bluuebunny/crossref_metadata_2025 huggingface dataset:
Importance of Shear in Site Assessment of Wind Turbine Fatigue Loads
Authors: Slot René M. M. , Svenningsen Lasse , Sørensen John D. , Thøgersen Morten L.
Published: July 2018

Wind turbines are subjected to fatigue loading during their entire lifetime due to the fluctuating excitation from the wind. To predict the fatigue damage, the design standard IEC 61400-1 describes how to parametrize an on-site specific wind climate using the wind speed, turbulence, wind shear, air density, and flow inclination. In this framework, shear is currently modeled by its mean value, accounting for neither its natural variance nor its wind speed dependence. This very simple model may lead to inaccurate fatigue assessment of wind turbine components, whose structural response is nonlinear with shear. Here we show how this is the case for flapwise bending of blades, where the current shear model leads to inaccurate and in worst case nonconservative fatigue assessments. Based on an optimization study, we suggest modeling shear as a wind speed dependent 60% quantile. Using measurements from almost one hundred sites, we document that the suggested model leads to accurate and consistent fatigue assessments of wind turbine blades, without compromising other main components such as the tower and the shaft. The proposed shear model is intended as a replacement to the mean shear, and should be used alongside the current IEC models for the remaining climate parameters. Given the large number of investigated sites, a basis for evaluating the uncertainty related to using a simplified statistical wind climate is provided. This can be used in further research when assessing the structural reliability of wind turbines by a probabilistic or semiprobabilistic approach.
Gold-Tin Solder Wetting Behavior for Package Lid Seals
Authors: Vianco Paul T. , Kilgo Alice C. , McKenzie Bonnie M.
Published: July 2018

This study examined the cause of nonwetted regions of the gold (Au) finish on iron-nickel (Fe–Ni) alloy lids that seal ceramic packages using the 80Au-20Sn solder (wt %, abbreviated Au–Sn) and their impact on the final lid-to-ceramic frame solder joint. The Auger electron spectroscopy (AES) surface and depth profile techniques identified surface and through-thickness contaminants in the Au metallization layer. In one case, the AES analysis identified background levels of carbon (C) contamination on the surface; however, the depth profile detected Fe and Ni contaminants that originated from the plating process. The Fe and Ni could impede the completion of wetting and spreading to the edge of the Au metallization. The Au layer of lids not exposed to a Au–Sn solder reflow step had significant surface and through-thickness C contamination. Inorganic contaminants were absent. Subsequent simulated reflow processes removed the C contamination from the Au layer without driving Ni diffusion from the underlying solderable layer. An Au metallization having negligible C contamination developed elevated C levels after exposure to a simulated reflow process due to C contamination diffusing into it from the underlying Ni layer. However, the second reflow step removed that contamination from the Au layer, thereby allowing the metallization to support the formation of lid-to-ceramic frame Au–Sn joints without risk to their mechanical strength or hermeticity.
Thermodynamic Considerations Related to Knock: Results From an Engine Cycle Simulation
Authors: Caton Jerald A.
Published: July 2018

The design and development of high efficiency spark-ignition engines continues to be limited by the consideration of knock. Although the topic of spark knock has been the subject of comprehensive research since the early 1900s, little has been reported on the coupling of the engine thermodynamics and knock. This work uses an engine cycle simulation together with a submodel for the knock phenomena to explore these connections. First, the autoignition characteristics as represented by a recent (2014) Arrhenius expression for the reaction time of the end gases are examined for a range of temperatures and pressures. In spite of the exponential dependence on temperature, pressure appears to dominate the ignition time for the conditions examined. Higher pressures (and higher temperatures) tend to enhance the potential for knock. Second, knock is determined as function of engine design and operating parameters. The trends are consistent with expectations, and the results provide a systematic presentation of knock occurrence. Engine parameters explored include compression ratio, engine speed, inlet pressure, start of combustion, heat transfer, and exhaust gas recirculation (EGR). Changes of cylinder pressures and temperatures of the unburned zone as engine parameters were varied are shown to be directly responsible for the changes of the knock characteristics.
A Test of the Rapid Formation of Design Cues for Product Body Shapes and Features
Authors: Du Ping , MacDonald Erin F.
Published: July 2018

Consumers often use a product's visual design as a mental shortcut to judge its unobservable attributes. Mental associations between visual design and unobservable attributes aid consumers in their judgments, and hypothetically reduce consumers' mental load. This paper describes a study that shows the possibility of quickly creating an association in subjects' minds between a holistic visual cue of a product—its body shape—and the general idea of “environmentally friendly” versus “not environmentally friendly,” a typically unobservable attribute. In this study, products' actual environmental friendliness was not measured. Subjects completed an association-building task, in which they developed mental associations between a product's visual cues and its “environmental friendliness” rating, an arbitrarily predetermined rating the authors supplied. The body shape was successfully used as a cue to subliminally communicate to subjects the product's “environmental friendliness.” As a comparison, an individual feature of the product was also used to cue; however, that was unsuccessful. An eye-tracking device was used to identify where subjects were focusing their eyes and for how long. In both the association-building task and a testing task that followed, subjects spent a greater percentage of time looking at the product's cued areas (the body and the selected feature). But during the testing task, subjects spent an even higher percentage of their time looking at the cued areas than they did during the association-building task. This indicates that mental associations, or cues, work to distribute mental load more efficiently.
A Thoria and Thorium Uranium Dioxide Nuclear Fuel Performance Model Prototype and Knowledge Gap Assessment
Authors: Bell J. S. , Chan P. K. , Prudil A.
Published: July 2018

