bluuebunny/crossref_metadata_2025_split huggingface dataset:
Data-Driven Method for Response Control of Nonlinear Random Dynamical Systems
Authors: Tian Yanping , Jin Xiaoling , Wu Lingling , Yang Ying , Wang Yong , Huang Zhilong 
Published: January 2021

AbstractThe response control of nonlinear random dynamical systems is an important but also difficult subject in scientific and industrial fields. This work merges the decomposition technique of feedback control and the data-driven identification method of stationary response probability density, converts the constrained functional extreme value problem associated with optimal control to an unconstrained optimization problem of multivariable function, and determines the optimal coefficients of preselected control terms by an optimization algorithm. This data-driven method avoids the difficulty of solving the stochastic dynamic programming equation or forward–backward stochastic differential equations encountered in classical control theories, the miss of the conservative mechanism in the nonlinear stochastic optimal control strategy, and the difficulty of judging the integrability and resonance of the controlled Hamiltonian systems encountered in the direct-control method. The application and efficacy of the data-driven method are illustrated by the random response control problems of the Duffing oscillator, van der Pol system, and a two degrees-of-freedom nonlinear system.
High-Pressure Optical Measurements of Temperature at Turbine Rotor Inlet Conditions
Authors: Egbert Scott C. , Zeltner Darrel , Rezasoltani Mohsen , Tree Dale R. 
Published: January 2021

Abstract
In gas turbine engines, the measurement of the rotor inlet temperature remains particularly challenging because of harsh operating conditions and limited access. The integrated spectral band ratio (ISBR) method is a nonintrusive optical emission gas temperature measurement technique suitable for this application. Optical fibers made of sapphire were used to transmit the radiative signal from the postcombustion zone to a Fourier transform infrared (FTIR) spectrometer. The ratio of spectral bands of H2O, nominally 100 cm−1 wide between 4600 and 6200 cm−1, was used to infer temperature. ISBR and thermocouple measurements were obtained during two temperature sweeps: one at high load and one at low load (pressures of 1.2 and 0.7 MPa, respectively). The average of three thermocouples 76 mm downstream of the ISBR measurements was on the order of 200 K lower than the ISBR temperatures, consistent with a radiative correction and the heat loss between the two measurements. The change in ISBR temperature (95 K) during the sweep was similar to the change in average thermocouple temperature (89 K). Repeatability of the optical measurement at a given operating condition was on the order of ±15 K and the absolute uncertainty of a single ISBR temperature measurement was estimated to be ±61 K. A linear correlation with an R2 value of 0.97 was also found between raw optical signal and thermocouple measurements, suggesting that once a calibrated measurement is obtained.
Single Task Optimization-Based Planar Box Delivery Motion Simulation and Experimental Validation
Authors: Xiang Yujiang , Tahmid Shadman , Owens Paul , Yang James 
Published: January 2021

Abstract
Box delivery is a complicated task and it is challenging to predict the box delivery motion associated with the box weight, delivering speed, and location. This paper presents a single task-based inverse dynamics optimization method for determining the planar symmetric optimal box delivery motion (multi-task jobs). The design variables are cubic B-spline control points of joint angle profiles. The objective function is dynamic effort, i.e., the time integral of the square of all normalized joint torques. The optimization problem includes various constraints. Joint angle profiles are validated through experimental results using root-mean-square-error (RMSE) and Pearson’s correlation coefficient. This research provides a practical guidance to prevent injury risks in joint torque space for workers who lift and deliver heavy objects in their daily jobs.
Elimination of Numerical Damping in the Stability Analysis of Noncompact Thermoacoustic Systems With Linearized Euler Equations
Authors: Hofmeister Thomas , Hummel Tobias , Berger Frederik , Klarmann Noah , Sattelmayer Thomas 
Published: January 2021

