bluuebunny/crossref_metadata_2025 huggingface dataset:
Spiral Tool Path Generation Method on Mesh Surfaces Guided by Radial Curves
Authors: Xu Jinting , Ji Yukun , Sun Yuwen , Lee Yuan-Shin
Published: July 2018

This paper presents a new spiral smoothing method to generate smooth curved tool paths directly on mesh surfaces. Spiral tool paths are preferable for computer numerical control (CNC) milling, especially for high-speed machining. At present, most spiral tool path generation methods aim mainly for pocketing, and a few methods for machining complex surface also suffer from some inherent problems, such as selection of projecting direction, preprocessing of complex offset contours, easily affected by the mesh or mesh deformation. To address the limitations, a new spiral tool path method is proposed, in which the radial curves play a key role as the guiding curves for spiral tool path generation. The radial curve is defined as one on the mesh surface that connects smoothly one point on the mesh surface and its boundary. To reduce the complexity of constructing the radial curves directly on the mesh surface, the mesh surface is first mapped onto a circular region. In this region, the radial lines, starting from the center, are planned and then mapped inversely onto the mesh surface, thereby forming the desired radial curves. By traversing these radial curves using the proposed linear interpolation method, a polyline spiral is generated, and then, the unfavorable overcuts and undercuts are identified and eliminated by supplementing additional spiral points. Spline-based technique of rounding the corners is also discussed to smooth the polyline spiral, thereby obtaining a smooth continuous spiral tool path. This method is able to not only greatly simplify the construction of radial curves and spiral tool path but also to have the ability of processing and smoothing complex surfaces. Experimental results are presented to validate the proposed method.
Influence of the Spatial and Temporal Interaction Between Diesel Pilot and Directly Injected Natural Gas Jet on Ignition and Combustion Characteristics
Authors: Fink Georg , Jud Michael , Sattelmayer Thomas
Published: July 2018

In this paper, pilot-ignited high pressure dual-fuel combustion of a natural gas jet is investigated on a fundamental basis by applying two separate single-hole injectors to a rapid compression expansion machine (RCEM). A Shadowgraphy system is used for optical observations, and the combustion progress is assessed in terms of heat release rates (HRRs). The experiments focus on the combined influence of injection timing and geometrical jet arrangement on the jet interaction and the impact on the combustion process. In a first step, the operational range for successful pilot self-ignition and transition to natural gas jet combustion is determined, and the restricting phenomena are identified by analyzing the shadowgraph images. Within this range, the combustion process is assessed by evaluation of ignition delays and HRRs. Strong interaction is found to delay or even prohibit pilot ignition, while it facilitates a fast and stable onset of the gas jet combustion. Furthermore, it is shown that the HRR is governed by the time of ignition with respect to the start of natural gas injection—as this parameter defines the level of premixing. Evaluation of the time of gas jet ignition within the operability map can therefore directly link a certain spatial and temporal interaction to the resulting heat release characteristics. It is finally shown that controlling the HRR through injection timing variation is limited for a certain angle between the two jets.
Research on the Profile Design of Surface Texture in Piston Ring of Internal Combustion Engine
Authors: Bifeng Yin , Dashu Gao , Shao Sun , Bo Xu , Hekun Jia
Published: July 2018

In this paper, a profile design of surface texture was applied for improving the tribological performance of piston ring–cylinder pair. The design of texture pattern was implemented by numerous textures of different depths in sliding speed direction to imitate the outline of barrel-shaped ring. The thickness and pressure distribution of oil film were obtained through a joint solution of modified Reynolds equation and other governing equations for textured surface. The results indicate that the novel texture pattern has the best overall performance in oil film thickness and friction force compared with normal surface textures, and the average friction power is 10.04% and 16.85% less than normal surface textures and barrel-shaped ring in the whole working cycle. Extra microhydrodynamic lubrication can be observed in the middle region of textured piston ring through the pressure distribution of oil film. At last, the experiment was conducted in a motored test rig and exhibited up to 3% reduction in friction power.
Investigation of Temperature Separation Inside Various Models of Ranque–Hilsch Vortex Tube: Convergent, Straight, and Divergent With the Help of Computational Fluid Dynamic Approach
Authors: Bazgir Adib , Nabhani Nader
Published: July 2018

In this paper, a Ranque–Hilsch vortex tube (RHVT) has been optimized utilizing convergent (φ), straight, and divergent (θ) axial angles for hot-tube. Effects of divergent (θ) and convergent (φ) angles on the flow behavior have been investigated by computational fluid dynamic (CFD) techniques. By using a renormalization group (RNG) k–ε turbulence model based on finite volume method, all the computations have been carried out. The isentropic efficiency (ηis) and coefficient of performance (COP) of machine was studied under five different divergent angles (θ), namely 1 deg, 2 deg, 3 deg, 4 deg, and 6 deg, two different convergent (φ) angles (φ) namely 1 deg and 2 deg adjusted to the hot-tube. Furthermore, some geometrical and operational parameters including cold outlet diameter, hot-tube length, and different inlet pressures and mass flow rates have been analyzed in detail (spanwisely) in order to optimize the cooling efficiency of vortex tube (straight). The results show that utilizing the divergent hot-tubes increases the isentropic efficiency (ηis) and COP of device for most values of inlet pressures, and helps to become more efficient than the other shape of vortex tubes (straight and convergent). Finally, some results of the CFD models have been validated by the available experimental and numerical data, which show reasonable agreement, and others are compared qualitatively.
A Method to Double the Extension Ability of Radial Jet Drilling Technology
Authors: Jingbin Li , Guangqing Zhang , Gensheng Li , Zhongwei Huang , Weichang Li
Published: July 2018