Thorium-based fuel cycles can improve fuel sustainability within the nuclear power industry. The Canadian supercritical water-cooled reactor (SCWR) concept uses this path to achieve the sustainability requirement of the Gen-IV Forum. The study of thorium dioxide/thoria ThO2-based fuel irradiation behavior is significantly less advanced than that of uranium dioxide (UO2) fuel, although ThO2 possesses superior thermal conductivity, thermal expansion, higher melting temperature, and oxidation resistance that may improve both fuel performance and safety. The fuel and sheath modeling tool (FAST), a fuel performance model for UO2 fuel, was developed at the Royal Military College of Canada (RMCC). FAST capability has been extended to include thoria (ThO2), thorium uranium dioxide (Th,U)O2, and thorium plutonium dioxide (Th,Pu)O2 as fuel pellet materials, to aid in designing and performance assessment of Th-based fuels, including SCWR (Th,Pu)O2 fuel. The development and integration of ThO2 and (Th,U)O2 models into the existing FAST model led to the multipellet material FAST (MPM-FAST). Model development was performed in collaboration between RMCC and Canadian Nuclear Laboratories (CNL). This paper presents an outline of the ThO2 and (Th,U)O2 MPM-FAST model, a comparison between modeling results with postirradiation examination (PIE) data from a test conducted at CNL, and an account of the knowledge gap between our ability to model ThO2 and (Th,U)O2 fuel compared to UO2. Results are encouraging when compared to PIE data.
Creep-Fatigue Behaviors and Life Assessments in Two Nickel-Based Superalloys
Authors: Wang Run-Zi , Wang Ji , Gong Jian-Guo , Zhang Xian-Cheng , Tu Shan-Tung , Zhang Cheng-Cheng
Published: July 2018

The aim of this paper is to investigate different factors, including dwell time, strain range, and strain ratio on creep-fatigue endurances in nickel-based Inconel 718 and GH4169 superalloys. We also summarize classic approaches for life assessments based on the generalizations of Coffin–Manson equation, linear damage summation (LDS), and strain-range partitioning (SRP) method. Each approach does have some degree of success in dealing with a specific set of creep–fatigue data. In order to evaluate the prediction capabilities of the validated approaches, a Bayesian information criterion (BIC) allowing for maximum likelihood and principle of parsimony is used to select the best performing model.
Measurement of the Excitation Source of an Axisymmetric Shallow Cavity Shear Layer
Authors: Mohamed S. , Graf H. R. , Ziada S.
Published: July 2018

The interaction of a cavity shear layer with the sound field of an acoustic mode can generate an aeroacoustic source which is capable of initiating and sustaining acoustic resonances in the duct housing the cavity. This aeroacoustic source is determined experimentally for an internal axisymmetric cavity exposed to high Reynolds number, fully developed turbulent pipe flow without the need to resolve the details of neither the unsteady flow field nor the flow-sound interaction process at the cavity. The experimental technique, referred to here as the standing wave method (SWM), employs six microphones distributed upstream and downstream of the cavity to evaluate the fluctuating pressure difference generated by the oscillating cavity shear layer in the presence of an externally imposed sound wave. The results of the aeroacoustic source are in good agreement with the concepts of free shear layer instability and the fluid-resonant oscillation behavior. The accuracy of the measurement technique is evaluated by means of sensitivity tests. In addition, the measured source is used to predict the self-excited acoustic resonance of a shallow cavity in a pipeline. Comparison of the predicted and measured results shows excellent prediction of the self-excited acoustic resonance, including the resonance frequency, the lock-in velocity range, and the amplitude of the self-generated acoustic resonance.
Enhanced Biogas Production in the Duckweed Anaerobic Digestion Process
Authors: Ren Hongyan , Jiang Nan , Wang Tao , Mubashar Omar M. , Ruan Wenquan , Ghafoor Abdul
Published: July 2018

In order to enhance biogas production in the anaerobic digestion of duckweed, and duckweed with excess sludge as single and mixed substrates, the effects of hot alkali pretreatment and variation of the ratio of substrate to inoculum were investigated. The results showed that the delayed stage of anaerobic gas generation could be shortened when the two substrates were mixed during methane production, to give a cumulative gas yield of 2963 mL, which was 11% higher than the calculated value for the complementary substrate. The methane content was 57%, which was 13% higher than that from the duckweed group and 9% higher than from the excess sludge group. Furthermore, the methane yield was improved by 8% after the duckweed was pretreated with hot alkali. When the substrate to inoculum ratio was 1:1, the maximum biogas production of 3309 mL was achieved, with a methane yield of 1883 mL which, respectively, increases of 151 mL and 304 mL compared with the worst group (1:2.5).
Differential Quadrature Free Vibration Analysis of Functionally Graded Thin Annular Sector Plates in Thermal Environments
Authors: Mirtalaie S. H.
Published: July 2018

