bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal Vibration Reduction of Flexible Rotor Systems by the Virtual Bearing Method
Authors: Liu Shibing , Yang Bingen
Published: October 2017

This paper presents a new approach to optimal bearing placement that minimizes the vibration amplitude of a flexible rotor system with a minimum number of bearings. The thrust of the effort is the introduction of a virtual bearing method (VBM), by which a minimum number of bearings can be automatically determined in a rotor design without trial and error. This unique method is useful in dealing with the issue of undetermined number of bearings. In the development, the VBM and a distributed transfer function method (DTFM) for closed-form analytical solutions are integrated to formulate an optimization problem of mixed continuous-and-integer type, in which bearing locations and bearing index numbers (BINs) (specially defined integer variables representing the sizes and properties of all available bearings) are selected as design variables. Solution of the optimization problem by a real-coded genetic algorithm yields an optimal design that satisfies all the rotor design requirements with a minimum number of bearings. Filling a technical gap in the literature, the proposed optimal bearing placement approach is applicable to either redesign of an existing rotor system for improvement of system performance or preliminary design of a new rotor system with the number of bearings to be installed being unforeknown.
Protonic Mobility of Neodymium Tungstate
Authors: Sadykov Vladislav A. , Bespalko Yulia N. , Pavlova Svetlana N. , Skriabin Pavel I. , Krasnov Alexey V. , Eremeev Nikita F. , Krieger Tamara A. , Sadovskaya Ekaterina M. , Belyaev Vladimir D. , Vinokurov Zakhar S.
Published: October 2017

This work aims at studying protonic transport of mixed proton–electron-conducting Nd5.5WO11.25-δ oxide synthesized by a citrate method as material for hydrogen separation membranes. Structure of samples was characterized by X-ray diffraction (XRD), and protonic mobility was studied using temperature-programmed desorption of H2O and isotope heteroexchange of the bulk protons with D2O as well as mass relaxation after an abrupt change of H2O partial pressure. The temperature range of Nd5.5WO11.25-δ efficient operation is 300–400 °C, where H+ tracer diffusion and chemical diffusion coefficients are ∼1 × 10−11 and ∼2 × 10−5 cm2/s, respectively, being comparable to or even better than those for similar systems. Hence, Nd5.5WO11.25-δ is a promising material for the design of hydrogen separation membranes.
Rotordynamic Stability Effects of Shrouded Centrifugal Impellers With Combined Whirl and Precession
Authors: Kim Eunseok , Palazzolo Alan
Published: October 2017

Whirling (translational) and precession (tilt) motion of the shrouded centrifugal impeller are possible vibration sources that can cause rotordynamic instability problems. Whirling motion of shrouded impellers and seals has been investigated by test and theory in the literature. However, there has been little study of the effects of coupled motion of whirling and precession of a centrifugal impeller on rotordynamic forces and moments using computational fluid dynamics (CFD). In the present study, the CFD approach for calculating the moment coefficients of the precessing impeller is developed and verified by comparison with the measured data for a precessing centrifugal compressor by Yoshida et al. (1996, “Measurement of the Flow in the Backshroud/Casing Clearance of a Precessing Centrifugal Impeller,” Sixth International Symposium on Transport Phenomena and Dynamics of Rotating Machinery, Honolulu, Hawaii, Vol. 2, pp. 151–160). A full set (4 × 4) of rotordynamic coefficient matrices is calculated, using two separate models of (a) a precessing impeller with a tilt angle and (b) a whirling impeller with dynamic eccentricity to investigate the stability of the impeller. Rotordynamic stability is evaluated by using the whirl frequency ratio of the coupled motion, obtained from the full rotordynamic coefficient matrices, to show that the precession motion has a significant impact on rotordynamic stability. A similar conclusion is reached based on the whirling plus precession response of a finite element (FE) structural rotordynamic model including the 4 × 4 rotordynamic coefficient matrices. A stability analysis using the rotordynamic coefficients indicates that the precession motion with the positive tilt angle increases the tendency toward destabilization of the rotor.
Specific Material Removal Rate Calculation in Five-Axis Grinding
Authors: Kountanya Raja , Guo Changsheng
Published: October 2017

Specific material removal rate (MRR) q′ was calculated for five-axis grinding in a virtual machining simulation environment (VMSE). The axis-symmetric tool rotational profile was arc-length parameterized. The twisted grazing curve due to the concurrent translation and rotation in every move was modeled through an exact velocity field and areal MRR density q″, positive in the front of the grazing curve on the tool surface. Variation of q′ and equivalent chip thickness h within the instantaneous engagement contour were deduced from q″. Illustrative results with a five-axis impeller blade finishing simulation are shown. The results were benchmarked against an average q′ calculated from the instantaneous MRR from the VMSE. As a function of time, maximum chip thickness hmax within the extents of contact along the tool profile in every move showed more isolated peaks than corresponding qmax′. Maximum cumulative material removed per unit length Qmax′ along the tool profile from all the moves was calculated to predict axial location of maximum risk of cutter degradation.  Qmax′ and hmax are useful metrics for tool path diagnosis and tool wear analysis.
The Reliability of a Component Under Several Distributed Cyclic Numbers at the Corresponding Constant Cyclic Stress Levels
Authors: Le Xiaobin
Published: October 2017

