bluuebunny/crossref_metadata_2025 huggingface dataset:
The “Spectrum Dip”: Dynamic Interaction of System Components
Authors: Scavuzzo Rudolph J. , (Jerry) Hill George D. , Saxe Peter
Published: October 2014

In the early 1960s, many full sized surface combatants, submarines and structural models were tested with underwater explosions in order to evaluate the shock load to the ship and internal equipment structures. Initially, shock spectra were calculated from base motion measurements of internal equipment and components. Attempts were made to envelop these spectra to develop shock design spectra inputs. At that time, earthquake engineers were using this enveloping method to develop design procedures from ground motion measurements to protect structures from earthquakes. However, for the measurements on ships, this procedure resulted in calculated loads that would have caused catastrophic failure of the equipment; yet the equipment had not failed on the ship tests. As a result, the data were re-analyzed over a period of over a year. It was concluded that the dynamic interaction of each component or structure reduced the measured spectral motion at the fixed-base frequencies of the structure by about an order of magnitude. In many cases, there was a dip in the shock spectra at the fixed-base frequencies: the “spectrum dip” phenomenon. This re-analysis led to shock spectra design curves for navy ships. This paper presents a review of an experimental study and analytical demonstration to explain the effect of dynamic interaction on the shock or response spectrum. In addition, a practical example of interaction of four single mass dynamic systems mounted on a realistic deck and subjected to a high impact shock input was studied by the authors and some of the results of that study are included.
Short Carbon Fiber-Reinforced Epoxy Tribomaterials Self-Lubricated by Wax Containing Microcapsules
Authors: Win Khun Nay , Zhang He , Tang Xiu-zhi , Yoon Yue Chee , Yang Jinglei
Published: October 2014

The effects of wax lubricant filled microcapsule content on the tribological properties of epoxy composites without or with 8 wt.% short carbon fibers (SCFs) were systematically investigated. The core percentage of the microcapsules used in this study was about 70 wt.%. The tribological results clearly showed that the friction and wear of the epoxy composites without or with SCFs tested against a 6 mm steel ball significantly decreased with increased microcapsule content from 2.5 to 10 wt.% as a result of the increased amount of released wax lubricant to lubricate rubbing surfaces. The epoxy composites with 8 wt.% SCFs exhibited the lower friction and wear than the ones without SCFs due to the combined lubricating effects of SCFs and released wax lubricant and the improved mechanical strength of the composites. It can be concluded that the higher microcapsule content gives rise to the lower friction and wear of the epoxy composites as the epoxy composites with 8 wt.% SCFs have the better tribological performance than the ones without SCFs.
Multi-Objective Robust Optimization Using a Postoptimality Sensitivity Analysis Technique: Application to a Wind Turbine Design
Authors: Wang Weijun , Caro Stéphane , Bennis Fouad , Soto Ricardo , Crawford Broderick
Published: October 2014

Toward a multi-objective optimization robust problem, the variations in design variables (DVs) and design environment parameters (DEPs) include the small variations and the large variations. The former have small effect on the performance functions and/or the constraints, and the latter refer to the ones that have large effect on the performance functions and/or the constraints. The robustness of performance functions is discussed in this paper. A postoptimality sensitivity analysis technique for multi-objective robust optimization problems (MOROPs) is discussed, and two robustness indices (RIs) are introduced. The first one considers the robustness of the performance functions to small variations in the DVs and the DEPs. The second RI characterizes the robustness of the performance functions to large variations in the DEPs. It is based on the ability of a solution to maintain a good Pareto ranking for different DEPs due to large variations. The robustness of the solutions is treated as vectors in the robustness function space (RF-Space), which is defined by the two proposed RIs. As a result, the designer can compare the robustness of all Pareto optimal solutions and make a decision. Finally, two illustrative examples are given to highlight the contributions of this paper. The first example is about a numerical problem, whereas the second problem deals with the multi-objective robust optimization design of a floating wind turbine.
Design of Compliant Bamboo Poles for Carrying Loads
Authors: Potwar Karna , Ackerman Jeffrey , Seipel Justin
Published: October 2014