In this paper, the free vibration behavior of functionally graded (FG) thin annular sector plates in thermal environment is studied using the differential quadrature method (DQM). The material properties of the FG plate are assumed to be temperature dependent and vary continuously through the thickness, according to the power-law distribution of the volume fraction of the constituents. The nonlinear temperature distribution along the thickness direction of the plate is considered. Based on the classical plate theory, the governing differential equations of motion of the plate are derived and solved numerically using DQM. The natural frequencies of thin FG annular sector plates in thermal environment under various combinations of clamped, free, and simply supported boundary conditions (BCs) are presented for the first time. To ensure the accuracy of the method, the natural frequencies of a pure metallic plate are calculated and compared with those existing in the literature for the homogeneous plate where the results are in good agreement. The effects of temperature field, BCs, volume fraction exponent, radius ratio, and the sector angle on the free vibrations of the FG-plate are examined.
Optimized Input-Shaped Model Reference Control on Double-Pendulum System
Authors: Fujioka Daichi , Singhose William
Published: July 2018

This paper presents an optimized input-shaped model reference control (OIS-MRC) for limiting oscillation of multimode flexible systems. The controller is analyzed by using it to control an uncertain, time-varying double pendulum using a linear single-pendulum reference model. Single- and double-pendulum dynamics are presented, and the significant natural frequency ranges of the double pendulum are calculated. A Lyapunov control law using only the first mode states of the plant is obtained. An optimization technique is used to obtain the OIS-MRC controller parameters that realizes the shortest time duration, while meeting a set of design constraints. The oscillation suppression, control effort reduction, and disturbance rejection performances of the proposed OIS-MRC controller are tested via numerical simulations and experiments. The OIS-MRC achieves a robust oscillation suppression performance, while reducing the rise time.
Hybridization Scheme for a Proton Exchange Membrane Fuel Cell/Supercapacitor System
Authors: Rodríguez Marco A. , Rastogi Alok , Skormin Victor
Published: July 2018

Proton exchange membrane (PEM) fuel cells suffer noticeable power loss when operated at high power output. This paper proposes a hybridization scheme for a PEM fuel cell/supercapacitor system operating in three different regimes: “Flat,” “Uphill,” and “Downhill.” Transitions among operational regimes are governed by logical statements, which compare operational parameters against threshold values. These threshold values were obtained using a genetic optimization (GO) algorithm. The hybridization problem is analyzed in a simulation environment before the solution is implemented in an actual laboratory prototype. Results and discussion are presented to demonstrate the soundness of the proposed solution. The approach presented in this paper is suitable for applications where sudden changes in power demand occur.
Modeling of Moisture Transport Into an Electronic Enclosure Using the Resistor-Capacitor Approach
Authors: Staliulionis Ž. , Conseil-Gudla H. , Mohanty S. , Jabbari M. , Ambat R. , Hattel J. H.
Published: July 2018

The aim of this paper is to model moisture ingress into a closed electronic enclosure under isothermal and non-isothermal conditions. As a consequence, an in-house code for moisture transport is developed using the Resistor-Capacitor (RC) method, which is efficient as regards computation time and resources. First, an in-house code is developed to model moisture transport through the enclosure walls driven by diffusion, which is based on the Fick's first and second law. Thus, the model couples a lumped analysis of moisture transport into the box interior with a modified one-dimensional (1D) analogy of Fick's second law for diffusion in the walls. Thereafter, under non-isothermal conditions, the moisture RC circuit is coupled with the same configuration of thermal RC circuit. The paper concerns the study of the impact of imperfections in the enclosure for the whole diffusion process. Moreover, a study of the impact of wall thickness, different diffusion coefficient, and initial conditions in the wall for the moisture transport is accomplished. Comparison of modeling and experimental results showed that the RC model is very applicable for simple and rough enclosure design. Furthermore, the experimental and modeling results indicate that the imperfections, with certain limits, do not have a significant effect on the moisture transport. The modeling of moisture transport under non-isothermal conditions shows that the internal moisture oscillations follow ambient temperature changes albeit with a delay. Although, moisture ingress is slightly dependent on ambient moisture oscillations; however, it is not so dominant until equilibrium is reached.
An Investigation on Duplex Nucleation in AZ91 Magnesium Alloy and Its Influence on High Temperature Mechanical Properties
Authors: Saber A. , Haghayeghi R. , Najafi H. , Shahbeigi-Roodposhti Peiman
Published: July 2018

