bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of the Purdue Experimental Turbine Aerothermal Laboratory for Optical and Surface Aerothermal Measurements
Authors: Paniagua G. , Cuadrado D. , Saavedra J. , Andreoli V. , Meyer T. , Solano J. P. , Herrero R. , Meyer S. , Lawrence D.
Published: July 2018

Following three decades of research in short duration facilities, Purdue University has developed an alternative turbine facility in view of the modern technology in computational fluid mechanics, structural analysis, manufacturing, heating, control, and electronics. The proposed turbine facility can operate continuously and also perform transients, suited for precise heat flux, efficiency, and optical measurement techniques to advance turbine aerothermo-structural engineering. The facility has two different test sections, linear and annular, to service both fundamental and applied research. The linear test section is completely transparent for optical imaging and spectroscopy, aimed at technology readiness levels (TRLs) of 1–2. The annular test section was designed with optical access to perform proof of concepts as well as validation of turbine component performance for relevant nondimensional parameters at TRLs of 3–4. The large mass flow rate (28 kg/s) combined with a minimum hub to tip ratio of 0.85 allows high spatial resolution. The Reynolds number (Re) extends from 60,000 to 3,000,000, based on the vane outlet flow properties with an axial chord of 0.06 m and a turning angle of 72 deg. The pressure ratio can be independently adjusted, enabling testing from low subsonic to Mach 3.2. This paper provides a detailed description of the sequential design methodology from zero-dimensional to three-dimensional (3D) unsteady analysis as well as of the measurement techniques available in this turbine facility.
Transient Performance of Separated Flows: Characterization and Active Flow Control
Authors: Saavedra J. , Paniagua G.
Published: July 2018

The aerothermal performance of the low-pressure turbine in unmanned aerial vehicles is significantly abated at high altitude, due to boundary layer separation. Different flow control strategies have been proposed to prevent boundary layer separation, such as dielectric barrier discharges (DBD) and synthetic jets. However, the optimization of the control approach requires a better characterization of the separated regions at transient conditions. The present investigation analyzes the behavior of separated flows, reporting the inception and separation length, allowing the development of efficient flow control methods under nontemporally uniform inlet conditions. The development of separated flows was investigated with numerical simulations including Unsteady Reynolds average Navier–Stokes (URANS) and large Eddy simulations (LES). The present research was performed on a wall-mounted hump, which imposes a pressure gradient representative of the suction side of low pressure turbines. Through sudden flow accelerations, we looked into the dynamic response of the shear layer detachment as it is modulated by the mean flow evolution. Similarly, we studied the behavior of the recirculation bubble under periodic disturbances imposed at various frequencies ranging from 10 to 500 Hz, at which the Reynolds number oscillates between 40,000 and 180,000. As a first step into the flow control, we added a slot to allow flow injection and ingestion upstream of the separation inception. Exploring the behavior of the separated region at different conditions, we defined the envelope for its periodic actuation. We found that by matching the actuator frequency with the frequency response of the separated region, the performance of the actuation is boosted.
Rotordynamic Characterization of a Staggered Labyrinth Seal: Experimental Test Data and Comparison With Predictions
Authors: Cangioli Filippo , Vannini Giuseppe , Pennacchi Paolo , Ciuchicchi Lorenzo , Nettis Leonardo , Chatterton Steven
Published: July 2018

As well known, the stability assessment of turbomachines is strongly related to internal sealing components. For instance, labyrinth seals are widely used in compressors, steam, and gas turbines and pumps to control the clearance leakage between rotating and stationary parts, owing to their simplicity, reliability, and tolerance to large thermal and pressure variations. Labyrinth seals working principle consists of reducing the leakage by imposing tortuous passages to the fluid that are effective on dissipating the kinetic energy of the fluid from high-pressure regions to low-pressure regions. Conversely, labyrinth seals could lead to dynamics issues. Therefore, an accurate estimation of their dynamic behavior is very important. In this paper, the experimental results of a long-staggered labyrinth seal will be presented. The results in terms of rotordynamic coefficients and leakage will be discussed as well as the critical assessment of the experimental measurements. Eventually, the experimental data are compared to the numerical results obtained with the new bulk-flow model (BFM) introduced in this paper.
An Experimental Study on Strain Hardening of Amorphous Thermosets: Effect of Temperature, Strain Rate, and Network Density
Authors: Tian Chuanshuai , Xiao Rui , Guo Jun
Published: July 2018

