bluuebunny/crossref_metadata_2025 huggingface dataset:
Bubble Motion in a Converging–Diverging Channel
Authors: Konda Harsha , Kumar Tripathi Manoj , Chandra Sahu Kirti
Published: December 2015

The migration of a bubble inside a two-dimensional converging–diverging channel is investigated numerically. A parametric study is conducted to investigate the effects of the Reynolds and Weber numbers and the amplitude of the converging–diverging channel. It is found that increasing the Reynolds number and the amplitude of the channel increases the oscillation of the bubble and promotes the migration of the bubble toward one of the channel wall. The bubble undergoes oblate–prolate deformation periodically at the early times, which becomes chaotic at the later times. This phenomenon is a culmination of the bubble path instability as well as the Segré–Silberberg effect.
Gate Design in Injection Molding of Microfluidic Components Using Process Simulations
Authors: Marhöfer David Maximilian , Tosello Guido , Islam Aminul , Hansen Hans Nørgaard
Published: December 2015

Just as in conventional injection molding of plastics, process simulations are an effective and interesting tool in the area of micro-injection molding. They can be applied in order to optimize and assist the design of the microplastic part, the mold, and the actual process. Available simulation software is however actually made for macroscopic injection molding. By means of the correct implementation and careful modeling strategy though, it can also be applied to microplastic parts, as it is shown in the present work. Process simulations were applied to two microfluidic devices (a microfluidic distributor and a mixer). The paper describes how the two devices were meshed in the simulations software to obtain a proper simulation model and where the challenges arose. One of the main goals of the simulations was the investigation of the filling of the parts. Great emphasis was also on the optimization of selected gate designs for both plastic parts. Subsequently, the simulation results were used to answer the question which gate design was the most appropriate with regard to the process window, polymer flow, and part quality. This finally led to an optimization of the design and the realization of this design in practice as actual steel mold. Additionally, the simulation results were critically discussed and possible improvements and limitations of the gained results and the deployed software were described. Ultimately, the simulation results were validated by cross-checking the flow front behavior of the polymer flow predicted by the simulation with the actual flow front at different time steps. These were realized by molding short shots with the realized molds and were compared to the simulations at the global, i.e., part level and at the local, i.e. feature level.
Model Predictive Control of Offshore Power Stations With Waste Heat Recovery
Authors: Pierobon Leonardo , Chan Richard , Li Xiangan , Iyengar Krishna , Haglind Fredrik , Ydstie Erik
Published: December 2015

The implementation of waste heat recovery units on oil and gas offshore platforms demands advances in both design methods and control systems. Model-based control algorithms can play an important role in the operation of offshore power stations. A novel regulator based on a linear model predictive control (MPC) coupled with a steady-state performance optimizer has been developed in the simulink language and is documented in the paper. The test case is the regulation of a power system serving an oil and gas platform in the Norwegian Sea. One of the three gas turbines is combined with an organic Rankine cycle (ORC) turbogenerator to increase the energy conversion efficiency. Results show a potential reduction of frequency drop up to 40% for a step in the load set-point of 4 MW, compared to proportional–integral control systems. Fuel savings in the range of 2–3% are also expected by optimizing on-the-fly the thermal efficiency of the plant.
Modeling the Creep of Hastelloy X and the Fatigue of 304 Stainless Steel Using the Miller and Walker Unified Viscoplastic Constitutive Models
Authors: Varela Luis A. , Stewart Calvin M.
Published: December 2015

Hastelloy X (HX) and 304 stainless steel (304SS) are widely used in the pressure vessel and piping industries, specifically in nuclear and chemical reactors, pipe, and valve applications. Both alloys are favored for their resistance to extreme environments, although the materials exhibit a rate-dependent mechanical behavior. Numerous unified viscoplastic models proposed in literature claim to have the ability to describe the inelastic behavior of these alloys subjected to a variety of boundary conditions; however, typically limited experimental data are used to validate these claims. In this paper, two unified viscoplastic models (Miller and Walker) are experimentally validated for HX subjected to creep and 304SS subjected to strain-controlled low cycle fatigue (LCF). Both constitutive models are coded into ansys Mechanical as user-programmable features. Creep and fatigue behavior are simulated at a broad range of stress levels. The results are compared to an exhaustive database of experimental data to fully validate the capabilities and performance of these models. Material constants are calculated using the recently developed Material Constant Heuristic Optimizer (macho) software. This software uses the simulated annealing algorithm to determine the optimal material constants through the comparison of simulations to a database of experimental data. A qualitative and quantitative discussion is presented to determine the most suitable model to predict the behavior of HX and 304SS.
Influences of Specimen Size and Temperature on Viscoelastic Tensile Properties of SU-8 Photoresist Films
Authors: Namazu Takahiro , Takio Kenichi , Inoue Shozo
Published: December 2015

