bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhancement of an Optimization-Based Damage Detection Technique
Authors: Yang Chulho , Chang Young Bae , Sa Jongsung , Park Junyoung
Published: March 2016

Various structural health monitoring (SHM) techniques utilizing vibration signals have been developed for identification of damages in a structure. Many of these studies are based on sensitivity analysis, finite element model (FEM) updating, and optimization techniques. FEM updating technique is one of the major techniques that iteratively minimizes the difference between the modal parameters measured from the real structure and the corresponding analytical predictions. This method would be more beneficial for typical continuous systems such as beams, plates, and shells which cannot be reasonably discretized. One of the drawbacks of these techniques is the large number of unknowns to be estimated. These techniques in the literature that use FEM updating to estimate perturbed parameters for all elements in the model can be time-consuming and ill-conditioned, even for relatively simple structures. The technique also requires a full and accurate finite element model for each monitored structure.

A new method to identify damages in a structure using embedded sensitivity functions and optimization algorithms is described and its performance is demonstrated in this paper. The perturbed frequency response function (FRF) is calculated using Taylor series expansion in terms of the baseline system and the embedded sensitivity functions. The optimization process minimizes the difference between the measured FRFs of the damaged structure and the perturbed FRFs calculated from the baseline structure. Structural damages are often characterized by changes in mechanical parameters such as stiffness, mass, and damping. Embedded sensitivity functions offer a means of determining the path that is followed from the baseline to the perturbed FRF of the structure.

The robustness and efficiency of suggested structural health monitoring method are discussed in this paper. The accuracy of damage estimation is investigated with respect to various types and values of damages, objective functions, frequency ranges, scale factors, procedures, and noise levels. Precise measurement and monitoring of vibration signals are critical for accurate detection of the location, type, and level of damage. However, in most practical mechanical systems, vibration tests may result in noise on the input or output measurements. Noise on the measurement affects the accuracy of the FRFs and identification of damages in a structure. Based on the results of the study, several parameters and factors in the optimization process and structural dynamics are suggested to enhance the efficiency and robustness of damage identification process.

It is shown that the iteration number of the optimization process is significantly reduced. Accurate estimate of damages can be obtained within the range of 2∼5% error with various enhancements applied to the technique.
Water Based Propellant for Cold Gas Thruster
Authors: Lee John B. , Huang Adam
Published: March 2016

Microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS) have produced ideas and techniques for creating new devices at the micro/nano scale. Nano/pico satellites have limited orientation capability partly due to the current state of microthruster devices. Development of a self-contained micro propulsion system would enable dynamic orbital maneuvering of pico- and nano-class satellites. The act of vaporizing a fluid via nanochannels to vacuum has not been studied and the limitations are unknown, but it could provide a novel method of propulsion for small satellites. However, solution properties are transient during vaporization which affects fluid flow. Thus, experiments have been designed to measure solution properties including density, evaporation rate, and vaporization pressure. A setup has been designed monitor the solution mass and volume inside a vacuum chamber. Evaporation of the solution is affected by the vacuum pressure, capillary tubing diameter, solution temperature, and solution concentration. When maintained at the solution vapor pressure, the vaporization rate has ranged from 0.003 to 0.025 grams per minute across the varying concentrations. Preliminary results have indicated some interesting trends regarding solution composition and vaporization rate. The results obtained from preliminary experiments will be used in conjunction with future experiments to determine the viability of nanochannels to be used in the small satellite propulsion system.
Probabilistic Analysis of Continuously Variable Transmission to Increase Reliability
Authors: Nkama Nkama E. , Alemayehu Fisseha M. , Endeshaw Haileyesus B. , Ekwaro-Osire Stephen , Pham Duc
Published: March 2016

Renewable energy has surfaced as a power source of interest of the world recently. Wind Energy has been the leading source of renewable energy development for the past several years. The biggest issue with wind energy are wind turbine (WT) drivetrain failures. The gearbox fails after three to seven years of operation while the expected lifetime of the WT is 20 years. The application to the automotive industry inspired the use of continuously variable transmissions (CVT) in a WT. The CVT considered in this study is the Nu-Vinci CVT technology, a Continuously Variable Planetary (CVP) transmission, designed by Fallbrook Technologies. This technology was selected because of its planetary configuration and its ability to transmit larger amounts of torque, which is required for WT applications. The goal of this research was to reduce the Cost of Energy (COE) by increasing the reliability of CVTs in WTs. In this study, two WT systems, one with CVT as the third stage (referred as ‘WT with CVT’) and another with three stage standard gearbox (referred as ‘WT with SG’), are considered. The research question in this study is ‘Does the use of CVTs improve the reliability of drivetrains of WTs?’ To answer this question three specific aims were developed. First, a computational framework had to be developed. Second, a probabilistic dynamic analysis was conducted. Third, a probabilistic analysis on the COE was performed. A computational framework was developed to guide the probabilistic analysis to determine power values and COE. The probability that the generator torque of the WT with CVT will be less than that of the WT with SG is found to be 50.67%. It was also shown that provided the same input speed and torque, the WT with CVT has a slightly higher power generation. In addition, it was shown that there is 54% probability that the WT with CVT will exhibit lower COE than WT with SG. The higher power production is attained while decreasing the COE. From these results, it can be inferred that the reliability of the drivetrain is improved using a CVT.
Analysis of Swirl Flow by Tube Inserts for CFD Study
Authors: Bouhairie Salem
Published: March 2016

