bluuebunny/crossref_metadata_2025 huggingface dataset:
Grid Trouble in Paradise
Authors: Gibson Tom
Published: July 2018

This article discusses why Hawaii needs to find new ways to handle the influx of solar power. In Hawaii, rooftop solar panels are popping up everywhere. However, the solar boom has also created some complications, including sudden changes or disruptions in the system or problems at the distribution side, when there are lots of PV connected at the rooftops. Electrical loads in homes fluctuate all the time as power-hungry appliances like air conditioners and water heaters turn on and off, resulting in a high probability of low load and too much power. Power can go back through the nearby substation transformer and cause a rise in the voltage. That the state is split into several small islands further complicates matters. Another challenge unique to Hawaii is that each island in Hawaii is its own independent grid, and there are no neighbors to depend on for power.
Gasoline Engine and Aftertreatment Modeling and Control
Authors: Jankovic Mrdjan
Published: July 2018

This article discusses the design of control system components for gasoline engines. Gasoline or, more precisely, spark ignition engines power a large majority of personal vehicles sold worldwide. A major task for the automakers is to provide good drivability and fuel economy while meeting increasingly stringent emission requirements. Achieving low emissions requires a significant reduction in cold start emissions and employment of catalytic converters to reduce tailpipe emissions once the engine is warmed up. The catalysts are loaded with precious metals – typically platinum, palladium, and rhodium. They achieve very high conversion efficiencies, but only if the engine is operated very close to stoichiometry that corresponds to the air-fuel ratio of about 14.6 for gasoline and of 9 for ethanol. Design of a control system component requires that an appropriate model be developed. The models range from very simple low-order, linear for the inner loop to a partial-differential-equation based model for the catalyst. In general, feedback controllers tolerate and even benefit from simpler models. Feed-forward control, estimation, diagnostics, and failure mode management requires more elaborate models.
Energy Storage Smooths the Duck Curve
Authors: Kosowatz John
Published: July 2018

Maintaining grid stability is a challenge as utilities rush to add renewable power to their generating portfolio. The business case for renewables is undeniable: as prices for wind turbines and solar panels keep dropping and the costs of installation go down, renewable electricity becomes some of the cheapest power available. But the inherently inconsistent nature of solar and wind energy has grid operators looking for new ways to seamlessly integrate their output into the system. This challenge is being faced around the world, and in the U.S. it is playing out initially in California.This article takes a closer look at the steps California is taking to smooth out the duck curve, a graph of power production over the course of a day that shows the timing imbalance between peak demand and renewable energy production.
Estimation of Minimum Spouting Velocity in a Rectangular Spouted Bed
Authors: Rowan Steven L. , Yang Jingsi , Bobek Michael C. , Breault Ronald W.
Published: July 2018

A study was conducted to explore the effects of static bed height, nozzle diameter, cone angle, and particle properties on the minimum spouting velocity in a 4 in × 1 in rectangular spouted bed. Tests were conducted with various solids materials (including 871 μm HPDE pellets, 3.2 mm nylon beads, 707 μm glass beads, and 1.5 mm alumina spheres), two gas inlet nozzle diameters, and two cone angles. Experimentally obtained minimum spouting velocities were compared to existing published correlations developed for cylindrical spouted beds. In each case, it was determined that the existing correlations did not adequately predict the minimum spouting velocity for a rectangular spouted bed. A new correlation is proposed.
Experimental Investigation of Using a Novel Insulation Material on the Functioning of a Solar Thermal Collector
Authors: Ihaddadene Nabila , Ihaddadene Razika , Betka Abdelwahaab
Published: July 2018

This research document presents a new insulation material for solar thermal collectors. Tests were carried out in the laboratory, on an active solar energy demonstration system (ET 200), illuminated with a halogen lamp instead of sun. In this paper, the polystyrene used as insulation in the ET 200 flat plate solar collector was replaced by the cheaper natural material based on clay and straw. The polystyrene in the experimental device is placed under the absorber plate and along the edges of the casing containing the components of the solar collector. In this work, only the polystyrene of the four similar edges was replaced by the composite material. The use of the clay and straw as insulation material instead of polystyrene increased temperature difference (T2 − T1) between the inlet and the outlet of the absorber by 0.9±0.14 °C (p < 0.05); thus, increasing the useful power transmitted to water in the solar collector. Compared to polystyrene, tank water was well heated using the proposed material (p < 0.05). This latter also improved the performance of the solar collector by 5.77%. So, it is recommended to use the cheapest nonpolluting material based on clay and straw instead of synthetic insulation to improve the performance of the solar collector.
Optimization of the Charge Motion in Internal Combustion Engines Driven by Sewage Gas for Combined Heat and Power Units
Authors: Konstantinoff Lucas , Möltner Lukas , Pillei Martin , Steiner Thomas , Dornauer Thomas , Herdin Günther , Mairegger Dominik
Published: July 2018