In this paper, the influences of specimen size and test temperature on the viscoelastic properties of SU-8 photoresist films are described. Films with the thicknesses of 1 μm and 10 μm are subjected to quasi-static uniaxial tensile tests and stress relaxation tests at temperatures ranging from 293 K to 473 K. The average glassy modulus at 293 K is 3.2 GPa, which decreases with an increase in the test temperature irrespective of specimen size. The mean fracture strain depends on film thickness as well as temperature. The fracture strain of the 1-μm thick films is approximately half of that of the 10-μm thick films at each temperature. Stress relaxation tests are conducted for constructing the master curves of the relaxation moduli. There is no apparent thickness dependence on the master curve. Above glass transition temperature, Tg, apparent activation energies for the two films are almost identical, whereas the activation energy for the thinner films is smaller than that for the thicker films below Tg. This size effect is discussed using Fourier transform infrared spectroscopy (FTIR).
Electromagnetic Embossing of Optical Microstructures
Authors: Langstädtler Lasse , Schönemann Lars , Schenck Christian , Kuhfuss Bernd
Published: December 2015

Electromagnetic forming (EMF) is a high-speed forming process that is already established in the macroworld. Due to its advantages like high deformation rate and cheaper tools, it is introduced to microforming. In this research, the replication of prismatic optical microstructures is investigated. EN AW-1050A (Al99.5) micrometal sheets with a thickness of 50 μm and 300 μm are electromagnetically micro-embossed. With this technique, it is possible to successfully replicate triangular cross section micro V-grooves of 86.6 μm in width and 24.1 μm in depth with an average surface roughness of Sa = 44 nm. The microstructures of the embossing tool are generated by diamond micro chiseling (DMC), a novel machining process to produce microstructures with discontinuous geometry, like miniature cube corner retro reflectors and V-grooves with well-defined endings.
A New Process Combining Micro-Electro-Discharge-Machining Milling and Sinking for Fast Fabrication of Microchannels With Draft Angle
Authors: Modica Francesco , Basile Vito , Marrocco Valeria , Fassi Irene
Published: December 2015

A comparison of the machining performance of micro-electro-discharge machining (EDM) milling and sinking is proposed considering the fabrication of microchannels with controlled sloped walls realized in a hardened steel workpiece. Adopting the fine-finishing machining regime for both micro-EDM techniques, the experimental results show that micro-EDM sinking is about ten times faster than milling in the worst case, though a lack of accuracy in the final microfeatures in the former case is detected due to not compensated tool wear. On the contrary, micro-EDM milling provides a better control of the microchannel dimensions. Finally, a microfilter mold for medical applications is machined in order to show the potential of the combination of both technologies.
Comparisons of Tribological and Vibration Behaviors of Textured Point Contacts of Bearing Steel Lubricated With Oil and Grease Under Starved Conditions
Authors: Sudeep U. , Tandon N. , Pandey R. K.
Published: December 2015

Friction, wear, and vibration behaviors of oil-and grease-lubricated laser textured point contacts formed between AISI 52100 steel surfaces have been experimentally investigated under the unidirectional sliding motion using a ball-on-disk configuration. The performance behaviors of lubricated concentrated contacts formed between the lapped disk/lapped ball and textured disk/lapped ball have been compared at two Hertzian pressures (0.4 GPa and 0.7 GPa) and two sliding speeds (0.8 m/s and 2.4 m/s) using lubricating oil and grease. For the geometric configuration of point contacts adopted in the investigations, the textured point contacts lubricated with grease yielded reductions in the friction coefficient and specific wear rate (SWR) of the balls as compared to the oil-lubricated textured contacts. Moreover, reduction in the amplitudes of vibrations (at normal contact resonance frequencies) has also been observed with the grease-lubricated textured point contacts in comparison to the corresponding oil-lubricated cases.
Aerothermal Investigation of a Single Row Divergent Narrow Impingement Channel by Particle Image Velocimetry and Liquid Crystal Thermography
Authors: Terzis Alexandros , Skourides Christoforos , Ott Peter , von Wolfersdorf Jens , Weigand Bernhard
Published: December 2015

Integrally cast turbine airfoils with wall-integrated cooling cavities are greatly applicable in modern turbines providing enhanced heat exchange capabilities compared to conventional cooling passages. In such arrangements, narrow impingement channels can be formed where the generated crossflow is an important design parameter for the achievement of the desired cooling efficiency. In this study, a regulation of the generated crossflow for a narrow impingement channel consisting of a single row of five inline jets is obtained by varying the width of the channel in the streamwise direction. A divergent impingement channel is therefore investigated and compared to a uniform channel of the same open area ratio. Flow field and wall heat transfer experiments are carried out at engine representative Reynolds numbers using particle image velocimetry (PIV) and liquid crystal thermography (LCT). The PIV measurements are taken at planes normal to the target wall along the centerline for each individual jet, providing quantitative flow visualization of jet and crossflow interactions. The heat transfer distributions on the target plate of the channels are evaluated with transient techniques and a multilayer of liquid crystals (LCs). Effects of channel divergence are investigated combining both the heat transfer and flow field measurements. The applicability of existing heat transfer correlations for uniform jet arrays to divergent geometries is also discussed.
Weakly Nonlinear Oscillatory Convection in a Rotating Fluid Layer Under Temperature Modulation
Authors: Kiran Palle , Bhadauria B. S.
Published: December 2015