Radial jet drilling (RJD) technology is an effective method to enhance oil and gas recovery by penetrating the near-wellbore damage zone, and increasing the drainage radius greatly. Recently, it is identified as a potential technology to develop the geothermal energy. But the extension ability, one of the most critical issues of the RJD, is limited. Because only high pressure flexible hose (HPFH), which is hard to be fed in and subjected to greater resistance by the diverter, can be used as the drill stem to turn from vertical to horizontal in the casing. In this paper, an innovative method to feed in the HPFH by the drag force generated by high velocity flow in narrow annulus is proposed. The drag force model is built, validated, and modified by theoretical and experimental ways. Results show that the resulting drag force, which is equivalent to the self-propelled force, can easily achieve and feed in the HPFH. There is a power law relationship between the drag force and the average velocity; the drag force increases linearly with the length of the narrow annulus. Higher average velocity and 1–1.5 m annulus length are recommended. According to force analysis, the extension ability of the RJD can be doubled theoretically by this method. The results of this paper will greatly promote the development of RJD technology.
Experimental Characterization and Numerical Modeling of the Interaction Between Carbon Fiber Composite Prepregs During a Preforming Process
Authors: Zhang Weizhao , Ma Xuan , Lu Jie , Zhang Zixuan , Jane Wang Q. , Su Xuming , Zeng Danielle , Mirdamadi Mansour , Cao Jian
Published: July 2018

Carbon fiber reinforced composites have received growing attention because of their superior performance and high potential for lightweight systems. An economic method to manufacture the parts made of these composites is a sequence of forming followed by a compression molding. The first step in this sequence is called preforming that forms the prepreg, which is the fabric impregnated with the uncured resin, to the product geometry, while the molding process cures the resin. Slip between different prepreg layers is observed in the preforming step, and it is believed to have a non-negligible impact on the resulting geometry. This paper reports a method to characterize the interaction between different prepreg layers, which should be valuable for future predictive modeling and design optimization. An experimental device was built to evaluate the interactions with respect to various industrial production conditions. The experimental results were analyzed for an in-depth understanding about how temperature, relative sliding speed, and fiber orientation affect the tangential interaction between two prepreg layers. Moreover, a hydro-lubricant model was introduced to study the relative motion mechanism of this fabric-resin-fabric system, and the results agreed well with the experiment data. The interaction factors obtained from this research will be implemented in a preforming process finite element simulation model.
A Comprehensive Wellbore Stability Model Considering Poroelastic and Thermal Effects for Inclined Wellbores in Deepwater Drilling
Authors: Chen Xuyue , Gao Deli , Yang Jin , Luo Ming , Feng Yongcun , Li Xin
Published: July 2018

Exploring and developing oil and gas in deepwater field is an important trend of the oil and gas industry. Development of deepwater oil and gas fields from a platform always requires a number of directional wells or extended reach wells targeting to different depth of water in various azimuth. Drilling of these wells is mostly associated with a series of wellbore instability problems that are not encountered in onshore or shallow water drilling. In the past decades, a number of studies on wellbore stability have been conducted. However, few of the models are specific for wellbore stability of the inclined deepwater wellbores. In this work, a comprehensive wellbore stability model considering poroelastic and thermal effects for inclined wellbores in deepwater drilling is developed. The numerical method of the model is also presented. The study shows that for a strike-slip stress regime, the wellbore with a low inclination poses more risk of wellbore instability than the wellbore with a high inclination. It also shows that cooling the wellbore will stabilize the wellbore while excessive cooling could cause wellbore fracturing, and the poroelastic effect could narrow the safe mud weight window. The highest wellbore collapse pressure gradients at all of the analyzed directions are obtained when poroelastic effect is taken into account meanwhile the lowest wellbore fracture pressure gradients at all of the analyzed directions are obtained when both of poroelastic effect and thermal effect are taken into account. For safe drilling in deepwater, both of thermal and poroelastic effects are preferably considered to estimate wellbore stability. The model provides a practical tool to predict the stability of inclined wellbores in deepwater drilling.
Thermal Performance Study of a Water Tank for a Solar System With a Fresnel Lens
Authors: Chen J. , Xu H. T. , Wang Z. Y. , Han S. P.
Published: July 2018

