bluuebunny/crossref_metadata_2025 huggingface dataset:
Confidence-Driven Design Optimization Using Gaussian Process Metamodeling With Insufficient Data
Authors: Li Mingyang , Wang Zequn
Published: August 2018

To reduce the computational cost, surrogate models have been widely used to replace expensive simulations in design under uncertainty. However, most existing methods may introduce significant errors when the training data is limited. This paper presents a confidence-driven design optimization (CDDO) framework to manage surrogate model uncertainty for probabilistic design optimization. In this study, a confidence-based Gaussian process (GP) modeling technique is developed to handle the surrogate model uncertainty in system performance predictions by taking both the prediction mean and variance into account. With a target confidence level, the confidence-based GP models are used to reduce the probability of underestimating the probability of failure in reliability assessment. In addition, a new sensitivity analysis method is proposed to approximate the sensitivity of the reliability at the target confidence level with respect to design variables, and thus facilitate the CDDO framework. Three case studies are introduced to demonstrate the effectiveness of the proposed approach.
Experimental
Characterization of Frost Growth on a Horizontal Plate Under Natural
Convection
Authors: Niroomand S. , Fauchoux M.
T. , Simonson C.
J.
Published: August 2018

This paper presents an experimental study on frost formation on a plate under natural convection conditions. Frost thickness, mass, density, and surface roughness are measured during each test. Frost thickness and roughness are measured using an image processing technique. The effect of operating conditions (temperature of the plate, and temperature and relative humidity of the air) on the properties of frost is investigated. Frost surface roughness is quantified using two parameters: the average roughness and the skewness of the roughness, which can describe the frost layer shape. The surface roughness of the frost layer is considerably higher than the roughness of a flat plate, which should be considered in frosting studies. In this paper, it is shown that frost surface roughness is related to the frost layer shape, porosity and density. It is also found that the plate temperature affects the frost surface roughness significantly; as the plate temperature decreases, the frost layer has a high average roughness and negative skewness, which correspond to a highly porous, low density frost layer. Increasing the air humidity and air temperature affects the average surface roughness slightly but not skewness of the frost surface.
Effects of Downstream Vane Bowing and Asymmetry on Unsteadiness in a Transonic Turbine
Authors: Clark John P. , Anthony Richard J. , Ooten Michael K. , Finnegan John M. , Dean Johnson P. , Ni Ron-Ho
Published: August 2018

Accurate predictions of unsteady forcing on turbine blades are essential for the avoidance of high-cycle-fatigue issues during turbine engine development. Further, if one can demonstrate that predictions of unsteady interaction in a turbine are accurate, then it becomes possible to anticipate resonant-stress problems and mitigate them through aerodynamic design changes during the development cycle. A successful reduction in unsteady forcing for a transonic turbine with significant shock interactions due to downstream components is presented here. A pair of methods to reduce the unsteadiness was considered and rigorously analyzed using a three-dimensional (3D), time-resolved Reynolds-Averaged Navier-Stokes (RANS) solver. The first method relied on the physics of shock reflections itself and involved altering the stacking of downstream components to achieve a bowed airfoil. The second method considered was circumferentially asymmetric vane spacing which is well known to spread the unsteadiness due to vane-blade interaction over a range of frequencies. Both methods of forcing reduction were analyzed separately and predicted to reduce unsteady pressures on the blade as intended. Then, both design changes were implemented together in a transonic turbine experiment and successfully shown to manipulate the blade unsteadiness in keeping with the design-level predictions. This demonstration was accomplished through comparisons of measured time-resolved pressures on the turbine blade to others obtained in a baseline experiment that included neither asymmetric spacing nor bowing of the downstream vane. The measured data were further compared to rigorous post-test simulations of the complete turbine annulus including a bowed downstream vane of nonuniform pitch.
On Operational Space Tracking Control of Robotic Manipulators With Uncertain Dynamic and Kinematic Terms
Authors: Cetin Kamil , Tatlicioglu Enver , Zergeroglu Erkan
Published: August 2018

In this study, a continuous robust-adaptive operational space controller that ensures asymptotic end-effector tracking, despite the uncertainties in robot dynamics and on the velocity level kinematics of the robot, is proposed. Specifically, a smooth robust controller is applied to compensate the parametric uncertainties related to the robot dynamics while an adaptive update algorithm is used to deal with the kinematic uncertainties. Rather than formulating the tracking problem in the joint space, as most of the previous works on the field have done, the controller formulation is presented in the operational space of the robot where the actual task is performed. Additionally, the robust part of the proposed controller is continuous ensuring the asymptotic tracking and relatively smooth controller effort. The stability of the overall system and boundedness of the closed loop signals are ensured via Lyapunov based arguments. Experimental results are presented to illustrate the feasibility and performance of the proposed method.
Performance Testing of an Axial Flow Fan Designed for Air-Cooled Heat Exchanger Applications
Authors: Wilkinson Michael B. , van der Spuy Sybrand J. , von Backström Theodor W.
Published: August 2018

