bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the Shear Modulus of Orthotropic Thin Sheets With the Anticlastic-Plate-Bending Experiment
Authors: Deng Nengxiu , Korkolis Yannis P.
Published: July 2018

The shear modulus of orthotropic thin sheets from three advanced high-strength steels (AHSS) is measured using the anticlastic-plate-bending (APB) experiment. In APB, a thin square plate is loaded by point forces at its four corners, paired in opposite directions. It thus assumes the shape of a hyperbolic paraboloid, at least initially. The principal stress directions coincide with the plate diagonals, and the principal stresses are equal and opposite. Hence, at 45 deg to these, a state of pure shear exists. A finite element (FE) study of APB is reported first, using both elastic and elastoplastic material models. This study confirms the theoretical predictions of the stress field that develops in APB. The numerical model is then treated as a virtual experiment. The input shear modulus is recovered through this procedure, thus validating this approach. A major conclusion from this numerical study is that the shear modulus for these three AHSS should be determined before the shear strain exceeds 2 × 10−4 (or 200 με). Subsequently, APB experiments are performed on the three AHSS (DP 980, DP 1180 and MS 1700). The responses recorded in these experiments confirm that over 3 × 10−4 strain (or 300 με) the response differs from the theoretically expected one, due to excessive deflections, yielding, changing contact conditions with the loading rollers and, in general, the breaking of symmetry. But under that limit, the responses recorded are linear, and can be used to determine the shear modulus.
Development of a Spouted Bed Reactor for Chemical Looping Combustion
Authors: van der Watt Johannes George , Laudal Daniel , Krishnamoorthy Gautham , Feilen Harry , Mann Michael , Shallbetter Ryder , Nelson Teagan , Srinivasachar Srivats
Published: July 2018

We have investigated a novel gas/solid contacting configuration for chemical looping combustion (CLC) with potential operating benefits. CLC configurations are typically able to achieve high fuel conversion efficiencies at the expense of high operating costs and low system reliability. The spouted fluid bed (SB) was identified as an improved reactor configuration for CLC, since it typically exhibits high heat transfer rates and offers the ability to use lower gas flows for material movement compared to bubbling beds (BB). Multiphase Flow with Interphase eXchanges (MFIX) software was used to establish a spouted fluid bed reactor design. An experimental setup was built to supplement the model. The experimental setup was also modified for testing under high temperature, reacting conditions (1073–1273 K). The setup was operated in either a spouted fluid bed or a bubbling bed regime to compare the performance attributes of each. Results for the reactor configurations are presented for CLC using a mixture of carbon monoxide and hydrogen as fuel. Compared to the bubbling bed, the spouted fluid bed reactor achieved an equivalent or better fuel conversion at a lower pressure drop over the material bed. The spouted fluid bed design represents a viable configuration to improve gas/solid contacting for efficient fuel conversion, lower energy requirements for material movement and increase operational robustness for CLC. The research laid the groundwork for future research into a multi-phase reacting flow CLC system. The system will be developed from computational fluid dynamic modeling and pilot-scale testing to expedite the development of CLC technologies.
Ultrasonic Welding of Carbon Fiber Reinforced Composite With Variable Blank Holding Force
Authors: Li Yang , Arinez Jorge , Liu Zhiwei , Hwa Lee Tae , Fan Hua-Tzu , Xiao Guoxian , Banu Mihaela , Jack Hu S.
Published: July 2018

Energy directors (EDs) have been widely used in ultrasonic welding (UW) of polymers and polymer-based composites. They help concentrate the welding energy and localize the weld at the location where the EDs are present. However, the utilization of EDs increases manufacturing cost and time, especially for complex parts and structures. This paper presents a method for UW of carbon fiber reinforced composite without using EDs. A reusable annular clamp (called a blankholder) is used as part of the weld tool to apply a variable force (called blank holding force) on the composite sheets during the UW. The effect of the blank holding force (BHF) on the weld formation is investigated. The results show that the duration of the BHF had significant impact on the weld formation. There is a critical duration with which a localized weld can form. Suitable durations of BHF at different levels of welding energy are determined by experiments. The main function of the BHF is to create an initial melting area by improving the contact condition. The initial melting area will act as an ED to concentrate the welding energy, and therefore, promotes the formation of a localized weld.
Additive Manufacturing for Health: State of the Art, Gaps and Needs, and Recommendations
Authors: Huang Yong , Schmid Steven R.
Published: July 2018

