bluuebunny/crossref_metadata_2025 huggingface dataset:
Pressure-Transient Behavior of Multisegment Horizontal Wells With Nonuniform Production: Theory and Case Study
Authors: He Youwei , Cheng Shiqing , Qin Jiazheng , Wang Yang , Chen Zhiming , Yu Haiyang
Published: July 2018

Field data indicate production profile along horizontal wells is nonuniform. This paper develops an analytical model of multisegment horizontal wells (MSHWs) to estimate rate distribution along horizontal wellbore, interpret the effective producing length (EPL), and identify underperforming horizontal sections using bottom-hole pressure (BHP) data. Pressure solutions enable to model an MSHW with nonuniform distribution of length, spacing, rate, and skin factor. The solution is verified with the analytical solution in commercial software. Type curves are generated to analyze the pressure-transient behavior. The second radial-flow (SRF) occurs for the MSHWs, and the duration of SRF depends on interference between segments. The pressure-derivative curve during SRF equals to 0.5/Np (Np denotes the number of mainly producing segments (PS)) under weak interference between segments. The calculated average permeability may be Np times lower than accurate value when the SRF is misinterpreted as pseudoradial-flow regime. The point (0, 0, h/2) are selected as the reference point, and symmetrical cases will generate different results, enabling us to distinguish them. Finally, field application indicates the potential practical application to identify the underperforming horizontal segments.
Dynamic Analysis of Planar Mechanical Systems With Clearance Joint Based on LuGre Friction Model
Authors: Tan Xiao , Chen Guoping , Sun Dongyang , Chen Yan
Published: July 2018

A computational methodology to model and analyze planar rigid mechanical system with stick–slip friction in revolute clearance joint is presented. In this work, the LuGre friction model, which captures the Stribeck effect and spring-like characteristics for stiction, is employed to estimate the stick–slip friction in revolute clearance joint. A hybrid contact force model, combining Lankarani–Nikravesh model, and improved elastic foundation model, is used to establish contact model. The generalized-α method, which can dissipate the spurious high-frequency responses caused by the strongly nonlinear contact force and friction in numerical simulation, is adopted to solve the equations of motion and make the result closer to the physics of the problem. A slider-crank mechanism with revolute clearance joint based on LuGre friction model and modified coulomb friction model are simulated, respectively, and utilized to discuss the influences of the Stribeck effect and stiction on dynamic behavior of the mechanism. Different test scenarios are considered to investigate the effects of the clearance size and friction coefficient on the dynamic response of the mechanism. The results show that the mechanism based on LuGre friction model has better energy dissipation characteristics, while there are stiction phenomena of the contacting surfaces in many cases. When the relative velocity is zero or close to zero, the contact force of mechanism based on the LuGre friction model is significantly lower than that based on the modified coulomb friction model. Clearance size and friction coefficient obviously affect dynamic behavior of the mechanism.
Gravity-Insensitive Flexure Pivot Oscillators
Authors: Kahrobaiyan M. H. , Thalmann E. , Rubbert L. , Vardi I. , Henein S.
Published: July 2018

Classical mechanical watch plain bearing pivots have frictional losses limiting the quality factor of the hairspring-balance wheel oscillator. Replacement by flexure pivots leads to a drastic reduction in friction and an order of magnitude increase in quality factor. However, flexure pivots have drawbacks including gravity sensitivity, nonlinearity, and limited stroke. This paper analyzes these issues in the case of the cross-spring flexure pivot (CSFP) and presents an improved version addressing them. We first show that the cross-spring pivot cannot be simultaneously linear, insensitive to gravity, and have a long stroke: the 10 ppm accuracy required for mechanical watches holds independently of orientation with respect to gravity only when the leaf springs cross at 12.7% of their length. But in this case, the pivot is nonlinear and the stroke is only 30% of the symmetrical (50% crossing) cross-spring pivot's stroke. The symmetrical pivot is also unsatisfactory as its gravity sensitivity is of order 104 ppm. This paper introduces the codifferential concept which we show is gravity-insensitive. It is used to construct a gravity-insensitive flexure pivot (GIFP) consisting of a main rigid body, two codifferentials, and a torsional beam. We show that this novel pivot achieves linearity or the maximum stroke of symmetrical pivots while retaining gravity insensitivity.
Drying Kinetics, Quality Assessment, and Economic Analysis of Bitter Gourd Flakes Drying Inside Forced Convection Greenhouse Dryer
Authors: Singh Chauhan Prashant , Kumar Anil , Nuntadusit Chayut , Mishra Shyam Sunder
Published: July 2018