An axial flow fan developed in the previous study is tested in order to characterize its performance. The M-fan, a 7.3152 m diameter rotor only axial flow fan was designed to perform well under the challenging operating conditions encountered in air-cooled heat exchangers. Preliminary computational fluid dynamics (CFD) results obtained using an actuator disk model (ADM) as well as a periodic three dimensional model indicate that the fan meets the specified performance targets, with an expected total-to-static efficiency of 59.4% and a total-to-static pressure rise of 114.7 Pa at the operating point. Experimental tests are performed on the M-fan in order to determine its performance across a full range of flow rates. A range of fan configurations are tested in order to ascertain the effect of tip clearance, blade angle, and hub configuration on fan performance. Due to the lack of a suitable facility for testing a large diameter fan, a scaled 1.542 m diameter model is tested on the ISO 5801 type A fan test facility at Stellenbosch University. A Reynolds-averaged Navier–Stokes CFD model representing the M-fan in the test facility is also developed in order to provide additional insight into the flow field in the vicinity of the fan blades. The results of the CFD model will be validated using the experimental data obtained. Both the CFD results and the experimental data obtained are compared to the initial CFD results for the full scale fan, as obtained in the previous study, by means of fan scaling laws. Experimental data indicate that the M-fan does not meet the pressure requirement set out in the initial study at the design blade setting angle of 34 deg. Under these conditions, the M-fan attains a total-to-static pressure rise of 102.5 Pa and a total-to-static efficiency of 56.4%, running with a tip gap of 2 mm. Increasing the blade angle is shown to be a potential remedy, improving the total-to-static pressure rise and efficiency obtained at the operating point. The M-fan is also shown to be highly sensitive to increasing tip gap, with larger tip gaps substantially reducing fan performance. The losses due to tip gap are also shown to be overestimated by the CFD simulations. Both experimental and numerically obtained results indicate lower fan total-to-static efficiencies than obtained in the initial CFD study. Results indicate that the M-fan is suited to its intended application, however, it should be operated with a smaller tip gap than initially recommended and a larger blade setting angle. Hub configuration is also shown to have an influence on fan performance, potentially improving performance at low flow rates.
Research on the Dynamics and Variable Characteristics of a Double-Swash-Plate Hydraulic Axial Piston Pump With Port Valves
Authors: Qian Pengcheng , Ji Zengqi , Zhu Bihai
Published: August 2018

Axial piston pumps with port valves are widely used in applications that require high pressure and high power. In the present research, a new type of double-swash-plate hydraulic axial piston pump (DSPHAPP) with port valves is presented. The structure and working principle of the pump are discussed, and the balance characteristics of the pump are analyzed. A mathematical model of the pump flow distribution mechanism considering the leakage is established, based on which the effects of centrifugal forces acting on the port valves, working pressure, and rotational speed on the flow distribution characteristics are studied. A new method of varying the displacement of the pump that changes the phase relation of the two swash plates is proposed, and the principle and regulating characteristics of the variable method are studied. A detailed analysis of the forces and moments acting on the cylinder and the bearing reaction forces is presented. Finally, the relationship between volumetric efficiency and working pressure, and rotational speed and variable angle, is presented. It is revealed through an analysis that the working principle of the pump is feasible, and that the variable method can meet the requirements of varying the displacement of the pump. The characteristics of static balance and dynamic balance of the double-swashplate pump have the advantage of reducing vibration and noise. The research results also show that the reasonable matching of the working pressure and rotational speed can increase the pump's working performance to its optimum level.
Experimental Evaluation of the Effect of Cycle Profile on the Durability of Commercial Lithium Ion Power Cells
Authors: Radhakrishnan K. N. , Coupar T. , Nelson D. J. , Ellis M. W.
Published: August 2018

The effect of the charge/discharge profile on battery durability is a critical factor for the application of batteries and for the design of appropriate battery testing protocols. In this work, commercial high-power prismatic lithium ion cells for hybrid electric vehicles (HEVs) were cycled using a pulse-heavy profile and a simple square-wave profile to investigate the effect of cycle profile on battery durability. The pulse-heavy profile was designed to simulate on-road conditions for a typical HEV, while the simplified square-wave profile was designed to have the same total charge throughput, but with lower peak currents. The 5 Ah batteries were cycled for 100 kAh with periodic performance tests to monitor the state of the batteries. Results indicate that, for the batteries tested, the capacity fade for the two profiles was very similar and was 11±0.5% compared to beginning of life (BOL). The change in internal resistance of the batteries during testing was also monitored and found to increase 21% and 12% compared to BOL for the pulse-heavy and square-wave profiles, respectively. The results suggest that simplified testing protocols using square-wave cycling may provide adequate insight into capacity fade behavior for more complex hybrid vehicle drive cycles.
Assessment of Elastic–Plastic and Electrical Properties of Printed Silver-Based Interconnects for Flexible Electronics
Authors: Cheng Hsien-Chie , Hong Ruei-You , Chen Wen-Hwa
Published: August 2018

