bluuebunny/crossref_metadata_2025 huggingface dataset:
A Semi-Analytical Model for Predicting Horizontal Well Performances in Fractured Gas Reservoirs With Bottom-Water and Different Fracture Intensities
Authors: Tan Yongsheng , Li Haitao , Zhou Xiang , Jiang Beibei , Wang Yongqing , Zhang Nan
Published: July 2018

Numerical simulation and prediction studies on horizontal well performances in gas reservoir are foundation for optimizing horizontal well completion process. To gain more understanding on this theory, a steady-state reservoir model coupling with wellbore is developed in the fractured gas reservoirs with bottom-water and different fracture intensities to predict the horizontal well performances. Based on the equivalent flow assumption, the fractured porous medium is transformed into anisotropic porous medium so that the gas reservoir flow model can be developed as a new model that incorporates formation permeability heterogeneity, reservoir anisotropy, and gas reservoir damage. The wellbore flow model which considers pressure drops in the tubing is applied. We compare this paper model solutions for inflow profile along the well to the numerical solutions obtained from a commercial simulator (ECLIPSE 2011), and the result shows a very good agreement. Moreover, sensitive analysis, in terms of various linear densities of fractures, matrix permeability, fracture width, and wellbore pressure drop, is implemented. The results show that the new model developed in this study can obtain a more practical representation to simulate the horizontal wells performance in fractured gas reservoir with different fracture intensities and bottom-water, thus can be used to optimize the parameters in horizontal well completion of fractured gas reservoirs with different fracture intensities and bottom-water.
Hybrid Nanocomposite Thermal Interface Materials: The Thermal Conductivity and the Packing Density
Authors: Zhang Tingting , Sammakia Bahgat G. , Yang Zhihao , Wang Howard
Published: July 2018

We have investigated a novel hybrid nanocomposite thermal interface material (TIM) that consists of silver nanoparticles (AgNPs), silver nanoflakes (AgNFs), and copper microparticles (CuMPs). Continuous metallic network form while AgNPs and AgNFs fuse to join bigger CuMPs upon hot compression, resulting in superior thermal and mechanical performances. The assembly temperature is as low as 125 °C due to the size effect of silver nanoparticulates. The thermal conductivity, k, of the hybrid nanocomposite TIMs is found to be in the range of 15–140 W/mK, exceeding best-performing commercial thermal greases, while comparable to high-end solder TIMs. The dependence of k on the solid packing density and the volume fraction of voids is discussed through comparing to model predictions.
Dynamic Data-Driven Combustor Design for Mitigation of Thermoacoustic Instabilities
Authors: Chattopadhyay Pritthi , Mondal Sudeepta , Ray Asok , Mukhopadhyay Achintya
Published: July 2018

A critical issue in design and operation of combustors in gas turbine engines is mitigation of thermoacoustic instabilities, because such instabilities may cause severe damage to the mechanical structure of the combustor. Hence, it is important to quantitatively assimilate the knowledge of the system conditions that would potentially lead to these instabilities. This technical brief proposes a dynamic data-driven technique for design of combustion systems by taking stability of pressure oscillations into consideration. Given appropriate experimental data at selected operating conditions, the proposed design methodology determines a mapping from a set of operating conditions to a set of quantified stability conditions for pressure oscillations. This mapping is then used as an extrapolation tool for predicting the system stability for other conditions for which experiments have not been conducted. Salient properties of the proposed design methodology are: (1) It is dynamic in the sense that no fixed model structure needs to be assumed, and a suboptimal model (under specified user-selected constraints) is identified for each operating condition. An information-theoretic measure is then used for performance comparison among different models of varying structures and/or parameters and (2) It quantifies a (statistical) confidence level in the estimate of system stability for an unobserved operating condition by using a Bayesian nonparametric technique. The proposed design methodology has been validated with experimental data of pressure time-series, acquired from a laboratory-scale lean-premixed swirl-stabilized combustor.
Experimental Validation of Graph-Based Hierarchical Control for Thermal Management
Authors: Pangborn Herschel C. , Koeln Justin P. , Williams Matthew A. , Alleyne Andrew G.
Published: July 2018

This paper proposes and experimentally validates a hierarchical control framework for fluid flow systems performing thermal management in mobile energy platforms. A graph-based modeling approach derived from the conservation of mass and energy inherently captures coupling within and between physical domains. Hydrodynamic and thermodynamic graph-based models are experimentally validated on a thermal-fluid testbed. A scalable hierarchical control framework using the graph-based models with model predictive control (MPC) is proposed to manage the multidomain and multi-timescale dynamics of thermal management systems. The proposed hierarchical control framework is compared to decentralized and centralized benchmark controllers and found to maintain temperature bounds better while using less electrical energy for actuation.
Magnus Wind Turbine Emulator With MPPT by Cylinder Rotation Control
Authors: Corrêa Leonardo Candido , Lenz João Manoel , Ribeiro Cláudia Garrastazu , Farret Felix Alberto
Published: July 2018