The probabilistic stress-number of cycles curve (P-S-N curve) approach is widely accepted for describing the fatigue strengths of materials. It is also a widely accepted fatigue theory for determining the reliability of a component under fatigue loadings. However, it is an unsolved issue in the P-S-N curve approach that the calculation of reliability of a component under several distributed cyclic numbers at the corresponding constant cyclic stress levels. Based on the commonly accepted concept of the equivalent fatigue damage, this paper proposes a new method to determine the reliability of the component under several distributed cyclic numbers at the corresponding constant cyclic stress levels. Four examples including two validation examples will be provided to demonstrate how to implement the proposed method for reliability calculation under such fatigue cyclic loading spectrum. The relative errors in validation examples are very small. So, the proposed method can be used to evaluate the reliability of a component under several distributed cyclic number at different stress levels.
Display Light Guide Swelling Due to Moisture Absorption
Authors: Cousins A. K. , Thiel G. H. , Wolak E. , Limaye G. , Tiku S.
Published: October 2017

Display light guides, commonly constructed of a polymer such as polymethyl methacrylate (PMMA), are known to be susceptible to moisture absorption, swelling, and warping in the field when exposed to elevated ambient humidity levels. This work presents a quantitative theoretical framework for calculating water absorption over time. In addition, a simple theory is laid out, which connects mass absorption of water to linear expansion of the polymer. Finally, a simple quantitative analysis of out-of-plane warping of the light guide is presented. Experimental data from laboratory PMMA coupons and two different sizes of large displays are used to establish the values of key parameters of the theoretical model. General purpose results for any size of PMMA display are presented. The approach can easily be adapted to light guides fabricated using other polymers.
Unsteady Flow and Pressure Pulsation Characteristics Analysis of Rotating Stall in Centrifugal Pumps Under Off-Design Conditions
Authors: Zhao Xiaoran , Xiao Yexiang , Wang Zhengwei , Luo Yongyao , Cao Lei
Published: October 2017

Unsteady flow phenomena like rotating stall frequently occur in centrifugal pumps under off-design conditions. Rotating stall could lead to flow instabilities and pressure pulsation, which affect the normal operation of pumps. The mechanism of rotating stall has not been sufficiently understood in previous researches. In this study, the impact of rotating stall in the impeller on centrifugal pump stability and pressure pulsation is numerically investigated. This paper aims to detect the unsteady flow characteristics inside the centrifugal pump by computational fluid dynamics technology, to analyze pressure pulsations caused by rotating stall and to explore the propagation mechanism of rotating stall. Unsteady numerical simulations are performed by ANSYS 16.0 to model the unsteady flow within the entire flow passage of a centrifugal pump under 0.4QBEP and 0.6QBEP working conditions. Through flow characteristics research, the generation and propagation of rotating stall are discovered. Flow separation appears near the leading edge of the pressure side and transforms into vortices, which move along the passage. Meanwhile, the stall cells rotate circumferentially in the impeller. Additionally, frequencies and amplitudes of pressure pulsations related to rotating stall are investigated by spectrum analysis. The results detect a possible characteristic frequency of rotating stall and show that the interaction between stall cells and the volute tongue could have an influence on rotor–stator interaction (RSI).
Nonlinear Lifting Line Theory Applied to Vertical Axis Wind Turbines: Development of a Practical Design Tool
Authors: Marten David , Pechlivanoglou Georgios , Navid Nayeri Christian , Oliver Paschereit Christian
Published: October 2017

Recently, a new interest in vertical axis wind turbine (VAWT) technology is fueled by research on floating support structures for large-scale offshore wind energy application. For the application on floating structures at multimegawatt size, the VAWT concept may offer distinct advantages over the conventional horizontal axis wind turbine (HAWT) design. As an example, VAWT turbines are better suited for upscaling, and at multimegawatt size, the problem of periodic fatigue cycles reduces significantly due to a very low rotational speed. Additionally, the possibility to store the transmission and electricity generation system at the bottom, compared to the tower top as in a HAWT, can lead to a considerable reduction of material logistics costs. However, as most VAWT research stalled in the mid 1990s, no sophisticated and established tools to investigate this concept further exist today. Due to the complex interaction between unsteady aerodynamics and movement of the floating structure, fully coupled simulation tools modeling both aero and structural dynamics are needed. A nonlinear lifting line free vortex wake (LLFVW) code was recently integrated into the open source wind turbine simulation suite qblade. This paper describes some of the necessary adaptions of the algorithm, which differentiates it from the usual application in HAWT simulations. A focus is set on achieving a high robustness and computational efficiency. A short validation study compares LLFVW results with those of a two-dimensional (2D) unsteady Reynolds-averaged Navier–Stokes (URANS) simulation.
Uncertainty Quantification of Leakages in a Multistage Simulation and Comparison With Experiments
Authors: Maria Mazzoni Cosimo , Ahlfeld Richard , Rosic Budimir , Montomoli Francesco
Published: October 2017

