bluuebunny/crossref_metadata_2025 huggingface dataset:
Spinning Liquid Gold
Authors: Kosowatz John
Published: July 2018

This article discusses the economic growth opportunities due to liquefied natural gas (LNG) in the United States. Advanced drilling and production techniques have given the United States more natural gas than its markets can handle. Converting that bounty into liquefied natural gas promises to transform the U.S. gas industry into a global energy power. LNG is the generally preferred form of natural gas for use in long-haul heavy-duty trucks, because liquefying it reduces volume. More fuel can be loaded into the tank. Local-use vehicles, which operate from a central yard, often use CNG. For LNG, the only serious limits that people are talking about today are related to infrastructure costs, particularly in the development of exports. Even if the international demand for LNG stays high, exports from the United States cannot happen for a few years because of the time needed for plant construction. Optimism reigns among players throughout the natural gas industry.
The Right Stuff
Authors: Molnar Michael F.
Published: July 2018

This article focuses on changes happening in the U.S. manufacturing industry through innovations. Fueling a true rebirth in innovation and economic growth requires investment in advanced manufacturing capabilities. Research, development, and design are intimately connected with product development and production – and proximity is essential. New ideas and insights for future improvements emerge as engineers and scientists struggle to resolve production problems, reduce costs, and improve performance. This type of iterative innovation enables manufacturers to build sustainable competitive advantages. Manufacturing plays a critical role in both innovation and jobs, and there is nothing inevitable about its decline. Many governments offer direct support to manufacturers. China, for example, offers tax incentives, low-cost factory space, and export subsidies. U.S. manufacturing is poised for a turnaround. The wage gap with foreign competitors has narrowed, U.S. companies have a greater appreciation of the hidden costs of long supply chains, and energy prices have been falling.
Gas Turbines - Major Greenhouse Gas Inhibitors
Authors: Langston Lee S.
Published: July 2018

This article explains how combined cycle gas turbine (CCGT) power plants can help in reducing greenhouse gas from the atmosphere. In the last 25 years, the development and deployment of CCGT power plants represent a technology breakthrough in efficient energy conversion, and in the reduction of greenhouse gas production. Existing gas turbine CCGT technology can provide a reliable, on-demand electrical power at a reasonable cost along with a minimum of greenhouse gas production. Natural gas, composed mostly of methane, is a hydrocarbon fuel used by CCGT power plants. Methane has the highest heating value per unit mass of any of the hydrocarbon fuels. It is the most environmentally benign of fuels, with impurities such as sulfur removed before it enters the pipeline. If a significant portion of coal-fired Rankine cycle plants are replaced by the latest natural gas-fired CCGT power plants, anthropogenic carbon dioxide released into the earth’s atmosphere would be greatly reduced.
Reduced Chemical Kinetic Mechanisms for Oxy/Methane Supercritical CO2 Combustor Simulations
Authors: Manikantachari K. R. V. , Vesely Ladislav , Martin Scott , Bobren-Diaz Jose O. , Vasu Subith
Published: July 2018

Reduced mechanisms are needed for use with computational fluid dynamic codes (CFD) utilized in the design of combustors. Typically, reduced mechanisms are created from a detailed mechanism, which contain numerous species and reactions that are computationally difficult to handle using most CFD codes. Recently, it has been shown that the detailed aramco 2.0 mechanism well predicted the available experimental data at high pressures and in highly CO2 diluted methane mixtures. Here, a 23-species gas-phase mechanism is derived from the detailed aramco 2.0 mechanism by path-flux-analysis method (PFA) by using CHEM-RC. It is identified that the reaction CH4 + HO2 ⇔ CH3 + H2O2 is very crucial in predicting the ignition delay times (IDTs) under current conditions. Further, it is inferred that species C2H3 and CH3OH are very important in predicting IDTs of lean sCO2 methane mixtures. Also, the 23-species mechanism presented in this work is able to perform on par with the detailed aramco 2.0 mechanism in terms of simulating IDTs, perfectly stirred-reactor (PSR) estimates under various CO2 dilutions and equivalence ratios, and prediction of turbulence chemistry interactions. It is observed that the choice of equation of state has no significant impact on the IDTs of supercritical CH4/O2/CO2 mixtures but it influences supercritical H2/O2/CO2 mixtures considered in this work.
Real-Time Processing of Engine Acoustic Emission for Diesel Injectors Diagnostic and Recentering
Authors: Ponti Fabrizio , Ravaglioli Vittorio , De Cesare Matteo
Published: July 2018