An emulator for the nonconventional Magnus wind turbine was designed and developed in this study. A brief discussion is made of this special case of horizontal axis wind generator and of the main physics principles involving the Magnus phenomenon. A mathematical model was used to emulate the static behavior of the Magnus wind turbine and a detailed analysis is presented about its peculiar rotating cylinder characteristics. Based on the relationship between cylinder blade rotation and power coefficient, a hill climb search algorithm was developed to perform maximum power point tracking. The impact of the cylinder's rotation speed on the turbine net output power was evaluated. A controlled direct current motor was used to provide torque, based on the Magnus turbine model, and drive a permanent magnet synchronous generator (PMSG); the latter was controlled by a buck converter in order to extract the maximum generated power (MGP). Simulations of the Magnus wind turbine model and its maximum power point tracking (MPPT) control are also presented. A prototype of the proposed emulator was developed and operated by a user-friendly LabVIEW interface. Measurements of the power delivered to the load were acquired for different wind speeds; these results were analyzed and compared with simulated values showing a good behavior of the emulator with respect to the turbine model. The proposed control technique for maximizing the output power was validated by emulated results. The modeling and development of the Magnus turbine emulator also serve to encourage further studies on generation and control with this wind machine.
Axial Vibration Suppression in a Partial Differential Equation Model of Ascending Mining Cable Elevator
Authors: Wang Ji , Koga Shumon , Pi Yangjun , Krstic Miroslav
Published: July 2018

Lifting up a cage with miners via a mining cable causes axial vibrations of the cable. These vibration dynamics can be described by a coupled wave partial differential equation-ordinary differential equation (PDE-ODE) system with a Neumann interconnection on a time-varying spatial domain. Such a system is actuated not at the moving cage boundary, but at a separate fixed boundary where a hydraulic actuator acts on a floating sheave. In this paper, an observer-based output-feedback control law for the suppression of the axial vibration in the varying-length mining cable is designed by the backstepping method. The control law is obtained through the estimated distributed vibration displacements constructed via available boundary measurements. The exponential stability of the closed-loop system with the output-feedback control law is shown by Lyapunov analysis. The performance of the proposed controller is investigated via numerical simulation, which illustrates the effective vibration suppression with the fast convergence of the observer error.
Crystal Viscoplasticity of a Ni-Base Superalloy in the Aged State
Authors: Kirka M. M. , Neu R. W.
Published: July 2018

Arising from long-term high temperature service, the microstructure of nickel-base (Ni-base) superalloy components undergoes thermally and deformation-induced aging characterized by isotropic coarsening and directional coarsening (rafting) of the γ′ precipitates. The net result of the morphological evolutions of the γ′ particles is a deviation of the mechanical behavior from that of the as-heat treated properties. To capture the influence of a rafted and isotropic aged microstructure states on the long-term constitutive behavior of a Ni-base superalloy undergoing thermomechanical fatigue (TMF), a temperature-dependent crystal viscoplasticity (CVP) constitutive model is extended to include the effects of aging. The influence of aging in the CVP framework is captured through the addition of internal state variables that measure the widening of the γ channels and in-turn update the material parameters of the CVP model. Through the coupling with analytical derived kinetic equations to the CVP model, the enhanced CVP model is shown to be in good agreement when compared to experimental behavior in describing the long-term aging effects on the cyclic response of a directionally solidified (DS) Ni-base superalloy used in hot section components of industrial gas turbines.
Dynamic Simulation and Control of an Active Roll Reduction System Using Free-Flooding Tanks With Vacuum Pumps
Authors: Xu Jiafeng , Ren Zhengru , Li Yue , Skjetne Roger , Halse Karl Henning
Published: July 2018

Ship roll motion is critical for offshore operations due to its lack of damping mechanism. This paper demonstrates a dynamic simulation scheme of an active roll reduction system using free-flooding tanks controlled by vacuum pumps. A tank is installed on each side of a catamaran. Both the tank hatches are opened to the sea and the air chambers of both tanks are connected by an air duct. Vacuum pumps and air valve stabilized the wave-induced roll motion by controlling the water levels in the tanks through a feedback controller. The catamaran is a dynamic model with single degree-of-freedom (DOF) in roll, and its hydrodynamic behavior is calculated using potential theory by SHIPX. The air chambers are modeled as isothermal processes of ideal gas. The behavior of the liquid flow in a tank is simulated by incompressible Reynolds-averaged Navier–Stokes solver with the volume of fluid model, then summarized as a response function for the vessel model. A simplified control plant model for the vacuum pumps is proposed where higher order behaviors are neglected and the external wave-induced load is unknown. A parameter-dependent observer and a backstepping controller are adopted to estimate the external load and to reduce the roll motion. The system stability is proved by Lyapunov's direct method. The performance of the entire system is evaluated in terms of roll reduction capability and power cost. The system is more suitable for roll reduction in low-speed or resting conditions.
Finite Element Analysis to Probe the Influence of Acetabular Shell Design, Liner Material, and Subject Parameters on Biomechanical Response in Periprosthetic Bone
Authors: Chatterjee Subhomoy , Kobylinski Sabine , Basu Bikramjit
Published: July 2018

