proposing a fast adjoint-based perturbation method. This method can be integrated into numerical frameworks that are industrial standard such as lumped-network models, Helmholtz and linearized Euler equations. The thermoacoustic stability of asymmetric combustion chambers is investigated by perturbing rotationally symmetric combustor models. The approach proposed in this paper is applied to a realistic three-dimensional combustion chamber model with an experimentally measured flame transfer function (FTF). The model equations are solved with a Helmholtz solver. Results for modes of zeroth, first, and second azimuthal order are presented and compared to exact solutions of the problem. A focus of the discussion is set on the loss of mode-degeneracy due to symmetry breaking and the capability of the perturbation theory to accurately predict it. In particular, an “inclination rule” that explains the behavior of degenerate eigenvalues at first order is proven.
Recursive Characteristics of a Running-in Attractor in a Ring-on-Disk Tribosystem
Authors: Ding Cong , Zhu Hua , Jiang Yu , Sun Guodong , Wei Chunling
Published: August 2018

To explore the recursive characteristics of a running-in attractor, recurrence plot (RP) and recursive parameters are used to investigate the dynamic features of the structure. The running-in attractor is constructed based on friction noise signals generated from the ring-on-disk wear experiments. The RPs of the running-in attractor are then reproduced in a two-dimensional space. Recursive parameters, recurrence rate (RR), entropy (ENTR), and trend of recurrence (RT) are calculated. Results show that the RP evolves from a disrupted pattern to a homogeneous pattern and then returns to a disrupted pattern in the entire wear process, corresponding to the “formation–stabilization–disappearance” stage of the running-in attractor. The RR and ENTR of the running-in attractor sharply increase at first, remain steady, and then sharply decrease. Moreover, the inclination of RT in the normal wear process is smaller than those in the other two processes. This observation reveals that the running-in attractor exhibits high stability and complexity. This finding may contribute to the running-in state identification, process prediction, and control.
Development of Wear Mechanism Maps for Acrylonitrile Butadiene Styrene Hybrid Composites Reinforced With Nano Zirconia and PTFE Under Dry Sliding Condition
Authors: Amrishraj D. , Senthilvelan T.
Published: August 2018

Acrylonitrile butadiene styrene (ABS) polymer is cost-effective and also possesses high toughness and resistance to corrosive chemicals. However, pure ABS does not show significant wear resistance and also it has a high friction coefficient. Incorporation of a solid lubricant and nanofiller in a polymer matrix improves its tribological properties significantly. The addition of solid lubricant makes it suitable for application where self-lubrication is desirable (sliding bearings, gears). This paper deals with the study of tribological behavior of ABS hybrid composites reinforced with nano zirconia and polytetrafluoroethylene (PTFE). ABS hybrid composites with varying proportions of nano zirconia and PTFE were prepared using melt blending. Dispersion of reinforcement in the polymer matrix has been studied with the help of transmission electron micrographs. Influence of reinforcements on the mechanical behavior is studied by tensile testing according to the ASTM standard. The tribological behavior of composites was determined in a pin-on-disk tribometer according to the ASTM G99 standard. Worn surfaces were analyzed using scanning electron microscope (SEM) in order to identify the different types of wear and various wear mechanisms. Transfer film formation was studied by analyzing the counterbody surface. A wear mechanism map has been developed, which helps in identifying various wear mechanisms involved under given loading conditions. The results reveal that the addition of PTFE reduces the wear rate and coefficient of friction (COF) significantly. Nano zirconia effectively transfers the load, thereby improving wear resistance, and the addition of PTFE results in continuous transfer film formation thereby reducing the COF. Also from the wear map, it has been identified that abrasion, adhesion, plowing, plastic deformation, melting, and delamination are the dominant wear mechanisms involved.
Design of Tilting-Pad Journal Bearings Considering Bearing Clearance Uncertainty and Reliability Analysis
Authors: da Silva Heitor Antonio Pereira , Nicoletti Rodrigo
Published: August 2018