In this work, the elastic–plastic properties of the printed interconnects on a glass substrate with Ag-filled polymer-conductor ink are evaluated through a theoretical framework based on finite element (FE) modeling of instrumented sharp indentation, experimental indentation, the concept of the representative strain, and dimensional analysis. Besides, the influences of the ink-solvent content and temperature on the elastic–plastic and electrical properties of the printed Ag-based interconnects are also addressed. First of all, parametric FE indentation analyses are carried out over a wide range of elastic–plastic material parameters. These parametric results together with the concept of the representative strain are used via dimensional analysis to constitute a number of dimensionless functions, and further the forward/reverse algorithms. The forward algorithm is used for describing the indentation load–depth relationship and the reverse for predicting the elastic–plastic parameters of the printed Ag-based interconnects. The proposed algorithms are validated through the correct predictions of the plastic properties of three known metals. At last, their surface morphology, microstructure, and elemental composition are experimentally characterized. Results show that the elastic–plastic properties and electrical sheet resistance of the printed Ag-based interconnects increase with the ink-solvent content, mainly due to the increase of carbon element as a result of the increased ink-solvent residue, whereas their elastic–plastic properties and electrical performance decreases with the temperature.
Low-Dimensional Components of Flows With Large Free/Moving-Surface Motion
Authors: Zhang Yi , Yim Solomon C.
Published: August 2018

Flow systems with highly nonlinear free/moving surface motion are common in engineering applications, such as wave impact and fluid-structure interaction (FSI) problems. In order to reveal the dynamics of such flows, as well as provide a reduced-order modeling (ROM) for large-scale applications, we propose a proper orthogonal decomposition (POD) technique that couples the velocity flow field and the level-set function field, as well as a proper normalization for the snapshots data so that the low-dimensional components of the flow can be retrieved with a priori knowledge of equal distribution of the total variance between velocity and level-set function data. Through numerical examples of a sloshing problem and a water entry problem, we show that the low-dimensional components obtained provide an efficient and accurate approximation of the flow field. Moreover, we show that the velocity contour and orbits projected on the space of the reduced basis greatly facilitate understanding of the intrinsic dynamics of the flow systems.
Thermoacoustic Instability Model With Porous Media: Linear Stability Analysis and the Impact of Porous Media
Authors: Dowd Cody S. , Meadows Joseph W.
Published: August 2018

Lean premixed (LPM) combustion systems are susceptible to thermoacoustic instability, which occurs when acoustic pressure oscillations are in phase with the unsteady heat release rates. Porous media has inherent acoustic damping properties and has been shown to mitigate thermoacoustic instability; however, theoretical models for predicting thermoacoustic instability with porous media do not exist. In the present study, a one-dimensional (1D) model has been developed for the linear stability analysis of the longitudinal modes for a series of constant cross-sectional area ducts with porous media using a n-Tau flame transfer function (FTF). By studying the linear regime, the prediction of acoustic growth rates and subsequently the stability of the system is possible. A transfer matrix approach is used to solve for acoustic perturbations of pressure and velocity, stability growth rate, and frequency shift without and with porous media. The Galerkin approximation is used to approximate the stability growth rate and frequency shift, and it is compared to the numerical solution of the governing equations. Porous media is modeled using the following properties: porosity, flow resistivity, effective bulk modulus, and structure factor. The properties of porous media are systematically varied to determine the impact on the eigenfrequencies and stability growth rates. Porous media is shown to increase the stability domain for a range of time delays (Tau) compared to similar cases without porous media.
Theoretical and Experimental Analyses of Directly Lubricated Tilting-Pad Journal Bearings With Leading Edge Groove
Authors: Hagemann Thomas , Schwarze Hubert
Published: August 2018

Flooded lubrication of tilting-pad journal bearings provides safe and robust operation for many applications due to a completely filled gap at the leading edge of each pad. Direct lubrication by leading edge grooves (LEG) located on the pads represents an alternative to restrictive end seals to ensure these conditions at the entrance to the convergent lubricant film. A theoretical model is presented that describes the specific influences of LEG design on operating characteristics. First, in contrast to conventional tilting-pad journal bearing designs, the LEG is a self-contained lube oil pocket, which is generally connected to an outer annular oil supply channel. Consequently, each LEG can feature a specific speed and load-dependent effective pocket pressure, which influences the pad tilting angle. Second, the thermal inlet mixing model must consider the specific flow conditions depending on the main flow direction within the film as well as the one between outer annular channel and pocket. The novel LEG model is integrated into a comprehensive bearing code and validated with test from a high performance test rig for a four tilting-pad bearing in load between pivot orientations. Within the investigated operating range good agreement between theoretical and experimental data is achieved if all boundary conditions are accurately considered. Additionally, the impact of single simplifications within the model is studied and evaluated. Finally, the test data are compared to results from the same test bearing with modified lubricant oil supply conditions in order to identify specific properties of LEG design.
Synchronization of Thermoacoustic Modes in Sequential Combustors
Authors: Bonciolini Giacomo , Noiray Nicolas
Published: August 2018