Abstract
The hybrid computational fluid dynamics/computational aeroacoustics (CFD/CAA) approach represents an effective method to assess the stability of noncompact thermoacoustic systems. This paper summarizes the state-of-the-art of this method, which is currently applied for the stability prediction of a lab-scale configuration of a perfectly premixed, swirl-stabilized gas turbine combustion chamber at the Thermodynamics institute of the Technical University of Munich. Specifically, 80 operational points, for which experimentally observed stability information is readily available, are numerically investigated concerning their susceptibility to develop thermoacoustically unstable oscillations at the first transversal eigenmode of the combustor. Three contributions are considered in this work: (1) flame driving due the deformation and displacement of the flame, (2) visco-thermal losses in the acoustic boundary layer and (3) damping due to acoustically induced vortex shedding. The analysis is based on eigenfrequency computations of the Linearized Euler Equations with the stabilized finite element method (sFEM). One main advancement presented in this study is the elimination of the nonphysical impact of artificial diffusion schemes, which is necessary to produce numerically stable solutions, but falsifies the computed stability results.
Modeling of Partially Wetting Liquid Film Using an Enhanced Thin Film Model for Aero-Engine Bearing Chamber Applications
Authors: Singh Kuldeep , Sharabi Medhat , Jefferson-Loveday Richard , Ambrose Stephen , Eastwick Carol , Cao Jing , Jacobs Adrian 
Published: January 2021

Abstract
In the case of aero-engine, thin lubricating film servers dual purpose of lubrication and cooling. Prediction of dry patches or lubricant starved region in bearing or bearing chambers are required for safe operation of these components. In this work, thin liquid film flow is numerically investigated using the framework of the Eulerian thin film model (ETFM) for conditions, which exhibit partial wetting phenomenon. This model includes a parameter that requires adjustment to account for the dynamic contact angle. Two different experimental data sets have been used for comparisons against simulations, which cover a wide range of operating conditions including varying the flowrate, inclination angle, contact angle, and liquid–gas surface tension coefficient. A new expression for the model parameter has been proposed and calibrated based on the simulated cases. This is employed to predict film thickness on a bearing chamber which is subjected to a complex multiphase flow. From this study, it is observed that the proposed approach shows good quantitative comparisons of the film thickness of flow down an inclined plate and for the representative bearing chamber. A comparison of model predictions with and without wetting and drying capabilities is also presented on the bearing chamber for shaft speed in the range of 2500 RPM to 10,000 RPM and flowrate in the range of 0.5 liter per minute (LPM) to 2.5 LPM.
Effects of Atmospheric Uncertainties on Sonic Boom Perceived Level
Authors: Reddy Sohail R. , Chitale Janhavi , Dulikravich George S. 
Published: January 2021

Abstract
This work quantifies the uncertainty in Stevens Mark VII Perceived Level of sonic booms due to uncertainties in atmospheric profiles. The influence of temperature, humidity, and wind profiles, at six cities around the globe, on the sonic boom loudness is calculated. The flow field around an aircraft was obtained by solving the three-dimensional (3D), compressible Euler equations using the UNS3D solver. The near-field pressure signature is then propagated through the atmosphere by solving the augmented Burgers equation using the sBOOM solver. The uncertainty is modeled using a nonintrusive polynomial chaos approach. A sensitivity analysis is performed to identify the altitude range and the atmospheric variable to which the Perceived Level is most sensitive. It was shown that the Perceived Level is not sensitive to any particular altitude but rather the atmospheric profiles. It was also seen that the Perceived Level is highly sensitive to humidity and temperature profiles and less sensitive to the wind profiles.
Multiscale Simulations of Polymer Flow Between Two Parallel Plates
Authors: Yan Hong-Ji , Wan Zhen-Hua , Qin Feng-Hua , Sun De-Jun 
Published: January 2021