The grain refinement of Mg–Al alloy AZ91 via carbon inoculation, including the significant role of Mn in advanced nucleation, was analyzed, and the corresponding mechanical properties and aging behavior were investigated. To this end, various amounts of C were added into the liquid at the desired temperatures. Al8Mn5 particles, which are suitable nucleation sites for α-Mg, were identified as the primary grain refiners. In situ particle formation, along with appropriate wetting and a suitable orientation relationship (OR), facilitated the grain refinement mechanism. Al4C3 particles contributed to heterogeneous nucleation by providing suitable Al8Mn5 nucleation sites. Mn removal resulted in poor grain refinement in the Mg–Al alloy. The Hall–Petch relationship, high-temperature tensile behavior, and aging mechanism of the samples refined by 1 wt % C addition (as the best grain refiner) are discussed and compared with industrial practice.
A Frictional Contact Element for Flexible Pipe Modeling With Finite Macroelements
Authors: Provasi Rodrigo , Toni Fernando Geremias , Martins Clóvis de Arruda
Published: July 2018

The layers of unbounded flexible pipes have relative movement, enhancing its capabilities to handle curvatures and moment loads. In a simplified approach, those pipes can be described using bonded elements; but to really capture this behavior, a frictional contact is utterly needed. In general, dealing with contact problems in computational mechanics is complicated, since it involves the constant evaluation of its status and can lead to convergence problems or simulation failure, due to intrinsically problematic and inefficient contact models or due to contact models that are insufficient to capture the desired details. The macroelement formulation, which was created to deal with flexible pipes in a simplified way, needed a frictional contact element to enhance the quality of results and closeness to real behavior. The major drawback for developing such element is the different nature of the nodal displacements descriptions. The first approach possible is the simplest contact model: it involves only the nodes in each contacting elements. The gap information and distances are evaluated using exclusively the nodal information. This kind of model provides good results with minimum computational effort, especially when considering small displacements. This paper proposes such element: a node-to-node contact formulation for macroelements. It considers that the nodal displacements of both nodes are in cylindrical coordinates with one of them using Fourier series to describe the displacements. To show model effectiveness, a case study with a cylinder using Fourier series and multiple helical elements connected with the contact element is done and shows great results.
Experimental Validation of a Three-Component Surrogate for Sasol-Isoparaffinic Kerosene in Single Cylinder Diesel Engine and Ignition Quality Tester
Authors: Alkhayat Samy , Trivedi Manan , Henein Naeim , Mukhopadhyay Sampad , Schihl Peter
Published: July 2018

Surrogates development is important to extensively investigate the combustion behavior of fuels. Development of comprehensive surrogates has been focusing on matching chemical and physical properties of their target fuel to mimic its atomization, evaporation, mixing, and auto-ignition behavior. More focus has been given to matching the derived cetane number (DCN) as a measure of the auto-ignition quality. In this investigation, we carried out experimental validation of a three-component surrogate for Sasol-Isoparaffinic Kerosene (IPK) in ignition quality tester (IQT) and in an actual diesel engine. The surrogate fuel is composed of three components (46% iso-cetane, 44% decalin, and 10% n-nonane on a volume basis). The IQT experiments were conducted as per ASTM D6890-10a. The engine experiments were conducted at 1500 rpm, two engine loads, and two injection timings. Analysis of ignition delay (ID), peak pressure, peak rate of heat release (RHR), and other combustion phasing parameters showed a closer match in the IQT than in the diesel engine. Comparison between the surrogate combustion behavior in the diesel engine and IQT revealed that matching the DCN of the surrogate to its respective target fuel did not result in the same negative temperature coefficient (NTC) profile—which led to unmatched combustion characteristics in the high temperature combustion (HTC) regimes, despite the same auto-ignition and low temperature combustion (LTC) profiles. Moreover, a comparison between the combustion behaviors of the two fuels in the IQT is not consistent with the comparison in the diesel engine, which suggests that the surrogate validation in a single-cylinder diesel engine should be part of the surrogate development methodology, particularly for low ignition quality fuels.
Loss Prediction in an Axial Compressor Cascade at Off-Design Incidences With Free Stream Disturbances Using Large Eddy Simulation
Authors: Leggett John , Priebe Stephan , Shabbir Aamir , Michelassi Vittorio , Sandberg Richard , Richardson Edward
Published: July 2018

Axial compressors may be operated under off-design incidences due to variable operating conditions. Therefore, a successful design requires accurate performance and stability limits predictions under a wide operating range. Designers generally rely both on correlations and on Reynolds-averaged Navier–Stokes (RANS), the accuracy of the latter often being questioned. The present study investigates profile losses in an axial compressor linear cascade using both RANS and wall-resolved large eddy simulation (LES), and compares with measurements. The analysis concentrates on “loss buckets,” local separation bubbles and boundary layer transition with high levels of free stream turbulence, as encountered in real compressor environment without and with periodic incoming wakes. The work extends the previous research with the intention of furthering our understanding of prediction tools and improving our quantification of the physical processes involved in loss generation. The results show that while RANS predicts overall profile losses with good accuracy, the relative importance of the different loss mechanisms does not match with LES, especially at off-design conditions. This implies that a RANS-based optimization of a compressor profile under a wide incidence range may require a thorough LES verification at off-design incidence.
Simulation of Coarse Droplet and Liquid Column Formed around Nozzle Outlets Due to Valve Wobble of a Gasoline Direct Injection Injector
Authors: Ishii Eiji , Yasukawa Yoshihito , Yoshimura Kazuki , Ogura Kiyotaka
Published: July 2018