Additive manufacturing (AM) involves using computer-controlled machines to fabricate three-dimensional (3D) structural and functional parts layer by layer. To date, ample AM application opportunities exist in the health field. Based on the outcomes at the 2016 National Science Foundation AM for Health workshop, this paper summarizes the current state, gaps and research needs, and recommendations related to AM for health, in particular, hard structure and medical product printing and soft construct bioprinting. Manufacturing-related knowledge gaps and needs mainly fall into the materials, design, process innovation, part characterization, and policy and education categories. Hard structures and medical products can be designed to integrate with tissues, and their gaps and needs are typically related to the material-process-property-functionality relationship. Bioprinting-specific gaps and needs include build material selection and construct design, printed construct preservation, process selection, scalability and modeling, bioprinting-induced cell injury management, postprinting tissue fusion and maturation, and printed construct evaluation. Research recommendations encompass aspects ranging from fundamental research support to development of suitable standards for clinical use of AM products and are summarized in terms of materials, design, process innovation, modeling, characterization, and policy and education. Hard structure and medical product-specific recommendations are mainly related to build materials and structure design. For bioprinting, recommendations are summarized based on preparation, bioprinting process, and postbioprinting treatment. Furthermore, a biomedical manufacturing landscape is proposed, the potential of bioprinting as transformative research is introduced, and manufacturing-related scientific challenges are listed.
Skeleton-Section Template Parameterization for Shape Optimization
Authors: Hu Ping , Yang Lei , Li Baojun
Published: July 2018

A technique based on a skeleton-section template for parameterizing finite element (FE) models is reported and applied to shape optimization of thin-walled beam components. The template consists of a skeletal curve and a set of cross-sectional profiles. The skeletal curve can be used to derive global model variations, while the cross section is designed to obtain local deformations of the given shape. A mesh deformation method based on the radial basis functions (RBF) interpolation is employed to derive the shape variations. Specifically, the skeleton-embedding space and an anisotropic distance metric are introduced to improve the RBF deformation method. To validate the applicability of the proposed template-based parameterization technique to general shape optimization frameworks, two proof-of-concept numerical studies pertaining to crashworthiness design of an S-shaped frame were implemented. The first case study focused on global deformations with the skeletal curve, and the second treated the cross-sectional profiles as design parameters to derive local reinforcements on the model. Both studies showed the efficiency of the proposed method in generation of quality shape variants for optimization. From the numerical results, considerable amount of improvements in crashworthiness performances of the S-shaped frame were observed as measured by the peak crushing force (PCF) and the energy absorption. We conclude that the proposed template-based parameterization technique is suitable for shape optimization tasks.
Composition Principle Based on Single-Open-Chain Unit for General Spatial Mechanisms and Its Application—In Conjunction With a Review of Development of Mechanism Composition Principles
Authors: Yang Ting-Li , Liu Anxin , Shen Huiping , Hang Lubin , Jeffery Ge Qiaode
Published: July 2018

Based on the general degree-of-freedom (DOF) formula for spatial mechanisms proposed by the author in 2012, the early single open chain (SOC)-based composition principle for planar mechanisms is extended to general spatial mechanisms in this paper. First, three types of existing mechanism composition principle and their characteristics are briefly discussed. Then, the SOC-based composition principle for general spatial mechanisms is introduced. According to this composition principle, a spatial mechanism is first decomposed into Assur kinematic chains (AKCs) and an AKC is then further decomposed into a group of ordered SOCs. Kinematic (dynamic) analysis of a spatial mechanism can then be reduced to kinematic (dynamic) analysis of AKCs and finally to kinematic (dynamic) analysis of ordered SOCs. The general procedure for decomposing the mechanism into ordered SOCs and the general method for determining AKC(s) contained in the mechanism are also given. Mechanism's kinematic (dynamic) analysis can be reduced to the lowest dimension (number of unknowns) directly at the topological structure level using the SOC-based composition principle. The SOC-based composition principle provides a theoretical basis for the establishment of a unified SOC-based method for structure synthesis and kinematic (dynamic) analysis of general spatial mechanisms.
Children and Adults With Rare Diseases Need Innovative Medical Devices
Authors: Peiris Vasum , Xu Kui , Agler Heather L. , Chen Eric A. , Gopal-Srivastava Rashmi , Lappin Brian M. , Lewis Debra Y. , Rao Gayatri R.
Published: July 2018

Rare diseases (RD) affect approximately 30 million Americans, half of whom are children. This study is the first to comprehensively evaluate their medical device needs via a survey of physicians. The study sought to identify and document the presumed unmet diagnostic and therapeutic device needs for RD management; clarify the magnitude of the potential unmet need; and generate meaningful data to inform medical device stakeholders. A cross-sectional nonprobability survey was conducted. The study population was drawn from the membership files of four groups: FDA Medical Devices Advisory Committee, Pediatric Advisory Committee, Pediatric Device Consortia, and National Institutes of Health (NIH) Rare Diseases Clinical Research Network. Only physician respondents with experience or knowledge regarding RD were eligible. Among eligible respondents, 90% confirmed the need for innovative devices to care for people with RD. Over 850 device needs were identified for 436 RD, with 74% of needs related to children. Pediatric physicians (OR = 2.11, 95% CI 1.01–4.39, P = 0.046) and physicians with more RD experience reflected greater dissatisfaction with existing devices (OR = 4.49, 95% CI 2.25–8.96, P < 0.0001). Creation of entirely new devices is the top recommendation for mitigating needs. This study demonstrates a major public health need for innovative medical devices to care for children and adults with RD. FDA and NIH support and seek opportunities to accelerate device development for these vulnerable patients.
Validation of an Experimental Setup to Reliably Simulate Flow Through Nonvalved Glaucoma Drainage Devices
Authors: Teo Tabitha H. T. , Ramani Ajay , Munden Paul M. , Wilson Sara E. , Kieweg Sarah L. , Dougherty Ronald L.
Published: July 2018

