bluuebunny/crossref_metadata_2025 huggingface dataset:
A Flow-Sediment Numerical Model Using One and Two Dimensions for the Yongding New Estuary
Authors: Tang Xingchen , Li Daming , Wang Xiao , Li Yanqing
Published: July 2018

This paper derived the continuity and momentum equations of solid–liquid two-phase flows using infinitesimal body analysis and obtained well-posed equations of two-dimensional (2D) flow-sediment movement. Based on the theory of solid–liquid two-phase flow, the momentum equations of the bedload sediment were deduced and a closed form of the 2D total sediment model equations was established. Then, the exchange mechanism of suspended sediment and bedload sediment and their computational method were elaborated on in great detail. Combined with the basic theory of one-dimensional (1D) flow-sediment movement, a flow-sediment numerical model of one and two dimensions was established for the region of Yongding New Estuary. A series of model verifications were carried out, which showed that the model can be adopted to simulate the flow-sediment movement in this region. This model was then applied for the environmental assessment of Taida Sea Reclamation Project. The conclusions indicate that the backwater effects of the proposed construction scheme would be fairly small and that the deposition amount in the river would be greatly reduced owing to the source of alongshore sediment transport being blocked by the project. This study provides a scientific model and method for the feasibility study and environmental assessments of construction projects.
Effects of Wall Heat Loss on Swirl-Stabilized Nonpremixed Flames With Localized Extinction
Authors: Zhang Huangwei
Published: July 2018

Large eddy simulation (LES) with three-dimensional conditional moment closure (CMC) subgrid model for combustion is applied to simulate a swirl-stabilized nonpremixed methane flame with localized extinction, with special focus on the effects of heat loss to the burner surface. The convective wall heat loss is modeled through introducing a source term in the conditionally filtered total enthalpy equation for the CMC cells adjacent to the wall. The mean heat flux is high on the middle surface of the bluff body, but relatively low near its edges. The turbulent heat flux based on the gradient of the resolved temperature is relatively low compared to the laminar counterpart, but increases with the turbulent intensity. The heat loss facilitates the occurrences of extinction and re-ignition for the CMC cells immediately adjacent to the wall, evidenced by comparing flame structures in the near-wall CMC cells. This can be directly linked to the increase of the mean conditional scalar dissipation near the wall in the heat loss case. Furthermore, the degree of local extinction near the bluff body measured by conditional reactedness at stoichiometry is intensified due to the wall heat loss. However, the results also show that there is negligible influence of wall heat loss on the probability density function (PDF) of the lift-off height, demonstrating the dominance of aerodynamic effects on flame stabilization. The results are in reasonable agreement with experimental measurements.
Effects of CO2 Addition on the Turbulent Flame Front Dynamics and Propagation Speeds of Methane/Air Mixtures
Authors: Reuter Christopher B. , Won Sang Hee , Ju Yiguang
Published: July 2018

Exhaust gas recirculation (EGR) is one of the most promising methods of improving the performance of power-generating gas turbines. CO2 is known to have the largest impact on flame behavior of any major exhaust species, but few studies have specified its thermal, kinetic, and transport effects on turbulent flames. Therefore, in this study, methane/air mixtures diluted with CO2 are experimentally investigated in a reactor-assisted turbulent slot (RATS) burner using OH planar laser-induced fluorescence (PLIF) measurements. CO2 addition is tested under both constant adiabatic flame temperature and variable adiabatic flame temperature conditions in order to elucidate its thermal, kinetic, and transport effects. Particular attention is paid to CO2's effects on the flame surface density, progress variable, turbulent burning velocity, and flame wrinkling. The experimental measurements reveal that CO2's thermal effects are the dominant factor in elongating the turbulent flame brush and decreasing the turbulent burning velocity. When thermal effects are removed by holding the adiabatic flame temperature constant, CO2's kinetic effects are the next most important factor, producing an approximately 5% decrease in the global consumption speed for each 5% of CO2 addition. The transport effects of CO2, however, tend to increase the global consumption speed, counteracting 30–50% of the kinetic effects when the adiabatic flame temperature is fixed. It is also seen that CO2 addition increases the normalized global consumption speed primarily through an enhancement of the stretch factor.
Effect of Operational Parameters on Combustion and Emissions in an Industrial Gas Turbine Combustor
Authors: Emami Mohsen D. , Shahbazian Hamidreza , Sunden Bengt
Published: July 2018