Diesel engine control strategies use complex injection patterns which are designed to meet the increasing request for engine-out emissions and fuel consumption reduction. As a result of the large number of tuneable injection parameters in modern injection systems (such as start and duration of each injection), injection patterns can be designed with many degrees-of-freedom. Each variation of the injection parameters modifies the whole combustion process and, consequently, engine-out emissions. Aging of the injection system usually affects injection location within the cycle as well as the amount of injected fuel (compared to the target value), especially for small pre-injections. Since diesel combustion is very sensitive to injection pattern variations, aging of injectors strongly affects engine behavior, in terms of both efficiency and pollutant emissions production. Moreover, such variations greatly affect other quantities related to the effectiveness of the combustion process, such as noise radiated by the engine. This work analyses the effects of pre-injection variations on combustion, pollutant emissions, and noise radiated by the engine. In particular, several experimental tests were run on a 1.3 L common rail diesel engine varying the amount of fuel injected in pre-injections. Torque delivered by the engine and center of combustion (MFB50) were kept constant using a specifically designed closed-loop combustion controller. During the tests, noise radiated by the engine was measured by properly processing the signal coming from a microphone faced to the engine block. The investigation of the correlation between the combustion process and engine noise can be used to setup a closed-loop algorithm for detecting and recentering injectors' drifts over time.
A Quantification of Jet Speed and Nanofiber Deposition Rate in Near-Field Electrospinning Through Novel Image Processing
Authors: Kim Jonghyun , Shin Dongwoon , Han Kyu-Bum , Chang Jiyoung
Published: July 2018

Electrospinning, one of the most effective ways of producing nanofibers, has been applied in as many fields throughout its long history. Starting with far-field electrospinning (FFES) and advancing to the near-field, the application area has continued to expand, but lack of understanding of the exact jet speed and fiber deposition rate is a major obstacle to entry into precision micro- to nano-scale manufacturing. In this paper, we, for the first time, analyze and predict the jet velocity and deposition rate in near-field electrospinning (NFES) through novel image analysis process. Especially, analog image is converted into a digital image, and then, the area occupied by the deposited fiber is converted into a velocity, through which the accuracy of the proposed method is proved to be comparable to direct jet speed measurement. Finally, we verified the proposed method can be applied to various process conditions without performing delicate experiments. This research not only will broaden the understanding of jet speed and fiber deposition rate in NFES but also will be applicable to various areas including patterning of the sensor, a uniform arrangement of nanofibers, energy harvester, reinforcing of composite, and reproducing of artificial tissue.
Experimental Evidence of Vibrational Resonance in a Mechanical Bistable Twin-Well Oscillator
Authors: Abusoua Abdrouf , Daqaq Mohammed F.
Published: July 2018

Vibrational resonance (VR) is a nonlinear phenomenon which occurs when a bistable system is subjected to a biharmonic excitation consisting of a small-amplitude resonant excitation and a large-amplitude high-frequency excitation. The result is that, under some conditions, the high-frequency excitation amplifies the resonant response associated with the slow dynamics. While VR was studied extensively in the open literature, most of the research studies used optical and electrical systems as platforms for experimental investigation. This paper provides experimental evidence that VR can also occur in a mechanical bistable twin-well oscillator and discusses the conditions under which VR is possible. The paper also demonstrates that the injection of the high frequency excitation can be used to change the effective stiffness of the slow response. This can be used for amplification/deamplification of the output signal which can be useful for sensitivity enhancement and/or vibration mitigation.
Experimental Study on Pressure Losses in Circular Orifices With Inlet Cross Flow
Authors: Feseker Daniel , Kinell Mats , Neef Matthias
Published: July 2018

The ability to understand and predict the pressure losses of orifices is important in order to improve the air flow within the secondary air system. This experimental study investigates the behavior of the discharge coefficient for circular orifices with inlet cross flow which is a common flow case in gas turbines. Examples of this are at the inlet of a film cooling hole or the feeding of air to a blade through an orifice in a rotor disk. Measurements were conducted for a total number of 38 orifices, covering a wide range of length-to-diameter ratios, including short and long orifices with varying inlet geometries. Up to five different chamfer-to-diameter and radius-to-diameter ratios were tested per orifice length. Furthermore, the static pressure ratio across the orifice was varied between 1.05 and 1.6 for all examined orifices. The results of this comprehensive investigation demonstrate the beneficial influence of rounded inlet geometries and the ability to decrease pressure losses, which is especially true for higher cross flow ratios where the reduction of the pressure loss in comparison to sharp-edged holes can be as high as 54%. With some exceptions, the chamfered orifices show a similar behavior as the rounded ones but with generally lower discharge coefficients. Nevertheless, a chamfered inlet yields lower pressure losses than a sharp-edged inlet. The obtained experimental data were used to develop two correlations for the discharge coefficient as a function of geometrical as well as flow properties.
Formulation of Euler–Lagrange Equations for Multidelay Fractional Optimal Control Problems
Authors: Effati Sohrab , Ali Rakhshan Seyed , Saqi Samane
Published: July 2018

In this paper, a new numerical scheme is proposed for multidelay fractional order optimal control problems where its derivative is considered in the Grunwald–Letnikov sense. We develop generalized Euler–Lagrange equations that results from multidelay fractional optimal control problems (FOCP) with final terminal. These equations are created by using the calculus of variations and the formula for fractional integration by parts. The derived equations are then reduced into system of algebraic equations by using a Grunwald–Letnikov approximation for the fractional derivatives. Finally, for confirming the accuracy of the proposed approach, some illustrative numerical examples are solved.
Metamaterial Window Glass
Authors: Heltzel Alex , Mann Tyler , Howell John R.
Published: July 2018