The generation of particulate matter (PM) is one problem with gasoline direct-injection engines. PM is generated in high-density regions of fuel. Uniform air/fuel mixtures and short fuel-spray durations with multiple injections are effective in enabling the valves of fuel injectors not to wobble and dribble. We previously studied what effects the opening and closing of valves had on fuel spray behavior and found that valve motions in the opening and closing directions affected spray behavior and generated coarse droplets during the end-of-injection. We focused on the effects of valve wobbling on fuel spray behavior in this study, especially on the behavior during the end-of-injection. The effects of wobbling on fuel spray with full valve strokes were first studied, and we found that simulated spray behaviors agreed well with the measured ones. We also studied the effects on fuel dribble during end-of-injection. When a valve wobbled from left to right, the fuel dribble decreased in comparison with a case without wobbling. When a valve wobbled from the front to the rear, however, fuel dribble increased. Surface tension significantly affected fuel dribble, especially in forming low-speed liquid columns and coarse droplets. Fuel dribble was simulated while changing the wetting angle on walls from 60 to 5 deg. We found that the appearance of coarse droplets in sprays decreased during the end-of-injection by changing the wetting angles from 60 to 5 deg.
Use of the Glycerin By-Product From Biodiesel Production for Power Generation
Authors: Pickett Derek , Depcik Christopher , Stagg-Williams Susan
Published: July 2018

Climate change is driving the world to investigate alternative sources of fuel. In order to address any potential economic shortfalls to biodiesel, one can look to its by-product, glycerin, as a potential revenue source. At the University of Kansas, a novel system converts glycerin over a nickel–alumina catalyst into a hydrogen-rich gas (syngas) that is sent to an engine-generator system in one continuous flow process. This effort describes the hardware employed in this system, and demonstrates the production of power from the reforming of glycerin. Comparison of the peak combustion pressure and combustion timing produced between the syngas generated from glycerin and propane combustion shows virtually no performance differences between the two fuels. However, emissions vary significantly due to a variance in air-to-fuel ratios between the two fuels that will require a re-optimization when running glycerin. This system has the potential to reduce power requirements at biodiesel production facilities by utilizing glycerin on-site in a low-cost manner.
Optimization of the Efficiency of Stall Control Using Air Injection for Centrifugal Compressors—Additional Findings
Authors: Halawa Taher
Published: July 2018

This study presents additional important findings to the results of the research paper; “Optimization of the efficiency of stall control using air injection for centrifugal compressors” published in the Journal of Engineering for Gas Turbines and Power in 2015 (Halawa, T., Gadala, M. S., Alqaradawi, M., and Badr, O., 2015, “Optimization of the Efficiency of Stall Control Using Air Injection for Centrifugal Compressors,” ASME J. Eng. Gas Turbines Power, 137(7), p. 072604). The aim of this study is to make a fine determination of the injection angle, which provides the best stable condition when the compressor operates close to stall condition. A relatively narrower range of injection angles with smaller intervals was selected comparing to the results of the referred published paper, which clarified that the best injection angle is 30 deg. External air was injected close to the diffuser entrance at the shroud surface. Injection was applied with mass flow rate equals 1.5% of the design compressor inlet mass flow rate with injection angles ranged from 16 deg to 34 deg measured from the tangential direction at the vaneless region. It was found that both of injection angles of 28 deg and 30 deg achieved the best results in terms of compressor stabilization but each one of them has a specific advantage comparing to the other one. Using injection angle of 28 deg provided the lowest kinetic energy losses while the best orientation of the fluid through diffuser resulted when using an injection angle of 30 deg.
Correlation Between Pressure Recovery of Highly Loaded Annular Diffusers and Integral Stage Design Parameters1
Authors: Mimic Dajan , Drechsel Bastian , Herbst Florian
Published: July 2018

Exhaust diffusers significantly enhance the available power output and efficiency of gas and steam turbines by allowing lower turbine exit pressures. The residual dynamic pressure of the turbine outflow is converted into static pressure, which is referred to as pressure recovery. Since total pressure losses and construction costs increase drastically with diffuser length, it is strongly preferred to design shorter diffusers with steeper opening angles. However, these designs are more susceptible to boundary layer separation. In this paper, the stabilizing properties of tip leakage vortices generated in the last rotor row and their effect on the boundary layer characteristics are examined. Based on analytical considerations, for the first time, a correlation between the pressure recovery of the diffuser and the integral rotor parameters of the last stage, namely, the loading coefficient, flow coefficient, and reduced frequency, is established. Experimental data and scale-resolving simulations, carried out with the shear stress transport scale-adaptive simulation (SST-SAS) method, both show excellent agreement with the correlation. Blade tip vortex strength predominantly depends on the amount of work exchanged between fluid and rotor, which in turn is described by the nondimensional loading coefficient. The flow coefficient influences mainly the orientation of the vortex, which affects the interaction between vortex and boundary layer. The induced velocity field accelerates the boundary layer, essentially reducing the thickness of the separated layer or even preventing separation locally.
Preliminary Design Method for Dense-Gas Supersonic Axial Turbine Stages
Authors: Bufi Elio A. , Cinnella Paola
Published: July 2018