A greenhouse dryer under forced convection mode is designed and fabricated with the integration of solar collector and variable speed exhaust fan. The developed system is used for bitter gourd flakes drying under three different air mass flow rates (0.0275, 0.0551, and 0826 kg/s). Moisture content of bitter gourd flakes was decreased effectively from 96.8% to 12.2% in 17 h with optimum air mass flow rate 0.0551 kg/s, whereas open sun drying has taken 26 h to reach 20.7% moisture content. The average greenhouse dryer efficiency was found to be 19.7% at 0.0551 kg/s air mass flow rate. Shrinkage (in terms of percentage) of dried bitter gourd flakes was found to be higher as 74% at 0.0275 kg/s air mass flow rate because of higher greenhouse room air temperature. Hardness of dried bitter gourd flakes was found to be highest as 365 g at 0.0275 kg/s air mass flow rate due to less air exchange rate and high inside room temperature. On the basis of statistical analysis, Prakash and Kumar model and Logarithmic model were selected as best drying models for greenhouse and open sun drying, respectively. The dehydration of higher moisture content crops inside developed greenhouse dryer was found to be more consistent. The designed greenhouse system is recommended for small farmers.
Fourier Spectral Phase Field Simulations of Elastically Anisotropic Heterogeneous Polycrystals
Authors: Allen J. B.
Published: July 2018

In this study, we developed a multi-order, phase field model to compute the stress distributions in anisotropically elastic, inhomogeneous polycrystals and study stress-driven grain boundary migration. In particular, we included elastic contributions to the total free energy density and solved the multicomponent, nonconserved Allen–Cahn equations via the semi-implicit Fourier spectral method. Our analysis included specific cases related to bicrystalline planar and curved systems as well as polycrystalline systems with grain orientation and applied strain conditions. The evolution of the grain boundary confirmed the strong dependencies between grain orientation and applied strain conditions and the localized stresses were found to be maximum within grain boundary triple junctions.
A Sequential Sampling Algorithm for Multistage Static Coverage Problems
Authors: Zhang Binbin , Huang Jida , Rai Rahul , Manjunatha Hemanth
Published: July 2018

In many system-engineering problems, such as surveillance, environmental monitoring, and cooperative task performance, it is critical to allocate limited resources within a restricted area optimally. Static coverage problem (SCP) is an important class of the resource allocation problem. SCP focuses on covering an area of interest so that the activities in that area can be detected with high probabilities. In many practical settings, primarily due to financial constraints, a system designer has to allocate resources in multiple stages. In each stage, the system designer can assign a fixed number of resources, i.e., agents. In the multistage formulation, agent locations for the next stage are dependent on previous-stage agent locations. Such multistage static coverage problems are nontrivial to solve. In this paper, we propose an efficient sequential sampling algorithm to solve the multistage static coverage problem (MSCP) in the presence of resource intensity allocation maps (RIAMs) distribution functions that abstract the event that we want to detect/monitor in a given area. The agent's location in the successive stage is determined by formulating it as an optimization problem. Three different objective functions have been developed and proposed in this paper: (1) L2 difference, (2) sequential minimum energy design (SMED), and (3) the weighted L2 and SMED. Pattern search (PS), an efficient heuristic algorithm has been used as optimization algorithm to arrive at the solutions for the formulated optimization problems. The developed approach has been tested on two- and higher dimensional functions. The results analyzing real-life applications of windmill placement inside a wind farm in multiple stages are also presented.
The Rayleigh Number Effect on the Periodic Heating of an Enclosure Filled With a Fluid and Discrete Solid Blocks
Authors: Moussa Mirehei S. , Lage José L.
Published: July 2018

The steady-periodic natural convection phenomenon inside a heated enclosure filled with disconnected, discrete solid blocks, and under horizontal, time-periodic heating is investigated numerically. This configuration is akin to several practical engineering applications, such as oven baking in food processing, heat treating of metal parts in materials processing, and storage and transportation of discrete solid goods in containerization. Because of the relative large size, and limited number of solid bodies placed inside the enclosure, the solid and fluid constituents are viewed separately and the process modeled using continuum balance equations for each with suitable compatibility conditions imposed at their interfaces. The periodic heating is driven by a sinusoidal in time hot-wall temperature, while maintaining the cold wall temperature constant, with top and bottom surfaces adiabatic. Results are presented in terms of hot and cold wall-averaged Nusselt numbers, time-varying energy capacity of the enclosure, and periodic isotherms and streamlines, for Ra varying from 103 to 107, Pr equal to 1, and 36 uniformly distributed, conducting and disconnected solid square blocks. The results explain why and how the effect of varying Ra on the convection process is significantly affected by the presence of the solid blocks. An analytical equation, valid for time-periodic heating, is proposed for anticipating the block interference effect with great accuracy, substantiating the distinct features of Nusselt versus Rayleigh observed when the blocks are present inside the enclosure.
Bonded Flexible Pipe Model Using Macroelements
Authors: Provasi Rodrigo , Toni Fernando Geremais , Martins Clóvis de Arruda
Published: July 2018