In this study, the influence of the charge motion on the internal combustion in a spark ignition sewage gas-driven engine (150 kW) for combined heat and power (CHP) units was investigated. For this purpose, the geometry of the combustion chamber in the immediate vicinity to the inlet valve seats was modified. The geometrical modification measures were conducted iteratively by integrative determination of the swirl motion on a flow bench, by laser-optical methods and consecutively by combustion analysis on a test engine. Two different versions of cylinder heads were characterized by dimensionless flow and swirl numbers prior to testing their on-engine performance. Combustion analysis was conducted with a cylinder pressure indication system for partial and full load, meeting the mandatory NOx limit of 500 mg m−3. Subsuming the flow bench results, the new valve seat design has a significant enhancing impact on the swirl motion but it also leads to disadvantages concerning the volumetric efficiency. A comparative consideration of the combustion rate delivers that the increased swirl motion results in a faster combustion, hence in a higher efficiency. In summary, the geometrical modifications close to the valve seat result in increased turbulence intensity. It was proven that this intensification raises the ratio of efficiency by 1.6%.
Process–Property Relationships for Fused Filament Fabrication on Preexisting Polymer Substrates
Authors: Pierson Harry A. , Chivukula Bharat
Published: July 2018

Recent advances in fused filament fabrication (FFF), such as five-axis printing, patching existing parts, and certain hybrid manufacturing processes, involve printing atop a previously manufactured polymer substrate. The success of these technologies depends upon the bond strength between the substrate and the newly added geometry. ANOVA and response surface methods were used to determine the effect of three process parameters on bond tensile strength: surface roughness, layer thickness, and raster angle. Experimental results indicate that the process–property relationships are not identical to those found in single, continuous FFF operations, and that the physical bonding mechanisms may also be different. Bond strength was found to be highly sensitive to surface roughness and layer thickness, and distinct optimal parameter settings exist. These results represent a first step toward understanding bond strength in such circumstances, allowing manufacturers to intelligently select process parameters for the production of both the substrate and the secondary geometry.
Multi-Objective Optimization of Parallel Tracking Mechanism Considering Parameter Uncertainty
Authors: Qi Yang , Sun Tao , Song Yimin
Published: July 2018

Multi-objective optimization of a typical parallel tracking mechanism considering parameter uncertainty is carried out in this paper. Both dimensional and sectional parameters are regarded as design variables. Workspace, kinematic, stiffness, and dynamic performances are simultaneously considered in formulating optimal objectives and constraint conditions. Considering manufacturing and assembling errors, parameter uncertainty is modeled and evaluated to minimize their effects on the optimized performances. Analytical models between objectives and design variables are established to improve the efficiency of optimization while its accuracy is assured. The study of parameter uncertainty and analytical mapping model is incorporated in the optimization of the parallel tracking mechanism. With the aid of particle swarm algorithm, a cluster of solutions, called Pareto frontier, are obtained. By proposing an index, a cooperative equilibrium point representing the balance among objectives is selected and the optimized parameters are determined. The present study is expected to help designers build optimized parallel tracking mechanism in an effective and efficient manner.
An Electrochemical Performance Characterization Method for Comparing PEFCs of Varying Channel Dimensions
Authors: Cooper Nathanial J. , Smith Travis L. , Santamaria Anthony D. , Wan Park Jae
Published: July 2018

A method which allows for the comparison of polymer electrolyte fuel cell (PEFC) bipolar plates (BPs) with various channel dimensions is outlined here. It is applied to data from an experiment with different channel and land width and channel depth combinations for interdigitated and parallel designs. Channel and land width and channel depth varied from 0.25 mm to 1 mm on six different BP designs, and two stoichiometries were tested. Each condition was performed three times for repeatability. The method calculates the performance of each condition after accounting for reversible voltage and overpotential changes due to varying pressure and after eliminating ohmic resistance as a variable. In these data, the interdigitated flow field outperformed the parallel flow field. Designs are compared using the BP permeability as a benchmark metric. The method then calculates the area-specific ohmic resistance (ASR) of the cell. It was difficult to draw hard conclusions about changes in the ASR between flow field designs, but there may be more consistent liquid water removal from the gas diffusion layer (GDL) with smaller channel dimensions. It was found that concentration losses seem to be primarily a result of channel width, rather than channel depth.
Robust Balancing Approach for Rotating Machines Based on Fuzzy Logic
Authors: Carvalho Vinícius Nunes , Rende Bruno Ferreira Resende , Silva Arinan Dourado Guerra , Ap Cavalini Aldemir , Steffen Valder
Published: July 2018