In this paper, we present an experimental study on strain hardening of amorphous thermosets. A series of amorphous polymers is synthesized with similar glass transition regions and different network densities. Uniaxial compression tests are then performed at two different strain rates spanning the glass transition region. The results show that a more pronounced hardening response can be observed as decreasing temperature and increasing strain rate and network density. We also use the Neo-Hookean model and Arruda–Boyce model to fit strain hardening responses. The Neo-Hookean model can only describe strain hardening of the lightly cross-linked polymers, while the Arruda–Boyce model can well describe hardening behaviors of all amorphous networks. The locking stretch of the Arruda–Boyce model decreases significantly with increasing network density. However, for each amorphous network, the locking stretch is the same regardless of the deformation temperature and rate. The hardening modulus exhibits a sharp transition with temperature. The transition behaviors of hardening modulus also vary with the network density. For lightly crosslinked networks, the hardening modulus changes 60 times with temperature. In contrast, for heavily crosslinked polymers, the hardening modulus in the glassy state is only 2 times of that in the rubbery state. Different from the results from molecular dynamic simulation in literatures, the hardening modulus of polymers in the glassy state does not necessarily increase with network density. Rather, the more significant hardening behaviors in more heavily crosslinked polymers are attributed to a lower value of the stretch limit.
Delamination of a Thin Film Driven by a Flat Cylindrical Shaft
Authors: Julien Scott E. , Wan Kai-Tak
Published: July 2018

An analytical model is derived for the delamination of a thin film from a rigid substrate by a cylindrical shaft with a flat end and finite radius. We show that, within certain limitations, a point-load model can be applied to the system, to give simple relations between the film-substrate energy of adhesion and the measured variables of applied shaft force, blister height, and blister radius. The results are applicable to systems where a finite size cylindrical shaft or disk generates delamination of the film from the substrate.
Crack Growth Resistance in Metallic Alloys: The Role of Isotropic Versus Kinematic Hardening
Authors: Martínez-Pañeda Emilio , Fleck Norman A.
Published: July 2018

The sensitivity of crack growth resistance to the choice of isotropic or kinematic hardening is investigated. Monotonic mode I crack advance under small scale yielding conditions is modeled via a cohesive zone formulation endowed with a traction–separation law. R-curves are computed for materials that exhibit linear or power law hardening. Kinematic hardening leads to an enhanced crack growth resistance relative to isotropic hardening. Moreover, kinematic hardening requires greater crack extension to achieve the steady-state. These differences are traced to the nonproportional loading of material elements near the crack tip as the crack advances. The sensitivity of the R-curve to the cohesive zone properties and to the level of material strain hardening is explored for both isotropic and kinematic hardening.
Homogenization of Mechanical Properties for Material Extrusion Periodic Lattice Structures Considering Joint Stiffening Effects
Authors: Park Sang-In , Rosen David W.
Published: July 2018

Many engineering applications utilize periodic lattice structures to take advantage of their favorable and tailorable mechanical properties. However, manufacturing the structures and evaluating their mechanical properties are still challenging. Additive manufacturing (AM) processes offer an alternative method to fabricate periodic lattice structures but the processes only approximate bounding part surfaces. Periodic lattice structures generally have two important geometrical characteristics, large bounding surfaces, and a large number of joints. Since geometric approximation errors on large bounding surfaces critically affect mechanical properties of the structures, designers and engineers should incorporate this degradation into mechanical property estimation procedures. In addition, the effects of joints should be analyzed in the estimation process, because joints reduce struts lengths, and as a result, they add stiffness to lattice structures. This paper presents a new homogenization approach to estimate mechanical properties of additively manufactured periodic lattice structures that is based on semirigid joint frame elements, and it takes into account effects of geometric approximation errors and joint stiffening. Effective structural parameters of a semirigid joint frame element are calculated from an as-fabricated voxel model to incorporate the geometric approximation errors. The semirigid joint frame element is integrated into a discrete homogenization process to evaluate joint stiffening effects. This paper reports results of parametric studies that investigate effects of AM process and joint properties on periodic lattice structures fabricated by material extrusion. This paper also compares estimates from the proposed approach and conventional homogenization approaches with test results. The comparison shows that the proposed method provides estimates that are more accurate.
Nested and Simultaneous Solution Strategies for General Combined Plant and Control Design Problems
Authors: Herber Daniel R. , Allison James T.
Published: July 2018

In this paper, general combined plant and control design or co-design problems are examined. The previous work in co-design theory imposed restrictions on the type of problems that could be posed. This paper lifts many of those restrictions. The problem formulations and optimality conditions for both the simultaneous and nested solution strategies are given. Due to a number of challenges associated with the optimality conditions, practical solution considerations are discussed with a focus on the motivating reasons for using direct transcription (DT) in co-design. This paper highlights some of the key concepts in general co-design including general coupling, the differences between the feasible regions for each strategy, general boundary conditions, inequality path constraints, system-level objectives, and the complexity of the closed-form solutions. Three co-design test problems are provided. A number of research directions are proposed to further co-design theory including tailored solution methods for reducing total computational expense, better comparisons between the two solution strategies, and more realistic test problems.
Emission of Carbonyl and Polyaromatic Hydrocarbon Pollutants From the Combustion of Liquid Fuels: Impact of Biofuel Blending
Authors: Dagaut Philippe , Bedjanian Yuri , Dayma Guillaume , Foucher Fabrice , Grosselin Benoît , Romanias Manolis , Shahla Roya
Published: July 2018