Enhancing a combustion system requires increased combustion efficiency, fuel savings, and reduction of combustion emissions. In this paper, the combustion of CH4 in the combustor of an industrial gas turbine is studied and NO and CO formation/emission is simulated numerically. The objective of the current work is to investigate the influence of combustive parameters and varying the percentage of distributed air flow rate via burning, recirculation, and dilution zone on the reactive flow characteristics, NOx and CO emissions. The governing equations of mass, momentum, energy, turbulence quantities Renormalized group (RNG) (k–ε), mixture fraction and its variance are solved by the finite volume method. The formation and emission of NOx is numerically simulated in a postprocessing fashion, due to the low concentration of the pollutants as compared to the main combustion species. The present work focuses on different physical mechanisms of NOx formation. The thermal-NOx and prompt-NOx mechanism are considered for modeling the NOx source term in the transport equation. Results show that in a gaseous-fueled combustor, the thermal NOx is the dominant mechanism for NOx formation. Particularly, the simulation provides more insight into the correlation between the maximum combustor temperature, exhaust average temperatures, and the thermal NO concentration. Results indicate that the exhaust temperature and NOx concentration decrease while the excess air factor increases. Moreover, results demonstrate that as the combustion air temperature increases, the combustor temperature increases and the thermal NOx concentration increases dramatically. Furthermore, results demonstrate that the NO concentration at the combustor exit is at maximum value in a swirl angle of 55 deg and a gradual rise in the NOx concentration is detected as the combustion fuel temperature increases. In addition, results demonstrate that the air distribution of the first case at laboratory conditions is optimal where the mass fractions of NO and CO are minimum.
Macro Flat-Plate Solar Thermal Collector With Rectangular Channels
Authors: Ibrahim Oussama , Younes Rafic , Ibrahim Mohamad
Published: July 2018

A macro rectangular-channel flat-plate solar thermal collector is designed and examined in this study. It consists of a set of adjacent macro rectangular channels formed between the upper, lower, and fin-parts of an absorber plate, thus, overcoming the necessary welding between the absorber plate and riser tubes used in conventional flat-plate collectors. An optimization model is suggested and solved to obtain an optimal design of the proposed collector. After that, a detailed dynamic mathematical model of this collector is presented and numerical simulation is carried out using matlab. Furthermore, a comparison with a conventional sheet-and-tube solar thermal collector is investigated and parametric analysis is conducted under both steady-state and dynamic conditions. The results reveal that the designed collector yields an enhancement of 8% for integrated thermal efficiency under transient regime and an average improvement of 12% for steady-state efficiency when compared with the conventional collector. In addition, the influence of the variation of different parameters, such as the mass flow rate of the heat transfer fluid (HTF), the thickness of different parts of the absorber plate, and the number of channels, on the performance of the proposed collector is presented. From an economical perspective, the cost of materials composing the new collector is less than that of materials composing the conventional one.
Discussion: “Three-Dimensional Stagnation Flow and Heat Transfer of a Viscous, Compressible Fluid on a Flat Plate” (Mozayyeni, H. R., and Rahimi, A. B., 2013, ASME J. Heat Transfer, 135(10), p. 101702)
Authors: Pantokratoras Asterios
Published: July 2018

The present comment concerns some doubtful results included in the discussed paper.
Structural Topology Optimization Using a Moving Morphable Component-Based Method Considering Geometrical Nonlinearity
Authors: Zhu Benliang , Chen Qi , Wang Rixin , Zhang Xianmin
Published: July 2018

The moving morphable component (MMC)-based method is a newly developed approach for topology optimization. In the MMC-based method, the design problem is formulated using a set of morphable components, and the optimized structural topologies are obtained by optimizing shapes, sizes, and locations of these components. However, the optimization process often tends to break the connection between the load area and the supported boundary. This disconnection has a strong influence on the convergence, especially when the large deformation effects are considered. In this paper, a method is developed for topology optimization of geometrically nonlinear structures by using the MMC-based method. A scheme is developed to address the disconnection issue in the optimization process. Several numerical examples are used to demonstrate the validity of the proposed method.
Porous LiMn2O4 Microspheres With Different Pore Size: Preparation and Application as Cathode Materials for Lithium Ion Batteries
Authors: Li Shiyou , Zhu Konglei , Liu Jinliang , Zhao Dongni , Cui Xiaoling
Published: July 2018

Three types of LiMn2O4 (LMO) microspheres with different pore size are prepared by a facile method, using porous MnCO3–MnO2 and Mn2O3 microspheres as the self-supporting template, for lithium ion batteries (LIBs) cathode material. Briefly, Mn2O3 and MnO2 microspheres are heated in air at 600 °C for 10 h to synthesize porous Mn2O3 spheres. Then the mixture of as-prepared spherical Mn2O3 and LiNO3 is calcined to obtain the LMOs. The morphology and structure of LMOs are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and nitrogen adsorption/desorption analyses. The result shows that the maximum pore diameters of LMOs are 17 nm, 19 nm, and 11 nm, respectively. All LMOs microspheres are composed of similar sized nanoparticles; however, the surface of these microspheres is strewed with dense tinier pores or sparse larger pores. Generally, the nanoparticles will reduce the path of Li+ ion diffusion and increases the reaction sites for lithium insertion/extraction. Moreover, the pores can provide buffer spaces for the volume changes during charge–discharge process. The electrochemical performances of LMOs are investigated and LMO2 exhibits extremely good electrochemical behavior, especially the rate capability. The as-prepared LMO2 delivers a discharge capacity of 124.3 mAh g−1 at 0.5 C, retaining 79.6 mAh g−1 even at 5 C. The LMO2 sample also shows good capacity retention of 96.9% after 100 cycles at 0.5 C.
Retracted: What Could Have Saved Fukushima From Its Severe Accident
Authors: Iino Kenji , Yoshioka Ritsuo , Fuchigami Masao , Nakao Masayuki
Published: July 2018

