bluuebunny/crossref_metadata_2025 huggingface dataset:
The
Combined Effects of Heat Loss and Reversibility on the Propagation of Planar Premixed Counterflow
Flames
Authors: Al-Malki Faisal
Published: July 2018

We study in this paper the combined effect of heat loss and reversibility on the propagation of planar flames formed within the counterflow configuration. The problem has been formulated first using the thermodiffusive model with constant density and then solved numerically using finite elements. The impact of four main parameters, namely the reversibility r, the heat loss κ, the strain rate ε, and the activation energy β, on the propagation of planar flames has been discussed in details. The study has shown that planar flames under reversible conditions behave qualitatively similar to those observed for irreversible reactions, which agree with the asymptotic findings. In the presence of heat loss, the problem exhibits multiplicity of solutions whose number and stability were found to vary according to the strain rate ε. In addition, the study has predicted the existence of a certain value of the reversibility parameter r beyond which the impact of reversibility becomes negligible. Finally, we have examined the stability of the solutions and determined the domain of stability of solutions and their multiplicity for this problem.
Design and Analysis for Uncertain Repetitive Control Systems With Unknown Disturbances
Authors: Sakthivel R. , Raajananthini K. , Selvaraj P. , Ren Y.
Published: July 2018

In this paper, the periodic tracking problem is considered for a class of continuous system with uncertainty, time-varying delay, and unknown bounded external disturbances. To be precise, in order to attenuate the unknown disturbance effectively, the equivalent-input-disturbance (EID) approach is incorporated into the developed algorithm. Then, the sufficient conditions that guarantee the asymptotic tracking performance of the system understudy are established based on the Lyapunov stability theorem. More precisely, Schur complement and free-weighting matrix approach are utilized to derive the main results. Moreover, the proposed EID-based modified repetitive controller (MRC) not only rejects the unknown external disturbance but also deals with the dead zone effect. Finally, two simulation examples are presented to verify the superiority of the proposed EID-based repetitive controller over the conventional repetitive controller.
Active Vibration Control of a Doubly Curved Composite Shell Stiffened by Beams Bonded With Discrete Macro Fiber Composite Sensor/Actuator Pairs
Authors: Daraji Ali H. , Hale Jack M. , Ye Jianqiao
Published: July 2018

Doubly curved stiffened shells are essential parts of many large-scale engineering structures, such as aerospace, automotive and marine structures. Optimization of active vibration reduction has not been properly investigated for this important group of structures. This study develops a placement methodology for such structures under motion base and external force excitations to optimize the locations of discrete piezoelectric sensor/actuator pairs and feedback gain using genetic algorithms for active vibration control. In this study, fitness and objective functions are proposed based on the maximization of sensor output voltage to optimize the locations of discrete sensors collected with actuators to attenuate several vibrations modes. The optimal control feedback gain is determined then based on the minimization of the linear quadratic index. A doubly curved composite shell stiffened by beams and bonded with discrete piezoelectric sensor/actuator pairs is modeled in this paper by first-order shear deformation theory using finite element method and Hamilton's principle. The proposed methodology is implemented first to investigate a cantilever composite shell to optimize four sensor/actuator pairs to attenuate the first six modes of vibration. The placement methodology is applied next to study a complex stiffened composite shell to optimize four sensor/actuator pairs to test the methodology effectiveness. The results of optimal sensor/actuator distribution are validated by convergence study in genetic algorithm program, ANSYS package and vibration reduction using optimal linear quadratic control scheme.
An Efficient Hybrid Analytical-Computational Method for Nonlinear Vibration of Spur Gear Pairs
Authors: Dai Xiang , Cooley Christopher G. , Parker Robert G.
Published: July 2018

This work develops a hybrid analytical-computational (HAC) method for nonlinear dynamic response in spur gear pairs. The formulation adopts a contact model developed in (Eritenel, T., and Parker, R. G., 2013, “Nonlinear Vibration of Gears With Tooth Surface Modifications,” ASME J. Vib. Acoust., 135(5), p. 051005) where the dynamic force at the mating gear teeth is determined from precalculated static results based on the instantaneous mesh deflection and position in the mesh cycle. The HAC method merges this calculation of the contact force based on an underlying finite element static analysis into a numerical integration of an analytical vibration model. The gear translational and rotational vibrations are calculated from a lumped-parameter analytical model where the crucial dynamic mesh force is calculated using a force-deflection function (FDF) that is generated from a series of static finite element analyses performed before the dynamic calculations. Incomplete tooth contact and partial contact loss are captured by the static finite element analyses and included in the FDF, as are tooth modifications. In contrast to typical lumped-parameter models elastic deformations of the gear teeth, including the tooth root strains and contact stresses, are calculated. Accelerating gears and transient situations can be analyzed. Comparisons with finite element calculations and available experiments validate the HAC model in predicting the dynamic response of spur gear pairs, including for resonant gear speeds when high amplitude vibrations are excited and contact loss occurs. The HAC model is five orders of magnitude faster than the underlying finite element code with almost no loss of accuracy.
Generic Properties of Flows in Low-Speed Axial Fans Operating at Load-Controlled Windmill
Authors: Ortolan Aurélie , Courty-Audren Suk-Kee , Lagha Massyl , Binder Nicolas , Carbonneau Xavier , Challas Florent
Published: July 2018