The implant stability and biomechanical response of periprosthetic bone in acetabulum around total hip joint replacement (THR) devices depend on a host of parameters, including design of articulating materials, gait cycle and subject parameters. In this study, the impact of shell design (conventional, finned, spiked, and combined design) and liner material on the biomechanical response of periprosthetic bone has been analyzed using finite element (FE) method. Two different liner materials: high density polyethylene–20% hydroxyapatite–20% alumina (HDPE–20%HA–20%Al2O3) and highly cross-linked ultrahigh molecular weight polyethylene (HC-UHMWPE) were used. The subject parameters included bone condition and bodyweight. Physiologically relevant load cases of a gait cycle were considered. The deviation of mechanical condition of the periprosthetic bone due to implantation was least for the finned shell design. No significant deviation was observed at the bone region adjacent to the spikes and the fins. This study recommends the use of the finned design, particularly for weaker bone conditions. For stronger bones, the combined design may also be recommended for higher stability. The use of HC-UHMWPE liner was found to be better for convensional shell design. However, similar biomechanical response was captured in our FE analysis for both the liner materials in case of other shell designs. Overall, the study establishes the biomechanical response of periprosthetic bone in the acetabular with preclinically tested liner materials together with new shell design for different subject conditions.
Evaluation and Prediction of Human Lumbar Vertebrae Endplate Mechanical Properties Using Indentation and Computed Tomography
Authors: Patel Ravi R. , Noshchenko Andriy , Dana Carpenter R. , Baldini Todd , Frick Carl P. , Patel Vikas V. , Yakacki Christopher M.
Published: July 2018

Current implant materials and designs used in spinal fusion show high rates of subsidence. There is currently a need for a method to predict the mechanical properties of the endplate using clinically available tools. The purpose of this study was to develop a predictive model of the mechanical properties of the vertebral endplate at a scale relevant to the evaluation of current medical implant designs and materials. Twenty vertebrae (10 L1 and 10 L2) from 10 cadavers were studied using dual-energy X-ray absorptiometry to define bone status (normal, osteopenic, or osteoporotic) and computed tomography (CT) to study endplate thickness (μm), density (mg/mm3), and mineral density of underlying trabecular bone (mg/mm3) at discrete sites. Apparent Oliver–Pharr modulus, stiffness, maximum tolerable pressure (MTP), and Brinell hardness were measured at each site using a 3 mm spherical indenter. Predictive models were built for each measured property using various measures obtained from CT and demographic data. Stiffness showed a strong correlation between the predictive model and experimental values (r = 0.85), a polynomial model for Brinell hardness had a stronger predictive ability compared to the linear model (r = 0.82), and the modulus model showed weak predictive ability (r = 0.44), likely due the low indentation depth and the inability to image the endplate at that depth (≈0.15 mm). Osteoporosis and osteopenia were found to be the largest confounders of the measured properties, decreasing them by approximately 50%. It was confirmed that vertebral endplate mechanical properties could be predicted using CT and demographic indices.
Simulating Heat Transfer Through Periodic Structures With Different Wall Temperatures: A Temperature Decomposition Method
Authors: Li Ping , Zhang Junfeng
Published: July 2018

To simulate heat transfer processes through periodic devices with nonuniform wall temperature distributions, we propose to decompose the regular temperature into two parts: namely the transient part and the equilibrium part. These two parts can be solved independently under their individual wall and inlet/outlet conditions. By calculating the flow field and the two component functions in one periodic module, one can easily generate the distributions of regular temperature in one or multiple modules. The algorithm and implementation are described in details, and the method is discussed thoroughly from mathematical, physical, and numerical aspects. Sample simulations are also presented to demonstrate the capacity and usefulness of this method for future simulations of thermal periodic flows using various numerical schemes.
Analysis of Deposition Methods for Lithium-Ion Battery Anodes Using Reduced Graphene Oxide Slurries on Copper Foil
Authors: Garofalo James , Lawler John , Walczyk Daniel , Koratkar Nikhil
Published: July 2018

Graphene oxide (GO) slurries were deposited onto copper foil for use in lithium-ion battery anodes to determine the best deposition method(s) for research or high-volume manufacturing. Four deposition methods were tested: doctor blade, Mayer rod, slot die, and low volume low pressure (LVLP) spray. Analytical models that link tooling and process characteristics to mass flow rate of slurry and the resulting dry deposition height are developed and validated experimentally. While all methods successfully produced functioning batteries, a number of different qualitative and quantitative metrics from experimental results identified the best method for both situations. Observations were recorded on adhesion, deposition consistency, usability, and cleanability. Data on specific discharge capacity were recorded to show performance over the anode lifetime and at different charge/discharge rates. The data indicate that anodes produced using reduced graphene oxide (rGO) deliver a specific charge storage capacity of 50 to 400 mAh/g at charge–discharge rates of 1 C to 0.05 C. Doctor blading proved to be best for laboratory setups because of its adjustability, while the Mayer rod shows promise for high-volume manufacturing due to better performance and the use of nonadjustable, dedicated tooling. All methods, analysis, and metrics are discussed.
Robust Tool Wear Monitoring Using Systematic Feature Selection in Turning Processes With Consideration of Uncertainties
Authors: Zhang Bin , Katinas Christopher , Shin Yung C.
Published: July 2018