This paper was removed from publication at the request of the authors. November 10, 2022
Hierarchical Stochastic Model in Bayesian Inference for Engineering Applications: Theoretical Implications and Efficient Approximation
Authors: Wu Stephen , Angelikopoulos Panagiotis , Beck James L. , Koumoutsakos Petros
Published: July 2018

Hierarchical Bayesian models (HBMs) have been increasingly used for various engineering applications. We classify two types of HBM found in the literature as hierarchical prior model (HPM) and hierarchical stochastic model (HSM). Then, we focus on studying the theoretical implications of the HSM. Using examples of polynomial functions, we show that the HSM is capable of separating different types of uncertainties in a system and quantifying uncertainty of reduced order models under the Bayesian model class selection framework. To tackle the huge computational cost for analyzing HSM, we propose an efficient approximation scheme based on importance sampling (IS) and empirical interpolation method (EIM). We illustrate our method using two engineering examples—a molecular dynamics simulation for Krypton and a pharmacokinetic/pharmacodynamics (PKPD) model for cancer drug.
Safety of Pipelines Subjected to Deterioration Processes Modeled Through Dynamic Bayesian Networks
Authors: Palencia O. G. , Teixeira A. P. , Guedes Soares C.
Published: July 2018

This paper studies the application of Dynamic Bayesian Networks (DBNs) for modeling degradation processes in oil and gas pipelines. A DBN tool consisting of a matlab code has been developed for performing inference on models. The tool is then applied for probabilistic modeling of the burst pressure of a pipe subjected to corrosion degradation and for safety assessment. The burst pressure is evaluated using the ASME B31G design method and other empirical formulas. A model for corrosion prediction in pipelines and its governing parameters are explicitly included into the probabilistic framework. Different sets of simulated corrosion measurements are used to increase the accuracy of the model predictions. Several parametric studies are conducted to investigate how changes in the observed corrosion (depth and length) and in the frequency of inspections affect the pipe reliability.
Exact Optimization of a Three-Element Dynamic Vibration Absorber: Minimization of the Maximum Amplitude Magnification Factor
Authors: Nishihara Osamu
Published: July 2018

In this study, the maximum amplitude magnification factor for a linear system equipped with a three-element dynamic vibration absorber (DVA) is exactly minimized for a given mass ratio using a numerical approach. The frequency response curve is assumed to have two resonance peaks, and the parameters for the two springs and one viscous damper in the DVA are optimized by minimizing the resonance amplitudes. The three-element model is known to represent the dynamic characteristics of air-damped DVAs. A generalized optimality criteria approach is developed and adopted for the derivation of the simultaneous equations for this design problem. The solution of the simultaneous equations precisely equalizes the heights of the two peaks in the resonance curve and achieves a minimum amplitude magnification factor. The simultaneous equations are solvable using the standard built-in functions of numerical computing software. The performance improvement of the three-element DVA compared to the standard Voigt type is evaluated based on the equivalent mass ratios. This performance evaluation is highly accurate and reliable because of the precise formulation of the optimization problem. Thus, the advantages of the three-element type DVA have been made clearer.
Exergy Analysis of a Flat Plate Solar Collector With Grooved Absorber Tube Configuration Using Aqueous ZnO–Ethylene Glycol
Authors: Kashyap Yash , Singh Apurva , Raja Sekhar Y.
Published: July 2018

In this study, the exergetic performance of a flat plate solar collector (FPSC) setup with ZnO-based ethylene glycol (EG)/water nanofluid as a working fluid has been evaluated against that of EG/water. As a passive means to augment the rate of heat transfer, internally grooved tubes of two different pitches (e = 0.43 and e = 0.44) have been examined and compared against the performance of plain tube. The mass flow rate was fixed at 0.015 kg/s and the volume fraction of ZnO nanoparticles is ф = 0.02% v/v. The results indicate an enhancement in exergy efficiency of 44.61% when using the grooved tube (e = 0.44) against plain tube without the nanofluid and 39.17% when nanofluid is used. Using the nanofluid enhanced the exergy efficiency of the FPSC by a maximum of 73.81%. Maximum exergy efficiency obtained was 5.95% for grooved tube (e = 0.44) with nanofluid as working fluid and is in good agreement with previous literature. Exergy destruction/irreversibility due to temperature differences and heat flow within the system has been reported. Sun-collector temperature difference accounts for nearly 86–94% of the irreversibility. The results for thermal efficiency of this experimental setup have been published and summarized in this study for reference.
Bridging Organ- and Cellular-Level Behavior in Ex Vivo Experimental Platforms Using Populations of Models of Cardiac Electrophysiology
Authors: Ledezma Carlos A. , Kappler Benjamin , Meijborg Veronique , Boukens Bas , Stijnen Marco , Tan P. J. , Díaz-Zuccarini Vanessa
Published: July 2018