This paper aims at underlining the existence of some generic properties of windmilling flows, partially spread in the literature but never clearly stated. Two kinds of axial machines are investigated from compressor mode to highly loaded windmill: a conventional fan with poor turbine performance and an optimized fan able to reach high efficiencies in both compressor and windmilling operations. Both simulations and experiments are used to perform the analysis. Three particular behaviors were identified as typical of fans operating at windmill: the inverse stacking of the speed lines visible in (Π, Qm) turbine maps, the appearance of a slope change on the loading-to-flow coefficient diagram at windmill, and a threshold effect occurring at highly loaded windmill.
An Investigation of the Structural Integrity of a Reactor Pressure Vessel Using Three-Dimensional Computational Fluid Dynamics and Finite Element Method Based Probabilistic Pressurized Thermal Shock Analysis for Optimizing Maintenance Strategy
Authors: Ruan Xiaoyong , Nakasuji Toshiki , Morishita Kazunori
Published: July 2018

The structural integrity of a reactor pressure vessel (RPV) is important for the safety of a nuclear power plant. When the emergency core cooling system (ECCS) is operated and the coolant water is injected into the RPV due to a loss-of-coolant accident (LOCA), the pressurized thermal shock (PTS) loading takes place. With the neutron irradiation, PTS loading may lead an RPV to fracture. Therefore, it is necessary to evaluate the performance of RPV during PTS loading to keep the reactor safety. In the present study, optimization of RPV maintenance is considered, where two different attempts are made to investigate the RPV integrity during PTS loading by employing the deterministic and probabilistic methodologies. For the deterministic integrity evaluation, three-dimensional computational fluid dynamics (3D-CFD) and finite element method (FEM) simulations are performed, and stress intensity factors (SIFs) are obtained as a function of crack position inside the RPV. As to the probabilistic integrity evaluation, on the other hand, a practically more useful spatial distribution of SIF on the RPV is calculated. By comparing the distribution thus obtained with the fracture toughness included as a part of the master curve, the dependence of conditional failure probabilities on the position inside the RPV is obtained. Using the spatial distribution of conditional failure probabilities in RPV, the priority of the inspection and maintenance is finally discussed.
A Geometric Approach to Obtain the Closed-Form Forward Kinematics of H4 Parallel Robot
Authors: Liu Yujiong , Kong Minxiu , Wan Neng , Ben-Tzvi Pinhas
Published: July 2018

To obtain the closed-form forward kinematics of parallel robots, researchers use algebra-based method to transform and simplify the constraint equations. However, this method requires a complicated derivation that leads to high-order univariate variable equations. In fact, some particular mechanisms, such as Delta, or H4 possess many invariant geometric properties during movement. This suggests that one might be able to transform and reduce the problem using geometric approaches. Therefore, a simpler and more efficient solution might be found. Based on this idea, we developed a new geometric approach called geometric forward kinematics (GFK) to obtain the closed-form solutions of H4 forward kinematics in this paper. The result shows that the forward kinematics of H4 yields an eighth degree univariate polynomial, compared with earlier reported 16th degree. Thanks to its clear physical meaning, an intensive discussion about the solutions is presented. Results indicate that a general H4 robot can have up to eight nonrepeated real solutions for its forward kinematics. For a specific configuration of H4, the nonrepeated number of real roots could be restricted to only two, four, or six. Two traveling plate configurations are discussed in this paper as two typical categories of H4. A numerical analysis was also performed for this new method.
Hyperbolic Runge–Kutta Method Using Evolutionary Algorithm
Authors: Arun Govind Neelan A. , Nair Manoj T.
Published: July 2018

A family of Runge–Kutta (RK) methods designed for better stability is proposed. Authors have optimized the stability of RK method by increasing the stability region by trading some of the higher order terms in the Taylor series. For flow involving shocks, compromising a few higher order terms will not affect convergence rate that is justified with an example. Though this kind of analysis began about three decades ago, most of the papers dealt with classical optimization and ended up in relatively nonoptimal values. Here, authors have overcome that by using evolutionary algorithm (EA), the result is refined using multisection method (MSM). The schemes designed based on this procedure have better stability than the classical RK methods, strong stability RK methods (SSPRK), and low dispersive and dissipative RK methods (LDDRK) of the same number of stages. Authors have tested the schemes on a variety of test cases and found some significant improvement.
Engine-Scalable Rotor Casing Convective Heat Flux Evaluation Using Inverse Heat Transfer Methods
Authors: Gonzalez Cuadrado David , Lozano Francisco , Andreoli Valeria , Paniagua Guillermo
Published: July 2018