Treatment of vision-threating elevated intraocular pressure (IOP) for severe glaucoma may require implantation of a glaucoma drainage device (GDD) to shunt aqueous humor (AH) from the anterior chamber of the eye and lower IOP to acceptable levels between 8 and 21 mm Hg. Nonvalved GDDs (NVGDDs) cannot maintain IOP in that acceptable range during the early postoperative period and require intra-operative modifications for IOP control during the first 30 days after surgery. Other GDDs have valves to overcome this issue, but are less successful with maintaining long-term IOP. Our research goal is to improve NVGDD postoperative performance. Little rigorous research has been done to systematically analyze flow/pressure characteristics in NVGDDs. We describe an experimental system developed to assess the pressure drop for physiologic flow rates through NVGDD-like microtubes of various lengths/diameters, some with annular inserts. Experimental pressure measurements for flow through hollow microtubes are within predictive theory's limits. For instance, a 50.4 μm inner diameter microtube yields an average experimental pressure of 33.7 mm Hg, while theory predicts 31.0–64.2 mm Hg. An annular example, with 358.8 μm outside and 330.7 μm inside diameters, yields an experimental pressure of 9.6 mm Hg, within theoretical predictions of 4.2–19.2 mm Hg. These results are repeatable and consistent over 25 days, which fits the 20–35 day period needed for scar tissue formation to achieve long-term IOP control. This work introduces a novel method for controlling IOP and demonstrates an experiment to examine this over 25 days. Future efforts will study insert size and degradable inserts.
Vibration Instability in a Large Motion Bistable Compliant Mechanism Due to Stribeck Friction
Authors: Niknam Alborz , Farhang Kambiz
Published: July 2018

The present paper investigates friction-induced self-excited vibration of a bistable compliant mechanism. A pseudo-rigid-body representation of the mechanism is used containing a hardening nonlinear spring and a viscous damper. The mass is suspended from above with the spring-damper combination leading to the addition of geometric nonlinearity in the equation of motion and position- and velocity-dependent normal contact force. Friction input provided by a moving belt in contact with the mass. An exponentially decaying function of sliding velocity describes the friction coefficient and, thereby, incorporates Stribeck effect of friction. Eigenvalue analysis is employed to investigate the local stability of the steady-state fixed points. It is observed that the oscillator experiences pitchfork and Hopf bifurcations. The effects of the spring nonlinearity and precompression, viscous damping, belt velocity, and the applied normal force on the number, position, and stability of the equilibrium points are investigated. Global system behavior is studied by establishing trajectory maps of the system. Critical belt speed is derived analytically and shown to be only the result of Stribeck effect of friction. It is found that one equilibrium point dominates the steady-state response for very low damping and negligible spring nonlinearity. The presence of damping and/or spring nonlinearity tends to diminish this dominance.
Steam-Oil Ratio in Steam-Solvent Coinjection Simulation for Homogeneous and Heterogeneous Bitumen Reservoirs
Authors: Venkatramani Arun Venkat , Okuno Ryosuke
Published: July 2018

This research presents a mechanistic analysis of expanding-solvent steam-assisted gravity drainage (ES-SAGD) for heterogeneous reservoirs in terms of cumulative steam-oil ratio (SOR) as a function of cumulative bitumen production. Simulation case studies for SAGD and ES-SAGD with normal hexane at 35 bars are conducted for geostatistical realizations of two types of heterogeneous Athabasca-bitumen reservoirs. For the first type, low-permeability mudstone barriers are oriented horizontally. For the second type, they are inclined and more representative of the middle McMurray member. The solubility of water in the oleic phase at elevated temperatures is properly modeled to ensure reliable comparison between steam-assisted gravity drainage (SAGD) and ES-SAGD. Simulation results show that ES-SAGD is less sensitive to heterogeneity than SAGD in terms of cumulative SOR. On average, the reduction in SOR due to steam-solvent coinjection is simulated to be greater under heterogeneity. The reduction in SOR is greater for reservoir models with inclined mudstone barriers than in those with horizontal mudstone barriers. Analysis of simulation results indicates that the injected solvent tends to accumulate more significantly under heterogeneity, which enhances the mechanisms of ES-SAGD, such as dilution of bitumen by solvent and reduced thermal losses to the overburden. Tortuous hydraulic paths and slower gravity drainage under heterogeneity enhance the mixing between solvent and bitumen in the transverse direction along the edge of a steam chamber. Then, a larger amount of the accumulated solvent tends to facilitate lower temperatures near the chamber edge.
Downhole Transient Flow Field and Heat Transfer Characteristics During Drilling With Liquid Nitrogen Jet
Authors: Cai Chengzheng , Yang Yugui , Liu Jiangfeng , Gao Feng , Gao Yanan , Zhang Zhizhen
Published: July 2018