A computational study of a metamaterial (MTM)-on-glass composite is presented for the purpose of increasing the energy efficiency of buildings in seasonal or cold climates. A full-spectrum analysis yields the ability to predict optical and thermal transmission properties from ultraviolet through far-infrared frequencies. An opportunity to increase efficiency beyond that of commercial low-emissivity glass is identified through a MTM implementation of Ag and dielectric thin-film structures. Three-dimensional finite difference time-domain (FDTD) simulations predict selective nonlinear absorption of near-infrared energy, providing the means to capture a substantial portion of solar energy during cold periods, while retaining high visible transmission and high reflectivity in far-infrared frequencies. The effect of various configuration parameters is quantified, with prediction of the net sustainability advantage. MTM window glass technology can be realized as a modification to commercial low-emissivity windows through the application of nanomanufactured films, creating the opportunity for both new and after-market sustainable construction.
Lattice Boltzmann Method for Combined Natural Convection Surface Radiation in Open Cavity
Authors: Msaddak Ayoub , Ben Salah Mohieddine , Sediki Ezeddine
Published: July 2018

Lattice Boltzmann method (LBM) is performed to study numerically combined natural convection and surface radiation inside an inclined two-dimensional open square cavity. The cavity is heated by a constant temperature at the wall facing the opening. The walls normal to the heated surface are assumed to be adiabatic, diffuse, gray, and opaque while the open boundary is assumed to be black at ambient temperature. A Bathnagar, Gross and Krook (BGK) collision model with double distribution function (D2Q9-D2Q4) is adopted. Effects of surface radiation, inclination angle, and Rayleigh number on the heat transfer are analyzed and discussed. Results are presented in terms of isotherms, streamlines, and Nusselt number. It was found that the presence of surface radiation enhances the heat transfer. The convective Nusselt number decreases with increasing surface emissivity as well as with Rayleigh number, while the total Nusselt number increases with increasing surface emissivity and Rayleigh number. The inclination angle has also a significant effect on flow and heat transfer inside the cavity. However, the magnitude of total heat transfer decreases considerably when open cavity is tilted downward.
Study the Effect of Tapering on the Nonlinear Behavior of an Exponentially Varying Width Piezoelectric Energy Harvester
Authors: Salmani H. , Rahimi G. H.
Published: July 2018

It has been shown that exponentially tapering the width of a vibration-based piezoelectric energy harvester will result in increasing electric power per mass in a specified frequency. In this paper, a nonlinear solution of an exponentially decreasing width piezoelectric energy harvester is presented. Piezoelectric, inertial, and geometric nonlinearities are included in the presented model, while the exponentially tapered piezoelectric beam's mass normalized mode shapes are utilized in Galerkin discretization. The developed nonlinear coupled equations of motion are solved using method of multiple scales (MMS), and the steady states results are verified by experiment in high amplitude excitation. Finally, the exponentially tapering parameter effect is studied, and it is concluded that the voltage per mass of the energy harvester is improved by tapering at high exciting acceleration amplitudes.
Effects of Area Ratio and Mean Rise Angle on the Aerodynamics of Interturbine Ducts
Authors: Zhang Yanfeng , Hu Shuzhen , Mahallati Ali , Zhang Xue-Feng , Vlasic Edward
Published: July 2018

This work, a continuation of a series of investigations on the aerodynamics of aggressive interturbine ducts (ITD), is aimed at providing detailed understanding of the flow physics and loss mechanisms in four different ITD geometries. A systematic experimental and computational study was carried out by varying duct outlet-to-inlet area ratios (ARs) and mean rise angles while keeping the duct length-to-inlet height ratio, Reynolds number, and inlet swirl constant in all four geometries. The flow structures within the ITDs were found to be dominated by the boundary layer separation and counter-rotating vortices in both the casing and hub regions. The duct mean rise angle determined the severity of adverse pressure gradient in the casing's first bend, whereas the duct AR mainly governed the second bend's static pressure rise. The combination of upstream wake flow and the first bend's adverse pressure gradient caused the boundary layer to separate and intensify the strength of counter-rotating vortices. At high mean rise angle, the separation became stronger at the casing's first bend and moved farther upstream. At high ARs, a two-dimensional separation appeared on the casing and resulted in increased loss. Pressure loss penalties increased significantly with increasing duct mean rise angle and AR.
State-of-the-Art Cooling Technology for a Turbine Rotor Blade
Authors: Town Jason , Straub Douglas , Black James , Thole Karen A. , Shih Tom I-P.
Published: July 2018