This paper presents a numerical study of the impact of tip gap uncertainties in a multistage turbine. It is well known that the rotor gap can change the gas turbine efficiency, but the impact of the random variation of the clearance height has not been investigated before. In this paper, the radial seals clearance of a datum shroud geometry, representative of steam turbine industrial practice, was systematically varied and numerically tested by means of unsteady computational fluid dynamics (CFD). By using a nonintrusive uncertainty quantification (UQ) simulation based on a sparse arbitrary moment-based approach, it is possible to predict the radial distribution of uncertainty in stagnation pressure and yaw angle at the exit of the turbine blades. This work shows that the impact of gap uncertainties propagates radially from the tip toward the hub of the turbine, and the complete span is affected by a variation of the rotor tip gap. This amplification of the uncertainty is mainly due to the low-aspect ratio of the turbine, and a similar behavior is expected in high pressure (HP) turbines.
Computational Analysis of Foil Air Journal Bearings Using a Runtime-Efficient Segmented Foil Model
Authors: Leister Tim , Baum Christoph , Seemann Wolfgang
Published: October 2017

This contribution is concerned with the development and the implementation of a foil air journal bearing model. For this purpose, the numerical procedure solving the Reynolds equation for compressible fluids has to be coupled to a compliant foil model. The presented beam-based approach is supposed to reproduce most of the experimentally known particularities in the mechanical behavior of the foil structure, while being at least as runtime-efficient as the commonly used simple elastic foundation model. The developed modeling approach will be validated by comparing simulation results to data found with a more complex reference model. In the analysis part, most notably, the top foil compliance is shown to deteriorate the load-carrying capacity of air bearings. Moreover, the influence of the top foil compliance on the dynamics of a rigid rotor supported by two foil air journal bearings will be discussed.
Rotordynamic Forces Acting on a Two-Stage Inducer
Authors: Nagao Naoki , Nagaura Katsuji , Tamura Tsutomu , Hasegawa Satoshi , Uchiumi Masaharu
Published: October 2017

Rocket turbopumps sometimes experience self-excited shaft vibration due to rotordynamic forces. To prevent this vibration, a key step is to establish a method to measure and evaluate the rotordynamic forces that act on turbopump components. In this study, we measured rotordynamic forces acting on a two-stage inducer using a rotordynamic test stand developed in 2012 at Kakuda Space Center. In noncavitating conditions, we did not observe strong nonlinearities in rotordynamic forces in the inducer at low flow rate conditions. The results of the pressure fluctuation on the inducer showed that rotordynamic forces were mainly excited in the second stage of the inducer. In cavitating conditions, we found that there is no strong nonlinearity between cavitating rotordynamic forces and the whirling frequency ratio in the inducer. These results show the robustness of the rotordynamic forces acting on the inducer against the flow rate and cavitation.
Analysis of Grinding Surface Creation by Single-Grit Approach
Authors: Chen X. , Öpöz T. T. , Oluwajobi A.
Published: October 2017

This paper presents some new research findings in the investigation of single-grit grinding in terms of surface creation. The investigation demonstrated that rubbing–plowing–cutting hypothesis of grinding material removal mechanism is valid in both experiments and simulations. A finite element model (FEM) was developed to simulate the material deformation during the grit interacts with the workpiece. It was found that the cutting mechanism is the more effective in the first half of the scratch where the grit penetrates the workpiece. The plowing is a prominent mechanism in the second half of the scratch where the grit is climbing up along the scratch path and uplifting the material at the front and the sides of it. This observation is very important to provide a greater insight into the difference between up-cut and down-cut grinding material removal mechanisms. Multipasses scratch simulations were performed to demonstrate the influence of plowing on the ground surface formation. Moreover, by analyzing the effects of grinding conditions, the shape of cutting edges, and friction in grinding zone on the grinding surface formation, some useful relations between grinding performance and controllable parameters have been identified. It has demonstrated that plowing has significant influences on ground surface formation and concluded that the influence of grit shape, friction, and grinding kinetic condition should be considered together for the plowing behavior control, which could provide a good guidance for the improvement of grinding efficiency.
Physics-Based Deformable Tire–Soil Interaction Model for Off-Road Mobility Simulation and Experimental Validation
Authors: Yamashita Hiroki , Jayakumar Paramsothy , Alsaleh Mustafa , Sugiyama Hiroyuki
Published: October 2017