The heat transfer characteristics of a rectangular water tank used in a solar water heating system with a Fresnel Len were investigated qualitatively and quantitatively through the theoretical and numerical methods. The water tank is 450 mm × 400 mm × 500 mm in size and consists of 15 layers of coil pipe placed at its center. The MIX number and exergy efficiency were studied to quantify the thermal stratification of this water tank. A flow field analysis was also carried out to understand the heat transfer mechanism inside the water tank. Results indicate that the Nusselt number of shell side is increased with the growth of Reynolds number. The MIX number suggested that the thermal stratification is enhanced and then reduced with increasing flow rate. A correlation is proposed to predict the Nusselt numbers on the shell side. A detailed flow field analysis indicated that the thermal stratification is highly related to the runoff time, buoyancy force, mixing process, and geometry of the water tank.
Simultaneous Effects of Nonlinear Mixed Convection and Radiative Flow Due to Riga-Plate With Double Stratification
Authors: Hayat Tasawar , Ullah Ikram , Alsaedi Ahmed , Ahamad Bashir
Published: July 2018

This paper addresses nonlinear mixed convection flow due to Riga plate with double stratification. Heat transfer analysis is reported for heat generation/absorption and nonlinear thermal radiation. Physical problem is mathematically modeled and nonlinear system of partial differential equations is achieved. Transformations are then utilized to obtain nonlinear system of ordinary differential equations. Homotopic technique is utilized for the solution procedure. Graphical descriptions for velocity, temperature, and concentration distributions are captured and argued for several set of physical variables. Features of skin friction and Nusselt and Sherwood numbers are also illustrated. Our computed results indicate that the attributes of radiation and temperature ratio variables enhance the temperature distribution. Moreover, the influence of buoyancy ratio and modified Hartmann number has revers effects on rate of heat transfer.
On Development and Dry Sliding Wear Behavior of Microwave Processed Ni/Al2O3 Composite Clad
Authors: Singh Bhupinder , Kaushal Sarbjeet , Gupta Dheeraj , Bhowmick Hiralal
Published: July 2018

In the present experimental study, the application of microwave heating is used to develop the composite clads of Ni-based metallic powder (matrix) and Al2O3 powder (reinforcement) on the surface of AISI 304 stainless steel substrate. A domestic microwave oven working at 2.45 GHz frequency and 900 W was used to conduct the experimental trials. The Ni + 10% Al2O3 composite clads were characterized through X-ray diffractometer (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and microhardness tests. The pin-on-disk type tribometer was used for analyzing the sliding wear behavior of Ni + 10% Al2O3 clads. The microstructural results revealed the presence of randomly dispersed Al2O3 particles inside Ni matrix. The average microhardness (Vicker's) of composite clad was enhanced by 3.5 times that of the substrate. The clad exhibited 156 times more wear resistance than AISI 304 substrate. Craters and groove formation were responsible for wear loss in the clad material while plastic deformation caused the failure of AISI 304 substrate.
A Computational Investigation of Fuel Chemical and Physical Properties Effects on Gasoline Compression Ignition in a Heavy-Duty Diesel Engine
Authors: Zhang Yu , Voice Alexander , Pei Yuanjiang , Traver Michael , Cleary David
Published: July 2018

Gasoline compression ignition (GCI) offers the potential to reduce criteria pollutants while achieving high fuel efficiency. This study aims to investigate the fuel chemical and physical properties effects on GCI operation in a heavy-duty diesel engine through closed-cycle, three-dimensional (3D) computational fluid dynamic (CFD) combustion simulations, investigating both mixing-controlled combustion (MCC) at 18.9 compression ratio (CR) and partially premixed combustion (PPC) at 17.3 CR. For this work, fuel chemical properties were studied in terms of the primary reference fuel (PRF) number (0–91) and the octane sensitivity (0–6) while using a fixed fuel physical surrogate. For the fuel physical properties effects investigation, six physical properties were individually perturbed, varying from the gasoline to the diesel range. Combustion simulations were carried out at 1375 RPM and 10 bar brake specific mean pressure (BMEP). Reducing fuel reactivity was found to influence ignition delay time (IDT) more significantly for PPC than for MCC. 0D IDT calculations suggested that the fuel reactivity impact on IDT diminished with an increase in temperature. Moreover, higher reactivity gasolines exhibited stronger negative coefficient (NTC) behavior and their IDTs showed less sensitivity to temperature change. In addition, increasing octane sensitivity was observed to result in higher fuel reactivity and shorter IDT. Under both MCC and PPC, all six physical properties showed little impact on global combustion behavior, NOx, and fuel efficiency. Among the physical properties investigated, only density showed a notable effect on soot emissions. Increasing density led to higher soot due to deteriorated air entrainment into the spray and the slower fuel-air mixing process.
Failure of Rubber Bearings Under Combined Shear and Compression
Authors: Mythravaruni P. , Volokh K. Y.
Published: July 2018

Rubber bearings, used for seismic isolation of structures, undergo large shear deformations during earthquakes as a result of the horizontal motion of the ground. However, the bearings are also compressed by the weight of the structure and possible traffic on it. Hence, failure analysis of rubber bearings should combine compression and shear. Such combination is considered in the present communication. In order to analyze failure, the strain energy density is enhanced with a limiter, which describes rubber damage. The inception of material instability and the onset of damage are marked by the violation of the condition of strong ellipticity, which is studied in the present work. Results of the studies suggest that horizontal cracks should appear because of the dominant shear deformation in accordance with the experimental observations. It is remarkable that compression delays failure in terms of the critical stretches.
Fabrication of Zinc–Tungsten Carbide Nanocomposite Using Cold Compaction Followed by Melting
Authors: Hwang Injoo , Guan Zeyi , Li Xiaochun
Published: July 2018