A study of thermal instability driven by buoyancy force is carried out in an initially quiescent infinitely extended horizontal rotating fluid layer. The temperature at the boundaries has been taken to be time-periodic, governed by the sinusoidal function. A weakly nonlinear stability analysis has been performed for the oscillatory mode of convection, and heat transport in terms of the Nusselt number, which is governed by the complex form of Ginzburg–Landau equation (CGLE), is calculated. The influence of external controlling parameters such as amplitude and frequency of modulation on heat transfer has been investigated. The dual effect of rotation on the system for the oscillatory mode of convection is found either to stabilize or destabilize the system. The study establishes that heat transport can be controlled effectively by a mechanism that is external to the system. Further, the bifurcation analysis also presented and established that CGLE possesses the supercritical bifurcation.
A Review on Graphical Methods for Modeling a Proton Exchange Membrane Fuel Cell
Authors: Bressel Mathieu , Ould Bouamama Belkacem , Hissel Daniel , Hilairet Mickael
Published: December 2015

Fuel cell systems represent a promising alternative energy converter. In the past years, researches have been conducted for their modeling, control, and diagnosis. The model should accurately reproduce the behavior without being too complex. Due to the highly multiphysical interactions and coupling within the fuel cell, using a graphical representation for developing this model seems well suited. This paper presents a review of recent literature on graphical representation of proton exchange membrane fuel cell (PEMFC). Three main graphical representations are discussed: bond graph (BG), EMR, and equivalent electrical circuit. Their fields of application will be shown as well.
Sensor Selection for Aircraft Engine Performance Estimation and Gas Path Fault Diagnostics
Authors: Simon Donald L. , Rinehart Aidan W.
Published: December 2015

This paper presents analytical techniques for aiding system designers in making aircraft engine health management sensor selection decisions. The presented techniques, which are based on linear estimation and probability theory, are tailored for gas turbine engine performance estimation and gas path fault diagnostics applications. They enable quantification of the performance estimation and diagnostic accuracy offered by different candidate sensor suites. For performance estimation, sensor selection metrics are presented for two types of estimators including a Kalman filter and a maximum a posteriori (MAP) estimator. For each type of performance estimator, sensor selection is based on minimizing the theoretical sum of squared estimation errors (SSEE) in health parameters representing performance deterioration in the major rotating modules of the engine. For gas path fault diagnostics, the sensor selection metric is set up to maximize correct classification rate (CCR) for a diagnostic strategy that performs fault classification by identifying the fault type that most closely matches the observed measurement signature in a weighted least squares sense. Results from the application of the sensor selection metrics to a linear engine model are presented and discussed. Given a baseline sensor suite and a candidate list of optional sensors, an exhaustive search is performed to determine the optimal sensor suites for performance estimation and fault diagnostics. For any given sensor suite, Monte Carlo simulation results are found to exhibit good agreement with theoretical predictions of estimation and diagnostic accuracies.
A Low-Order Model for Predicting Turbocharger Turbine Unsteady Performance
Authors: Cao Teng , Xu Liping
Published: December 2015

In this paper, a low-order model for predicting performance of radial turbocharger turbines is presented. The model combines an unsteady quasi-three-dimensional (Q3D) computational fluid dynamics (CFD) method with multiple one-dimensional (1D) meanline impeller solvers. The new model preserves the critical volute geometry features, which is crucial for the accurate prediction of the wave dynamics and retains effects of the rotor inlet circumferential nonuniformity. It also still maintains the desirable properties of being easy to set-up and fast to run. The model has been validated against a experimentally validated full 3D unsteady Reynolds-averaged Navier–Stokes (URANS) solver. The loss model in the meanline model is calibrated by the full 3D RANS solver under the steady flow states. The unsteady turbine performance under different inlet pulsating flow conditions predicted by the model was compared with the results of the full 3D URANS solver. Good agreement between the two was obtained with a speed-up ratio of about 4 orders of magnitude (∼104) for the low-order model. The low-order model was then used to investigate the effect of different pulse wave amplitudes and frequencies on the turbine cycle averaged performance. For the cases tested, it was found that compared with quasi-steady performance, the unsteady effect of the pulsating flow has a relatively small impact on the cycle-averaged turbine power output and the cycle-averaged mass flow capacity, while it has a large influence on the cycle-averaged ideal power output and cycle-averaged efficiency. This is related to the wave dynamics inside the volute, and the detailed mechanisms responsible are discussed in this paper.
Model-Based Analysis of Friction-Induced Subsynchronous Whirl for a Rotor Contacting With Clearance Bearings Under Axial Load
Authors: Cole Matthew O. T. , Hawkins Lawrence
Published: December 2015