The combustion of conventional fuels (diesel and Jet A-1) with 10–20% vol oxygenated biofuels (ethanol, 1-butanol, methyl octanoate, rapeseed oil methyl ester (RME), diethyl carbonate, tri(propylene glycol)methyl ether, i.e., CH3(OC3H6)3OH, and 2,5-dimethylfuran (2,5-DMF)) and a synthetic paraffinic kerosene (SPK) was studied. The experiments were performed using an atmospheric pressure laboratory premixed flame and a four-cylinder four-stroke diesel engine operating at 1500 rpm. Soot samples from kerosene blends were collected above a premixed flame for analysis. Polyaromatic hydrocarbons (PAHs) were extracted from the soot samples. After fractioning, they were analyzed by high-pressure liquid chromatography (HPLC) with UV and fluorescence detectors. C1 to C8 carbonyl compounds (CBCs) were collected at the diesel engine exhaust on 2,4-dinitrophenylhydrazine coated cartridges (DNPH) and analyzed by HPLC with UV detection. The data indicated that blending conventional fuels with biofuels has a significant impact on the emission of both CBCs and PAHs adsorbed on soot. The global concentration of 18 PAHs (1-methyl-naphthalene, 2-methyl-naphthalene, and the 16 U.S. priority EPA PAHs) on soot was considerably lowered using oxygenated fuels, except 2,5-DMF. Conversely, the total carbonyl emission increased by oxygenated biofuels blending. Among them, ethanol and 1-butanol were found to increase considerably the emissions of CBCs.
An Analytical Structural Strain Method for Steel Umbilical in Low Cycle Fatigue
Authors: Wang Wei , Pei Xianjun
Published: July 2018

Pipes, especially risers, pipelines, and umbilicals, are extensively used in the subsea production system. Umbilical, as a controlling component of subsea production system, as well as other pipes, will resist reeling, unreeling, and additional processing before on-site installation, which might lead to yielding and plastic deformation of the pipe. This plastic deformation often results in low cycle fatigue (LCF) issue of the pipes, and how to effectively estimate the corresponding fatigue life has become a topic of practical engineering interest. In the present paper, a structural strain method is applied to determine the elastic core of the pipe and to calculate the pseudo structural stress. The pseudo structural stress concept has been applied to analyze the pipe in LCF regime. Further, the results obtained have been compared with the experimental and other available data. It can be seen that the results coincide well with the experimental data. In addition to the demonstrated effectiveness, the key advantage of this pseudo structural stress approach is the simplicity in dealing with girth-welded pipe sections, since finite element stress analysis is unnecessary.
Approximate Solution of the Fokker–Planck Equation for a Multidegree of Freedom Frictionally Damped Bladed Disk Under Random Excitation
Authors: Förster Alwin , Panning-von Scheidt Lars , Wallaschek Jörg
Published: July 2018

Bladed disks are subjected to different types of excitations, which cannot, in any, case be described in a deterministic manner. Fuzzy factors, such as slightly varying airflow or density fluctuation, can lead to an uncertain excitation in terms of amplitude and frequency, which has to be described by random variables. The computation of frictionally damped blades under random excitation becomes highly complex due to the presence of nonlinearities. Only a few publications are dedicated to this particular problem. Most of these deal with systems of only one or two degrees-of-freedom (DOFs) and use computational expensive methods, like finite element method or finite differences method (FDM), to solve the determining differential equation. The stochastic stationary response of a mechanical system is characterized by the joint probability density function (JPDF), which is driven by the Fokker–Planck equation (FPE). Exact stationary solutions of the FPE only exist for a few classes of mechanical systems. This paper presents the application of a semi-analytical Galerkin-type method to a frictionally damped bladed disk under influence of Gaussian white noise (GWN) excitation in order to calculate its stationary response. One of the main difficulties is the selection of a proper initial approximate solution, which is applicable as a weighting function. Comparing the presented results with those from the FDM, Monte–Carlo simulation (MCS) as well as analytical solutions proves the applicability of the methodology.
Quantification of the Impact of Uncertainties in Operating Conditions on the Flame Transfer Function With Nonintrusive Polynomial Chaos Expansion
Authors: Avdonin Alexander , Polifke Wolfgang
Published: July 2018

Nonintrusive polynomial chaos expansion (NIPCE) is used to quantify the impact of uncertainties in operating conditions on the flame transfer function (FTF) of a premixed laminar flame. NIPCE requires only a small number of system evaluations, so it can be applied in cases where a Monte Carlo simulation is unfeasible. We consider three uncertain operating parameters: inlet velocity, burner plate temperature, and equivalence ratio. The FTF is identified in terms of the finite impulse response (FIR) from computational fluid dynamics (CFD) simulations with broadband velocity excitation. NIPCE yields uncertainties in the FTF due to the uncertain operating conditions. For the chosen uncertain operating bounds, a second-order expansion is found to be sufficient to represent the resulting uncertainties in the FTF with good accuracy. The effect of each operating parameter on the FTF is studied using Sobol indices, i.e., a variance-based measure of sensitivity, which are computed from the NIPCE. It is observed that in the present case, uncertainties in the FIR as well as in the phase of the FTF are dominated by the equivalence-ratio uncertainty. For frequencies below 150 Hz, the uncertainty in the gain of the FTF is also attributable to the uncertainty in equivalence-ratio, but for higher frequencies, the uncertainties in velocity and temperature dominate. At last, we adopt the polynomial approximation of the output quantity, provided by the NIPCE method, for further uncertainty quantification (UQ) studies with modified input uncertainties.
Influence of the Position of Oil Drain Holes of a Piston on Lubricating Oil Consumption
Authors: Hasegawa Hiroki , Kikuhara Koji , Ito Akemi , Nishijima Shunsuke , Inui Masatsugu , Akamatsu Hirotaka
Published: July 2018

