bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinematic Analysis of Foldable Plate Structures With Rolling Joints
Authors: Jianguo Cai
Published: December 2015

Rolling joints, which are created by attaching two cylindrical surfaces of equal radius using two or more thin tapes or cable, are used for rigid origami considering the panel thickness. First, the concept and two implementation methods of this joint are given. Then planar linkages are chosen to study the mobility and kinematics of foldable plate structures with rolling joints. It can be found that the rolling joints preserve the full-cycle-motion of foldable plate structures. From the closure equations of linkages, the results show that the outputs of linkages with rolling joints are the same as that with traditional revolute joints if the lengths of links are equal. However, the results are different when the lengths of links are unequal. Moreover, the difference between linkages with rolling joints and revolute joints increases with an increase of the size of rolling joints.
Design and Analysis of a Cable-Driven Articulated Rehabilitation System for Gait Training
Authors: Alamdari Aliakbar , Krovi Venkat
Published: December 2015

Assisted motor therapies play a critical role in enhancing functional musculoskeletal recovery and neurological rehabilitation. Our long-term goal is to assist and automate the performance of repetitive motor-therapy of the human lower limbs. Hence, in this paper, we examine the viability of a light-weight and reconfigurable hybrid (articulated-multibody and cable) robotic system for assisting lower-extremity rehabilitation and analyze its performance. A hybrid cable-actuated articulated-multibody system is formed when multiple cables are attached from a ground-frame to various locations on an articulated-linkage-based orthosis. Our efforts initially focus on developing an analysis and simulation framework for the kinematics and dynamics of the cable-driven lower limb orthosis. A Monte Carlo approach is employed to select configuration parameters including cuff sizes, cuff locations, and the position of fixed winches. The desired motions for the rehabilitative exercises are prescribed based upon motion patterns from a normative subject cohort. We examine the viability of using two controllers—a joint-space feedback-linearized PD controller and a task-space force-control strategy—to realize trajectory- and path-tracking of the desired motions within a simulation environment. In particular, we examine performance in terms of (i) coordinated control of the redundant system; (ii) reducing internal stresses within the lower-extremity joints; and (iii) continued satisfaction of the unilateral cable-tension constraints throughout the workspace.
Microplane-Triad Model for Elastic and Fracturing Behavior of Woven Composites
Authors: Kirane Kedar , Salviato Marco , Bažant Zdeněk P.
Published: December 2015

A multiscale model based on the framework of microplane theory is developed to predict the elastic and fracturing behavior of woven composites from the mesoscale properties of the constituents and the weave architecture. The effective yarn properties are obtained by means of a simplified mesomechanical model of the yarn, based on a mixed series and parallel coupling of the fibers and of the polymer within the yarns. As a novel concept, each of the several inclined or aligned segments of an undulating fill and warp yarn is represented by a triad of orthogonal microplanes, one of which is normal to the yarn segment while another is normal to the plane of the laminate. The constitutive law is defined in terms of the microplane stress and strain vectors. The elastic and inelastic constitutive behavior is defined using the microplane strain vectors which are the projections of the continuum strain tensor. Analogous to the principle of virtual work used in previous microplane models, a strain energy density equivalence principle is employed here to obtain the continuum level elastic and inelastic stiffness tensors, which in turn yield the continuum level stress tensor. The use of strain vectors rather than tensors makes the modeling conceptually clearer as it allows capturing the orientation of fiber failures, yarn cracking, matrix microcracking, and interface slip. Application of the new microplane-triad model for a twill woven composite shows that it can realistically predict all the orthotropic elastic constants and the strength limits for various layups. In contrast with the previous (nonmicroplane) models, the formulation can capture the size effect of quasi-brittle fracture with a finite fracture process zone (FPZ). Explicit finite-element analysis gives a realistic picture of progressive axial crushing of a composite tubular crush can initiated by a divergent plug. The formulation is applicable to widely different weaves, including plain, twill, and satin weaves, and is easily extensible to more complex architectures such as hybrid weaves as well as two- and three-dimensional braids.
On Creep Fatigue Interaction of Components at Elevated Temperature
Authors: Barbera Daniele , Chen Haofeng , Liu Yinghua
Published: December 2015

The accurate assessment of creep–fatigue interaction is an important issue for industrial components operating with large cyclic thermal and mechanical loads. An extensive review of different aspects of creep fatigue interaction is proposed in this paper. The introduction of a high temperature creep dwell within the loading cycle has relevant impact on the structural behavior. Different mechanisms can occur, including the cyclically enhanced creep, the creep enhanced plasticity and creep ratchetting due to the creep fatigue interaction. A series of crucial parameters for crack initiation assessment can be identified, such as the start of dwell stress, the creep strain, and the total strain range. A comparison between the ASME NH and R5 is proposed, and the principal differences in calculating the aforementioned parameters are outlined. The linear matching method (LMM) framework is also presented and reviewed, as a direct method capable of calculating these parameters and assessing also the steady state cycle response due to creep and cyclic plasticity interaction. Two numerical examples are presented, the first one is a cruciform weldment subjected to cyclic bending moment and uniform high temperature with different dwell times. The second numerical example considers creep fatigue response on a long fiber reinforced metal matrix composite (MMC), which is subjected to a cycling uniform thermal field and a constant transverse mechanical load. All the results demonstrate that the LMM is capable of providing accurate solutions, and also relaxing the conservatisms of the design codes. Furthermore, as a direct method, it is more efficient than standard inelastic incremental finite element analysis.
Rotorcraft Hard Landing Mitigation Using Robotic Landing Gear
Authors: Kiefer J. , Ward M. , Costello M.
Published: December 2015