A fast preliminary design methodology for supersonic organic Rankine cycle (ORC) stator and rotor axial turbine blades with low degree of reaction is presented. First, the stator and rotor blade mean-line profiles are designed by using the two-dimensional (2D) method of characteristics (MOC), extended to gases governed by general equations of state (EOS). We focus more specifically on working fluids with medium to high molecular complexity, operating at thermodynamic conditions such that the fundamental derivative of gas dynamics Γ is lower than one in a significant portion of the flow field. For rotor blades, MOC is combined with a free-vortex method to achieve a smooth deflection of the supersonic incoming flow. A numerical approach is developed for solving the unique incidence problem in the case of gases governed by general EOS. Both stator and rotor blade geometries designed according to the inviscid MOC model are subsequently corrected to account for the development of viscous boundary layers by solving the compressible integral boundary layer equations extended to dense gases. The resulting blade designs are assessed by means of computational fluid dynamics (CFD) simulations based on a high-order finite volume solver equipped with advanced thermodynamic and transport-property models. Properly accounting for dense gas and viscous effects at an early design stage is found to improve the expected performance of ORC turbine rows significantly and delivers valuable baseline profiles for any further optimization.
Dynamic Relaxation Using Continuous Kinetic Damping—Part I: Basic Algorithm
Authors: Jung Samuel , Kim Tae-Yun , Yoo Wan-Suk
Published: July 2018

Dynamic relaxation (DR) is the most widely used approach for static equilibrium analyses. Specifically, DR compels dynamic systems to converge to a static equilibrium through the addition of fictitious damping. DR methods are classified by the method in which fictitious damping is applied. Conventional DR methods use a fictitious mass matrix to increase the fictitious damping while maintaining numerical stability. There are many calculation methods for the fictitious mass matrix; however, it is difficult to select the appropriate method. In addition, these methods require a stiffness matrix of a model, which makes it difficult to apply nonlinear models. To resolve these problems, a new DR method that uses continuous kinetic damping (CKDR) is proposed in this study. The proposed method does not require the fictitious mass matrix and any tuning coefficients, and it possesses a second-order convergence rate. The aforementioned advantages are unique and significant when compared to those of conventional methods. The stability and convergence rate were analyzed by using an eigenvalue analysis and demonstrated by simulating nonlinear models of a pendulum and cable. Simple but representative models were used to clearly demonstrate the features of the proposed DR method and to enable the reproducibility of the verification results.
On
Coexistence of Fractional-Order Hidden
Attractors
Authors: Borah Manashita
Published: July 2018

This paper proposes new fractional-order (FO) models of seven nonequilibrium and stable equilibrium systems and investigates the existence of chaos and hyperchaos in them. It thereby challenges the conventional generation of chaos that involves starting the orbits from the vicinity of unstable manifold. This is followed by the discovery of coexisting hidden attractors in fractional dynamics. All the seven newly proposed fractional-order chaotic/hyperchaotic systems (FOCSs/FOHSs) ranging from minimum fractional dimension (nf) of 2.76 to 4.95, exhibit multiple hidden attractors, such as periodic orbits, stable foci, and strange attractors, often coexisting together. To the best of the our knowledge, this phenomenon of prevalence of FO coexisting hidden attractors in FOCSs is reported for the first time. These findings have significant practical relevance, because the attractors are discovered in real-life physical systems such as the FO homopolar disc dynamo, FO memristive system, FO model of the modulation instability in a dissipative medium, etc., as analyzed in this work. Numerical simulation results confirm the theoretical analyses and comply with the fact that multistability of hidden attractors does exist in the proposed FO models.
The Characteristics of Innovative, Mechanical Products—10 Years Later
Authors: Hölttä-Otto Katja , Otto Kevin , Song Chaoyang , Luo Jianxi , Li Timothy , Seepersad Carolyn C. , Seering Warren
Published: July 2018

Ten years prior to this paper, innovative mechanical products were analyzed and found to embody multiple innovation characteristics—an average of two more than competing products in the marketplace. At the time, it was not known whether these products would be successful over time and whether the number or type of innovation characteristics would be related with success. In this work, products from the previous study were categorized into well- and under-adopted products. Also, each product was categorized according to the type of firm that launched it: a new venture or an established firm. The innovative products enjoyed a success rate of 77% on average. The success was not dependent on the number or type of innovation characteristics embodied by the product. However, products developed in new ventures embody, on average, one more innovation characteristic and enjoy a slightly higher success rate than those launched by established firms.
Fundamental Machining Characteristics of Ultrasonic-Assisted Electrochemical Grinding of Ti–6Al–4V
Authors: Li Sisi , Wu Yongbo , Nomura Mitsuyoshi , Fujii Tatsuya
Published: July 2018