An increase in lubricating oil consumption in a gasoline engine causes an increase in particulate matters in exhaust gases, poisoning the catalyst after treatment devices, abnormal combustion in a turbo-charged gasoline engine, and so on. Recent trend of low friction of a piston and piston ring tends to increase in lubricating oil consumption. Therefore, reducing oil consumption is required strongly. In this study, the effect of the position of oil drain holes on oil pressure under the oil ring and lubricating oil consumption was investigated. The oil pressure under the oil ring is measured using fiber optic pressure sensors and pressure generation mechanisms were investigated. Lubricating oil consumption was also measured using sulfur tracer method and the effects of oil drain holes hence the oil pressure were evaluated. Four types of arrangement of oil drain holes were tested. The oil pressure variations under the oil ring in the circumferential direction was measured. An increase in oil pressure was found during down-stroke of the piston. The lowest oil pressure was found for the piston with four oil drain holes. Two holes nearby the front/rear end of the piston skirt showed relatively lower pressure. The measured results of oil consumption showed good agreement to measured oil pressure under the oil ring. It was found that oil pressure under the oil ring affected oil consumption, and oil drain holes set near the front/rear end of the piston skirt were effective for reducing oil consumption.
Optimized Cyclic Water Injection Strategy for Oil Recovery in Low-Permeability Reservoirs
Authors: Sun* Xiaofei , Zhang Yanyu , Wu Jie , Xie Mengke , Hu Hang
Published: July 2018

With the worldwide decline in conventional oil production, tremendous unconventional resources, such as low-permeability reservoirs, are becoming increasingly important. Cyclic water injection (CWI) as an oil recovery method has attracted increasing attention in the present environment of low oil prices. However, the optimal CWI strategy is difficult to determine for a mature oilfield due to the involvement of multiple wells with multiple operational parameters. Thus, our main focus in this paper is to present a novel and systematic approach to optimize CWI strategies by studying a typical low-permeability, namely, reservoir G21. To this end, a comprehensive method that combines the advantages of streamline simulation and fuzzy comprehensive evaluation (FCE) was proposed to identify water channeling in the reservoir. Second, the reliability of the method was verified using tracer tests. Finally, a new hybrid optimization algorithm, the simulated annealing-genetic algorithm (SAGA), coupled with a reservoir simulator was developed to determine an optimal CWI strategy for the low-permeability reservoir. The results show that the CWI technique is viable as a primary means in the present environment of low oil prices to improve the waterflood performance in low-permeability reservoirs. The oil recovery of the most efficient strategy increases by 6.8% compared to conventional waterflooding. The asymmetric CWI scheme is more efficient than the symmetric CWI scheme for the low-permeability reservoir.
Initiation Pressure and Corresponding Initiation Mode of Drilling Induced Fracture in Pressure Depleted Reservoir
Authors: Gao Qi , Cheng Yuanfang , Yan Chuanliang , Jiang Long , Han Songcai
Published: July 2018

With the production of oil and gas from the reservoir for a long period of time, pore pressure will decline from the initial value to a lower level, which narrows the safety mud weight window, and consequently, makes it easier to generate the drilling induced fracture (DIF). In this paper, a new analytical model is proposed for predicting initiation pressure and corresponding initiation mode of DIF in the pressure depleted reservoir. The effect of pore pressure decline on stress field is considered. Formation around the borehole is divided into plastic zone and elastic zone according to the geomechanical parameters, and small deformation theory is adopted in both of the plastic zone and the elastic zone. For the plastic zone, the nonlinear constitutive relationship is captured using equivalent stress and equivalent strain. In addition, excess pore pressure theory is introduced to describe the pore pressure change during the drilling process owing to the formation of mudcake on the borehole wall. Then, the stress and pore pressure distribution in these two zones and the radius of the plastic zone are obtained. Meanwhile, the theoretical formula of initiation pressure and the corresponding initiation mode of DIF are derived. The reliability of the new model is validated by comparing the obtained results with other published models and the field measured data.
Well Placement Optimization With Cat Swarm Optimization Algorithm Under Oilfield Development Constraints
Authors: Hongwei Chen , Qihong Feng , Xianmin Zhang , Sen Wang , Wensheng Zhou , Fan Liu
Published: July 2018