A unique, beneficial feature of rotorcraft is their flexibility in aircraft-to-ground interfacing. For a variety of reasons, hard landings can occur when the descent rate of the aircraft is larger than intended. The resulting impact can result in vehicle damage, structural failure, injuries, etc. To reduce these risks, an attractive solution is the implementation of a robotic legged landing gear (RLLG) system. The system softens a hard landing by acting as a shock absorber with a relatively large stroke, allowing the aircraft to decelerate over a much larger distance compared with a tradition landing gear system. This paper explores the mitigation of rotorcraft hard landings via RLLG through a comprehensive multibody dynamics simulation tool. The purpose of this study is to demonstrate the efficacy of the RLLG as a robust solution to reduce loads during hard landings for multiple landing configurations. The results show that when using RLLG in place of conventional landing gear, peak loads are reduced by approximately 70–90%, depending on the landing conditions. Through Monte Carlo simulation, robotic landing gear system performance is shown to be robust to uncertain conditions.
A Wind Farm Optimal Control Algorithm Based on Wake Fast-Calculation Model
Authors: Bo Gu , Yongqian Liu , Jie Yan , Li Li , Shun Kang
Published: December 2015

A wake fast-calculation model is developed, which can calculate the wind speed distribution of wind farms accurately and efficiently under varying wind speed and wind direction. Based on the wake fast-calculation model, a wind farm optimal controlling model is established to optimize the axial induction factors of wind turbines solving by particle swarm optimization (PSO) algorithm. In this way, the overall wind farm power output can be maximized and the wake losses can be minimized. Horns Rev wind farm in Denmark is selected as the case study, and the calculation results show that the wind farm optimal control algorithm based on the wake fast-calculation model is effective.
Impact of Gurney Flaplike Strips on the Aerodynamic and Vortex Flow Characteristic of a Reverse Delta Wing
Authors: Lee T.
Published: December 2015

The impact of Gurney flaplike strips, of different geometric configurations and heights, on the aerodynamic characteristics and the tip vortices generated by a reverse delta wing (RDW) was investigated via force-balance measurement and particle image velocimetry (PIV). The addition of side-edge strips (SESs) caused a leftward shift of the lift curve, resembling a conventional trailing-edge flap. The large lift increment overwhelmed the corresponding drag increase, thereby leading to an improved lift-to-drag ratio compared to the baseline wing. The lift and drag coefficients were also found to increase with the strip height. The SES-equipped wing also produced a strengthened vortex compared to its baseline wing counterpart. The leading-edge strips (LESs) were, however, found to persistently produce a greatly diffused vortex flow as well as a small-than-baseline-wing lift in the prestall α regime. The downward LES delivered a delayed stall and an increased maximum lift coefficient compared to the baseline wing. The LESs provide a potential wingtip vortex control alternative, while the SESs can enhance the aerodynamic performance of the RDW.
Estimating Over Temperature and Its Duration in a Flat Plate With Sudden Changes in Heating and Cooling
Authors: Lee Chien-Shing , Shih Tom I-P. , Mark Bryden Kenneth
Published: December 2015

When the operating condition of a gas turbine engine changes from one steady-state to another, the cooling must ensure that the solid's temperatures never exceed the maximum allowable throughout the transient process. Exceeding the maximum allowable temperature is possible even though cooling is increased to compensate for the increase in heating because there is a time lag in how the solid responds to changes in its convective heating and cooling environments. In this paper, a closed-form solution (referred to as the 1D model) is derived to estimate the over temperature and its duration in a flat plate subjected to sudden changes in heating and cooling rates. For a given change in heating rate, the 1D model can also be used to estimate the minimum cooling needed to ensure that the new steady-state temperature will not exceed the maximum allowable. In addition, this model can estimate the temperature the material must be cooled to before imposing a sudden increase in heat load to ensure no over temperature throughout the transient process. Comparisons with the exact solutions show the 1D model to be accurate within 0.1%. This 1D model was generalized for application to problems in multidimensions. The generalized model was used to estimate the duration of over temperature in a two-dimensional problem involving variable heat transfer coefficient (HTC) on the cooled side of a flat plate and provided results that match the exact solution within 5%.
Thermal Convection of a Non-Fourier Fluid in a Vertical Slot
Authors: Niknami Mohammad , Khayat Roger E.
Published: December 2015

