bluuebunny/crossref_metadata_2025 huggingface dataset:
The Impact of Pad Flexibility on the Rotordynamic Coefficients of Tilting-Pad Journal Bearings
Authors: Gaines Jennifer E. , Childs Dara W.
Published: December 2015

Static and dynamic load tests were performed on a three-pad, rocker-pivot, tilting-pad journal bearing (TPJB) with three interchangeable pad configurations, each with measurably different pad flexibilities. Measured dynamic-stiffness data for the bearing were readily fitted by a frequency-independent, constant-coefficient [K][C][M] model. The test-bearing had a 101.74 mm diameter with L/D = 0.6. Tests were conducted over the speed range of 6–12 krpm, with unit loads varying from 0.172 to 1.724 MPa. An ISO VG 46 lubricant was used as the test fluid. Pad flexibility was characterized as the change in the pad's bending stiffness or the change in pad thickness. A finite-element model (FEM) was created to predict the structural bending stiffness of each pad configuration, showing a significant pad flexibility increase as pad thickness decreased. To examine the effect of pad flexibility on the rotordynamic coefficients, the measured results were compared across pad configurations and showed that the pad flexibility increase reduced the direct damping coefficients by 12–20%. As pad flexibility increased, the direct-stiffness coefficients could increase or decrease, depending on the unit load. They varied from an increase of 12% at low unit loads to a decrease of 3% at high unit loads. Results show that the pad's structural bending stiffness or flexibility is important when predicting the bearing’s dynamic performance. Damping is consistently overpredicted when neglecting pad flexibility. A nondimensional pad flexibility parameter αflex was developed. It related the average deflection across the pad surface to the pad's arc length and was to relate the pad flexibility of multiple bearings of different sizes. A bearing code was used to predict the percent change in direct damping coefficients for rigid-pad/flexible-pivot and flexible-pad/flexible-pivot models for a surface speed of 54 m/s and a unit load of 783 kPa for the three-pad configuration tested here plus five additional tested bearings from the literature. For the minimum pad thickness configuration tested here, the code predicted a 20% drop in predicted Cxx (off-load axis direct damping) when comparing a model that included pad flexibility with a model that neglected pad flexibility. In terms of αflex, the two thinnest pad configurations tested here are quite flexible compared to both TPJB's pads used in industry and previously tested TPJB pads.
Efficient Computation of Thermoacoustic Modes in Industrial Annular Combustion Chambers Based on Bloch-Wave Theory
Authors: Mensah Georg A. , Campa Giovanni , Moeck Jonas P.
Published: December 2015

Most annular combustors feature a discrete rotational symmetry so that the full configuration can be obtained by copying one burner-flame segment a certain number of times around the circumference. A thermoacoustic model based on the Helmholtz equation then admits special solutions of the so-called Bloch type that can be obtained by considering one segment only. We show that a significant reduction in computational effort for the determination of thermoacoustic modes can be achieved by exploiting this concept. The framework is applicable even in complex cases including an inhomogeneous temperature field and a frequency-dependent, spatially distributed flame response. A parametric study on a three-dimensional combustion chamber model is conducted using both the full-scale chamber simulation and a one-segment model with the appropriate Bloch-type boundary conditions. The results for both computations are compared in terms of mode frequencies and growth rates as well as the corresponding mode shapes. The same is done for a more complex industrial configuration. These comparisons demonstrate the benefits of the Bloch-wave based analysis.
Influences of Design Parameters on a Double Serpentine Convergent Nozzle
Authors: Sun Xiao-lin , Wang Zhan-xue , Zhou Li , Liu Zeng-wen , Shi Jing-wei
Published: December 2015

Serpentine nozzles are supplied in stealth bombers and unmanned aerial vehicles (UAVs) to evidently suppress the infrared radiation signatures (IRSs) emitted by engine exhausts. It is commonly known that excessive geometric parameters are included in the double serpentine nozzle design and, as a result, the aim of this paper is to study the influences of the design parameters on the performance of double serpentine nozzle. To this end, the design method of the serpentine nozzle was concisely introduced, and the qualifications to completely shield turbine were given. Simulations using six different turbulence models were conducted and compared to the experimental data in order to determine the suitable turbulence model for serpentine duct simulations. Then, the effects of geometric design parameters at the first serpentine paragraph exit (the dimensionless width of W1/D, area of A1/Ain, and offset distance of ΔY1/L1) on the flowfield, and the performance of double serpentine nozzle was investigated numerically. The validation study shows that the simulations with shear-stress transport (SST) κ–ω turbulence model adopted can accurately predict the flux rate, the axial thrust, and the static pressure of the experimental nozzle, and therefore, SST κ–ω turbulence model is the most suitable turbulence model in the selected six turbulence models to be used for the simulation of the double serpentine nozzles. The numerical results show that friction loss increases with the increment of W1/D due to the increased wetted perimeter, but small value of W1/D would lead to large secondary flow loss; even the shock loss appears because of the steep curvature of the second turning. Small area of the first serpentine duct A1/Ain induces high flow velocity in the first duct, which corresponds to large friction loss. Steep offset distance of the first serpentine duct ΔY1/L1 induces high local losses. As the geometric design parameters of the double serpentine nozzle interact mutually with the qualifications to completely shield the turbine, the range of design parameters should be synthetically chosen during the design progress. Thus, the width of the first serpentine duct W1/D is recommended to be from 1.0 to 1.3. The area of the first serpentine duct A1/Ain should be as large as possible, and the offset distance of the first serpentine ΔY1/L1 should be small in the permission range of the design parameters.
Effect of Valve Opening/Closing Setup on Computational Fluid Dynamics Prediction of Engine Flows
Authors: Yang Xiaofeng , Keum Seunghwan , Kuo Tang-Wei
Published: December 2015