In this paper, we propose a two-step methodology to evaluate the convective heat flux along the rotor casing using an engine-scalable approach based on discrete Green's functions . The first step consists in the use of an inverse heat transfer technique to retrieve the heat flux distribution on the shroud inner wall by measuring the temperature of the outside wall; the second step is the calculation of the convective heat flux at engine conditions, using the experimental heat flux and the Green functions engine-scalable technique. Inverse methodologies allow the determination of boundary conditions; in this case, the inner casing surface heat flux, based on measurements from outside of the system, which prevents aerothermal distortion caused by routing the instrumentation into the test article. The heat flux, retrieved from the inverse heat transfer methodology, is related to the rotor tip gap. Therefore, for a given geometry and tip gap, the pressure and temperature can also be retrieved. In this work, the digital filter method is applied in order to take advantage of the response of the temperature to heat flux pulses. The discrete Green's function approach employs a matrix to relate an arbitrary temperature distribution to a series of pulses of heat flux. In this procedure, the terms of the Green's function matrix are evaluated with the output of the inverse heat transfer method. Given that key dimensionless numbers are conserved, the Green's functions matrix can be extrapolated to engine-like conditions. A validation of the methodology is performed by imposing different arbitrary heat flux distributions, to finally demonstrate the scalability of the Green's function method to engine conditions. A detailed uncertainty analysis of the two-step routine is included based on the value of the pulse of heat flux, the temperature measurement uncertainty, the thermal properties of the material, and the physical properties of the rotor casing.
Numerical Investigation of the Pressure-Time Method Considering Pipe With Variable Cross Section
Authors: Saemi Simindokht , Raisee Mehrdad , Cervantes Michel J. , Nourbakhsh Ahmad
Published: July 2018

A common method to calculate the flow rate and consequently hydraulic efficiency in hydropower plants is the pressure-time method. In the present work, the pressure-time method is studied numerically by three-dimensional (3D) simulations and considering the change in the pipe cross section (a contraction). Four different contraction angles are selected for the investigations. The unsteady Reynolds-averaged Navier–Stokes (URANS) equations and the low-Reynolds k–ω shear stress transport (SST) turbulence model are used to simulate the turbulent flow. The flow physics in the presence of the contraction, and during the deceleration period, is studied. The flow rate is calculated considering all the losses: wall shear stress, normal stresses, and also flux of momentum in the flow. The importance of each term is evaluated showing that the flux of momentum plays a most important role in the flow rate estimation while the viscous losses term is the second important factor. To extend the viscous losses calculations applicability to real systems, the quasi-steady friction approach is employed. The results showed that considering all the losses, the increase in the contraction angle does not influence the calculated errors significantly. However, the use of the quasi-steady friction factor introduces a larger error, and the results are reliable approximately up to a contraction angle of ϴ = 10 deg. The reason imparts to the formation of a local recirculation zone upstream and inside the contraction, which appears earlier as the contraction angle increases. This feature cannot be captured by the quasi-steady friction models, which are derived based on the fully developed flow assumption.
Novel Friction-Assisted Tube Forming Methods: A Comparison of Microstructure and Mechanical Properties
Authors: Hosseini S. H. , Sedighi M.
Published: July 2018

Expanding performance of friction power in material processing techniques, considerably improves the process efficiency while decreases required load and increases imposed strain by the localized material softening. This paper proposes friction-assisted tube forming (FATF) and friction-assisted tube extrusion (FATE) to deform cylindrical tubes for desirable radius and thickness. These methods were successfully examined on commercially pure copper tubes. Finite element (FE) analyses were executed to simulate heat generation, temperature, and strain fields. Using friction power in the presented methods significantly reduced processing force and enhanced imposed strain. Therefore, FATF and FATE show a great capability to forming and extrusion of the cylindrical tubes with minimum processing power. Mechanical properties of the processed tubes showed considerable changes in which yield strength and ultimate tensile strength increased 4.6 and 1.6 times greater than those from the initial values. Dynamically recrystallized fine grains with mean size of 8.3 μm were obtained compared with 60 μm for the annealed sample.
Influence of Geometric Design Parameters Onto Vibratory Response and High-Cycle Fatigue Safety for Turbine Blades With Friction Damper
Authors: Hüls Matthias , Panning-von Scheidt Lars , Wallaschek Jörg
Published: July 2018