Flexible pipes are structures composed by many layers that vary in composition and shapes. The structural behavior of each layer is defined by the role it must play. The construction of flexible pipes is such that the layers are unbounded, with relative movement between them. Even though this characteristic is what enables its high bending compliant behavior, if the displacements involved are small, a bonded analysis is interesting to grasp the general characteristics of the problem. The bonded hypothesis means that there is no movement relative between layers, which is fine for a small displacement analysis. It also creates a lower bound for the movement, since when considering increasingly friction coefficient values, it tends to the bonded situation. The main advantage of such hypothesis is that the system becomes linear, leading to fast solving problems (when compared to full frictional analysis) and giving insights to the pipe behavior. The authors have previously developed a finite element based one called macroelements. This model enables a fast-solving problem with less memory consumption when compared to multipurpose software. The reason behind it is the inclusion of physical characteristics of the problem, enabling the reduction in both number of elements and memory used and, since there are less elements and degrees-of-freedom, faster solved problems. In this paper, the advantages of such model are shown by using examples that are representative of a simplified, although realistic, flexible pipe. Comparisons between the macroelement model and commercial software are made to show its capabilities.
An Experimental Study of Influence of Lubrication Methods on Efficiency and Contact Fatigue Life of Spur Gears
Authors: Moss J. , Kahraman A. , Wink C.
Published: July 2018

An experimental investigation of spur gear behavior was conducted with the aim of quantifying the impact of lubrication methods and conditions on the power losses and contact fatigue lives. Variations of dip and jet-lubrication are defined, and these behaviors were observed as a function of the lubrication conditions. Both types of measurements were performed using the same type of back-to-back test machines and the same spur gear test articles such that their evaluations can be correlated. Power loss experiments were performed under both loaded and unloaded conditions to determine both load-independent (spin) and load-dependent (mechanical) losses. Sets of long-cycle contact fatigue experiments were performed under the same lubrication conditions to determine macropitting lives in a statistically meaningful manner. Results indicate that the spin power losses are impacted by the lubrication method significantly while the mechanical losses are not influenced. Contact fatigue lives from jet-lubricated tests are comparable to those under dip-lubricated conditions ones as long as jet velocities are sufficient.
A Novel Method for the Design of Proximity Sensor Configuration for Rotor Blade Tip Timing
Authors: Diamond David H. , Stephan Heyns P.
Published: July 2018

Blade tip timing (BTT) is a noncontact method for measuring turbomachinery blade vibration. Proximity sensors are mounted circumferentially around the turbomachine casing and used to measure the tip displacements of blades during operation. Tip deflection data processing is nontrivial due to complications such as aliasing and high levels of noise. Specialized BTT algorithms have been developed to extract the utmost amount of information from the signals. The effectiveness of these algorithms is, however, influenced by the circumferential spacing between the proximity sensors. If the spacing is suboptimal, an algorithm can fail to measure dangerous blade vibration. This paper presents a novel optimization approach that determines the optimal spacing between proximity sensors.
A Linearization Method of Piecewise Linear Systems Based on Frequency Domain Characteristics With Application to Semi-Active Control of Vibration
Authors: Sireteanu Tudor , Solomon Ovidiu , Mitu Ana-Maria , Giuclea Marius
Published: July 2018

In this paper, a new approach is presented for linearization of piecewise linear systems with variable dry friction, proportional with absolute value of relative displacement. The transmissibility factors of considered systems, defined in terms of root-mean-square (RMS) values, are obtained by numerical time integration of motion equations for a set of harmonic inputs with constant amplitude and different frequencies. A first-order linear differential system is attached to the considered piecewise linear system such as the first component of solution vector of attached system to have the same transmissibility factor as the chosen output of nonlinear system. This method is applied for the semi-active control of vibration with balance logic strategy. Applications to base isolation of rotating machines and vehicle suspensions illustrate the effectiveness of the proposed linearization method.
Prognostic Health Monitoring Method for Fatigue Failure of Solder Joints on Printed Circuit Boards Based on a Canary Circuit
Authors: Hirohata Kenji , Hisakuni Yousuke , Omori Takahiro
Published: July 2018

Devices mounted on printed circuit boards (PCBs) are subject to temperature variations resulting from power switching and ambient temperature changes, and may be subject to random dynamic load histories from sources such as vibration. Since solder material is mechanically the most ductile part, fatigue failure may occur in solder joints. Health monitoring for fatigue life under field conditions is a key issue for improving availability and serviceability for maintenance. We have developed a failure precursor detection technology and a fatigue life estimation method for ball grid array (BGA) solder joints, based on a canary circuit. This method estimates fatigue failure life of an actual circuit by detecting failure connections in a canary circuit (a dummy circuit of daisy-chained solder joints). The canary circuit is designed to fail before the actual circuit under the same failure mode by using accelerated reliability testing and inelastic stress simulation. A feasibility study of the failure probability estimation method is conducted by applying the method to a PCB on which a BGA component is mounted. It is confirmed that the fatigue life under a thermal cyclic load can be estimated from a canary circuit, that estimation of fatigue life under a random dynamic load is feasible, and that the estimation results are consistent with results from actual random vibration tests. The proposed method is found to be useful for prognostic health monitoring of solder joint fatigue failure.
Onset of Nucleate Boiling Detection in a Boiler Tube by Wavelet Transformation of Vibration Signals
Authors: Yadavar Nikravesh Seyed Majid , Taheri Hossein
Published: July 2018