Abstract
A modified multiscale method without constitutive equation is proposed to investigate the microscopic information and macroscopic flow properties of polymeric fluid with the memory effect between parallel plates. In this method, the domain is entirely described by macromodel with isolated molecular dynamics simulations applied to calculate the necessary local stresses. The present method is first verified by the creep-recovery motion and pressure-driven flow, and all results are in excellent agreement with the available numerical solutions in literature. Then, the method is extended to simulate two typical problems of relatively large spatial scale in general beyond the capability of molecular dynamics simulations. In the planar Couette flow, the relationship between macroscopic properties and the time evolution of local molecular information is investigated in detail without long time averaging. All results that are consistent with nonequilibrium molecular dynamics and literature qualitatively or quantitatively demonstrate the validity of present multiscale method in simulating transient viscoelastic flows and the capacity to obtain the polymer information. In the pressure-driven flow, a general monotonically decreasing relationship between the maximum or average velocities and the polymer concentrations has been found regardless of the polymer chain length. Particularly, the reference concentration that satisfies a power law with chain length is closely related to the overlap concentration, and the reference velocity is exactly the relevant velocity of Newtonian fluid with corresponding zero shear rate viscosity.
Verification of Probabilistic Fracture Mechanics Analysis Code for Reactor Pressure Vessel
Authors: Li Yinsheng , Katsumata Genshichiro , Masaki Koichi , Hayashi Shotaro , Itabashi Yu , Nagai Masaki , Suzuki Masahide , Kanto Yasuhiro 
Published: January 2021

Abstract
Nowadays, it has been recognized that probabilistic fracture mechanics (PFM) is a promising methodology in structural integrity assessments of aged pressure boundary components of nuclear power plants, because it can rationally represent the influencing parameters in their inherent probabilistic distributions without over conservativeness. A PFM analysis code PFM analysis of structural components in aging light water reactor (PASCAL) has been developed by the Japan Atomic Energy Agency to evaluate the through-wall cracking frequencies of domestic reactor pressure vessels (RPVs) considering neutron irradiation embrittlement and pressurized thermal shock (PTS) transients. In addition, efforts have been made to strengthen the applicability of PASCAL to structural integrity assessments of domestic RPVs against nonductile fracture. A series of activities has been performed to verify the applicability of PASCAL. As a part of the verification activities, a working group was established with seven organizations from industry, universities, and institutes voluntarily participating as members. Through one-year activities, the applicability of PASCAL for structural integrity assessments of domestic RPVs was confirmed with great confidence. This paper presents the details of the verification activities of the working group, including the verification plan, approaches, and results.
An Improved Creep-Fatigue Life Model Involving the Cyclic Softening/Hardening and Stress Relaxation Effect
Authors: Zhang Xiao-Cheng , Gong Jian-Guo , Gao Fu-Hai , Xuan Fu-Zhen 
Published: January 2021

Abstract
In this work, improved creep-fatigue life prediction models based on time fraction (TF) and ductility exhaustion (DE) rule are established for creep-fatigue life prediction of components at elevated temperatures. Cyclic softening/hardening and stress relaxation models for cyclic softening/hardening material are incorporated in the model. Materials data conducted by authors and collected from references are employed for validations. Results indicated that the improved models proposed could present more realistic evolution behavior of materials than the half-life models. The differences of the predicted lives based on the improved models and half-life models are dependent on cyclic behaviors of materials. The predicted life by the improved model is lower than that gained by the half-life model for cyclic softening steels, while it is higher than that by the half-life model for cyclic hardening steels. In addition, the DE rule could overcome the influence of cyclic softening/hardening on creep-fatigue life prediction more significantly than the TF rule.
Model-Based Thermodynamic Analysis of a Hydrogen-Fired Gas Turbine With External Exhaust Gas Recirculation
Authors: Bexten Thomas , Jörg Sophia , Petersen Nils , Wirsum Manfred , Liu Pei , Li Zheng 
Published: January 2021