The dynamic characteristics of tilting-pad journal bearings (TPJBs) are strongly related to their geometric parameters, most importantly the bearing clearance. In turn, the bearing clearance in TPJBs is strongly dependent on the machining tolerances of the bearing parts and their assembling. Considering that, the machining tolerances of the pads can be of the same magnitude order of the oil film thickness in the bearing, it is uncertain that the TPJB will have the originally designed geometry after assembling. Therefore, the resultant dynamic characteristics of the TPJB also become uncertain. In this work, we present an investigation of tilting-pad bearings and their equivalent dynamic coefficients when subjected to dimensional variability. First, we perform a stochastic analysis of the system using a thermo-hydrodynamic (THD) model of the tilting-pad bearing and considering the bearing clearance in each pad as an independent random variable (varying between minimum and maximum values). We show that the scattering of the results of the dynamic coefficients is limited by the values obtained from TPJBs with all pads with maximum or minimum possible clearances. Second, we apply the concepts of reliability analysis to develop a design procedure for tilting-pad bearings. This design methodology considers the results obtained in the stochastic analysis and it allows the Engineer to appropriately design the bearing for a given probability of success or, inversely, a given probability of failure. Such approach assures a level of reliability to the dynamic coefficients of designed TPJBs in face of their dimensional variability.
Small-World Outer Synchronization of Small-World Chaotic Networks
Authors: Arellano-Delgado A. , López-Gutiérrez R. M. , Martínez-Clark R. , Cruz-Hernández C.
Published: August 2018

In this work, small-world outer synchronization of coupled small-world networks is presented. In particular, we use Newman and Watts model to achieve small-world outer synchronization of small-world chaotic networks with Chua's oscillators like chaotic nodes. By means of extensive numerical simulations, we show that the new outer connections between existing networks decrease the necessary coupling strength to achieve outer synchronization. Two scenarios of interest are studied, (i) small-world outer synchronization with unidirectional outer connections (with chaotic master network), and (ii) small-world outer synchronization with bidirectional outer connections (without chaotic master network). In both scenarios, the isolated networks are bidirectionally coupled using Chua's oscillators like chaotic nodes.
Modeling and Analysis of Tier 4 Locomotives Operating in a High-Altitude Tunnel
Authors: McElhaney Kevin S. , Mischler Robert
Published: August 2018

Tunnels represent one of the most severe operating conditions for diesel engines in diesel-electric locomotive applications, specifically for nonventilated tunnels located at high elevation. High ambient air temperatures are observed in these tunnels due to heat rejected from the locomotive engines through the exhaust and engine cooling and lubrication systems. Engine protection algorithms cause the maximum allowable engine horsepower to be reduced due to these conditions leading to a reduction in train speed and occasionally train stall. A first law based model was developed to simulate the performance of a train pulled by GE diesel-electric locomotives equipped with medium speed diesel engines in a high altitude and nonventilated tunnel. The model was compared against and calibrated to actual tunnel operation data of EPA Tier 2 compliant locomotives. The model was then used to study the impact of engine design changes required for EPA Tier 4 compliant locomotives, specifically the introduction of exhaust gas recirculation (EGR), on engine, locomotive, and train performance in the tunnel. Simulations were completed to evaluate engine control strategies targeting same or better train performance than the EPA Tier 2 compliant locomotive baseline case. Simulation results show that the introduction of EGR reduces train performance in the tunnel by increasing the required reduction in engine horsepower, but is slightly offset by improved performance from other engine design changes. The targeted engine and train performance could be obtained by disabling EGR during tunnel operation.
A Modulated Voltage Waveform for Enhancing the Travel Range of Dielectric Elastomer Actuators
Authors: Arora Nitesh , Kumar Pramod , Joglekar M. M.
Published: August 2018

This paper presents a method to achieve high deformability levels in dielectric elastomer actuators (DEAs) by applying a modulated voltage waveform. The method relies on supplying the electrostatic energy during the specific phase of the oscillation cycle, resulting in the enhanced travel range at a relatively low driving voltage. We consider a standard sandwich configuration of the DE actuator with neo-Hookean material model and outline an energy-based approach for delineating the underlying principles of the proposed method. A comparison of the deformability levels achieved using the quasi-static, Heaviside step, and the modulated input waveforms is presented. Significant reduction in instability voltages together with a considerable increase in the stable actuation limit is observed in the case of the modulated voltage input. The estimates of the stability thresholds are validated by integrating the equation of motion obtained using Hamilton's principle. The effect of energy dissipation is assessed by considering variations in the quality factor. Further, a qualitative comparison with experimental observations is presented highlighting the practical feasibility of the method. This investigation can find its potential use in the design and development of DEAs subjected to a time-dependent motion.
Unraveling the Effect of Material Properties and Geometrical Factors on Ballistic Penetration Energy of Nanoscale Thin Films
Authors: Meng Zhaoxu , Keten Sinan
Published: August 2018