Condition monitoring and fault diagnosis techniques are increasingly used for assurance of machine condition and safe operation of the systems and structures. For this purpose, preliminary data about the machine performance are obtained from the system and signal processing techniques are used to extract features and final information regarding the machine performance. One type of the primary data that can be obtained from a system is the vibration responses of the system. Vibration responses of dynamical systems are usually nonstationary signals. In boilers and heat exchangers, generation and collapse of the vapor bubbles due to overheating can generate vibration in the tubes. These vibrations could be detected and identified in terms of location and time of occurrence for future maintenance and modification of the system and process. In this paper, a nonstationary vibration analysis method based on Morlet wavelet transform is presented for detection of onset of nucleate boiling (ONB) in a boiler tube. Comparison of the results by wavelet transform and visual observation of the ONB shows the capability and accuracy (less than 3% difference) of the proposed technique for detection of ONB in a boiler tube.
On the Combination of Large Eddy Simulation and Phenomenological Soot Modeling to Calculate the Smoke Index From Aero-Engines Over a Large Range of Operating Conditions
Authors: Lamouroux J. , Richard S. , Male Q. , Staffelbach G. , Dauptain A. , Misdariis A.
Published: July 2018

Nowadays, models predicting soot emissions are neither able to describe correctly fine effects of technological changes on sooting trends nor sufficiently validated at relevant operating conditions to match design office quantification needs. Yet, phenomenological descriptions of soot formation, containing key ingredients for soot modeling exist in the literature, such as the well-known Leung et al. model (Combust Flame 1991). However, when blindly applied to aeronautical combustors for different operating conditions, this model fails to hierarchize operating points compared to experimental measurements. The objective of this work is to propose an extension of the Leung model over a wide range of condition relevant of gas turbines operation. Today, the identification process can hardly be based on laboratory flames since few detailed experimental data are available for heavy-fuels at high pressure. Thus, it is decided to directly target smoke number values measured at the engine exhaust for a variety of combustors and operating conditions from idling to take-off. A large eddy simulation approach is retained for its intrinsic ability to reproduce finely unsteady behavior, mixing, and intermittency. In this framework, The Leung model for soot is coupled to the thickened flame model (TFLES) for combustion. It is shown that pressure-sensitive laws for the modeling constant of the soot surface chemistry are sufficient to reproduce engine emissions. Grid convergence is carried out to verify the robustness of the proposed approach. Several cases are then computed blindly to assess the prediction capabilities of the extended model.
Auto Takeoff and Precision Terminal-Phase Landing Using an Experimental Optical Flow Model for Global Positioning System/Inertial Navigation System Enhancement
Authors: Al-Sharman Mohammad K. , Al-Jarrah Mohammad Amin , Abdel-Hafez Mamoun
Published: July 2018

The high estimated position error in current commercial-off-the-shelf (GPS/INS) impedes achieving precise autonomous takeoff and landing (TOL) flight operations. To overcome this problem, in this paper, we propose an integrated global positioning system (GPS)/inertial navigation system (INS)/optical flow (OF) solution in which the OF provides an accurate augmentation to the GPS/INS. To ensure accurate and robust OF augmentation, we have used a robust modeling method to estimate OF based on a set of real-time experiments conducted under various simulated helicopter-landing scenarios. Knowing that the accuracy of the OF measurements is dependent on the accuracy of the height measurements, we have developed a real-time testing environment to model and validate the obtained dynamic OF model at various heights. The performance of the obtained OF model matches the real OF sensor with 87.70% fitting accuracy. An accuracy of 0.006 m/s mean error between the real OF sensor velocity and the velocity of the OF model is also achieved. The velocity measurements of the obtained OF model and the position of the GPS/INS are used in performing a dynamic model-based sensor fusion algorithm. In the proposed solution, the OF sensor is engaged when the vehicle approaches a landing spot that is equipped with a predefined landing pattern. The proposed solution has succeeded in performing a helicopter auto TOL with a maximum position error of 27 cm.
Robust Multi-Objective Optimization of Solid Oxide Fuel Cell–Gas Turbine Hybrid Cycle and Uncertainty Analysis
Authors: Sharma Shivom , Maréchal François
Published: July 2018