In computational fluid dynamics (CFD) simulations of internal combustion engines, one of the critical modeling parameters is the valve setup. A standard workaround is to keep the valve opens at a certain clearance (minimum valve lift), while imposing a solid boundary to mimic valve closure. This method would yield a step change in valve lift during opening and closing event, and different valve event timing than hardware. Two parametric studies were performed to examine (a) the effect of the minimum valve lift and (b) the effect of grid resolution at the minimum valve lift on predicted in-cylinder flow fields in Reynolds-averaged Navier–Stokes (RANS) simulations. The simulation results were compared with the state-of-the-art particle image velocimetry (PIV) measurement from a two-valve transparent combustion chamber (TCC-3) engine. The comparisons revealed that the accuracy of flow simulation is sensitive to the choice of minimum valve lift and grid resolution in the valve seat region. In particular, the predicted in-cylinder flow field during the intake process was found to be very sensitive to the valve setup. A best practice CFD valve setup strategy is proposed as a result of these parametric studies. The proposed CFD valve setup was applied to large eddy simulation (LES) of TCC-3 engine and preliminary results showed noticeable improvement already. Further evaluation of the valve setup strategy for LES simulations is ongoing and will be reported in a separate report.
Experimental Characterization of the Vertical and Lateral Heat Transfer in Three-Dimensional Stacked Die Packages
Authors: Oprins Herman , Cherman Vladimir , Van der Plas Geert , De Vos Joeri , Beyne Eric
Published: December 2015

In this paper, we present the experimental characterization of three-dimensional (3D) packages using a dedicated stackable test chip. An advanced complementary metal oxide silicon (CMOS) test chip with programmable power distribution has been designed, fabricated, stacked, and packaged in molded and bare die 3D packages. The packages have been experimentally characterized in test sockets with and without cooling and soldered to the printed circuit board (PCB). Using uniform and localized hot spot power distribution, the thermal self-heating and thermal coupling resistance and the lateral spreading in the 3D packages have been studied. Furthermore, the measurements have been used to characterize the thermal properties of the die–die interface and to calibrate a thermal model for the calculation of equivalent properties of underfilled μbump arrays. This model has been applied to study the tradeoff between the standoff height reduction and the underfill thermal conductivity increase in order to reduce the interdie thermal resistance.
Modeling Thermal Microspreading Resistance in Via Arrays
Authors: Fish Michael , McCluskey Patrick , Bar-Cohen Avram
Published: December 2015

As thermal management techniques for three-dimensional (3D) chip stacks and other high-power density electronic packages continue to evolve, interest in the thermal pathways across substrates containing a multitude of conductive vias has increased. To reduce the computational costs and time in the thermal analysis of through-layer via (TXV) structures, much research to date has focused on defining effective anisotropic thermal properties for a pseudohomogeneous medium using isothermal boundary conditions. While such an approach eliminates the need to model heat flow through individual vias, the resulting properties are found to depend on the specific boundary conditions applied to a unit TXV cell. More specifically, effective properties based on isothermal boundary conditions fail to capture the local “microspreading” resistance associated with more realistic heat flux distributions and local hot spots on the surface of these substrates. This work assesses how the thermal microspreading resistance present in arrays of vias in interposers, substrates, and other package components can be properly incorporated into the modeling of these arrays. We present the conditions under which spreading resistance plays a major role in determining the thermal characteristics of a via array and propose methods by which designers can both account for the effects of microspreading resistance and mitigate its contribution to the overall thermal behavior of such substrate–via systems. Finite element modeling (FEM) of TXV unit cells is performed using commercial simulation software (ansys).
Evaluation of the Maximum Evaporation Rate in Small-Scale Indirect Solar Dryers
Authors: Blanco-Cano Lucía , Soria-Verdugo Antonio , Miguel Garcia-Gutierrez Luis , Ruiz-Rivas Ulpiano
Published: December 2015