Unbalance is one of the most common malfunctions found in rotating machines generating high vibration amplitudes that can lead to fatigue and wear of rotor elements. There are several well-known balancing techniques wherein one of the most widespread approaches is the so-called influence coefficients method (IC method). Aiming to increase the robustness of the standard IC method, in this paper, a revised IC balancing methodology for rotating machines is proposed. In this sense, a preprocessing stage is applied to access the uncertainties affecting the rotating machine. In this sense, measurement data sets evaluated under the fuzzy logic approach are used. Thus, the rotor vibration responses measured over a long period are considered by means of a fuzzy transformation (defining unbalance fuzzy sets). The unbalance condition of the rotating machine is determined through a defuzzification process. This unbalance condition is then introduced in the IC method algorithm aiming at obtaining correction weights and associated angular positions that increase the balancing robustness as compared with the classical approach. Numerical and experimental studies are used to evaluate the effectiveness of the proposed methodology. The obtained results illustrate the capacity to increase the balancing overall robustness.
An Investigation of the Combustion Process of a Heavy-Duty Natural Gas-Diesel Dual Fuel Engine
Authors: Li Hailin , Liu Shiyu , Liew Chetmun , Gatts Timothy , Wayne Scott , Clark Nigel , Nuszkowski John
Published: July 2018

This paper investigates the effect of the addition of natural gas (NG) and engine load on the cylinder pressure, combustion process, brake thermal efficiency, and methane combustion efficiency of a heavy-duty NG-diesel dual fuel engine. Significantly increased peak cylinder pressure (PCP) was only observed with the addition of NG at 100% load. The addition of a relatively large amount NG at high load slightly retarded the premixed combustion, significantly increased the peak heat release rate (PHRR) of the diffusion combustion, decreased the combustion duration, and advanced combustion phasing. The accelerated combustion process and increased heat release rate (HRR) at high load were supported by the increased NOx emissions with the addition of over 3% NG (vol.). By comparison, when operated at low load, the addition of a large amount of NG decreased the PHRR of the premixed combustion and slightly increased the PHRR during the late diffusion combustion. Improved brake thermal efficiency was only observed with the addition of a relatively large amount of NG at high load. The improved thermal efficiency was due to a decrease in combustion duration and the shifting of the combustion phasing toward the optimal phasing. The overall combustion efficiency of the dual fuel operation was always lower than diesel-only operation as indicated by the excess emissions of the unburned methane and carbon monoxide from dual fuel engine. This deteriorated the potential of dual fuel engine in further improving the brake thermal efficiency although the combustion duration of dual fuel engine at high load was much shorter than diesel only operation. The addition of NG at low load should be avoided due to the low combustion efficiency of NG and the decreased thermal efficiency. Approaches capable of further improving the in-cylinder combustion efficiency of NG should enable further improvement in the brake thermal efficiency.
Plastic Limit Loads for Pipe-in-Pipes With Circumferential Through-Wall Cracks Based on Finite Element Analyses
Authors: Kim Se-Chang , Choi Jae-Boong , Kim Hyun-Su , Huh Nam-Su , Kim Kyunghoon
Published: July 2018

Pipe-in-pipes (PIPs) are generally applied to the extreme environments such as deep-sea and next-generation reactors due to their functionality and robustness. Thus, it is important to estimate the fracture behaviors of PIPs for integrity assessment of this unique piping system. In this work, the plastic collapse behaviors of PIPs with circumferential through-wall cracks (TWCs) are investigated based on three-dimensional finite element (FE) limit analysis, where the crack is assumed to be located at the inner pipe of PIPs. As for loading conditions, internal pressure, axial tension, and global bending moment are considered. In particular, the bending restraint effect induced by interconnection between the inner and outer pipes of PIPs is quantified through the FE analyses considering a practical range of geometries of PIPs. Based on the FE analysis results, the tabular and closed-form solutions of the plastic limit loads of the circumferential through-wall cracked PIPs are proposed, and then, validated against numerical simulations.
A Multiple-Domain Matrix Support to Capture Rationale for Engineering Design Changes
Authors: Siddharth L. , Sarkar Prabir
Published: July 2018

Design changes are necessary to sustain the product against competition. Due to technical, social, and financial constraints, an organization can only implement a few of many change alternatives. Hence, a wise selection of a change alternative is fundamentally influential for the growth of the organization. Organizations lack knowledge bases to effectively capture rationale for a design change; i.e., identifying the potential effects a design change. In this paper, (1) we propose a knowledge base called multiple-domain matrix that comprises the relationships among different parameters that are building blocks of a product and its manufacturing system. (2) Using the indirect change propagation method, we capture these relationships to identify the potential effects of a design change. (3) We propose a cost-based metric called change propagation impact (CPI) to quantify the effects that are captured from the multiple-domain matrix. These individual pieces of work are integrated into a web-based tool called Vatram. The tool is deployed in a design environment to evaluate its usefulness and usability.
Kinematic Synthesis of a D-Drive MEMS Device With Rigid-Body Replacement Method
Authors: Sanò Paolo , Verotti Matteo , Bosetti Paolo , Belfiore Nicola P.
Published: July 2018