Sequential combustion constitutes a major technological step-change for gas turbines applications. This design provides higher operational flexibility, lower emissions, and higher efficiency compared to today's conventional architectures. Like any constant pressure combustion system, sequential combustors can undergo thermoacoustic instabilities. These instabilities potentially lead to high-amplitude acoustic limit cycles, which shorten the engine components' lifetime, and therefore, reduce their reliability and availability. In the case of a sequential system, the two flames are mutually coupled via acoustic and entropy waves. This additional interstages interaction markedly complicates the already challenging problem of thermoacoustic instabilities. As a result, new and unexplored system dynamics are possible. In this work, experimental data from our generic sequential combustor are presented. The system exhibits many different distinctive dynamics, as a function of the operation parameters and of the combustor arrangement. This paper investigates a particular bifurcation, where two thermoacoustic modes synchronize their self-sustained oscillations over a range of operating conditions. A low-order model of this thermoacoustic bifurcation is proposed. This consists of two coupled stochastically driven nonlinear oscillators and is able to reproduce the peculiar dynamics associated with this synchronization phenomenon. The model aids in understanding what the physical mechanisms that play a key role in the unsteady combustor physics are. In particular, it highlights the role of entropy waves, which are a significant driver of thermoacoustic instabilities in this sequential setup. This research helps to lay the foundations for understanding the thermoacoustic instabilities in sequential combustion systems.
Computational Rod Model With User-Defined Nonlinear Constitutive Laws
Authors: Fatehiboroujeni Soheil , Palanthandalam-Madapusi Harish J. , Goyal Sachin
Published: August 2018

Computational rod models have emerged as efficient tools to simulate the bending and twisting deformations of a variety of slender structures in engineering and biological applications. The dynamics of such deformations, however, strongly depends on the constitutive law in bending and torsion that, in general, may be nonlinear, and vary from material to material. Jacobian-based computational rod models require users to change the Jacobian if the functional form of the constitutive law is changed, and hence are not user-friendly. This paper presents a scheme that automatically modifies the Jacobian based on any user-defined constitutive law without requiring symbolic differentiation. The scheme is then used to simulate force-extension behavior of a coiled spring with a softening constitutive law.
Combination Parametric Resonance of Nonlinear Unbalanced Rotating Shafts
Authors: Qaderi M. S. , Hosseini S. A. A. , Zamanian M.
Published: August 2018

In this paper, dynamic response of a rotating shaft with geometrical nonlinearity under parametric and external excitations is investigated. Resonances, bifurcations, and stability of the response are analyzed. External excitation is due to shaft unbalance and parametric excitation is due to periodic axial force. For this purpose, combination resonances of parametric excitation and primary resonance of external force are assumed. Indeed, simultaneous effect of nonlinearity, parametric, and external excitations are investigated using analytical method. By applying the method of multiple scales, four ordinary nonlinear differential equations are obtained, which govern the slow evolution of amplitude and phase of forward and backward modes. Eigenvalues of Jacobian matrix are checked to find the stability of solutions. Both periodic and quasi-periodic motion were observed in the range of study. The influence of various parameters on the response of the system is studied. A main contribution is that the parametric excitation in the presence of nonlinearity can be used to suppress the forward synchronous vibration. Indeed, in the presence of combination parametric excitation, the energy is transferred from forward whirling mode to backward one. This property can be applied in control of rotor unbalance vibrations.
Multi-Information Source Fusion and Optimization to Realize ICME: Application to Dual-Phase Materials
Authors: Ghoreishi Seyede Fatemeh , Molkeri Abhilash , Srivastava Ankit , Arroyave Raymundo , Allaire Douglas
Published: August 2018