Among the major concerns for high aspect-ratio, turbine blades are forced and self-excited (flutter) vibrations, which can cause failure by high-cycle fatigue (HCF). The introduction of friction damping in turbine blades, such as by coupling of adjacent blades via under platform dampers, can lead to a significant reduction of resonance amplitudes at critical operational conditions. In this paper, the influence of basic geometric blade design parameters onto the damped system response will be investigated to link design parameters with functional parameters like damper normal load, frequently used in nonlinear dynamic analysis. The shape of a simplified turbine blade is parameterized along with the under platform damper configuration. The airfoil is explicitly included into the parameterization in order to account for changes in blade mode shapes. For evaluation of the damped system response, a reduced-order model for nonlinear friction damping is included into an automated three-dimensional (3D) finite element analysis (FEA) tool-chain. Based on a design of experiments approach, the design space will be sampled and surrogate models will be trained on the received dataset. Subsequently, the mean and interaction effects of the geometric design parameters onto the resonance amplitude and safety against HCF will be outlined. The HCF safety is found to be affected by strong secondary effects onto static and resonant vibratory stress levels. Applying an evolutionary optimization algorithm, it is shown that the optimum blade design with respect to minimum vibratory response can differ significantly from a blade designed toward maximum HCF safety.
On the Evaluation and Consideration of Fracture Mechanical Notch Support Within a Creep-Fatigue Lifetime Assessment
Authors: Kontermann Christian , Almstedt Henning , Müller Falk , Oechsner Matthias
Published: July 2018

Changes within the global energy market and a demand for a more flexible operation of gas- and steam-turbines lead to higher utilization of main components and raise the question how to deal with this challenge. One strategy to encounter this is to increase the accuracy of the lifetime assessment by quantifying and reducing conservatisms. At first the impact of considering a fracture mechanical notch support under creep-fatigue loading is studied by discussing the results of an extensive experimental program performed on notched round-bars under global strain control. A proposal of how to consider this fracture mechanical notch support within a lifetime assessment is discussed within the second part of the paper. Here, a theoretical finite element method (FEM)-based concept is introduced and validated by comparing the theoretical prediction with the results of the previously mentioned experimental study. Finally, the applicability of the developed and validated FEM-based procedure is demonstrated.
Capability of the Bayesian Forecasting Method to Predict Field Time Series
Authors: Gatta Nicolò , Venturini Mauro , Manservigi Lucrezia , Fabio Ceschini Giuseppe , Bechini Giovanni
Published: July 2018

This paper addresses the challenge of forecasting the future values of gas turbine measureable quantities. The final aim is the simulation of “virtual sensors” capable of producing statistically coherent measurements aimed at replacing anomalous observations discarded from the time series. Among the different available approaches, the Bayesian forecasting method (BFM) adopted in this paper uses the information held by a pool of observations as knowledge base to forecast the values at a future state. The BFM algorithm is applied in this paper to Siemens field data to assess its prediction capability, by considering two different approaches, i.e., single-step prediction (SSP) and multistep prediction (MSP). While SSP predicts the next observation by using true data as base of knowledge, MSP uses previously predicted data as base of knowledge to perform the prediction of future time steps. The results show that BFM single-step average prediction error can be very low, when filtered field data are analyzed. On the contrary, the average prediction error achieved in case of BFM multistep prediction is remarkably higher. To overcome this issue, the BFM single-step prediction scheme is also applied to clusters of time-wise averaged data. In this manner, an acceptable average prediction error can be achieved by considering clusters composed of 60 observations.
Analysis of a Fuel Flexible Micro Gas Turbine Combustor Through Numerical Simulations
Authors: Bo Alessandro , Giacomazzi Eugenio , Messina Giuseppe , Di Nardo Antonio
Published: July 2018

The work in this paper investigates on how a fuel flexible microgas turbine (MGT) combustion chamber, developed by ANSALDO ENERGIA and installed in a Turbec T100 P MGT, can operate when transferring from natural gas (NG) to a hydrogen-rich syngas. A syngas composition, which satisfies the fuel supply system specifications, is identified. Such syngas contains (by volume) 45% of hydrogen, 50% of carbon dioxide, and 5% of methane. The transfer procedure from NG to syngas is defined and modeled. A series of nonreactive and reactive Reynolds-averaged numerical simulations (RANS) on a full-scale three-dimensional (3D) model of the combustion chamber is then performed. The thermo-fluid dynamics inside its casing, the combustion regimes, the heat transfer across the liner walls as well as NOx emissions are evaluated. Results provide useful information on the operational problems associated with the fuel change and on how to define a successful fuel transfer procedure.
Emulsion Jet in Crossflow Atomization Characteristics and Dynamics
Authors: Leask Scott B. , McDonell Vincent G. , Samuelsen Scott
Published: July 2018