In this paper, a microsystem with prescribed functional capabilities is designed and simulated. In particular, the development of a straight line path generator micro electro mechanical system (MEMS) device is presented. A new procedure is suggested for avoiding branch or circuit problems in the kinematic synthesis problem. Then, Ball's point detection is used to validate the obtained pseudo-rigid body model (PRBM). A compliant MEMS device is obtained from the PRBM through the rigid-body replacement method by making use of conjugate surfaces flexure hinges (CSFHs). Finally, the functional capability of the device is investigated by means of finite element analysis (FEA) simulations and experimental testing at the macroscale.
Toward Cost-Effective Boundary Layer Transition Computations With Large-Eddy Simulation
Authors: Jee Solkeun , Joo Jongwook , Lin Ray-Sing
Published: July 2018

An efficient large-eddy simulation (LES) approach is investigated for laminar-to-turbulent transition in boundary layers. This approach incorporates the boundary-layer stability theory. Primary instability and subharmonic perturbations determined by the boundary-layer stability theory are assigned as forcing at the inlet of the LES computational domain. This LES approach reproduces the spatial development of instabilities in the boundary layer, as observed in wind tunnel experiments. Detailed linear growth and nonlinear interactions that lead to the H-type breakdown are well captured and compared well to previous direct numerical simulation (DNS). Requirements in the spatial resolution in the transition region are investigated with connections to the resolution in turbulent boundary layers. It is shown that the subgrid model used in this study is apparently dormant in the overall transitional region, allowing the right level of the growth of small-amplitude instabilities and their nonlinear interactions. The subgrid model becomes active near the end of the transition where the length scales of high-order instabilities become smaller in size compared to the given grid resolution. Current results demonstrate the benefit of the boundary-layer forcing method for the computational cost reduction.
Mathematical Modeling of a Biomass Steam Gasifier—A Modified Equilibrium Approach
Authors: Gröbl Thomas , Walter Heimo
Published: July 2018

A large potential is contributed to the energetic utilization of biomass, whereby thermochemical gasification seems to be especially interesting. In order to contribute to a better understanding of the thermochemical conversion process in the gasifier, mathematical models are used. An intensive effort is made in development of mathematical models describing the gasification process and a large number of models, considerably differing in their degree of simplification, and their applications are reported in literature. In the present article, a brief review of models applied, mainly focused on equilibrium models, is provided and a robust and flexible modified stoichiometric equilibrium model, for modeling a novel gasifier, is presented.
Development of Modified Affinity Law for Centrifugal Pump to Predict the Effect of Viscosity
Authors: Morrison Gerald , Yin Wenjie , Agarwal Rahul , Patil Abhay
Published: July 2018

The purpose of this research is to investigate the flow behavior inside a mixed flow type pump operating with fluids of different viscosities using computational fluid dynamics (CFD) with the goal to establish additional terms for the pump affinity laws to scale pump performance including the effects of viscosity. Several sets of fluids of different viscosities and densities are simulated under various operating conditions. The effect of viscosity on the performance of the impeller and diffuser is discussed. Changes in the pump performance due to fluid viscosity are characterized using the dimensionless flow coefficient, head coefficient, and rotational Reynolds number. The result, which can be regarded as the modified pump affinity laws for viscosity flows, was obtained based on the relationships between dimensionless coefficients. The modified affinity laws agreed well with the CFD results. Further study was conducted to validate the relationships using previously published test data for a semi axial pump design (specific speed, Ns: 3869) tested with fluid viscosity ranging from 1 cp to 1020 cp and in-house testing of a split vane impeller pump (Ns: 3027) and a helicoaxial pump (Ns: 5281) using 1 cp and 5 cp viscosity fluid. The modified affinity laws accurately models the performance dependence upon viscosity. As with the standard affinity laws, a pump's functional relationship varies with each pump design. Yet the modified affinity laws produce a single common curve for all operating conditions and viscosities for a specific pump.
Parametric Instability and Localization of Vibrations in Three-Blade Wind Turbines
Authors: Ikeda Takashi , Harata Yuji , Ishida Yukio
Published: July 2018

Nonlinear vibration characteristics of three-blade wind turbines are theoretically investigated. The wind turbine is modeled as a coupled system, consisting of a flexible tower with two degrees-of-freedom (2DOF), and three blades, each with a single degree of freedom (SDOF). The blades are subjected to steady winds. The wind velocity increases proportionally with height due to vertical wind shear. The natural frequency diagram is calculated with respect to the rotational speed of the wind turbine. The corresponding linear system with parametric excitation terms is analyzed to determine the rotational speeds where unstable vibrations appear and to predict at what rotational speeds the blades may vibrate at high amplitudes in a real wind turbine. The frequency response curves are then obtained by applying the swept-sine test to the equations of motion for the nonlinear system. They exhibit softening behavior due to the nonlinear restoring moments acting on the blades. Stationary time histories and their fast Fourier transform (FFT) results are also calculated. In the numerical simulations, localization phenomena are observed, where the three blades vibrate at different amplitudes. Basins of attraction (BOAs) are also calculated to examine the influence of a disturbance on the appearance of localization phenomena.
Thermal and Flow Characteristics of Water–Nitrogen Taylor Flow Inside Vertical Circular Tubes
Authors: Zhang Jingzhi , Li Wei
Published: July 2018