Effective internal and external cooling of airfoils is key to maintaining component life for efficient gas turbines. Cooling designs have spanned the range from simple internal convective channels to more advanced double-walls with shaped film-cooling holes. This paper describes the development of an internal and external cooling concept for a state-of-the-art cooled turbine blade. These cooling concepts are based on a review of literature and patents, as well as, interactions with academic and industry turbine cooling experts. The cooling configuration selected and described in this paper is referred to as the “baseline” design, since this design will simultaneously be tested with other more advanced blade cooling designs in a rotating turbine test facility using a “rainbow turbine wheel” configuration. For the baseline design, the leading edge is cooled by internal jet impingement and showerhead film cooling. The midchord region of the blade contains a three-pass serpentine passage with internal discrete V-shaped trip strips to enhance the internal heat transfer coefficient (HTC). The film cooling along the midchord of the blade uses multiple rows of shaped diffusion holes. The trailing edge is internally cooled using jet impingement and externally film cooled through partitioned cuts on the pressure side of the blade.
A Design of Coverage Area for Textured Surface of Sliding Journal Bearing Based on Genetic Algorithm
Authors: Zhang Hui , Hafezi Mahshid , Dong Guangneng , Liu Yang
Published: July 2018

This paper aims to improve the tribological performance of journal bearings by optimizing the coverage area of circular microtextures in divergent region of the sleeve. A numerical model is proposed to calculate the friction coefficient and bearing load of textured journal bearings. The surface of the sleeve is divided into rectangular squares. Textures that located at the center of rectangular grids are assumed to be present or absent, marked as 1 and 0, respectively. Afterward, different texture coverage area arrangements are evolved and selected based on the genetic algorithm (GA). The area of semi-elliptical shape is obtained as the novel and preferable textured coverage area design for journal bearings. Influences of width and eccentricity ratio are discussed, which confirm the semimajor and semiminor axes of the semi-elliptical shape of texture coverage area equal to one-third of the circumferential length and half of the width of the journal bearing, respectively.
Application of Monte Carlo Simulation to Design of Sampler and Detector in Radiation Monitoring System
Authors: Sugihara Kei , Sakai Hirotaka , Hattori Kanako , Tanaka Genki , Hayashi Mitsunobu , Ito Toshiaki , Oda Naotaka
Published: July 2018

In this study, the applicability of Monte Carlo code particle and heavy ion transport code system (PHITS) [Sato et al. (2013, “Particle and Heavy Ion Transport Code System PHITS, Version 2.52,” J. Nucl. Sci. Technol., 50(9), pp. 913–923)] to the equipment design of sampler and detector in the radiation monitoring system was evaluated by comparing calculation results with experimental results obtained by actual measurements of radioactive materials. In modeling a simulation configuration, reproducing the energy distribution of beta-ray emitted from specific nuclide by means of Fermi Function was performed as well as geometric arrangement of the detector in the sampler volume. The reproducing and geometric arrangement proved that the calculation results are in excellent matching with actual experimental results. Moreover, reproducing the Gaussian energy distribution to the radiation energy deposition was performed according to experimental results obtained by the multi-channel analyzer. Through the modeling and the Monte Carlo simulation, key parameters for equipment design were identified and evaluated. Based on the results, it was confirmed that the Monte Carlo simulation is capable of supporting the evaluation of the equipment design.
Challenges in Three-Dimensional Printing of High-Conductivity Copper
Authors: El-Wardany Tahany I. , She Ying , Jagdale Vijay N. , Garofano Jacquelynn K. , Liou Joe J. , Schmidt Wayde R.
Published: July 2018

With recent advancements in additive manufacturing (AM) technology, it is possible to deposit copper conductive paths and insulation layers of an electric machine in a selective controlled manner. AM of copper enables higher fill factors that improves the internal thermal conduction in the stator core of the electric machine (induction motor), which will enhance its efficiency and power density. This will reduce the motor size and weight and make it more suitable for aerospace and electric vehicle applications, while reducing/eliminating the rare-earth dependency. The objective of this paper is to present the challenges associated with AM of copper coils having 1 × 1 mm cross section and complex features that are used in producing ultra-high efficiency induction motor for traction applications. The paper also proposes different approaches that were used by the authors in attempts to overcome those challenges. The results of the developed technologies illustrate the important of copper powder treatment to help in flowing the powder easier during deposition. In addition, the treated powder has higher resistance to surface oxidation, which led to a high reduction in porosity formation and improved the quality of the copper deposits. The laser powder direct energy deposition (LPDED) process modeling approach helps in optimizing the powder deposition path, the laser power, and feed rate that allow the production of porosity free thin wall and thin floor components. The laser powder bed fusion (LPBF) models identify the optimum process parameters that are used to produce test specimens with >90% density and minimum porosity.
A Novel Four-Dimensional No-Equilibrium Hyper-Chaotic System With Grid Multiwing Hyper-Chaotic Hidden Attractors
Authors: Zhang Sen , Zeng Yi Cheng , Jun Li Zhi
Published: July 2018

