bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular Simulation of Methane Adsorption Behavior on Coal: Effects of Maturity and Moisture Content
Authors: Miao Yanan , Luan Guoliang , Zhao Chaojie , Li Yong 
Published: November 2022

Abstract
The adsorption behaviors of multiphase fluids in coal are vital for estimating their transfer and flow mechanisms. In this study, taking the classical coal structures as instances, the impacts of maturities and moisture contents of coal on the methane adsorption capacities and thermodynamic properties were analyzed and determined by molecular simulations. Specifically, the simulated pressures were varied from 0 to 16 MPa, and three temperatures (298 K, 323 K, and 348 K) were considered. In addition, the competitive adsorption capacities of water/methane molecules were evaluated and the critical value of moisture content affecting the isosteric adsorption heat of methane was determined. Furthermore, a quantitative relationship between the gas adsorption amount and adsorption equilibrium pressure under a three-phase “solid–gas–liquid” action was established. The simulated results showed that taking the intermediate-rank coals as examples, the absolute adsorption capacities of methane molecules on different moist coals reduced by 28.3%, 35.1%, 46.9%, and 62.3%, respectively (at uniform pressure–temperature status) in comparison to their dry status. In addition, when the moisture content was lower than 1.4 wt%, the average isosteric adsorption heat remained almost stable. However, when the moisture content exceeded 1.4 wt%, the average isosteric adsorption heat increased sharply with the increase in the water content. Finally, linear function formulas yielded a good fitting accuracy range for the low- and intermediate-rank coals; in comparison, for the high-rank coal, an exponential function formula obtained a better fitting accuracy than a linear one.
Atomization Characteristics of Low-Volatility Heavy Fuel for Low-Pressure Direct Injection Aviation Piston Engines
Authors: Liu Rui , Huang Kaisheng , Qiao Yuan , Ji Haocheng , Wu Hao 
Published: November 2022

Abstract
Due to safety and convenience, aviation heavy fuel (AHF) is quite suitable for use as an energy source in aviation piston engines for small aerial drones, although its atomization is an important issue. The purpose of this article is to present the atomization mechanism of AHF during low-pressure direct injection (LPDI) and the results of the investigation of the mixing process and flow state of fuel–air two-phase flows. In this study, experimental data were obtained for parameters of fuel spray, which verified the improved calculation model of LPDI that considered the primary atomization of AHF inside the premixing chamber. The influences of injection pressure, ambient pressure, and AHF temperature on the spray characteristics were compared and analyzed. Increasing the injection pressure reduced the spray cone angle and increased the spray area. The penetration distance increased, and the Sauter mean diameter (SMD) of the fuel droplets decreased. Increasing the ambient pressure had significant effects on penetration distance and SMD. The spray area decreased, and the spray cone angle showed small variations. Increasing the AHF temperature had small effects on the penetration distance, and the SMD obviously decreased with increasing fuel temperature. The spray cone angle increased slightly, and the spray area decreased. The results showed that low-volatility AHF for safe and stable engine combustion could be achieved with air-assisted LPDI. In addition, the efficient atomization of AHF can be effectively implemented through the combined adjustment of injection control and physical and chemical parameters.
Influence of Multiaxial Far Field Loadings on the Fatigue Crack-Growth Behaviour by Using Corner-Crack and Cruciform Specimen
Authors: Conrad F. , Kontermann C. , Blug A. , Bertz A. , Carl D. , Oechsner M. 
Published: November 2022