Heat transfer and flow characteristics of Taylor flows in vertical capillaries with tube diameters ranging from 0.5 mm to 2 mm were studied numerically with the volume of fluid (VOF) method. Streamlines, bubble shapes, pressure drops, and heat transfer characteristics of the fully developed gas–liquid Taylor flow were investigated in detail. The numerical data fitted well with experimental results and with the predicted values of empirical correlations. The results indicate that the dimensionless liquid film thickness and bubble rising velocity increase with increasing capillary number. Pressure drops in liquid slug region are higher than the single-phase flow because of the Laplace pressure drop. The flow pattern dependent model and modified flow separation model which takes Bond number and Reynolds number into account can predict the numerical pressure drops well. Compared with the single-phase flow, less time is needed for the Taylor flow to reach a thermal fully developed status. The Nusselt number of Taylor flow is about 1.16–3.5 times of the fully developed single-phase flow with a constant wall heat flux. The recirculation regions in the liquid and gas slugs can enhance the heat transfer coefficient and accelerate the development of the thermal boundary layer.
Slow Pyrolysis of the Sewage Sludge With Additives: Calcium Oxide and Lignite
Authors: Pawlak-Kruczek Halina , Krochmalny Krystian , Wnukowski Mateusz , Niedzwiecki Lukasz
Published: July 2018

Sewage sludge is a waste from the water treatment installations. It is used in agriculture. However, due to various environmental restrictions, not all of the sewage sludge can be utilized within that sector. Using this resource as a sustainable energy source might be an interesting alternative to the landfilling. Some of the fuel-related properties of sewage sludge make it difficult to be used as a fuel without preprocessing. Torrefaction is a promising pretreatment technique that could prove itself suitable to be used for improving sewage sludge. Additives might be used for obtaining some further improvements, either during the torrefaction stage or further at the final energy conversion stage (combustion, gasification, etc.). This paper presents the results of torrefaction experiments performed with sewage sludge from the local water treatment facility. Torrefaction was performed with laboratory-scale rotary reactor at three different temperatures (250 °C, 275 °C, and 300 °C). Cotorrefaction of sewage sludge with lignite was also performed. Torrefaction tests with quicklime (CaO) as an additive were also performed. Fuel-related properties of products of torrefaction and feedstock were determined. By-product of torrefaction, called torgas, was also a subject of the analysis. Propensity of the torrefied product to absorb moisture was assessed. Thermogravimetric analysis (TGA) of raw and torrefied samples was performed in order to compare the behavior of raw and torrefied materials during subsequent pyrolysis.
Computational Fluid Dynamics Modeling of Flashing Flow in Convergent-Divergent Nozzle
Authors: Dang Le Quang , Mereu Riccardo , Besagni Giorgio , Dossena Vincenzo , Inzoli Fabio
Published: July 2018

In this paper, a computational fluid dynamics model of flashing flow, which considers the thermal nonequilibrium effect, has been proposed. In the proposed model, based on the two-phase mixture approach, the phase-change process depends on the difference between the vaporization pressure and the vapor partial pressure. The thermal nonequilibrium effect has been included by using ad hoc modeling of the boiling delay. The proposed model has been applied to the case of two-dimensional axisymmetric convergent-divergent nozzle, which is representative of well-known applications in nuclear and energy engineering applications (e.g., the primary flow in the motive nozzle of ejectors). The numerical results have been validated based on a benchmark case from the literature and have been compared with the numerical results previously obtained by different research groups. The proposed approach has shown a good level of agreement as regards the global and the local experimental fluid dynamic quantities. In addition, sensitivity analyses have been carried out concerning (a) grid independency, (b) turbulence modeling approaches, (c) near-wall treatment approaches, (d) turbulence inlet parameters, and (e) semi-empirical coefficients. In conclusion, the present paper aims to provide guidelines for the simulation of flash boiling flow in industrial applications.
Modified Lewis Number and Buoyancy Ratio Effects on Turbulent Double-Diffusive Convection in Porous Media Using the Thermal Nonequilibrium Model
Authors: de Lemos Marcelo J. S. , Carvalho Paulo H. S.
Published: July 2018

This work presents a study of double-diffusive free convection in a porous square cavity under turbulent flow regime and with aiding drive. The thermal nonequilibrium model was employed to analyze the energy and mass transport across the enclosure. Governing equations were time- and volume-averaged according to the double-decomposition concept. Analysis of a modified Lewis number, Lem, showed that for porous media, this parameter presents opposite behavior when varying the thermal conductivity ratio or the Schmidt number, while maintaining the same value for Lem. Differently form free flow, the existence of the porous matrix contributes to the overall thermal diffusivity of the medium, whereas mass diffusivity is only effective within the fluid phase for an inert medium. Results indicated that increasing Lem through an increase in Sc reduces flow circulation inside porous cavities, reducing Nuw and increasing Shw. Results further indicate that increasing the buoyancy ratio N promotes circulation within the porous cavity, leading to an increase in turbulence levels within the boundary layers. Partial contributions of each phase of the porous cavity (solid and fluid) to the overall average Nusselt number become independent of n for higher values of the thermal conductivity ratio, ks/kf. Further, for high values of ks/kf, the average Nusselt number drops as N increases.
Flow
Channelization Method to Enhance Transformer Radiator Cooling
Capacity
Authors: Dasgupta Subhashish , Nandwana Anurag , Ravikumar K.
Published: July 2018