The instability of steady natural convection of a non-Fourier fluid of the single-phase lagging (SPL) type between two vertical surfaces maintained at different temperatures is studied. SPL fluids possess a relaxation time, which reflects the delay in the response of the heat flux and the temperature gradient. The SPL model is particularly relevant to low-temperature liquids, ultrafast processes, and nanofluids (with a retardation time added in this case). Linear stability analysis is employed to obtain the critical state parameters, such as critical Grashof numbers. For intermediate Prandtl numbers (Pr = 7.5), when non-Fourier level exceeds a certain value, the neutral stability curve comprises a Fourier branch and an oscillatory branch. In this case, oscillatory convection increasingly becomes the mode of preference, compared to both conduction and stationary convection. Critical Grashof number decreases for fluids with higher non-Fourier levels.
Low-Temperature Melting of Silver Nanoparticles in Subcooled and Saturated Water
Authors: Lee Soochan , Phelan Patrick E. , Taylor Robert A. , Prasher Ravi , Dai Lenore
Published: December 2015

Continuous, laser-heated boiling heat transfer experiments with silver nanofluids were conducted to identify the nonequilibrium melting behavior of silver nanoparticles in de-ionized (DI) water. Experimental results with transmission electron microscopy (TEM) and dynamic light scattering (DLS) suggest that surface melting of silver nanoparticles (which have a bulk melting point of 961 °C) can occur at ambient pressure when particles are suspended in saturated, and even subcooled (e.g., <100 °C) water due to the localized (volumetric) heat absorption. These findings are supported by calculating a temperature-dependent Hamaker constant of silver nanofluid—i.e., the interaction between interfaces (Ag-melt-water) at the melting temperature. This finding is significant because of the difficulty to identify the melting of silver nanoparticles in water at present, even though it is important to understand such potential melting to use aqueous silver nanofluids in solar applications.
Influence of Microscale Surface Modification on Impinging Flow Heat Transfer Performance
Authors: Taha T. J. , Lefferts L. , Van der Meer T. H.
Published: December 2015

An experimental approach has been used to investigate the influence of a thin layer of carbon nanotubes (CNTs) on the convective heat transfer performance under impinging flow conditions. A successful synthesis of CNT layers was achieved using a thermal catalytic vapor deposition process (TCVD) on silicon sample substrates. Three different structural arrangements, with fully covered, inline, and staggered patterned layers of CNTs, were used to evaluate their heat transfer potential. Systematic surface characterizations were made using scanning electron microscope (SEM) and confocal microscopy. The external surface area ratio of fully covered, staggered, and inline arrangement was obtained to be 4.57, 2.80, and 2.89, respectively. The surface roughness of the fully covered, staggered, and inline arrangement was measured to be (Sa = 0.365 μm, Sq = 0.48 μm), (Sa = 0.969 μm, Sq = 1.291 μm), and (Sa = 1.668 μm, Sq = 1.957 μm), respectively. On average, heat transfer enhancements of 1.4% and − 2.1% were obtained for staggered and inline arrangement of the CNTs layer. This is attributed to the negligible improvement on the effective thermal resistance due to the small area coverage of the CNT layer. In contrast, the fully covered samples enhanced the heat transfer up to 20%. The deposited CNT layer plays a significant role in reducing the effective thermal resistance of the sample, which contributes to the enhancement of heat transfer.
Thermal Instability in a Rotating Vertical Porous Layer Saturated by a Nanofluid
Authors: Govender S.
Published: December 2015

An analytical investigation of the onset on convection in a vertical porous layer saturated by a nanofluid is presented. The Darcy model is used for the vertical porous layer and a linear stability analysis is used to determine the convection threshold in terms of the key parameters for the nanofluid. This study reveals that the Taylor number and gravity effects are passive, and that the most critical mode is roll cells aligned with the vertical axis of rotation. The critical Rayleigh number is presented in terms of the nanofluid parameters for both stationary and oscillatory convection.
Vibration Suppression of a Strain Gradient Microscale Beam Via an Adaptive Lyapunov Control Strategy
Authors: Nojoumian Mohammad Ali , Vatankhah Ramin , Salarieh Hassan
Published: December 2015

Vibration suppression of a strain gradient Euler–Bernoulli beam in presence of disturbance and uncertainties is considered in this investigation. Vibration of the system is suppressed by an adaptive boundary controller which has robustness to the environmental and control effort disturbances. The direct Lyapunov stability theorem is used to design the controller and adaptation law. The numerical results are presented to demonstrate the effectiveness of the proposed controller.
Absolute Stability Analysis Using the Liénard Equation: A Study Derived From Control of Fuel Cell Ultracapacitor Hybrids
Authors: Nowak William , Geiyer Daniel , Das Tuhin
Published: December 2015