Chemical process optimization problems often have multiple and conflicting objectives, such as capital cost, operating cost, production cost, profit, energy consumptions, and environmental impacts. In such cases, multi-objective optimization (MOO) is suitable in finding many Pareto optimal solutions, to understand the quantitative tradeoffs among the objectives, and also to obtain the optimal values of decision variables. Gaseous fuel can be converted into heat, power, and electricity, using combustion engine, gas turbine (GT), or solid oxide fuel cell (SOFC). Of these, SOFC with GT has shown higher thermodynamic performance. This hybrid conversion system leads to a better utilization of natural resource, reduced environmental impacts, and more profit. This study optimizes performance of SOFC–GT system for maximization of annual profit and minimization of annualized capital cost, simultaneously. For optimal SOFC–GT designs, the composite curves for maximum amount of possible heat recovery indicate good performance of the hybrid system. Further, first law energy and exergy efficiencies of optimal SOFC–GT designs are significantly better compared to traditional conversion systems. In order to obtain flexible design in the presence of uncertain parameters, robust MOO of SOFC–GT system was also performed. Finally, Pareto solutions obtained via normal and robust MOO approaches are considered for parametric uncertainty analysis with respect to market and operating conditions, and solution obtained via robust MOO found to be less sensitive.
Effects of Chemical Composition on the Electromechanical Properties of Microfluidically Synthesized Hydrogel Beads
Authors: Kudtarkar Kaushik , Johnson Michael , Iglesias Patricia , Smith Thomas W. , Schertzer Michael J.
Published: July 2018

This investigation demonstrates microfluidic synthesis of monodisperse hydrogel beads with controllable electromechanical properties. Hydrogel beads were synthesized using aqueous monomer solutions containing difunctional macromer, ionic liquid monomer, and photoinitiator. Electromechanical properties of these beads were measured at compression ratios up to 20% to examine their potential use in vibrational energy harvesters. Bead stiffness decreased dramatically as water content increased from 19% to 60%. As water content and compression ratio increased, electrical permittivity of beads increased, while resistivity decreased. As ionic liquid monomer concentration increased from 0% to 4%, relative permittivity increased by 30–45% and resistivity decreased by 70–80%.
Combined Effect of Sampling and Coulomb Friction on Haptic Systems Dynamics
Authors: Budai Csaba , Kovács László L. , Kövecses József
Published: July 2018

Dissipation mechanisms and dissipative forces play a pivotal role in the operations and performance of human-machine interfaces and particularly in haptic systems. Dissipation is a very difficult phenomenon to model. Coulomb friction in general can be the most influential element in systems involving multiple direct contact connections such as joints with transmissions or mechanically guided components. Coulomb friction includes nonsmooth discontinuity and can induce complex dynamic behaviors. The effect of Coulomb friction is often neglected in haptics. The part of the literature which deals with friction mainly focuses on friction compensation and/or simulation of friction for haptic rendering. In this paper, the nature of the dynamic behavior caused by Coulomb friction in haptic sampled-data systems is illustrated by experiment, analysis, and simulation. It is also demonstrated that a simple model can represent this behavior and show the effects of the haptic system parameters on this dynamics.
Development, Distribution, and Maintenance of Application Security Controls for Nuclear
Authors: Waedt Karl , Ding Yongjian , Ciriello Antonio , Lou Xinxin
Published: July 2018

The generic concept of security controls, as initially deployed in the information security domain, is gradually used in other business domains, including industrial security for critical infrastructure and cybersecurity of nuclear safety instrumentation & control (I&C). A security control, or less formally, a security countermeasure can be any organizational, technical, or administrative measure that helps in reducing the risk imposed by a cybersecurity threat. The new IAEA NST036 lists more than 200 such countermeasures. NIST SP800-53 Revision 4 contains about 450 pages of security countermeasure descriptions, which are graded according to three levels of stringency. In order to facilitate and formalize the process of developing, precisely describing, distributing, and maintaining more complex security controls, the application security controls (ASC) concept is introduced by the new ISO/IEC 27034 multipart standard. An ASC is an extensible semiformal representation of a security control (extensible markup language or javascript object notation-based), which contains a set of mandatory and optional parts as well as possible links to other ASCs. A set of ASCs may be developed by one company and shipped together with a product of another company. ISO/IEC 27034-6 assumes that ASCs are developed by an organization or team specialized in security and that the ASCs are forwarded to customers for direct use or for integration into their own products or services. The distribution of ASCs is supported and formalized by the organization normative frameworks (ONFs) and application normative frameworks (ANFs) deployed in the respective organizational units. The maintenance and continuous improvement of ASCs is facilitated by the ONF process and ANF process. This paper will explore the applicability of these industry standards based ASC lifecycle concepts for the nuclear domain in line with IEC 62645, IEC 62859, and the upcoming IEC 63096. It will include results from an ongoing bachelor thesis and master thesis, mentored by two of the authors, as well as nuclear-specific deployment scenarios currently being evaluated by a team of cybersecurity Ph.D. candidates.
Design of a Single Degree-of-Freedom, Adaptable Electromechanical Gait Trainer for People With Neurological Injury
Authors: Yul Shin Sung , Deshpande Ashish D. , Sulzer James
Published: July 2018