Most oil-cooled equipment like transformers are provided with radiators or heat exchangers, for the heated oil to exchange heat with the surrounding air by natural convection cooling, assisting the overall cooling process. While such radiators are effective accessories in controlling equipment temperature rise, it is ever desirable to further enhance the cooling capacity by design modifications or incorporating simplistic and cost-effective cooling technologies. In this study, computational fluid dynamic (CFD) analysis has been performed to evaluate the possibility of improving radiator performance by flow channelizing structures. Significant benefits (up to 17% increase in heat transfer coefficient) of imposing such structures, like a top chimney and an enclosure surrounding the radiator, were obtained. Although several past studies have confirmed that natural convection cooling effect can be intensified by flow channelization, the phenomenon is unique to a particular application. Given the wide variety in applications, in terms of shape, size, and structural features, it is necessary to study the effect in a given application of interest. This study points to a new direction in enhancing the cooling capacity of transformer radiators, inducing flow channelization, an easy-to-implement and cost-effective technology. Further, the study offers interesting learnings regarding flow channelization effects, which are invaluable guidelines for designers of future radiators.
Regenerative Hydraulic Assisted Turbocharger
Authors: Zeng Tao , Upadhyay Devesh , Sun Harold , Curtis Eric , Zhu Guoming G.
Published: July 2018

Engine downsizing and down-speeding are essential in order to meet future U.S. fuel economy (FE) mandates. Turbocharging is one technology to meet these goals. Fuel economy improvements must, however, be achieved without sacrificing performance. One significant factor impacting drivability on turbocharged engines is typically referred to as “turbolag.” Since turbolag directly impacts the driver's torque demands, it is usually perceptible as an undesired slow transient boost response or as a sluggish torque response. High throughput turbochargers (TC) are especially susceptible to this dynamic and are often equipped with variable geometry turbines (VGT) to mitigate some of this effect. Assisted boosting techniques that add power directly to the TC shaft from a power source that is independent of the engine have been shown to significantly reduce turbolag. Single unit assisted turbochargers are either electrically assisted or hydraulically assisted. In this study, a regenerative hydraulically assisted turbocharger (RHAT) system is evaluated. A custom-designed RHAT system is coupled to a light duty diesel engine and is analyzed via vehicle and engine simulations for performance and energy requirements over standard test cycles. Supplier-provided performance maps for the hydraulic turbine, hydraulic turbopump were used. A production controller was coupled with the engine model and upgraded to control the engagement and disengagement of RHAT, with energy management strategies. Results show some interesting dynamics and shed light on system capabilities especially with regard to the energy balance between the assist and regenerative functions. Design considerations based on open-loop simulations are used for sizing the high-pressure accumulator. Simulation results show that the proposed RHAT turbocharger system can significantly improve engine transient response. Vehicle level simulations that include the driveline were also conducted and showed potential for up to 4% fuel economy improvement over the FTP 75 drive cycle. This study also identified some technical challenges related to optimal design and operation of the RHAT. Opportunities for additional fuel economy improvements are also discussed.
Reliability Modeling for Gear Door Lock System With Dependent
Failures Based on Copula
Authors: Shen Linjie , Zhang Yugang , Zhuang Xinchen , Guo Bozhi
Published: July 2018

The gear door lock system (GDLS) is a hydraulic and mechatronic system with high degree of complexity and uncertainty, making the performance assessment of the system especially intractable. We develop copula models to estimate the reliability of GDLS with dependent failure modes. Based on the working principle of the GDLS, kinematic and dynamic model with imperfect joints is built in which Latin hypercube sampling (LHS) and kernel smoothing density are utilized to obtain the marginal failure probabilities. Then, copula models are utilized to describe the dependence between the two function failure modes. Furthermore, to be more accurate, mixed copula models are developed. The squared Euclidean distance is adopted to estimate the parameters of the above reliability models. Finally, the Monte Carlo simulation is conducted to evaluate different reliability models.
Particle Image Velocimetry Experiment and Computational Fluid Dynamics Simulation of Flow Around Rigid Cylinder
Authors: Wang Guangyao , Tian Ye , Kinnas Spyros A.
Published: July 2018

This work focuses on the study of the flow around a rigid cylinder with both particle image velocimetry (PIV) experiment and computational fluid dynamics (CFD) simulation. PIV measurements of the flow field downstream of the cylinder are first presented. The boundary conditions for CFD simulations are measured in the PIV experiment. Then the PIV flow is compared with both Reynolds-averaged Navier–Stokes (RANS) two-dimensional (2D) and large eddy simulation (LES) three-dimensional (3D) simulations performed with ANSYS fluent. The velocity vector fields and time histories of velocity are analyzed. In addition, the time-averaged velocity profiles and Reynolds stresses are analyzed. It is found that, in general, LES (3D) gives a better prediction of flow characteristics than RANS (2D).
Numerical Prediction of Added Power in Seaway
Authors: Shigunov Vladimir
Published: July 2018