Integrated Computational Materials Engineering (ICME) calls for the integration of computational tools into the materials and parts development cycle, while the Materials Genome Initiative (MGI) calls for the acceleration of the materials development cycle through the combination of experiments, simulation, and data. As they stand, both ICME and MGI do not prescribe how to achieve the necessary tool integration or how to efficiently exploit the computational tools, in combination with experiments, to accelerate the development of new materials and materials systems. This paper addresses the first issue by putting forward a framework for the fusion of information that exploits correlations among sources/models and between the sources and “ground truth.” The second issue is addressed through a multi-information source optimization framework that identifies, given current knowledge, the next best information source to query and where in the input space to query it via a novel value-gradient policy. The querying decision takes into account the ability to learn correlations between information sources, the resource cost of querying an information source, and what a query is expected to provide in terms of improvement over the current state. The framework is demonstrated on the optimization of a dual-phase steel to maximize its strength-normalized strain hardening rate. The ground truth is represented by a microstructure-based finite element model while three low fidelity information sources—i.e., reduced order models—based on different homogenization assumptions—isostrain, isostress, and isowork—are used to efficiently and optimally query the materials design space.
A Linear Poroelastic Analysis of Time-Dependent Crack-Tip Fields in Polymer Gels
Authors: Yu Yalin , Bouklas Nikolaos , Landis Chad M. , Huang Rui
Published: August 2018

Based on a linear poroelastic formulation, we present an asymptotic analysis of the transient crack-tip fields for stationary cracks in polymer gels under plane-strain conditions. A center crack model is studied in detail, comparing numerical results by a finite element method to the asymptotic analysis. The time evolution of the crack-tip parameters is determined as a result of solvent diffusion coupled with elastic deformation of the gel. The short-time and long-time limits are obtained for the stress intensity factor and the crack-tip energy release rate under different chemo-mechanical boundary conditions (immersed versus not-immersed, displacement versus load controlled). It is found that, under displacement-controlled loading, the crack-tip energy release rate increases monotonically over time for the not-immersed case, but for the immersed case, it increases first and then decreases, with a long-time limit lower than the short-time limit. Under load control, the energy release rate increases over time for both immersed and not-immersed cases, with different short-time limits but the same long-time limit. These results suggest that onset of crack growth may be delayed until the crack-tip energy release rate reaches a critical value if the applied displacement or traction is subcritical but greater than a threshold.
Differential Effects of Isoproterenol on Regional Myocardial Mechanics in Rat Using Three-Dimensional Cine DENSE Cardiovascular Magnetic Resonance
Authors: Zhang Xiaoyan , Liu Zhan-Qiu , Singh Dara , Powell David K. , Chung Charles S. , Campbell Kenneth S. , Wenk Jonathan F.
Published: August 2018

The present study assessed the acute effects of isoproterenol on left ventricular (LV) mechanics in healthy rats with the hypothesis that β-adrenergic stimulation influences the mechanics of different myocardial regions of the LV wall in different ways. To accomplish this, magnetic resonance images were obtained in the LV of healthy rats with or without isoproterenol infusion. The LV contours were divided into basal, midventricular, and apical regions. Additionally, the midventricular myocardium was divided into three transmural layers with each layer partitioned into four segments (i.e., septal, inferior, lateral, and anterior). Peak systolic strains and torsion were quantified for each region. Isoproterenol significantly increased peak systolic radial strain and circumferential-longitudinal (CL) shear strain, as well as ventricular torsion, throughout the basal, midventricle, and apical regions. In the midventricle, isoproterenol significantly increased peak systolic radial strain, and induced significant increases in peak systolic circumferential strain and longitudinal strain in the septum. Isoproterenol consistently increased peak systolic CL shear strain in all midventricular segments. Ventricular torsion was significantly increased in nearly all segments except the inferior subendocardium. The effects of isoproterenol on LV systolic mechanics (i.e., three-dimensional (3D) strains and torsion) in healthy rats depend on the region. This region dependency is also strain component-specific. These results provide insight into the regional response of LV mechanics to β-adrenergic stimulation in rats and could act as a baseline for future studies on subclinical abnormalities associated with the inotropic response in heart disease.
Effects of Microribs on the Thermal Behavior of Transcritical n-Decane in Asymmetric Heated Rectangular Mini-Channels Under Near Critical Pressure
Authors: Li Xin , Qin Jiang , Zhang Silong , Cui Naigang , Bao Wen
Published: August 2018

Microrib is a very promising heat transfer enhancement method for the design of scramjet regenerative cooling channels. In this paper, a three-dimensional numerical model has been built and validated to parametrically investigate the thermal behavior of transcritical n-Decane in mini cooling channels with microribs under near critical pressure. The results have shown that the height and pitch of microrib perform a nonmonotonic effect on the convective heat transfer coefficient of n-Decane inside the cooling channel and the optimal microrib parameters stay at low values due to dramatic changes of coolant thermophysical properties in the near critical region. Due to severe thermal stratification and near critical conditions, there will be a significant recirculation zone in vertical direction near microrib, and its interaction with the strong secondary flow in axial direction caused by limited channel width of mini-channel will largely enhance the local convective heat transfer and its downstream region. Besides, the dramatically changing thermophysical properties of n-Decane will lead to a locally remarkable heat transfer enhancement phenomenon similar to impingement cooling at the front edge of microribs.
A Moving Morphable Component Based Topology Optimization Approach for Rib-Stiffened Structures Considering Buckling Constraints
Authors: Zhang Weisheng , Liu Ying , Du Zongliang , Zhu Yichao , Guo Xu
Published: August 2018