The petroleum and petrochemical industries continually seek mechanical methods to improve heat transfer in shell-and-tube heat exchangers. Tube bundle inserts are popular mechanical devices that help improve performance. The increase in the tubeside heat transfer coefficient by the insert allows for a decrease in required shellside flow length, assuming single tube pass. The flow length reduction allows for designing higher velocities and subsequent shellside shear rates, to help reduce crude oil fouling potential.

This work presents some of HTRI’s ongoing experimental measurements and preliminary Computational Fluid Dynamics (CFD) simulations. CFD visualization of swirl flow dynamics and heat transfer inside the augmented tube provides insight on complex flow physics, which is misunderstood.

Heat Transfer Research, Inc. (HTRI) collected experimental data for in-tube single-phase flow using twisted tape inserts in the Tubeside Single-Phase Unit (TSPU) situated in the Research and Technology Center (RTC). Our data will be used to calibrate ANSYS FLUENT CFD simulations of a tube with a twisted tape swirl insert. We first performed plain tube simulations and compared the heat transfer results with open literature measurements, for validation. We will modify the CFD tube model to have a swirl flow insert, and compare numerical results against open literature experimental data of diabatic single-phase swirl flow.

In future, we will compute heat transfer (heating and cooling) and pressure drop for tube insert configurations at laminar and turbulent Reynolds numbers from 3000 to 500000. The range of tubeside Reynolds numbers required the use of the laminar, transition, and Realizable k-epsilon turbulence models with scalable wall functions.

This study describes some of the mechanisms behind turbulent swirl flow augmentation inside a tube, as well as the limitations of conventional in-tube heat transfer correlations applied to swirl flow inserts.
Performance Analysis of Biologically Inspired Honeycomb Structured Heat Exchanger
Authors: Rahman Mosfequr , Iqbal Sakib , Calamas David
Published: March 2016

The process of heat exchange between two fluids that are at different temperatures and separated by a solid wall occurs in many engineering applications. The device used to implement this exchange is termed a heat exchanger (HE), and specific applications may be found in space heating and air-conditioning, power generation, waste heat recovery, and chemical processing. Increasing heat transfer coefficient and making heat exchanger compact for various applications like in spacecraft, underwater vehicle, unmanned Ariel vehicle is one of the main challenges. Biologically-inspired design (or BID) has become an important and increasingly wide-spread movement in design for environmentally-conscious sustainable development. By definition, BID is based on cross-domain analogies; further, biologically-inspired approaches to design have a certain degree of openness to innovation. Compact heat exchanger can reduce the space and weight of any locomotives and spacecraft. Structural elements inspired from nature possess compactness and stability. Honeycomb structure allows minimize the spacing between cells which makes it possible to use thinnest possible metal boundary wall between two fluids. A rectangle structure can also do the same thing but it has less surface area, which will essentially decrease the volume of heat exchanger. Honeycomb structure provides high surface area to volume ratio which can be utilized to increase heat transfer coefficient of a heat exchanger and thus make compact system.

In this computational study, bio-inspired simple honeycomb structured and spiral finned honeycomb structured counter flow heat exchanger has been three dimensionally simulated using finite element methods in commercial software COMSOL. This work is used to reduce the weight of heat exchangers in steam reforming reactors. There is a good correlation when the fluid temperature is the same in all cells. There is also a good temperature gradient in the fluid owing to laminar flow. 3D modeling showed that a careful representation of the inlet is needed for realistic results. A tube-shell heat exchanger is also simulated using FEA in COMSOL. Spiral finned heat exchanger provides additional surface area in cost of pressure drop. The performance characteristics of honeycomb heat exchanger showed an increase in heat transfer rate with least vortex formation.
On Improvement of PIV Measurements in the High-Shear Layer of a Wall-Bounded Flow
Authors: Skifton Richard S. , Budwig Ralph S.
Published: March 2016