By using a simple state feedback control technique and introducing two new nonlinear functions into a modified Sprott B system, a novel four-dimensional (4D) no-equilibrium hyper-chaotic system with grid multiwing hyper-chaotic hidden attractors is proposed in this paper. One remarkable feature of the new presented system is that it has no equilibrium points and therefore, Shil'nikov theorem is not suitable to demonstrate the existence of chaos for lacking of hetero-clinic or homo-clinic trajectory. But grid multiwing hyper-chaotic hidden attractors can be obtained from this new system. The complex hidden dynamic behaviors of this system are analyzed by phase portraits, the time domain waveform, Lyapunov exponent spectra, and the Kaplan–York dimension. In particular, the Lyapunov exponent spectra are investigated in detail. Interestingly, when changing the newly introduced nonlinear functions of the new hyper-chaotic system, the number of wings increases. And with the number of wings increasing, the region of the hyper-chaos is getting larger, which proves that this novel proposed hyper-chaotic system has very rich and complicated hidden dynamic properties. Furthermore, a corresponding improved module-based electronic circuit is designed and simulated via multisim software. Finally, the obtained experimental results are presented, which are in agreement with the numerical simulations of the same system on the matlab platform.
Weathering/Ageing of Liquefied Natural Gas Cargoes During Marine Transport and Processing on Floating Storage Units and FSRU
Authors: Wood David A. , Kulitsa Maksym
Published: July 2018

The phenomenon of liquefied natural gas (LNG) cargo weathering is considered in terms of the conditions influencing boil-off gas (BOG) rates during the offshore movements and handling of LNG on marine LNG carriers (LNGC), floating storage and regasification unit (FSRU), and floating storage units (FSU). The range of compositions (grades) of commercially traded LNG is significantly broader than the range of compositional changes caused by typical storage times for offshore LNG cargoes. The different nitrogen and natural gas–liquid concentrations of LNG cargoes (i.e., ethane and heavier C2+ components) significantly influence the impacts of weathering and ultimately determine whether the LNG delivered to customers is within sales specifications or not. The BOG from LNG in storage is richer in methane and nitrogen; if nitrogen is present in the LNG, otherwise just richer in methane, than the LNG from which it is derived. This leads to the LNG becoming richer in the C2+ components as ageing progresses. LNG weathering is shown not to play a significant role in the rollover phenomenon of LNG moved and stored offshore, because nitrogen contents are low (typically < 1.0%) and auto-stratification is rarely an issue. LNG stored for long periods on FSU (greater than 8 weeks, or so) experiences significant weathering effects, but most LNG processed by FSRU (and most FSU) has a residence time of less than 30 days or so, in which case weathering has only minor operational impacts. Weathering rates and LNG compositional changes on FSRU for different LNG grades are provided.
Analysis of Spatial and Temporal Step Parameters During Crutch-Assisted Gait as a Dual-Task: A Pilot Study
Authors: Ridao-Fernández Carmen , Ojeda Joaquín , Chamorro-Moriana Gema
Published: July 2018

The main objective was to analyze the changes in the spatial and temporal step parameters during a dual-task: walking with a forearm crutch to partially unload the body weight of the subject. The secondary objective was to determine the influence of the use of the crutch with the dominant or nondominant hand in the essential gait parameters. Seven healthy subjects performed gait without crutches (GWC) and unilateral assisted gait (UAG) with the crutch carried out by dominant hand (dominant crutch (DC)) and nondominant hand (nondominant crutch (NDC)). Gait was recorded using a Vicon System; the GCH System 2.0 and the GCH Control Software 1.0 controlled the loads. The variables were step length, step period, velocity, step width, and step angle. The Wilcoxon signed-rank test compared GWC and UAG while also analyzing the parameters measured for both legs with DC and NDC in general and in each subject. Wilcoxon test only found significant differences in 1 of the 15 general comparisons between both legs. In the analysis by subject, step length, step period, and velocity showed significant differences between GWC and UAG. These parameters obtained less differences in DC. The effect of a forearm crutch on UAG caused a reduction in step length and velocity, and an increase in step period. However, it did not entail changes in step angle and step width. UAG was more effective when the DC carried the crutch. The unloading of 10% body weight produced an assisted gait which closely matched GWC.
A Novel Parameter Optimization Method for the Driving System of High-Speed Parallel Robots
Authors: Liu Xin-Jun , Han Gang , Xie Fugui , Meng Qizhi , Zhang Sai
Published: July 2018

Driving system parameters optimization, especially the optimal selection of specifications of motor and gearbox, is very important for improving high-speed parallel robots' performance. A very challenging issue is parallel robots' performance evaluation that should be able to illustrate robots' performance accurately and guide driving system parameters optimization effectively. However, this issue is complicated by parallel robots' anisotropic translational and rotational dynamic performance, and the multiparameters of motors and gearboxes. In this paper, by separating the influence of translational and rotational degrees-of-freedom (DOFs) on robots' performance, a new dynamic performance index is proposed to reflect the driving torque in instantaneous acceleration. Then, the influence of driving system's multiparameters on robots' driving torque in instantaneous acceleration and cycle time in continuous motion is investigated. Based on the investigation, an inertia matching index is further derived which is more suitable for minimizing the driving torque of parallel robots with translational and rotational DOFs. A comprehensive parameterized performance atlas is finally established. Based on this atlas, the performance of a high-speed parallel robot developed in this paper can be clearly evaluated, and the optimal combination of motors and gearboxes can be quickly selected to ensure low driving torque and high pick-and-place frequency.
Optimizing Design With Extensive Simulation Data: A Case Study of Designing a Vacuum-Assisted Biopsy Tool
Authors: Lin Chi-Lun , Coffey Dane , Keefe Daniel , Erdman Arthur
Published: July 2018