This paper describes a robust tool wear monitoring scheme for turning processes using low-cost sensors. A feature normalization scheme is proposed to eliminate the dependence of signal features on cutting conditions, cutting tools, and workpiece materials. In addition, a systematic feature selection procedure in conjunction with automated signal preprocessing parameter selection is presented to select the feature set that maximizes the performance of the predictive tool wear model. The tool wear model is built using a type-2 fuzzy basis function network (FBFN), which is capable of estimating the uncertainty bounds associated with tool wear measurement. Experimental results show that the tool wear model built with the selected features exhibits high accuracy, generalized applicability, and exemplary robustness: The model trained using 4140 steel turning test data could predict the tool wear for Inconel 718 turning with a root-mean-square error (RMSE) of 7.80 μm and requests tool changes with a 6% margin on average. Furthermore, the developed method was successfully applied to tool wear monitoring of Ti–6Al–4V alloy despite different mechanisms of tool wear, i.e., crater wear instead of flank wear.
Experimental Study of Ion Current Signals and Characteristics in an Internal Combustion Rankine Cycle Engine Based on Water Injection
Authors: Kang Zhe , Wu Zhijun , Fu Lezhong , Deng Jun , Hu Zongjie , Li Liguang
Published: July 2018

The internal combustion Rankine cycle (ICRC) engine utilizes pure oxygen as the oxidant instead of air during combustion to prevent the generation of nitrogen oxide emissions and lower the cost of CO2 recovery. To control combustion intensity and increase efficiency, water injection technology is implemented as it can increase the in-cylinder working fluid during combustion process. To further enhance the system thermal efficiency, the injected water is heated using coolant and waste heat before being directly injected into combustion chamber. The main challenge of controlling the ICRC engine is the interaction between water injection process and combustion stability. Ion current detection provides a potential solution of real-time detection of in-cylinder combustion status and water injection process simultaneously. In this paper, the characteristics of ion current signal in an ICRC engine were studied. The results indicate the ion current signal is primarily affected by the combination of trapped water vapor injected in the last cycle and in-cylinder combustion intensity. The water vapor contributes to the ionization reactions, which lead to enhanced ion current signals under water cycle. The ion current signal is capable of reflecting the operating conditions of the in-cylinder water injector. The phase of the ion current peak value has a linear relation as the water injection timing is delayed, and ion current detection technology has the potential to detect the combustion phase under different engine loads in an internal combustion Rankine cycle engine.
Effects of Postweld Heat-Treatment on Girth Weld Tensile Property and Microstructure of High-Frequency Electric Resistance Welded Pipe for API X80 Grade Casing Pipe
Authors: Goto Sota , Toyoda Shunsuke , Ide Shinsuke , Okazaki Yukihiko , Nakashima Kota
Published: July 2018

The girth weld tensile properties of API X80 grade high-frequency electric resistance welded (HFW) steel pipe for surface casing with the chemical composition of 0.05C–1.6Mn–0.06Nb (mass %) and the diameter of 558.8 mm and wall thickness of 25.4 mm were investigated by simulated postweld heat-treatment (PWHT). The tensile specimens taken from girth butt welded pipe were heat-treated under the conditions of 625 °C × 2 h and 675 °C × 2 h in an air furnace in order to simulate PWHT of casing products. The result of the girth weld tensile test of the heat-treated specimens showed that yield strength and tensile strength decreased very little and these properties sufficiently satisfied the API X80 specification. The change in strength due to heat treatment was discussed based on microscopic observation of the submicrostructures of the base metal by the electron back-scattered diffraction (EBSD) technique, transmission electron microscopy, X-ray diffraction (XRD), and the extraction residue precipitate classification method. The authors concluded that the fine NbC with a diameter of 12–18 nm, which precipitated during the heat treatment, prevented the decrease of strength due to the slight grain growth and dislocation recovery associated with PWHT. Additionally, the effect of PWHT conditions was evaluated by using small-scale laboratory specimens obtained from the base metal. Tensile properties were summarized as a function of the tempering parameter. As a result, strength remained almost constant at the tempering parameter equivalent to the PWHT conditions of 625 °C × 16 h.
Low-Complexity Passive Vehicle Suspension Design Based on Element-Number-Restricted Networks and Low-Order Admittance Networks
Authors: Hu Yinlong , Chen Michael Z. Q.
Published: July 2018