Abstract
Climate science shows that the limitation of global warming requires a rapid transition toward net-zero emissions of green house gases on a global scale. Expanding renewable power generation in a significant way is seen as an imperative measure within this transition. To compensate for the inherent volatility of wind- and solar-based power generation, flexible and dispatchable power generation technologies such as gas turbines are required. If operated with CO2-neutral fuels such as hydrogen or in combination with carbon capture plants, a green house gases-neutral gas turbine operation can be achieved. An effective leverage to enhance carbon capture efficiency and a possible measure to safely burn hydrogen in gas turbines is the partial external recirculation of exhaust gas. By means of a model-based analysis of a state-of-the-art industrial gas turbine, this study initially assesses the thermodynamic impact caused by a fuel switch from natural gas to hydrogen. Although positive trends such as increasing net electrical power output and thermal efficiency can be observed, the overall effect on the gas turbine process is only minor. In a following step, the partial external recirculation of exhaust gas is evaluated and compared both for the combustion of natural gas and hydrogen, regardless of potential combustor design challenges. The influence of altering working fluid properties throughout the whole gas turbine process is thermodynamically evaluated for ambient temperature recirculation and recirculation at an elevated temperature (303.15 K). A reduction in thermal efficiency as well as non-negligible changes in relevant process variables can be observed. These changes are more distinctive at a higher recirculation temperature.
Partial Premixing Effects on the Reacting Jet of a High-Pressure Axially Staged Combustor
Authors: Genova Tommy , Otero Michelle , Reyes Jonathan , Martin Scott , Ahmed Kareem 
Published: January 2021

Abstract
The effects of partial premixing on a reacting jet-in-crossflow is investigated in a five atmosphere axially staged combustor at stationary gas turbine relevant conditions. The facility consists of a dump style headend burner that provides a crossflow with a quasi-uniform velocity and temperature profile to the axial stage to isolate the effects of the jet-in-crossflow. The headend burner is run with methane and air at a lean equivalence ratio to match industry emission standards. For this work, the total air to the headend and axial stage is kept constant, and fuel is split between the headend and axial stage to represent different gas turbine loading conditions. For the cases analyzed, the fuel split to the axial stage went up to 25%. The axial stage consists of an optically accessible test section with a coaxial injector that provides variability to how long the methane and air can mix before entering the facility. Three different premixed levels are studied: fully premixed, nonpremixed, and partially premixed. The flow-field characteristics of the reacting jet-in-crossflow are analyzed using particle image velocimetry (PIV), and flame behavior is quantified by employing CH* chemiluminescence. NO measurements are made at the exit of the facility using a Horiba emissions analyzer. Two different flames are observed: flames that burn in the leeward recirculation region and flames that burn at the core of the jet.
Employing Computational Fluid Dynamics to Derive Beddoes–Leishman Model Airfoil Parameters for Vertical Axis Wind Turbines
Authors: Hand Brian , Kelly Ger , Cashman Andrew 
Published: January 2021

AbstractThe blades of a vertical axis wind turbine (VAWT) experience large variations in the angle of attack at low tip-speed ratios and induce blade force oscillation. These unsteady aerodynamic effects must be considered in the VAWT aerodynamic modelling methodology by utilizing a dynamic stall model. The Beddoes–Leishman (B–L) dynamic stall model is a popular method to simulate the unsteady VAWT blade dynamic stall aerodynamics. However, a limitation of the B–L dynamic stall model is the number of the airfoil dependent parameters derived from both steady and unsteady experimental measurements. In this paper, a methodology is described to compute these B–L dynamic stall model airfoil coefficients utilizing a computational fluid dynamics (CFD) model. This method permits the calculation of the blade dynamic stall characteristics over a range of reduced pitch rates by employing a user-defined sliding mesh motion technique. Furthermore, the variation in the blade Reynolds number is accounted for by conducting simulations at the maximum and minimum VAWT envelope operating limits. Aerodynamic blade force experimental measurements are used to compare the predictions from a low-order model with airfoil data extracted CFD and experiments. This approach expands the applicability of the B–L dynamic stall model for large-scale VAWTs.
Wave Interaction With a Pair of Submerged Floating Tunnels in the Presence of An Array of Submerged Porous Breakwaters
Authors: Kaligatla R. B. , Sharma Manisha , Sahoo T. 
Published: January 2021