The particles utilized in particle image velocimetry (PIV) form a biased dispersion near interfaces that, in turn, lead to biased velocity measurements. This lack of seeding in the high shear region of the flow always biases the velocity measurement high as the particles are, on average, towards the far end of an interrogation window (IW) — opposite of the wall. By observing the ensemble-averaged IW particle-dispersion centroid as the corrected measurement location against the industry standard of the geometric center of the IW, this paper puts forth a methodology to correct for the biased error in flow measurements very near the wall. A typical correction to the reported velocity measurement location within a wall layer flow was seen to be approximately 75% from the geometric center to the edge of an IW. This methodology can easily be implemented in any PIV code with the express purpose of removing a source of bias error that forms by reporting measurements at the geometric center of an IW.
Multi-Objective Optimization of a Simplified Car Body Using Computational Fluid Dynamics
Authors: Bakshi Soham , Jawad Badih A. , Arslan Selin , Yee Kingman , Liu Liping
Published: March 2016

Today’s strict fuel economy requirement produces the need for the cars to have really optimized shapes among other characteristics as optimized cooling packages, reduced weight, to name a few. With the advances in automotive technology, tight global oil resources, lightweight automotive design process becomes a problem deserving important consideration. It is not however always clear how to modify the shape of the exterior of a car in order to minimize its aerodynamic resistance. Air motion is complex and operates differently at different weather conditions. This gap can be covered by the use of adjoint solvers which predict the sensibility of the aerodynamic forces to changes of the geometry. Alternatively, Computational Fluid Dynamics (CFD) solvers can be partnered with optimization software which guide model design changes and evaluate the corresponding results. Design changes can be executed by modifying a parameterized geometry or using mesh morphing techniques. With the advances in computational fluid dynamics, design optimization methods in the aerodynamic design are more important than ever. In the present paper, ANSYS Fluent will be used in conjunction with the optimization software ANSYS DesignXplorer to study ways of reducing drag and lift for a simplified car body. ANSYS simulation software allows one to predict, with confidence, the impact of fluid flows on the product throughout design and manufacturing as well as during end use. CFD is a complex technology involving strongly coupled non-linear partial differential equations which attempt to computationally simulate theoretical and experimental models in a discrete domain of complex geometric shape. A detailed assessment of errors and uncertainties has to concern itself with the three roots of CFD: theory, experiment, and computation. Further, the application of CFD is rapidly expanding with the growth in computational resources. The body in question in this study is the Ahmed body [1] which has been used numerous times for CFD code validation. This geometry represents a road legal car which is used to study the effect of different forces like, aerodynamic drag force, lift force, and some other major forces which affect a car’s motion significantly. Despite being a simple body, accurate prediction of its aerodynamic performance often requires very accurate and computationally expensive calculations. We would like to investigate if meaningful optimizations can be achieved by using reduced resources, by analyzing how air at different velocity affect the body and what changes might be necessary for a further optimized performance.

The purpose here is not to predict the absolute values of drag for this body, but to demonstrate that optimization can be performed with limited resources relying on information about drag deltas rather than absolute values. Keeping limiting resources in mind, a grid independence study wasn’t done.
Wideband Acoustic Luneburg Lens Based on Graded Index Phononic Crystal
Authors: Wang Chia-Fu , Tsai Chia-Nien , Chang I-Ling , Chen Lien-Wen
Published: March 2016

The present study proposes a wideband two-dimensional Luneburg lens using graded phononic crystals (GPCs). We present a method to broaden the range of operation frequency of the Luneburg lens based on GPCs. The GPCs is composed of circular cylindrical rods with triangular lattice air background. In long wavelength limit assumption, periodic structure behaves like a homogeneous medium since dispersion relations is almost linear. The effective refractive index can be tuned by adjusting the filling ratio. The plan wave expansion method is utilized to calculate the band structures of the locally GPCs and the effective refractive index of the locally GPCs with different filling ratio. Finite element simulations was employed to confirm the acoustic properties of designed device. Our numerical simulations demonstrate that the operation frequency range of GPCs of circular cylindrical rods arranged as triangular array is much wider than those of square array. A wideband acoustic Luneburg lens can be achieved by using graded phononic crystals of triangular array.
Numerical Investigations of the Effect of Flow Arrangement and Number of Layers on the Performance of Multi-Layer Microchannel Heat Sinks
Authors: Effat M. B. , AbdelKarim M. S. , Hassan O. , Abdelgawad M.
Published: March 2016

With the advance of miniaturization technology, more and more electronic components are placed onto small electronic chips. This leads to the generation of high amounts of thermal energy that should be removed for the safe operation of these electronic components. Microchannel heat sinks, where electronic chips are liquid cooled instead of the conventional air cooling techniques, were proposed as a means to improve cooling rates. Later on, double layer micro channel heat sinks were suggested as an upgrade to single layer microchannel heat sinks with a better thermal performance. In the present study the effects of increasing the number of layers of the microchannel heat sink to three-layers as well as the effect of changing the flow arrangements (counter and parallel flows) within the three channel layers on the thermal performance of the heat sink were investigated. In all investigated cases the temperature distribution over the base of the microchannel heat sink system and the total pressure drop are reported. A range of mass flow rates from 1×10−4 to 5×10−4 kg/s was considered. Uniform heat flux conditions were considered during the study. COMSOL Multiphysics finite element package was employed for the numerical analysis. Results indicate significant enhancement in the uniformity of the temperature on the processor surface when multi-layer channels were employed, compared to the single-layer case. The uniformity in the temperature distribution was accompanied by reduction of pressure drop across channels for the same mass flow rate and heat flux conditions. The counter flow arrangement showed the best temperature distribution with the uniform heat flux cases.
A Novel WSGG Model Based on Weighted Absorption-Emission Coefficients
Authors: Brittes Rogério , Cassol Fabiano , Roman Centeno Felipe , França Francis H. R.
Published: March 2016