For rotors supported by active magnetic bearings (AMBs), clearance bearings are commonly used to provide backup support under loss of AMB functionality. Test data from real machines shows that vibration during touchdown on backup bearings may involve steady forward whirling of the rotor with a subsynchronous frequency. This excitation is believed to be due to friction forces transmitted between the rotor and a bearing end-face under axial load. This paper proposes a new analytical approach to model and predict such friction-driven forward whirl behaviors. A set of constraint equations are derived that relate a circular whirl motion of arbitrary orbital speed to the frequency response functions for the rotor-housing structure. This model is coupled with an evaluation of Coulomb friction associated with slip between the rotor and the supporting end-face of a thrust bearing. The resulting equations can be used to compute a set of possible whirl motions via a root-finding procedure. A case study is undertaken for a 140 kW energy storage flywheel. Model-based predictions are compared with measured data from spin-down tests and show a good level of agreement. The study confirms the role of friction-related forces in driving forward-whirl response behaviors. It also highlights the key role of housing and machine support characteristics in response behavior. This influence is shown to be complex and not open to simple physical interpretation. Therefore, the proposed analytical method is seen as a useful tool to investigate this influence while avoiding the need for time consuming numerical simulations.
Decentralized Vibration and Shape Control of Structures With Colocated Sensors and Actuators
Authors: Ghasemi A. H. , Hoagg Jesse B. , Seigler T. M.
Published: December 2015

This paper introduces a decentralized shape and vibration controller for structures with large and potentially unknown system order, model-parameter uncertainty, and unknown disturbances. Controller implementation utilizes distributed, colocated, and independent actuator–sensor pairs. Controller design requires knowledge of the relative degrees of the actuator and sensor dynamics and upper bounds on the diagonal elements of system's high-frequency gain matrix. Closed-loop performance is determined by a parameter gain, which can be viewed as the cutoff frequency of a low-pass filter. For sufficiently large parameter gain, the closed-loop performance is arbitrarily small. Numerical examples are used to demonstrate the application and effectiveness of the decentralized controller, and we present experimental results for a setup consisting of a cantilever beam with piezoelectric actuators and strain-gauge sensors.
A Method for Thermal Performance Characterization of Ultrathin Vapor Chambers Cooled by Natural Convection
Authors: Patankar Gaurav , Mancin Simone , Weibel Justin A. , Garimella Suresh V. , MacDonald Mark A.
Published: December 2015

Vapor chamber technologies offer an attractive approach for passive cooling in portable electronic devices. Due to the market trends in device power consumption and thickness, vapor chamber effectiveness must be compared with alternative heat spreading materials at ultrathin form factors and low heat dissipation rates. A test facility is developed to experimentally characterize performance and analyze the behavior of ultrathin vapor chambers that must reject heat to the ambient via natural convection. The evaporator-side and ambient temperatures are measured directly; the condenser-side surface temperature distribution, which has critical ergonomics implications, is measured using an infrared (IR) camera calibrated pixel-by-pixel over the field of view and operating temperature range. The high thermal resistance imposed by natural convection in the vapor chamber heat dissipation pathway requires accurate prediction of the parasitic heat losses from the test facility using a combined experimental and numerical calibration procedure. Solid metal heat spreaders of known thermal conductivity are first tested, and the temperature distribution is reproduced using a numerical model for conduction in the heat spreader and thermal insulation by iteratively adjusting the external boundary conditions. A regression expression for the heat loss is developed as a function of measured operating conditions using the numerical model. A sample vapor chamber is tested for heat inputs below 2.5 W. Performance metrics are developed to characterize heat spreader performance in terms of the effective thermal resistance and the condenser-side temperature uniformity. The study offers a rigorous approach for testing and analysis of new vapor chamber designs, with accurate characterization of their performance relative to other heat spreaders.
Relationship Between the Intermetallic Compounds Growth and the Microcracking Behavior of Lead-Free Solder Joints
Authors: An Tong , Qin Fei
Published: December 2015

This paper investigates the formation and the growth of the intermetallic compound (IMC) layer at the interface between the Sn3.0Ag0.5Cu Pb-free solder and the Cu substrate during isothermal aging at 150 °C. We measure the thickness of the IMC layer and the roughness of the solder/IMC interface, and these two factors are assumed to control the tensile behavior of the solder joints. First, it utilizes the tensile tests of the aged solder joints for analyzing the effect of the IMC growth on the tensile behavior of the solder joints. Then, the microcracking behavior of the IMC layer is investigated by finite element method (FEM). In addition, qualitative numerical simulations are applied to study the effect of the IMC layer thickness and the solder/IMC interfacial roughness on the overall response and the failure mode of solder joints. The experimental results indicate that when the aging time increases, both the thickness and the roughness of the IMC layer have a strong influence on the strength and the failure mode of solder joints. The numerical simulation results suggest that the overall strength of solder joints is reduced when the IMC layer is thick and the solder/IMC interface is rough, and the dominant failure mode migrates to the microcracks within the IMC layer when the IMC layer is thick and the solder/IMC interface is flat.
Structural Stiffness of X-750 Alloy Bump Foil Strips for Compliant Foil Bearings With Different Heat Treatments
Authors: Duan Wenbo , Sun Yanhua , Ding Chunhua , Yu Lie
Published: December 2015