Carriage of heavy loads is common in developing countries and can impart large repetitive forces on the body that could lead to musculoskeletal fatigue and injury. Compliant bamboo poles have been used to carry heavy loads in Asia for generations and could be a low-cost, sustainable, and culturally acceptable way to minimize the forces acting on the body during load carriage. Experimental evidence of running with a 15 kg load suspended from a pair of compliant poly(vinyl chloride), or PVC, poles shows that the poles act as a vibration-isolating suspension, which can reduce the peak forces on the body during locomotion. However, it is currently not well-understood how to design and optimize poles for load carrying such that the peak forces on the body are minimized during carrying. Further, current users of bamboo poles do not have a reliable way to measure forces on the body and so cannot empirically optimize their poles for force reduction. Our objective is to determine the geometric and material design parameters that optimize bamboo poles for load carriage and to develop recommendations that could make it easier for load carriers to fabricate well-suited poles. Our approach is to synthesize a predictive model of walking and running from the field of biomechanics, which can predict the peak forces on the body as a function of pole stiffness, with a bending beam model of the bamboo pole that relates pole geometry and material to the effective pole stiffness. We first check our model's ability to predict the experimental results from a well-established study with PVC poles. We then extend the predictive design study to include a wider range of stiffness values and pole geometries that may be more effective and realistic for practical load carrying situations. Based on stiffness, deflection, strength, and pole mass design constraints, we specify an appropriate range of dimensions for selecting bamboo poles to carry a 15 kg load. The design methodology presented could simplify the selection and design of bamboo carrying poles in order to reduce the likelihood of musculoskeletal injury.
Validation of a Novel Spine Test Machine
Authors: Mannen Erin M. , Ranu Sahibjit S. , Villanueva Ana M. , Friis Elizabeth A.
Published: October 2014

A novel spine test machine was developed for physiological loading of spinal segments. It can be used in conjunction with external motion-capture systems (EMCS) to measure angular displacement, but can also measure in-plane rotations directly, though the inherent error is unknown. This study quantified error inherent in the displacement measurement of the machine. Synthetic specimens representative of cadaveric spinal specimens were tested. Machine displacement was compared to EMCS displacement. The maximum machine displacement error was <2 deg for lumbar and thoracic specimens. The authors suggest that researchers use EMCS in conjunction with the test machine when high accuracy measurements are required.
Verification of the Linear Matching Method for Limit and Shakedown Analysis by Comparison With Experiments
Authors: Ure James , Chen Haofeng , Tipping David
Published: October 2014

The linear matching method (LMM), a direct numerical method for determining shakedown and ratchet limits of components, has seen significant development in recent years. Previous verifications of these developments against cyclic nonlinear finite element analysis (FEA) have shown favorable results, and now this verification process is being extended to include comparisons with experimental results. This paper presents a comparison of LMM analysis with experimental tests for limit loads and shakedown limits available in the literature. The limit load and shakedown limits were determined for pipe intersections and nozzle-sphere intersections, respectively, thus testing the accuracy of the LMM when analyzing real plant components. Details of the component geometries, materials and test procedures used in the experiments are given. Following this a description of the LMM analysis is given which includes a description of how these features have been interpreted for numerical analysis. A comparison of the results shows that the LMM is capable of predicting accurate yet conservative limit loads and shakedown limits.
Predictions of Operational Degradation of the Fan Stage of an Aircraft Engine Due to Particulate Ingestion
Authors: Grazia De Giorgi Maria , Campilongo Stefano , Ficarella Antonio
Published: October 2014

A numerical evaluation of the effects of volcanic ash ingestion in a turbofan engine was carried out, with particular regard to the prediction of the erosion damage to fan blades. The ash concentration level examined in the study was below the flight limit because the aim of this study is to investigate the damage due to long-term exposure to low concentration levels. The work aims to the implementation of a numerical methodology that takes into account the geometry change of the fan blades during the exposure to volcanic ash. A dimensional and morphological characterization of a real volcanic ash sample from the Mount Etna volcano has been performed to model the particle flow dynamics using a computational fluid dynamics (CFD) code. The fan performance in terms of the total pressure increase was calculated for both the baseline and damaged geometries to quantify the performance deterioration trend with respect to the particle exposure time. For the calculation of the eroded fan performance, two different numerical approaches were considered. In the first approach, the erosion rate (ER) was evaluated based on the initial blade geometry and was held constant. In the second approach, the ER was updated as the erosion of the blade continued. The second approach shows a higher deterioration of the pressure rise across the fan, suggesting that the variation of the ER due to the blade shape modification cannot be neglected in the calculations.
An Experimental Investigation of Reactivity-Controlled Compression Ignition Combustion in a Single-Cylinder Diesel Engine Using Hydrous Ethanol
Authors: Fang Wei , Fang Junhua , Kittelson David B. , Northrop William F.
Published: October 2014