Load-following in solid oxide fuel cells (SOFCs), hybridized with an ultracapacitor for energy storage, refers to an operating mode where the fuel cell's generated power follows the variable power demand, delivering the total demanded power at steady-state. Implementing this operating mode presents a rich set of problems in dynamical systems and control. This paper focuses on state-of-charge (SOC) control of the ultracapacitor during load-following, under transient constraints, and in the presence of an unknown nonlinearity. The problem is generalized to stabilization of a plant containing a cascaded connection of a driver and a driven dynamics, where the former is nonlinear and largely unknown. Closed-loop stability of the system is studied as a Lur'e problem and via energy-based Lyapunov equations, but both impose conservative conditions on the nonlinearity. An alternate approach is developed, where the closed-loop dynamics are formulated as a class of Liénard equations. The corresponding analysis, which is based on the nonlinear characteristics of the Liénard equation, yields more definitive and less conservative stability criteria. Additional conditions that lead to limit cycles are also derived, and a bifurcation pattern is revealed. The generality of the proposed approach indicates applicability to a variety of nonlinear systems.
Influence of Residual Stress and Temperature on the Cyclic Hardening Response of M50 High-Strength Bearing Steel Subjected to Rolling Contact Fatigue
Authors: Bhattacharyya Abir , Subhash Ghatu , Arakere Nagaraj , Allison Bryan D. , McCoy Bryan
Published: December 2015

Microstructural and mechanical characterization investigations on three variants of a through-hardened M50 bearing steel are presented to compare and contrast their performances under rolling contact fatigue (RCF) loading. Baseline (BL) variant of M50 steel bearing balls is subjected to: (i) a surface nitriding treatment and (ii) a surface mechanical processing treatment, to obtain distinct microstructures and mechanical properties. These balls are subjected to RCF loading for several hundred million cycles at two different test temperatures, and the subsequent changes in subsurface hardness and compressive stress–strain response are measured. It was found that the RCF-affected subsurface regions grow larger in size at higher temperature. Micro-indentation hardness measurements within the RCF-affected regions revealed an increase in hardness in all the three variants. The size of the RCF-affected region and intensity of hardening were the largest in the BL material and smallest in the mechanically processed (MP) material. Based on Goodman's diagram, it is shown that the compressive residual stress reduces the effective fully reversed alternating stress amplitude and thereby retards the initiation and evolution of subsurface plasticity within the material during RCF loading. It is quantitatively shown that high material hardness and compressive residual stress are greatly beneficial for enhancing the RCF life of bearings.
A New Methodology for Modeling and Free Vibrations Analysis of Rotating Shaft Based on the Timoshenko Beam Theory
Authors: Mirtalaie S. H. , Hajabasi M. A.
Published: December 2015

The linear lateral free vibration analysis of the rotor is performed based on a new insight on the Timoshenko beam theory. Rotary inertia, gyroscopic effects, and shear deformations are included, but the torsion is neglected and a new dynamic model is presented. It is shown that if the total rotation angle of the beam cross section is considered as one of the degrees-of-freedom of the Timoshenko rotor, as is common in the literature, some terms are missing in the modeling of the global dynamics of the system. The total deflection of the beam cross section is divided into two steps, first the Euler angles relations are employed to establish the curved geometry of the beam due to the elastic deformation of the beam centerline and then the shear deformations was superposed on it. As a result of this methodology and the mutual interaction of shear and Euler angles some variable coefficient terms appeared in the kinetic energy of the system which makes the problem be classified as the parametrically excited systems. A linear coupled variable coefficient system of differential equations is derived while the variable coefficient terms have been missing in all previous studies in the literature. The free vibration behavior of parametrically excited system is investigated by perturbation method and compared with the common Rayleigh, Timoshenko, and higher-order shear deformable spinning beam models in the rotordynamics. The effects of rotating speed and slenderness ratio are studied on the forward and backward natural frequencies and the critical speeds of the system are examined. The study demonstrates that the shear and Euler angles interaction affects the high-frequency free vibrations behavior of the spinning beam especially for higher slenderness ratio and rotating speeds of the rotor.
Interface Reactions Between Sealing Glass and Metal Interconnect Under Static and Dynamic Heat Treatment Conditions
Authors: Peng Lian , Zhu Qingshan , Xie Zhaohui , Wang Ping
Published: December 2015

Chemical compatibility of sealing glass with metal interconnects is a critical issue for planar solid oxide fuel cell (SOFC). In this paper, interface reactions between a sealing glass and a ferritic metal interconnect (SS410) are tested under three different heat treatment conditions: sealing (static), aging (static), and thermal cycling (dynamic). The results show that the BaCrO4 crystals with two different morphology (round-shaped and needle-shaped) form both at the three-phase boundary (where air, glass, and SS410 meet) and on the surface of the sealing glass under the three conditions. Round-shaped BaCrO4 crystals form with low O2 concentration and short reaction time. Needle-shaped BaCrO4 crystals form with high O2 concentration and long reaction time. For the thermal cycling condition, the BaCrO4 formed at early stages causes the delamination of the sealing interface. Then, O2 diffuses into the interior interface along the delamination path, which results in the formation of BaCrO4 at the interior interface. The delamination-enhanced BaCrO4 formation during thermal cycling will lead to crack along the sealing interface, causing the striking increase of leak rates.
Prediction of Sand Transport and Deposition in a Two-Pass Internal Cooling Duct
Authors: Singh Sukhjinder , Tafti Danesh K.
Published: December 2015