Abstract
In this article, a coupled model is proposed for wave interaction with a pair of submerged floating tunnels in the presence of an array of bottom-standing trapezoidal porous breakwaters. The theory of Sollitt and Cross is adopted to govern the fluid flow inside the porous medium. For constant water-depth, the eigenfunction expansion method is employed, whereas for varying water-depth, the eigenfunction expansion method along with the mild-slope approximation is employed. The solutions, thus derived, are matched at the shared boundaries under defined physical conditions. First, the performance of a single breakwater of impermeable and permeable type in reducing wave forces on tunnels is analyzed. Next, the performance of two and three submerged breakwaters is studied. The reflection and transmission coefficients of waves are high in the absence of the submerged breakwater and in the presence of an impermeable breakwater. These coefficients significantly reduce in the presence of the submerged porous breakwater. As a result, the horizontal and vertical forces acting on bridges and tunnels are substantially subsided. Wave forces on tunnels reduce with an increase in the angle of incidence. Multiple porous breakwaters show better performance in mitigating wave forces on tunnels. Higher wave force on tunnels is noticed in intermediate water-depth. The findings can enhance the knowledge of submerged porous breakwaters’ performance in reducing wave loads on bridges and tunnels.
Enhancements on Dissimilar Friction Stir Welding Between AZ31 and SPHC Mild Steel With Al–Mg as Powder Additives
Authors: bin Muhamad Mohd Ridha , Raja Sufian , Jamaludin Mohd Fadzil , Yusof Farazila , Morisada Yoshiaki , Suga Tetsuo , Fujii Hidetoshi 
Published: January 2021

Abstract
Dissimilar materials joining between AZ31 magnesium alloy and SPHC mild steel with Al–Mg powder additives were successfully produced by the friction stir welding process. Al–Mg powder additives were set in a gap between AZ31 and SPHC specimen’s butt prior to welding. The experiments were performed for different weight percentages of Al–Mg powder additives at welding speeds of 25 mm/min, 50 mm/min, and 100 mm/min with a constant tool rotational speed of 500 rpm. The effect of powder additives and welding speed on tensile strength, microhardness, characterization across welding interface, and fracture morphology was investigated. Tensile test results showed a significant enhancement of tensile strength of 150 MPa for 10% Al and Mg (balance) powder additives welded joint as compared to the tensile strength of 125 MPa obtained for the welded joint without powder additives. The loss of aluminum in the alloy is compensated by the addition of the Al–Mg powder during welding under a suitable heat input condition identified by varying welding speeds. Microstructural analysis revealed that the Al–Mg powder was well mixed and dispersed at the interface of the joint at a welding speed of 50 mm/min. The intermetallic compound detected in the welding interface contributed to the welding strength.
A Numerical Study on the Effects of Acoustic Forcing on Fuel Spray Dynamics in Gas Turbines
Authors: Treleaven Nicholas C. W. , Garmory Andrew , Page Gary J. 
Published: January 2021

Abstract
In the case of aircraft engines, the fuel is injected as a liquid spray which may play a role in thermoacoustic instabilities through creating changes to the mixture fraction inside the combustion chamber. This study uses two-phase incompressible non-reacting large eddy simulation with Lagrangian particle tracking to show how spray droplets of different sizes can be affected by large scale hydrodynamic structures and acoustic forcing. The forcing is applied at the inlets of a truncated computational domain that only includes the geometry downstream of the fuel injector using the newly developed PODFS (proper orthogonal decomposition Fourier series) method. The PODFS is a model that can reproduce the effects of acoustic forcing by extracting planes of data from an auxiliary acoustically forced compressible unsteady Reynolds averaged Navier-Stokes simulation. A proper orthogonal decomposition analysis shows that fuel droplets of a typical size seen in jet engines are more sensitive to acoustic and hydrodynamic structures than droplets with an order of magnitude larger or smaller diameter, consistent with their Stokes number. Phase and azimuthally averaged results show that fluctuations of the spray mixture fraction represented by large droplets affect the total spray mixture fraction much more than fluctuations of the small droplets. An additional intermittent spray dispersion mechanism was identified that is due to intermittent vorticity being generated between the two outer injector flow passages. An injector design modification has been suggested that will reduce the prevalence of this mechanism.