A physics-based deformable tire–soil interaction simulation capability that can be fully integrated into the monolithic multibody dynamics computer algorithm is developed by extending a deformable tire model based on the flexible multibody dynamics approach to off-road mobility simulations with a moving soil patch technique and it is validated against test data. A locking-free nine-node brick element is developed for modeling large plastic soil deformation using the multiplicative finite strain plasticity theory along with the capped Drucker–Prager failure criterion. To identify soil parameters including cohesion and friction angle, the triaxial compression test is carried out, and the soil model developed is validated against the test data. In addition to the component level validation for the tire and soil models, the tire–soil interaction simulation capability developed in this study is validated against the soil bin mobility test results. The tire forces and rolling resistance coefficients predicted by the simulation model agree well with the test results. It is shown that effect of the wheel loads and tire inflation pressures is well captured in the simulation model. Furthermore, it is demonstrated that the moving soil patch technique, with which soil behavior only in the vicinity of the rolling tire is solved to reduce the soil model dimensionality, leads to a significant reduction in computational time, thereby enabling use of the high-fidelity physics-based tire–soil interaction model in the large-scale off-road mobility simulation.
Effect of Internal Crossflow Velocity on Film Cooling Effectiveness—Part II: Compound Angle Shaped Holes
Authors: McClintic John W. , Anderson Joshua B. , Bogard David G. , Dyson Thomas E. , Webster Zachary D.
Published: October 2017

In gas turbine engines, film cooling holes are commonly fed with an internal crossflow, the magnitude of which has been shown to have a notable effect on film cooling effectiveness. In Part I of this study, as well as in a few previous studies, the magnitude of internal crossflow velocity was shown to have a substantial effect on film cooling effectiveness of axial shaped holes. There is, however, almost no data available in the literature that shows how internal crossflow affects compound angle shaped film cooling holes. In Part II, film cooling effectiveness, heat transfer coefficient augmentation, and discharge coefficients were measured for a single row of compound angle shaped film cooling holes fed by internal crossflow flowing both in-line and counter to the spanwise direction of coolant injection. The crossflow-to-mainstream velocity ratio was varied from 0.2 to 0.6 and the injection velocity ratio was varied from 0.2 to 1.7. It was found that increasing the magnitude of the crossflow velocity generally caused degradation of the film cooling effectiveness, especially for in-line crossflow. An analysis of jet characteristic parameters demonstrated the importance of crossflow effects relative to the effect of varying the film cooling injection rate. Heat transfer coefficient augmentation was found to be primarily dependent on injection rate, although for in-line crossflow, increasing crossflow velocity significantly increased augmentation for certain conditions.
Time-Domain Modeling of Varying Dynamic Characteristics in Thin-Wall Machining Using Perturbation and Reduced-Order Substructuring Methods
Authors: Tuysuz Oguzhan , Altintas Yusuf
Published: October 2017

The dynamic response of thin-walled parts becomes time and tool position dependent due to material removal along the toolpath. This article proposes a new reduced-order workpiece dynamic parameters update model using substructuring and perturbation methods. The removed volumes between discrete locations along the toolpath are defined as substructures of the initial global workpiece. The dynamically reduced-order initial workpiece structure and the removed substructures are obtained with model order reduction techniques. Equations of motion of the workpiece are updated in time-domain by rigidly coupling fictitious substructures having the negative mass and stiffness of the removed material. Instead of solving the generalized eigenvalue problem repeatedly along the toolpath, the mode shapes of the in-process workpiece are perturbed using the mass and stiffness of the removed substructures. Convergence of the perturbation is improved by integrating a vector sequence convergence accelerating algorithm. The corresponding updated mode frequencies are evaluated using Rayleigh Quotient with the perturbed mode shapes. The proposed reduced-order time-domain dynamics update model is verified in five-axis ball-end milling tests on a thin-walled twisted fan blade, and its predictions are also compared against the authors’ previously developed frequency-domain reduced-order model. It is shown that the newly introduced model is ∼4 times more computationally efficient than the frequency-domain model.
Cloud-Based Parallel Machine Learning for Tool Wear Prediction
Authors: Wu Dazhong , Jennings Connor , Terpenny Janis , Kumara Soundar , Gao Robert X.
Published: October 2017

The emergence of cloud computing, industrial internet of things (IIoT), and new machine learning techniques have shown the potential to advance prognostics and health management (PHM) in smart manufacturing. While model-based PHM techniques provide insight into the progression of faults in mechanical components, certain assumptions on the underlying physical mechanisms for fault development are required to develop predictive models. In situations where there is a lack of adequate prior knowledge of the underlying physics, data-driven PHM techniques have been increasingly applied in the field of smart manufacturing. One of the limitations of current data-driven methods is that large volumes of training data are required to make accurate predictions. Consequently, computational efficiency remains a primary challenge, especially when large volumes of sensor-generated data need to be processed in real-time applications. The objective of this research is to introduce a cloud-based parallel machine learning algorithm that is capable of training large-scale predictive models more efficiently. The random forests (RFs) algorithm is parallelized using the MapReduce data processing scheme. The MapReduce-based parallel random forests (PRFs) algorithm is implemented on a scalable cloud computing system with varying combinations of processors and memories. The effectiveness of this new method is demonstrated using condition monitoring data collected from milling experiments. By implementing RFs in parallel on the cloud, a significant increase in the processing speed (14.7 times in terms of increase in training time) has been achieved, with a high prediction accuracy of tool wear (eight times in terms of reduction in mean squared error (MSE)).
Improved Spectral Absorption Coefficient Grouping Strategies in Radiation Heat Transfer Calculations for H2O–CO2-Soot Mixtures
Authors: Zhou Yue , Wang Qiang , Hu Haiyang
Published: October 2017