Proper well placement can improve the oil recovery and economic benefits during oilfield development. Due to the nonlinear and complex properties of well placement optimization, an effective optimization algorithm is required. In this paper, cat swarm optimization (CSO) algorithm is applied to optimize well placement for maximum net present value (NPV). CSO algorithm, a heuristic algorithm that mimics the behavior of a swarm of cats, has characteristics of flexibility, fast convergence, and high robustness. Oilfield development constraints are taken into account during well placement optimization process. Rejection method, repair method, static penalization method, dynamic penalization method and adapt penalization method are, respectively, applied to handle well placement constraints and then the optimal constraint handling method is obtained. Besides, we compare the CSO algorithm optimization performance with genetic algorithm (GA) and differential evolution (DE) algorithm. With the selected constraint handling method, CSO, GA, and DE algorithms are applied to solve well placement optimization problem for a two-dimensional (2D) conceptual model and a three-dimensional (3D) semisynthetic reservoir. Results demonstrate that CSO algorithm outperforms GA and DE algorithm. The proposed CSO algorithm can effectively solve the constrained well placement optimization problem with adapt penalization method.
Nested Plant/Controller Codesign Using G-Optimal Design and Continuous Time Adaptation Laws: Theoretical Framework and Application to an Airborne Wind Energy System
Authors: Deese Joe , Vermillion Chris
Published: July 2018

This paper presents a nested codesign (combined plant and controller design) formulation that uses optimal design of experiments (DoE) techniques at the upper level to globally explore the plant design space, with continuous-time control parameter adaptation laws used at the lower level. The global design space exploration made possible through optimal DoE techniques makes the proposed methodology appealing for complex, nonconvex optimization problems for which legacy approaches are not effective. Furthermore, the use of continuous-time adaptation laws for control parameter optimization allows for the extension of the proposed optimization framework to the experimental realm, where control parameters can be optimized during experiments. At each full iteration, optimal DoE are used to generate a batch of plant designs within a prescribed design space. Each plant design is tested in either a simulation or experiment, during which an adaptation law is used for control parameter optimization. Two techniques are proposed for control parameter optimization at each iteration: extremum seeking (ES) and continuous-time DoE. The design space is reduced at the end of each full iteration, based on a response surface characterization and quality of fit estimate. The effectiveness of the approach is demonstrated for an airborne wind energy (AWE) system, where the plant parameters are the center of mass location and stabilizer area, and the control parameter is the trim pitch angle.
Influence of Variable Geometry Compressor on Transient Performance of Counter-Rotating Open Rotor Engines
Authors: Silva Vinícius Tavares , Bringhenti Cleverson , Tomita Jesuino Takachi , Petit Olivier
Published: July 2018

This work describes a methodology used for counter-rotating (CR) propellers performance estimation. The method is implemented in an in-house program for gas turbine performance prediction, making possible the simulation of the counter-rotating open rotor (CROR) architecture. The methodology is used together with a variable geometry compressor control strategy to avoid surge conditions. Two cases are simulated under transient operation for both fixed and variable geometry compressor. The influence of the variable geometry control on the transient performance of CROR engines is evaluated and a comprehensive understanding on the transient behavior of this type of engine could be obtained. It is shown that the use of the variable geometry compressor control does not significantly affect the overall engine performance, while avoiding the surge conditions, thus ensuring the engine operation safety.
Highly Directional Acoustic Waves Generated by a Horned Parametric Acoustic Array Loudspeaker
Authors: Tong L. H. , Lai S. K. , Yan J. W. , Li C.
Published: July 2018

Acoustic horns can enhance the overall efficiency of loudspeakers to emanate highly directional acoustic waves. In this work, a theoretical model is developed to predict difference frequency acoustic fields generated by a parametric array loudspeaker (PAL) with a flared horn. Based on this model, analytical solutions are obtained for exponentially horned PALs. A numerical analysis on the performance of horned PALs subject to various horn parameters (i.e., horn length and flare constant) is implemented. To compare with nonhorned parametric acoustic array (PAA) devices, it is able to generate highly directional acoustic wave beams for a wide range of difference frequencies, in which the generated sound pressure levels at low frequencies can be significantly enhanced. In addition, the equivalent radius of a nonhorned emitter that matches the directivity achieved by a horned one is also quantitatively investigated. The present research will provide useful guidelines for the design and optimization of horned parametric array equipment.
Construction of Analysis-Suitable Vascular Models Using Axis-Aligned Polycubes
Authors: Updegrove Adam R. , Shadden Shawn C. , Wilson Nathan M.
Published: July 2018

Image-based modeling is an active and growing area of biomedical research that utilizes medical imaging to create patient-specific simulations of physiological function. Under this paradigm, anatomical structures are segmented from a volumetric image, creating a geometric model that serves as a computational domain for physics-based modeling. A common application is the segmentation of cardiovascular structures to numerically model blood flow or tissue mechanics. The segmentation of medical image data typically results in a discrete boundary representation (surface mesh) of the segmented structure. However, it is often desirable to have an analytic representation of the model, which facilitates systematic manipulation. For example, the model then becomes easier to union with a medical device, or the geometry can be virtually altered to test or optimize a surgery. Furthermore, to employ increasingly popular isogeometric analysis (IGA) methods, the parameterization must be analysis suitable. Converting a discrete surface model to an analysis-suitable model remains a challenge, especially for complex branched structures commonly encountered in cardiovascular modeling. To address this challenge, we present a framework to convert discrete surface models of vascular geometries derived from medical image data into analysis-suitable nonuniform rational B-splines (NURBS) representation. This is achieved by decomposing the vascular geometry into a polycube structure that can be used to form a globally valid parameterization. We provide several practical examples and demonstrate the accuracy of the methods by quantifying the fidelity of the parameterization with respect to the input geometry.
A Fluid–Structure Interaction Model of the Left Coronary Artery
Authors: Meza Daphne , Rubenstein David A. , Yin Wei
Published: July 2018