This paper focuses on the structural stiffness of bump foils which are used for compliant foil bearings with different heat treatments. After heat treatments in vacuum environments, the mechanical properties of the foil strips were tested, and the structural stiffness was estimated from the static load versus displacement curves obtained from the experiments. High cycle dynamic load tests were also applied to the bump foil under different cycle loads, and the shape of the foil was scanned after the tests to measure the height variation of the bumps. The results show that the modulus of elasticity and strength of Inconel X-750 strip with thickness of 0.1 mm after different treatments are lower than that with the thickness of 0.18 mm at room temperature. Moreover, the sample foil strips which have been treated with a lower solution anneal temperature at 980 °C (2 hrs) and precipitation heat treatment at 732 °C (16 hrs) have the largest modulus of elasticity and strength at room temperature. Therefore, heat treatments have a great influence on the structure stiffness of the bump foil. At last, the results of the high cycle dynamic load tests show that the bump foil with suitable heat treatment will have a good load capacity and stress-relaxation property.
Investigations of Different Liquid Based Spectrum Beam Splitters for Combined Solar Photovoltaic Thermal Systems
Authors: Joshi S. S. , Dhoble A. S. , Jiwanapurkar P. R.
Published: December 2015

In the spectrum beam split approach of combined solar photovoltaic thermal system (PVT), the complete solar spectrum is splitted. The unwanted part of the solar spectrum for photovoltaic (PV) applications is filtered out and is used separately as heat. In this work, some inexpensive, clear, and easily available selective fluids are identified which can be used as both volumetric heat absorbers and selective spectrum filters for C-Si-based PVT. The electrical performance of a C-Si solar PV cell using these fluid-based filters is analyzed using a solar simulator at 1 Sun, AM 1.5 G. To check the volumetric heat absorbing potential, the required thermophysical properties of these selected fluids are estimated using a solar radiation pyranometer and standard experiments. The study concludes that water, coconut oil, and hydrotreated silicone transformer oil are some of the potential beam splitters and heat absorbers suitable for C-Si based spectrum beam split PVT applications.
Advances in Quantification of Meniscus Tensile Mechanics Including Nonlinearity, Yield, and Failure
Authors: Peloquin John M. , Santare Michael H. , Elliott Dawn M.
Published: December 2015

The meniscus provides crucial knee function and damage to it leads to osteoarthritis of the articular cartilage. Accurate measurement of its mechanical properties is therefore important, but there is uncertainty about how the test procedure affects the results, and some key mechanical properties are reported using ad hoc criteria (modulus) or not reported at all (yield). This study quantifies the meniscus' stress–strain curve in circumferential and radial uniaxial tension. A fiber recruitment model was used to represent the toe region of the stress–strain curve, and new reproducible and objective procedures were implemented for identifying the yield point and measuring the elastic modulus. Patterns of strain heterogeneity were identified using strain field measurements. To resolve uncertainty regarding whether rupture location (i.e., midsubstance rupture versus at-grip rupture) influences the measured mechanical properties, types of rupture were classified in detail and compared. Dogbone (DB)-shaped specimens are often used to promote midsubstance rupture; to determine if this is effective, we compared DB and rectangle (R) specimens in both the radial and circumferential directions. In circumferential testing, we also compared expanded tab (ET) specimens under the hypothesis that this shape would more effectively secure the meniscus' curved fibers and thus produce a stiffer response. The fiber recruitment model produced excellent fits to the data. Full fiber recruitment occurred approximately at the yield point, strongly supporting the model's physical interpretation. The strain fields, especially shear and transverse strain, were extremely heterogeneous. The shear strain field was arranged in pronounced bands of alternating positive and negative strain in a pattern similar to the fascicle structure. The site and extent of failure showed great variation, but did not affect the measured mechanical properties. In circumferential tension, ET specimens underwent earlier and more rapid fiber recruitment, had less stretch at yield, and had greater elastic modulus and peak stress. No significant differences were observed between R and DB specimens in either circumferential or radial tension. Based on these results, ET specimens are recommended for circumferential tests and R specimens for radial tests. In addition to the data obtained, the procedural and modeling advances made in this study are a significant step forward for meniscus research and are applicable to other fibrous soft tissues.
Modeling of Finned-Tube Evaporator Using Neural Network and Response Surface Methodology
Authors: Li Ze-Yu , Shao Liang-Liang , Zhang Chun-Lu
Published: December 2015