In the present work, strategies for the grouping of the spectral absorption coefficients used in multiscale (MS) multigroup (MG) full-spectrum k-distribution models were improved by considering the effects of variations in both temperature and species molar ratio on the correlated-k characteristics of the spectra of H2O–CO2-soot mixtures. The improvements in the accuracy of predictions of radiation heat transfer characteristics resulting from these new grouping strategies were evaluated using a series of semi-one-dimensional (1D) cases with significant temperature, participating species molar ratio, and pressure inhomogeneities. Finally, evaluations of grouping strategies were presented on calculation of the full-spectrum thermal images of an actual aeroengine combustor.
Quantifying the Shape of Pareto Fronts During Multi-Objective Trade Space Exploration
Authors: Unal Mehmet , Warn Gordon P. , Simpson Timothy W.
Published: October 2017

Recent advances in simulation and computation capabilities have enabled designers to model increasingly complex engineering problems, taking into account many dimensions, or objectives, in the problem formulation. Increasing the dimensionality often results in a large trade space, where decision-makers (DM) must identify and negotiate conflicting objectives to select the best designs. Trade space exploration often involves the projection of nondominated solutions, that is, the Pareto front, onto two-objective trade spaces to help identify and negotiate tradeoffs between conflicting objectives. However, as the number of objectives increases, an exhaustive exploration of all of the two-dimensional (2D) Pareto fronts can be inefficient due to a combinatorial increase in objective pairs. Recently, an index was introduced to quantify the shape of a Pareto front without having to visualize the solution set. In this paper, a formal derivation of the Pareto Shape Index is presented and used to support multi-objective trade space exploration. Two approaches for trade space exploration are presented and their advantages are discussed, specifically: (1) using the Pareto shape index for weighting objectives and (2) using the Pareto shape index to rank objective pairs for visualization. By applying the two approaches to two multi-objective problems, the efficiency of using the Pareto shape index for weighting objectives to identify solutions is demonstrated. We also show that using the index to rank objective pairs provides DM with the flexibility to form preferences throughout the process without closely investigating all objective pairs. The limitations and future work are also discussed.
Controllability Ellipsoid to Evaluate the Performance of Mobile Manipulators for Manufacturing Tasks
Authors: Canfield Stephen L. , Nkhumise Reabetswe M.
Published: October 2017

This paper develops an approach to evaluate a state-space controller design for mobile manipulators using a geometric representation of the system response in tool space. The method evaluates the robot system dynamics with a control scheme and the resulting response is called the controllability ellipsoid (CE), a tool space representation of the system’s motion response given a unit input. The CE can be compared with a corresponding geometric representation of the required motion task (called the motion polyhedron) and evaluated using a quantitative measure of the degree to which the task is satisfied. The traditional control design approach views the system response in the time domain. Alternatively, the proposed CE views the system response in the domain of the input variables. In order to complete the task, the CE must fully contain the motion polyhedron. The optimal robot arrangement would minimize the total area of the CE while fully containing the motion polyhedron. This is comparable to minimizing the power requirements of robot design when applying a uniform scale to all inputs. It will be shown that changing the control parameters changes the eccentricity and orientation of the CE, implying a preferred set of control parameters to minimize the design motor power. When viewed in the time domain, the control parameters can be selected to achieve desired stability and time response. When coupled with existing control design methods, the CE approach can yield robot designs that are stable, responsive, and minimize the input power requirements.
Design and Evaluation of a Robotic Device for Automated Tail Vein Cannulations in Rodent Models
Authors: Fromholtz Alex , Balter Max L. , Chen Alvin I. , Leipheimer Josh M. , Shrirao Anil , Maguire Timothy J. , Yarmush Martin L.
Published: October 2017

Preclinical testing in rodent models is a ubiquitous part of modern biomedical research and commonly involves accessing the venous bloodstream for blood sampling and drug delivery. Manual tail vein cannulation is a time-consuming process and requires significant skill and training, particularly since improperly inserted needles can affect the experimental results and study outcomes. In this paper, we present a miniaturized, robotic medical device for automated, image-guided tail vein cannulations in rodent models. The device is composed of an actuated three degrees-of-freedom (DOFs) needle manipulator, three-dimensional (3D) near-infrared (NIR) stereo cameras, and an animal holding platform. Evaluating the system through a series of workspace simulations and free-space positioning tests, the device exhibited a sufficient work volume for the needle insertion task and submillimeter accuracy over the calibration targets. The results indicate that the device is capable of cannulating tail veins in rodent models as small as 0.3 mm in diameter, the smallest diameter vein required to target.
Experimental Investigation on Buckling of Ellipsoidal Head of Steel Nuclear Containment
Authors: Li Keming , Zheng Jinyang , Zhang Zekun , Gu Chaohua , Zhang Xiaoping , Liu Shenghua , Ge Honghui , Gu Caisheng , Lin Guanghua
Published: October 2017