The absorption coefficient of participating species, such as CO2 and H2O, shows very irregular dependence with the wavenumber, which makes it difficult the spectral integration of the radiative transfer equation (RTE). This task can be performed with the line-by-line (LBL) integration, which is very computationally expensive due to the vast amount of spectral lines that span the spectrum. As alternatives to the LBL integration, there are global models, such as the weighted-sum-of-gray-gases (WSGG) and the spectral line weighted-sum-of-gray gases (SLW). These models replace the integration with respect to the wavenumber by the summation over a certain number of gray gases, thus reducing the computational effort. This paper shows a modification of the WSGG model, in which the absorption and emission coefficients of each gray gas are considered to be function of the temperature. The model, named WSGG with non-constant coefficients (NCC-WSGG), is applied to solve a few non-isothermal and non-homogeneous problems. The results show very satisfactory agreement with the LBL integration.
Modeling and Analysis of Energy Load Management Using Advanced Off-Peak Controlled Heat Pump System With Thermal Storage Under Different Time and Weather Conditions
Authors: Heidar Esfehani Hamidreza , Kriegel Martin
Published: March 2016

In this present paper, an advanced model of a ground source heat pump (GSH) system coupled with thermal energy storage (TES) is simulated and performed under a developed load management control strategy in order to supply a residential complex by taking the advantage of cheap excess electricity of the grid network during off-peak hours, where demand is in its lowest rate. Analyzing the performance of the system under different time and weather conditions leads to recognizing the effective parameters on thermal performance of the system which leads to achieve the optimal system efficiency and output energy. The proposed system with off-peak control scenario produces flexible heat supply profile which covers peak load consumptions whilst can smooth the electricity production peaks, caused by introduction of renewable energies, and prevents high rates of energy loss consequently.
On the Design of a Sustainable Production Line: The MetaCAM Tool
Authors: Fysikopoulos Apostolos , Alexopoulos Theocharis , Pastras George , Stavropoulos Panos , Chryssolouris Georgios
Published: March 2016

Nowadays, manufacturing enterprises face enormous environmental challenges, due to complex and diverse economic trends, including shorter product life cycles, rapid advances in science and technology, increased diversity in customer demands and globalization of production activities. Consequently, the cost is highly affected by environmentally related factors. Energy efficiency is one of the main factors, which together with waste management, affect manufacturing decisions. The complexity and diversity of the factors that determine energy efficiency require intelligent systems for their optimization at each “manufacturing level”. Manufacturing decisions should be taken as fast as possible and with the highest possible accuracy. Artificial intelligence/machine learning tools have made significant progress during the last decade and are suitable for such applications. The main objective of the current study is that an architecture for the development of a networked, online, decision support tool, be provided towards achieving sustainable value chain management. The main idea behind the proposed design is that stakeholders be assisted in taking decisions towards improving the energy and eco-efficiency of the entire value chain or parts of it. This is suggested within the context of a multi-objective optimization procedure, taking into account other important decision making attributes, such as flexibility, quality and time for the final reduction in the overall cost. This architecture incorporates real time information modules that interact with online monitoring systems, using any available information within the value chain and the existing IT tools. A partial realization of the proposed idea is implemented in the form of a user friendly software tool (the MetaCAM tool). This based, decision support tool aiming to optimize a current production line or to propose alternatives for the manufacturing of a product. The tool performs optimization based on a set of predefined criteria, namely energy, waste, cost and time. For each of these criteria, the end-user selects the desired weight factor in order to drive the optimization procedure accordingly. The tool presents the characteristics of the setup of the proposed optimized line and maintains all used data and calculations in order to be reused when necessary. For the tool’s validation, three real case studies from different industrial sectors have been used. The first case study comes from the domestic appliances sector (refrigerator door panel), the second one from the automotive sector (a two seat bench for light commercial vehicles) and finally, the third case study derives from the aeronautics sector and deals with the production of the loading ramp hinge of a military aircraft.
An Integrated Approach to the Planning of Manual Assembly Lines
Authors: Pintzos George , Matsas Markos , Triantafyllou Christos , Papakostas Nikolaos , Chryssolouris George
Published: March 2016

Manual assembly planning methodologies have been in the center of industrial and academic research for many decades, since the manual assembly costs may often account for even half of the total manufacturing expenses. The existing and emerging manufacturing trends, such as mass customization and personalization, require fast responses when it comes to the conception and realization of the relevant manufacturing systems. Even though, work methodologies, such as concurrent engineering, have been proposed and applied, gaps still exist among product development, configuration and manufacturing. The Current Product Lifecycle (PLM) systems focus on the coordination of activities among engineers of different disciplines. However, they are unable to provide actual decision support functionality to decision makers. Moreover, solutions for the different phases of assembly planning have been proposed, without nevertheless taking into account the holistic nature of assembly planning that spans the different engineering phases.