Dual-fuel reactivity-controlled compression ignition (RCCI) combustion using port injection of a less reactive fuel and early-cycle direct injection (DI) of a more reactive fuel has been shown to yield both high thermal efficiency and low NOX and soot emissions over a wide engine operating range. Conventional and alternative fuels such as gasoline, natural gas, and E85 as the lower reactivity fuel in RCCI have been studied by many researchers; however, published experimental investigations of hydrous ethanol use in RCCI are scarce. Making greater use of hydrous ethanol in internal combustion engines has the potential to dramatically improve the economics and life cycle carbon dioxide emissions of using bioethanol. In this work, an experimental investigation was conducted using 150 proof hydrous ethanol as the low reactivity fuel and commercially available diesel as the high reactivity fuel in an RCCI combustion mode at various load conditions. A modified single-cylinder diesel engine was used for the experiments. Based on previous studies on RCCI combustion by other researchers, early-cycle split-injection strategy of diesel fuel was used to create an in-cylinder fuel reactivity distribution to maintain high thermal efficiency and low NOX and soot emissions. At each load condition, timing and mass fraction of the first diesel injection was held constant, while timing of the second diesel injection was swept over a range where stable combustion could be maintained. Since hydrous ethanol is highly resistant to auto-ignition and has large heat of vaporization, intake air heating was needed to obtain stable operations of the engine. The study shows that 150 proof hydrous ethanol can be used as the low reactivity fuel in RCCI through 8.6 bar indicated mean effective pressure (IMEP) and with ethanol energy fraction up to 75% while achieving simultaneously low levels of NOX and soot emissions. With increasing engine load, less intake heating is needed and exhaust gas recirculation (EGR) is required to maintain low NOX emissions.
An Experimental Investigation of the Use of Combined Resistivity and Temperature Logs for Scale Monitoring In Carbonate Formations During CO2 Sequestration
Authors: Adebayo Abdulrauf Rasheed , Al-Yousef Hasan Y. , Mahmoud Mohammed
Published: October 2014

This study investigates the prospect of using permanent downhole resistivity and temperature sensors for scale monitoring during CO2 sequestration in saline carbonate aquifer. Current industry practice involves continuous geochemical analysis of produced formation water and petrographic analysis of cuttings at the surface. A major limitation of such methods is that formation scale dynamics is not captured in situ and in real time. Moreover, high cost and compositional change of produced fluid caused by evolution of dissolved gases are other setbacks. In this study, resistivity and temperature measurements were logged continuously for several months at 30 min interval during CO2 storage in brine saturated core samples. Carbonate samples were acquired from Indiana outcrops in the United States and cut into cylindrical cores. Samples were saturated with synthetic formation brine and CO2 was injected and stored at a temperature of 45 °C, pore pressure of 2000 psig, and an overburden pressure of 2500 psig. The pressure, temperature and resistivity of samples were collected and transmitted to a PC computer at an interval of 30 min for the period of storage. A base line log recorded after CO2 injection but prior to CO2/brine/rock interaction (CBRI) allowed us to track onset of dissolution and precipitation. Deflection away from the baseline either inward or outward during the period of storage marks two distinct reaction phenomenon-dissolution and precipitation. Our hypothesis was justified by results of geochemical analysis of prestorage brine and poststorage brine, and also by petrographic study of the cores. Several other tests were also run to ensure consistency. This study is new compared to previous works in the following ways: Many previous works focused on the applicability of electrical resistivity measurements to track CO2 migration by way of resistivity change as a function of CO2 saturation changes during CO2 sequestration. Many others also studied the effect of CO2 injection on the petrophysical and electrical properties of rocks. Previous works of these types used continuous flow of fluid in and out of the sample and such flow experiments lasted only few hours. The fate of formation resistivity under static condition and at longer storage period was not considered.
Transient Thermal-Hydraulic Responses of the Nuclear Steam Generator Secondary Side to a Main Steam Line Break1
Authors: Jo Jong Chull , Moody Frederick J.
Published: October 2014

This paper presents a multidimensional numerical analysis of the transient thermal-hydraulic response of a steam generator (SG) secondary side to a double-ended guillotine break of the main steam line attached to the SG at a pressurized water reactor (PWR) plant. A simplified analysis model is designed to include both the SG upper space, which the steam occupies and a part of the main steam line between the SG outlet nozzle and the pipe break location upstream of the main steam isolation valve. The transient steam flow through the analysis model is simulated using the shear stress transport (SST) turbulence model. The steam is treated as a real gas. To model the steam generation by heat transfer from the primary coolant to the secondary side coolant for a short period during the blow down process following the main steam line break (MSLB) accident, a constant amount of steam is assumed to be generated from the bottom of the SG upper space part. Using the numerical approach mentioned above, calculations have been performed for the analysis model having the same physical dimensions of the main steam line pipe and initial operational conditions as those for an actual operating plant. The calculation results have been discussed in detail to investigate their physical meanings and validity. The results demonstrate that the present computational fluid dynamics (CFD) model is applicable for simulating the transient thermal-hydraulic responses in the event of the MSLB accident including the blowdown-induced dynamic pressure disturbance in the SG. In addition, it has been found that the dynamic hydraulic loads acting on the SG tubes can be increased by 2–8 times those loads during the normal reactor operation. This implies the need to re-assess the potential for single or multiple SG tube ruptures due to fluidelastic instability for ensuring the reactor safety.
Random Bulk Properties of Heterogeneous Rectangular Blocks With Lognormal Young's Modulus: Effective Moduli
Authors: Dimas Leon S. , Veneziano Daniele , Giesa Tristan , Buehler Markus J.
Published: October 2014