The inability to discern between pathology and physiological variability is a key issue in cardiac electrophysiology since this prevents the use of minimally invasive acquisitions to predict early pathological behavior. The goal of this work is to demonstrate how experimentally calibrated populations of models (ePoM) may be employed to inform which cellular-level pathologies are responsible for abnormalities observed in organ-level acquisitions while accounting for intersubject variability; this will be done through an exemplary computational and experimental approach. Unipolar epicardial electrograms (EGM) were acquired during an ex vivo porcine heart experiment. A population of the Ten Tusscher 2006 model was calibrated to activation–recovery intervals (ARI), measured from the electrograms, at three representative times. The distributions of the parameters from the resulting calibrated populations were compared to reveal statistically significant pathological variations. Activation–recovery interval reduction was observed in the experiments, and the comparison of the calibrated populations of models suggested a reduced L-type calcium conductance and a high extra-cellular potassium concentration as the most probable causes for the abnormal electrograms. This behavior was consistent with a reduction in the cardiac output (CO) and was confirmed by other experimental measurements. A proof of concept method to infer cellular pathologies by means of organ-level acquisitions is presented, allowing for an earlier detection of pathology than would be possible with current methods. This novel method that uses mathematical models as a tool for formulating hypotheses regarding the cellular causes of observed organ-level behaviors, while accounting for physiological variability has been unexplored.
Experimental Analysis of Small Diameter Brush Seals and Comparisons With Theoretical Predictions
Authors: Deville Lilas , Arghir Mihaï
Published: July 2018

The paper presents the experimental results obtained for brush seals of 38 mm diameter operating with air at pressure differences up to 7 bars and rotation frequencies up to 500 Hz. The seals had bristles of 70 μm diameter, made of Haynes 25. Seals with two radial interferences (0 and 100 μm) between the brush and the rotor were tested. The presented running in procedure underlines the influence of the initial wear on the brush temperatures. The test results consisted of leakage mass flow rates. The temperatures of a limited number of points on the brush and on the rotor were also recorded. The results confirmed the important impact of the radial interference on the leakage. The test data were further confronted with theoretical predictions obtained with an original model. The model considers the brush as a deformable porous medium. Its local porosity and permeability are obtained from a fluid–structure interaction between the bristle pack and the leakage flow. The comparisons showed nearly close values of the mass flow rates. The differences between experimental and theoretical predictions are considered to be due to an underestimation of the porosity because the model neglects the friction forces between bristles and between the bristles and the rotor.
Comparative Fluid–Structure Interaction Analysis of Polymeric Transcatheter and Surgical Aortic Valves' Hemodynamics and Structural Mechanics
Authors: Ghosh Ram P. , Marom Gil , Rotman Oren M. , Slepian Marvin J. , Prabhakar Saurabh , Horner Marc , Bluestein Danny
Published: July 2018

Transcatheter aortic valve replacement (TAVR) has emerged as an effective alternative to conventional surgical aortic valve replacement (SAVR) in high-risk elderly patients with calcified aortic valve disease. All currently food and drug administration approved TAVR devices use tissue valves that were adapted to but not specifically designed for TAVR use. Emerging clinical evidence indicates that these valves may get damaged during crimping and deployment—leading to valvular calcification, thrombotic complications, and limited durability. This impedes the expected expansion of TAVR to lower-risk and younger patients. Viable polymeric valves have the potential to overcome such limitations. We have developed a polymeric SAVR valve, which was optimized to reduce leaflet stresses and offer a thromboresistance profile similar to that of a tissue valve. This study compares the polymeric SAVR valve's hemodynamic performance and mechanical stresses to a new version of the valve—specifically designed for TAVR. Fluid–structure interaction (FSI) models were utilized and the valves' hemodynamics, flexural stresses, strains, orifice area, and wall shear stresses (WSS) were compared. The TAVR valve had 42% larger opening area and 27% higher flow rate versus the SAVR valve, while WSS distribution and mechanical stress magnitudes were of the same order, demonstrating the enhanced performance of the TAVR valve prototype. The TAVR valve FSI simulation and Vivitro pulse duplicator experiments were compared in terms of the leaflets' kinematics and the effective orifice area. The numerical methodology presented can be further used as a predictive tool for valve design optimization for enhanced hemodynamics and durability.
Evaluating the Affective Aspect of Intuitive Interactions Using Image Schemas
Authors: Asikhia Obokhai Kess , Setchi Rossitza
Published: July 2018

Intuitive use is a desirable feature in product and interface design. Until recently, however, there has been little research on the affective aspects of intuitive use. This paper contributes to the research in this area by proposing a systematic analytical method for assessing the affective aspect of intuitive use; the method uses an ontology of image schemas, computational semantics, and a sentiment analysis to determine the affect associated with interactions. The approach is evaluated through an empirical study involving 40 participants who completed a task with two products. The results show that the approach links the image schemas used for the completion of a task to the affective experiences of the users. The study has the potential to lead to improvements in design and the improved evaluation of intuitive use because it allows experiences to be linked directly to the specific image schemas employed in the design.
Predictive Modeling of Droplet Formation Processes in Inkjet-Based Bioprinting
Authors: Wu Dazhong , Xu Changxue
Published: July 2018