Design by Dragging (DBD) [1] is a virtual design tool, which displays three-dimensional (3D) visualizations of many simulation results obtained by sampling a large design space and ties this visual display together with a new user interface. The design space is explored through mouse-based interactions performed directly on top of the 3D data visualizations. Our previous study [1] introduced the realization of DBD with a simplistic example of biopsy needle design under a static bending force. This paper considers a realistic problem of designing a vacuum-assisted biopsy (VAB) needle that brings in more technical challenges to include dynamic tissue reaction forces, nonlinear tissue deformation, and progressive tissue damage in an integrated visualization with design suggestions. The emphasis is placed on the inverse design strategy in DBD, which involves clicking directly on a stress (or other output field parameter) contour and dragging it to a new (usually preferable) position on the contour. Subsequently, the software computes the best fit for the design variables for generating a new output stress field based on the user input. Three cases demonstrated how the inverse design can assist users in intuitively and interactively approaching desired design solutions. This paper illustrates how virtual prototyping may be used to replace (or reduce reliance on) purely experimental trial-and-error methods for achieving optimal designs.
Transient Optimization of Natural Gas Networks Using Intelligent Algorithms
Authors: Khanmirza Esmaeel , Madoliat Reza , Pourfard Ali
Published: July 2018

Compressor stations in natural gas networks should perform such that time-varying demands of customers are fulfilled while all of the system constraints are satisfied. Power consumption of compressor stations impose the most operational cost to a gas network so their optimal performance will lead to significant money saving. In this paper, the gas network transient optimization problem is addressed. The objective function is the sum of the compressor's power consumption that should be minimized where compressor speeds and the value status are decision variables. This objective function is nonlinear which is subjected to nonlinear and combinatorial constraints including both discrete and continuous variables. To handle this challenging optimization problem, a novel approach based on using two different structure intelligent algorithms, namely the particle swarm optimization (PSO) and cultural algorithm (CA), is utilized to find the optimum of the decision variables. This approach removes the necessity of finding an explicit expression for the power consumption of compressors as a function of decision variables as well as the calculation of objective function derivatives. The objective function and constraints are evaluated in the transient condition by a fully implicit finite difference numerical method. The proposed approach is applied on a real gas network where simulation results confirm its accuracy and efficiency.
Thermodynamic Analysis on Reaction Characteristics of the Coupling Steam, CO2 and O2 Reforming of Methane
Authors: Yan Yunfei , Yan Hongyu , Li Lixian , Zhang Li , Yang Zhongqing
Published: July 2018

This study presents an analysis of coupling steam, CO2 and O2 reforming of CH4 using the thermodynamic equilibrium constant method. Effects of molar ratio of O2/CH4, H2O/CH4 and CO2/CH4 on reforming characteristics in both carbon deposition and carbon-free systems are analyzed. The results indicate that CH4 conversion rate, H2, and CO yield increase with increasing O2/CH4 molar ratio in two systems. In addition, the carbon elimination is achieved when O2/CH4 ratio increases to 0.31, and changing the amount of O2 can be an effective way to alter n(H2)/n(CO) ratio in the carbon deposition systems. CH4 conversion rate increases with increasing H2O/CH4 ratio in the carbon-free system, while it declines in the carbon deposition system. H2O plays a role of altering n(H2)/n(CO) ratio, and its effects on two systems are opposite. The deposited carbon is totally eliminated when H2O/CH4 ratio increases to 0.645. The increase of CO2/CH4 molar ratio leads to a rapid increase of CO2 conversion when CO2/CH4 ratio is less than 0.5. A slightly change of CO2/CH4 ratio can result in a huge difference on n(H2)/n(CO) ratio in both systems, and carbon elimination is achieved at CO2/CH4 = 0.99. The analyzed results have theoretical significance to efficiently catalyze methane coupling.
Compact Direct Methanol Fuel Cell: Design Approach Using Commercial Micropumps
Authors: McDonald Robert C. , Hamdan Monjid
Published: July 2018