As a novel jet technology, liquid nitrogen jet (LNJ) is expected to effectively break rocks and further provide a high-efficiency method for drilling, especially geothermal drilling. Using this technology, rocks can be broken down by the coupled effects of cryogenic cooling and jet impingement. In this study, transient downhole jet flow field and heat transfer during drilling with LNJ were simulated. Then, the distributions of temperature (including LNJ and ambient rock), velocity, and pressure at different times were analyzed. Finally, the effects of the parameters on jet impingement and rock cooling performance were discussed. Results indicated that cryogenic LNJ could be efficiently generated in the downhole region. The temperature of the rock surface remarkably decreased as the LNJ reached the bottomhole. The high-speed LNJ caused axial impingement and radial shear effects on the bottomhole rock. The rock cooling performance caused by the LNJ was influenced by the initial rock temperature. With the increase of the initial rock temperature, the drop amplitude of the rock temperature also increased. The impingement capability of the LNJ was improved by increasing the nozzle diameter and the nozzle pressure drop. With the increase of standoff distance, the wall pressure and the radial velocity of the bottomhole decreased while increasing the impingement scope. The confining pressure hardly influenced the rock cooling performance and jet impingement capability, thereby indicating that LNJ could work even at high confining pressure conditions.
A Microstructure-Based Model for Creep of Gamma Prime Strengthened Nickel-Based Superalloys
Authors: Oruganti Ramkumar , Shukla Adarsh , Nalawade Sachin , Sarkar Sanket , Sivakumar K. G. V. , Vishwanath T. , Sondhi Sanjay , Wessman Andrew , Wei Daniel , Powell Andrew , Bain Kenneth , Schaeffer Jon , Peck Arthur , Arnett Michael , Shastry Girish , Mastromatteo Francesco
Published: July 2018

This paper outlines a microstructure-based model relating gamma prime microstructure and grain size of Ni-base alloys to their creep behavior. The ability of the model to explain creep of multiple superalloys with a single equation and parameter set is demonstrated. The only parameters that are changed from alloy to alloy are related to the gamma prime characteristics and grain size. This model also allows prediction of creep performance as a function of heat treatment and explains some apparently contradictory data from the literature.
Degradation of Aerodynamic Performance of an Intermediate-Pressure Steam Turbine Due to Erosion of Nozzle Guide Vanes and Rotor Blades
Authors: Yonezawa Koichi , Kagayama Tomoki , Takayasu Masahiro , Nakai Genki , Sugiyama Kazuyasu , Sugita Katsuhiko , Umezawa Shuichi
Published: July 2018

Deteriorations of nozzle guide vanes (NGVs) and rotor blades of a steam turbine through a long-time operation usually decrease a thermal efficiency and a power output of the turbine. In this study, influences of blade deformations due to erosion are discussed. Experiments were carried out in order to validate numerical simulations using a commercial software ANSYS-cfx. The numerical results showed acceptable agreements with experimental results. Variation of flow characteristics in the first stage of the intermediate pressure steam turbine is examined using numerical simulations. Geometries of the NGVs and the rotor blades are measured using a 3D scanner during an overhaul. The old NGVs and the rotor blades, which were used in operation, were eroded through the operation. The erosion of the NGVs leaded to increase of the throat area of the nozzle. The numerical results showed that rotor inlet velocity through the old NGVs became smaller and the flow angle of attack to the rotor blade leading edge became smaller. Consequently, the rotor power decreased significantly. Influences of the flow angle of at the rotor inlet were examined by parametric calculations and results showed that the angle of attack was an important parameter to determine the rotor performance. In addition, the influence of the deformation of the rotor blade was examined. The results showed that the degradation of the rotor performance decreased in accordance with the decrease of blade surface area.
Quantification of Preferential Contribution of Reynolds Shear Stresses and Flux of Mean Kinetic Energy Via Conditional Sampling in a Wind Turbine Array
Authors: Kadum Hawwa Falih , Knowles Devin , Cal Raúl Bayoán
Published: July 2018

Conditional statistics are employed in analyzing wake recovery and Reynolds shear stress (RSS) and flux directional out of plane component preference. Examination of vertical kinetic energy entrainment through describing and quantifying the aforementioned quantities has implications on wind farm spacing, design, and power production, and also on detecting loading variation due to turbulence. Stereographic particle image velocimetry measurements of incoming and wake flow fields are taken for a 3 × 4 model wind turbine array in a scaled wind tunnel experiment. Reynolds shear stress component is influenced by ⟨uv⟩ component, whereas ⟨vw⟩ is more influenced by streamwise advection of the flow; u, v, and w being streamwise, vertical, and spanwise velocity fluctuations, respectively. Relative comparison between sweep and ejection events, ΔS⟨uiuj⟩, shows the role of streamwise advection of momentum on RSS values and direction. It also shows their tendency to an overall balanced distribution. ⟨uw⟩ intensities are associated with ejection elevated regions in the inflow, yet in the wake, ⟨uw⟩ is linked with sweep dominance regions. Downward momentum flux occupies the region between hub height and top tip. Sweep events contribution to downward momentum flux is marginally greater than ejection events'. When integrated over the swept area, sweeps contribute 55% of the net downward kinetic energy flux and 45% is the ejection events contribution. Sweep dominance is related to momentum deficit as its value in near wake elevates 30% compared to inflow. Understanding these quantities can lead to improved closure models.
Numerical and Experimental Analyses of Static and Dynamic Characteristics for Partially Helically Grooved Liquid Annular Seals
Authors: Nagai Keisuke , Koiso Kazuki , Kaneko Satoru , Taura Hiroo , Watanabe Yusuke
Published: July 2018