This paper is concerned with the low-complexity passive suspension design problem, aiming at improving vehicle performance in the meanwhile maintaining simplicity in structure for passive suspensions. Two methods are employed to construct the low-complexity passive suspensions. Using the first method, the number of each element is restricted to one, and the performance for all networks with one inerter, one damper, and one spring is evaluated, where best configurations for different vehicle settings are identified. Using the second method, low-order admittance networks whose orders of admittance functions are no larger than three are utilized. Design methods are proposed by directly using the positive realness conditions imposed on the admittance functions. The effectiveness of the proposed methods is numerically demonstrated, and the comparison between these two constructing methods is conducted.
Coupled State-Dependent Riccati Equation Control for Continuous Time Nonlinear Mechatronics Systems
Authors: Wang Xin , Yaz Edwin E. , Schneider Susan C.
Published: July 2018

This paper considers a novel coupled state-dependent Riccati equation (SDRE) approach for systematically designing nonlinear quadratic regulator (NLQR) and H∞ control of mechatronics systems. The state-dependent feedback control solutions can be obtained by solving a pair of coupled SDREs, guaranteeing nonlinear quadratic optimality with inherent stability property in combination with robust L2 type of disturbance reduction. The derivation of this control strategy is based on Nash's game theory. Both finite and infinite horizon control problems are discussed. An under-actuated robotic system, Furuta rotary pendulum, is used to examine the effectiveness and robustness of this novel nonlinear control approach.
Numerical Modeling of Stall and Poststall Events of a Single Pitching Blade of a Cycloidal Rotor
Authors: Singh Kuldeep , Páscoa José Carlos
Published: July 2018

In the present work, a numerical study is carried out to compare the performance of seven turbulence models on a single pitching blade of cycloidal rotor operating in deep dynamic stall regime at moderate Reynolds number. The investigated turbulence models were: (i) kω-shear stress transport (SST), (ii) kω-SST with γ, (iii) transition SST (γ–Reθ), (iv) scale adaptive simulation (SAS), (v) SAS coupled with transition SST, (vi) SAS with γ, and (vii) detached eddy simulation (DES) coupled with transition kω-SST. The wake vortices evolution and shedding analysis are also carried out for the pitching blade. The performance of the investigated turbulence models is evaluated at various critical points on the hysterias loop of lift and drag coefficients. The predictions of the investigated turbulence models are in good agreement at lower angle of attack, i.e., αu ≤ 20 deg. The detailed quantitative analysis at critical points showed that the predictions of SAS and transition SST-SAS turbulence models are in better agreement with the experimental results as compared to the other investigated models. The wake vortices analysis and fast Fourier transport analysis showed that the wake vortex characteristics of a pitching blade are significantly different than those for the low amplitude oscillating blade at the higher reduced frequency.
Investigations on Additive Manufacturing of Ti–6Al–4V by Microplasma Transferred Arc Powder Deposition Process
Authors: Sawant Mayur S. , Jain N. K.
Published: July 2018

This paper presents investigation findings on additive manufacturing (AM) aspects of Ti6Al4V by microplasma transferred arc powder deposition (μ-PTAPD) process in continuous and dwell-time mode. Pilot experiments were conducted to identify feasible values of six important parameters of μ-PTAPD process for single-layer deposition followed by 27 main experiments varying three parameters. Energy consumption aspects were used to identify optimum values of parameters varied during main experiments for multilayer deposition. It revealed that higher values of flow rate of powder and travel speed of deposition head result in smaller values of power consumption per unit flow rate of powder and energy consumption per unit traverse length. Continuous and dwell-time modes were used to study deposition characteristics, microstructure, lamellae widths, wear characteristics, tensile properties, fractography of tensile specimen, wear mechanism, and microhardness of multilayer depositions. Dwell-time deposition yielded higher effective wall width (EWW), deposition efficiency (DE), yield strength, ultimate strength, microhardness, surface straightness, lower strain, wear volume and friction coefficient, and smaller lamellar width. It had good deposition quality with fine partial martensite and basket-weave microstructure. Fractography analysis exhibited fine dimple rupture for dwell-time multilayer deposition and occurrence of elongated regions for continuous multilayer deposition. Wear of dwell-time multilayer deposition occurred by microploughing and microcutting resulting in smaller wear debris. Comparison of Ti6Al4V depositions by different processes revealed that dwell-time μ-PTAPD process is cost-effective than laser-based processes and energy efficient than pulsed plasma arc process.
A Novel Control Strategy for Pilot Controlled Proportional Flow Valve With Internal Displacement-Flow Feedback
Authors: Wang He , Wang Xiaohu , Huang Jiahai , Wang Jun , Quan Long
Published: July 2018