A containment of a nuclear power plant is a final barrier against the release of radioactive materials and withstands internal pressure due to an accident. Buckling is a critical failure mode of an ellipsoidal head of steel containment vessel under internal pressure. First, a vessel was designed to measure buckling pressure and shape of the ellipsoidal head. Second, an experiment was successfully performed on an ellipsoidal head which has a diameter of 4797 mm, a radius-to-height ratio of 1.728, and a thickness of 5.5 mm. The initial shape and deformations of the ellipsoidal head were measured by using three-dimensional (3D) laser scanners. The detailed buckling characteristics including shapes, deformations, strains of buckles, and buckling pressures were obtained. Finally, initial buckling pressures were predicted by nonlinear finite element analysis considering the initial measured and the initial perfect shapes of the ellipsoidal head, respectively. The agreement between the initial experimental buckling pressure and that predicted by the analysis considering the initial measured shape is good.
Design of an Open-Source Binary Micromultileaf Collimator for a Small Animal Microradiotherapy System
Authors: Prajapati Surendra , Cox Benjamin , Swader Robert , Petry George , Eliceiri Kevin W. , Jeraj Robert , Mackie Thomas R.
Published: October 2017

Intensity modulated radiation therapy (IMRT) is performed on a regular basis in the clinic to create complex radiation fields to treat cancer, but it has not been implemented in microradiotherapy (mRT) for preclinical systems. A multileaf collimator (MLC) is an integral part of a radiotherapy system that allows IMRT application. Presented here is the development of a key component of an open source mRT system for preclinical research. We have designed and fabricated a binary micro multileaf collimator (bmMLC) for mRT that can provide 1 mm or better resolution at isocenter and attenuate over 98% of a 250 kVp X-ray beam. This is the smallest collimator system designed for RT systems, with 20 brass leaves, each 0.5 mm thick, creating a physical field opening of 1 cm × 1 cm. The mode of actuation for the leaves was rotational, rather than linear, which is typical in larger clinical RT systems. The design presented here met the identified design requirements and represents a rigorous design process, during which several less successful designs were investigated and eventually discarded. After the fabrication of the design, dosimetric characteristics were tested and requirements were met. The final bmMLC designs and technical documents are made available as open-source.
Effect of Phosphate Additive for Thermal Stability in a Vanadium Redox Flow Battery
Authors: Yeon Sun-Hwa , So Jae Young , Yun Jin Hee , Park Se-Kook , Shin Kyoung-Hee , Jin Chang-Soo , Lee Yun Jung
Published: October 2017

Organic/inorganic materials are investigated as additives to improve the stability of a vanadium electrolyte for a vanadium redox flow battery (VRFB) at operating temperatures of 25 °C and 40 °C. Among these materials, the most effective additive is chosen based on the thermal stability and electrochemical performance with a long inhibition time. Through precipitation time and electrochemical measurements, the results show that the best inhibition effect is achieved by adding sodium pyrophosphate dibasic (SPD, H2Na2O7P2) as an additive at a considerably high H2SO4 concentration (3M) electrolyte, indicating an improved redox reversibility and electrochemical activity. Nonflow cell assembled with the SPD additive exhibits larger discharge capacity retentions of 40% than a blank solution with the retentions of 2% at 600 cycles at 40 °C. In the case of flow cell, the capacity retention on the SPD additive shows 55.4%, which is 5.3% higher than the blank solution at 40 °C and 180 cycles. The morphology of the precipitation is investigated by SEM, which exhibits more severe V2O5 precipitation amount on the carbon felt electrode used in the blank electrolyte at 40 °C, which causes larger capacity losses compared to cells assembled with the SPD additive electrolyte.
Control-Oriented Methods for Turbomachinery Noise Simulation
Authors: Lau Alex Siu Hong , Zhong Siyang , Huang Xun
Published: October 2017

This paper presents an innovative stability analysis and design approach for time-domain impedance boundary conditions to simulate noise propagation and radiation from a lined turbomachinery duct in the presence of a mean flow. A control-oriented model is developed for the stability analysis of the impedance boundary condition by using generalized function at the lining surface. The mean flow effect and sound propagation are considered in the model as well. Then, the numerical stability issue is analyzed by using the Bode plots before stabilized accordingly by employing the phase lead compensator method, which results in a rational transfer function. Finally, the corresponding time-domain implementation is achieved by using the so-called controllable canonical form rather than an inconvenient convolution operation. The performance of the current proposed approach is first validated in an in-duct propagation case by comparing to analytical solutions obtained by employing the Wiener–Hopf method and then demonstrated in a couple of duct acoustic problems with representative turbomachinery setups. The innovative cross-disciplinary nature of the current proposed approach can shed light on impedance problems and is very useful to time-domain acoustic simulations for turbomachinery applications.
Investigation of Flame Structure and Soot Formation in a Single Sector Model Combustor Using Experiments and Numerical Simulations Based on the Large Eddy Simulation/Conditional Moment Closure Approach
Authors: Giusti Andrea , Mastorakos Epaminondas , Hassa Christoph , Heinze Johannes , Magens Eggert , Zedda Marco
Published: October 2017