Stiffened structures are widely used in industry. However, how to optimally distribute the stiffening ribs on a given base plate remains a challenging issue, partially because the topology and geometry of stiffening ribs are often represented in a geometrically implicit way in traditional approaches. This implicit treatment may lead to problems such as high computational cost (caused by the large number of design variables, geometry constraints in optimization, and large degrees-of-freedom (DOF) in finite element analysis (FEA)) and the issue of manufacturability. This paper presents a moving morphable component (MMC)-based approach for topology optimization of rib-stiffened structures, where the topology and the geometry of stiffening ribs are explicitly described. The proposed approach displays several prominent advantages, such as (1) both the numbers of design variables and DOF in FEA are reduced substantially; (2) the proper manufacture-related geometry requirements of stiffening ribs can be readily satisfied without introducing any additional constraint. The effectiveness of the proposed approach is further demonstrated with numerical examples on topology optimization of rib-stiffened structures with buckling constraints.
Computational Synthesis of Large Deformation Compliant Mechanisms Undergoing Self and Mutual Contact
Authors: Kumar Prabhat , Saxena Anupam , Sauer Roger A.
Published: August 2018

Topologies of large deformation contact-aided compliant mechanisms (CCMs), with self and mutual contact, exemplified via path generation applications, are designed using the continuum synthesis approach. Design domain is parameterized using honeycomb tessellation. Assignment of material to each cell, and generation of rigid contact surfaces, are accomplished via suitably sizing and positioning negative circular masks using the stochastic hill-climber search. To facilitate contact analysis, boundary smoothing is implemented. Mean value coordinates are employed to compute shape functions, as many regular hexagonal cells get degenerated into irregular, concave polygons as a consequence of boundary smoothing. Both geometric and material nonlinearities are considered. The augmented Lagrange multiplier method with a formulated active set strategy is employed to incorporate both self and mutual contact. Synthesized contact-aided compliant continua trace paths with single, and importantly, multiple kinks and experience multiple contact interactions pertaining to both self and mutual contact modes.
Reliability Study on a New Integrity Pressure Relief Device in Nonrefillable Steel Gas Cylinder
Authors: Jin Weiya , Li Yuebing , Zhou Mingjue , Gao Zengliang
Published: August 2018

A new integrity pressure relief device in a nonrefillable steel gas cylinder is proposed and tested. Instead of a rupture disk welded on the opening of the head, the new integrity pressure relief device is machined by stamping a circular groove on the vessel head, which not only avoids an additional penetration on the head but also reduces the manufacture cost. To ensure the safety and reliability of the device, its performance is evaluated using a reliability method based on material properties and burst pressure. The effect of stamping pressure on the groove depth is investigated, and then, the material properties taken from different locations are tested. Tensile properties taken along the circumferential direction of the cylinder are suggested to be used to predict burst pressure of the new integrity pressure relief device. The tolerance of the burst pressure in a percentage is analyzed, and a probabilistic model is built. The reliability analysis shows that the batch of cylinders with the integrity pressure relief device has a very high qualified probability.
Conjugate Heat Transfer Methodology for Thermal Design and Verification of Gas Turbine Cooled Components
Authors: Winchler Lorenzo , Andreini Antonio , Facchini Bruno , Andrei Luca , Bonini Alessio , Innocenti Luca
Published: August 2018

Gas turbine design has been characterized over the years by a continuous increase of the maximum cycle temperature, justified by a corresponding increase of cycle efficiency and power output. In such way, turbine components heat load management has become a compulsory activity, and then, a reliable procedure to evaluate the blades and vanes metal temperatures is, nowadays, a crucial aspect for a safe components design. In the framework of the design and validation process of high pressure turbine cooled components of the BHGE NovaLTTM 16 gas turbine, a decoupled methodology for conjugate heat transfer prediction has been applied and validated against measurement data. The procedure consists of a conjugate heat transfer analysis in which the internal cooling system (for both airfoils and platforms) is modeled by an in-house one-dimensional thermo-fluid network solver, the external heat loads and pressure distribution are evaluated through 3D computational fluid dynamics (CFD) analysis and the heat conduction in the solid is carried out through a 3D finite element method (FEM) solution. Film cooling effect has been treated by means of a dedicated CFD analysis, implementing a source term approach. Predicted metal temperatures are finally compared with measurements from an extensive test campaign of the engine in order to validate the presented procedure.
A Review of Direct Drive Proportional Electrohydraulic Spool Valves: Industrial State-of-the-Art and Research Advancements
Authors: Tamburrano Paolo , Plummer Andrew R. , Distaso Elia , Amirante Riccardo
Published: August 2018