The study presented in this paper is based on a methodology that integrates three distinct steps, regarding assembly planning; the generation of assembly related information, from the Computer Aided Design (CAD) files of an assembly, the calculation of the relevant process times from functions, generated through empirical measurements and the assembly line balancing of a line, based on the information gathered. The innovative aspect of this approach relies on the advancement of the relevant technologies as well as on their integration into a common working practice. The methodology enables the estimation of production related values in the later phases of product design or in the early phases of manufacturing planning. The generation of assembly precedence diagrams is made in an automatic way through the extraction of information on collision detection and the parts’ relations. This application is developed in the form of an add-on to a commercial CAD software suite. It utilizes features that are available in a wide range of such systems. The second step relies on the identification of specific features of parts, such as dimensions and mass. This information is then used as input in the functions already proposed in the academic literature for the estimation of the relevant process times for each part. Finally, the assembly line balancing is performed through the generation of the precedence diagram and the estimated process times, via a web-based service, which makes use of advanced optimization techniques.

In order for this methodology to be evaluated, a case study is presented by using the CAD file of an automotive sub-assembly. The case study demonstrates each step separately, beginning with the generation of the precedence diagram down to the balancing of the assembly line.
Pressure and Thermophysical Property of Gas Dependence of Effective Thermal Conductivity of a Porous Silica Insulator
Authors: Nutsugah Redeemer , Mensah Patrick , Akwaboa Stephen , Martin Michael
Published: March 2016

The thermal conductivity of a high-temperature calcium silicate block insulation product was measured in gaseous environments at pressures up to 100 bar at room temperature. The thermal conductivity of the porous material was tested in nitrogen, argon, and carbon dioxide gaseous environments. These tests were performed in a newly-constructed pressure chamber integrated with a thermal conductivity testing device. A standardized testing method was employed in the design of the apparatus. The test method used was based on the ASTM c177, the guarded-hot-plate method [1]. Tests performed in a carbon dioxide pressure medium have produced data with thermal conductivity as a nonlinear function of pressure. The results of tests conducted using nitrogen and argon show that the variations of thermal conductivity of the porous silica insulating material are linear functions of pressure and specific heat (Cv) of the fill gas. Tests performed in a nitrogen gaseous environment have relatively higher thermal conductivity values than thermal conductivity values at corresponding pressures in argon gaseous environment. This trend is attributable to the higher thermophysical property values of nitrogen than those of argon. This observation suggests that the thermophysical properties of the fill gas have significant effect on the effective thermal conductivity of the porous material. Thermal conductivity data collected in both nitrogen and argon pressure media have coefficients of determination (r2) of 0.9955 and 0.9956, respectively. An exponential function fitted to the carbon dioxide data produced a coefficient of determination of 0.9175. A precision study for the newly-constructed steady-state thermal conductivity measuring apparatus was performed in atmospheric air. With a standard deviation of 0.00076 W/m · K and a mean thermal conductivity value of 0.07294 W/m · K, a 95% confidence interval was assumed for a sample space size of 13 for the baseline tests in air. This produced a precision error of ±0.00046 W/m · K (±0.63%), a mean bias error of ±0.00955 W/m · K (±13.09%), and a mean steady-state error of ±1.67%. Hence, the total uncertainty in the mean thermal conductivity value of the baseline tests in atmospheric air could be reported as 0.07294W/m · K ± 13.22% with 95% confidence. The result of the precision study is indicative of the reliability of the apparatus. The single-sample precision uncertainty in thermal conductivity values at varying pressures in the various fill gases were estimated based on the standard deviation of the repeated tests in atmospheric air as 0.001166W/m · K.
Magnesium Incorporated Polycaprolactone-Based Composite Nanofibers
Authors: Rijal Nava P. , Adhikari Udhab , Bhattarai Narayan
Published: March 2016