In this work, a single sector lean burn model combustor operating in pilot only mode has been investigated using both experiments and computations with the main objective of analyzing the flame structure and soot formation at conditions relevant to aero-engine applications. Numerical simulations were performed using the large eddy simulation (LES) approach and the conditional moment closure (CMC) combustion model with detailed chemistry and a two-equation model for soot. The CMC model is based on the time-resolved solution of the local flame structure and allows to directly take into account the phenomena associated to molecular mixing and turbulent transport, which are of great importance for the prediction of emissions. The rig investigated in this work, called big optical single sector rig, allows to test real scale lean burn injectors. Experiments, performed at elevated pressure and temperature, corresponding to engine conditions at part load, include planar laser-induced fluorescence of OH (OH-PLIF) and phase Doppler anemometry (PDA) and have been complemented with new laser-induced incandescence (LII) measurements for soot location. The wide range of measurements available allows a comprehensive analysis of the primary combustion region and can be exploited to further assess and validate the LES/CMC approach to capture the flame behavior at engine conditions. It is shown that the LES/CMC approach is able to predict the main characteristics of the flame with a good agreement with the experiment in terms of flame shape, spray characteristics and soot location. Finite-rate chemistry effects appear to be very important in the region close to the injection location leading to the lift-off of the flame. Low levels of soot are observed immediately downstream of the injector exit, where a high amount of vaporized fuel is still present. Further downstream, the fuel vapor disappears quite quickly and an extended region characterized by the presence of pyrolysis products and soot precursors is observed. The strong production of soot precursors together with high soot surface growth rates lead to high values of soot volume fraction in locations consistent with the experiment. Soot oxidation is also very important in the downstream region resulting in a decrease of the soot level at the combustor exit. The results show a very promising capability of the LES/CMC approach to capture the main characteristics of the flame, soot formation, and location at engine relevant conditions. More advanced soot models will be considered in future work in order to improve the quantitative prediction of the soot level.
Prediction of Combustion Noise in a Model Combustor Using a Network Model and a LNSE Approach
Authors: Ullrich Wolfram C. , Mahmoudi Yasser , Lackhove Kilian , Fischer André , Hirsch Christoph , Sattelmayer Thomas , Dowling Ann P. , Swaminathan Nedunchezhian , Sadiki Amsini , Staufer Max
Published: October 2017

The reduction of pollution and noise emissions of modern aero engines represents a key concept to meet the requirements of the future air traffic. This requires an improvement in the understanding of combustion noise and its sources, as well as the development of accurate predictive tools. This is the major goal of the current study where the low-order thermo-acoustic network (LOTAN) solver and a hybrid computational fluid dynamics/computational aeroacoustics approach are applied on a generic premixed and pressurized combustor to evaluate their capabilities for combustion noise predictions. LOTAN solves the linearized Euler equations (LEE) whereas the hybrid approach consists of Reynolds-averaged Navier–Stokes (RANS) mean flow and frequency-domain simulations based on linearized Navier–Stokes equations (LNSE). Both solvers are fed in turn by three different combustion noise source terms which are obtained from the application of a statistical noise model on the RANS simulations and a post-processing of incompressible and compressible large eddy simulations (LES). In this way, the influence of the source model and acoustic solver is identified. The numerical results are compared with experimental data. In general, good agreement with the experiment is found for both the LOTAN and LNSE solvers. The LES source models deliver better results than the statistical noise model with respect to the amplitude and shape of the heat release spectrum. Beyond this, it is demonstrated that the phase relation of the source term does not affect the noise spectrum. Finally, a second simulation based on the inhomogeneous Helmholtz equation indicates the minor importance of the aerodynamic mean flow on the broadband noise spectrum.
Ball Grid Array Interconnection Properties of Solderable Polymer–Solder Composites With Low-Melting-Point Alloy Fillers
Authors: Yim Byung-Seung , Shin Young-Eui , Kim Jong-Min
Published: October 2017

In this work, a novel ball grid array (BGA) interconnection process has been developed using solderable polymer–solder composites (SPCs) with low-melting-point alloy (LMPA) fillers to enhance the processability of the conventional capillary underfill technique and to overcome the limitations of the no-flow underfill technique. To confirm the feasibility of the proposed technique, a BGA interconnection test was performed using four types of SPCs with a different LMPA concentration (from 0 to 5 vol %). After the BGA interconnection process, the interconnection characteristics, such as morphology of conduction path and electrical properties of the BGA assemblies, were inspected and compared. The results indicated that BGA assemblies using SPC without LMPA fillers showed weak conduction path formation, including open circuit (solder bump loss) or short circuit formation because of the expansion of air voids within the interconnection area due to the relatively high reflow peak temperature. Meanwhile, assemblies using SPC with 3 vol % LMPAs showed stable metallurgical interconnection formation and electrical resistance due to the relatively low-reflow peak temperature and favorable selective wetting behavior of molten LMPAs for the solder bumps and Cu metallizations.
Free Vibration Analysis of Functionally Graded Plates on Two-Parameter Elastic Supports and in Contact With Stationary Fluid
Authors: Shahbaztabar Arash , Ranji Ahmad Rahbar
Published: October 2017