Numerical and experimental analyses of the static and dynamic characteristics of the liquid annular seals with axially partial helical grooves were conducted to investigate the effects of the axial length gal of a helically grooved section in a seal stator. The numerical solution and experimental procedures were applied in the same manner as in previous studies on through-helically grooved seals, wherein the grooves extend across the seal length. The numerical results qualitatively agreed with the experimental results, demonstrating the validity of the numerical analysis. The leakage flow rate Q was lower in the partially helically grooved seals than that of conventional through-helically grooved seals across a small range of rotor spinning velocities. In contrast, the reduction in Q due to the pumping effect caused by the spin of the rotor diminished with the decrease in gal. For a small concentric whirling motion of the rotor, the radial dynamic reaction force Fr and magnitude of variation in the tangential dynamic reaction force Ft with the whirling angular velocity increased with the decrease in gal, and their values approached the corresponding values for the smooth-surface seal. Under the same rotor whirling velocity, the Ft for the partially helically grooved seals became lower than that for the smooth-surface seal (similar to the case for the through-helically grooved seal), although decreasing gal tended to increase Ft. These results suggest that partially helically grooved seals can improve the efficiency and stability margin of the pumps because of the reduction in leakage flow rate and suppression of the rotor forward whirling motion (with large radial and tangential dynamic reaction forces) as compared to conventional through-helically grooved seals.
Particulate Bound Trace Metals and Soot Morphology of Gasohol Fueled Gasoline Direct Injection Engine
Authors: Sharma Nikhil , Agarwal Rashmi A. , Agarwal Avinash Kumar
Published: July 2018

Direct injection spark ignition or gasoline direct injection (GDI) engines are superior in terms of relatively higher thermal efficiency and power output compared to multipoint port fuel injection engines and direct injection diesel engines. In this study, a 500 cc single cylinder GDI engine was used for experiments. Three gasohol blends (15% (v/v) ethanol/methanol/butanol with 85% (v/v) gasoline) were chosen for this experimental study and were characterized to determine their important fuel properties. For particulate investigations, exhaust particles were collected on a quartz filter paper using a partial flow dilution tunnel. Comparative investigations for particulate mass emissions, trace metal concentrations, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) analyses, and high-resolution transmission electron microscopy (HR-TEM) imaging of the particulate samples collected from different test fuels at different engine loads were performed. For majority of the experimental conditions, gasohols showed relatively lower trace metal concentration in particulates compared to gasoline. HR-TEM images showed that higher engine loads and presence of oxygen in the test fuels increased the soot reactivity. Multicore shells like structures were visible in the HR-TEM images due to growth of nuclei, and rapid soot formation due to relatively higher temperature and pressure environment of the engine combustion chamber. Researches world-over are trying to reduce particulate emissions from GDI engines; however there is a vast research gap for such investigations related to gasohol fueled GDI engines. This paper critically assesses and highlights comparative morphological characteristics of gasohol fueled GDI engine.
Effect of Impurities on Compressor and Cooler in Supercritical CO2 Cycles
Authors: Vesely Ladislav , Manikantachari K. R. V. , Vasu Subith , Kapat Jayanta , Dostal Vaclav , Martin Scott
Published: July 2018

With the increasing demand for electric power, the development of new power generation technologies is gaining increased attention. The supercritical carbon dioxide (S-CO2) cycle is one such technology, which has relatively high efficiency, compactness, and potentially could provide complete carbon capture. The S-CO2 cycle technology is adaptable for almost all of the existing heat sources such as solar, geothermal, fossil, nuclear power plants, and waste heat recovery systems. However, it is known that optimal combinations of operating conditions, equipment, working fluid, and cycle layout determine the maximum achievable efficiency of a cycle. Within an S-CO2 cycle, the compression device is of critical importance as it is operating near the critical point of CO2. However, near the critical point, the thermo-physical properties of CO2 are highly sensitive to changes of pressure and temperature. Therefore, the conditions of CO2 at the compressor inlet are critical in the design of such cycles. Also, the impurity species diluted within the S-CO2 will cause deviation from an ideal S-CO2 cycle as these impurities will change the thermodynamic properties of the working fluid. Accordingly, the current work examines the effects of different impurity compositions, considering binary mixtures of CO2 and He, CO, O2, N2, H2, CH4, or H2S on various S-CO2 cycle components. The second part of the study focuses on the calculation of the basic cycles and component efficiencies. The results of this study will provide guidance and define the optimal composition of mixtures for compressors and coolers.
Parabolic Trough Solar Collector for Medium Temperature Applications: An Experimental Analysis of the Efficiency and Length Optimization by Using Inserts
Authors: Elton D. N. , Arunachala U. C.
Published: July 2018