A theoretical study on the maximum evaporation rate obtainable in a small-scale indirect solar dryer is presented, considering evaporation of free water. A mathematical model of the evolution of the temperature and the specific humidity of the airflow along the drying chamber is presented. Based on the results, some simplifications are proposed and justified in order to calculate the maximum evaporation rate as a function of a reduced number of parameters, to study their effect. The results show that the effect of the air mass flow rate on the maximum evaporation rate depends on the aspect ratio of the drying chamber, defined as the ratio of the total drying area to the cross section in the drying chamber. Design and operation criteria can be extracted from the results. As a global result, for the typical range of dimensions and air mass flow rates employed in solar dryers, the drying chamber aspect ratio should be between 200 and 300 to obtain a proper evaporation rate. Within that range, doubling the air mass flow rate the maximum evaporation rate obtainable increases around 20%.
Design Requirements for Annulus Fibrosus Repair: Review of Forces, Displacements, and Material Properties of the Intervertebral Disk and a Summary of Candidate Hydrogels for Repair
Authors: Long Rose G. , Torre Olivia M. , Hom Warren W. , Assael Dylan J. , Iatridis James C.
Published: December 2015

There is currently a lack of clinically available solutions to restore functionality to the intervertebral disk (IVD) following herniation injury to the annulus fibrosus (AF). Microdiscectomy is a commonly performed surgical procedure to alleviate pain caused by herniation; however, AF defects remain and can lead to accelerated degeneration and painful conditions. Currently available AF closure techniques do not restore mechanical functionality or promote tissue regeneration, and have risk of reherniation. This review determined quantitative design requirements for AF repair materials and summarized currently available hydrogels capable of meeting these design requirements by using a series of systematic PubMed database searches to yield 1500+ papers that were screened and analyzed for relevance to human lumbar in vivo measurements, motion segment behaviors, and tissue level properties. We propose a testing paradigm involving screening tests as well as more involved in situ and in vivo validation tests to efficiently identify promising biomaterials for AF repair. We suggest that successful materials must have high adhesion strength (∼0.2 MPa), match as many AF material properties as possible (e.g., approximately 1 MPa, 0. 3 MPa, and 30 MPa for compressive, shear, and tensile moduli, respectively), and have high tensile failure strain (∼65%) to advance to in situ and in vivo validation tests. While many biomaterials exist for AF repair, few undergo extensive mechanical characterization. A few hydrogels show promise for AF repair since they can match at least one material property of the AF while also adhering to AF tissue and are capable of easy implantation during surgical procedures to warrant additional optimization and validation.
Chemical-Looping Combustion of Hard Coal: Autothermal Operation of a 1 MWth Pilot Plant
Authors: Ohlemüller Peter , Busch Jan-Peter , Reitz Michael , Ströhle Jochen , Epple Bernd
Published: December 2015

Chemical-looping combustion (CLC) is an emerging carbon capture technology that is characterized by a low energy penalty, low carbon dioxide capture costs, and low environmental impact. To prevent the contact between fuel and air, an oxygen carrier is used to transport the oxygen needed for fuel conversion. In comparison to a classic oxyfuel process, no air separation unit is required to provide the oxygen needed to burn the fuel. The solid fuel, such as coal, is gasified in the fuel reactor (FR), and the products from gasification are oxidized by the oxygen carrier. There are promising results from the electrically heated 100 kWth unit at Chalmers University of Technology (Sweden) or the 1 MWth pilot at Technische Universität Darmstadt (Germany) with partial chemical-looping conditions. The 1 MWth CLC pilot consists of two interconnected circulating fluidized bed reactors. It is possible to investigate this process without electrically heating due to refractory-lined reactors and coupling elements. This work presents the first results of autothermal operation of a metal oxide CLC unit worldwide using ilmenite as oxygen carrier and coarse hard coal as fuel. The FR was fluidized with steam. The results show that the oxygen demand of the FR required for a complete conversion of unconverted gases was in the range of 25%. At the same time, the carbon dioxide capture efficiency was low in the present configuration of the 1 MWth pilot. This means that unconverted char left the FR and burned in the air reactor (AR). The reason for this is that no carbon stripper unit was used during these investigations. A carbon stripper could significantly enhance the carbon dioxide capture efficiency.
Implicit Large Eddy Simulation of a Stalled Low-Pressure Turbine Airfoil
Authors: Memory C. L. , Chen J. P. , Bons J. P.
Published: December 2015

Time-accurate numerical simulations were conducted on the aft-loaded L1A low-pressure turbine airfoil at a Reynolds number of 22,000 (based on inlet velocity magnitude and axial chord length). This flow condition produces a nonreattaching laminar separation zone on the airfoil suction surface. The numerical code TURBO is used to simulate this flow field as an implicit large eddy simulation (ILES). Generally, good agreement was found when compared to experimental time-averaged and instantaneous flow measurements. The numerical separation zone is slightly larger than that in the experiments, though integrated wake loss values improved from Reynolds-averaged Navier–Stokes (RANS)-based simulations. Instantaneous snapshots of the numerical flow field showed the Kelvin Helmholtz instability forming in the separated shear layer and a large-scale vortex shedding pattern at the airfoil trailing edge. These features were observed in the experiments with similar sizes and vorticity levels. Power spectral density analyses revealed a global passage oscillation in the numerics that was not observed experimentally. This oscillation was most likely a primary resonant frequency of the numerical domain.
Experimental and Numerical Models of Complex Clinical Scenarios; Strategies to Improve Relevance and Reproducibility of Joint Replacement Research
Authors: Bechtold Joan E. , Swider Pascal , Goreham-Voss Curtis , Soballe Kjeld
Published: December 2015