This work presents the atomization characteristics and dynamics of water-in-heptane (W/H) emulsions injected into a gaseous crossflow. W/H mixtures were tested while varying momentum flux ratios and aerodynamic Weber numbers. Different injector orifice diameters and orifice length-to-diameter ratios were used to test the generality of the results. The atomization properties of W/H mixtures were compared with properties of neat water and neat heptane to evaluate the effect of an emulsion on droplet sizing, cross-sectional stability and dispersion, and jet penetration depth. Liquid dynamics were extracted through analyzing instantaneous spray measurements and dynamic mode decomposition (DMD) on high-speed video recordings of the atomization processes. Correlations were proposed to establish preliminary relationships between fundamental spray processes and test conditions. These correlations allowed for emulsion behavior to be compared with neat liquid behavior. The use of emulsions induces greater spray instability than through using neat liquids, likely due to the difficulty in injecting a stable emulsion. Neat liquid correlations were produced and successfully predicted various spray measurements. These correlations, however, indicate that injector geometry has an effect on spray properties, which need to be addressed independently. The emulsions are unable to adhere to the neat liquid correlations suggesting that an increased number of correlation terms are required to adequately predict emulsion behavior.
Design and Application of a Multidisciplinary Predesign Process for Novel Engine Concepts
Authors: Reitenbach Stanislaus , Krumme Alexander , Behrendt Thomas , Schnös Markus , Schmidt Thomas , Hönig Sandrine , Mischke Robert , Mörland Erwin
Published: July 2018

The purpose of this paper is to present a multidisciplinary predesign process and its application to three aero-engine models. First, a twin spool mixed flow turbofan engine model is created for validation purposes. The second and third engine models investigated comprise future engine concepts: a counter rotating open rotor (CROR) and an ultrahigh bypass turbofan. The turbofan used for validation is based on publicly available reference data from manufacturing and emission certification. At first, the identified interfaces and constraints of the entire predesign process are presented. An important factor of complexity in this highly iterative procedure is the intricate data flow, as well as the extensive amount of data transferred between all involved disciplines and among different fidelity levels applied within the design phases. To cope with the inherent complexity, data modeling techniques have been applied to explicitly determine required data structures of those complex systems. The resulting data model characterizing the components of a gas turbine and their relationships in the design process is presented in detail. Based on the data model, the entire engine predesign process is presented. Starting with the definition of a flight mission scenario and resulting top level engine requirements, thermodynamic engine performance models are developed. By means of these thermodynamic models, a detailed engine component predesign is conducted. The aerodynamic and structural design of the engine components are executed using a stepwise increase in level of detail and are continuously evaluated in context of the overall engine system.
Prediction of Solar Photovoltaic/Thermal Collector Power Output Using Fuzzy Logic
Authors: Sridharan M. , Jayaprakash G. , Chandrasekar M. , Vigneshwar P. , Paramaguru S. , Amarnath K.
Published: July 2018

In recent years, solar PV/T water collectors have been identified as one of the most promising hybrid devices. It is a combination of solar photovoltaic (PV) and solar flat plate collector (FPC) systems capable of generating electrical and thermal power simultaneously. This study presents a model which predicts solar PV/T collector power output using fuzzy logic techniques. A fuzzy logic model was established to predict power output of PV/T with respect to changes in input process and FPC output power. Membership functions were allocated in connection with each model input. Experimental tests conducted during the month of December 2016 are compared with the developed fuzzy model to verify predicted results. The results indicate an agreement between fuzzy model and experimental results with an accuracy of 94.38% and error of 5.62%.
Measured Static and Rotordynamic Characteristics of a Smooth-Stator/Grooved-Rotor Liquid Annular Seal
Authors: Alex Moreland J. , Childs Dara W. , Bullock Joshua T.
Published: July 2018

Electric submersible pumps (ESPs) utilize grooved-rotor/smooth-stator (SS/GR) seals to reduce leakage and break up contaminants within the pumped fluid. Additionally, due to their decreased surface area (when compared to a smooth seal), grooved seals decrease the chance of seizure in the case of rotor-stator rubs. Despite their use in industry, the literature does not contain rotordynamic measurements for smooth-stator/circumferentially grooved-rotor liquid annular seals. This paper presents test results consisting of leakage measurements and rotordynamic coefficients for a SS/GR liquid annular sdeal. Both static and dynamic variables are investigated for various imposed preswirl ratios (PSRs), static eccentricity ratios (0–0.8), axial pressure drops (2–8 bars), and running speeds (2–8 krpm). The seals' static and dynamic features are compared to those of a smooth seal with the same length, diameter, and minimum radial clearance. Results show that the grooves reduce leakage at lower speeds (less than 5 krpm) and higher axial pressure drops, but does little at higher speeds. The grooved seal's direct stiffness is generally negative, which would be detrimental to pump rotordynamics. As expected, increasing preswirl increases the magnitude of cross-coupled stiffness and increases the whirl frequency ratio (WFR). When compared to the smooth seal, the grooved seal has smaller effective damping coefficients, indicative of poorer stability characteristics.
In Situ Thermal Nondestructive Evaluation for Assessing Part Quality During Composite Automated Fiber Placement
Authors: Gregory Elizabeth , Juarez Peter
Published: July 2018