We investigate the effective elastic properties of disordered heterogeneous materials whose Young's modulus varies spatially as a lognormal random field. For one-, two-, and three-dimensional (1D, 2D, and 3D) rectangular blocks, we decompose the spatial fluctuations of the Young's log-modulus F=lnE into first- and higher-order terms and find the joint distribution of the effective elastic tensor by multiplicatively combining the term-specific effects. The analytical results are in good agreement with Monte Carlo simulations. Through parametric analysis of the analytical solutions, we gain insight into the effective elastic properties of this class of heterogeneous materials. The results have applications to structural/mechanical reliability assessment and design.
Four-Bar Mechanism's Proportional-Derivative and Neural Adaptive Control for the Thorax of the Micromechanical Flying Insects
Authors: Lungu Romulus , Sepcu Lucian , Lungu Mihai
Published: October 2014

The paper focuses on the dynamics and control of the nondeformable and deformable four-bar mechanism (three of the bars are mobile and one is fixed), this being a subsystem of the micromechanical flying insects' (MFIs) thorax. The control of the mechanism (six-order system described by Lagrange equations) is initially achieved by using a proportional-derivative (PD) control law, a Newton–Raphson type algorithm, and the Lyapunov theory. Because the thorax's dynamics is strongly nonlinear and is characterized by fast time varying coefficients, the PD control law cannot always guarantee small overshoot and angular rates; to overcome this drawback, over the control law PD component we superpose a neural adaptive component which compensate the error of the global nonlinearity's approximation associated to the thorax's dynamics. The two obtained control systems are validated by complex numerical simulations.
The Influence of Boundary Conditions on Tip Leakage Flow
Authors: Coull John D. , Atkins Nicholas R.
Published: October 2014

Much of the current understanding of tip leakage flow has been derived from detailed cascade studies. Such experiments are inherently approximate since it is difficult to simulate the boundary conditions that are present in a real machine, particularly the secondary flows convecting from the upstream stator row and the relative motion of the casing and blade. The problem is further complicated when considering the high pressure turbine rotors of aero engines, where the high Mach numbers must also be matched in order to correctly model the aerodynamics and heat transfer of the leakage flow. More engine-representative tests can be performed on high-speed rotating turbines, but the experimental resolution achievable in such setups is limited. In order to examine the differences between cascade and engine boundary conditions, this paper presents a numerical investigation into the impact of inlet conditions and relative casing motion (RCM) on the leakage flow of a high-pressure turbine rotor. The baseline calculation uses a simplified inlet condition and no relative endwall motion, in typical cascade fashion. Only minor changes to the leakage flow are induced by introducing either a more realistic inlet condition or RCM. However, when both of these conditions are applied simultaneously, the pattern of leakage flow is significantly altered, with ingestion of flow over much of the early suction surface. The paper explores the physical processes driving the changes, the impact on performance and the implications for future experimental investigations.
Experimental Investigation Into the Effects of the Steady Wake-Tip Clearance Vortex Interaction in a Compressor Cascade
Authors: Krug Andreas , Busse Peter , Vogeler Konrad
Published: October 2014

An important aspect of the aerodynamic flow field in the tip region of axial compressor rotors is the unsteady interaction between the tip clearance vortex (TCV) and the incoming stator wakes. In order to gain an improved understanding of the mechanics involved, systematic studies need to be performed. As a first step toward the characterization of the dynamic effects caused by the relative movement of the blade rows, the impact of a stationary wake-induced inlet disturbance on a linear compressor cascade with tip clearance will be analyzed. The wakes were generated by a fixed grid of cylindrical bars with variable pitch being placed at discrete pitchwise positions. This paper focuses on experimental studies conducted at the newly designed low-speed cascade wind tunnel in Dresden. The general tunnel configuration and details on the specific cascade setup will be presented. Steady state flow field measurements were carried out using five-hole probe traverses up- and downstream of the cascade and accompanied by static wall pressure readings. 2D-particle image velocimetry (PIV) measurements complemented these results by visualizing the blade-to-blade flow field. Hence, the structure of the evolving secondary flow system is evaluated and compared for all tested configurations.
Importance of Material Properties and Porosity of Bone on Mechanical Response of Articular Cartilage in Human Knee Joint—A Two-Dimensional Finite Element Study
Authors: Venäläinen Mikko S. , Mononen Mika E. , Jurvelin Jukka S. , Töyräs Juha , Virén Tuomas , Korhonen Rami K.
Published: October 2014