Zinc (Zn) is an important material for numerous applications since it has pre-eminent ductility and high ultimate tensile strain, as well high corrosion resistivity and good biocompatibility. However, since Zn suffers from low mechanical strengths, most of the applications would use Zn as a coating or alloying element. In this study, a new class of Zn-based material with a significantly enhanced mechanical property is developed. The zinc-10 vol % tungsten carbide (Zn-10WC) nanocomposite was fabricated by cold compaction followed by a melting process. The Zn-10WC nanocomposites offer a uniform nanoparticle dispersion with little agglomeration, exhibiting significantly enhanced mechanical properties by micropillar compression tests and microwire tensile testing. The nanocomposites offer an over 200% and 180% increase in yield strength and ultimate tensile strength (UTS), respectively. The strengthening effect could be attributed to Orowan strengthening and grain refinement induced by nanoparticles.
Discussion of Tag Gas Method Using in China Experimental Fast Reactor for Failed Fuel Assembly Location
Authors: Yewang Bie , Donghui Zhang , Wenbin Xiong , Huwei Li , Mingyu Wu , Xinzhe Wang
Published: July 2018

As the first fast reactor of China, the safety of China Experimental Fast Reactor (CEFR) is extremely important, and will decide the future of Chinese fast reactor project. The fuel failure detection system of CEFR provides surveillance and protection for the first barrier-fuel cladding of CEFR, so it is one of the most important systems for the safety of CEFR. As tag gas method is an important method for fuel-failure location in fast reactor, CEFR has a medium-term and long-term plan of using this method to locating failed fuel assemblies. This paper introduces the main principle of tag gas method, summarizes the application of this method, and compares the advantages and disadvantages of each fuel failure location method. Combining the design characteristics of CEFR, this work analyzes the selection principle of tag gas isotopes and the effects on heat transfer capability of fuel element while tag gas filled in. Meanwhile, according to the detection ability of mass spectrometer and the foreign advanced utilization experiences of tag gas method, some suggestions are provided.
Energy Analysis in a Pump-Turbine During the Load Rejection Process
Authors: Fu Xiaolong , Li Deyou , Wang Hongjie , Zhang Guanghui , Li Zhenggui , Wei Xianzhu , Qin Daqing
Published: July 2018

Complex energy conversion and energy dissipation occur in pump-turbines during the load rejection process. However, the underlying fluid mechanism is not clear. In order to solve these problems, in this study, a three-dimensional (3D) transient turbulent flow in a pump-turbine, with clearance during the load rejection process, was simulated using the method of coupling of the rigid rotor motion with flow and dynamic mesh technology. The simulated rotational speed shows good agreement with the experimental data. Most of the differences of rotational speed between simulations and experiments are very small and lower than 5%. Based on the numerical simulation, the energy conversion process, loss distribution, and flow mechanism in a pump-turbine were analyzed using the method of coupling of the entropy production analysis with the flow analysis. The results indicate that the load rejection process of a pump-turbine is an energy-dissipation process where the energy is converted among various energy forms. After load rejection, the hydraulic loss in the reverse pump process distributes primarily in the stay/guide vanes (GV), the vaneless space, and near draft tube inlet. While the hydraulic losses in the runaway process and the braking process are distributed mainly in the elbow section of the draft tube, the clearance of runner (RN), and the vaneless space, the hydraulic losses are mainly caused by viscous dissipation effects of the vortex flows, including the flow separation vortices, the shedding vortices of flow wake, the secondary flow, and the backflow.
Modeling and Simulation of Deepwater Pipeline S-Lay With Coupled Dynamic Positioning
Authors: Ai Shangmao , Sun Liping , Tao Longbin , Yim Solomon C.
Published: July 2018

Dynamic position (DP) control and pipeline dynamics are the two main parts of the deepwater S-lay simulation model. In this study, a fully coupled analysis tool for deepwater S-lay deployment by dynamically positioned vessels is developed. The method integrates the major aspects related to numerical simulation, including coupled pipeline motion and roller contact forces. The roller–pipe interaction is incorporated in the S-lay pipeline model using a contact search method based on a lumped-mass (LM) formulation in global coordinates. A proportional-integration-differentiation (PID) controller and a Kalman filter are applied in the vessel motion equation to calculate the thrust allocation of the DP system in time domain. Numerical simulation results showed that the dynamic effects add a significant contribution to the tension, but have little influence on the maximum pipe stress and strain. The dynamic response of the coupled S-lay and DP pipeline deployment system increases the demand on the tensioner load carrying capability as well as the maximum DP thruster power.
Evaluation of Rolling Contact Fatigue of a Carburized Wind Turbine Gear Considering the Residual Stress and Hardness Gradient
Authors: Wang Wei , Liu Huaiju , Zhu Caichao , Bocher Philippe , Liu Heli , Sun Zhangdong
Published: July 2018