The Ti–6Al–4V is a widely used alloy in the aerospace industry. In order to improve the grindability of Ti–6Al–4V, a hybrid material removal process is proposed in this study. This process is a combination of ultrasonic assisted grinding (UAG) and electrochemical grinding (ECG), hereafter called ultrasonic assisted electrochemical grinding (UAECG). For confirming the feasibility of the proposed technique, an experimental setup was constructed and the fundamental machining characteristics of UAECG in the grinding of Ti–6Al–4V were experimentally investigated. The results obtained from the investigation can be summarized as follows: (1) the normal and tangential forces in UAECG were decreased approximately 57% and 56%, respectively, comparing with conventional grinding (CG). (2) The work-surface roughness Ra both in ECG and UAECG was negative correlation to the electrolytic voltage, UI, and the surface damage; (3) the wheel radius wear in UAECG was considerably smaller than that in ECG when UI < 10 V. The chip adhesion and the grain fracture mainly affected the working lives of the wheels in ECG and UAECG, whereas the wheel wear in CG was predominantly attributed to the grain drop out; (4) a titanium dioxide (TiO2) layer, which had a 78 nm thickness was achieved on the work surface in the condition of UI = 20 V, leading that the Vickers microhardness of work surface in ultrasonic assisted electrochemical was lower than that in CG by 15%.
Optimization Design of a Walkable Fixture Mechanism
Authors: Wan Xiao-Jin , Zhang Hanjie
Published: July 2018

In this paper, a novel fixture mechanism with combining a mobility of the legged robot and advantages of parallel mechanism is designed to hold the different size and shape, large-scale workpiece. The proposed mobile fixture mechanism holds the workpiece as a parallel manipulator while it walks as a legged robot. This kind of robotized fixtures can possess high self-configurable ability to accommodate a wider variety of products. In order to obtain the best kinematic dexterity and accuracy characteristics, comprehensive performance optimization is performed by non-dominated-genetic algorithm (NSGA-II). In the optimization procedure, a conventional kinematic transformation matrix (Jacobian matrix) and error propagation matrix are obtained through derivation and differential motion operations. The singular values and condition number based on velocity Jacobians and error amplification factors based on error propagation matrix are derived; in addition, relative pose error range of end effector is also derived. On the basis of the above measure indices, three kinds of nonlinear optimization problems are defined to obtain the optimal architecture parameters for better kinematic accuracy and dexterity in workspace. Comparison analyses of the optimized results are performed.
Multi-Input–Multi-Output Control of a Utility-Scale, Shaftless Energy Storage Flywheel With a Five-Degrees-of-Freedom Combination Magnetic Bearing
Authors: Li Xiaojun , Palazzolo Alan
Published: July 2018

The modeling and control of a recently developed utility-scale, shaftless, hubless, high strength steel energy storage flywheel system (SHFES) are presented. The novel flywheel is designed with an energy/power capability of 100 kWh/100 kW and has the potential of a doubled energy density when compared to conventional technologies. In addition, it includes a unique combination magnetic bearing (CAMB) capable of providing five-degrees-of-freedom (5DOF) magnetic levitation. Initial test results show that the CAMB, which weighs 544 kg, can provide a stable lift-up and levitation control for the 5543 kg flywheel. The object of this paper is to formulate and synthesize a detailed model as well as to design and simulate a closed-loop control system for the proposed flywheel system. To this end, the CAMB supporting structures are considered flexible and modeled by finite element modeling. The magnetic bearing is characterized experimentally by static and frequency-dependent coefficients, the latter of which are caused by eddy current effects and presents a challenge to the levitation control. Sensor-runout disturbances are also measured and included. System nonlinearities in power amplifiers and the controller are considered as well. Even though the flywheel has a large ratio of the primary-to-transversal moment of inertias, multi-input–multi-output (MIMO) feedback control demonstrates its effectiveness in canceling gyroscopic toques at the designed operational spinning speed. Various stages of proportional and derivative (PD) controllers, lead/lag compensators, and notch filters are implemented to suppress the high-frequency sensor disturbances, structural vibrations, and rotor imbalance effects.
A Generic Function for Automated Modeling and Feedforward Control of Planetary Gear Sets
Authors: Huang Jianfeng , Zhang Jianlong , Huang Wei , Yin Chengliang
Published: July 2018