Mechanical behavior of bone is determined by the structure and intrinsic, local material properties of the tissue. However, previously presented knee joint models for evaluation of stresses and strains in joints generally consider bones as rigid bodies or linearly elastic solid materials. The aim of this study was to estimate how different structural and mechanical properties of bone affect the mechanical response of articular cartilage within a knee joint. Based on a cadaver knee joint, a two-dimensional (2D) finite element (FE) model of a knee joint including bone, cartilage, and meniscus geometries was constructed. Six different computational models with varying properties for cortical, trabecular, and subchondral bone were created, while the biphasic fibril-reinforced properties of cartilage and menisci were kept unaltered. The simplest model included rigid bones, while the most complex model included specific mechanical properties for different bone structures and anatomically accurate trabecular structure. Models with different porosities of trabecular bone were also constructed. All models were exposed to axial loading of 1.9 times body weight within 0.2 s (mimicking typical maximum knee joint forces during gait) while free varus–valgus rotation was allowed and all other rotations and translations were fixed. As compared to results obtained with the rigid bone model, stresses, strains, and pore pressures observed in cartilage decreased depending on the implemented properties of trabecular bone. Greatest changes in these parameters (up to −51% in maximum principal stresses) were observed when the lowest modulus for trabecular bone (measured at the structural level) was used. By increasing the trabecular bone porosity, stresses and strains were reduced substantially in the lateral tibial cartilage, while they remained relatively constant in the medial tibial plateau. The present results highlight the importance of long bones, in particular, their mechanical properties and porosity, in altering and redistributing forces transmitted through the knee joint.
Fatigue Life of Curved Panels Under Combined Loading
Authors: Jean-Michel Dhainaut
Published: October 2014

The nonlinear response of shallow shells subjected to combined acoustic and thermal loads is analyzed using an efficient nonlinear modal finite element (FE) formulation. The acoustic loads have non-Gaussian probabilistic characteristics and are simulated by an algorithm capable of reliably converging to a target power spectral density (PSD) function and marginal probability density function (PDF). Factors contributing to the panel structural stiffness, softening and hardening effects, and modal contribution are also investigated along with their impact on the root-mean-square responses. The Palmgren–Miner cumulative damage theory in combination with the rainflow counting (RFC) cycles methods was used to estimate the panel fatigue life. Parametric studies for cylindrical and spherical curved panels considering stacking laminations, radii of curvatures, acoustic and thermal loads are studied in detail.
A Global Simulation Method for Flexible Multibody Systems With Variable Topology Structures
Authors: Guo Wenhao , Wang Tianshu
Published: October 2014

By means of a recursive formulation method, a generalized impulse–momentum-balance method, and a constraint violation elimination (CVE) method, we propose a new global simulation method for flexible multibody systems with kinematic structure changes. The constraint equations of a pair of adjacent bodies, considering body flexibility in Cartesian space, are derived for a recursive formulation. Constraint equations in configuration space, which are obtained from the constraints presented in this paper via recursive formulation, are very useful for modeling different kinematic structures and impacting governing equations. The novelty is that the impact governing equations, which calculate the jumps of generalized velocities, are modified by taking velocity-level CVE into consideration. Numerical examples are given to validate the presented method. Simulation results show that the new method can effectively suppress constraint drifts at the velocity level and stabilize constraint violations at the position level.
A Coupled Ordinates Method for Convergence Acceleration of the Phonon Boltzmann Transport Equation
Authors: Loy James M. , Mathur Sanjay R. , Murthy Jayathi Y.
Published: October 2014

Sequential numerical solution methods are commonly used for solving the phonon Boltzmann transport equation (BTE) because of simplicity of implementation and low storage requirements. However, they exhibit poor convergence for low Knudsen numbers. This is because sequential solution procedures couple the phonon BTEs in physical space efficiently but the coupling is inefficient in wave vector (K) space. As the Knudsen number decreases, coupling in K space becomes dominant and convergence rates fall. Since materials like silicon have K-resolved Knudsen numbers that span two to five orders of magnitude at room temperature, diffuse-limit solutions are not feasible for all K vectors. Consequently, nongray solutions of the BTE experience extremely slow convergence. In this paper, we develop a coupled-ordinates method for numerically solving the phonon BTE in the relaxation time approximation. Here, interequation coupling is treated implicitly through a point-coupled direct solution of the K-resolved BTEs at each control volume. This implicit solution is used as a relaxation sweep in a geometric multigrid method which promotes coupling in physical space. The solution procedure is benchmarked against a traditional sequential solution procedure for thermal transport in silicon. Significant acceleration in computational time, between 10 and 300 times, over the sequential procedure is found for heat conduction problems.
A Note on the Correspondence Between Certain Nanofluid Flows and Standard Fluid Flows
Authors: Turkyilmazoglu Mustafa
Published: October 2014

This note introduces a rescaling approach that greatly simplifies the evaluation of flow and physical parameters such as skin friction and heat transfer rate in recent single phase nanofluids research for which the nanofluids begin to create a non-Newtonian fluid after 5–6% volumetric concentration of nanoparticles. Much of the task is hence reduced to a particular case for a chosen fluid. By the help of specified transformations, the nanofluid results can be obtained from known properties of regular fluid. Such rescaling is shown to work well for the rotating disk boundary layer flow in nanofluid, and thus sheds light upon the future studies of this kind when further physical mechanism are taken into account.
Application of Possibilistic C-Means for Fault Detection in Nuclear Power Plant Data
Authors: Perasso Annalisa , Campi Cristina , Toraci Cristian , Benvenuto Francesco , Piana Michele , Massone Anna Maria
Published: October 2014