A new response surface methodology (RSM) based neural network (NN) modeling method is proposed for finned-tube evaporator performance evaluation under dry and wet conditions. Two RSM designs, Box–Behnken design (BBD) and central composite design (CCD), are applied to collect a small but well-designed dataset for NN training, respectively. Compared with additional 7000 sets of test data, for all the evaporator performance including total cooling capacity, sensible heat ratio and pressure drops on both refrigerant and air sides, the standard deviation (SD) and coefficient of determination of trained NNs are less than 2% and higher than 0.998, respectively, under dry conditions while those are less than 4% and greater than 0.974, respectively, under wet conditions. Classic quadratic polynomial response surface models were also included for reference. By comparison, the proposed model achieves higher accuracy. Finally, parametric study based on the trained NNs is conducted. This new method can remarkably downsize the training dataset and mitigate the over-fitting risk of NN.
Generalized Aerodynamic Modeling of Dynamic Wake Curvature for Open Rotors With Slender Blades
Authors: Goulos Ioannis
Published: December 2015

This paper elaborates on the theoretical development of an analytical approach, capable of modeling the effect of dynamic wake curvature on the aeroelastic response of open rotors with slender blades. The classical solution of incompressible, potential flow derived for a curved vortex tube of uniform vorticity strength is employed. The previously developed curved vortex tube analysis is mathematically generalized to account for arbitrary radial and circumferential variations of circulatory disk loading. An orthogonality analysis is carried out to obtain a finite set of inflow perturbation coefficients that describe the aerodynamic effect of wake curvature in a generalized manner. The end result is a set of integral expressions that provide the interharmonic coupling between the inflow perturbations on the rotor disk due to a curved trailing wake and the corresponding variations of disk loading. The obtained perturbation coefficients are subsequently superimposed upon an existing finite-state induced flow model that assumes a skewed, noncurved cylindrical wake. The developed mathematical approach for fluid mechanics is coupled with an unsteady blade element aerodynamics model, a rotor blade structural mechanics model, and a nonlinear rotor dynamics model. The combined formulation is implemented in an existing helicopter flight mechanics code. The overall method is initially employed to assess the effect of wake curvature on the dynamic response of a small-scale articulated rotor with a flap frequency ratio equal to unity. Subsequently, the integrated model is deployed to investigate the influence of wake curvature and inflow modeling fidelity on the predicted oscillatory blade loads and transient control response of a full-scale helicopter rotor. Comparisons are carried out with flight test measurements as well as with complex free-wake analysis methods. It is shown that including the effect of wake curvature is essential for predicting the transient control response of the investigated rotor. Good agreement is demonstrated between the proposed analytical model and nonlinear predictions carried out by resolving the complex wake geometry. The developed fluid mechanics formulation is a time-accurate method derived from first-principles and is applicable to both axial and nonaxial flow conditions.
Experimental Investigation of Flow Instability in a Turbocharger Ported Shroud Compressor
Authors: Guillou Erwann , Gancedo Matthieu , Gutmark Ephraim
Published: December 2015

Turbocharger centrifugal compressors are equipped with a “ported shroud” to reduce flow instabilities at low mass flow rates. This passive stability control device using flow recirculation has been demonstrated to extend the surge margin of a compressor without substantially sacrificing performance. However, the actual working mechanisms of the system are not well understood. In this paper, the relationship between inlet flow recirculation and instability control is studied using stereoscopic particle image velocimetry (PIV) in conjunction with dynamic pressure transducers at the inlet of the turbocharger compressor with and without ported shroud. Both stable and unstable operational points are analyzed using phase-locked PIV measurements during surge. Detailed description of unstable flow in the centrifugal compressor is presented by reconstructing the complex flow structure evolution in the compressor inlet during surge. Rather than one-dimensional, the surge flow is characterized by a three-dimensional structure of both entering and exiting swirling flows, alternating in magnitude during a self-excited pressure cycle. The correlation between pressure and velocity measurements shows that the development of compressor unsteadiness is concurrent with swirling reversed flow at the impeller tip. The impact of the ported shroud on the inlet velocity flowfield is evidenced by the presence of localized flow recirculation. Stability improvement due to the ported shroud is thus a result of removing swirling backflow from the impeller inducer tip and recirculating it into the impeller inlet to increase the near shroud inlet blade loading and the incidence angle.
A New Test Facility to Investigate Film Cooling on a Nonaxisymmetric Contoured Turbine Endwall—Part II: Heat Transfer and Film Cooling Measurements
Authors: Kneer Johannes , Puetz Franz , Schulz Achmed , Bauer Hans-Jörg
Published: December 2015

The present work is part of a comprehensive heat transfer and film-cooling study on a locally cooled nonaxisymmetric contoured turbine endwall. A new test rig consisting of a linear cascade of three prismatic vanes at unity scale and exchangeable endwall has been established. The rig is operated in an open-loop configuration at a reduced main gas temperature of 425 K, an exit Mach number of 0.5, and an exit Reynolds number of 1.6 × 106. Air is used both as main gas and coolant; a realistic density ratio is achieved by cooling the coolant below freezing. In the first part of the study, aerodynamic measurements are presented. This paper concentrates on film cooling of the contoured endwall with special emphasis on data acquisition and reduction for the application of the superposition principle of film cooling. The first experimental results from thermographic measurements are discussed.
Comparison of the Straight Adiabatic Capillary Tube Expansion Devices Used in Refrigeration Systems Operating With Refrigerants R134a and R1234yf
Authors: Harish Kruthiventi S. S. , Venkatarathnam G.
Published: December 2015