It is crucial to investigate the dynamic mechanical behavior of materials at the nanoscale to create nanostructured protective systems that have superior ballistic impact resistance. Inspired from recent experimental advances that enable ballistic materials testing at small scales, here we report a comparative analysis of the dynamic behavior of nanoscale thin films made from multilayer graphene (MLG), polymer, gold, and aluminum under high-speed projectile impact. We employ atomistic and coarse-grained (CG) molecular dynamics (MD) simulations to measure the ballistic limit velocity (V50) and penetration energy (Ep) of these nanoscale films and investigate their distinctive failure mechanisms over a wide range of impact velocities (Vi). For the local penetration failure mechanism observed in polymer and metal films, we find that the intrinsic mechanical properties influence Ep at low Vi, while material density tends to govern Ep at high Vi. MLG films uniquely show a large impact propagation zone (IPZ), which transfers the highly localized impact energy into elastic deformation energy in a much larger area through cone wave propagation. We present theoretical analyses that corroborate that the size of IPZ should depend not only on material properties but also on a geometrical factor, specifically, the ratio between the projectile radius and film thickness. This study clearly illustrates how material properties and geometrical factors relate to the ballistic penetration energy, thereby allowing a quantitative comparison of the nanoscale ballistic response of different materials.
On Stability of Specific Adhesion of Particles to Membranes in Simple Shear Flow
Authors: Moshaei Mohammad Hossein , Tehrani Mohammad , Sarvestani Alireza
Published: August 2018

Adhesion of carrier particles to the luminal surface of endothelium under hemodynamic flow conditions is critical for successful vascular drug delivery. Endothelial cells (ECs) line the inner surface of blood vessels. The effect of mechanical behavior of this compliant surface on the adhesion of blood-borne particles is unknown. In this contribution, we use a phase-plane method, first developed by Hammer and Lauffenburger (1987, “A Dynamical Model for Receptor-Mediated Cell Adhesion to Surfaces,” Biophys. J., 52(3), p. 475), to analyze the stability of specific adhesion of a spherical particle to a compliant interface layer. The model constructs a phase diagram and predicts the state of particle adhesion, subjected to an incident simple shear flow, in terms of interfacial elasticity, shear rate, binding affinity of cell adhesive molecules, and their surface density. The main conclusion is that the local deformation of the flexible interface inhibits the stable adhesion of the particle. In comparison with adhesion to a rigid substrate, a greater ligand density is required to establish a stable adhesion between a particle and a compliant interface.
Numerical Investigation on Film Cooling Performance of Fusiform Diffusion Holes
Authors: An Bai-Tao , Liu Jian-Jun
Published: August 2018

This paper presents a numerical investigation of the film-cooling performance of a kind of diffusion hole with a fusiform cross section. Relative to the rectangular diffusion hole, the up- and/or downstream wall of the fusiform diffusion hole is outer convex. Under the same metering section area, six fusiform diffusion holes were divided into two groups with cross-sectional widths of W = 1.7D and W = 2.0D, respectively. Three fusiform cross section shapes in each group included only downstream wall outer convex, only upstream wall outer convex, or a combination of both. Simulations were performed in a flat plate model using a 3D steady computational fluid dynamics method under an engine-representative condition. The simulation results showed that the fusiform diffusion hole with only an outer convex upstream wall migrates the coolant laterally toward the hole centerline, and then forms or enhances a tripeak effectiveness pattern. Conversely, the fusiform diffusion hole with an outer convex downstream wall intensely expands the coolant to the hole two sides, and results in a bipeak effectiveness pattern, regardless of the upstream wall shape. Compared with the rectangular diffusion holes, the fusiform diffusion holes with only an upstream wall outer convex significantly increase the overall effectiveness at high blowing ratios. The increased magnitude is approximately 20% for the hole of W = 1.7D at M = 2.5. Besides, the fusiform diffusion holes with an outer convex upstream wall increase the discharge coefficient about 5%, within the moderate to high blowing ratio range.
A Unified Analytical Method of Stress Analysis for Tubesheet—Part III: Applicable Configuration of Heat Exchanger
Authors: Zhu Hongsong , Zhai Jinguo
Published: August 2018

Based on the unified analytical (UA) method and the unified and refined analytical (URA) method of stress analysis for fixed tubesheet (TS) heat exchangers (HEXs), floating head, and U-tube HEXs, the applicable configuration of HEX which depends on the combination of the TS edge conditions is discussed in this paper. Comparison shows that the UA and the URA methods cover a wide range of HEX configurations well beyond established ASME methods.