bluuebunny/crossref_metadata_2025 huggingface dataset:
Applicability of Miniature Compact Tension Specimens for Fracture Toughness Evaluation of Highly Neutron Irradiated Reactor Pressure Vessel Steels
Authors: Ha Yoosung , Tobita Tohru , Ohtsu Takuyo , Takamizawa Hisashi , Nishiyama Yutaka
Published: July 2018

The applicability of miniature compact tension (Mini-C(T)) specimens to fracture toughness evaluation of neutron-irradiated reactor pressure vessel (RPV) steels was investigated. Three types of RPV steels neutron-irradiated to a high-fluence region were prepared and manufactured as Mini-C(T) specimens according to Japan Electric Association Code (JEAC) 4216-2015. Through careful selection of the test temperature by considering previously obtained mechanical properties data, valid fracture toughness, and reference temperature (To) was obtained with a relatively small number of specimens. Comparing the fracture toughness and To values determined using other larger specimens with those determined using the Mini-C(T) specimens, To values of both unirradiated and irradiated Mini-C(T) specimens were found to be the acceptable margin of error. The scatter of 1T-equivalent fracture toughness values of both unirradiated and irradiated materials obtained using Mini-C(T) specimens did not differ significantly from the values obtained using larger specimens. The correlation between the Charpy 41 J transition temperature (T41J) and the To values agreed very well with that of the data in the literature, regardless of specimen size and fracture toughness of the materials before irradiation. Based on these findings, it was concluded that Mini-C(T) specimens can be applied to fracture toughness evaluation of neutron-irradiated materials without significant specimen size dependence.
Dynamic
Heat Transfer Study of a Triangular-Shaped Latent Heat Storage Unit for the Attic Space of a
Domestic Dwelling
Authors: Tabassum Tonny , Hasan Mainul , Begum Latifa
Published: July 2018

A two-dimensional (2D) numerical study is carried out to investigate the thermal performance of an impure phase-change material (PCM) in an equilateral triangular-shaped double pipe heat exchanger. To tackle the irregular boundaries, a nonorthogonal body-fitted coordinate (BFC) transformation technique is employed. The nondimensional transformed curvilinear conservation equations for mass, momentum, and energy are written in terms of physical variables and they are solved using a control-volume based finite difference method on a staggered grid arrangement. The developed model is then used to study the effects of the inner tube wall temperature, the initial temperature of the solid PCM, and the shape, as well as the position of the inner tube in the annulus on the melting characteristics, and cumulatively stored energy. Various quantities such as average Nusselt numbers over the inner tube surface, the total and complete melt fractions, and the latent and total stored energies all as a function of the melting time are reported. A correlation for the average Nusselt number on the inner tube wall is also provided. The numerical results show that the shape and the placement of the inner tube are crucial for the efficient design of a latent heat thermal energy storage (LHTES) system. The storage of energy is greatly influenced by the change of the inner tube wall temperature compared to the change of initial solid PCM temperature.
A New Spin on Small-Scale Combustor Geometry
Authors: Bohan Brian T. , Polanka Marc D.
Published: July 2018

The ultra-compact combustor (UCC) is an innovative combustor system alternative to traditional turbine engine combustors with the potential for engine efficiency improvements with a reduced volume. Historically, the UCC cavity had been configured such that highly centrifugally loaded combustion took place in a recessed circumferential cavity positioned around the outside diameter (OD) of the engine. One of the obstacles with this design was that the combustion products had to migrate radially across the span of a vane while being pushed downstream by a central core flow. This configuration proved difficult to produce a uniform temperature distribution at the first turbine rotor. The present study has taken a different spin on the implementation of circumferential combustion. Namely, it aims to combine the combustion and space saving benefits of the highly centrifugally loaded combustion of the UCC in a new combustor orientation that places the combustor axially upstream of the turbine versus radially outboard. An iterative design approach was used to computationally analyze this new geometry configuration with the goal of fitting within the casing of a JetCat P90RXi. This investigation revealed techniques for implementation of this concept including small-scale combustor centrifugal air loading development, maintaining combustor circumferential swirl, combustion stability, and fuel distribution are reported. The final combustor configuration was manufactured and experimentally tested, validating the computational results. Furthermore, dramatic improvements in the uniformity of the turbine inlet temperature profiles are revealed over historical UCC concepts.
Turbulent Spray Combustion Modeling Using Various Kinetic Solvers and Turbulence Models
Authors: Piehl J. A. , Samimi Abianeh O. , Goyal A. , Bravo L.
Published: July 2018