Sand transport and deposition is investigated in a two-pass internal cooling ribbed geometry at near engine conditions. Large-eddy simulation (LES) calculations are performed for bulk Reynolds number of 25,000 to calculate flow field and heat transfer. Constant wall temperature boundary condition is used to investigate the effect of temperature on particle deposition. Three different wall temperatures of 950 °C, 1000 °C, and 1050 °C are considered. Particle sizes in range 5–25 μm are considered. A new deposition model which accounts for particle composition, temperature, impact velocity and angle and material properties of particle and surface is developed and applied. Calculated impingement and deposition patterns are discussed for different exposed surfaces in the two pass geometry. Other than the leading rib faces, the highest particle impingement and deposition is observed in the bend region and first quarter of the second pass. Significant deposition is observed in the two pass geometry for all three wall temperatures considered. Particle impingement and hence deposition is dominated by larger particles except in the downstream half of the bend region. In total, approximately 38%, 59%, and 67% of the injected particles deposit in the two passes, for the three wall temperatures of 950 °C, 1000 °C, and 1050 °C, respectively. While particle impingement is highest for wall temperature of 950 °C, higher deposition is observed for 1000 °C and 1050 °C cases. Deposition increases significantly with wall temperature. For 1000 °C, roughly 12% of the impacting particles deposit. For 1050 °C, approximately 23% of the particles deposit on impact. For all the three cases, the second pass experiences higher deposition compared to the first pass due to higher turbulence and direct impingement.
Microfeature Heat Exchanger Using Variable-Density Arrays for Near-Isothermal Cold-Plate Operation
Authors: Gallandat Noris , Hesse Danielle , Rhett Mayor J.
Published: December 2015

The purpose of this paper is to demonstrate the possibility to selectively tune the convective heat transfer coefficient in different sections of a heat sink by varying the density of microfeatures in order to minimize temperature gradients between discrete heat sources positioned along the flow path. Lifetime of power electronics is strongly correlated to the thermal management of the junction. Therefore, it is of interest to have constant junction temperatures across all devices in the array. Implementation of microfeature enhancement on the convective side improves the heat transfer due to an increase in surface area. Specific shapes such as micro-hydrofoils offer a reduced pressure drop allowing for combined improvement of heat transfer and flow performance. This study presents experimental results from an array of three discrete heat sources (20 × 15 mm) generating 100 W/cm2 and positioned in line along the flow path with a spacing of 10 mm between each of the sources. The heat sink was machined out of aluminum 6061, and micro-hydrofoils with a characteristic length of 500 μm were embedded in the cold plate. The cooling medium used is water at a flow rate of 3.6–13.4 g/s corresponding to a Reynolds number of 420–1575. It is demonstrated that the baseplate temperature can be maintained below 90 °C, and the difference between the maximum temperatures of each heat source is less than 6.7 °C at a heat flux of 100 W/cm2 and a water flow rate of 4.8 g/s.
Tissue-Engineering for the Study of Cardiac Biomechanics
Authors: Ma Stephen P. , Vunjak-Novakovic Gordana
Published: December 2015

The notion that both adaptive and maladaptive cardiac remodeling occurs in response to mechanical loading has informed recent progress in cardiac tissue engineering. Today, human cardiac tissues engineered in vitro offer complementary knowledge to that currently provided by animal models, with profound implications to personalized medicine. We review here recent advances in the understanding of the roles of mechanical signals in normal and pathological cardiac function, and their application in clinical translation of tissue engineering strategies to regenerative medicine and in vitro study of disease.
Influence of Channel Geometry and Flow Variables on Cyclone Cooling of Turbine Blades
Authors: Bruschewski Martin , Scherhag Christian , Schiffer Heinz-Peter , Grundmann Sven
Published: December 2015

A study examining the internal cooling of turbine blades by swirling flow is presented. The sensitivity of swirling flow is investigated with regard to Reynolds number, swirl intensity, and the common geometric features of blade-cooling ducts. The flow system consists of a straight and round channel that is attached to a swirl generator with tangential inlets. Different orifices and 180-deg bends are employed as channel outlets. The experiments were carried out with magnetic resonance velocimetry (MRV) for which water was used as flow medium. As the main outcome, it was found that the investigated flows are highly sensitive to the conditions at the channel outlet. However, it was also discovered that for some outlet geometries the flow field remains the same. The associated flow features a favorable topology for heat transfer; the majority of mass is transported in the annular region close to the channel walls. Together with its high robustness, it is regarded as an applicable flow type for the internal cooling of turbine blades. A large eddy simulation (LES) was conducted to analyze the heat transfer characteristic of the associated flow for S0=3 and Re=20,000. The simulation showed an averaged Nusselt number increase of factor 4.7 compared to fully developed flow. However, a pressure loss increase of factor 43 must be considered as well.
Bayesian Uncertainty Integration for Model Calibration, Validation, and Prediction
Authors: Mullins Joshua , Mahadevan Sankaran
Published: December 2015