Capillary tube expansion devices are used extensively in small refrigeration and unitary air conditioning systems. R1234yf is likely to replace R134a in the next few years in many small refrigeration systems worldwide because of the new environmental regulations being proposed. In this paper, we compare the length and diameter of capillary tube required when R134a and R1234yf are used in a typical small refrigeration system. The minimum diameter of the capillary tube required has been estimated using the speed of sound of the refrigerant leaving the capillary tube in the two-phase state. The two-phase speed of sound routine developed by us can be used with both pure fluids and mixtures.
Bubbles Transient Growth in Saturation Boiling of PF-5060 Dielectric Liquid on Dimpled Cu Surfaces
Authors: Suszko Arthur , El-Genk Mohamed S.
Published: December 2015

Investigated is the transient growth of vapor bubbles in saturation boiling of PF-5060 dielectric liquid on 10 × 10 mm, uniformly heated Cu surfaces with circular dimples, at an applied heat flux of 0.5 W/cm2. At such low heat flux, the surfaces are populated with growing discrete bubbles, emanating mostly from the manufactured dimples. The 300, 400, and 500 μm diameter and 200 μm deep dimples are manufactured in a triangular lattice with a pitch-to-diameter ratio of 2.0; thus, the total number of dimples increases with decreasing the dimple diameter. Captured video images of growing discrete bubbles at a speed of 210 frames per second (fps) confirm that the bubble diameter increases proportional to the square root of the growth time, and the bubble departure diameter and detachment frequency increase with increasing the dimple diameter. The total volumetric growth rate and diameter of the bubbles at departure increase with increasing the dimple diameter, ∼1.81, ∼4.75, and ∼8.2 mm3/s and ∼738 μm, ∼963 μm, and ∼1051 μm for the 300, 400, and 500 μm diameter dimples, respectively. The corresponding bubble detachment frequency is ∼8.6 Hz, ∼10.2 Hz, and ∼13.5 Hz, respectively. The fraction of the active dimples for bubble nucleation on the surfaces with 300, 400, and 500 μm dimples, at an applied heat flux of 0.5 W/cm2, is ∼0.85, ∼0.64, and ∼0.53, respectively. On these surfaces, the estimated bubble volume at departure is ∼0.21 mm3, ∼0.47 mm3, and ∼0.61 mm3, and the corresponding rate of energy removed by a single bubble is ∼1.99 mW, ∼5.24 mW, and ∼9.02 mW, respectively. These results help explain the measured enhancements in nucleate boiling and the critical heat flux (CHF) on the dimpled Cu surfaces.
Analysis of the Reliability of a Jet Engine Compressor Rotor Blade Containing a Fatigue Crack
Authors: Lee Dooyoul , Achenbach Jan D.
Published: December 2015

The reliability of a jet engine compressor rotor blade containing a fatigue crack has been assessed based on the eddy current inspection (ECI) response of both the actual rotor blade and bolt hole specimens containing cracks of known lengths. The detection threshold and the probability of detection (POD) curve have been determined. A dynamic Bayesian network (DBN) model was used to quantify uncertainties. The model encompasses a realistic ECI response model, so that it is possible to consider all relevant inspection data types. Factors which contribute the most to the variation of crack length have been determined by sensitivity analysis and have been calibrated using the field inspection data. Part of the inspection data was used to validate the calibrated model, and a Bayes factor of 9.93 which corresponds to a confidence level of 91% has been obtained. Based on the control level for the reliability index βctrl = 3, and the reliability indices calculated from the calibrated model, the recommended interval for the first inspection has been determined as 1600 hrs. This interval is smaller than the current interval which is 3200 hrs.
Macroscopic Modeling of In Vivo Drug Transport in Electroporated Tissue
Authors: Boyd Bradley , Becker Sid
Published: December 2015

This study develops a macroscopic model of mass transport in electroporated biological tissue in order to predict the cellular drug uptake. The change in the macroscopic mass transport coefficient is related to the increase in electrical conductivity resulting from the applied electric field. Additionally, the model considers the influences of both irreversible electroporation (IRE) and the transient resealing of the cell membrane associated with reversible electroporation. Two case studies are conducted to illustrate the applicability of this model by comparing transport associated with two electrode arrangements: side-by-side arrangement and the clamp arrangement. The results show increased drug transmission to viable cells is possible using the clamp arrangement due to the more uniform electric field.
Mechanical Integrity of a Decellularized and Laser Drilled Medial Meniscus
Authors: Lakes Emily H. , Matuska Andrea M. , McFetridge Peter S. , Allen Kyle D.
Published: December 2015