Free vibration analysis of functionally graded (FG) rectangular plates on two-parameter elastic foundation and vertically coupled with fluid is the objective of this work. The fluid domain is considered to be infinite in length, but it is bounded in depth and width directions, and the effects of hydrostatic pressure and free surface waves are not taken into account. The mechanical properties of the FG plates are assumed to vary continuously through the thickness direction according to a power-law distribution of the volume fraction of the constituents. The accuracy and applicability of the formulation is illustrated by comparison studies with those reported in the open literature. At the end, parametric studies are carried out to examine the impact of different parameters on the natural frequencies.
Lateral Earth Pressure Coefficient of Soils Subjected to Freeze–Thaw
Authors: Zhao Xiaodong , Zhou Guoqing , Wang Bo , Jiao Wei , Yu Jing
Published: October 2017

Artificial frozen soils (AFS) have been used widely as temporary retaining walls in strata with soft and water-saturated soil deposits. After excavations, frozen soils thaw, and the lateral earth pressure penetrates through the soils subjected to freeze–thaw, and acts on man-made facilities. Therefore, it is important to investigate the lateral pressure (coefficient) responses of soils subjected to freeze–thaw to perform structure calculations and stability assessments of man-made facilities. A cubical testing apparatus was developed, and tests were performed on susceptible soils under conditions of freezing to a stable thermal gradient and then thawing with a uniform temperature (Fnonuni–Tuni). The experimental results indicated a lack of notable anisotropy for the maximum lateral preconsolidated pressures induced by the specimen’s compaction and freeze–thaw. However, the freeze–thaw led to a decrement of lateral earth pressure coefficient  K0, and  K0 decrement under the horizontal Fnonuni–Tuni was greater than that under the vertical Fnonuni–Tuni. The measured  K0 for normally consolidated and over-consolidated soil specimens exhibited anisotropic characteristics under the vertical Fnonuni–Tuni and horizontal Fnonuni–Tuni treatments. The anisotropies of  K0 under the horizontal Fnonuni–Tuni were greater than that under the vertical Fnonuni–Tuni, and the anisotropies were more noticeable in the unloading path than that in the loading path. These observations have potential significances to the economical and practical design of permanent retaining walls in soft and water-saturated soil deposits.
Complexification-Averaging Analysis on a Giant Magnetostrictive Harvester Integrated With a Nonlinear Energy Sink
Authors: Fang Zhi-Wei , Zhang Ye-Wei , Li Xiang , Ding Hu , Chen Li-Qun
Published: October 2017

The present study aims to investigate the steady-state response regimes of a device comprising a nonlinear energy sink (NES) and a giant magnetostrictive energy harvester utilizing analytical approximation. The complexification-averaging (CX-A) technique is generalized to systems defined by differential algebraic equations (DAEs). The amplitude-frequency responses are compared with numerical simulations for validation purposes. The tensile and compressive stresses of giant magnetostrictive material (GMM) are checked to ensure that the material functions properly. The energy harvested is calculated and the comparison of transmissibility of the apparatus with and without NES–GMM is exhibited to reveal the performance of vibration mitigation. Then, the stability and bifurcations are examined. The outcome demonstrates that the steady-state periodic solutions of the system undergo saddle-node (SN) bifurcation at a certain set of parameters. In the meantime, no Hopf bifurcation is observed. The introduction of NES and GMM for vibration reduction and energy harvesting brings about geometric nonlinearity and material nonlinearity. By computing both the responses of the primary system equipped with the NES only and the NES–GMM, it is indicated that the added GMM can dramatically modify the steady-state dynamics. A further optimization with respect to the cubic stiffness, the damper of NES, and the amplitude of excitation is conducted, respectively. The boundary where the giant magnetostrictive energy harvester is out of work is pointed out as well during the process of optimizing.
The Use of Damping Based Semi-Active Control Algorithms in the Mechanical Smart-Spring System
Authors: Gustavo Rocha Vieira Wander , Nitzsche Fred , De Marqui Carlos
Published: October 2017

In recent decades, semi-active control strategies have been investigated for vibration reduction. In general, these techniques provide enhanced control performance when compared to traditional passive techniques and lower energy consumption if compared to active control techniques. In semi-active concepts, vibration attenuation is achieved by modulating inertial, stiffness, or damping properties of a dynamic system. The smart spring is a mechanical device originally employed for the effective modulation of its stiffness through the use of semi-active control strategies. This device has been successfully tested to damp aeroelastic oscillations of fixed and rotary wings. In this paper, the modeling of the smart spring mechanism is presented and two semi-active control algorithms are employed to promote vibration reduction through enhanced damping effects. The first control technique is the smart-spring resetting (SSR), which resembles resetting control techniques developed for vibration reduction of civil structures as well as the piezoelectric synchronized switch damping on short (SSDS) technique. The second control algorithm is referred to as the smart-spring inversion (SSI), which presents some similarities with the synchronized switch damping (SSD) on inductor technique previously presented in the literature of electromechanically coupled systems. The effects of the SSR and SSI control algorithms on the free and forced responses of the smart-spring are investigated in time and frequency domains. An energy flow analysis is also presented in order to explain the enhanced damping behavior when the SSI control algorithm is employed.