This paper presents data from an innovative nondestructive evaluation (NDE) method for automated composite fiber placement fabrication. Using Infrared images of the fiber, as it was being placed, we are able to provide valuable information about the quality of the part during fabrication. Herein, we discuss the methodology for data collection and processing. The described in situ thermal NDE process is found to be applicable for identifying fiber tow overlaps, gaps, twists, puckering, and poor ply adhesion prior to cure, thereby reducing the time and cost associated with post cure flaw repair or scrapping parts. This paper also describes the process of assembling data sets for an entire part beyond simple frame by frame analysis. Example data sets for both a flat part and a larger cylindrical part are presented to demonstrate the type of defect characterization information that can be obtained.
Design of Acoustic Liner in Small Gas Turbine Combustor Using One-Dimensional Impedance Models
Authors: Kim Daesik , Jung Seungchai , Park Heeho
Published: July 2018

The side-wall cooling liner in a gas turbine combustor serves main purposes—heat transfer and emission control. Additionally, it functions as a passive damper to attenuate thermoacoustic instabilities. The perforations in the liner mainly convert acoustic energy into kinetic energy through vortex shedding at the orifice rims. In the previous decades, several analytical and semi-empirical models have been proposed to predict the acoustic damping of the perforated liner. In the current study, a few of the models are considered to embody the transfer matrix method (TMM) for analyzing the acoustic dissipation in a concentric tube resonator with a perforated element and validated against experimental data in the literature. All models are shown to quantitatively appropriately predict the acoustic behavior under high bias flow velocity conditions. Then, the models are applied to maximize the damping performance in a realistic gas turbine combustor, which is under development. It is found that the ratio of the bias flow Mach number to the porosity can be used as a design guideline in choosing the optimal combination of the number and diameter of perforations in terms of acoustic damping.
Analytical Study of Thermo-Physical Performance of Nanofluid Loaded Hybrid Double Slope Solar Still
Authors: Sahota Lovedeep , Gupta V. S. , Tiwari G. N.
Published: July 2018

In the present paper, efforts has been made to study the thermophysical performance (properties) of N photovoltaic thermal flat plate collectors coupled with double slope solar still (N-PVT-FPC-DSSS) and operating with helically coiled heat exchanger. The analysis has been performed for the optimized concentration of NPs (Al2O3 0.107%; TiO2 0.093%; and CuO 0.131%) and optimized basin fluid (base fluid/nanofluid) mass (50 kg) for different weather conditions of the month May (New Delhi). The Nusselt number (Nu) and Rayleigh number (Ra) are functions of thermophysical properties of nanofluids and strongly influence the natural convective heat transfer coefficient in the solar still. Therefore, these numbers have also been investigated for base fluid and Al2O3, TiO2, and CuO–water-based nanofluids in detail. Significant enhancement in natural convective heat transfer coefficient (Al2O3 67.03%; TiO2 63.56%; and CuO 71.23%) and Nusselt number (Al2O3 119.72%; TiO2 98.64%; CuO 151.62%) has been observed. The monthly productivity of the hybrid system found to be higher by using nanofluids (320.77 kg TiO2; 338.23 kg Al2O3, and 355.46 CuO) as expected from the heat transfer results. Moreover, the comparative study between the proposed hybrid system and passive DSSS has been carried out.
An Inverse Method for Optimizing Elastic Properties Considering Multiple Loading Conditions and Displacement Criteria
Authors: Smyl Danny
Published: July 2018

Significant research effort has been devoted to topology optimization (TO) of two- and three-dimensional structural elements subject to various design and loading criteria. While the field of TO has been tremendously successful over the years, literature focusing on the optimization of spatially varying elastic material properties in structures subject to multiple loading states is scarce. In this article, we contribute to the state of the art in material optimization by proposing a numerical regime for optimizing the distribution of the elastic modulus in structural elements subject to multiple loading conditions and design displacement criteria. Such displacement criteria (target displacement fields prescribed by the designer) may result from factors related to structural codes, occupant comfort, proximity of adjacent structures, etc. In this work, we utilize an inverse problem based framework for optimizing the elastic modulus distribution considering N target displacements and imposed forces. This approach is formulated in a straight-forward manner such that it may be applied in a broad suite of design problems with unique geometries, loading conditions, and displacement criteria. To test the approach, a suite of optimization problems are solved to demonstrate solutions considering N = 2 for different geometries and boundary conditions.
Fatigue Design Recommendations for Conical Connections in Tubular Structures
Authors: Lotsberg Inge
Published: July 2018