The cost of therapy is one of the most significant barriers to recovery after neurological injury. Robotic gait trainers move the legs through repetitive, natural motions imitating gait. Recent meta-analyses conclude that such training improves walking function in neurologically impaired individuals. While robotic gait trainers promise to reduce the physical burden on therapists and allow greater patient throughput, they are prohibitively costly. Our novel approach is to design a new single degree-of-freedom (DoF) robotic trainer that maintains the key advantages of the expensive trainers but with a simplified design to reduce cost. Our primary design challenge is translating the motion of a single actuator to an array of natural gait trajectories. We address this with an eight-link Jansen mechanism that matches a generalized gait trajectory. We then optimize the mechanism to match different trajectories through link length adjustment based on nine different gait patterns obtained from gait database of 113 healthy individuals. To physically validate the range in gait patterns produced by the simulation, we tested kinematic accuracy on a motorized wooden proof-of-concept of the gait trainer. The simulation and experimental results suggested that an adjustment of two links can reasonably fit a wide range of gait patterns under typical within-subject variance. We conclude that this design could provide the basis for a low-cost, patient-based electromechanical gait trainer for neurorecovery.
A Level Set Method With a Bounded Diffusion for Structural Topology Optimization
Authors: Zhu Benliang , Wang Rixin , Li Hai , Zhang Xianmin
Published: July 2018

In level-set-based topology optimization methods, the spatial gradients of the level set field need to be controlled to avoid excessive flatness or steepness at the structural interfaces. One of the most commonly utilized methods is to generalize the traditional Hamilton−Jacobi equation by adding a diffusion term to control the level set function to remain close to a signed distance function near the structural boundaries. This study proposed a new diffusion term and built it into the Hamilton-Jacobi equation. This diffusion term serves two main purposes: (I) maintaining the level set function close to a signed distance function near the structural boundaries, thus avoiding periodic re-initialization, and (II) making the diffusive rate function to be a bounded function so that a relatively large time-step can be used to speed up the evolution of the level set function. A two-phase optimization algorithm is proposed to ensure the stability of the optimization process. The validity of the proposed method is numerically examined on several benchmark design problems in structural topology optimization.
A Parametric Study on a Subcritical CO2/NH3 Cascade Refrigeration System for Low Temperature Applications
Authors: Yilmaz Baris , Mancuhan Ebru , Erdonmez Nasuh
Published: July 2018

Adverse effects of synthetic refrigerants on the environment have led to replacing them with natural refrigerants. The common candidates are ammonia, carbon dioxide, and several hydrocarbon compounds and their mixtures. Ammonia has been used mainly in large-scale cooling purposes such as large-scale supermarkets and climatic rooms. However, in such systems, leakage of ammonia may arise severe results on human health and may damage products in the cooled space. Recently, in last decade, a well-known refrigerant, CO2, has gained more attention to be applied in refrigeration systems due to having prominent thermo-physical properties. The performance analysis of a CO2/NH3 cascade (CAS) system has been theoretically examined in the current study. The detailed performance analysis of the system and optimization of the operating parameters have been studied extensively. In addition, the second-law analysis of the system with both cycles has been performed. Optimum operating conditions of the system are also determined and correlations are developed. Finally, the coefficient of performance (COP) correlations developed by several researchers in literature and those of current study are compared against available experimental COP results. The comparisons showed that the proposed correlations can be utilized for the accurate prediction of the COP of a cascade CO2/NH3 system within the studied range of operating conditions.
Analysis of Numerical Error in One-Dimensional Storage Tank Models for Solar Energy System Simulations
Authors: Unrau C. M. , Lightstone M. F.
Published: July 2018

This study investigates the temperature profiles predicted by trnsys one-dimensional (1D) thermal storage tank models for typical charging conditions. Simulation parameters, such as grid spacing and time-step size, were varied to observe the changes in the numerical error when compared with an exact analytical solution. A Taylor series expansion was also performed on the discretized, 1D, advection–diffusion equation to obtain an expression for this numerical error. A numerical diffusion term was found which could be used to improve the prediction of the temperature profile in a storage tank simulation. Finally, the influence of this error on predictions of the annual solar fraction for a domestic hot water system was explored.
Quantification of Wear in Cylinder Bores Based on Wear Volume Profile Assessment
Authors: Obara R. B.
Published: July 2018

Despite the importance of precise evaluation of wear volume losses from cylinders, several factors make the investigation of large surface areas from cylinder bores a hard issue. Topography analysis has been widely used to quantify wear in cylinders but no method was found in the literature for the quantification of wear volume losses considering the whole stroke length of cylinder bores. In this work, three-dimensional (3D) measurements were taken from a gasoline engine tested in dynamometer for 625 h and wear volume profiles were obtained for all cylinders. The results from the proposed method showed good agreement with both the variation of the core height and the visual analysis from stereo images.
Reliability Methods for Bimodal Distribution With First-Order Approximation
Authors: Hu Zhangli , Du Xiaoping
Published: July 2018