This paper reviews the state of the art of directly driven proportional directional hydraulic spool valves, which are widely used hydraulic components in the industrial and transportation sectors. First, the construction and performance of commercially available units are discussed, together with simple models of the main characteristics. The review of published research focuses on two key areas: investigations that analyze and optimize valves from a fluid dynamic point of view, and then studies on spool position control systems. Mathematical modeling is a very active area of research, including computational fluid dynamics (CFD) for spool geometry optimization, and dynamic spool actuation and motion modeling to inform controller design. Drawbacks and advantages of new designs and concepts are described in the paper.
Correlation of Warpage Distribution With the Material Property Scattering for Warpage Range Prediction of PBGA Components
Authors: Zhang Qiming , Lo Jeffery C. C. , Ricky Lee S. W. , Xu Wei
Published: August 2018

In recent years, due to the increased size of ball grid array (BGA) devices, the assembly of BGAs on printed circuit boards through surface mount technology has encountered unprecedented challenges from thermal warpage. The excessive warpage of BGAs in the reflow process may cause manufacture problems and even the risk of failure. Thus, it is essential to acquire warpage values and corresponding distribution ranges of BGAs before the surface mount technology process. In order to avoid assembly failure, theoretically, it is necessary to guarantee that all BGA devices meet the acceptance requirement of relevant standards. Generally, a large number of samples should be measured to obtain a relatively reliable warpage data distribution in the reflow temperature range, which makes this test quite costly and extremely time consuming. This study proposes another method to estimate the BGA warpage value and its possible corresponding range from the material property point of view. Because the mechanism of BGA warpage is related to the coefficient of thermal expansion (CTE) mismatch between the different materials, the warpage data scattering can be correlated with the scattering of material properties through finite element method (FEM) analysis. With a known mean value and range of material properties, the warpage value and corresponding distribution range can be solved. A sensitivity study is also presented in this paper. The accuracy of the proposed method is evaluated and the corresponding warpage data fluctuation range is estimated. From the comparison of the simulation and experiment results, determining the material properties could lead to a reasonable prediction of warpage in both the qualitative and quantitative sense. The proposed methodology for BGA warpage estimation can be used for academic research and industrial applications.
Influence of Microstructure on the High-Frequency Ultrasound Measurement of Peak Density
Authors: Stromer Jeremy , Ladani Leila
Published: August 2018

Peak density is an ultrasound measurement, which has been found to vary according to microstructure, and is defined as the number of local extrema within the resulting power spectrum of an ultrasound measurement. However, the physical factors which influence peak density are not fully understood. This work studies the microstructural characteristics which affect peak density through experimental, computationa,l and analytical means for high-frequency ultrasound of 22–41 MHz. Experiments are conducted using gelatin-based phantoms with glass microsphere scatterers with diameters of 5, 9, 34, and 69 μm and number densities of 1, 25, 50, 75, and 100 mm−3. The experiments show the peak density to vary according to the configuration. For example, for phantoms with a number density of 50 mm−3, the peak density has values of 3, 5, 9, and 12 for each sphere diameter. Finite element simulations are developed and analytical methods are discussed to investigate the underlying physics. Simulated results showed similar trends in the response to microstructure as the experiment. When comparing scattering cross section, peak density was found to vary similarly, implying a correlation between the total scattering and the peak density. Peak density and total scattering increased predominately with increased particle size but increased with scatterer number as well. Simulations comparing glass and polystyrene scatterers showed dependence on the material properties. Twenty-four of the 56 test cases showed peak density to be statistically different between the materials. These values behaved analogously to the scattering cross section.
Finite Element Analysis and Experimental Validation of Transfer Function of Rotating Shaft System With Both an Open Crack and Anisotropic Support Stiffness
Authors: Yao Qiang , Inoue Tsuyoshi , Yabui Shota
Published: August 2018

In this paper, transfer function of rotating shaft system for detecting transverse open crack is developed. Rotating shaft system is modeled using one-dimensional finite element method (1D-FEM), and quantitative analysis is performed. Open crack is modeled as weak asymmetry rotating with shaft's rotation. It is known that, when both open crack and support stiffness anisotropy coexist, various frequency components of shaft's vibration are generated through their successive interaction. This paper evaluates the order of these components, and concludes that first five main components are enough to investigate interaction of open crack and support stiffness anisotropy. Then, five sets of transfer functions for these components are derived. The validity of this set of transfer functions is confirmed by numerical simulation. Moreover, excitation experiment utilizing active magnetic bearing (AMB) is performed, and the validity of derived transfer function was verified experimentally.
Influence of Nonaxisymmetric Confinement on the Hydrodynamic Stability of Multinozzle Swirl Flows
Authors: Subramanian Harish G. , Manoharan Kiran , Hemchandra Santosh
Published: August 2018