The present indoor experimental study is focused on performance enhancement of a parabolic trough collector (PTC) with twisted tape insert by incorporating an innovative Soltrace®—mathematical model—differential heating combination. This simulation-based methodology is very useful in analyzing the system behavior under defined environmental conditions. By the use of insert, the circumferential temperature difference has been dropped considerably in all cases compared to plain receiver. Hence, this gain is reflected in both instantaneous and thermo-hydraulic efficiency. As the role of inserts is justified in different thermal parameters, the system evaluation factors have been defined as H-W-B constants. Further, to take into account the influence of enhanced heat transfer on geometry, receiver length optimization has been performed which gave a maximum of 26% short in length of the receiver with best twist ratio under the transition flow regime. Hence, for moderate flow and medium temperature applications, inserts are useful. The range of Reynolds number considered in the experimental study is 2600–24,000 to analyze the flow regime based effect.
A Study of the Mechanical Forces on Aphakic Iris-Fixated Intraocular Lenses
Authors: Khongar Peyman Davvalo , Pralits Jan Oscar , Soleri Paolo , Romano Mario , Repetto Rodolfo
Published: July 2018

Iris-fixated aphakic intraocular lenses (IFIOL) are used in cataract surgery when more common intraocular lenses (IOL) cannot be adopted because of the absence of capsular bag support. These lenses can be implanted on either the posterior or the anterior surface of the iris. In this work, we study whether one of these options is preferable over the other from the mechanical point of view. In particular, we focus on the forces that the IFIOL transmits to the iris, which are associated with the risk of lens dislocation. We study the problem numerically and consider aqueous flow induced by saccadic rotations in the cases of an IFIOL in the anterior and posterior sides of the iris. The considered IFIOL is the Artisan Aphakia +30.0 D lens (IFIOL) produced by Ophtec BV. We perform the simulations in openfoam. We find that the forces transmitted by the aphakic IFIOL to the iris are significantly higher in the case of posterior implantation. This suggests that lens implantation on the posterior surface of the iris might be associated with a higher risk of lens dislocation, when an inadequate amount of iris tissue is enclavated during implantation.
Multifidelity Recursive Cokriging for Dynamic Systems' Response Modification
Authors: Bregant Luigi , Parussini Lucia , Pediroda Valentino
Published: July 2018

In order to perform the accurate tuning of a machine and improve its performance to the requested tasks, the knowledge of the reciprocal influence among the system's parameters is of paramount importance to achieve the sought result with minimum effort and time. Numerical simulations are an invaluable tool to carry out the system optimization, but modeling limitations restrict the capabilities of this approach. On the other side, real tests and measurements are lengthy, expensive, and not always feasible. This is the reason why a mixed approach is presented in this work. The combination, through recursive cokriging, of low-fidelity, yet extensive, numerical model results, together with a limited number of highly accurate experimental measurements, allows to understand the dynamics of the machine in an extended and accurate way. The results of a controllable experiment are presented and the advantages and drawbacks of the proposed approach are also discussed.
Numerical Study of Impingement Cooling of Aviation Kerosene at Supercritical Conditions
Authors: Xing Yunfei , Zhong Fengquan , Zhang Xinyu
Published: July 2018

In the present paper, numerical study of flow and heat transfer properties of RP-3 kerosene at liquid and supercritical conditions in an impingement model is conducted with renormalization group (RNG) k−ε turbulence model and a ten-species surrogate of kerosene. The independence of grids is first studied, and the numerical results are compared with experimental data for validation. Characteristics of flow and heat transfer of kerosene flow in the impingement model are studied with different inlet mass flow rates and different inlet temperatures. The velocity and temperature field show similar profile compared to that of air impingement. The heat transfer rates increase first with the increasing of inlet temperature and then decrease suddenly when the inlet temperature is 500 K.
Process Mapping and In-Process Monitoring of Porosity in Laser Powder Bed Fusion Using Layerwise Optical Imaging
Authors: Imani Farhad , Gaikwad Aniruddha , Montazeri Mohammad , Rao Prahalada , Yang Hui , Reutzel Edward
Published: July 2018