A fluid–structure interaction (FSI) model of a left anterior descending (LAD) coronary artery was developed, incorporating transient blood flow, cyclic bending motion of the artery, and myocardial contraction. The three-dimensional (3D) geometry was constructed based on a patient's computed tomography angiography (CTA) data. To simulate disease conditions, a plaque was placed within the LAD to create a 70% stenosis. The bending motion of the blood vessel was prescribed based on the LAD spatial information. The pressure induced by myocardial contraction was applied to the outside of the blood vessel wall. The fluid domain was solved using the Navier–Stokes equations. The arterial wall was defined as a nonlinear elastic, anisotropic, and incompressible material, and the mechanical behavior was described using the modified hyper-elastic Mooney–Rivlin model. The fluid (blood) and solid (vascular wall) domains were fully coupled. The simulation results demonstrated that besides vessel bending/stretching motion, myocardial contraction had a significant effect on local hemodynamics and vascular wall stress/strain distribution. It not only transiently increased blood flow velocity and fluid wall shear stress, but also changed shear stress patterns. The presence of the plaque significantly reduced vascular wall tensile strain. Compared to the coronary artery models developed previously, the current model had improved physiological relevance.
An Acoustomechanical Constitutive Model of Gel Considering Cavitation Effect in Exposure to Ultrasound
Authors: Huang Qinyi , Pan Yihui , Zhong Zheng
Published: July 2018

In this paper, an acoustomechanical constitutive model is developed to describe the heating effect of a tissue-mimicking gel by cavitation in exposure to high-intensity focused ultrasound (HIFU). An internal variable, representing the evolution of cavitation process, is introduced into the Helmholtz free energy under the framework of thermodynamics that combines the acoustic radiation stress theory and the nonlinear elasticity theory together. Thus, the internal variable is related to the cavitation process and the mechanical energy dissipation of a tissue-mimicking gel from a macroscopic viewpoint. Since the temperature rise of cavitation phenomenon is more remarkable than that of heating waves, the temperature inside the tissue-mimicking gel rises rapidly mainly due to large amounts of cavitation bubbles. This phenomenon can be quantitatively described by the present model, which fits the existing experimental data well.
Finite Element Based Full-Life Cyclic Stress Analysis of 316 Grade Nuclear Reactor Stainless Steel Under Constant, Variable, and Random Fatigue Loading
Authors: Barua Bipul , Mohanty Subhasish , Listwan Joseph T. , Majumdar Saurindranath , Natesan Krishnamurti
Published: July 2018

Although S∼N curve-based approaches are widely followed for fatigue evaluation of nuclear reactor components and other safety critical structural systems, there is a chance of large uncertainty in estimated fatigue lives. This uncertainty may be reduced by using a more mechanistic approach such as physics based three-dimensional (3D) finite element (FE) methods. In a recent paper (Barua et al., 2018, ASME J. Pressure Vessel Technol., 140(1), p. 011403), a fully mechanistic fatigue modeling approach which is based on time-dependent stress–strain evolution of material over the entire fatigue life was presented. Based on this approach, in this work, FE-based cyclic stress analysis was performed on 316 nuclear grade reactor stainless steel (SS) fatigue specimens, subjected to constant, variable, and random amplitude loading, for their entire fatigue lives. The simulated results are found to be in good agreement with experimental observation. An elastic-plastic analysis of a pressurized water reactor (PWR) surge line (SL) pipe under idealistic fatigue loading condition was performed and compared with experimental results.
Semitheoretical Prediction of the Wetting Characteristics of Aqueous Ionic Liquid Solution on an Aluminum Finned-Tube Desiccant Contactor
Authors: Giannetti Niccolo , Varela Richard Jayson , Ariyadi Hifni , Yamaguchi Seiichi , Saito Kiyoshi , Wang Xin-Ming , Nakayama Hiroshi
Published: July 2018

This study involves exploring a new design of an internally cooled/heated desiccant contactor by using a new ionic liquid (IL) solution as the sorptive solution. In order to optimize its operative performance, a semitheoretical model based on the principle of minimum energy is developed to predict the film rupture and wetting ability of the IL solution over a comprehensive range of IL mass fraction and flow rates. A first experimental validation of the fundamental equations of the theoretical model is presented and used as a reference to minimize deviations between predicted results and measured data by calibrating dedicated characteristic coefficients. The noteworthy quantitative and qualitative agreement in the whole range of IL mass fractions and flow rates is promising for contributing to the design of optimized system configurations and control strategies.
Dynamic Assessment and Modeling of the Modal Frequencies and Shapes of Bovine Tibia
Authors: Yassine Reem , Fakhreddine Ali , Sayegh Mohammad , Mustapha Samir , Hamade Ramsey F.
Published: July 2018