Conical connections are important structural members for the integrity of most types of welded tubular structures. They are for example used in traditional jacket structures for oil and gas production and in monopiles for support of wind turbines where an optimal design is aimed for. From contact with the industry, it is noted that there is uncertainty about the basis for the stress concentration factors (SCF) for conical connections in design standards for fatigue assessment. This is related to how fabrication tolerances are accounted for and how a transition in thickness from the cone to the tubular or the cylinder should be made to minimize stresses due to thickness transitions and fabrication tolerances. Analytical expressions for stress concentrations at conical transitions are outlined in this paper to get a better understanding of the effect of thickness of the cone and the cylinder. By a proper basis for fatigue design, it is possible to control additional stresses from thickness transitions and fabrication tolerances at these connections.
Design Space Exploration of a Beam Flexible Hub Concept for an Inside-Out Ceramic Turbine Using a Simplified Rotordynamic Finite Element Model
Authors: Landry Céderick , Dubois Patrick K. , Plante Jean-Sébastien , Charron François , Picard Mathieu
Published: July 2018

This paper presents a new flexible hub design for the inside-out ceramic turbine (ICT) rotor configuration. This configuration is used in microturbines to integrate ceramic blades in order to increase turbine inlet temperature (TIT), which leads to higher cycle efficiency values. The ICT uses an outer composite rim to load the ceramic blades in compression by converting the centrifugal loads of the blades into hoop stresses in the composite rim. High stresses in the composite rim lead to high radial displacement of the blades. This displacement is compensated by using flexible hub in order to maintain the contact with the blades. However, hub flexibility can lead to rotordynamic problems as heavy hub deformation will induce high stresses in it. Thus, stresses in the hub are induced by both rotordynamics and centrifugation, requiring a multi-objective design process, which has yielded geometries that limited, until now, the blade tip speed to 358 m/s. In this paper, a simplified rotordynamics finite element model of a flexible hub is developed to allow quick design iterations. Using the model, a design space exploration of this hub concept is done while considering centrifugation and rotordynamics. Experimental validation is conducted on a simplified ICT prototype up to 129 krpm, i.e., an equivalent blade tip speed of 390 m/s. Finally, predictions from the experimentally calibrated model show that the tested prototype hub could reach a blade tip speed of 680 m/s.
Rotor Damped Natural Frequencies and Stability Under Reduced Oil Supply Flow Rates to Tilting-Pad Journal Bearings
Authors: Nichols Bradley R. , Fittro Roger L. , Goyne Christopher P.
Published: July 2018

Reduced oil supply flow rates in fluid film bearings can cause cavitation, or lack of a fully developed film layer, over one or more of the pads due to starvation. Reduced oil flow has the well-documented effects of higher bearing operating temperatures and decreased power losses; however, little experimental data are available on its effects on system stability and dynamic performance. The study looks at the effects of oil supply flow rate on dynamic bearing performance by comparing experimentally identified damped natural frequencies and damping ratios to predictive models. A test rig consisting of a flexible rotor and supported by two tilting pad bearings in flooded housings is utilized in this study. Tests are conducted over a range of supercritical operating speeds and bearing loads while systematically reducing the oil supply flow rates provided to the bearings. Shaft response measured as a magnetic actuator is used to perform sine sweep excitations of the rotor. A single-input, multiple-output system identification technique is then used to obtain frequency response functions (FRFs) and modal parameters. All experimental results are compared to predicted results obtained from bearing models based on thermoelastohydrodynamic (TEHD) lubrication theory. Both flooded and starved model flow assumptions are considered and compared to the data. Differences in the predicted trends of the models and the experimental data across varying operating conditions are examined. Predicted pressure profiles and dynamic coefficients from the models are presented to help explain any differences in trends.
Characterization of a Supersonic Turbine Downstream of a Rotating Detonation Combustor
Authors: Liu Z. , Braun J. , Paniagua G.
Published: July 2018

Rotating detonation combustors (RDCs) offer theoretically a significant total pressure increase, which may result in enhanced cycle efficiency. The fluctuating exhaust of RDC, however, induces low supersonic flow and large flow angle fluctuations at several kHz, which affects the performance of the downstream turbine. In this paper, a numerical methodology is proposed to characterize a supersonic turbine exposed to fluctuations from RDC without any dilution. The inlet conditions of the turbine were extracted from a three-dimensional (3D) unsteady Reynolds-averaged Navier–Stokes simulation of a nozzle attached to a rotating detonation combustor, optimized for minimum flow fluctuations and a mass-flow averaged Mach number of 2 at the nozzle outlet. In a first step, a supersonic turbine able to handle steady Mach 2 inflow was designed based on a method of characteristics solver and total pressure loss was assessed. Afterward, unsteady simulations of eight stator passages exposed to periodic oblique shocks were performed. Total pressure loss was evaluated for several oblique shock frequencies and amplitudes. The unsteady stator outlet profile was extracted and used as inlet condition for the unsteady rotor simulations. Finally, a full stage unsteady simulation was performed to characterize the flow field across the entire turbine stage. Power extraction, airfoil base pressure, and total pressure losses were assessed, which enabled the estimation of the loss mechanisms in supersonic turbine exposed to large unsteady inlet conditions.
Adaptive Control of a Robot-Assisted Tele-Surgery in Interaction With Hybrid Tissues
Authors: Kolbari Hamidreza , Sadeghnejad Soroush , Bahrami Mohsen , Ali Kamali E.
Published: July 2018