In traditional reliability problems, the distribution of a basic random variable is usually unimodal; in other words, the probability density of the basic random variable has only one peak. In real applications, some basic random variables may follow bimodal distributions with two peaks in their probability density. When binomial variables are involved, traditional reliability methods, such as the first-order second moment (FOSM) method and the first-order reliability method (FORM), will not be accurate. This study investigates the accuracy of using the saddlepoint approximation (SPA) for bimodal variables and then employs SPA-based reliability methods with first-order approximation to predict the reliability. A limit-state function is at first approximated with the first-order Taylor expansion so that it becomes a linear combination of the basic random variables, some of which are bimodally distributed. The SPA is then applied to estimate the reliability. Examples show that the SPA-based reliability methods are more accurate than FOSM and FORM.
A Numerical and Experimental Study of Distribution of the Residual Stress on the Shot Peened Low Alloy Steel
Authors: Trung Pham Quang , Butler David Lee , Idapalapati Sridhar
Published: July 2018

Shot peening is a cold working process, which is used to enhance the properties of materials, especially the fatigue life as it induces large compressive residual stresses in the subsurface of materials. In this paper, the effect of the shot peening process on the topography of the shot peened surface and the distribution of the residual stresses in the subsurface of the material was systematically investigated. A technique to estimate the shot peening coverage was employed using a finite element model which was further developed using experimental results for increased accuracy. The comparison between the numerical and experimental studies gives a good agreement of the distribution of the residual stresses in the subsurface of the shot peened material. The shot peening pressure and media size are two main factors affecting on the presence of compressive residual stresses in the subsurface of the material.
Ceramic Matrix Composite Materials for Engine Exhaust Systems on Next-Generation Vertical Lift Vehicles
Authors: Walock Michael J. , Heng Vann , Nieto Andy , Ghoshal Anindya , Murugan Muthuvel , Driemeyer Dan
Published: July 2018

Future gas turbine engines will operate at significantly higher temperatures (∼1800 °C) than current engines (∼1400 °C) for improved efficiency and power density. As a result, the current set of metallic components (titanium-based and nickel-based superalloys) will be replaced with ceramics and ceramic matrix composites (CMCs). These materials can survive the higher operating temperatures of future engines at significant weight savings over the current metallic components, i.e., advanced ceramic components will facilitate more powerful engines. While oxide-based CMCs may not be suitable candidates for hot-section components, they may be suitable for structural and/or exhaust components. However, a more thorough understanding of the performance under relevant environment of these materials is needed. To this end, this work investigates the high-temperature durability of a family of oxide–oxide CMCs (Ox–Ox CMCs) under an engine-relevant environment. Flat Ox–Ox CMC panels were cyclically exposed to temperatures up to 1150 °C, within 240 m/s (∼0.3 M) gas flows and hot sand impingement. Front and backside surface temperatures were monitored by a single-wavelength (SW) pyrometer and thermocouple, respectively. In addition, an infrared (IR) camera was used to evaluate the damage evolution of the samples during testing. Flash thermography nondestructive evaluation (NDE) was used to elucidate defects present before and after thermal exposure.
Numerical Modeling of a Wave Turbine and Estimation of Shaft Work
Authors: Jagannath Ravichandra R. , Bane Sally P. M. , Razi Nalim M.
Published: July 2018

Wave rotors are periodic-flow devices that provide dynamic pressure exchange and efficient energy transfer through internal pressure waves generated due to fast opening and closing of ports. Wave turbines are wave rotors with curved channels that can produce shaft work through change of angular momentum from inlet to exit. In the present work, conservation equations with averaging in the transverse directions are derived for wave turbines, and quasi-one-dimensional model for axial-channel non-steady flow is extended to account for blade curvature effects. The importance of inlet incidence is explained and the duct angle is optimized to minimize incidence loss for a particular boundary condition. Two different techniques are presented for estimating the work transfer between the gas and rotor due to flow turning, based on conservation of angular momentum and of energy. The use of two different methods to estimate the shaft work provides confidence in reporting of work output and confirms internal consistency of the model while it awaits experimental data for validation. The extended wave turbine model is used to simulate the flow in a three-port wave rotor. The work output is calculated for blades with varying curvature, including the straight axial channel as a reference case. The dimensional shaft work is reported for the idealized situation where all loss-generating mechanisms except flow incidence are absent, thus excluding leakage, heat transfer, friction, port opening time, and windage losses. The model developed in the current work can be used to determine the optimal wave turbine designs for experimental investment.
Robustness Analysis of a Simple and Augmented Proportional Plus Derivative Controller in Trajectory Following Robots Using the Floquet Theory
Authors: Sandeep Reddy B. , Ghosal Ashitava
Published: July 2018

This paper deals with the issue of robustness in control of robots using the proportional plus derivative (PD) controller and the augmented PD controller. In the literature, a variety of PD and model-based controllers for multilink serial manipulator have been claimed to be asymptotically stable for trajectory tracking, in the sense of Lyapunov, as long as the controller gains are positive. In this paper, we first establish that for simple PD controllers, the criteria of positive controller gains are insufficient to establish asymptotic stability, and second that for the augmented PD controller the criteria of positive controller gains are valid only when there is no uncertainty in the model parameters. We show both these results for a simple planar two-degrees-of-freedom (2DOFs) robot with two rotary (R) joints, following a desired periodic trajectory, using the Floquet theory. We provide numerical simulation results which conclusively demonstrate the same.
Hierarchical Metamodeling of the Air Bending Process
Authors: Strano Matteo , Semeraro Quirico , Iorio Lorenzo , Sofia Roberto
Published: July 2018