This paper introduces a generic function for automated modeling and feedforward control of planetary gears (PGs). Given the information on configuration, namely, the internal connection relationship between each PG, location of external torques, location and locking state of each clutch, this function outputs a ready-to-use kinetic model. The derived model can then be converted into numeric form by substituting the symbols in the matrix with real values and used for simulation, analysis or controller design. Since the output of the function is in symbolic form, it provides the theoretically most accurate results. Furthermore, compared to other kinds of automated modeling techniques for PG, the proposed function is: (a) more “straightforward” in a sense that it relies solely on direct matrix formulation and no other methods such as system identification are needed and therefore can be implemented in a single environment such as matlab; (b) more “generic” since it is capable of deriving both full-degrees-of-freedom (DOF) and reduced-DOF models for virtually any configuration regardless of the number, connection, and location of input/output shafts or clutches. By exchanging certain variables in the list of unknowns and knowns, the function can also be used to facilitate the design of feedforward controllers.
A Simple and Fast Method for Calculating Properties Across a Condensation Shock
Authors: Babu V.
Published: July 2018

A simple procedure for calculating the pressure at the onset and termination of condensation shocks that occur in steam nozzles and steam turbine blade passages is presented. In addition, the location of the termination of the condensation shock with reference to the throat location is also predicted. The procedure is based entirely on thermodynamic and gas dynamic considerations, without using a model for droplet nucleation and growth and the nozzle profile. The only input required is the stagnation condition at the inlet to the nozzle. The procedure requires the solution of a system of algebraic equations which can be accomplished quite easily. Calculations have been carried out for several inlet stagnation conditions and the predictions are compared with the available experimental data. The agreement is seen to be reasonable considering the simplicity of the procedure.
Performance Analysis of a Solid Oxide Fuel Cell-Gasifier Integrated System in Co-Trigenerative Arrangement
Authors: Fragiacomo Petronilla , De Lorenzo Giuseppe , Corigliano Orlando
Published: July 2018

The use of renewable sources, such as woody biomass waste, for energy purposes helps to reduce the consumption of fossil fuels and therefore the production of associated pollutants and greenhouse gases. Solid oxide fuel cells (SOFCs) are devices that convert the chemical energy of a product gas produced by a gasifier of biomass waste, before being suitably purified, directly into electric energy, with conversion efficiency, which is higher than that of other conventional energy systems. Since they operate at high temperature, they make available also thermal energy, which can be used for co- and tri-generation purposes. This paper aims at studying the arrangement of a complete trigenerative energy system composed of a gasifier of waste biomass; an energy unit represented by a SOFC system; an absorption cooling section for the conversion into cooling energy of the waste heat. In its layout, the SOFC energy unit considers the anode off gas recirculation, a postcombustor to energize the exhaust stream, and a preheater for the fresh gases entering. The integrated plant is completed by means of batteries for electric energy storage and hot water tanks and thermal energy storage. An ad hoc developed numerical modeling is used to choose the working point of the SOFC energy system at which to operate it and to analyze its energy behavior under syngas feeding. Two biomass-derived syngas are analyzed: one from woody biomass and one from urban solid waste gasification. Hence, the entire integrated plant is analyzed for both feeding types. The energy analysis of the integrated SOFC/gasifier is carried out based on a fixed quantity of biomass waste to be processed in an existing gasifier. Then, the design of the SOFC energy section is carried out. The integrated plant is then applied to a case study to satisfy the energy needs of a user of the tertiary sector. Therefore, based on this, the procedure continues with sizing the cooling section for the cooling power delivery in the warm season, the batteries to store the electric energy to be delivered, and the hot water tanks for the thermal energy storage to be delivered as heat when necessary or to feed the absorption cooling plant. The integrated SOFC/Gasifier defined can be considered as a high-efficiency tri-generator capable of accomplishing an energy valorization of high quality waste biomass.
A Comparative Study of Syngas Production From Two Types of Biomass Feedstocks With Waste Heat Recovery
Authors: Islam Shahid , Dincer Ibrahim
Published: July 2018

This paper deals with an integrated biomass system developed for syngas production with waste heat recovery option and analyzes this system thermodynamically using both energy and exergy approaches. Also, an aspenplus simulation model is developed to demonstrate comparative gasification analyses of wood (Birch) and olive waste using Gibbs reactor for syngas production. Gibbs free energy minimization technique is applied to calculate the equilibrium of chemical reactions. In this newly developed model, the heat of the product syngas and the waste heat from the flue gas are recovered through a unique integration of four heat exchangers to produce steam for the gasification process. The sensitivity analyses are performed to observe the variations in the concentration of the methane, carbon monoxide and carbon dioxide in syngas against various operating conditions. Furthermore, the performance of gasifier is indicated through cold gas energy efficiency (CGE) and cold gas exergy efficiency (CGEX). The overall energy and exergy analyses are also conducted, and the comparisons reveal that the biomass composed of olive waste yields high magnitude of overall and cold gas energy efficiencies, whereas wood (Birch) yields high magnitude of overall and cold gas exergy efficiencies. Moreover, the energy of the product syngas is recovered through an expander which enhances energy and exergy efficiencies of the overall system. The present results show that the CGE, CGEX, and overall energetic and exergetic efficiencies follow a decreasing trend with the increase in combustion temperature. The proposed system has superior and unique features as compared to conventional biomass gasification systems.