This paper proposes a comprehensive approach to prediction under uncertainty by application to the Sandia National Laboratories verification and validation challenge problem. In this problem, legacy data and experimental measurements of different levels of fidelity and complexity (e.g., coupon tests, material and fluid characterizations, and full system tests/measurements) compose a hierarchy of information where fewer observations are available at higher levels of system complexity. This paper applies a Bayesian methodology in order to incorporate information at different levels of the hierarchy and include the impact of sparse data in the prediction uncertainty for the system of interest. Since separation of aleatory and epistemic uncertainty sources is a pervasive issue in calibration and validation, maintaining this separation in order to perform these activities correctly is the primary focus of this paper. Toward this goal, a Johnson distribution family approach to calibration is proposed in order to enable epistemic and aleatory uncertainty to be separated in the posterior parameter distributions. The model reliability metric approach to validation is then applied, and a novel method of handling combined aleatory and epistemic uncertainty is introduced. The quality of the validation assessment is used to modify the parameter uncertainty and add conservatism to the prediction of interest. Finally, this prediction with its associated uncertainty is used to assess system-level reliability (a prediction goal for the challenge problem).
Progress in Creep-Resistant Steels for High Efficiency Coal-Fired Power Plants
Authors: Abe Fujio
Published: December 2015

Recent progress in creep-resistant bainitic, martensitic, and austenitic steels for high efficiency coal-fired power plants is comprehensively reviewed with emphasis on long-term creep strength and microstructure stability at grain boundaries (GBs). The creep strength enhanced ferritic (CSEF) steels, such as Grade 91 (9Cr–1Mo–0.2V–0.05Nb), Grade 92 (9Cr–0.5Mo–1.8W–VNb), and Grade 122 (11Cr–0.4Mo–2W–1CuVNb), can offer the highest potential to meet the required flexibility for ultra-supercritical (USC) power plants operating at around 600 °C, because of their smaller thermal expansion and larger thermal conductivity than austenitic steels and Ni base alloys. Further improvement of creep strength of martensitic 9 to 12Cr steels has been achieved by substituting a part or all of Mo with W and also by the addition of Co, V, Nb, and boron. A martensitic 9Cr–3W–3Co–VNb steel strengthened by boron and MX nitrides, designated MARBN, exhibits not only much higher creep strength of base metal than Grade 91, Grade 92, and Grade 122 but also substantially no degradation in creep strength due to type IV fracture in welded joints at 650 °C. High-strength bainitic 2.25 to 3Cr steels have been developed by enhancing solid solution hardening due to W and precipitation hardening due to (V,Nb)C carbides in bainitic microstructure. The improvement of creep strength of austenitic steels has been achieved by solid solution hardening due to the addition of Mo, W, and nitrogen and by precipitation hardening due to the formation of fine MX (M = Ti, Nb, X = C, N), NbCrN, M23C6, Cu phase, and Fe2(Mo,W) Laves phase. The boundary and sub-boundary hardening are shown to be the most important strengthening mechanism in creep of creep-resistant steels and is enhanced by fine dispersions of precipitates along boundaries.
Viscoelastic–Viscoplastic Cyclic Deformation of Polycarbonate Polymer: Experiment and Constitutive Model
Authors: Yu Chao , Kang Guozheng , Lu Fucong , Zhu Yilin , Chen Kaijuan
Published: December 2015

A series of uniaxial tests (including multilevel loading–unloading recovery, creep-recovery, and cyclic tension–compression/tension ones) were performed to investigate the monotonic and cyclic viscoelastic–viscoplastic deformations of polycarbonate (PC) polymer at room temperature. The results show that the PC exhibits strong nonlinearity and rate-dependence, and obvious ratchetting occurs during the stress-controlled cyclic tension–compression/tension tests with nonzero mean stress, which comes from both the viscoelasticity and viscoplasticity of the PC. Based on the experimental observation, a nonlinear viscoelastic–viscoplastic cyclic constitutive model is then constructed. The viscoelastic part of the proposed model is constructed by extending the Schapery's nonlinear viscoelastic model, and the viscoplastic one is established by adopting the Ohno–Abdel-Karim's nonlinear kinematic hardening rule to describe the accumulation of irrecoverable viscoplastic strain produced during cyclic loading. Furthermore, the dependence of elastic compliance of the PC on the accumulated viscoplastic strain is considered. Finally, the capability of the proposed model is verified by comparing the predicted results with the corresponding experimental ones of the PC. It is shown that the proposed model provides reasonable predictions to the various deformation characteristics of the PC presented in the multilevel loading–unloading recovery, creep-recovery, and cyclic tension–compression/tension tests.
Chirality Induced by Structural Transformation in a Tensegrity: Theory and Experiment
Authors: Zhang Li-Yuan , Zhao Zi-Long , Zhang Qing-Dong , Feng Xi-Qiao
Published: December 2015