Turbulent spray combustion of n-dodecane was modeled at relevant engine conditions using two combustion models (direct integration of chemistry (DIC) and flamelet generated manifolds (FGM)) and multifidelity turbulence models (dynamic structure large eddy simulation (LES) and renormalization group (RNG) Reynolds-averaged Naiver–Stokes (RANS)). The main objective of this work is to study the effect of various combustion and turbulence models on spray behavior and quantify these effects. To reach these objectives, a recently developed kinetic mechanism and well-established spray models were utilized for the three-dimensional turbulent spray simulation at various combustion chamber initial gas temperature and pressure conditions. Fine mesh with a size of 31 μm was utilized to resolve small eddies in the periphery of the spray. In addition, a new methodology for mesh generation was proposed and investigated to simulate the measured data fluctuation in the CFD domain. The pressure-based ignition delay, flame lift-off length (LOL), species concentrations, spray, and jet penetrations were modeled and compared with measured data. Differences were observed between various combustion and turbulence models in predicting the spray characteristics. However, these differences are within the uncertainties, error, and variations of the measured data.
Bilateral Adaptive Control of Nonlinear Teleoperation Systems With Uncertain Dynamics and Dead-Zone
Authors: Liu Xia , Tavakoli Mahdi
Published: July 2018

Dead-zone is one of the most common hard nonlinearities ubiquitous in master–slave teleoperation systems, particularly in the slave robot joints. However, adaptive control techniques applied in teleoperation systems usually deal with dynamic uncertainty but ignore the presence of dead-zone. Dead-zone has the potential to remarkably deteriorate the transparency of a teleoperation system in the sense of position and force tracking performance or even destabilizing the system if not compensated for in the control scheme. In this paper, an adaptive bilateral control scheme is proposed for nonlinear teleoperation systems in the presence of both uncertain dynamics and dead-zone. An adaptive controller is designed for the master robot with dynamic uncertainties and the other is developed for the slave robot with both dynamic uncertainties and unknown dead-zone. The two controllers are incorporated into the four-channel bilateral teleoperation control framework to achieve transparency. The transparency and stability of the closed-loop teleoperation system is studied via a Lyapunov function analysis. Comparisons with the conventional adaptive control which merely deal with dynamic uncertainties in the simulations demonstrate the validity of the proposed approach.
Effects of Exhaust Gas Recirculation Constituents on Methyl Decanoate Auto-Ignition: A Kinetic Study
Authors: Zhang Jiabo , Zhai Jiaqi , Ju Dehao , Huang Zhen , Han Dong
Published: July 2018

Biodiesel engines are found to have improved soot, hydrocarbon (HC), and carbon monoxide (CO) emissions, with modestly increased nitrogen oxides (NOx) emissions. Exhaust gas recirculation (EGR) could be used for the NOx emissions control, especially in the fuel-kinetics-dominated engine combustion concepts. A detailed chemical kinetic model of methyl decanoate (MD), a biodiesel surrogate fuel, was used here to simulate the two-stage auto-ignition process of biodiesel with EGR addition. The effects of EGR constituents, including carbon dioxide (CO2), water vapor (H2O), CO and H2, were identified in a constant-pressure ignition process and in a variable pressure, variable volume process. Firstly, numerical methods were used to isolate the dilution, thermal, and chemical effects of CO2 and H2O at a constant pressure. It was found that in the biodiesel auto-ignition processes, the dilution effects of CO2 and H2O always played the primary role. Their thermal and chemical effects mainly influenced the second-stage ignition, and the chemical effect of H2O was more significant than CO2. The triple effects of CO and H2 were also analyzed at the same temperature and pressure conditions. Additionally, the sensitivity analysis and reaction pathway analysis were conducted to elucidate the chemical effects of CO and H2 on the ignition processes at different temperatures. Finally, based on a variable pressure, variable volume model simulating the engine compression stroke, the effects of CO2, H2O, CO and H2 addition under the engine operational conditions were studied and compared to those under the constant pressure conditions.
Extension of Fuel Flexibility by Combining Intelligent Control Methods for Siemens SGT-400 Dry Low Emission Combustion System
Authors: Liu Kexin , Hubbard Phill , Sadasivuni Suresh , Bulat Ghenadie
Published: July 2018

Extension of gas fuel flexibility of a current production SGT-400 industrial gas turbine combustor system is reported in this paper. A SGT-400 engine with hybrid combustion system configuration to meet a customer's specific requirements was string tested. This engine was tested with the gas turbine package driver unit and the gas compressor-driven unit to operate on and switch between three different fuels with temperature-corrected Wobbe index (TCWI) varying between 45 MJ/m3, 38 MJ/m3, and 30 MJ/m3. The alteration of fuel heating value was achieved by injection or withdrawal of N2 into or from the fuel system. The results show that the engine can maintain stable operation on and switching between these three different fuels with fast changeover rate of the heating value greater than 10% per minute without shutdown or change in load condition. High-pressure rig tests were carried out to demonstrate the capabilities of the combustion system at engine operating conditions across a wide range of ambient conditions. Variations of the fuel heating value, with Wobbe index (WI) of 30 MJ/Sm3, 33 MJ/Sm3, 35 MJ/Sm3, and 45 MJ/Sm3 (natural gas, NG) at standard conditions, were achieved by blending NG with CO2 as diluent. Emissions, combustion dynamics, fuel pressure, and flashback monitoring via measurement of burner metal temperatures, were the main parameters used to evaluate the impact of fuel flexibility on combustor performance. Test results show that NOx emissions decrease as the fuel heating value is reduced. Also note that a decreasing fuel heating value leads to a requirement to increase the fuel supply pressure. Effect of fuel heating value on combustion was investigated, and the reduction in adiabatic flame temperature and laminar flame speed was observed for lower heating value fuels. The successful development program has increased the capability of the SGT-400 standard production dry low emissions (DLE) burner configuration to operate with a range of fuels covering a WI corrected to the normal conditions from 30 MJ/N·m3 to 49 MJ/N·m3. The tests results obtained on the Siemens SGT-400 combustion system provide significant experience for industrial gas turbine burner design for fuel flexibility.
Centrifugal Compressor Design for Near-Critical Point Applications
Authors: Ameli Alireza , Afzalifar Ali , Turunen-Saaresti Teemu , Backman Jari
Published: July 2018