Carburized gears are applied extensively in large-scale heavy duty machines such as wind turbines. The carburizing and quenching processes not only introduce variations of hardness from the case to the core but also generate a residual stress distribution, both of which affect the rolling contact fatigue (RCF) during repeated gear meshing. The influence of residual stress distribution on the RCF risk of a carburized wind turbine gear is investigated in the present work. The concept of RCF failure risk is defined by combining the local material strength and the multi-axial stress condition resulting from the contact. The Dang Van multi-axial fatigue criterion is applied. The applied stress field is calculated through an elastic-plastic contact finite element model. Residual stress distribution and the hardness profile are measured and compared with existed empirical formula. Based upon the Pavlina–Tyne relationship between the hardness and the yield strength, the gradient of the local material strength is considered in the calculation of the RCF failure risk. Effects of the initial residual stress peak value and its corresponding depth position are studied. Numerical results reveal that compressive residual stress (CRS) is beneficial to RCF fatigue life while tensile residual stress (TRS) increases the RCF failure risk. Under heavy load conditions where plasticity occurs, the accumulation of the plastic strain within the substrate is significantly affected by the initial residual stress distribution.
Using Machine Learning to Analyze Factors Determining Cycle-to-Cycle Variation in a Spark-Ignited Gasoline Engine
Authors: Kodavasal Janardhan , Abdul Moiz Ahmed , Ameen Muhsin , Som Sibendu
Published: July 2018

In this work, we have applied a machine learning (ML) technique to provide insights into the causes of cycle-to-cycle variation (CCV) in a gasoline spark-ignited (SI) engine. The analysis was performed on a set of large eddy simulation (LES) calculations of a single cylinder of a four-cylinder port-fueled SI engine. The operating condition was stoichiometric, without significant knock, at a load of 16 bar brake mean effective pressure (BMEP), at an engine speed of 2500 rpm. A total of 123 cycles was simulated. Of these, 49 were run in sequence, while 74 were run in parallel. For the parallel approach, each cycle is initialized with its own synthetic turbulent field to generate CCV, as a part of another work performed by us. In this work, we used 3D information from all 123 cycles to compute flame topology and pre-ignition flow-field metrics. We then evaluated correlations between these metrics and peak cylinder pressure (PCP) employing an ML technique called random forest. The computed metrics form the inputs to the random forest model, and PCP is the output. This model captures the effect of all inputs, as well as interactions between them owing to its decision-tree structure. The goal of this work is to demonstrate (as a first step) that ML models can implicitly learn complex relationships between the pre-ignition flow-fields, the flame shapes, and the eventual outcome of the cycle (whether a cycle will be a high or a low cycle).
Experimental Test of Properties of KCl–MgCl2 Eutectic Molten Salt for Heat Transfer and Thermal Storage Fluid in Concentrated Solar Power Systems
Authors: Xu Xiankun , Wang Xiaoxin , Li Peiwen , Li Yuanyuan , Hao Qing , Xiao Bo , Elsentriecy Hassan , Gervasio Dominic
Published: July 2018

The eutectic mixture of MgCl2–KCl molten salt is a high temperature heat transfer and thermal storage fluid able to be used at temperatures up to 800 °C in concentrating solar thermal power systems. The molten salt thermophysical properties are reported including vapor pressure, heat capacity, density, viscosity, thermal conductivity, and the corrosion behavior of nickel-based alloys in the molten salt corrosion at high temperatures. Correlations of the measured properties as functions of molten salt temperatures are presented for industrial applications. The test results of tensile strength of two nickel-based alloys exposed in the molten salt at a temperature of 800 °C from 1-week length to 16-week length are reported. It was found that the corrosion and strength loss is rather low when the salt is first processed to remove water and oxygen.
Effectiveness of Central Swirlers in the Thermal Uniformity of Jet-in-Crossflow Mixing
Authors: Elgammal Tarek , Amano Ryoichi S.
Published: July 2018

The present paper introduces the analysis-led-design concept in attaining the thermal homogeneity at the exit section of a mixing chamber. Staggered holes (SH) chamber type is representing jet-in-crossflow (JICF) where cold air is injected radially into an axially flowing hot air with a different velocity. Streamlined body of prolate-spheroid shape is fitted in the center of the chamber, and equipped with swirl generating fins (Swirlers). Numerical simulations were first run to predict the flow and energy fields and assess the performance of seven cases representing distinct swirlers setting (shape, dimension, and number). An unsteady turbulent condition was adopted considering high Reynolds number (Re) at the boundaries and large eddy simulation (LES) model for solving the eddy motion in the domain. Afterward, experimental measurements worked on validating the numerical results through proving the effectiveness of the recommended swirler design. Graphical and tabulated results showed the difference between the mixing patterns in thermal dimensionless numbers (normalized mixture fraction and uniformity factor), and consideration of total pressure drop was taken. All swirling designs enhanced the mixing process by generating substantial central swirl besides the small eddies formed from the jet interaction. Numerically, average uniformity improvement achieved in all cases studied was 46%, while the recommended geometry (football with four short rectangular swirlers, F4SR) is 16% better than plain football (FB), but loses pressure by 17%. Upon experimentation, F4SR had almost the same positive outcomes against plain football and SH by 24% and 47%, respectively. Finally, F4SR acts well at lower Re.
Multiobjective Optimization of a Heat-Sink Design Using the Sandwiching Algorithm and an Immersed Boundary Conjugate Heat Transfer Solver
Authors: Andersson Tommy , Nowak Dimitri , Johnson Tomas , Mark Andreas , Edelvik Fredrik , Küfer Karl-Heinz
Published: July 2018