Direct methanol fuel cells (DMFC) are typically supplied under pressure or capillary action with a solution of methanol in water optimized for the best specific power and power density at an operating temperature of about 60 °C. Methanol and water consumption at the anode together with water and methanol losses through membrane due to crossover create an imbalance over time so the fuel concentration at the anode drifts from the optimal ratio. In the present study, we demonstrate a DMFC with a means for continuous adjustment of water and methanol content in the anode fuel mixture of an air-breathing DMFC to maintain the optimal concentration for maximum and continuous power. Two types of piezoelectric micropumps were programmed to deliver the two liquids at the designated rate to maintain optimal concentration at the anode during discharge. The micropumps operate over a wide range of temperature, can be easily reprogrammed and can operate in any orientation. A study of performance at different current densities showed that at 100 mA/cm2, the self-contained, free convection, air-breathing cell delivers 31.6 mW/cm2 of electrode surface with thermal equilibrium reached at 52 °C. The micropumps and controllers consume only 2.6% of this power during 43 h of continuous unattended operation. Methanol utilization is 1.83 Wh cm−3.
A Method for Calculating and Continuing Static Solutions for Flexible Multibody Systems
Authors: Meijaard J. P.
Published: July 2018

A method to calculate static solutions for mechanical systems containing rigid and flexible bodies modeled by finite elements is described. The formulation of the equations makes use of generalized strains, which leads to an extended set of equations for both these generalized strains and nodal coordinates, together with constraint equations imposing the relations between these two groups of coordinates. The associated Lagrangian multipliers are the generalized stresses. The resulting iteration scheme appears to be quite robust in comparison with more traditional methods, especially if some displacements are prescribed. Once a static solution has been found, the linearized equations of motion about this solution can be obtained in terms of a set of minimal coordinates, that is, in the degrees-of-freedom (DOFs). In addition, a continuation method is described for tracing a branch of static solutions if some parameters are varied. The method is of the familiar predictor–corrector type with a linear or cubic predictor and a corrector with a step size constraint. Applications to a large-deflection problem of a curved cantilever beam, large deflections of a fluid-conveying tube and its resulting instability, and the buckling of an overconstrained parallel leaf-spring mechanism due to misalignment are given.
Enhanced Heat Transfer Using Microporous Copper Inverse Opals
Authors: Lee Hyoungsoon , Maitra Tanmoy , Palko James , Kong Daeyoung , Zhang Chi , Barako Michael T. , Won Yoonjin , Asheghi Mehdi , Goodson Kenneth E.
Published: July 2018

Enhanced boiling is one of the popular cooling schemes in thermal management due to its superior heat transfer characteristics. This study demonstrates the ability of copper inverse opal (CIO) porous structures to enhance pool boiling performance using a thin CIO film with a thickness of ∼10 μm and pore diameter of 5 μm. The microfabricated CIO film increases microscale surface roughness that in turn leads to more active nucleation sites thus improved boiling performance parameters such as heat transfer coefficient (HTC) and critical heat flux (CHF) compared to those of smooth Si surfaces. The experimental results for CIO film show a maximum CHF of 225 W/cm2 (at 16.2 °C superheat) or about three times higher than that of smooth Si surface (80 W/cm2 at 21.6 °C superheat). Optical images showing bubble formation on the microporous copper surface are captured to provide detailed information of bubble departure diameter and frequency.
Damkohler Number Analysis in Lean Blow-Out of Toroidal Jet Stirred Reactor
Authors: Guan Yifei , Novosselov Igor
Published: July 2018

Lean blowout (LBO) prediction based on the local parameters in the laboratory toroidal jet-stirred reactor (TJSR) is investigated. The reactor operated on methane is studied using three-dimensional computational fluid dynamics (CFD); the results are compared with the experimental data. Skeletal chemical kinetic mechanism with the eddy dissipation concept (EDC) model is used. Flow bifurcation in the radial (poloidal) plane due to the interaction between counter-rotating vortices creates one dominating poloidal recirculation zone (PRZ) and one weaker toroidal recirculation zone (TRZ). The Damkohler (Da) number in the reactor is the highest in the stabilization vortex; it varies from about Da ∼ 2 at ϕ = 0.55 to Da ∼ 0.2–0.3 at LBO conditions. Due to the reduced turbulent dissipation rate in PRZ, the Da number is an order of magnitude higher than in TRZ. The global blowout event is predicted at the local Da = 0.2 in PRZ. Local blowout events in the regions of low Da can lead to flame instability and to a global flame blowout at a higher fuel–air ratio than predicted by the CFD. Local Da nonuniformity can be used for optimization and analysis of combustion system stability. Further research in the process parameterization and application to the practical combustion system is needed.
Increasing Inducer Stability and Suction Performance With a Stability Control Device
Authors: Lundgreen R. , Maynes D. , Gorrell S. , Oliphant K.
Published: July 2018

An inducer is used as the first stage of high suction performance pump. It pressurizes the fluid to delay the onset of cavitation, which can adversely affect performance in a centrifugal pump. In this paper, the performance of a water pump inducer has been explored with and without the implementation of a stability control device (SCD). This device is an inlet cover bleed system that removes high-energy fluid near the blade leading edge and reinjects it back upstream. The research was conducted by running multiphase, time-accurate computational fluid dynamic (CFD) simulations at the design flow coefficient and at low, off-design flow coefficients. The suction performance and stability for the same inducer with and without the implementation of the SCD has been explored. An improvement in stability and suction performance was observed when the SCD was implemented. Without the SCD, the inducer developed backflow at the blade tip, which led to rotating cavitation and larger rotordynamic forces. With the SCD, no significant cavitation instabilities developed, and the rotordynamic forces remained small. The lack of cavitation instabilities also allowed the inducer to operate at lower inlet pressures, increasing the suction performance of the inducer.
Strengthening Effect of Soft Thin Coatings
Authors: Goltsberg R. , Levy S. , Kligerman Y. , Etsion I.
Published: July 2018