The supercritical CO2 (sCO2) Brayton cycle has been attracting much attention to produce the electricity power, chiefly due to its higher thermal efficiency with the relatively lower temperature at the turbine inlet compared to other common energy conversion cycles. Centrifugal compressor operating conditions in the supercritical Brayton cycle are commonly set in vicinity of the critical point, owing to smaller compressibility factor and eventually lower compressor work. This paper investigates and compares different centrifugal compressor design methodologies in close proximity to the critical point and suggests the most accurate design procedure based on the findings. An in-house mean-line design code, which is based on the individual enthalpy loss models, is compared to stage efficiency correlation design methods. Moreover, modifications are introduced to the skin friction loss calculation to establish an accurate one-dimensional design methodology. Moreover, compressor performance is compared to the experimental measurements.
A Pseudo-Static Model for Dynamic Analysis on Frequency Domain of Distributed Compliant Mechanisms
Authors: Ling Mingxiang , Howell Larry L. , Cao Junyi , Jiang Zhou
Published: July 2018

This paper presents a pseudo-static modeling methodology for dynamic analysis of distributed compliant mechanisms to provide accurate and efficient solutions. First, a dynamic stiffness matrix of the flexible beam is deduced, which has the same definition and a similar form as the traditional static compliance/stiffness matrix but is frequency dependent. Second, the pseudo-static modeling procedure for the dynamic analysis is implemented in a statics-similar way based on D'alembert's principle. Then, all the kinematic, static and dynamic performances of compliant mechanisms can be analyzed based on the pseudo-static model. The superiority of the proposed method is that when it is used for the dynamic modeling of compliant mechanisms, the traditional dynamic modeling procedures, such as calculation of the elastic and kinetic energies as well as using Lagrange's equation, are avoided and the dynamic modeling is converted to a statics-similar problem. Comparison of the proposed method with an elastic-beam-based model in previous literature and finite element analysis for an exemplary XY precision positioning stage reveals its high accuracy and easy operation.
Ship Vertical Loads From Using an Adaptive Mesh Pressure Integration Technique for Froude–Krylov Forces Calculation
Authors: Rodrigues José Miguel , Guedes Soares C.
Published: July 2018

Dynamic vertical bending moments are determined for a military vessel hull in still water and under head waves, with a weakly nonlinear method. The domain for hydrostatic and undisturbed pressures integration is time-variant and generated with a quad-tree adaptive mesh algorithm, on which exact formulations for pressure on polygonal elements are used. Linear radiation and diffraction pressures, on another mesh superimposed with the aforementioned one, are calculated with a frequency domain code. Results are compared with published experimental ones for small and large wave heights.
Direct Assessment of the Acoustic Scattering Matrix of a Turbulent Swirl Combustor by Combining System Identification, Large Eddy Simulation and Analytical Approaches
Authors: Merk Malte , Silva Camilo , Polifke Wolfgang , Gaudron Renaud , Gatti Marco , Mirat Clément , Schuller Thierry
Published: July 2018

This study assesses and compares two alternative approaches to determine the acoustic scattering matrix of a premixed turbulent swirl combustor: (1) The acoustic scattering matrix coefficients are obtained directly from a compressible large eddy simulation (LES). Specifically, the incoming and outgoing characteristic waves f and g extracted from the LES are used to determine the respective transmission and reflection coefficients via System Identification (SI) techniques. (2) The flame transfer function (FTF) is identified from LES time series data of upstream velocity and heat release rate. The transfer matrix of the reactive combustor is then derived by combining the FTF with the Rankine–Hugoniot (RH) relations across a compact heat source and a transfer matrix of the cold combustor, which is deduced from a linear network model. Linear algebraic transformation of the transfer matrix consequently yields the combustor scattering matrix. In a cross-comparison study that includes comprehensive experimental data, it is shown that both approaches successfully predict the scattering matrix of the reactive turbulent swirl combustor.
Technology-Based Recontouring of Blade Integrated Disks After Weld Repair
Authors: Denkena Berend , Mücke Arne , Schumacher Tim , Langen Demian , Hassel Thomas
Published: July 2018