Thirteen long tibia (bovine) bones were utilized in vitro to experimentally extract modal frequencies in the cranial-caudal (C-C) and medial–lateral (M–L) planes. Bones were instrumented with four single-axis accelerometers uniformly placed along the length of the bone and hammer impacted at different locations in both planes. Frequency response function (FRF) and complex mode indicator function (CMIF) techniques were used to identify the modal frequencies. CMIF has an advantage of detecting closely spaced modes by excluding misinterpreted peaks. It was found that the difference between the two methods did not exceed 2.98%. CMIF data were more consistent when varying impact location. The effect of bone's geometrical attributes on modal frequencies was statistically scrutinized and highly correlated parameters were identified. Bone length exhibited high correspondence to frequencies (p < 0.05) for practically all modes. Also, four simple equations were developed, relating modes 1 and 2 in the C-C and M-L planes to bone length. To determine the first and second modal shapes, subset of 6 tibia bones was further instrumented. Mode shapes were extracted in the C-C and M-L planes.
On the Significance of the Higher-Order Stress in Riser Vortex-Induced Vibrations Responses
Authors: Wu Jie , Yin Decao , Lie Halvor , Larsen Carl M. , Baarholm Rolf J. , Liapis Stergios
Published: July 2018

Vortex-induced vibrations (VIV) can lead to fast accumulation of fatigue damage and increased drag loads for slender marine structures. VIV responses mainly occur at the vortex shedding frequency, while higher harmonics can also be excited. Recent VIV model tests with flexible pipes have shown that higher harmonics in the crossflow (CF) direction can contribute to the fatigue damage significantly due to its higher frequency. Rigid cylinder experiments show that the CF third-order harmonics are more pronounced when the motion orbit is close to a “figure 8” shape and the cylinder is moving against the flow at its largest CF motion. However, there is still lack of understanding of when and where higher harmonics occur for a flexible pipe. Therefore, significant uncertainty remains on how to account for fatigue damage due to higher harmonics in VIV prediction. In the present paper, representative VIV data from various riser model test campaigns are carefully studied and analyzed. The key parameters that influence the magnitude of the third-order harmonic stress are found to be the bending stiffness, the reduced velocity, and the orbit stability. The experimental data are analyzed in order to assess the impact of each parameter on the third-order harmonic stress. A preliminary empirical response model to estimate the maximum CF third-order harmonic stress based on these identified structural and hydrodynamic parameters has been proposed. The results of this study will contribute to reduce the uncertainty and unnecessary conservatism in VIV prediction.
Experimental and Numerical Study on the Flow Reduction in the Moonpool of Floating Offshore Structure
Authors: Yoo Seon Oh , Kim Hyun Joe , Lee Dong Yeon , Kim Booki , Yang Seung Ho
Published: July 2018

Recently, drillship moonpools are getting longer and wider for the higher operability. With this trend, violent internal flows are getting more concerned in terms of the safety and operability, which have been reported during the operations even in mild seas. Also, it is well known that the internal flow gives higher resistance during the transit of drillship. In this study, to see the effect of larger damping devices, a series of experimental and numerical study was carried out for the four moonpool designs; the ordinary plain moonpool, the moonpool with a recess deck, the moonpool with an isolated recess deck (island deck), and moonpool with a combination of island deck, splash plates, and wave absorber. From the model tests, it was found that the internal flow of the moonpool was significantly reduced by the application of the wave absorber. In case of the moonpool with the island deck, the sloshing mode oscillations was not observed due to the gap flow between the inner wall of the moonpool and the recess. For the in-depth understanding of the flow behaviors and characteristics, the internal flow of the moonpool has been investigated using Reynolds-averaged Navier–Stokes based computational fluid dynamics (CFD) code. The various moonpool designs were simulated to identify the effect of each device for the internal flow reduction of the moonpool. The CFD analysis results with regular waves, the water surface responses inside moonpool such as the flow pattern and resonance frequency, were compared with model test results and showed reasonably good agreements.
Problems and Perspectives in Seismic Quantitative Risk Analysis of Chemical Process Plants
Authors: Caputo Antonio C. , Paolacci Fabrizio , Bursi Oreste S. , Giannini Renato
Published: July 2018

Earthquakes represent a class of natural-technical (NaTech) hazards which in the past have been responsible of major accidents and significant losses in many industrial sites. However, while codes and standards are issued to design specific structures and equipment in both the civil and industrial domain, established procedures for seismic quantitative risk assessment (QRA) of process plants are not yet available. In this paper, a critical review of seismic QRA methods applicable to process plants is carried out. Their limitations are highlighted and areas where further research is needed are identified. This will allow to refine modeling tools in order to increase the capabilities of risk analysis in process plants subjected to earthquakes.
Performance Analysis of an Intermediate-Temperature-SOFC/Gas Turbine Hybrid System Using Gasified Biomass Fuel in Different Operating Modes
Authors: Lv Xiaojing , Ding Xiaoyi , Weng Yiwu
Published: July 2018