The goal of this work is to understand the effect of process conditions on lack of fusion porosity in parts made using laser powder bed fusion (LPBF) additive manufacturing (AM) process, and subsequently, to detect the onset of process conditions that lead to lack of fusion-related porosity from in-process sensor data. In pursuit of this goal, the objectives of this work are twofold: (1) quantify the count (number), size and location of pores as a function of three LPBF process parameters, namely, the hatch spacing (H), laser velocity (V), and laser power (P); and (2) monitor and identify process conditions that are liable to cause porosity through analysis of in-process layer-by-layer optical images of the build invoking multifractal and spectral graph theoretic features. These objectives are important because porosity has a significant impact on the functional integrity of LPBF parts, such as fatigue life. Furthermore, linking process conditions to defects via sensor signatures is the first step toward in-process quality assurance in LPBF. To achieve the first objective, titanium alloy (Ti–6Al–4V) test cylinders of 10 mm diameter × 25 mm height were built under differing H, V, and P settings on a commercial LPBF machine (EOS M280). The effect of these process parameters on count, size, and location of pores was quantified based on X-ray computed tomography (XCT) images. To achieve the second objective, layerwise optical images of the powder bed were acquired as the parts were being built. Spectral graph theoretic and multifractal features were extracted from the layer-by-layer images for each test part. Subsequently, these features were linked to the process parameters using machine learning approaches. Through these image-based features, process conditions under which the parts were built were identified with the statistical fidelity over 80% (F-score).
An Analytical Computation of Temperature Field Evolved in Directed Energy Deposition
Authors: Li Jianyi , Wang Qian , (Pan) Michaleris Panagiotis
Published: July 2018

This paper presents an analytical computation of temperature field evolved in a directed energy deposition process, using single-bead walls as illustrating examples. Essentially, the temperature field evolution during the deposition of a wall is computed by super-position of the temperature field generated by the laser source depositing the current bead and that induced from each of the past beads (layers). First, the transient solution to a point heat source in a semi-infinite body is applied to describe each individual temperature field. Then, to better describe temperature contribution from a past bead, a pair of virtual heat sources with positive and negative powers is assigned for each past bead to compute the temperature field under cooling. In addition, mirrored heat sources through a reflexion technique are introduced to define adiabatic boundaries of the part and to account for substrate thickness. In the end, three depositions of Ti-6AL-4V walls with different geometries and interlayer dwell times on an Optomec® laser engineering net shaping (LENS) system are used to validate the proposed analytical computation, where predicted temperatures at several locations of the substrate show reasonable agreement with the in situ temperature measurements with prediction error rate ranging from 12% to 27%. Furthermore, temperature distributions predicted by the proposed model are compared to finite element simulations. The proposed analytical computation for temperature field could be potentially used in model-based feedback control for thermal history in the deposition, which could affect microstructure evolution and other properties of the final part.
Topology Optimization of Structures Made of Discrete Geometric Components With Different Materials
Authors: Kazemi Hesaneh , Vaziri Ashkan , Norato Julián A.
Published: July 2018

We present a new method for the simultaneous topology optimization and material selection of structures made by the union of discrete geometric components, where each component is made of one of multiple available materials. Our approach is based on the geometry projection method, whereby an analytical description of the geometric components is smoothly mapped onto a density field on a fixed analysis grid. In addition to the parameters that dictate the dimensions, position, and orientation of the component, a size variable per available material is ascribed to each component. A size variable value of unity indicates that the component is made of the corresponding material. Moreover, all size variables can be zero, signifying the component is entirely removed from the design. We penalize intermediate values of the size variables via an aggregate constraint in the optimization. We also introduce a mutual material exclusion constraint that ensures that at most one material has a unity size variable in each geometric component. In addition to these constraints, we propose a novel aggregation scheme to perform the union of geometric components with dissimilar materials. These ingredients facilitate treatment of the multi-material case. Our formulation can be readily extended to any number of materials. We demonstrate our method with several numerical examples.
Stress Intensity Factors for Transformed Surface Flaws and Remaining Fatigue Lives Based on Flaw-to-Surface Proximity Rules
Authors: Hasegawa Kunio , Strnadel Bohumir , Li Yinsheng , Lacroix Valery
Published: July 2018

Subsurface flaws are sometimes found as blowholes near free surfaces of structural components. Net-section stress at the ligament between the free component surface and the subsurface flaw increases when the ligament size is short. It can be easily expected that the stress intensity factor at the tip of the subsurface flaw increases with decreasing the ligament size. Fitness-for-service (FFS) codes provide flaw-to-surface proximity rules, which are transformation from subsurface to surface flaw. Although the concepts of the proximity rules of the FFS codes are the same, the specific criteria for the rules on transforming subsurface flaws to surface flaws are significantly different among FFS codes. This study demonstrates the proximity criteria provided by the FFS codes and indicates that the increment of the stress intensity factors before and after the transformation depends on the flaw aspect ratio and the ligament size at the transformation from subsurface to surface flaws. In addition, it is shown that remaining fatigue lives for pipes with flaws are strongly affected by the ligament size at the transformation from subsurface to surface flaws.
Pulsatile Perfusion Bioreactor for Biomimetic Vascular Impedances
Authors: Prim David A. , Potts Jay D. , Eberth John F.
Published: July 2018