This research review aims to focus attention on the effect of specific surgical and host factors on implant fixation, and the importance of accounting for them in experimental and numerical models. These factors affect (a) eventual clinical applicability and (b) reproducibility of findings across research groups. Proper function and longevity for orthopedic joint replacement implants relies on secure fixation to the surrounding bone. Technology and surgical technique has improved over the last 50 years, and robust ingrowth and decades of implant survival is now routinely achieved for healthy patients and first-time (primary) implantation. Second-time (revision) implantation presents with bone loss with interfacial bone gaps in areas vital for secure mechanical fixation. Patients with medical comorbidities such as infection, smoking, congestive heart failure, kidney disease, and diabetes have a diminished healing response, poorer implant fixation, and greater revision risk. It is these more difficult clinical scenarios that require research to evaluate more advanced treatment approaches. Such treatments can include osteogenic or antimicrobial implant coatings, allo- or autogenous cellular or tissue-based approaches, local and systemic drug delivery, surgical approaches. Regarding implant-related approaches, most experimental and numerical models do not generally impose conditions that represent mechanical instability at the implant interface, or recalcitrant healing. Many treatments will work well in forgiving settings, but fail in complex human settings with disease, bone loss, or previous surgery. Ethical considerations mandate that we justify and limit the number of animals tested, which restricts experimental permutations of treatments. Numerical models provide flexibility to evaluate multiple parameters and combinations, but generally need to employ simplifying assumptions. The objectives of this paper are to (a) to highlight the importance of mechanical, material, and surgical features to influence implant–bone healing, using a selection of results from two decades of coordinated experimental and numerical work and (b) discuss limitations of such models and the implications for research reproducibility. Focusing model conditions toward the clinical scenario to be studied, and limiting conclusions to the conditions of a particular model can increase clinical relevance and research reproducibility.
Sandia Verification and Validation Challenge Problem: A PCMM-Based Approach to Assessing Prediction Credibility
Authors: Beghini Lauren L. , Hough Patricia D.
Published: December 2015

The process of establishing credibility in computational model predictions via verification and validation (V&V) encompasses a wide range of activities. Those activities are focused on collecting evidence that the model is adequate for the intended application and that the errors and uncertainties are quantified. In this work, we use the predictive capability maturity model (PCMM) as an organizing framework for evidence collection activities and summarizing our credibility assessment. We discuss our approaches to sensitivity analysis, model calibration, model validation, and uncertainty quantification and how they support our assessments in the solution verification, model validation, and uncertainty quantification elements of the PCMM. For completeness, we also include some limited assessment discussion for the remaining PCMM elements. Because the computational cost of performing V&V and the ensuing predictive calculations is substantial, we include discussion of our approach to addressing computational resource considerations, primarily through the use of response surface surrogates and multiple mesh fidelities.
Economic Analysis of Model Validation for a Challenge Problem
Authors: Paez Paul J. , Paez Thomas L. , Hasselman Timothy K.
Published: December 2015

It is now commonplace for engineers to build mathematical models of the systems they are designing, building, or testing. And, it is nearly universally accepted that phenomenological models of physical systems must be validated prior to use for prediction in consequential scenarios. Yet, there are certain situations in which testing only or no testing and no modeling may be economically viable alternatives to modeling and its associated testing. This paper develops an economic framework within which benefit–cost can be evaluated for modeling and model validation relative to other options. The development is presented in terms of a challenge problem. We provide a numerical example that quantifies when modeling, calibration, and validation yield higher benefit–cost than a testing only or no modeling and no testing option.
Effect of Flat Belt Thickness on Steady-State Belt Stresses and Slip
Authors: Wasfy Tamer M. , Yildiz Cagkan , Wasfy Hatem M. , Peters Jeanne M.
Published: December 2015

A necessary condition for high-fidelity dynamic simulation of belt-drives is to accurately predict the belt stresses, pulley angular velocities, belt slip, and belt-drive energy efficiency. In previous papers, those quantities were predicted using thin shell, beam, or truss elements along with a Coulomb friction model. However, flat rubber belts have a finite thickness and the reinforcements are typically located near the top surface of the belt. In this paper, the effect of the belt thickness on the aforementioned response quantities is studied using a two-pulley belt-drive. The belt rubber matrix is modeled using three-dimensional brick elements. Belt reinforcements are modeled using one-dimensional truss elements at the top surface of the belt. Friction between the belt and the pulleys is modeled using an asperity-based Coulomb friction model. The pulleys are modeled as cylindrical rigid bodies. The equations of motion are integrated using a time-accurate explicit solution procedure.
Effect of Roll Configuration on the Leveling Effectiveness of Tail-Up Bent Plate Using Finite-Element Analysis
Authors: Hyung Seo Jae , Van Tyne Chester J. , Hoon Moon Young
Published: December 2015