Since the meniscus has limited capacity to self-repair, creating a long-lasting meniscus replacement may help reduce the incidence of osteoarthritis (OA) after meniscus damage. As a first step toward this goal, this study evaluated the mechanical integrity of a decellularized, laser drilled (LD) meniscus as a potential scaffold for meniscal engineering. To evaluate the decellularization process, 24 porcine menisci were processed such that one half remained native tissue, while the other half was decellularized in sodium dodecyl sulphate (SDS). To evaluate the laser drilling process, 24 additional menisci were decellularized, with one half remaining intact while the other half was LD. Decellularization did not affect the tensile properties, but had significant effects on the cyclic compressive hysteresis and unconfined compressive stress relaxation. Laser drilling decreased the Young's modulus and instantaneous stress during unconfined stress relaxation and the circumferential ultimate strength during tensile testing. However, the losses in mechanical integrity in the LD menisci were generally smaller than the variance observed between samples, and thus, the material properties for the LD tissue remained within a physiological range. In the future, optimization of laser drilling patterns may improve these material properties. Moreover, reseeding the construct with cells may further improve the mechanical properties prior to implantation. As such, this work serves as a proof of concept for generating decellularized, LD menisci scaffolds for the purposes of meniscal engineering.
Three-Dimensional Viscoelastic Simulation for Injection/Compression Molding Based on Arbitrary Lagrangian Eulerian Description
Authors: Cao Wei , Hua Shaozhen , Zhang Shixun , Wang Tao , Wang Yaming , Li Haimei , Liu Chuntai , Shen Changyu
Published: December 2015

Different from conventional injection molding (CIM), injection/compression molding (ICM) evolves boundary variation in gapwise direction. In order to describe melt flow characteristics in ICM correctly, a new material derivative based on arbitrary Lagrangian Eulerian (ALE) description was introduced to modify the material derivatives in the governing and constitutive equations. To avoid large amount of calculation and weak stability of integral numerical method, an iterative approach employing twofold iterations was proposed to decouple the interdependence between velocity, stress, and temperature. The initial values of material parameters in constitutive equations were obtained or fitted by rheological experiments. The ICM experiments for an iso-thick and a var-thick rectangular panel were carried out to validate the proposed method and find the special characteristics of ICM. In addition, the photoelastic tests on a quarter of spherical part processed by ICM were conducted to identify the relationship between residual flow-induced stress distributions and flow fields. Both simulations and experiments show that the pressure profile displays a plateau during compression, temperature decreases with time according to exponential law, large flow-induced stress originates in thick transitional region, flow start, and flow end areas, and gravity has significant effect on meltfront for thick part ICM. The good agreement between experiments and simulations indicates that the current method can properly describe the flow characteristics of ICM.
A New Bernoulli Wavelet Operational Matrix of Derivative Method for the Solution of Nonlinear Singular Lane–Emden Type Equations Arising in Astrophysics
Authors: Balaji S.
Published: December 2015

In this paper, a new method is presented for solving generalized nonlinear singular Lane–Emden type equations arising in the field of astrophysics, by introducing Bernoulli wavelet operational matrix of derivative (BWOMD). Bernoulli wavelet expansions together with this operational matrix method, by taking suitable collocation points, converts the given Lane–Emden type equations into a system of algebraic equations. Solution to the problem is identified by solving this system of equations. Further applicability and simplicity of the proposed method has been demonstrated by some examples and comparison with other recent methods. The obtained results guarantee that the proposed BWOMD method provides the good approximate solution to the generalized nonlinear singular Lane–Emden type equations.
Asymptotic Stability and Chaotic Motions in Trajectory Following Feedback Controlled Robots
Authors: Sandeep Reddy B. , Ghosal Ashitava
Published: December 2015

A feedback controlled robot manipulator with positive controller gains is known to be asymptotically stable at a set point and for trajectory following in the sense of Lyapunov. However, when the end-effector of a robot or its joints are made to follow a time-dependent trajectory, the nonlinear dynamical equations modeling the feedback controlled robot can also exhibit chaotic motions and as a result cannot follow a desired trajectory. In this paper, using the example of a simple two-degree-of-freedom robot with two rotary (R) joints, we take a relook at the asymptotic stability of a 2R robot following a desired time-dependent trajectory under a proportional plus derivative (PD) and a model-based computed torque control. We demonstrate that the condition of positive controller gains is not enough and the gains must be large for chaos not to occur and for the robot to asymptotically follow a desired trajectory. We apply the method of multiple scales (MMS) to the two nonlinear second-order ordinary differential equations (ODEs), which describes the dynamics of the feedback controlled 2R robot, and derive a set of four first-order slow flow equations. At a fixed point, the Routh–Hurwitz criterion is used to obtain values of proportional and derivative gains at which the controller is asymptotically stable or indeterminate. For the model-based control, a parameter representing model mismatch is used and the controller gains for a chosen mismatch parameter value are obtained. From numerical simulations with controller gain values in the indeterminate region, it is shown that for some values, the nonlinear dynamical equations are chaotic, and hence, the 2R robot cannot follow the desired trajectory and be asymptotically stable.