The widespread adoption of blade integrated disks (blisks) made of titanium demands tailored regeneration processes to increase sustainability and economic efficiency. High standards regarding geometrical accuracy and functional properties as well as the unique characteristics of each type of damage complicate the repair. Thus, flexible and well-designed processes are necessary. Typically, material deposit is followed by a milling or grinding process to restore the original shape. Here, the individual repair processes not only have to be controlled but also their interaction. For example, depending on the resulting microstructure of the welded seam, the recontouring process needs to be adapted to minimize tool wear as well as shape deviations of the complex blade geometries. In this paper, the process chain for a patch repair is examined, consisting of a tungsten inert gas (TIG) welding process followed by five-axis ball nose end milling. Conventional TIG as well as a modified TIG process producing a finer grain structure and enhanced mechanical properties of deposited material was investigated. Grain refinement was achieved by SiC particles added to the weld pool. Based on the characteristics of the fusion material and static stiffness of the component, a methodology is introduced to minimize shape deviation induced by the subsequent milling process. Special attention is given to tool orientation, which has a significant impact on the kinematics and resulting process forces during milling. An electromagnetic guided machine tool is used for compensation of workpiece deflection.
Multivariable Extremum Seeking for Joint-Space Trajectory Optimization of a High-Degrees-of-Freedom Robot
Authors: Bagheri Mostafa , Krstić Miroslav , Naseradinmousavi Peiman
Published: July 2018

In this paper, a novel analytical coupled trajectory optimization of a seven degrees-of-freedom (7DOF) Baxter manipulator utilizing extremum seeking (ES) approach is presented. The robotic manipulators are used in network-based industrial units, and even homes, by expending a significant lumped amount of energy, and therefore, optimal trajectories need to be generated to address efficiency issues. These robots are typically operated for thousands of cycles resulting in a considerable cost of operation. First, coupled dynamic equations are derived using the Lagrangian method and experimentally validated to examine the accuracy of the model. Then, global design sensitivity analysis is performed to investigate the effects of changes of optimization variables on the cost function leading to select the most effective ones. We examine a discrete-time multivariable gradient-based ES scheme enforcing operational time and torque saturation constraints in order to minimize the lumped amount of energy consumed in a path given; therefore, time-energy optimization would not be the immediate focus of this research effort. The results are compared with those of a global heuristic genetic algorithm (GA) to discuss the locality/globality of optimal solutions. Finally, the optimal trajectory is experimentally implemented to be thoroughly compared with the inefficient one. The results reveal that the proposed scheme yields the minimum energy consumption in addition to overcoming the robot's jerky motion observed in an inefficient path.
Pool Boiling of Low-Global Warming Potential Replacements for R134a on a Reentrant Cavity Surface
Authors: Kedzierski M. A. , Lin L. , Kang D.
Published: July 2018

This paper quantifies the pool boiling performance of R134a, R1234yf, R513A, and R450A on a flattened, horizontal reentrant cavity surface. The study showed that the boiling performance of R134a on the Turbo-ESP exceeded that of the replacement refrigerants for heat fluxes greater than 20 kW m−2. On average, the heat flux for R1234yf and R513A was 16% and 19% less than that for R134a, respectively, for R134a heat fluxes between 20 kW m−2 and 110 kW m−2. The heat flux for R450A was on average 57% less than that of R134a for heat fluxes between 30 kW m−2 and 110 kW m−2. A model was developed to predict both single-component and multicomponent pool boiling of the test refrigerants on the Turbo-ESP surface. The model accounts for viscosity effects on bubble population and uses the Fritz equation to account for increased vapor production with increasing superheat. Both loss of available superheat and mass transfer resistance effects were modeled for the refrigerant mixtures. For most heat fluxes, the model predicted the measured superheat to within ±0.31 K.
Modeling Creep Deformation and Damage Behavior of Tempered Martensitic Steel in the Framework of Additive Creep Rate Formulation
Authors: Christopher J. , Choudhary B. K.
Published: July 2018

Additive creep rate model has been developed to predict creep strain-time behavior of materials important to engineering creep design of components for high temperature applications. The model has two additive formulations: the first one is related to sine hyperbolic rate equation describing primary and secondary creep deformation based on the evolution of internal stress with strain/time, and the second defines the tertiary creep rate as a function of tertiary creep strain. In order to describe creep data accurately, tertiary creep rate relation based on MPC-Omega methodology has been appropriately modified. The applicability of the model has been demonstrated for tempered martensitic plain 9Cr-1Mo steel for different applied stresses at 873 K. Based on the observations, a power law relationship between internal stress and applied stress has been established for the steel. Further, a higher creep damage accumulation with increasing life fraction has been observed at low stresses than those obtained at high stresses.
Micro Copper Pillar Interconnection Using Thermosonic Flip Chip Bonding
Authors: Wu Bo , Zhang Shuanghai , Wang Fuliang , Chen Zhuo
Published: July 2018

The incorporation of a micro copper pillar is considered as the major interconnection method in three-dimensional (3D) integrated circuit (IC) intergradation under high-density I/O conditions. To achieve low-temperature bonding, this study investigated the thermosonic flip chip bonding of a copper pillar with a tin cap. The effect of bonding force on bonding strength was studied, and an average bonding strength 2500 g (approximately 84.8 MPa) was obtained in 2 s, at an optimized bonding force of 0.11 N per 40 μm pillar bump, and substrate temperature of 200 °C. Additionally, the effect of the bonding force on bonding interface microstructure and intermetallic compounds (IMCs) was also investigated. Tin whiskers were also observed at the bonding interface at low bonding forces.
A Contribution for the Assessment of Discretization Error Estimators Based on Grid Refinement Studies
Authors: Eça L. , Vaz G. , Hoekstra M.
Published: July 2018