The finite-element method (FEM) has been used to numerically investigate the effect of work roll configuration on the leveling effectiveness of tail-up bent plates. Leveling is a process used to minimize shape defects, including flatness imperfections and uniformity of internal stresses in shape-critical applications. Leveling plays an important role in delivering the desired plate shape and meeting the required product standards. To simulate the roller leveling effectiveness of tail-up bent plates, an initially flat plate was plastically bent prior to leveling and was passed through the leveling rolls. Leveling effectiveness was estimated by the vertical displacements of tail-up bent plates with two different roll configurations. One configuration adopts a gradually increasing roll gap, while the other configuration maintains the same roll gap in the first two sets of rolls and gradually increases the roll gap for the later rolls. For comparison purposes, the entry and exit roll gaps of the two roll configurations are set to the same roll gap. To verify the accuracy of the numerical simulations, actual leveling experiments were performed using tail-up bent plates. The results show that the roll configuration significantly influences the leveling effectiveness of the tail-up bent plates. Higher leveling effectiveness is obtained for a leveling configuration that imparts more severe deformation at the earlier leveling stages. Through the analysis, the work roll configuration is determined to be essential to increase leveling effectiveness of tail-up bent plates.
Tool Deflection Error of Three-Axis Computer Numerical Control Milling Machines, Monitoring and Minimizing by a Virtual Machining System
Authors: Soori Mohsen , Arezoo Behrooz , Habibi Mohsen
Published: December 2015

Virtual manufacturing systems carry out the simulation of manufacturing processes in digital environment in order to increase accuracy as well as productivity in part production. There are different error sources in machine tools, such as tool deflection, geometrical deviations of moving axis, and thermal distortions of machine tool structures. The errors due to tool deflection are caused by cutting forces and have direct effects on dimensional accuracy, surface roughness of the parts, and efficient life of the cutting tool, holder, and spindle. This paper presents an application of virtual machining systems in order to improve the accuracy and productivity of part manufacturing by monitoring and minimizing the tool deflection error. The tool deflection error along machining paths is monitored to present a useful methodology in controlling the produced parts with regard to desired tolerances. Suitable tool and spindle can also be selected due to the ability of error monitoring. In order to minimize the error, optimization technique based on genetic algorithms is used to determine optimized machining parameters. Free-form profile of virtual and real machined parts with tool deflection error is compared in order to validate reliability as well as accuracy of the software.
A Novel Sampling Technique for Probabilistic Static Coverage Problems
Authors: Zhang Binbin , Adurthi Nagavenkat , Rai Rahul , Singla Puneet
Published: December 2015

Resource allocation in the presence of constraints is an important activity in many systems engineering problems such as surveillance, infrastructure planning, environmental monitoring, and cooperative task performance. The resources in many important problems are agents such as a person, machine, unmanned aerial vehicles (UAVs), infrastructures, and software. Effective execution of a given task is highly correlated with effective allocation of resources to execute the task. An important class of resource allocation problem in the presence of limited resources is static coverage problem. In static coverage problems, it is necessary to allocate resources (stationary configuration of agents) to cover an area of interest so that an event or spatial property of the area can be detected or monitored with high probability. In this paper, we outline a novel sampling algorithm for the static coverage problem in presence of probabilistic resource intensity allocation maps (RIAMs). The key intuition behind our sampling approach is to use the finite number of samples to generate an accurate representation of RIAM. The outlined sampling technique is based on an optimization framework that approximates the RIAM with piecewise linear surfaces on the Delaunay triangles and optimizes the sample placement locations to decrease the difference between the probability distribution and Delaunay triangle surface. Numerical results demonstrate that the algorithm is robust to the initial sample point locations and has superior performance in a wide range of theoretical problems and real-life applications. In a real-life application setting, we demonstrate the efficacy of the proposed algorithm to predict the position of wind stations for monitoring wind speeds across the U.S. The algorithm is also used to give recommendations on the placement of police cars in San Francisco and weather buoys in Pacific Ocean.
Longitudinal Analysis of Mechanism and Machine Theory: Geospatial Productivity, Journal Citation Networks, and Researcher Communities
Authors: Chen Dar-Zen , Lee Ya-Yun
Published: December 2015