A finite element analysis was used to study the onset of plasticity of a coated sphere compressed by a rigid flat. This was done for soft coatings on a harder substrate. Generally, the results agree very well with the findings in the literature for the opposite case of an indentation of a rigid sphere into a coated flat, with a soft coating. In this case, a weakening prevails over the entire range of coating thicknesses, resulting in critical loads (at yield inception) lower than the critical load of the uncoated contact. However, a surprising strengthening effect was discovered, in this study, for very thin coating thicknesses resulting in a higher resistance to plasticity, compared to an uncoated sphere. This phenomenon resembles a mirror image of the opposite weakening effect which was reported for very thin hard coatings. These results may suggest that when very thin coatings are to be applied in a spherical contact, a softer, rather than harder, coating should be considered in order to increase the contact's resistance to plasticity inception.
Analysis of Cone Wave Reflection in Finite-Size Elastic Membranes and Extension of the Ballistic Impact Problem From Elastic to Viscoelastic Membranes
Authors: Singh Amit , Keten Sinan
Published: July 2018

The transverse ballistic impact on a two-dimensional (2D) membrane causes a truncated deformation cone to develop in the wake of tensile implosion waves. Here, the cone wave reflected from the finite boundaries of the elastic membrane has been studied analytically. A first-order linear nonhomogeneous differential equation for the ratio of the reflected cone wave front velocity to the speed of tensile waves is derived, which is further used to calculate the traveling time taken by the reflected cone wave to reach to the projectile surface. Since the reflected wave starts when the membrane is already in a deformed configuration, the speed of the reflected cone wave is a function of radius r in the cylindrical coordinates as opposed to almost constant speed of the incoming cone wave studied in the literature. The analytical results are validated with molecular dynamics (MD) simulations of the ballistic impact of projectiles onto a single layer of coarse-grained (CG) graphene. In the second part of the paper, we analyze the membrane impact problem for linear isotropic viscoelastic materials and find that the tensile wave speed for stresses and displacements is the same as that obtained in the case of a linear isotropic elastic material. We also show that only under special conditions, self-similar solutions for the cone wave are possible in viscoelastic materials modeled by Maxwell, Kelvin–Voigt, or a combination of similar models. Our findings lay some grounds on which further studies on the ballistic response of viscoelastic materials can be performed.
Experimental Evidence of the Thermal Cloak Based on the Path Design of the Heat Flux
Authors: He Xiao , Yang Tianzhi , Wu Linzhi
Published: July 2018

We recently showed theoretically that the infinite singularity of the thermal cloak designed by transformation thermodynamics could be eliminated by a new method—the path design of the heat flux without any approximation. In this paper, we present the experimental evidence of such a new strategy of thermal cloak, that is, a truly singularity-free thermal cloak. We fabricate such a transient thermal cloak device without using extreme material parameters. The experimental results show fully controlled, transient cloaking behavior, which are perfectly consistent with the theoretical derivations and simulated results. Since one can flexibly design the path of heat flux in the cloak, it has the large degree-of-freedom to construct thermal cloaks with the specific distributions of material parameters. The new method provides a new blue print for the transient thermal protection of a specific target.
Experimental Analysis of Dielectric Barrier Discharge Plasma Actuators Thermal Characteristics Under External Flow Influence
Authors: Rodrigues F. F. , Pascoa J. C. , Trancossi M.
Published: July 2018

Dielectric barrier discharge (DBD) plasma actuators have several applications within the field of active flow control. Separation control, wake control, aircraft noise reduction, modification of velocity fluctuations, or boundary layer control are just some examples of their applications. They present several attractive features such as their simple construction, very low mass, fast response, low power consumption, and robustness. Besides their aerodynamic applications, these devices have also possible applications within the field of heat transfer, for example film cooling applications or ice formation prevention. However, due to the extremely high electric fields in the plasma region and consequent impossibility of applying classic intrusive techniques, there is a relative lack of information about DBDs thermal characteristics. In an attempt to overcome this scenario, this work describes the thermal behavior of DBD plasma actuators under different flow conditions. Infra-red thermography measurements were performed in order to obtain the temperature distribution of the dielectric layer and also of the exposed electrode. During this work, we analyzed DBD plasma actuators with different dielectric thicknesses and also with different dielectric materials, whose thermal behavior is reported for the first time. The results allowed to conclude that the temperature distribution is not influenced by the dielectric thickness, but it changes when the actuator operates under an external flow. We also verified that, although in quiescent conditions the exposed electrode temperature is higher than the plasma region temperature, the main heat energy dissipation occurs in the dielectric, more specifically in the plasma formation region.