This work used the established mathematic models of an intermediate-temperature solid oxide fuel cell (IT-SOFC) and gas turbine (GT) hybrid system fueled with wood chip gas to investigate the load performance and safe characteristic under off-design conditions. Three different operating modes (mode A: regulating the fuel proportionally, and the air is passively regulated. Mode B: regulating the fuel only. Mode C: simultaneously regulating the fuel and air) were chosen, and the component safety factors (such as fuel cell maximum temperature, compressor surge margin, carbon deposition in reformer) were considered. Results show that when the operation modes A and C are executed, the hybrid system output power can be safely changed from 41% to 104%, and 45% to 103%, respectively. When mode B is executed, the load adjustment range of hybrid system is from 20% to 134%, which is wider than that of two above operation modes. However, the safety characteristic in this case is very complicated. The system will suffer from two potential malfunctions caused by too lower temperature entering turbine and CH4/CO cracking in reforming reactor when it operates in low load conditions. When the system operates in the high load conditions exceeding 130% of relative power, the potential thermal cracking of fuel cell will be occurred.
A Three-Dimensional-Printed Patient-Specific Phantom for External Beam Radiation Therapy of Prostate Cancer
Authors: Lee Christopher L. , Dietrich Max C. , Desai Uma G. , Das Ankur , Yu Suhong , Xiang Hong F. , Carl Jaffe C. , Hirsch Ariel E. , Nicolas Bloch B.
Published: July 2018

This paper presents the design evolution, fabrication, and testing of a novel patient and organ-specific, three-dimensional (3D)-printed phantom for external beam radiation therapy (EBRT) of prostate cancer. In contrast to those found in current practice, this phantom can be used to plan and validate treatment tailored to an individual patient. It contains a model of the prostate gland with a dominant intraprostatic lesion (DIL), seminal vesicles, urethra, ejaculatory duct, neurovascular bundles, rectal wall, and penile bulb generated from a series of combined T2-weighted/dynamic contrast-enhanced magnetic resonance (MR) images. The iterative process for designing the phantom based on user interaction and evaluation is described. Using the CyberKnife System at Boston Medical Center, a treatment plan was successfully created and delivered. Dosage delivery results were validated through gamma index calculations based on radiochromic film measurements which yielded a 99.8% passing rate. This phantom is a demonstration of a methodology for incorporating high-contrast MR imaging into computed-tomography-based radiotherapy treatment planning; moreover, it can be used to perform quality assurance (QA).
Nanostructured Carbon Electrodes for Increased Power Density in Flow Thermo-Electrochemical Generator Heat Sinks
Authors: Kazim Ali H. , Cola Baratunde A.
Published: July 2018

Heat is a by-product of all energy conversion mechanisms. Efforts to utilize and dissipate heat remain a challenge for further development and optimization of energy conversion devices. Stationary thermo-electrochemical cell is a low cost method to harvest heat; however, it suffers from low power density. Flow thermo-electrochemical cell (fTEC) heat sink presents itself as a unique solution as it can simultaneously scavenge and remove heat to maintain devices in the operating range. In this work, multiwalled nanotube (MWNT) electrodes have been used and electrode configuration has been changed to maximize the temperature difference over a small interelectrode separation. As a result, power per unit area of fTEC heat sink has been improved by more than seven-fold to 0.36 W/m2.
Effects of Particle Size Distribution on Compacted Density of Lithium Iron Phosphate 18650 Battery
Authors: Chen Lei , Chen Zhenyu , Liu Shuaishuai , Gao Biaofeng , Wang Junwei
Published: July 2018

The effects of particle size distribution on compacted density of as-prepared spherical lithium iron phosphate (LFP) LFP-1 and LFP-2 materials electrode for high-performance 18650 Li-ion batteries are investigated systemically, while the selection of two commercial materials LFP-3 and LFP-4 as a comparison. The morphology study and physical characterization results show that the LFP materials are composed of numerous particles with an average size of 300–500 nm, and have well-developed interconnected pore structure and a specific surface area of 13–15 m2/g. For CR2032 coin-type cell, the specific discharge capacities of the LFP-1 and LFP-2 are about 165 mAh/g at 0.2 C. For 18650 batteries, results indicate that the LFP-3 material has the highest compacted density of 2.52 g/cm3 at a concentrated particle size distribution such as D10 = 0.56 μm, D50 = 1.46 μm, and D90 = 6.53 μm. By mixing two different particle sizes of LFP-1 and LFP-2, the compaction density can be increased significantly from 1.90 g/cm3 to 2.25 g/cm3.
Polymer Modulus of Elasticity and Hardness From Impact Data
Authors: Sherif Hany A. , Almufadi Fahad A.
Published: July 2018

The present paper introduces a simple method to predict the modulus of elasticity and the hardness of polymeric materials that range from soft elastomers to hard plastics. Hertzian elastic impact model is used to define the relationship between the contact time duration and the maximum force of normal contact due to the impact of a hard sphere indenter with the tested polymer sample. It is shown that the adopted model and experimental method can be used as a tool for extracting the magnitude of the complex modulus of elasticity. Moreover, a new impact index is shown to be proportional to the polymer shore hardness. Theoretical and experimental results based on the force–time signals are consistent and show good correlation.