Additive manufacturing is driving major innovations in many areas such as biomedical engineering. Recent advances have enabled three-dimensional (3D) printing of biocompatible materials and cells into complex 3D functional living tissues and organs using bio-printable materials (i.e., bioink). Inkjet-based bioprinting fabricates the tissue and organ constructs by ejecting droplets onto a substrate. Compared with microextrusion-based and laser-assisted bioprinting, it is very difficult to predict and control the droplet formation process (e.g., droplet velocity and volume). To address this issue, this paper presents a new data-driven approach to predicting droplet velocity and volume in the inkjet-based bioprinting process. An imaging system was used to monitor the droplet formation process. To investigate the effects of polymer concentration, excitation voltage, dwell time, and rise time on droplet velocity and volume, a full factorial design of experiments (DOE) was conducted. Two predictive models were developed to predict droplet velocity and volume using ensemble learning. The accuracy of the two predictive models was measured using the root-mean-square error (RMSE), relative error (RE), and coefficient of determination (R2). Experimental results have shown that the predictive models are capable of predicting droplet velocity and volume with sufficient accuracy.
Natural Frequency Optimization of Variable-Density Additive Manufactured Lattice Structure: Theory and Experimental Validation
Authors: Cheng Lin , Liang Xuan , Belski Eric , Wang Xue , Sietins Jennifer M. , Ludwick Steve , To Albert
Published: July 2018

Additive manufacturing (AM) is now capable of fabricating geometrically complex geometries such as a variable-density lattice structure. This ability to handle geometric complexity provides the designer an opportunity to rethink the design method. In this work, a novel topology optimization algorithm is proposed to design variable-density lattice infill to maximize the first eigenfrequency of the structure. To make the method efficient, the lattice infill is treated as a continuum material with equivalent elastic properties obtained from asymptotic homogenization (AH), and the topology optimization is employed to find the optimum density distribution of the lattice structure. Specifically, the AH method is employed to calculate the effective mechanical properties of a predefined lattice structure as a function of its relative densities. Once the optimal density distribution is obtained, a continuous mapping technique is used to convert the optimal density distribution into variable-density lattice structured design. Two three-dimensional (3D) examples are used to validate the proposed method, where the designs are printed by the EOS direct metal laser sintering (DMLS) process in Ti6Al4V. Experimental results obtained from dynamical testing of the printed samples and detailed simulation results are in good agreement with the homogenized model results, which demonstrates the accuracy and efficiency of the proposed method.
Throwing, Catching, and Balancing of a Disk With a Disk-Shaped End Effector on a Two-Link Manipulator
Authors: Erumalla Sandeep R. , Pasupuleti Sujithkumar , Ryu Ji-Chul
Published: July 2018

In this paper, nonprehensile throwing, catching, and balancing of a disk-shaped object by a two-link planar manipulator mounted with a disk-shaped end effector are presented. Given a goal position, which is out of the robot's reachable space, the required release position and velocity for throwing are first determined. The throwing manipulation is proposed in a way that the arm follows a planned trajectory between the ready and the release position to achieve the required velocity at the release position. Catching is performed in a way that it reduces impact when making contact. Balancing control is then applied to the disk-shaped end effector to prevent the object from falling after catching. The proposed approach was implemented on an experimental setup built for verification and the results are provided.
A Specimen Extraction Instrument Based on Braided Fiber Tube for Natural Orifice Translumenal Endoscopic Surgery
Authors: Li Jinhua , Zhang Zemin , Wang Shuxin , Shang Zufeng , Zhang Guokai
Published: July 2018

Natural orifice translumenal endoscopic surgery (NOTES) has offered significant advantages of less pain, reduced recovery time, and minimized scar after operation, demonstrating a promising development prospect. However, the large-size specimen extraction remains challenging for NOTES, due to the narrow space of the human natural orifices. To address such difficulties, a specimen extraction method that utilizes the braided fiber tube (BFT) structure with excellent retractility to accommodate and bind the bulky specimen has been proposed. Based on the theory of helical spring, the geometric model and the mechanical model of the BFT are established, and experiments have been performed to verify the accuracy of the derived mechanical model. In addition, a tensile test of using the BFT to extract large specimens via a small channel is carried out, which verifies the stable extraction performance of the proposed design. The BFT will not be damaged when extracting the specimen with a diameter less than 1.75 times of the channel diameter. A NOTES-specific specimen extraction instrument is designed according to the characteristics of NOTES, and it has three degrees-of-freedom and is able to actively capture different specimen by using a suction cup. Finally, specimen extraction experiments on NOTES multitasking platform phantom have been conducted using the prototyped instrument to validate its feasibility and effectiveness.
Inverse Fracture in DWTT and Brittle Crack Behavior in Large-Scale Brittle Crack Arrest Test
Authors: Tagawa Tetsuya , Amano Toshihiko , Hiraide Takashi , Sakimoto Takahiro , Igi Satoshi , Fujishiro Taishi , Hara Takuya , Inoue Takehiro , Aihara Shuji
Published: July 2018