Recent advances in developing composite nanofibers are of great interest for scientific community due to their wide range of potential applications in biomedical engineering such as drug delivery, wound healing, tissue engineering and implant coatings. Here, we present a fabrication of Mg incorporated polycaprolactone/low molecular weight chitosan (PCL/LMW-CS) composite nanofiber via an electrospinning technique. PCL, a synthetic polymer, has good mechanical properties, whereas, chitosan, a natural polymer, has good bio-functional properties and good cell adhesion properties. Furthermore, magnesium is the second most abundant intracellular cation in the body and is important to metabolism. These nanofibers were characterized by using Scanning Electron Microscopy (SEM), ImageJ, and Instron Universal Testing Machine.
Modeling Droplets Shearing and Coalescence Using a Population Balance Method in Produced Water Treatment Systems
Authors: Motin Abdul , Walsh John M. , Bénard André
Published: March 2016

Quantification of oil droplet shearing in produced water treatment facilities is a crucial aspect of operations for the oil and gas industry. In this paper, a detail mathematical modeling of droplet breakage and coalescence using a Population Balance Method (PBM) is addressed. The PBM models the dynamics of droplet size distribution due continuous interactions between individual droplets (such as coalescence and breakup). An understanding of the PBM in regards to the conservation of mass of dispersed droplets is also developed. A stand-alone PBM is used for calculating coalescence and breakage rates in a system having homogeneous mixture and constant turbulent energy dissipation. A coupled computational fluid dynamics-PBM approach is also implemented in a hydrocyclone to examine the local rates of droplet breakup and coalescence. Effects of the turbulent intensity and the interfacial tension of an oil-water mixture and the volume fraction of the dispersed phase on the time evolution of volume fraction distribution and Sauter mean diameter are examined. Results show that, for typical fluid properties associated with produced water, droplet-droplet coalescence is dominant over droplet breakage when the turbulent energy dissipation (ε) is small; the opposite is found for regions associated with high energy dissipation. In a hydrocyclone, the rate of droplets shearing is significant near the entry and at the inlet chamber; this rate decreases downstream. The research outcomes based on the stand-alone PBM and coupled CFD-PBM approaches allow us to identify and redesign the critical part of the water treating facilities to minimize shearing of dispersed droplets.
Film Cooling Performance of Tripod Holes on the Endwall Upstream of a First Stage Nozzle Guide Vane
Authors: Ravi Bharath Viswanath , Deshpande Samruddhi , Ramesh Sridharan , Dhilipkumar Prethive Dhilip , Ekkad Srinath
Published: March 2016

In view of the growing energy demand, there is an increasing need to augment the thermal efficiency of gas turbine engines. The thermal efficiency and power output of gas turbine engines increase with increasing overall pressure ratio which in turn leads to an increase in turbine inlet temperature. The maximum permissible turbine inlet temperature is limited by the material strength of the components of the gas turbine engines. In this regard, it is important to ensure that the endwalls of the first stage nozzle guide vane, which is one of the critical regions, are adequately cooled. The cooling of the endwall is of particular interest because the leading edge region along the endwall of the stator vane experiences high heat transfer rates resulting from formation of horseshoe vortices. In this paper, the performance of upstream purge slot has been compared against discrete film cooling holes. Three different cooling configurations — slot, cylindrical holes and tripod holes have been investigated by comparing the adiabatic film cooling effectiveness. Furthermore, the effect of coolant to mainstream mass flow ratio on the effectiveness of the different cooling schemes has also been studied. The steady-state experiments were conducted in a low speed, linear cascade wind tunnel. Spatially resolved temperature data was captured using infrared thermography technique to compute adiabatic film cooling effectiveness. Amongst the configurations studied, slot ejection offered the best cooling performance at all mass flow ratios. The performance of tripod ejection was comparable to slot ejection at mass flow ratios between 0.5 and 1.5, with the difference in laterally averaged effectiveness being ∼5%. However, at the highest mass flow ratio (MFR=2.5), the difference increased to ∼20%. Low effectiveness values were observed downstream of cylindrical ejection which could be attributed to jet lift-off.
A Numerical Study of the Unsteady Flow Field and Tonal Hydrodynamic Sound of a Centrifugal Pump
Authors: Cai Jian-Cheng , Pan Jie , Guzzomi Andrew
Published: March 2016

In this paper, the 3-D unsteady turbulent flow inside a centrifugal pump is investigated by computational fluid dynamics (CFD) in ANSYS CFX, using Detached Eddy Simulation (DES) as the turbulence approach. The pump has a single end-suction and a single volute discharge. The impeller is semi-open (unshrouded with baseplate) and has five backswept blades and pump-out back blades. The CFD model of the pump consists of the inlet, the impeller, and the volute. A sliding mesh technique has been applied to the interfaces in order to allow unsteady interactions between the rotating impeller and the stationary parts. These unsteady interactions generate pressure fluctuations over the volute casing and blade surfaces that are hydroacoustic dipoles according to Lighthill’s acoustic analogy theory. The pressure fluctuation spectra at the volute tongue show that pressure fluctuations are generated mainly by the discrete components related to the impeller rotation at low frequencies, especially the blade-passing frequency (BPF) component. This component is approximately 1% of the reference dynamic pressure 0.5ρν22 where ν2 is the circumferential velocity at the impeller outlet. The discrete components with frequency larger than 4 times BPF are no longer obvious in the spectra. Compared to the experimental results, the CFD simulation predicts much lower amplitudes for the broad band pressure fluctuations. This is reasonable, because DES combines a classical Reynolds averaged Navier Stokes (RANS) simulation with elements of Large Eddy Simulation (LES), and both RANS and LES use average methods which filter out the high frequency fluctuations. Nevertheless, CFD is capable of accurately predict the BPF component.