Pulsatile waves of blood pressure and flow are continuously augmented by the resistance, compliance, and inertance properties of the vasculature, resulting in unique wave characteristics at distinct anatomical locations. Hemodynamically generated loads, transduced as physical signals into resident vascular cells, are crucial to the maintenance and preservation of a healthy vascular physiology; thus, failure to recreate biomimetic loading in vitro can lead to pathological gene expression and aberrant remodeling. As a generalized approach to improve native and engineered blood vessels, we have designed, built, and tested a pulsatile perfusion bioreactor based on biomimetic impedances and a novel five-element electrohydraulic analog. Here, the elements of an incubator-based culture system were formulaically designed to match the vascular impedance of a brachial artery by incorporating both the inherent (systemic) and added elements of the physical system into the theoretical approach. Freshly harvested porcine saphenous veins were perfused within a physiological culture chamber for 6 h and the relative expression of seven known mechanically sensitive remodeling genes analyzed using the quantitative polymerase chain reaction (qPCR) method. Of these, we found plasminogen activator inhibitor-1 (SERPINE1) and fibronectin-1 (FN1) to be highly sensitive to differences between arterial- and venous-like culture conditions. The analytical approach and biological confirmation provide a framework toward the general design of long-term hemodynamic-mimetic vascular culture systems.
Power and Thermal Constraints-Driven Modeling and Optimization for Through Silicon Via-Based Power Distribution Network
Authors: Zhu Weijun , Dong Gang , Yang Yintang
Published: July 2018

The design of three-dimensional (3D) power delivery network (PDN) is constrained by both power and thermal integrity. Through-silicon via (TSV) as an important part of transmission power and heat in stack, the rational design of TSV layout is particularly important. Using minimal TSV area to achieve the required 3D PDN is significant to reduce manufacturing costs and increase integration. In this paper, we propose electrical and thermal models of 3D PDN, respectively, and we use them to solve the 3D voltage drop and temperature distribution problems. The accuracy and efficiency of our proposed methods are demonstrated by simulation measurement. Combining these two methods, a layer-based optimization solution is developed and allows us to adjust the TSV density for different layers while satisfying the global power and thermal constraints. This optimization is scalable and has the same guiding value for multichip stacks with different functions and constraints. A setup of four-chip stack is used to demonstrate the feasibility of this optimization and a large TSV area saving is achieved by this method.
Electrokinetic Behavior of Heat-Treated Mycobacterium Bacillus Calmette-Guérin Cells
Authors: Lee Hyun-Boo , Inoue Shinnosuke , Kim Jong-Hoon , Jeong Minjoong , Chung Jae-Hyun
Published: July 2018

Dielectrophoresis (DEP) can be an effective tool to show the physiological change of bacterial cells. The behavior of bacterial cells under an electric field is complicated due to the combined effects of electrokinetic phenomena. This paper presents the study of the electrokinetic behavior of heat-treated Mycobacterium bovis Bacillus Calmette-Guérin (BCG) cells for a cell counting method. Through numerical and experimental study, heat-treated BCG cells are compared with control BCG cells. At various frequencies with the medium conductivity of 0.07 S/m, the equilibrium positions of both control- and heat-treated cells are analyzed in the combined fields of DEP and AC electroosmosis (ACEO). As DEP changes from negative to positive in electroosmotic flow, the equilibrium position of cells is bifurcated from the upper center between two electrodes onto the edges of both electrodes. It was found that the cells floating on electrodes should not be counted as attracted cells because the floating was resulted from the combined effect of the negative DEP and ACEO. According to the analysis, an optimum frequency is proposed to differentiate control cells from heat-treated cells using a cell counting method. The presented study will offer physical insight for the cell counting to differentiate live and dead Mycobacterium bovis BCG cells treated with heat and drugs.
Combined Airfoil and Snubber Design Optimization of Turbine Blades With Respect to Friction Damping
Authors: Hüls Matthias , Scheidt Lars Panning-von , Wallaschek Jörg
Published: July 2018

A major concern for new generations of large turbine blades is forced and self-excited (flutter) vibrations, which can cause high-cycle fatigue (HCF). The design of friction joints is a commonly applied strategy for systematic reduction of resonance amplitudes at critical operational conditions. In this paper, the influence of geometric blade design parameters onto the damped system response is investigated for direct snubber coupling. A simplified turbine blade geometry is parametrized and a well-proven reduced-order model for turbine blade dynamics under friction damping is integrated into a 3D finite element tool-chain. The developed process is then used in combination with surrogate modeling to predict the effect of geometric design parameters onto the vibrational characteristics. As such, main and interaction effects of design variables onto static normal contact force and resonance amplitudes are determined for a critical first bending mode. Parameters were found to influence the static normal contact force based on their effect on elasticity of the snubber, torsional stiffness of the airfoil and free blade untwist. The results lead to the conclusion that geometric design parameters mainly affect the resonance amplitude equivalent to their influence on static normal contact force in the friction joint. However, it is demonstrated that geometric airfoil parameters influence blade stiffness and are significantly changing the respective mode shapes, which can lead to lower resonance amplitudes despite an increase in static contact loads. Finally, an evolutionary optimization is carried out and novel design guidelines for snubbered blades with friction damping are formulated.