The present study is focused on the construction of a well-performing pilot controlled proportional flow valve with internal displacement-flow feedback. A novel control strategy for the valve is proposed in which the flow rate through the valve is directly controlled. The linear mathematical model for the valve is established and a fuzzy proportional–integral–derivative (PID) controller is designed for the flow control. In order to obtain the flow rate used as feedback rapidly and accurately in real-time, back propagation neural network (BPNN) is employed to predict the flow rate through the valve with the pressure drop through the main orifice and main valve opening, and the predicted value is used as the feedback. Both simulation and experimental results show that the predicted value obtained by BPNN is reliable and available for the feedback. The proposed control strategy is effective with which the flow rate through the valve remains almost constant when the pressure drop through the main orifice increases and the valve can be applied to the conditions where the independence of flow rate and load is required. For the valve with the proposed control strategy, the nonlinearity is less than 5.3%, the hysteresis is less than 4.2%, and the bandwidth is about 16 Hz. The static and dynamic characteristics are reasonable and acceptable.
The Rapid Cooling Effect on Microstructure of Nickel-Based Alloys Welding Joint
Authors: Zhao LiBing , Zheng Zhentai , Wang Zelong , Qi Jianing , Lei Yunfeng , He Meng
Published: July 2018

Fusion welding of nickel-based alloys is often associated with coarse grains and severe segregation, which finally results in the increase of hot cracking susceptibility and poor mechanical properties. Conventional gas tungsten arc welding (GTAW) can aggravate these phenomena, which is mainly due to its high heat input and low cooling rate. In this paper, the cooling rate was enhanced by spraying liquid nitrogen during the welding process. Compared to conventional GTAW, the rapid cooling produced narrower heat affected zone (HAZ) width and more equiaxed grains in the fusion zone, thus higher hardness distribution was also achieved in this condition. In addition, γ′ phase exhibited a dispersed distribution, and segregation has been improved. The results show that the HAZ width is decreased by about 50%, and the fusion zone consisting of the finest equiaxed grains and the lowest segregation was obtained, when the heat sink located on one side 10 mm away from the weld centerline. Also, fine equiaxed grains and the dispersed distribution of γ′ phase could improve the grain boundary strength and reduce the incidence of liquid films along grain boundaries, contributing to prevent nickel-based alloys welding hot cracking from initiating.
Constitutive Behavior for Quenching of Al–Cu–Mg Alloy With Consideration of Precipitation
Authors: Wu Jianjun , Guo Ruichao
Published: July 2018

The deformation behavior of as-quenched 2024 Al–Cu–Mg alloy has been experimentally studied. The experiments are designed to cool specimens to the desired temperature with a constant cooling rate, i.e., 5 K/s. Isothermal tensile tests are performed over a range of 573–723 K temperature and (0.01, 0.1, and 1 s−1) strain rates to find out the flow stresses and microstructures after deformation. Due to the nonuniform deformation mechanisms (solid solution versus solid solution and precipitation), two types of Arrhenius model are established for the temperature range of 573–673 K and 673–723 K, respectively. For temperature between 573 and 673 K, the activation energy is dependent on temperature and strain rate, and the value of activation energy decreases with the increases of temperature and strain rate. Compared with the ideal variation trend with no consideration of precipitation, the largest difference of activation energy is found at the temperature of 623 K which is the nose temperature of 2024 alloy.
Numerical Study on Merging and Interaction of Jet Diffusion Flames
Authors: Ho T. C. , Fu S. C. , Chao Christopher Y. H. , Gupta Sharad
Published: July 2018

A high velocity jet fire can cause catastrophic failure due to flame impingement or radiation. The scenario becomes more complicated when multiple jet fires exist following ignition of release from pressure relief valves (PRV) as the thermal effect not only distorts the individual jet flame but also changes the flame height and temperature profile and such kind of high velocity jet flames have not been studied in the past. Therefore, prediction of the flame shape including the merging and interaction of multiple jet fires is essential in risk analysis. In this paper, fire interaction of two high velocity (>10 m/s) jet fires is investigated using computational fluid dynamics (CFD) techniques. Different radiation models are analyzed and validated by experimental data from the literature. Based on the simulation result, the merging of high velocity jet fires is divided into three stages. An empirical equation considering the fire interaction for the average flame height with different release velocities and separation distance is developed. The flame height increases dramatically when the separation distance decreases resulting in a shortage of oxygen. So, part of the methane is reacted in a higher height, which explains the change in the merging flame height and temperature.
Investigation of Heterogeneous Joule Heating as the Explanation for the Transient Electroplastic Stress Drop in Pulsed Tension of 7075-T6 Aluminum
Authors: Ruszkiewicz Brandt J. , Mears Laine , Roth John T.
Published: July 2018

The electroplastic effect can be predicted and modeled as a 100% bulk heating/softening phenomenon in the quasi-steady-state; however, these same models do not accurately predict flow stress in transient cases. In this work, heterogeneous Joule heating is examined as the possible cause for the transient stress drop during quasi-static pulsed tension of 7075-T6 aluminum. A multiscale finite element model is constructed where heterogeneous thermal softening is explored through the representation of grains, grain boundaries, and precipitates. Electrical resistivity is modeled as a function of temperature and dislocation density. In order to drive the model to predict the observed stress drop, the bulk temperature of the specimen exceeds experiment, while the dislocation density and grain boundary electrical resistivity exceed published values, thereby suggesting that microscale heterogeneous heating theory is not the full explanation for the transient electroplastic effect. A new theory for explaining the electroplastic effect based on dissolution of bonds is proposed called the Electron Stagnation Theory.
Conjugate Heat Transfer Predictions for Subcooled Boiling Flow in a Horizontal Channel Using a Volume-of-Fluid Framework
Authors: Langari M. , Yang Z. , Dunne J. F. , Jafari S. , Pirault J.-P. , Long C. A. , Thalackottore Jose J.
Published: July 2018