This paper describes a classification method for automatic fault detection in nuclear power plant (NPP) data. The method takes as input time series associated to specific parameters and realizes signal classification by using a clustering algorithm based on possibilistic C-means (PCM). This approach is applied to time series recorded in a CANDU® power plant and is validated by comparison with results provided by a classification method based on principal component analysis (PCA).
Crack Branching Characteristics at Different Propagation Speeds: From Quasi-Static to Supersonic Regime
Authors: Jia Y. J. , Liu B.
Published: October 2014

Classical dynamic fracture mechanics predicts that the crack branching occurs when crack propagation speed exceeds a subsonic critical velocity. In this paper, we performed simulations on the dynamic fracture behaviors of idealized discrete mass–spring systems. It is interesting to note that a crack does not branch when traveling at supersonic speed, which is consistent with others' experimental observations. The mechanism for the characteristics of crack branching at different propagation speeds is studied by numerical and theoretical analysis. It is found that for all different speed regimes, the maximum circumferential stress near the crack tip determines the crack branching behaviors.
Moment Measurements in Dynamic and Quasi-Static Spine Segment Testing Using Eccentric Compression are Susceptible to Artifacts Based on Loading Configuration
Authors: Van Toen Carolyn , Carter Jarrod W. , Oxland Thomas R. , Cripton Peter A.
Published: October 2014

The tolerance of the spine to bending moments, used for evaluation of injury prevention devices, is often determined through eccentric axial compression experiments using segments of the cadaver spine. Preliminary experiments in our laboratory demonstrated that eccentric axial compression resulted in “unexpected” (artifact) moments. The aim of this study was to evaluate the static and dynamic effects of test configuration on bending moments during eccentric axial compression typical in cadaver spine segment testing. Specific objectives were to create dynamic equilibrium equations for the loads measured inferior to the specimen, experimentally verify these equations, and compare moment responses from various test configurations using synthetic (rubber) and human cadaver specimens. The equilibrium equations were verified by performing quasi-static (5 mm/s) and dynamic experiments (0.4 m/s) on a rubber specimen and comparing calculated shear forces and bending moments to those measured using a six-axis load cell. Moment responses were compared for hinge joint, linear slider and hinge joint, and roller joint configurations tested at quasi-static and dynamic rates. Calculated shear force and bending moment curves had similar shapes to those measured. Calculated values in the first local minima differed from those measured by 3% and 15%, respectively, in the dynamic test, and these occurred within 1.5 ms of those measured. In the rubber specimen experiments, for the hinge joint (translation constrained), quasi-static and dynamic posterior eccentric compression resulted in flexion (unexpected) moments. For the slider and hinge joints and the roller joints (translation unconstrained), extension (“expected”) moments were measured quasi-statically and initial flexion (unexpected) moments were measured dynamically. In the cadaver experiments with roller joints, anterior and posterior eccentricities resulted in extension moments, which were unexpected and expected, for those configurations, respectively. The unexpected moments were due to the inertia of the superior mounting structures. This study has shown that eccentric axial compression produces unexpected moments due to translation constraints at all loading rates and due to the inertia of the superior mounting structures in dynamic experiments. It may be incorrect to assume that bending moments are equal to the product of compression force and eccentricity, particularly where the test configuration involves translational constraints and where the experiments are dynamic. In order to reduce inertial moment artifacts, the mass, and moment of inertia of any loading jig structures that rotate with the specimen should be minimized. Also, the distance between these structures and the load cell should be reduced.
Local Dynamic Stability of Spine Muscle Activation and Stiffness Patterns During Repetitive Lifting
Authors: Graham Ryan B. , Brown Stephen H. M.
Published: October 2014

To facilitate stable trunk kinematics, humans must generate appropriate motor patterns to effectively control muscle force and stiffness and respond to biomechanical perturbations and/or neuromuscular control errors. Thus, it is important to understand physiological variables such as muscle force and stiffness, and how these relate to the downstream production of stable spine and trunk movements. This study was designed to assess the local dynamic stability of spine muscle activation and rotational stiffness patterns using Lyapunov analyses, and relationships to the local dynamic stability of resulting spine kinematics, during repetitive lifting and lowering at varying combinations of lifting load and rate. With an increase in the load lifted at a constant rate there was a trend for decreased local dynamic stability of spine muscle activations and the muscular contributions to spine rotational stiffness; although the only significant change was for the full state space muscle activation stability (p < 0.05). With an increase in lifting rate with a constant load there was a significant decrease in the local dynamic stability of spine muscle activations and the muscular contributions to spine rotational stiffness (p ≤ 0.001 for all measures). These novel findings suggest that the stability of motor inputs and the muscular contributions to spine rotational stiffness can be altered by external task demands (load and lifting rate), and therefore are important variables to consider when assessing the stability of the resulting kinematics.
Development and Performance Evaluation of a Multi-PID Muscle Loading Driven In Vitro Active-Motion Shoulder Simulator and Application to Assessing Reverse Total Shoulder Arthroplasty
Authors: William Giles Joshua , Miguel Ferreira Louis , Singh Athwal George , Andrew Johnson James
Published: October 2014