This paper presents grid refinement studies for statistically steady, two-dimensional (2D) flows of an incompressible fluid: a flat plate at Reynolds numbers equal to 107, 108, and 109 and the NACA 0012 airfoil at angles of attack of 0, 4, and 10 deg with Re = 6 × 106. Results are based on the numerical solution of the Reynolds-averaged Navier–Stokes (RANS) equations supplemented by one of three eddy-viscosity turbulence models of choice: the one-equation model of Spalart and Allmaras and the two-equation models k – ω SST and k−kL. Grid refinement studies are performed in sets of geometrically similar structured grids, permitting an unambiguous definition of the typical cell size, using double precision and an iterative convergence criterion that guarantees a numerical error dominated by the discretization error. For each case, different grid sets with the same number of cells but different near-wall spacings are used to generate a data set that allows more than one estimation of the numerical uncertainty for similar grid densities. The selected flow quantities include functional (integral), surface, and local flow quantities, namely, drag/resistance and lift coefficients; skin friction and pressure coefficients at the wall; and mean velocity components and eddy viscosity at specified locations in the boundary-layer region. An extra set of grids significantly more refined than those proposed for the estimation of the numerical uncertainty is generated for each test case. Using power law extrapolations, these extra solutions are used to obtain an approximation of the exact solution that allows the assessment of the performance of the numerical uncertainty estimations performed for the basis data set. However, it must be stated that with grids up to 2.5 (plate) and 8.46 (airfoil) million cells in two dimensions, the asymptotic range is not attained for many of the selected flow quantities. All this data is available online to the community.
Flow Inhomogeneities in a Realistic Aeronautical Gas-Turbine Combustor: Formation, Evolution, and Indirect Noise
Authors: Giusti Andrea , Magri Luca , Zedda Marco
Published: July 2018

Indirect noise generated by the acceleration of combustion inhomogeneities is an important aspect in the design of aero-engines because of its impact on the overall noise emitted by an aircraft and the possible contribution to combustion instabilities. In this study, a realistic rich-quench-lean (RQL) combustor is numerically investigated, with the objective of quantitatively analyzing the formation and evolution of flow inhomogeneities and determining the level of indirect combustion noise in the nozzle guide vane (NGV). Both entropy and compositional noise are calculated in this work. A high-fidelity numerical simulation of the combustion chamber, based on the large-eddy simulation (LES) approach with the conditional moment closure (CMC) combustion model, is performed. The contributions of the different air streams to the formation of flow inhomogeneities are pinned down and separated with seven dedicated passive scalars. LES-CMC results are then used to determine the acoustic sources to feed an NGV aeroacoustic model, which outputs the noise generated by entropy and compositional inhomogeneities. Results show that non-negligible fluctuations of temperature and composition reach the combustor's exit. Combustion inhomogeneities originate both from finite-rate chemistry effects and incomplete mixing. In particular, the role of mixing with dilution and liner air flows on the level of combustion inhomogeneities at the combustor's exit is highlighted. The species that most contribute to indirect noise are identified and the transfer functions of a realistic NGV are computed. The noise level indicates that indirect noise generated by temperature fluctuations is larger than the indirect noise generated by compositional inhomogeneities, although the latter is not negligible and is expected to become louder in supersonic nozzles. It is also shown that relatively small fluctuations of the local flame structure can lead to significant variations of the nozzle transfer function, whose gain increases with the Mach number. This highlights the necessity of an on-line solution of the local flame structure, which is performed in this paper by CMC, for an accurate prediction of the level of compositional noise. This study opens new possibilities for the identification, separation, and calculation of the sources of indirect combustion noise in realistic aeronautical gas turbines.
Automated Design Optimization of a Small-Scale High-Swirl Cavity-Stabilized Combustor
Authors: Briones Alejandro M. , Burrus David L. , Sykes Joshua P. , Rankin Brent A. , Caswell Andrew W.
Published: July 2018

A numerical optimization study is performed on a small-scale high-swirl cavity-stabilized combustor. A parametric geometry is created in cad software that is coupled with meshing software. The latter automatically transfers meshes and boundary conditions to the solver, which is coupled with a postprocessing tool. Steady, incompressible three-dimensional simulations are performed using a multiphase Realizable k-ε Reynolds-averaged Navier-Stokes (RANS) approach with a nonadiabatic flamelet progress variable (FPV) model. There are nine geometrical input parameters. There are five output parameters, viz., pattern factor (PF), RMS of the profile factor deviation, averaged exit temperature, averaged exit swirl angle, and total pressure loss. An iterative design of experiments (DOE) with a recursive Latin hypercube sampling (LHS) is performed to filter the most important input parameters. The five major input parameters are found with Spearman's order-rank correlation and R2 coefficient of determination. The five input parameters are used for the adaptive multiple objective (AMO) optimization. This provided a candidate design point with the lowest weighted objective function, which was verified through computational fluid dynamic (CFD) simulation. The combined filtering and optimization procedures improve the baseline design point in terms of pattern and profile factor. The former halved from that of the baseline design point, whereas the latter turned from an outer peak to a center peak profile, closely mimicking an ideal profile. The exit swirl angle favorably increased 25%. The averaged exit temperature and the total pressure losses remained nearly unchanged from the baseline design point.
Understanding of Nafion Membrane Additive Behaviors in Proton Exchange Membrane Fuel Cell Conditioning
Authors: Zhao Nana , Xie Zhong , Shi Zhiqing
Published: July 2018