The drop weight tear test (DWTT) has been widely used to evaluate the resistance of linepipe steels against brittle fracture propagation. Although there is an ambiguity in the evaluation of DWTT results if inverse fracture appears on the fracture surfaces, the cause of inverse fracture is not yet fully understood. In the present work, DWTTs were performed with X65, X70, and X80 steel linepipes. In addition to the conventional DWTT specimen with a pressed notch (PN), PN specimens with a back slot (BS) and specimens with a chevron notch (CN) or static precrack (SPC) were also examined, and the fracture appearances in different strengths and different initial notch types were compared. Although the frequency of inverse fracture in these DWTTs was different with each material and each specimen type, there was no material or specimen type that was entirely free from inverse fracture. The purpose of the DWTT is to evaluate the brittle crack arrestability of the material in a pressurized linepipe. Therefore, the DWTT results should be examined with a running brittle crack arrest (BCA) test. A large-scale BCA test with temperature gradient was also performed with the X65 mother plate, and the shear area fraction measured in the DWTT fracture surface was compared with the local shear lip thickness fraction in the BCA test. Based on the results, the count of inverse fracture in the DWTT was discussed in comparison with the long BCA behavior in the BCA test.
General
Correlation for Heat Transfer to Gas–Liquid Flow in Vertical
Channels
Authors: Shah Mirza
M.
Published: July 2018

A general correlation is presented for heat transfer during flow of gas–liquid mixtures flowing in vertical channels prior to dry out. It has been verified with a wide range of data that include upward and downward flow in heated and cooled tubes, annuli, and rectangular channels. The data are from 19 studies and include 14 gas–liquid mixtures with a wide range of properties. The parameters include pressure 1–6.9 bar, temperature 16–115 °C, liquid Reynolds number from 2 to 127,231, superficial gas and liquid velocities up to 87 and 13 m/s, respectively, and ratio of superficial gas and liquid velocities 0.03–1630. The 1022 data points are predicted by the new correlation with mean absolute deviation (MAD) of 18.1%. Several other correlations were also compared to the same data and had MAD of 28.6–45.5%.
Applicability
of Heat Mirrors in Reducing Thermal Losses in Concentrating Solar
Collectors
Authors: Khullar Vikrant , Mahendra Prashant , Mittal Madhup
Published: July 2018

In the present work, a novel parabolic trough receiver design has been proposed. The proposed design is similar to the conventional receiver design except for the envelope and the annulus part. Here, a certain portion of the conventional glass envelope is coated with Sn-In2O3 and also Sn-In2O3 coated glass baffles are provided in the annulus part to reduce the radiative losses. The optical properties of the coated glass are such that it allows most of the solar irradiance to pass through, but reflects the emitted long wavelength radiations back to the absorber tube. Sn-In2O3 coated glass is referred to as “transparent heat mirror.” Thus, effectively reducing the heat loss area and improving the thermal efficiency of the solar collector. A detailed one-dimensional steady-state heat transfer model has been developed to predict the performance of the proposed receiver design. It was observed that while maintaining the same external conditions (such as ambient/initial temperatures, wind speed, solar insolation, flow rate, and concentration ratio), the heat mirror-based parabolic trough receiver design has about 3–5% higher thermal efficiency as compared to the conventional receiver design. Furthermore, the heat transfer analysis reveals that depending on the spatial incident solar flux distribution, there is an optimum circumferential angle (θ = θoptimum, where θ is the heat mirror circumferential angle) up to which the glass envelope should be coated with Sn-In2O3. For angles higher than the optimum angle, the collector efficiency tends to decrease owing to increase in optical losses.
A Fast Algorithm on Minimum-Time Scheduling of an Autonomous Ground Vehicle Using a Traveling Salesman Framework
Authors: Bakshi Soovadeep , Yan Zeyu , Chen Dongmei , Qian Qiang , Chen Yinan
Published: July 2018

Manufacturing automation, especially through implementation of autonomous ground vehicle (AGV) technology, has been under intensive study due to increased productivity and reduced variations. The objective of this paper is to present an algorithm on scheduling of an AGV that traverses desired locations on a manufacturing floor. Although many algorithms have been developed to achieve this objective, most of them rely on exhaustive search, which is time-consuming. A novel two-step algorithm that generates “good,” but not necessarily optimal, solutions for relatively large data sets (≈1000 points) is proposed, taking into account time constraints. A tradeoff analysis of computational expense versus algorithm performance is discussed. The algorithm enables the AGV to find a tour, which is as good as possible within the time constraint, using which it can travel through all given coordinates before returning to the starting location or a specified end point. Compared to exhaustive search methods, this algorithm generates results within a stipulated computation time of 30 s on a laptop personal computer.
Detection of Flat-Bottom Holes in Conductive Composites Using Active Microwave Thermography
Authors: Mirala Ali , Foudazi Ali , Ghasr Mohammad Tayeb , Donnell Kristen M.
Published: July 2018