Chiral structures have many technologically significant applications in engineering. In this paper, we investigate, both theoretically and experimentally, the structural transformation from a symmetric X-shaped tensegrity to a chiral structure under uniaxial tension. When the applied tensile force exceeds a critical value, the initially achiral structure would exhibit snap-through buckling. At the critical state, the in-plane deformation mode of the tensegrity switches into an off-plane one. The critical condition of the structural transformation is provided in terms of structural parameters. An experiment was performed to validate the theoretical model. This work may not only deepen our understanding of the stability of tensegrities but also help design chiral structures for engineering applications.
On Cavitation in Rubberlike Materials
Authors: Lev Yoav , Volokh Konstantin Y.
Published: December 2015

Microscopic voids can irreversibly grow into the macroscopic ones under hydrostatic tension. To explain this phenomenon, it was suggested in the literature to use the asymptotic value of the hydrostatic tension in the plateau yieldlike region on the stress–stretch curve obtained for the neo-Hookean model. Such an explanation has two limitations: (a) it relies on analysis of only one material model and (b) the hyperelasticity theory is used for the explanation of the failure phenomenon. In view of the mentioned limitations, the objective of the present note is twofold. First, we simulate the cavity expansion in rubber by using various experimentally calibrated hyperelastic models in order to check whether the stress–stretch curves have the plateau yieldlike regions independently of the constitutive law. Second, we repeat simulations via these same models enhanced with a failure description. We find (and that was not reported in the literature) that the process of cavity expansion simulated via hyperelastic constitutive models exhibiting stiffening, due to unfolding of long molecules, is completely stable and there are no plateau yieldlike regions on the stress–stretch curves associated with cavitation. In addition, we find that the instability in the form of yielding observed in experiments does appear in all simulations when the constitutive laws incorporate failure description with energy limiters.
Flexoelectricity: A Perspective on an Unusual Electromechanical Coupling
Authors: Krichen Sana , Sharma Pradeep
Published: December 2015

The ability of certain materials to convert electrical stimuli into mechanical deformation, and vice versa, is a prized property. Not surprisingly, applications of such so-called piezoelectric materials are broad—ranging from energy harvesting to self-powered sensors. In this perspective, written in the form of question-answers, we highlight a relatively understudied electromechanical coupling called flexoelectricity that appears to have tantalizing implications in topics ranging from biophysics to the design of next-generation multifunctional nanomaterials.
Riccati-Based Discretization for Nonlinear Continuous-Time Systems
Authors: Nguyen-Van Triet , Hori Noriyuki
Published: December 2015

A discretization method is proposed for a rather general class of nonlinear continuous-time systems, which can have a piecewise-constant input, such as one under digital control via a zero-order-hold device. The resulting discrete-time model is expressed as a product of the integration-gain and the system function that governs the dynamics of the original continuous-time system. This is made possible with the use of the delta or Euler operator and makes comparisons of discrete and continuous time systems quite simple, since the difference between the two forms is concentrated into the integration-gain. This gain is determined in the paper by using the Riccati approximation of a certain gain condition that is imposed on the discretized system to be an exact model. The method is shown to produce a smaller error norm than one uses the linear approximation. Simulations are carried out for a Lotka–Volterra and an averaged van der Pol nonlinear systems to show the superior performance of the proposed model to ones known to be online computable, such as the forward-difference, Kahan's, and Mickens' methods. Insights obtained should be useful for developing digital control laws for nonlinear continuous-time systems, which is currently limited to the simplest forward-difference model.
Rational ANCF Thin Plate Finite Element
Authors: Pappalardo Carmine M. , Yu Zuqing , Zhang Xiaoshun , Shabana Ahmed A.
Published: December 2015