The accuracy of computational fluid dynamic (CFD)-based heat transfer predictions have been examined of relevance to liquid cooling of IC engines at high engine loads where some nucleate boiling occurs. Predictions based on (i) the Reynolds Averaged Navier-Stokes (RANS) solution and (ii) large eddy simulation (LES) have been generated. The purpose of these simulations is to establish the role of turbulence modeling on the accuracy and efficiency of heat transfer predictions for engine-like thermal conditions where published experimental data are available. A multiphase mixture modeling approach, with a volume-of-fluid interface-capturing method, has been employed. To predict heat transfer in the boiling regime, the empirical boiling correlation of Rohsenow is used for both RANS and LES. The rate of vapor-mass generation at the wall surface is determined from the heat flux associated with the evaporation phase change. Predictions via CFD are compared with published experimental data showing that LES gives only slightly more accurate temperature predictions compared to RANS but at substantially higher computational cost.
Effects of Pressure Boundary on Dynamic Torque Behavior of Hydroviscous Drive
Authors: Cui Jianzhong , Liu Jun , Xie Fangwei , Wang Cuntang , Hou Pengliang
Published: July 2018

The object of this work is to investigate the effect of the change of film pressure resulting from axial squeeze-film motion between driving and driven disks on the performance of hydroviscous drive (HVD). A simplified mathematical model of the steady and laminar flow between parallel disks is established with consideration of three kinds of pressure boundary conditions. Some analytical solutions of film thickness, rotate speed of driven disk, viscous torque, and total torque are obtained. The numerical results show that the torque response depends on the relationship between the inlet pressure and the outlet pressure when considering the Dirichlet boundary conditions. The soft-start under Dirichlet boundary conditions and Mixed boundary conditions reflects the constant-torque startup and torque control startup, respectively. Compared with the two boundary conditions above, the soft-start under pressure profile boundary from Neumann boundary conditions has advantages for speed regulation. The effects of the ratio of inner and outer radius on the torque profiles and soft-start time are mainly related to Dirichlet boundary conditions and pressure profile boundary from Neumann boundary conditions.
Flow Characterization of Supersonic Jets Issuing From Double-Beveled Nozzles
Authors: Wu Jie , Lim H. D. , Wei Xiaofeng , New T. H. , Cui Y. D.
Published: July 2018

Supersonic jets at design Mach number of 1.45 issuing from circular 30 deg and 60 deg double-beveled nozzles have been investigated experimentally and numerically in the present study, with a view to potentially improve mixing behavior. Reynolds-averaged Navier–Stokes (RANS) simulations of the double-beveled nozzles and a benchmark nonbeveled nozzle were performed at nozzle-pressure-ratios (NPR) between 2.8 and 5.0, and the results are observed to agree well with Schlieren visualizations obtained from a modified Z-type Schlieren system. Double-beveled nozzles are observed to produce shorter potential core lengths, modifications to the first shock cell lengths that are sensitive toward the NPR and jet half-widths that are typically wider and narrower along the trough-to-trough (TT) and peak-to-peak (PP) planes, respectively. Lastly, using double-beveled nozzles leads to significant mass flux ratios at NPR of 5.0, with a larger bevel-angle demonstrating higher entrainment levels.
Roll-to-Roll Mechanical Peeling for Dry Transfer of Chemical Vapor Deposition Graphene
Authors: Xin Hao , Zhao Qishen , Chen Dongmei , Li Wei
Published: July 2018

Scaling up graphene fabrication is a critical step for realizing industrial applications of chemical vapor deposition (CVD) graphene, such as large-area flexible displays and solar cells. In this study, a roll-to-roll (R2R) graphene transfer system using mechanical peeling is proposed. No etching of graphene growth substrate is involved; thus, the process is economical and environmentally benign. A prototype R2R graphene transfer machine was developed. Experiments were conducted to test the effects of relevant process parameters, including linear film speed, separation angle, and the guiding roller diameter. The linear film speed was found to have the highest impact on the transferred graphene coverage, followed by the roller diameter, while the effect of separation angle was statistically insignificant. Furthermore, there was an interaction effect between the film speed and roller diameter, which can be attributed to the competing effects of tensile strain and strain rate. Overall, the experimental results showed that larger than 98% graphene coverage could be achieved with high linear film speed and large guiding roller diameter, demonstrating that a large-scale dry graphene transfer process is possible with R2R mechanical peeling.
PDSIDES—A Knowledge-Based Platform for Decision Support in the Design of Engineering Systems
Authors: Ming Zhenjun , Nellippallil Anand Balu , Yan Yan , Wang Guoxin , Goh Chung Hyun , Allen Janet K. , Mistree Farrokh
Published: July 2018