Active microwave thermography (AMT) is an integrated nondestructive testing (NDT) technique that utilizes a microwave-based thermal excitation and subsequent thermal measurement. AMT has shown potential for applications in the transportation, infrastructure, and aerospace industries. This paper investigates the potential of AMT for detection of defects referred to as flat-bottom holes (FBHs) in composites with high electrical conductivity such as carbon fiber-based composites. Specifically, FBHs of different dimensions machined in a carbon fiber reinforced polymer (CFRP) composite sheet are considered. Simulation and measurement results illustrate the potential for AMT as a NDT tool for inspection of CFRP structures. In addition, a dimensional analysis of detectable defects is provided including a radius-to-depth ratio threshold for successful detection.
Model of Effect of Hot Gas Ingress on Temperatures of Turbine Disks
Authors: Michael Owen J. , Tang Hui , Lock Gary D.
Published: July 2018

Ingress is the leakage of hot mainstream gas through the rim-seal clearance into the wheel-space between the rotating turbine disk (the rotor) and the adjacent stationary casing (the stator). The high-pressure rotor is purged by a radial outflow of air from the high-pressure compressor, and this cooling air is also used to reduce the ingress. The engine designer needs to predict the stator and rotor temperatures as a function of cooling-flow rate. The sealing effectiveness determines how much air is needed to reduce or prevent ingress; although there are numerous theoretical and experimental papers on the effectiveness of different seal geometries, there are few papers on the effect of ingress on the temperature of the rotating disk. This is an unsolved problem of great practical importance: under high stress, a small increase in metal temperature can significantly reduce operating life. In this paper, conservation equations and control volumes are used to develop theoretical equations for the exchange of mass, concentration and enthalpy in an adiabatic rotor–stator system when ingress occurs. It is assumed that there are boundary layers on the rotor and stator, separated by an inviscid rotating core, and the fluid entrained from the core into the boundary layer on the rotor is recirculated into that on the stator. The superposed cooling flow protects the rotor surface from the adverse effects of hot-gas ingress, which increases the temperature of the fluid entrained into the rotor boundary layer. A theoretical model has been developed to predict the relationship between the sealing effectiveness on the stator and the adiabatic effectiveness on the rotor, including the effects of both ingress and frictional heating. The model involves the use of a nondimensional buffer parameter, Ψ, which is related to the relative amount of fluid entrained into the rotor boundary layer. The analysis shows that the cooling flow acts as a buffer, which attenuates the effect of hot gas ingress on the rotor, but frictional heating reduces the buffer effect. The theoretical effectiveness curves are in good agreement with experimental data obtained from a rotor–stator heat-transfer rig, and the results confirm that the buffer effect increases as the sealing effectiveness of the rim seals decreases. The analysis quantifies the increase in the adiabatic rotor temperature due to direct frictional heating, which is separate from the increase due to the combined effects of the ingress and the indirect frictional heating of the entrained fluid. These combined effects are reduced as Ψ increases, and Ψ = 1 at a critical flow rate above which there is no entrained fluid and consequently no indirect heating of the rotor. The model also challenges the conventional physical interpretation of ingress as, in general, not all the hot gas that enters the rim-seal clearance can penetrate into the wheel-space. The ingress manifests itself through a mixing of enthalpy, which can be exchanged even if no ingested fluid enters the wheel-space.
A Method to Analyze the Contact Stress of Dovetail Attachments in Aeroengine
Authors: Zhang Shuo , Shen Xiuli , Dong Shaojing , Zhang Ye , Hu Wentong
Published: July 2018

Finite element method (FEM) has been used to find out the fundamental reason of shape function due to the nonconvergence of stress in calculating the trapezoidal tooth dovetail attachments of aeroengine. We have used two different methods, representing actual models, for the calculation of contact stress. Comparative analysis of these methods, and the already reported ones, led us to conclude that the displacement extraction method is better and efficient for the engineering applications. This method was successively applied to contact model of indenter with shaped edge, a model with an inclined contact surface and dovetail attachment model, while these stress results are compared with that of photoelastic. Moreover, we found that the photoelastic and displacement error in extraction method is small and the method can be widely used for the calculation of structural stress with sharp edge.
Compressor Instability Analysis Within a Hybrid System Subject to Cycle Uncertainties
Authors: Cuneo Alessandra , Traverso Alberto , Massardo Aristide F.
Published: July 2018

The dynamic modeling of energy systems can be used for different purposes, obtaining important information both for the design phase and control system strategies, increasing the confidence during experimental phase. Such analysis in dynamic conditions is generally performed considering fixed values for both geometrical and operational parameters such as volumes, orifices, but also initial temperatures, pressure. However, such characteristics are often subject to uncertainty, either because they are not known accurately or because they may depend on the operating conditions at the beginning of the relevant transient. With focus on a gas turbine fuel cell hybrid system (HS), compressor surge may or may not occur during transients, depending on the aforementioned cycle characteristics; hence, compressor surge events are affected by uncertainty. In this paper, a stochastic analysis was performed taking into account an emergency shut-down (ESD) in a fuel cell gas turbine HS, modeled with TRANSEO, a deterministic tool for the dynamic simulations. The aim of the paper is to identify the main parameters that impact on compressor surge margin. The stochastic analysis was performed through the response sensitivity analysis (RSA) method, a sensitivity-based approximation approach that overcomes the computational burden of sampling methods. The results show that the minimum surge margin occurs in two different ranges of rotational speed: a high-speed range and a low-speed range. The temperature and geometrical characteristics of the pressure vessel, where the fuel cell is installed, are the two main parameters that affect the surge margin during an emergency shut down.
Accurate Nonlinear Dynamics and Mode Aberration of Rotating Blades
Authors: Filippi M. , Pagani A. , Carrera E.
Published: July 2018