The thermal management is an ever increasing challenge in advanced electronic devices. In this paper, simulation-based optimization is applied to improve the design of a plate-fin heat-sink in terms of operational cost and thermal performance. The proposed framework combines a conjugate heat transfer solver, a CAD engine and an adapted Sandwiching algorithm. A key feature is the use of novel immersed boundary (IB) techniques that allows for automated meshing which is perfectly suited for parametric design optimization.
Influence of Charge Motion and Compression Ratio on the Performance of a Combustion Concept Employing In-Cylinder Gasoline and Natural Gas Blending
Authors: Sevik James , Pamminger Michael , Wallner Thomas , Scarcelli Riccardo , Wooldridge Steven , Boyer Brad , Miers Scott , Hall Carrie
Published: July 2018

The present paper represents a small piece of an extensive experimental effort investigating the dual-fuel operation of a light-duty spark ignited engine. Natural gas (NG) was directly injected into the cylinder and gasoline was injected into the intake-port. Direct injection (DI) of NG was used in order to overcome the power density loss usually experienced with NG port-fuel injection (PFI) as it allows an injection after intake valve closing. Having two separate fuel systems allows for a continuum of in-cylinder blend levels from pure gasoline to pure NG operation. The huge benefit of gasoline is its availability and energy density, whereas NG allows efficient operation at high load due to improved combustion phasing enabled by its higher knock resistance. Furthermore, using NG allowed a reduction of carbon dioxide emissions across the entire engine map due to the higher hydrogen-to-carbon ratio. Exhaust gas recirculation (EGR) was used to (a) increase efficiency at low and part-load operation and (b) reduce the propensity of knock at higher compression ratios (CRs) thereby enabling blend levels with greater amount of gasoline across a wider operating range. Two integral engine parameters, CR and in-cylinder turbulence levels, were varied in order to study their influence on efficiency, emissions, and performance over a specific speed and load range. Increasing the CR from 10.5 to 14.5 allowed an absolute increase in indicated thermal efficiency of more than 3% for 75% NG (25% gasoline) operation at 8 bar net indicated mean effective pressure (IMEP) and 2500 rpm. However, as anticipated, the achievable peak load at CR 14.5 with 100% gasoline was greatly reduced due to its lower knock resistance. The in-cylinder turbulence level was varied by means of tumble plates (TPs) as well as an insert for the NG injector that guides the injection “spray” to augment the tumble motion. The usage of TPs showed a significant increase in EGR dilution tolerance for pure gasoline operation, however, no such impact was found for blended operation of gasoline and NG.
Fracture of Elastomeric Materials by Crosslink Failure
Authors: Mao Yunwei , Anand Lallit
Published: July 2018

If an elastomeric material is subjected to sufficiently large deformations, it eventually fractures. There are two typical micromechanisms of failure in such materials: chain scission and crosslink failure. The chain scission failure mode is mainly observed in polymers with strong covalent crosslinks, while the crosslink failure mode is observed in polymers with weak crosslinks. In two recent papers, we have proposed a theory for progressive damage and rupture of polymers with strong covalent crosslinks. In this paper, we extend our previous framework and formulate a theory for modeling failure of elastomeric materials with weak crosslinks. We first introduce a model for the deformation of a single chain with weak crosslinks at each of its two ends using statistical mechanics arguments, and then upscale the model from a single chain to the continuum level for a polymer network. Finally, we introduce a damage variable to describe the progressive damage and failure of polymer networks. A central feature of our theory is the recognition that the free energy of elastomers is not entirely entropic in nature; there is also an energetic contribution from the deformation of the backbone bonds in a chain and/or the crosslinks. For polymers with weak crosslinks, this energetic contribution is mainly from the deformation of the crosslinks. It is this energetic part of the free energy which is the driving force for progressive damage and fracture of elastomeric materials. Moreover, we show that for elastomeric materials in which fracture occurs by crosslink stretching and scission, the classical Lake–Thomas scaling—that the toughness Gc of an elastomeric material is proportional to 1/G0, with G0=NkBϑ the ground-state shear modulus of the material—does not hold. A new scaling is proposed, and some important consequences of this scaling are remarked upon.
Effects of Inclination Angle, Orientation Angle, and Hole Length on Film Cooling Effectiveness of Rectangular Diffusion Holes
Authors: An Bai-Tao , Liu Jian-Jun , Zhou Si-Jing
Published: July 2018