The pressure fluctuations on the casing and blade surfaces are extracted and modelled as the stationary and rotary dipoles, respectively, according to the Ffowcs Williams and Hawkings (FW-H) equation of the acoustic analogy theory. After Fast Fourier Transform, the spectra of the pressure fluctuations are obtained, and are used to predict the tonal hydrodynamic sound radiation at BPF and its low order harmonics. The sound radiation of casing surface dipoles is calculated by extracting the tonal components, and performing a surface integration with the fundamental solution to Helmholtz equation as the kernel. A frequency domain formulation of the FW-H equation with the moving surface dipole is employed to predict the tonal blade noise. The results from these acoustical simulations show that the sound power generated by the casing surface dipole is three orders of magnitude higher than that of the blade surface dipole, and the main hydroacoustic sources are located at the volute tongue.
Application of Advanced Model of Zr-Based Cladding Oxidation in Steam-Oxygen-Nitrogen Gas Mixtures to Separate Effects Tests and Integral Experiments
Authors: Vasiliev Alexander
Published: March 2016

During postulated design-basis or beyond-design-basis accident at nuclear power plant with PWR or BWR, the high temperature oxidation of Zr-based fuel claddings in H2O-O2-N2 gas atmosphere could take place.

Recent experimental observations showed that the oxidation of those claddings in the air (or, more generally, in oxygen-nitrogen and steam-nitrogen mixtures) behaves in much more aggressive way (linear or enhanced parabolic kinetics) compared to oxidation in pure steam (standard parabolic kinetics).

This is why an advanced model of Zr-based cladding oxidation was developed. For calculations of cladding oxidation in oxygen-nitrogen and steam-nitrogen mixtures, the effective oxygen diffusion coefficient in ZrO2+ZrN layer formed in cladding is used. The diffusion coefficient enhancement factor depends on ZrN content in ZrO2+ZrN layer.

A numerical scheme was realized to determine ZrO2+ZrN/α-Zr(O) and α-Zr(O)/β-Zr layers boundaries relocation and layers transformations in claddings.

The model was implemented to the SOCRAT best estimate computer modeling code. The SOCRAT code with advanced model of oxidation was successfully used for calculations of separate effects tests and air ingress integral experiments QUENCH-10, QUENCH-16 and PARAMETER-SF4.
Hybrid Solar Desalination to Produce Fresh Water, Electrical Power With Energy Storage
Authors: Kowalski Gregory J. , Zenouzi Mansour , Modaresifar Masoud
Published: March 2016

The numerical analysis of solar desalination processes in a unique tray was extended to include an RED device to produce electricity either during operation or using the stored concentrated salt mixture. The motivation for this using device was based on an exergy analysis and the second law efficiency. Previous analysis illustrated how the exergy analysis could be used to identify the irreversibilities in the system and indicated modifications to increase the performance of the tray design desalinator for the sensible energy content of the discharge. The exergy related to the higher concentration level of the discharge is now investigated for a RED device. These analyses are extended to investigate the potential of using the higher salinity of the out flowing brine to produce electrical energy by using the reversed electrodialysis (RED) process. The RED process which converts 70–80% of the change in Gibbs energy to electricity uses the concentrated brine to produce electrical power while the freshwater is being produced. The analysis demonstrates it is possible to produce a maximum electrical output of 0.32 kJ/kg for the expected concentration differences. Using the predicted mass flow over the day of 6 kg/(day m2) it is expected that one could produce approximately 1.9 kJ/(day m2) of electricity in addition to the freshwater production.
Kriging-Based Reliability Analysis and Variance-Based Sensitivity Analysis for an Idler Shaft
Authors: Cui Weimin , Guo Wei , Sun Zhongchao , Yu Tianxiang
Published: March 2016

In order to analyze the reason of failure and improve the reliability of the idler shaft, this paper studies the reliability and sensitivity for the idler shaft based on Kriging model and Variance Methods respectively. The finite element analysis (FEA) of idler shaft is studied in ABAQUS firstly. Then, combining the performance function and various random variables, the Kriging model of idler shaft is established and verified. Based on Kriging model which has been established, the relationship between random variables and the response value is studied, and the function reliability is calculated which explains why the failure of the idler shaft occurred frequently in service. Finally, the variance-based sensitivity method is used for sensitivity analysis of influence factors, the result shows that the reliability of idler shaft is sensitive to the inner diameter of body A and inner diameter of body B, which could contribute for the analysis and further improvement of idler shaft.
Development and Evaluation of Fuel Cell Buses
Authors: El-Sayed Mohamed E. M.
Published: March 2016

Vehicles powered by hydrogen fuel cells produce zero emissions of greenhouse-gases. For this reason, hydrogen fuel cell bus technology has been regarded as a viable alternative for the future of green mass transportation. As a result, several hydrogen fuel cell buses are being commissioned for trials and evaluations on numerous routes worldwide.