Nonlinear dynamics and mode aberration of rotating plates and shells are discussed in this work. The mathematical formalism is based on the one-dimensional (1D) Carrera unified formulation (CUF), which enables to express the governing equations and related finite element arrays as independent of the theory approximation order. As a consequence, three-dimensional (3D) solutions accounting for couplings due to geometry, material, and inertia can be included with ease and with low computational costs. Geometric nonlinearities are incorporated in a total Lagrangian scenario and the full Green-Lagrange strains are employed to outline accurately the equilibrium path of structures subjected to inertia, centrifugal forces, and Coriolis effect. A number of representative numerical examples are discussed, including multisection blades and shells with different radii of curvature. Particular attention is focused on the capabilities of the present formulation to deal with nonlinear effects, and comparison with s simpler linearized approach shows evident differences, particularly in the case of deep shells.
Phase
Change Material Freezing in an Energy Storage Module for a Micro Environmental Control
System
Authors: Ezzat
Khalifa H. , Koz Mustafa
Published: July 2018

This study analyzes phase change material (PCM) freezing process in a novel latent heat storage device (LHSD). Heat is removed from the PCM with an embedded evaporator. A mathematical model of freezing in a finite-thickness PCM slab is presented. An experimentally validated reduced-order model (ROM) based on the mathematical model was developed to analyze the heat transfer between the freezing PCM and an evaporating refrigerant flowing inside a flat, microchannel tube coil embedded in the PCM. A detailed finite element model (FEM) of the same device was also developed and employed to verify the validity of the ROM over a wider range of conditions. The freezing times and total “cooling” stored in the PCM computed by the ROM agree very well with those computed by the detailed FEM. The ROM executes in ∼1 min for a full heat exchanger, compared with more than 10 h for the FEM, making the former much more practical for use in parametric analysis and optimization of design alternatives.
Dynamic Behavior Analysis of a Rotor System Based on a Nonlinear Labyrinth-Seal Forces Model
Authors: Zhang Enjie , Jiao Yinghou , Chen Zhaobo
Published: July 2018

Taking the flow field features of labyrinth seal into consideration, the fluid force generated from the seal cavity, which is spatially separated into two regions, is modeled with the perturbation method. The rotor orbit defined in the perturbation analysis is spatio-temporal varied, which is quite different from the usually preconditioned elliptical track. Meanwhile, the nonlinear fluid force originating from the seal clearance is delineated by the Muszynska's model. Based on the short bearings assumption, a nonlinear oil-film force model is employed. The rotating shaft is simulated by Timoshenko beam finite element with the consideration of geometric asymmetry. Applying the Lagrange's equations, the motion equations of the rotor-bearing-labyrinth seal system are derived. By means of spectrum cascades, bifurcation diagrams, Poincaré maps, etc., the numerical analysis of the system dynamic characteristics is conducted. The results show that abundant nonlinear behaviors can be triggered in the speed-up. The instability threshold and the vibration amplitude of the rotor system are, respectively, enhanced and reduced by the increasing inlet pressure. With shorter seal length, the sealing effect is decreased, whereas the system stability is improved. The fluid-whip phenomenon can be eliminated by increasing the mass unbalance eccentricity at a certain rotational speed.
Forced Response Reduction of a Blisk by Means of Intentional Mistuning
Authors: Beirow Bernd , Kühhorn Arnold , Figaschewsky Felix , Bornhorn Alfons , Repetckii Oleg V.
Published: July 2018

The effect of intentional mistuning has been analyzed for an axial turbocharger blisk with the objective of limiting the forced response due to low engine order excitation (LEO). The idea behind the approach was to increase the aerodynamic damping for the most critical fundamental mode in a way that a safe operation is ensured without severely losing aerodynamic performance. Apart from alternate mistuning, a more effective mistuning pattern is investigated, which has been derived by means of optimization employing genetic algorithms. In order to keep the manufacturing effort as small as possible, only two blade different geometries have been allowed, which means that an integer optimization problem has been formulated. Two blisk prototypes have been manufactured for purpose of demonstrating the benefit of the intentional mistuning pattern identified in this way: A first one with and a second one without employing intentional mistuning. The real mistuning of the prototypes has been experimentally identified. It is shown that the benefit regarding the forced response reduction is retained in spite of the negative impact of unavoidable additional mistuning due to the manufacturing process. Independently, further analyzes have been focused on the robustness of the solution by considering increasing random structural mistuning and aerodynamic mistuning as well. The latter one has been modeled by means of varying aerodynamic influence coefficients (AIC) as part of Monte Carlo simulations. Reduced order models have been employed for these purposes.