Film-cooling effectiveness of rectangular diffusion holes under an inclination angle α = 45 deg, an orientation angle β = 45 deg, and a length-to-diameter ratio of L/D = 8.5 were, respectively, examined in a flat-plate experimental facility using the pressure sensitive paint (PSP) technique. Experiments were performed at a density ratio of DR = 1.38 and a mainstream turbulence intensity of Tu = 3.5%. The semicircle sidewall rectangular diffusion hole varied at three cross-sectional aspect ratios, i.e., AS = 3.4, 4.9, and 6.6. The tested results were compared with the baseline design with an inclination angle α = 30 deg, an orientation angle β = 0 deg, and a length-to-diameter ratio L/D = 6. A three-dimensional (3D) numerical simulation method was employed to analyze the flow field. The experimental results showed that the increased inclination angle converted the bi- or tri-peak effectiveness pattern of the baseline design to a single-peak pattern, weakened the lateral diffusion of coolant, and consequently decreased cooling effectiveness obviously. The decreased magnitude amplified with the increase of cross-sectional aspect ratio and blowing ratio. The adding of orientation angle seriously weakened the cooling effectiveness of the baseline design, and the blowing ratio and cross-sectional aspect ratio had almost no effect on overall cooling effectiveness. The elongated hole length provided a uniform distribution of lateral cooling effectiveness, which produced differential effects on the bi- or tri-peak pattern. The elongated hole length decreased the cooling effectiveness on the near hole region, but had less effects on overall cooling effectiveness, except the high blowing ratio.
A Thermo-Economic and Emissions Analysis of Different Sanitary-Water Heating Units Embedded Within Fourth-Generation District-Heating Systems
Authors: Poredoš Primož , Vidrih Boris , Kitanovski Andrej , Poredoš Alojz
Published: July 2018

This paper presents the results of a thermo-economic (TE), primary-energy-factor and CO2-equivalent (CO2 (eq)), emissions-sensitivity analysis for the preparation of sanitary hot water (SHW) in fourth-generation district-heating systems. The annual required additional heat for the SHW provided by a local heating unit, based on an air-to-water heat pump (AWHP), a natural-gas boiler (NG boiler), and an electrical resistance heater (ERH), was determined using a trnsys simulation. Additionally, the seasonal performance factor (SPF) of the HP under consideration was determined. The study considered three possible supply temperatures, i.e., 35, 40, and 45 °C. The results show that a local heating unit based on an AWHP is most efficient in terms of the used primary energy (PE) and CO2 (eq) emissions. This unit is also the second best in terms of TE performance. The unit based on a NG boiler is much more appropriate than an ERH unit in terms of both the primary energy factor (PEF) and the CO2 (eq) emission factors for an electricity generation mix (EGM) that has values higher than the average for the EU-28. The heat generated by this NG unit is also cheaper than the heat produced by an ERH based on the average price for electricity in the EU-28.
Numerical Investigation of Crossflow Separation on the A-Pillar of a Passenger Car
Authors: Bonitz Sabine , Larsson Lars , Löfdahl Lennart , Sebben Simone
Published: July 2018

The flow around passenger cars is characterized by many different separation structures, typically leading to vortices and areas of reversed flow. The flow phenomena in these patches show a strong interaction and the evolution of flow structures is difficult to understand from a physical point of view. Analyzing surface properties, such as pressure, vorticity, or shear stress, helps to identify different phenomena, but still it is not well understood how these are created. This paper investigates the crossflow separation (CFS) on the A-pillar of a passenger car using numerical simulations. It is discussed how the CFS and the resulting A-pillar vortex can be identified as well as how it is created. Additionally, the vortex strength is determined by its circulation to understand and discuss how the vortex preserves until it merges with the rear wake of the vehicle.
Tribological Performance of Textured Surfaces Created by Modulation-Assisted Machining
Authors: Tock Andrew , Gandhi Rahul , Saldana Christopher , Iglesias Patricia
Published: July 2018

Methods for scalable surface texturing continue to receive significant attention due to the importance of microtextured surfaces toward improving friction, wear, and lubrication ability of mechanical devices. Controlled textures on surfaces act as fluid reservoirs and receptacles for debris and wear particles, reducing friction and wear of mating components. There are numerous fabrication techniques that can be used to create microsized depressions on surfaces, but each has limitations in terms of control and scalability. In the present study, modulation-assisted machining (MAM) is demonstrated as a viable approach to produce such textures, offering a potentially cost-effective approach for scalable production of these features on component surfaces. In this work, the wear behavior of several textured surfaces created by MAM was studied using a ball-on-flat reciprocating tribometer. Textured and untextured alloy 360 brass disks were mated with stainless steel AISI 440C balls under lubricated conditions and variable sliding distance. The textured surfaces exhibited noticeably reduced wear under the longer sliding distances and the tribological performance of the surfaces depended on the size of the microdimples. Wear mechanisms are elucidated from the optical microscopy, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) observations and the implications for using such surfaces in practice are briefly discussed.
Characterization of Plastic Anisotropy of AA5182-O Sheets During Prestraining and Subsequent Annealing
Authors: Wang Kaifeng , Zhou Bonan , Li Jingjing , Carsley John E. , Li Yang
Published: July 2018

This paper described the effects of prestraining and annealing on plastic anisotropy (r-value) of aluminum alloy 5182-O sheets including two prestrain paths and two annealing conditions. During the prestraining and annealing processes, r-value changed depending on prestrain paths and annealing conditions. Although there were slight changes of the normal anisotropy coefficient, r¯, during prestraining and annealing processes, the planar anisotropy coefficient, Δr, increased significantly, especially for the uniaxial prestrain condition. This could accelerate the development of earing during a sheet forming operation. Also, the corresponding sheet textures in rolling direction (RD)/TD plane after prestraining and annealing processes were observed through electron backscatter diffraction (EBSD) analysis to explain the r-value changes, where the viscoplastic self-consistent (VPSC) model was used to correlate the determined texture to measured r-values. It is found that the sheet texture also had significant changes relating to the prestrain paths and annealing conditions resulting in varied r-values.
Effect of Ramp Angle on the Anti-Loosening Ability of Wedge Self-Locking Nuts Under Vibration
Authors: Liu Jianhua , Gong Hao , Ding Xiaoyu
Published: July 2018