In this paper, a rational absolute nodal coordinate formulation (RANCF) thin plate element is developed and its use in the analysis of curved geometry is demonstrated. RANCF finite elements are the rational counterpart of the nonrational absolute nodal coordinate formulation (ANCF) finite elements which employ rational polynomials as basis or blending functions. RANCF finite elements can be used in the accurate geometric modeling and analysis of flexible continuum bodies with complex geometrical shapes that cannot be correctly described using nonrational finite elements. In this investigation, the weights, which enter into the formulation of the RANCF finite element and form an additional set of geometric parameters, are assumed to be nonzero constants in order to accurately represent the initial geometry and at the same time preserve the desirable ANCF features, including a constant mass matrix and zero centrifugal and Coriolis generalized inertia forces. A procedure for defining the control points and weights of a Bezier surface defined in a parametric form is used in order to be able to efficiently create RANCF/ANCF FE meshes in a straightforward manner. This procedure leads to a set of linear algebraic equations whose solution defines the RANCF coordinates and weights without the need for an iterative procedure. In order to be able to correctly describe the ANCF and RANCF gradient deficient FE geometry, a square matrix of position vector gradients is formulated and used to calculate the FE elastic forces. As discussed in this paper, the proposed finite element allows for describing exactly circular and conic sections and can be effectively used in the geometry and analysis modeling of multibody system (MBS) components including tires. The proposed RANCF finite element is compared with other nonrational ANCF plate elements. Several numerical examples are presented in order to demonstrate the use of the proposed RANCF thin plate element. In particular, the FE models of a set of rational surfaces, which include conic sections and tires, are developed.
Lyapunov Stability of Commensurate Fractional Order Systems: A Physical Interpretation
Authors: Trigeassou Jean-Claude , Maamri Nezha , Oustaloup Alain
Published: December 2015

Lyapunov stability of linear commensurate order fractional systems is revisited with the energy balance principle. This methodology is based on the concept of fractional energy stored in inductor and capacitor components, where natural decrease of the stored energy is caused by internal Joule losses. Previous stability results are interpreted, thanks to an equivalent fictitious fractional RLC circuit. Energy balance is used to analyze the usual Lyapunov function and to provide a physical interpretation to the weighting positive matrix. Moreover, the classical linear matrix inequality (LMI) condition is interpreted in terms of internal and external Joule losses.
Dynamic Behavior of Flexible Multiple Links Captured Inside a Closed Space
Authors: Shafei A. M. , Shafei H. R.
Published: December 2015

This work presents a systematic method for the dynamic modeling of flexible multiple links that are confined within a closed environment. The behavior of such a system can be completely formulated by two different mathematical models. Highly coupled differential equations are employed to model the confined multilink system when it has no impact with the surrounding walls; and algebraic equations are exploited whenever this open kinematic chain system collides with the confining surfaces. Here, to avoid using the 4 × 4 transformation matrices, which suffers from high computational complexities for deriving the governing equations of flexible multiple links, 3 × 3 rotational matrices based on the recursive Gibbs-Appell formulation has been utilized. In fact, the main aspect of this paper is the automatic approach, which is used to switch from the differential equations to the algebraic equations when this multilink chain collides with the surrounding walls. In this study, the flexible links are modeled according to the Euler–Bernoulli beam theory (EBBT) and the assumed mode method. Moreover, in deriving the motion equations, the manipulators are not limited to have only planar motions. In fact, for systematic modeling of the motion of a multiflexible-link system in 3D space, two imaginary links are added to the n real links of a manipulator in order to model the spatial rotations of the system. Finally, two case studies are simulated to demonstrate the correctness of the proposed approach.
Heating Position Planning in Laser Forming of Single Curved Shapes Based on Probability Convergence
Authors: Shen Hong , Zheng Yutao , Wang Han , Yao Zhenqiang
Published: December 2015

Inverse problem in laser forming involves the heating position planning and the determination of heating parameters. In this study, the heating positions are optimized in laser forming of single curved shapes based on the processing efficiency. The algorithm uses a probability function to initialize the heating position that is considered to be the bending points. The optimization process is to minimize the total processing time through adjusting the heating positions by considering the boundary conditions of the offset distances, the minimum bending angle, and the minimum distance between two adjacent heating positions. The optimized results are compared with those obtained by the distance-based model as well as the experimental data.
An Evaluation Methodology for Design Concept Communication Using Digital Prototypes
Authors: Arastehfar Soheil , Liu Ying , Feng Lu Wen
Published: December 2015

Digital prototypes (DPs) allow designers to communicate design concepts to users by rendering physical characteristics of the concepts. To enhance user understanding of the concepts, it is important that the users be able to make better estimates of the values of the characteristics. Correctness of the estimates can depend on two crucial factors: the ability of DPs to render the physical characteristics and the way the DPs are used to communicate the physical characteristics. However, little attention has been paid to the latter. A DP can be used in different ways, e.g., it can be projected on different backgrounds, or be manipulated using different input/output devices. Hence, it is important to identify an effective way of using DPs, via an assessment of the effectiveness of various ways. This paper introduces a methodology for evaluating the effectiveness of communication of physical characteristics to users using DPs. The methodology is used to assess the degree to which users can correctly and quickly estimate the values of the characteristics through interactions with DPs. Such assessments are then analyzed with statistical methods and hypothesis tests to reveal the effectiveness. To validate the proposed methodology, the size of hand-held electronic consumer products, such as smartphones, is considered in a case study. In the study, the effectiveness of two communication setups is evaluated. The same DP is used in both setups, while the environments and input devices are different. The experimental results show that the evaluated effectiveness can reflect how successful the setups are, and can help select the best way of using the DP, i.e., by providing a better environment, a better input device, or a combination of both.