We hypothesize that by providing decision support for designers we can speed up the design process and facilitate the creation of quality cost-effective designs. One of the challenges in providing design decision support is that the decision workflows embody various degrees of complexity due to the inherent complexity embodied in engineering systems. To tackle this, we propose a knowledge-based Platform for Decision Support in the Design of Engineering Systems (PDSIDES). PDSIDES is built on our earlier works that are anchored in modeling decision-related knowledge with templates using ontologies to facilitate execution and reuse. In this paper, we extend the ontological decision templates to a computational platform that provides knowledge-based decision support for three types of users, namely, template creators, template editors, and template implementers, in original design, adaptive design, and variant design, respectively. The efficacy of PDSIDES is demonstrated using a hot rod rolling system (HRRS) design example.
Robust Adaptive Impedance Control With Application to a Transfemoral Prosthesis and Test Robot
Authors: Azimi Vahid , Abolfazl Fakoorian Seyed , Tien Nguyen Thang , Simon Dan
Published: July 2018

This paper presents, compares, and tests two robust model reference adaptive impedance controllers for a three degrees-of-freedom (3DOF) powered prosthesis/test robot. We first present a model for a combined system that includes a test robot and a transfemoral prosthetic leg. We design these two controllers, so the error trajectories of the system converge to a boundary layer and the controllers show robustness to ground reaction forces (GRFs) as nonparametric uncertainties and also handle model parameter uncertainties. We prove the stability of the closed-loop systems for both controllers for the prosthesis/test robot in the case of nonscalar boundary layer trajectories using Lyapunov stability theory and Barbalat's lemma. We design the controllers to imitate the biomechanical properties of able-bodied walking and to provide smooth gait. We finally present simulation results to confirm the efficacy of the controllers for both nominal and off-nominal system model parameters. We achieve good tracking of joint displacements and velocities, and reasonable control and GRF magnitudes for both controllers. We also compare performance of the controllers in terms of tracking, control effort, and parameter estimation for both nominal and off-nominal model parameters.
Characterizing the Stimulated Reservoir Volume During Hydraulic Fracturing-Connecting the Pressure Fall-Off Phase to the Geomechanics of Fracturing
Authors: Sarvaramini Erfan , Dusseault Maurice B. , Gracie Robert
Published: July 2018

Microseismic imaging of the hydraulic fracturing operation in the naturally fractured rocks confirms the existence of a stimulated volume (SV) of enhanced permeability. The simulation and characterization of the SV evolution is uniquely challenging given the uncertainty in the nature of the rock mass fabrics as well as the complex fracturing behavior of shear and tensile nature, irreversible plastic deformation and damage. In this paper, the simulation of the SV evolution is achieved using a nonlocal poromechanical plasticity model. Effects of the natural fracture network are incorporated via a nonlocal plasticity characteristic length, ℓ. A nonlocal Drucker–Prager failure model is implemented in the framework of Biot's theory using a new implicit C0 finite element method. First, the behavior of the SV for a two-dimensional (2D) geomechanical injection problem is simulated and the resulting SV is assessed. It is shown that breakdown pressure and stable fracturing pressure are the natural outcomes of the model and both depend upon ℓ. Next, the post-shut-in behavior of the SV is analyzed using the pressure and pressure derivative plots. A bilinear flow regime is observed and it is used to estimate the flow capacity of the SV. The results show that the flow capacity of the SV increases as ℓ decreases (i.e., as the SV behaves more like a single hydraulic fracture); however, for 0.1m≤ℓ≤1m, the calculated flow capacity indicates that the conductivity of the SV is finite. Finally, it is observed that as ℓ tends to zero, the flow capacity of the SV tends to infinity and the SV behaves like a single infinitely conducting fracture.
Characterization of Interfacial Properties of Graphene-Reinforced Polymer Nanocomposites by Molecular Dynamics-Shear Deformation Model
Authors: Park Chanwook , Yun Gun Jin
Published: July 2018

In this paper, we present an approach for characterizing the interfacial region using the molecular dynamics (MD) simulations and the shear deformation model (SDM). The bulk-level mechanical properties of graphene-reinforced nanocomposites strongly depend on the interfacial region between the graphene and epoxy matrix, whose thickness is about 6.8–10.0 Å. Because it is a challenge to experimentally investigate mechanical properties of this thin region, computational MD simulations have been widely employed. By pulling out graphene from the graphene/epoxy system, pull-out force and atomic displacement of the interfacial region are calculated to characterize the interfacial shear modulus. The same processes are applied to 3% grafted hydroxyl and carboxyl functionalized graphene (OH-FG and COOH-FG)/epoxy (diglycidyl ether of bisphenol F (DGEBF)/triethylenetetramine (TETA)) systems, and influences of the functionalization on the mechanical properties of the interfacial region are studied. Our key finding is that, by functionalizing graphene, the pull-out force moderately increases and the interfacial shear modulus considerably decreases. We demonstrate our results by comparing them with literature values and findings from experimental papers.