Durability and cost are the two major factors limiting the large-scale implementation of fuel cell technology for use in commercial, residential, or transportation applications. The conditioning cost is usually negligible for making proton exchange membrane fuel cells (PEMFCs) at R&D or demo stage with several tens of stacks each year. However, with industry's focus shifting from component development to commercial high-volume manufacturing, the conditioning process requires significant additional capital investments and operating costs, thus becomes one of the bottlenecks for PEMFC manufacturing, particularly at a high production volume (>1000 stack/year). To understand the mechanisms behind PEMFC conditioning, and to potentially reduce conditioning time or even to eliminate the conditioning process, the conditioning behaviors of commercial Nafion™ XL100 and Nafion® NRE 211 membranes were studied. The potential effects of the membrane additive on fuel cell conditioning were diagnosed using in situ electrochemical impedance spectroscopy (EIS). It was found that the membrane additive led to the significant variation of the charge transfer resistance in EIS during conditioning, which affected the conditioning behavior of the membrane electrode assembly (MEA).
Development of a New High-Strength Steel for Low Pressure Steam Turbine End-Stage Blades
Authors: Teuber Hannes , Barnikel Jochen , Dankert Michael , David Walter , Ghicov Andrei , Voss Simon
Published: July 2018

Influenced by the growing share of Renewable Energies, higher flexibility and increased efficiency of fossil power plants as well as improved cost efficiency in production of turbine components are evident market trends. Daily cycling in turbine operations leads to advanced requirements for robust design especially of rotating parts. Low pressure (LP) steam turbine end-stage blades with larger exhaust areas are one lever to increase the efficiency of the turbine by reduction of exhaust losses and also to realize cost-efficient single flow exhaust applications. Consequently, blade steels with improved mechanical properties are required. The results of the development of a new high-strength precipitation-hardening (PH) steel for LP end-stage blade application with significantly enhanced material properties are reported. The paper covers the testing strategy applied and information on crucial material parameters like improved low cycle and high cycle fatigue (HCF) behavior while keeping good stress corrosion cracking (SCC) resistance and corrosion fatigue (CF) properties. Furthermore, first manufacturing experiences and validation results from a full-scale component test rig are presented.
An Efficient Approach for the Frequency Analysis of Nonaxisymmetric Rotating Structures: Application to a Coupled Bladed Birotor System
Authors: Dumartineix Cécile , Chouvion Benjamin , Thouverez Fabrice , Parent Marie-Océane
Published: July 2018

The improvement of efficiency in the design of turbomachines requires a reliable prediction of the vibrating behavior of the whole structure. The simulation of blades vibrations is decisive and this is usually based on elaborated finite element model restricted to the bladed-disk. However, the blades dynamic behavior can be strongly affected by interactions with other parts of the engine. Global dynamic studies that consider these other parts are required but usually come with a high numerical cost. In the case of a birotor architecture, two coaxial rotors with different rotating speeds can be coupled with a bearing system. The mechanical coupling between the shafts generates energy exchange that alters the dynamic behavior of the blades. The equations of motion of the whole structure that take into account the coupling contain periodic time-dependent coefficients due to the difference of rotational speed between both rotors. Equations of this kind, with variable coefficients, are typically difficult to solve. This study presents a preprocessing method to guarantee the elimination of time-dependent coefficients in the birotor equations of motion. This method is tested with a simplified finite element model of two bladed-disks coupled with linear stiffnesses. We obtain accurate results when comparing frequency analysis of preprocessed equations with time-integration resolution of the initial set of equations. The developed methodology also offers a substantial time saving.
Numerical Study on NOx Reduction in Pulse Detonation Combustion by Using Steam Injection Decoupled From Detonation Development
Authors: Hanraths Niclas , Tolkmitt Fabian , Berndt Phillip , Djordjevic Neda
Published: July 2018