This paper presents a longitudinal analysis through bibliometrics from three perspectives: geospatial analysis of research productivity, citation network analysis of journals, and top productive researchers with research communities. The purpose of these analyses is to detect the development and research trends of mechanism and machine theory (MMT) field. The results indicate that the productivity of MMT publications shows a growing trend. The United States (U.S.) has dominated MMT publications, but its ratio has dropped off approximately twenty percent in the past three decades, while China (CN) has rapidly grown in its quantity and ratio of MMT publications. The concentration of MMT publications among various countries has declined over time. Through citation network analysis, the relationships between journals in the MMT field are identified and their variations over periods are derived. The citations have been centered between five related journals and three core journals. Additionally, the evolution of research communities corresponding to the top 30 productive researchers and the distribution of the publications in each community among countries are identified.
Resilience Modeling and Quantification for Engineered Systems Using Bayesian Networks
Authors: Yodo Nita , Wang Pingfeng
Published: December 2015

The concept of engineering resilience has received a prevalent attention from academia as well as industry because it contributes a new means of thinking about how to withstand against disruptions and recover properly. Although the concept of resilience was scholarly explored in diverse disciplines, there are only few which focus on how to quantitatively measure the engineering resilience. This paper is dedicated to explore the gap between quantitative and qualitative assessment of engineering resilience in the domain of designing engineered systems in industrial applications. A conceptual framework is first proposed for modeling engineering resilience, and then Bayesian network (BN) is employed as a quantitative tool for the assessment and analysis of the resilience for engineered systems. Two industrial-based case studies, supply chain and production process, are employed to demonstrate the proposed approach. The proposed resilience quantification and analysis approach using BNs would empower system designers to have a better grasp of the weakness and strength of their own systems against system disruptions induced by adverse failure events.
Theoretical Method for Calculating the Unit Curve of Gear Integrated Error
Authors: Shi Zhaoyao , Wang Xiaoyi , Shu Zanhui
Published: December 2015

A theoretical method is proposed in this paper to calculate the unit curve of gear integrated error (GIE). The calculated GIE unit curve includes the quasi-static transmission error (TE) curves of the approach stage, the involute stage, and the recession stage of the ZI worm and helical gear transmission. The misalignments between the two axes of the worm and gear, as well as the modifications or errors of the tooth flanks of the gear, are considered in the procedure of calculation. Optimization algorithm is introduced to replace the solving of implicit differential equations of the conventional tooth contact analysis (TCA) method. It is proved that the proposed method is clearer and more convenient than the conventional TCA methods in calculating the GIE unit curve. The correctness and merits of the proposed method are verified by two experiments.
Designing Multi-Axis Force–Torque Sensors by Minimizing the Amplitudes of Their Nonlinear Displacements
Authors: Bekhti R. , Cardou P. , Duchaine V.
Published: December 2015

Compliant multi-axis force–torque sensors play a crucial role in many emerging robotic applications, such as telemanipulation, haptic devices and human-robot physical interaction. In order to synthesize the compliant architectures at the core of these sensors, several researchers have devised performance indices from mechanism theory. This paper follows the same approach, but includes the innovation of using the changes in the compliant mechanism geometry as a new performance index. Once external forces are applied, the compliant mechanism deviates from its unloaded configuration, and thus, changes in geometry prevent the sensor from exhibiting a linear response. In order to minimize this nonlinear behavior, the potential sources of error are analyzed by applying linear algebra techniques to the expression of the Cartesian force mapping. Two performance indices are then presented and combined. The first index measures the variations of the Jacobian matrix about the unloaded configuration. The second index measures the amplification of the error arising from the joint displacements measurement. The resulting indices can be expressed symbolically, making them easier to evaluate and synthesize. Finally, we apply the performance indices we have developed to simple compliant mechanisms, and discuss the results.
Design and Testing of an Innovative Wire Transmission for a Quarter-Turn Actuator
Authors: Pugi L. , Galardi E. , Lucchesi N.
Published: December 2015

The object of this work is the development of an innovative wire actuator in collaboration with Velan ABV S.p.A., which will be mainly used in applications in which high efficiency and linear behavior are desirable specifications. In this work, the main features of the proposed actuator, which is protected by a patent, are evaluated and compared with respect to a conventional solution consisting of a scotch yoke (SY) transmission system. The comparison is performed using both the simulation results and the experimental data. In order to identify the efficiency and the dynamical response of the innovative actuator, the authors have designed a hydraulic test rig, which can be configured to perform different testing procedures. In this way, it is possible to perform both static tests to identify actuator efficiency, and dynamic ones, in which an assigned load or a valve impedance function is simulated to verify the response of the tested actuator in realistic conditions. Finally, the proposed test rig has been successfully employed to perform both reliability and fatigue tests in which the actuator is subjected to realistic and repetitive loads.
Isotropic Compliance in E(3): Feasibility and Workspace Mapping
Authors: Verotti Matteo , Belfiore Nicola P.
Published: December 2015