In a haptic teleoperation system, which interacts with unknown and hybrid environments, it is important to achieve stability and transparency. In medical usages, the utilization of knowledge on the tissues behavior in a controller design can improve the performance of the surgery in a robot-assisted telesurgery. Simultaneous interaction with hard and soft tissues makes it difficult to achieve stability and transparency. To deal with this difficulty, two controller schemes are designed. At first, a nonlinear mathematical model (inspired by the Hunt-Crossley (HC) model), which has the properties of soft and hard tissues, is combined with the slave side dynamic. In the second approach, the reaction force applied by hybrid tissues during the transition between tissues of different properties is modeled as an unknown force acting on the slave side. In a four-channel (4-CH) architecture, nonlinear adaptive controllers are designed without any knowledge about the parameters of the master, the slave robot, and the environment. For both control schemes, Lyapunov candidate functions provide a way to ensure the stability and transparency in the presence of uncertainties. The testbed comprises two Novint Falcon robots functioning as master and slave robots. Moreover, the experiments are performed on various objects, including a soft cube, a hard cube, and a phantom tissue. This paper rigorously evaluates the performances of the proposed methods, comparing them with each other and other previous schemes. Experimental and numerical results demonstrate the effectiveness of the proposed control schemes.
Criteria for Best Performance of Pre-Optimized Solid Dampers
Authors: Gastaldi Chiara , Gola Muzio M.
Published: July 2018

This paper furthers recent research by these authors. The starting point is the pre-optimization of solid dampers, which ensures that all dampers bound to “misbehave” are excluded since the early design stage. The authors now enlarge the scope of their investigations to explore those damper configurations selected inside the admissible design area. The purpose of the paper is to present a set of criteria apt to select a damper configuration which not only avoids unwanted situations, but in addition guarantees high performance under different design conditions. The analysis starts with the definition of a set of requirements a high performance damper should meet. In detail, the present investigation seeks to answer the following questions: in the low excitation regime, what is the frequency shift and the stiffening effect each damper can provide? for increasing excitation levels, which damper will start slipping sooner? in the high excitation regime, which damper provides the maximum dissipation? Like pre-optimization, it does not involve nonlinear finite element calculations, and unlike existing optimization procedures, is not linked to a specific set of blades the damper may be coupled to. The numerical prediction of the blade-damper coupled dynamics is here used only for validation purposes. The approach on which this paper rests is fully numerical; however, real contact parameters are taken from extensive experimental investigations made possible by those purposely developed test rigs which are the distinctive mark of the AERMEC Lab of Politecnico di Torino.
Dual Drive Booster for a Two-Spool Turbofan: High Shaft Power Offtake Capability for More Electric Aircraft and Hybrid Aircraft Concepts
Authors: Kloos Vadim , Speak Trevor H. , Sellick Robert J. , Jeschke Peter
Published: July 2018

The effects of high shaft power offtake (POT) in a direct drive, a geared drive, and a novel turbofan configuration are investigated. A design and off-design performance analysis shows the configuration specific limitations and advantages. The more electric aircraft (MEA) concept promises to offer advantages with respect to aircraft performance, maintenance, and operating costs. The engines for the MEA concept are based on conventional turbofan architectures. These engines are designed for significantly increased shaft POT that is required by the airframe, and the shaft power is usually taken off the high-pressure (HP) spool. This can impair the off-design performance of the engine and lead to compromises during engine design and to operability limitations. Taking the power off the low-pressure (LP) spool mitigates some of the problems but has other limitations. In this work, an alternative novel turbofan architecture is investigated for its potential to avoid the problems related to high shaft POTs. This architecture is called the dual drive booster because it uses a summation gearbox to drive the booster from both the LP and HP spool. The shaft power, if taken off the booster spool, is effectively provided by both the LP and HP spools, which allows the provision of very high power levels. This new concept is benchmarked against a two-spool direct drive and a geared drive turbofan (GTF). Furthermore, it is described, how the new architecture can incorporate an embedded motor generator. The presented concept mitigates some of the problems, which are encountered during high POT in conventional configurations. In particular, the core compressors are less affected by a change in shaft POT. This allows higher POTs and gives more flexibility during engine design and operation. Additionally, the potential to use the new configuration as a gas turbine-electric hybrid engine is assessed, where electrical power boost is applied during critical flight phases. The ability to convert additional shaft power is compared with conventional configurations. Here, the new configuration also shows superior behavior because the core compressors are significantly less affected by power input than in conventional configurations. The spool speed and its variation are more suitable for electrical machines than in conventional configuration with LP spool power transfer. The dual drive booster concept is particularly suited for applications with high shaft POTs and inputs, and should be considered for propulsion of MEAs.