Interaction between coherent flow oscillations and the premixed flame sheet in combustors can result in coherent unsteadiness in the global heat release response. These coherent flow oscillations can either be self-excited (e.g., the precessing vortex core) or result from the hydrodynamic response of the flow field to acoustic forcing. Recent work has focused on understanding the various instability modes and fundamental mechanisms that control hydrodynamic instability in single nozzle swirl flows. However, the effect of multiple closely spaced nozzles as well as the nonaxisymmetric nature of the confinement imposed by the combustor liner on swirl nozzle flows remains as yet unexplored. We study the influence of internozzle spacing and nonaxisymmetric confinement on the local temporal and spatiotemporal stability characteristics of multinozzle flows in this paper. The base flow model for the multinozzle case is constructed by superposing contributions from a base flow model for each individual nozzle. The influence of the flame is captured by specifying a spatially varying base flow density field. The nonaxisymmetric local stability problem is posed in terms of a parallel base flow with spatial variations in the two directions perpendicular to the streamwise direction. We investigate the case of a single nozzle and three nozzles arranged in a straight line within a rectangular combustor. The results show that geometric confinement imposed by the combustor walls has a quantitative impact on the eigenvalues of the hydrodynamic modes. Decreasing nozzle spacing for a given geometric confinement configuration makes the flow more unstable. The presence of an inner shear layer (ISL) stabilized flame results in an overall stabilization of the flow instability. We also discuss qualitatively, the underlying vorticity dynamics mechanisms that influence the characteristics of instability modes in triple nozzle flows.
Design of a High Gain Observer Optimization Method for the State Synchronization of Nonlinear Perturbed Chaotic Systems
Authors: Daldoul Ines , Tlili Ali Sghaier
Published: August 2018

This paper propounds addressing the design of a high gain observer optimization method in order to ensure a reliable state synchronization of nonlinear perturbed chaotic systems. The salient feature of the developed approach lies in the optimization of the high gain observer by using the optimal control theory associated with a proposed numerical algorithm. Thereby, an innovative quadratic optimization criterion is proposed to calculate the required optimal value of the observer setting parameter θ, characterizing the observation gain and corresponding to the minimal value of the cost function, by achieving a compromise between the correction term of the state observer and its observation error. Moreover, the exponential stability of the high gain observer is demonstrated within the Lyapunov framework. The efficacy of the designed approach is highlighted by numerical simulation on two prominent examples of nonlinear perturbed chaotic systems.
Bubble Lifecycle During Heterogeneous Nucleate Boiling
Authors: Pandey Vinod , Biswas Gautam , Dalal Amaresh , Welch Samuel W. J.
Published: August 2018

Heterogeneous nucleate boiling over a flat surface has been studied through complete numerical simulations. During the growth and departure of the vapor bubble, the interface is tracked following a coupled level-set and volume of fluid approach. A microlayer evaporation model similar to Sato and Niceno [“A depletable microlayer model for nucleate pool boiling,” J. Comput. Phys. 300, 20–52 (2015)] has been deployed in this investigation. A detailed study of the changes in microlayer structure as a result of different modes of boiling scenario has been performed. The departure diameter is found to increase with an increase in substrate superheat. The predicted departure diameter has been compared with the available experimental and analytical results. A power-law curve has been obtained for depicting the growth rate of bubble depending on the degree of superheat at the wall. The space–time averaged wall-heat flux at different values of superheat temperature of substrate is obtained. Bubble growth during subcooled boiling at a low and intermediate subcooled degree has been observed through direct numerical simulations. The variations in bubble dynamics after departure in saturated and subcooled liquid states have been compared.
Energy Saving Potential of a Combined Solar and Natural Gas-Assisted Vapor Absorption Building Cooling System
Authors: Singh Gaurav , Das Ranjan
Published: August 2018

A building energy simulation study is carried out to analyze the performance of a triple-hybrid single-effect vapor absorption cooling system (VACS) operated by solar, natural gas, and auxiliary electricity-based cogeneration. A high capacity small office building subjected to different climatic conditions is considered. The system is designed to continuously maintain a specified building comfort level throughout the year under diverse environmental conditions. Simulations are done at different generator temperatures to investigate the performance in terms of total annual electric energy consumption, heating energy, and the coefficient of performance (COP). The performance of the present VACS is compared with the conventional compression-based system, which demonstrates the electric energy and cost saving potentials of the proposed VACS. Simulation outcomes are well-validated against benchmark data from national renewable energy laboratory and energy conservation building code. Interestingly, it is found that beyond a certain collector area, surplus energy savings can be acquired with the present triple-hybrid VACS as compared to the compression-based cooling. Results also show that COP of the simulated system is in line with experimental values available in the literature. Finally, recommendations are given to operate the complete system on solar and biomass resources, which provide encouraging opportunity for agriculture-based countries.