The paper describes a numerical approach to predict required added power for propulsion in waves. Such predictions are important to address fuel consumption in seaway and define suitable operating point and sea margin, as well as for routing optimization and hull performance monitoring. Added resistance and, in general, drift forces and moments due to waves are key input parameters for added power requirements. The three-dimensional Rankine source-patch method was used to compute them. The method solves the problem in the frequency domain, linearizing wave-induced motions around the fully nonlinear steady flow. The added power software combines added resistance and drift forces and moments in irregular waves with wind forces and moments, calm-water maneuvering forces and moments, rudder and propeller forces, and propulsion and engine model and provides associated resistance and power as well as changes in ship propulsion in waves. The approach is demonstrated for a container ship to compare predictions with full-scale data.
A Phenomenological Model for the Solidification of Eutectic and Hypoeutectic Alloys Including Recalescence and Undercooling
Authors: Chiumenti M. , Cervera M. , Salsi E. , Zonato A.
Published: July 2018

In this work, a novel phenomenological model is proposed to study the liquid-to-solid phase change of eutectic and hypoeutectic alloy compositions. The objective is to enhance the prediction capabilities of the solidification models based on a-priori definition of the solid fraction as a function of the temperature field. However, the use of models defined at the metallurgical level is avoided to minimize the number of material parameters required. This is of great industrial interest because, on the one hand, the classical models are not able to predict recalescence and undercooling phenomena, and, on the other hand, the complexity as well as the experimental campaign necessary to feed most of the microstructure models available in the literature make their calibration difficult and very dependent on the chemical composition and the treatment of the melt. Contrarily, the proposed model allows for an easy calibration by means of few parameters. These parameters can be easily extracted from the temperature curves recorded at the hot spot of the quick cup test, typically used in the differential thermal analysis (DTA) for the quality control of the melt just before pouring. The accuracy of the numerical results is assessed by matching the temperature curves obtained via DTA of eutectic and hypoeutectic alloys. Moreover, the model is validated in more complex casting experiments where the temperature is measured at different thermocouple locations and the metallurgical features such as grain size and nucleation density are obtained from an exhaustive micrography campaign. The remarkable agreement with the experimental evidence validates the predicting capabilities of the proposed model.
Self-Lubricating and Friction Performance of a Three-Dimensional-Printed Journal Bearing
Authors: Lee Yeong-Jae , Lee Kwang-Hee , Lee Chul-Hee
Published: July 2018

In recent years, through the development of three-dimensional (3D) printing technology, 3D‐printed parts have been used in various industries, such as medical equipment and robotics. Various 3D printing methods have been developed. Today, a 3D printer can be used even in precision parts, such as bolts and bearings. In this study, journal bearings are manufactured by a 3D printer to evaluate friction performance and self-lubricating performance. The journal bearings are fabricated using two types of 3D printing method: fused deposition modeling (FDM) and selective laser sintering (SLS). The specimens manufactured by FDM are produced by plastic materials with three-layer thicknesses. Nylon-based materials and aluminum-based materials are used to fabricate the SLS specimen. Micropores are created in the specimens during the printing process. Therefore, the self-lubricating performance can occur by micropores. The experimental setup is designed and constructed to evaluate the friction performance by varying rotational speed and the radial load. Through this study, the self-lubricating performance and friction performance of 3D-printed journal bearings are evaluated, and proper operating conditions for 3D-printed bearings are suggested.
Additional Injury Prevention Criteria for Impact Attenuation Surfacing Within Children's Playgrounds
Authors: Eager David , Hayati Hasti
Published: July 2018

More than four decades have passed since the introduction of safety standards for impact attenuation surfaces (IAS) used in playgrounds. Falls in children's playground are a major source of injuries and IAS is one of the best methods of preventing severe head injuries. However, the ability of IAS in prevention of other types of injuries, such as upper limb fractures, is unclear. Accordingly, in this paper, ten synthetic playground surfaces were tested to examine their performance beyond the collected head injury criterion (HIC) and maximum G-force (Gmax) outputs recommended by ASTM F1292. The aim of this work was to investigate any limitations with current safety criteria and proposing additional criteria to filter hazardous IAS that technically comply with the current 1000 HIC and 200 Gmax thresholds. The proposed new criterion is called the impulse force criterion (If). If combines two important injury predictor characteristics, namely: HIC duration that is time duration of the most severe impact; and the change in momentum that addresses the IAS properties associated with bounce. Additionally, the maximum jerk (Jmax), the bounce, and the IAS absorbed work are presented. HIC, Gmax, If, and Jmax followed similar trends regarding material thickness and drop height. Moreover, the bounce and work done by the IAS on the falling missile at increasing drop heights was similar for all surfaces apart from one viscoelastic foam sample. The results presented in this paper demonstrate the limitations of current safety criteria and should, therefore, assist future research to reduce long-bone injuries in playgrounds.
Constitutive Equations and Finite Element Implementation of Isochronous Nonlinear Viscoelastic Behavior
Authors: Sepiani Hossein , Polak Maria Anna , Penlidis Alexander
Published: July 2018