Despite the tremendous effort of researchers and manufacturing engineers in improving the predictability of the air bending process, there is still a strong need for comprehensive and dependable prediction models. Currently, available modeling approaches all present some relevant limitations in practical applications. In this paper, we propose a new method, which represents an improvement over all existing modeling and prediction techniques. The proposed method can be used for accurate prediction of the main response variables of the air bending process: the angle α after springback and the bend deduction BD. The metamodeling method is based on the hierarchical fusion of different kinds of data: the deterministic low-fidelity response of numerical finite element method (FEM) simulations and the stochastic high fidelity response of experimental tests. The metamodel has been built over a very large database, unprecedented in the scientific literature on air bending, made of more than 500 numerical simulations and nearly 300 experimental tests. The fusion is achieved first by interpolating the FEM simulations with a kriging predictor; then, the hierarchical metamodel is built as a linear regression model of the experimental data, using the kriging predictor among the regressors. The accuracy of the method has been proved using a variant of the leave-one-out cross validation technique. The quality of the prediction yielded by the proposed method significantly over-performs the current prediction of the press brake on-line numerical control.
Magnetohydrodynamics Stagnation-Point Flow of Sisko Liquid With Melting Heat Transfer and Heat Generation/Absorption
Authors: Hayat Tasawar , Ullah Ikram , Alsaedi Ahmed , Asghar Saleem
Published: July 2018

This research concentrates on melting heat transfer in magnetohydrodynamics (MHD) flow of Sisko fluid bounded by a sheet with nonlinear stretching velocity. Modeling and analysis have been carried out in the presence of heat generation/absorption and magnetic field. Transformation procedure is implemented in obtaining nonlinear differential system. Convergence series solutions are developed. The solution for different influential parameters is analyzed. Skin friction coefficient and heat transfer rate are analyzed. It is observed that the qualitative results of magnetic field and melting heat transfer on velocity are similar.
Convective Heat Transfer Coefficients of Multifaceted Longitudinal and Transversal Bricks of Lattice Setting in Tunnel Kilns
Authors: Abou-Ziyan Hosny Z. , Almesri Issa F. , Alrahmani Mosab A. , Almutairi Jaber H.
Published: July 2018

This paper reports the local multifaceted and area-averaged convective heat transfer coefficients (CHTCs) of longitudinal and transverse bricks arranged in lattice brick setting in tunnel kilns, using a three-dimensional (3D) computational fluid dynamics (CFD) model. A mesh sensitivity analysis was performed and the model was validated against reported experimental data in tunnel kilns. Three turbulence models were tested: the standard k–ε, re-normalization group (RNG) k–ε, and k–ω. The k–ω model provided the closest results to the experimental data. The CHTCs from the front, back, left, and right faces of the longitudinal and transverse bricks were calculated under various conditions. Area-averaged CHTCs for bricks were determined from the multifaceted CHTCs. Effects of rows, layers, and walls on faces and area-averaged CHTCs were investigated. A sensitivity analysis was performed to explore the effect of flow channels on the CHTCs. The numerical results showed that the CHTCs are enhanced by 17% for the longitudinal bricks and 27% for the transverse bricks when a uniform flow is reached in the tunnel kilns. Also, similar area-averaged CHTCs for the longitudinal and transverse bricks were obtained as a result of the uniform flow. Therefore, the specific energy consumption, quality, and quantity of brick production could be enhanced.
Thermal Management of Single- and Dual-Tank Fuel-Flow Topologies Using an Optimal Control Strategy
Authors: Huang P. G. , Doman D. B.
Published: July 2018

The effect of fuel topology and control on thermal endurance of aircraft using fuel as a heat transfer agent was studied using an optimal dynamic solver (OPT). The dynamic optimal solutions of the differential equations governing the heat transfer of recirculated fuel flows for single- and dual-tank arrangements were obtained. The method can handle sudden jumps of operating conditions across different operating zones during mission and/or situations when control parameters have reached their physical limits. Although this method is robust in providing an optimal control strategy to prolong thermal endurance of aircrafts, it is not ideal for practical application because the method required iterative procedures to solve expensive nonlinear equations. The linear quadratic regulator (LQR), the feedback controller, can be derived by linearizing the adjoint equations at trim points to offer a simple control strategy, which can then be implemented directly in the feedback control hardware. The solutions obtained from both OPT and LQR were compared, and it was found two solutions were almost identical except in regions having sudden jump of operation conditions. Finally, a comparison between single- and dual-tank arrangements was made to demonstrate the importance of the flow topology. The study shows the dual-tank arrangement allows flexibility in how energy is managed and can release energy faster than a single-tank topology and hence provides improved aircraft thermal endurance.