Recently, the wedge self-locking nut, a special anti-loosening product, is receiving more attention because of its excellent reliability in preventing loosening failure under vibration conditions. The key characteristic of a wedge self-locking nut is the special wedge ramp at the root of the thread. In this work, the effect of ramp angle on the anti-loosening ability of wedge self-locking nuts was studied systematically based on numerical simulations and experiments. Wedge self-locking nuts with nine ramp angles (10 deg, 15 deg, 20 deg, 25 deg, 30 deg, 35 deg, 40 deg, 45 deg, and 50 deg) were modeled using a finite element (FE) method, and manufactured using commercial production technology. Their anti-loosening abilities under transversal vibration conditions were analyzed based on numerical and experimental results. It was found that there is a threshold value of the initial preload below which the wedge self-locking nuts would lose their anti-loosening ability. This threshold value of initial preload was then proposed for use as a criterion to evaluate the anti-loosening ability of wedge self-locking nuts quantitatively and to determine the optimal ramp angle. Based on this criterion, it was demonstrated, numerically and experimentally, that a 30 deg wedge ramp resulted in the best anti-loosening ability among nine ramp angles studied. The significance of this study is that it provides an effective method to evaluate the anti-loosening ability of wedge self-locking nuts quantitatively, and determined the optimal ramp angle in terms of anti-loosening ability. The proposed method can also be used to optimize other parameters, such as the material properties and other dimensions, to guarantee the best anti-loosening ability of wedge self-locking nuts.
Custom-Fit Three-Dimensional-Printed BiPAP Mask to Improve Compliance in Patients Requiring Long-Term Noninvasive Ventilatory Support
Authors: Wu Ying Ying , Acharya Deepshikha , Xu Camilla , Cheng Boyle , Rana Sandeep , Shimada Kenji
Published: July 2018

Noninvasive ventilator support using bi-level positive airway pressure/continuous positive airway pressure (BiPAP/CPAP) is commonly utilized for chronic medical conditions like sleep apnea and neuromuscular disorders like amyotrophic lateral sclerosis (ALS) that lead to weakness of respiratory muscles. Generic masks come in standard sizes and are often perceived by patients as being uncomfortable, ill-fitting, and leaky. A significant number of patients are unable to tolerate the masks and eventually stop using their devices. The goal of this project is to develop custom-fit masks to increase comfort, decrease air leakage, and thereby improve patient compliance. A single-patient case study of a patient with variant ALS was performed to evaluate the custom-fit masks. His high nose bridge and overbite of lower jaw caused poor fit with generic masks, and he was noncompliant with his machine. Using desktop Stereolithography three-dimensional (3D) printing and magnetic resonance imaging (MRI) data, a generic mask was extended with a rigid interface such that it was complementary to the patient's unique facial contours. Patient or clinicians interactively select a desired mask shape using a newly developed computer program. Subsequently, a compliant silicone layer was applied to the rigid interface. Ten different custom-fit mask designs were made using computer-aided design software. Patient evaluated the comfort, extent of leakage, and satisfaction of each mask via a questionnaire. All custom-fit masks were rated higher than the standard mask except for two. Our results suggest that modifying generic masks with a 3D-printed custom-fit interface is a promising strategy to improve compliance with BiPAP/CPAP machines.
Techno-Economic Analysis of a Carbon Capture Chemical Looping Combustion Power Plant
Authors: Ogidiama Oghare Victor , Abu Zahra Mohammad , Shamim Tariq
Published: July 2018

High energy penalty and cost are major obstacles in the widespread use of CO2 capture techniques for reducing CO2 emissions. Chemical looping combustion (CLC) is an innovative means of achieving CO2 capture with less cost and low energy penalty. This paper conducts a detailed techno-economic analysis of a natural gas-fired CLC-based power plant. The power plant capacity is 1000 MWth gross power on a lower heating value basis. The analysis was done using Aspen Plus. The cost analysis was done by considering the plant location to be in the United Arab Emirates. The plant performance was analyzed by using the cost of equipment, cost of electricity, payback period, and the cost of capture. The performance of the CLC system was also compared with a conventional natural gas combined cycle plant of the same capacity integrated with post combustion CO2 capture technology. The analysis shows that the CLC system had a plant efficiency of 55.6%, electricity cost of 5.5 cents/kWh, payback time of 3.77 years, and the CO2 capture cost of $27.5/ton. In comparison, a similar natural gas combined cycle (NGCC) power plant with CO2 capture had an efficiency of 50.6%, cost of electricity of 6.1 cents/kWh, payback period of 4.57 years, and the capture cost of $42.9/ton. This analysis shows the economic advantage of the CLC integrated power plants.