A manipulator control system, for which isotropic compliance holds in the Euclidean space E(3), can be significantly simplified by means of diagonal decoupling. However, such simplification may introduce some limits to the region of the workspace where the sought property can be achieved. The present investigation reveals how to detect which peculiar subset, among four different classes, a given manipulator belongs to. The paper also introduces the concept of control gain ratio for each specific single-input/single-output joint control law in order to limit the maximum gain required to achieve the isotropic compliance condition.
Singularity Traces of Single Degree-of-Freedom Planar Linkages That Include Prismatic and Revolute Joints
Authors: Almestiri Saleh M. , Murray Andrew P. , Myszka David H. , Wampler Charles W.
Published: December 2015

This paper extends the general method to construct a singularity trace for single degree-of-freedom (DOF), closed-loop linkages to include prismatic along with revolute joints. The singularity trace has been introduced in the literature as a plot that reveals the gross motion characteristics of a linkage relative to a designated input joint and a design parameter. The motion characteristics identified on the plot include a number of possible geometric inversions (GIs), circuits, and singularities at any given value for the input link and the design parameter. An inverted slider–crank and an Assur IV/3 linkage are utilized to illustrate the adaptation of the general method to include prismatic joints.
Integrating Solar Cells Into Flapping Wing Air Vehicles for Enhanced Flight Endurance
Authors: Perez-Rosado Ariel , Bruck Hugh A. , Gupta Satyandra K.
Published: December 2015

Flapping wing aerial vehicles (FWAVs) may require charging in the field where electrical power supply is not available. Flexible solar cells can be integrated into wings, tail, and body of FWAVs to harvest solar energy. The harvested solar energy can be used to recharge batteries and eliminate the need for external electrical power. It can also be used to increase the flight time of the vehicle by supplementing the battery power. The integration of solar cells in wings has been found to alter flight performance because solar cells have significantly different mechanical and density characteristics compared to other materials used for the FWAV construction. Previously, solar cells had been successfully integrated into the wings of Robo Raven, a FWAV developed at the University of Maryland. Despite changes in the aerodynamic forces, the vehicle was able to maintain flight and an overall increase in flight time was achieved. This paper investigates ways to redesign Robo Raven to significantly increase the wing area and incorporate solar cells into the wings, tail, and body. Increasing wing area allows for additional solar cells to be integrated, but there are tradeoffs due to the torque limitations of the servomotors used to actuate the wings as well changes in the lift and thrust forces that affect payload capacity. These effects were modeled and systematically characterized as a function of the wing area to determine the impact on enhancing flight endurance. In addition, solar cells were integrated into the body and the tail. The new design of Robo Raven generated a total of 64% more power using on-board solar cells, and increased flight time by 46% over the previous design. They were also able to recharge batteries at a similar rate to commercial chargers.
In Vivo Knee Contact Force Prediction Using Patient-Specific Musculoskeletal Geometry in a Segment-Based Computational Model
Authors: Ding Ziyun , Nolte Daniel , Kit Tsang Chui , Cleather Daniel J. , Kedgley Angela E. , Bull Anthony M. J.
Published: December 2015

Segment-based musculoskeletal models allow the prediction of muscle, ligament, and joint forces without making assumptions regarding joint degrees-of-freedom (DOF). The dataset published for the “Grand Challenge Competition to Predict in vivo Knee Loads” provides directly measured tibiofemoral contact forces for activities of daily living (ADL). For the Sixth Grand Challenge Competition to Predict in vivo Knee Loads, blinded results for “smooth” and “bouncy” gait trials were predicted using a customized patient-specific musculoskeletal model. For an unblinded comparison, the following modifications were made to improve the predictions: further customizations, including modifications to the knee center of rotation; reductions to the maximum allowable muscle forces to represent known loss of strength in knee arthroplasty patients; and a kinematic constraint to the hip joint to address the sensitivity of the segment-based approach to motion tracking artifact. For validation, the improved model was applied to normal gait, squat, and sit-to-stand for three subjects. Comparisons of the predictions with measured contact forces showed that segment-based musculoskeletal models using patient-specific input data can estimate tibiofemoral contact forces with root mean square errors (RMSEs) of 0.48–0.65 times body weight (BW) for normal gait trials. Comparisons between measured and predicted tibiofemoral contact forces yielded an average coefficient of determination of 0.81 and RMSEs of 0.46–1.01 times BW for squatting and 0.70–0.99 times BW for sit-to-stand tasks. This is comparable to the best validations in the literature using alternative models.
Physical Analysis of Rotor-to-Stator Rub in a Large-Capacity Low-Pressure Steam Turbogenerator
Authors: Cha Seogju , Na Sungsoo
Published: December 2015

Excessive vibration in large-capacity turbine generators can lead to expensive repairs and downtime with associated loss of operational income. Therefore, it is vital to detect the rubbing location in the rotor system at an early stage. The challenge is in achieving this without the expense and labor of complete disassembly. In this study, we present a practical tool for estimating the rubbing locations in a large-capacity rotor system from the shaft vibration patterns at each bearing. The measurement and analysis were performed on the rotor system of an 800-MW class large-capacity turbine generator. Three vibration patterns were observed in the machine operating on-site and were explained in terms of vibration modal analysis and the unbalance response characteristics to identify the rubbing locations. These results will be of interest to industrial engineers and have the potential to increase savings in operation costs.
Design of Experiments to Investigate Geometric Effects on Fluid Leakage Rate in a Balance Drum Seal
Authors: Morgan Neal R. , Wood Houston G. , Untaroiu Alexandrina
Published: December 2015