In vitro active shoulder motion simulation can provide improved understanding of shoulder biomechanics; however, accurate simulators using advanced control theory have not been developed. Therefore, our objective was to develop and evaluate a simulator which uses real-time kinematic feedback and closed loop proportional integral differential (PID) control to produce motion. The simulator’s ability to investigate a clinically relevant variable—namely muscle loading changes resulting from reverse total shoulder arthroplasty (RTSA)—was evaluated and compared to previous findings to further demonstrate its efficacy. Motion control of cadaveric shoulders was achieved by applying continuously variable forces to seven muscle groups. Muscle forces controlling each of the three glenohumeral rotational degrees of freedom (DOF) were modulated using three independent PID controllers running in parallel, each using measured Euler angles as their process variable. Each PID controller was configured and tuned to control the loading of a set of muscles which, from previous in vivo investigations, were found to be primarily responsible for movement in the PID’s DOF. The simulator’s ability to follow setpoint profiles for abduction, axial rotation, and horizontal extension was assessed using root mean squared error (RMSE) and average standard deviation (ASD) for multiple levels of arm mass replacement. A specimen was then implanted with an RTSA, and the effect of joint lateralization (0, 5, 10 mm) on the total deltoid force required to produce motion was assessed. Maximum profiling error was <2.1 deg for abduction and 2.2 deg for horizontal extension with RMSE of <1 deg. The nonprofiled DOF were maintained to within 5.0 deg with RMSE <1.0 deg. Repeatability was high, with ASDs of <0.31 deg. RMSE and ASD were similar for all levels of arm mass replacement (0.73–1.04 and 0.14–0.22 deg). Lateralizing the joint’s center of rotation (CoR) increased total deltoid force by up to 8.5% body weight with the maximum early in abduction. This simulator, which is the first to use closed loop control, accurately controls the shoulder’s three rotational DOF with high repeatability, and produces results that are in agreement with previous investigations. This simulator’s improved performance, in comparison to others, increases the statistical power of its findings and thus its ability to provide new biomechanical insights.
Harnessing Biomechanics to Develop Cartilage Regeneration Strategies
Authors: Athanasiou Kyriacos A. , Responte Donald J. , Brown Wendy E. , Hu Jerry C.
Published: October 2014

As this review was prepared specifically for the American Society of Mechanical Engineers H.R. Lissner Medal, it primarily discusses work toward cartilage regeneration performed in Dr. Kyriacos A. Athanasiou's laboratory over the past 25 years. The prevalence and severity of degeneration of articular cartilage, a tissue whose main function is largely biomechanical, have motivated the development of cartilage tissue engineering approaches informed by biomechanics. This article provides a review of important steps toward regeneration of articular cartilage with suitable biomechanical properties. As a first step, biomechanical and biochemical characterization studies at the tissue level were used to provide design criteria for engineering neotissues. Extending this work to the single cell and subcellular levels has helped to develop biochemical and mechanical stimuli for tissue engineering studies. This strong mechanobiological foundation guided studies on regenerating hyaline articular cartilage, the knee meniscus, and temporomandibular joint (TMJ) fibrocartilage. Initial tissue engineering efforts centered on developing biodegradable scaffolds for cartilage regeneration. After many years of studying scaffold-based cartilage engineering, scaffoldless approaches were developed to address deficiencies of scaffold-based systems, resulting in the self-assembling process. This process was further improved by employing exogenous stimuli, such as hydrostatic pressure, growth factors, and matrix-modifying and catabolic agents, both singly and in synergistic combination to enhance neocartilage functional properties. Due to the high cell needs for tissue engineering and the limited supply of native articular chondrocytes, costochondral cells are emerging as a suitable cell source. Looking forward, additional cell sources are investigated to render these technologies more translatable. For example, dermis isolated adult stem (DIAS) cells show potential as a source of chondrogenic cells. The challenging problem of enhanced integration of engineered cartilage with native cartilage is approached with both familiar and novel methods, such as lysyl oxidase (LOX). These diverse tissue engineering strategies all aim to build upon thorough biomechanical characterizations to produce functional neotissue that ultimately will help combat the pressing problem of cartilage degeneration. As our prior research is reviewed, we look to establish new pathways to comprehensively and effectively address the complex problems of musculoskeletal cartilage regeneration.
Prediction of Edge Crack in Cold Rolling of Silicon Steel Strip Based on an Extended Gurson–Tvergaard–Needleman Damage Model
Authors: Sun Quan , Chen Jianjun , Pan Hongliang
Published: October 2014