We present a phenomenological three-dimensional (3D) nonlinear viscoelastic constitutive model for time-dependent analysis. Based on Schapery's single integral constitutive law, a solution procedure has been provided to solve nonlinear viscoelastic behavior. This procedure is applicable to 3D problems and uses time- and stress-dependent material properties to characterize the nonlinear behavior of material. The equations describing material behavior are chosen based on the measured material properties in a short test time frame. This estimation process uses the Prony series material parameters, and the constitutive relations are based on the nonseparable form of equations. Material properties are then modified to include the long-term response of material. The presented model is suitable for the development of a unified computer code that can handle both linear and nonlinear viscoelastic material behavior. The proposed viscoelastic model is implemented in a user-defined material algorithm in abaqus (UMAT), and the model validity is assessed by comparison with experimental observations on polyethylene for three uniaxial loading cases, namely short-term loading, long-term loading, and step loading. A part of the experimental results have been conducted by (Liu, 2007, “Material Modelling for Structural Analysis of Polyethylene,” M.Sc. thesis, University of Waterloo, Waterloo, ON Canada), while the rest are provided by an industrial partner. The research shows that the proposed finite element model can reproduce the experimental strain–time curves accurately and concludes that with proper material properties to reflect the deformation involved in the mechanical tests, the deformation behavior observed experimentally can be accurately predicted using the finite element simulation.
Decentralized Feedback Control of Pumping Losses and NOx Emissions in Diesel Engines
Authors: Salehi Rasoul , Martz Jason , Stefanopoulou Anna , Vernham Bruce , Uppalapati Lakshmidhar , Prashant Baliga Bantwal
Published: July 2018

A novel decentralized control architecture is developed based on a feedback from the pressure difference across the engine which is responsible for the pumping losses and the exhaust gas recirculation (EGR) flow in diesel engines. The controller is supplemented with another feedback loop based on NOx emissions measurement. Aiming for simple design and tuning, the two control loops are designed and discussed: one manipulates the variable geometry turbine (VGT) actuator and the other manipulates the EGR valve. An experimentally validated mean-value diesel engine model is used to analyze the best pairing of actuators and set points. Emphasis is given to the robustness of this pairing based on gain changes across the entire operating region, since swapping the pairing needs to be avoided. The VGT loop is designed to achieve fast cylinder air charge increase in response to a rapid pedal tip-in by a feedforward term based on the real-time derivative of the desired boost pressure. The EGR loop relies on a feedback measurement from a NOx sensor and a real-time estimation of cylinder oxygen ratio, χcyl. The engine model is used for evaluating the designed controllers over the federal test procedure (FTP) for heavy duty (HD) vehicles. Results indicate that the control system meets all targets, namely fast air charge and χcyl control during torque transients, robust NOx control during steady-state operation, and controlled pumping losses in all conditions.
Hybrid-Electric Turbocharger and High-Speed SiC Variable-Frequency Drive Using Sensorless Control Algorithm
Authors: Carpenter Andrew L. , Beechner Troy L. , Tews Brian E. , Yelvington Paul E.
Published: July 2018

Electrically assisted engine boosting systems lend themselves to better throttle response, wider effective operating ranges, and can provide the ability to extract excess energy during deceleration and high-load events (and store it in a vehicle's onboard batteries). This can lead to better overall vehicle performance, emissions, and efficiency while allowing for further engine downsizing and increased power density. In this research effort, a hybrid-electric turbocharger, variable-frequency drive (VFD), and novel sensorless control algorithm were developed. An 11 kW permanent-magnet (PM) machine was coupled to a commercial turbocharger via an in-line, bolt-on housing attached to the compressor inlet. A high-efficiency, high-temperature VFD, consisting of custom control and power electronics, was also developed. The VFD uses SiC MOSFETS to achieve high-switching frequency and can be cooled using an existing engine coolant loop operating at up to 105 °C at an efficiency greater than 98%. A digital sliding mode-observer sensorless speed control algorithm was created to command and regulate speed and achieved ramp rates of over 68,000 rpm/s. A two-machine benchtop motor/generator test stand was constructed for initial testing and tuning of the VFD and sensorless control algorithm. A gas blow-down test stand was constructed to test the mechanical operation of the hybrid-electric turbocharger and speed control using the VFD. In addition, a liquid-pump cart was assembled for high-temperature testing of the VFD. Initial on-engine testing is planned for later this year. This paper intends to present a design overview of the in-line, hybrid-electric device, VFD, and performance characterization of the electronics and sensorless control algorithm.