Grove configuration has a direct influence on the performance of the labyrinth seal. In this study, the geometry of the groove cavities in a water balance drum labyrinth seal was varied to investigate the effects on fluid leakage. A design of experiments (DOEs) study varied the groove cavity cross section through various trapezoidal shapes with one or both internal base angles obtuse. The grooves are parameterized by the groove width connected to the jet-flow region, the internal entrance and exit angles, the flat width inside the groove, and the depth. The corners inside the groove cavity are filleted with equal radii. As with the baseline model, the grooves are evenly spaced along the seal length and identical copies of each other. The flow path starting at the rear of the pump impeller and proceeding through the seal was created as a 5-deg sector computational fluid dynamics (CFD) model in ansys cfx. Three five-level factorial designs were selected for the cases where the entrance angle is obtuse and the exit angle is acute, the exit angle obtuse and entrance angle acute, and both angles were obtuse. The feasible geometries from each factorial design were selected based on the nonlinear geometric constraints, and CFD simulation experiments were performed in ansys cfx. The leakage results from these simulation experiments were then analyzed by multifactor linear regression to create prediction equations relating the geometric design variables to leakage and enable geometric optimization for minimum leakage. Streamline plots along the seal cross section were then used to visualize the flow and understand regression trends. This study investigates the effect of groove cavities with obtuse internal entrance and exit angles on vortex size and position and subsequent seal leakage.
The Effect of In-Cylinder Turbulence on Lean, Premixed, Spark-Ignited Engine Performance
Authors: Breaux Baine , Hoops Chris , Glewen William
Published: December 2015

The intensity and structure of in-cylinder turbulence is known to have a significant effect on internal combustion engine performance. Changes in flow structure and turbulence intensity result in changes to the rate of heat release, cylinder wall heat rejection, and cycle-to-cycle combustion variability. This paper seeks to quantify these engine performance consequences and identify fundamental similarities across a range of high-speed, medium-bore, lean-burn, spark-ignited reciprocating engines. In-cylinder turbulence was manipulated by changing the extent of intake port-induced swirl as well as varying the level of piston-generated turbulence. The relationship between in-cylinder turbulence and engine knock is also discussed. Increasing in-cylinder turbulence generally reduces combustion duration, but test results reveal that increasing swirl beyond a critical point can cause a lengthening of burn durations and greatly reduced engine performance. This critical swirl level is related to the extent of small-scale, piston-generated turbulence present in the cylinder. Increasing in-cylinder turbulence generally leads to reduced cycle-to-cycle variability and increased detonation margin (DM). The overall change in thermal efficiency was dependent on the balance of these factors and wall heat transfer, and varied depending on the operational constraints for a given engine and application. Single cylinder engine test data, supported with three-dimensional computational fluid dynamics (CFD) results, are used to demonstrate and explain these basic combustion engine principles.
Influence of Preflame and Postflame Mixing on NOx Formation in a Reacting Premixed Jet in Hot Cross Flow
Authors: Ahrens Denise , Kolb Michael , Hirsch Christoph , Sattelmayer Thomas
Published: December 2015

Axial staging in premixed gas turbine combustors is a promising option for the increase in firing temperature without NOx penalty and for the improvement of turndown ratio, which is limited by the onset of CO-emissions. The configuration of greatest interest is the combination of state of the art premixed combustion in the primary stage with secondary injectors near the turbine inlet, which feed additional jets of premixed combustible mixture into the hot cross flow. Regarding NOx, this configuration is particularly beneficial (1) if the overall mixing quality in the first stage is limited, (2) if the difference between primary zone flame temperature and turbine inlet temperature due to air addition along the combustor is large, and (3) if a high degree of mixing in the second stage is achieved. The potential of this promising combustion concept was investigated in a large scale atmospheric test rig. For the study presented below, scaling of the second stage according to Karlovitz number similarity was chosen. This leads to smaller jet diameters and higher injection velocities compared to scaling based on Damköhler number applied in an earlier study. The impact of the higher velocities at the injector outlet on the flow field, on the liftoff height of the flame and on NOx formation is analyzed. A chemical network model is presented, which illustrates the effects of preflame and postflame mixing on NOx formation under atmospheric and high pressure conditions. In addition, this model is used to study the interactions of chemistry with mixing between the reacting jet and cross flow. On the basis of atmospheric testing and reactor modeling, predictions for engine pressure are made assuming similar liftoff as well as pre and postflame mixing. These results are further analyzed regarding the NOx reduction potential at different equivalence ratios and residence times. Finally, it is discussed under which conditions the investigated configuration can be beneficially applied to reduce NOxemissions of real engines.