Edge cracking is commonly observed in cold rolling process. However, its failure mechanism is far from fully understanding due to the complex stresses and plastic flow conditions of steel strip under the rolling condition. In this paper, an extended Gurson–Tvergaard–Needleman (GTN) damage model coupled with Nahshon–Hutchinson shear damage mechanism was introduced to investigate the damage and fracture behavior of steel strip in cold rolling. The results show that extended GTN damage model is efficient in predicting the occurrence of edge crack in cold rolling, and the prediction is more accurate than that of the original GTN damage model. The edge cracking behavior under various cold rolling process parameters is investigated. It comes to the conclusion that edge crack extension increases with the increase of the reduction ratio, tension and the decrease of the roller radius and friction coefficient. The influence of shear damage becomes more significant in rolling condition with a larger reduction ratio, smaller roller radius, lower friction force, and tension.
Differential Quadrature Method for Stability Analysis of Dynamic Systems With Multiple Delays: Application to Simultaneous Machining Operations
Authors: Ding Ye , Niu Jinbo , Zhu Limin , Ding Han
Published: October 2014

This paper proposes a semi-analytical solution via the differential quadrature method (DQM) for stability analysis of linear multi-degree-of-freedom second-order systems with multiple delays. The vibration systems are reformulated as a delayed differential equation (DDE) in state–space form. With the derivative of the state vector with respect to time at an arbitrary discrete-time point being expressed as a linear weighted sum of the values of the state vector, the original DDE is approximated by a set of algebraic equations, leading to the Floquet transition matrix. Based on Floquet theory, the stability of the systems is then determined by checking the eigenvalues of the transition matrix. The computational accuracy and efficiency are demonstrated through comparison with existing methods via numerical examples. As an application, the proposed method is employed to predict chatter stability in simultaneous machining operations, providing a reference for the choice of machining parameters.
An Intelligent Prognostic System for Gear Performance Degradation Assessment and Remaining Useful Life Estimation
Authors: Wang Dong , Miao Qiang , Zhou Qinghua , Zhou Guangwu
Published: October 2014

Gears are widely used in machines to transmit torque from one shaft to another shaft and to change the speed of a power source. Gear failure is one of the major causes for mechanical transmission system breakdown. Therefore, early gear faults must be immediately detected prior to its failure. Once early gear faults are diagnosed, gear remaining useful life (RUL) should be estimated to prevent any unexpected gear failure. In this paper, an intelligent prognostic system is developed for gear performance degradation assessment and RUL estimation. For gear performance degradation assessment, which aims to monitor current gear health condition, first, the frequency spectrum of gear acceleration error signal is mathematically analyzed to design a high-order complex Comblet for extracting gear fault related signatures. Then, two health indicators called heath indicator 1 and health indicator 2 are constructed to detect early gear faults and assess gear performance degradation, respectively, using two individual dynamic Bayesian networks. For gear RUL estimation, which aims to predict future gear health condition, a general sequential Monte Carlo algorithm is applied to iteratively infer gear failure probability density function (FPDF), which is used to predict gear residual lifetime. One case study is investigated to illustrate how the developed prognostic system works. The vibration data collected from a gearbox accelerated life test are used in this paper, where the gearbox started from a brand-new state, and ran until gear tooth failure. The results show that the developed prognostic system is able to detect early gear faults, track gear performance degradation, and predict gear RUL.
Nonlinear Dynamics of a Simplified Model of an Overhung Rotor Subjected to Intermittent Annular Rubs
Authors: Zilli Andrea , Williams Robin J. , Ewins David J.
Published: October 2014

The dynamic forced response of a two-degrees-of-freedom model of an unbalanced overhung rotor with clearance and symmetric piecewise-linear stiffness is examined in the time domain. The stiffness nonlinearity is representative of the contact between the rotor and a concentric stator ring. This rubbing interaction comes as a result of the rotor transient motion initiated by the sudden application of a static unbalance, such as in a blade loss scenario. The focus of this study is on the range of rotor speeds above resonance, where the contact between rotor and stator is characterized by a “bouncing” or intermittent type of behavior. Brute-force numerical bifurcation analysis on the long-term forced response revealed ranges of rotation frequency for which there is bistability between nonimpacting synchronous equilibrium and impacting subsynchronous motion. It is found that, for sufficiently high levels of transient energy in the rotor, there exists the possibility for the solution to jump into a stable limit cycle characterized by three nonharmonically related frequencies, namely, the synchronous response frequency and the forward and backward whirl frequencies. A simple relationship defining the point of synchronization between these three components is proposed as an explanation to the region of bistability detected. The stiffening effect induced by the contact nonlinearity enables this synchronization to be maintained over a range of forcing frequencies rather than just at the single condition determined from the nominal whirl mode frequencies.