Recently, the focus has been laid on the characteristics of pollutant emissions from pulse detonation combustion (PDC). Initial studies indicate possibly high nitrogen oxides (NOx) emissions, so the assessment of potential primary reduction methods is advisable. The present work considers the following reduction methods: lean combustion, nitrogen and steam dilution, as well as flue gas recirculation. Since such changes in the combustion mixture reduce its reactivity and thus detonability, they can impair a reliable operation in technical systems. In order to explore the potential and limitations of each of these reduction methods, they are compared for mixtures featuring an identical characteristic detonation cell size at given initial conditions. Furthermore, building upon the use of steam dilution, a modified method to add steam to the combustible mixture is investigated. In order to avoid the strong reduction of mixture detonability by steam addition and ensure a robust detonation formation, steam is injected into the already developed detonation front. It was found that, for sufficiently even steam distribution, NOx reduction comparable to a premixed dilution could be achieved. This approach enables the realization of NOx reduction in PDC also for such conditions, for which premix dilution is not feasible. Therefore, combining the premix dilution with postshock injection offers a promising strategy to substantially reduce NOx emissions from PDC, while at the same time ensuring its reliable operation.
Audio-Based Tool Condition Monitoring in Milling of the Workpiece Material With the Hardness Variation Using Support Vector Machines and Convolutional Neural Networks
Authors: Kothuru Achyuth , Nooka Sai Prasad , Liu Rui
Published: July 2018

Machining industry has been evolving toward implementation of automation into the processes for higher productivity and efficiency. Although many studies have been conducted in the past to develop intelligent monitoring systems in various application scenarios of machining processes, most of them just focused on cutting tools without considering the influence of the nonuniform hardness of workpiece material. This study develops a compact, reliable, and cost-effective tool condition monitoring (TCM) system to detect the cutting tool wear in machining of the workpiece material with hardness variation. The generated audible sound signals during the machining process are analyzed by state-of-the-art artificial intelligent techniques, support vector machine (SVM) and convolutional neural network (CNN), to predict the tool wear and the hardness variation of the workpiece. A four-level classification model is developed for the system to detect the tool wear condition based on the width of the flank wear land and the hardness variation of the workpiece. This study also involves the comparative analysis between two employed artificial intelligent techniques to evaluate the performance of the model in prediction. The proposed TCM system has shown a high prediction accuracy in detecting the tool wear from the audible sound into the proposed multiclassification wear level in end milling of the nonuniform hardened workpiece.
Theory and Analytical Solutions to Coupled Processes of Transport and Deformation in Dual-Porosity Dual-Permeability Poro-Chemo-Electro-Elastic Media
Authors: Liu Chao , Mehrabian Amin , Abousleiman Younane N.
Published: July 2018

The linear theory of dual-porosity and dual-permeability poro-chemo-electro-elasticity is presented. The theory outlines the dual-continuum formulation of multiple coupled processes involving solid deformation, pore fluid flow, and electrically charged species transport, within and in between two coexisting porosity systems of a fluid-saturated, poro-elastic medium. The described formulation is used to derive the analytical solutions to the inclined wellbore problem and axisymmetric Mandel-Type problem of dual-porosity, dual-permeability poro-chemo-electro-elasticity. The effects of chemical and electrical potentials on the distributions of stress and pore pressure are demonstrated by numerical examples pertaining to the considered problems. It is shown that the fully coupled nature of the solutions rigorously captures the seemingly anomalous time variations of the effective stress as driven by the pore fluid pressure disturbances, as well as the distribution and movement of anions/cations within the dual-porosity porous medium. The existing subset of published solutions on the subject is successfully reproduced as special cases of the solutions presented in this paper.
Optimal Design and Experimental Research of the Anti-Cavitation Structure in the Water Hydraulic Relief Valve
Authors: Xu He , Wang Haihang , Hu Mingyu , Jiao Liye , Li Chang
Published: July 2018

Water hydraulics relief valves are essential components of hydraulic systems. These valves maintain the desired pressure and thereby prevent other components from being damaged. During operation of the relief valve, the water flow often cavitates in the valve port owing to the rapid decline in pressure, affecting the stability and safety of the hydraulic system. To improve relief valve performance, an optimal design of the valve was determined. Using a computational fluid dynamics approach, the effects of the valve core design and the nonsmooth groove structure of the valve seat on the jet flow structure were modeled and tested. The anti-cavitation structure was optimized parametrically, and the ideal valve port structure was determined. Tests were conducted to compare cavitation in the water hydraulics relief valve with and without the anti-cavitation structures. Results of these tests showed evident enhancement of cavitation performance.
Mach Number Effect on Symmetric and Antisymmetric Modes of Base Pressure Fluctuations
Authors: Vikramaditya N. S. , Viji M.
Published: July 2018

An experimental study aimed at evaluating the influence of Mach number on the base pressure fluctuations of a cylindrical afterbody was performed over a wide range of Mach numbers from subsonic to supersonic speeds. Time-averaged results indicate that the coefficient of base pressure drops with the increase in the freestream Mach number at subsonic speeds and increases at supersonic Mach numbers. The coefficient of root-mean-square of the pressure fluctuations follows a decreasing trend with the increase in the Mach number. Examination of the spectra reveals different mechanisms dominate the pressure fluctuations from the center to the periphery of the base as well as with the change in the Mach number. Analysis of the azimuthal coherence indicates that all the dominant tones in the spectra can be classified either into a symmetric or an antisymmetric mode at subsonic Mach numbers. However, at supersonic Mach numbers, all the dominant tones in the spectra are symmetric in nature. The results from the cross-correlation suggest that two possible mechanisms of recirculation bubble pulsing and convective motions/vortex shedding are driving the dynamics on the base at subsonic Mach numbers. However, at supersonic Mach numbers, only single mechanism of the recirculation bubble pulsing dominates. Moreover, it indicates that the symmetric mode is associated with the dynamics of the recirculation bubble and the antisymmetric mode is related to the convective motions/vortex shedding.
Grooved Pipe Joints on Shipboard Applications
Authors: Dole Douglas
Published: July 2018