Despite the relevance of the technology and sincere trials efforts of several fuel cell buses, the progress in the development and utilization of hydrogen fuel cell bus technology has been sluggish at best. In addition, the road to full commercialization of fuel cell buses for public transportation is undefined, unclear, and risky for developers, planners, as well as mass transient end users.

Most of the fuel cell buses being tried on the road today are built or converted with the rate of one bus at time. In most cases, a fuel cell system integrator combines a fuel cell from one of the few available suppliers with the bus body from a bus manufacturer for trial or technology demonstration. Accordingly, most of the fuel cell buses being evaluated today could be considered as prototypes or proof of concept.

The key characteristics and attributes upon which these buses are being evaluated such as affordability, durability, and reliability have not been matured and validated through a rigorously structured and controlled mass production process. Consequently the results of these evaluations could be misleading.

For proper and more objective evaluation of fuel cell bus technologies better understanding of controlled and validated mass production processes is necessary. Unfortunately, there are no documented efforts that address fuel cell buses production concerns. In this paper, development and evaluation issues related to hydrogen fuel cell buses and technologies will be addressed. In addition, some of the key characteristics of fuel cell buses will be studied.
Performance Analysis of Multi-Layer Thermoelectric Generators to be Used in a Thermoelectric Generator-Stirling Engine Hybrid System
Authors: Rahman Mohammed Waliur , Mahkamov Khamid
Published: March 2016

This paper demonstrates the performance analysis of various arrangements of thermoelectric generators to be used for the combination of a Low Temperature Difference Stirling Engine-Thermoelectric Generator hybrid system. To estimate whether the deployed Stirling Engines will perform on satisfactory level it is necessary to determine if a sufficient thermal flux can be provided to the heating part of the Low Temperature Difference Stirling Engine (LTD SE) from the “cold” side of the thermoelectric generator or their combination. This paper reports study results on the performance of a single layer and a cascaded two-layer thermoelectric generator made up of bulk material. These two generators were connected in series and in parallel to produce the combined thermoelectric module operating as a three-layer generator. Also computational data on the temperature distribution across the layers has been obtained using Finite Element Analysis as a part of ANSYS software. Results obtained demonstrate that both the single and two-layer generators provide sufficient heat flux to drive LTD SEs but the total power output from the two-layer generator-Stirling Engine system is considerable higher when the engine is coupled to a single and three-layered thermoelectric generator.
Elucidation of the High Cycle Fatigue Damage Mechanism of Modified 9Cr-1Mo Steel at Elevated Temperature
Authors: Murakoshi Takuya , Ochi Motoyuki , Suzuki Ken , Miura Hideo
Published: March 2016

Modified 9Cr-1Mo steel is one of the heat-resistant steels developed for steam generator in a FBR (Fast Breeder Reactor). When it is used in a FBR, the lifetime of the steel under HCF (High Cycle Fatigue) and V-HCF (Very-High Cycle Fatigue) caused by flow-induced vibration has to be considered for assuring its long-term reliability up to 1011 cycles. Since previous studies showed that the fatigue limit did not appear up to 108 cycles, it is necessary to investigate the fatigue strength of this alloy in cycles higher than 108 cycles. In this study, in order to clarify high cycle fatigue strength and fracture mechanism of the modified 9Cr-1Mo steel, the change of the lath martensitic strengthening structure was observed in detail on the surface of specimens fractured by rotary bending fatigue tests by using EBSD (Electron Back-Scatter Diffraction) method. The Kernel Average Misorientation (KAM) value obtained from the EBSD analysis was used for the quantitative evaluation of the change of the lath martensitic texture. It was found that the average KAM values clearly decreased on the surface areas of the fractured specimens after the application of 107-108 cycles of fatigue loading at temperatures higher than 550°C. This result indicates that degradation of the lath martensitic texture occurred around the surface of specimens tested at the temperature higher than 550°C. In order to quantitatively evaluate the decrease of its strength, a hardness test was performed at room temperature by using a nanoindentation method. It was confirmed that the surface hardness of specimens decreased drastically in the specimens fractured at temperatures higher than 550°C. From these results, it was concluded that the effective 0.2%-proof stress decreased during the fatigue tests by the degradation of the lath martensitic texture caused by the fatigue loading at elevated temperatures. Further analyses are indispensable for explicating the damage mechanism more in detail.