Grooved piping has been used on shipboard applications since the early 1920’s, first in the United Kingdom than many other parts of the world. It gained rapid acceptance in the UK for its many advantages over flange connections. In the US it was used on many Merchant and Naval vessels constructed during World War II, partly for its speed of installation, but also for its less fussy tolerance requirements with regard to pipe length and joint alignment. It has since grown to become used worldwide in many types of vessels. This paper enumerates grooved pipe joints advantages and its technical underpinnings.

Paper published with permission.
Design and Certification of Type C Independent Tanks for Gas Fuelled Ships
Authors: Thomas Roy , Patel Harish
Published: July 2018

The design and certification of Type C independent tanks for gas fuelled ships presents a unique set of challenges. This paper examines some of these challenges and provides a step-by-step overview of the design and certification process for these tanks. Apart from design considerations, this paper also elaborates on some of the fabrication, inspection and testing requirements for these tanks.

Paper published with permission.
Fully Constrained Platform and its Applications
Authors: Lee Li
Published: July 2018

This paper presents a new ocean platform concept, the fully constrained platform (FCP). In a nut-shell, FCP is a fixed-in-place deepwater platform concept, which has the least amount of motion in harsh environment, compared to all other deepwater platforms currently in use. For an intermediate water depth, from 100 to 1,000 ft, the FCP concept could be competitive to existing designs. FCP is the core technology for a new class of marine structures, and has the potential to be used anywhere in world’s ocean for any purpose, which requires a support structure with minimum motions.

Paper published with permission.
Development of Autonomous Underwater Vehicle for Marine Application
Authors: Khastgir Siddartha , Sahoo Anubhav
Published: July 2018

Last decade has seen a spurt in autonomous technologies in military and civilian sectors. The search for oil and gas is moving into ever deeper waters, and the need for coastal surveillance and climatic monitoring, makes underwater autonomous assistance quite obvious for a developing nation like India with thousands of kilometres of coastline. Using such platforms in these endeavours provides an efficient way to keep human life out of harm’s way in hostile environments.

The prototype developed has its navigation based on an internal IMU (Inertial Mass Unit) and the software is extensible to support DVL (Doppler Velocity Logger) based navigation. Near range object detection and path planning is achieved via Image Processing and using two surge and one heave thrusters the bot can operate in three degrees of freedom. The modular structure allows for the addition of extra sensors like pressure, temperature and manipulators like grippers and torpedoes. It has a Intel Atom processor, which runs the control algorithms for motion and required task completion.

Paper published with permission.
Nutritional Intake in Australian Football Players: Sports Nutrition Knowledge and Macronutrient and Micronutrient Intake
Authors: Lohman Rachel , Carr Amelia , Condo Dominique
Published: July 2018

This study compared the energy, macronutrient, and micronutrient intake in elite and sub-elite Australian football players and compared nutritional intake to current recommendations. Sports nutrition knowledge was also quantified and compared between elite and sub-elite players. Nutritional intake was quantified in elite (n = 35) and sub-elite (n = 31) players using the Automated Self-Administered 24-Hour Dietary Assessment Tool. The 88-item Sports Nutrition Knowledge Questionnaire was used to quantify knowledge related to general nutrition concepts, fluid, recovery, weight control, and supplements. Elite players had a higher nutritional intake (mean ± SD) for energy (14,140 ± 5,887 kJ [elite players] vs 10,412 ± 3,316 kJ [sub-elite players]; P = .002) and fat (40% ± 6% [elite players] vs 34% ± 6% [sub-elite players]; P < .001). Protein intake exceeded the recommended intake in 77% of elite players and 68% of sub-elite players, and carbohydrate intake was below the recommended intake for 91% of elite players and 97% of sub-elite players. Sodium intake recommendations were exceeded by 100% of elite and sub-elite players. Both elite and sub-elite players answered 51% of the Sports Nutrition Knowledge Questionnaire questions correctly. The percentage of correctly answered questions specific to supplements was 27% for elite players and 18% for sub-elite players. The results of the current investigation suggest that Australian football players’ nutritional intake is inconsistent with current recommendations for macronutrients and some micronutrients. Furthermore, players may benefit from additional knowledge of the risks and benefits of supplement use.
A physical model for efficient ranking in networks
Authors: De Bacco Caterina , Larremore Daniel B. , Moore Cristopher
Published: July 2018

A simple physical model enables rapid detection and extraction of linear hierarchies in large networks.
Radical chain repair: The hydroalkylation of polysubstituted unactivated alkenes
Authors: Povie Guillaume , Suravarapu Sankar Rao , Bircher Martin Peter , Mojzes Melinda Meyer , Rieder Samuel , Renaud Philippe
Published: July 2018

A bioinspired repair process allows to expand the synthetic scope of radical reactions.