Abstract
By means of fracture mechanics evaluation concepts, the most accurate possible estimation of the crack growth behaviour of complex and highly loaded structures is to be aimed for a more efficient use of components, a more precise planning of inspection intervals and for the realization of advanced design approaches. Standard fracture mechanics specimen used in materials testing are globally subjected to purely uniaxial loading. In contrast, the technical components usually experience multi-axial stresses due to the external loads and to their complex geometry. The influence of multi-axial far-field loads on the crack propagation rate and the crack closure behaviour is unclear and controversially discussed in literature. In this context, the crack propagation behaviour of uniaxially loaded corner-crack specimens and multiaxially loaded cruciform specimens is systematically studied in this investigation. Here, the multiaxiality condition is characterized by the so-called T-stress and systematically varied within the tests. The results so far show no significant influence of the far-field multiaxiality or the T-stress on the crack propagation behaviour. However, the evaluation of the crack closure behaviour indicates that an engineering approach for thin-walled structures leads to a non-conservative estimation.
A Dedicated Model Reduction Method for Turbo-Machines Using a Critical Speed Subspace
Authors: D’Alessandro Francesco , Festjens Hugo , Chevallier Gael , Cogan Scott , Benamara Tariq , Sainvitu Caroline 
Published: November 2022

Abstract
Finite element models representing industrial scale turbo-machines have reached today a very large number of degrees of freedom. The large size of these models requires the use of reduced order modelling to make the simulations computationally affordable. However, the physical characteristics (i.e. modes shapes and natural frequencies) of a rotating machine depend on the rotating speed of the system and classical modal reduction approaches are not efficient in this case. A classical modal basis does not allow to decompose the unbalance response of a rotating system into independent components because the normal modes are evaluated for a constant rotating speed. They are thus invariant and insensitive to the rotating speed variation. In this work a method is proposed to evaluate a reduction basis composed only by the modes excited when the system runs through its own critical speeds. This method produces an essential basis of modes which is optimal for the identification of the main components of the unbalance response of a rotating system. The development of this reduction basis is firstly formulated mathematically. Then, the ‘critical speed basis’ is employed to reduce a real finite element model of about 100 DOFs and it is compared with a classical modal basis. Finally, the efficiency of the proposed reduction method is tested in a non-linear framework.
Effect of System Mode and Structural Damping Perturbation on the Mistuned Forced Response and Aerodynamic Damping of Embedded Compressor Rotors
Authors: Hegde Shreyas , Inge Jonathan D. , Kielb Robert 
Published: November 2022

Abstract
This paper is a continuation of previous papers by the authors that focuses on predicting the mistuned embedded rotor blade forced response. The compressor under consideration is a part of a 3.5stage rig located at Purdue University. Previously, the current authors have discussed the impact of sideband travelling wave forcing functions on the mistuned response and pinned down the reason for a constant underprediction in the amplification factor. This prompted further research to determine the sensitivity of the response to a known change in the system mode. In the first section of the current paper, the authors perturb the system modes frequencies in a probabilistic manner and compute the influence of the system mode on the mistuning amplification factor. The second part of this study involves determining the impact of a perturbation in the structural damping on the mistuned response. The study is also extended to an aerodynamic dynamic analysis wherein the impact of a perturbation in system mode frequency and structural damping is determined both individually and as a combined influence. Finally, a brief investigation of system eigenvalues and eigenvectors is conducted to understand the impact of mistuning on aerodynamic damping suppression. This analysis is joined with a broad examination of the relationship between damping and the extent of mistuning. The key conclusions from this paper are: 1) The mistuned forced response was highly sensitive to the system mode input, i.e., although the input was probabilistic, the output was deterministic. 2) Since the aerodynamic damping dominates in the case study, a change in the structural damping parameter has minimal effect on the mistuned response, particularly the mistuning amplification factor. 3) The results of the flutter analysis show that a perturbation in the system mode frequency stabilizes the system much faster than a perturbation in the structural damping, and the latter has minimal influence on the eigenvalues of the solution. 4) Under the application of mistuning, compression of the damping components of the complex eigenvalues is dominant over the expansion of the frequency components and is amplified when the structural coupling is not considered. 5) In cases of both random and near alternate blade mistuning, the relationship between mistuning and damping is positive up to a point, after which further increasing mistuning begins to reduce system damping.
Fracture Mechanics-Based Structural Integrity Assessment of Aero-Engine Turbine Disks Under Overspeed Conditions
Authors: Zhu Jiangchao , Madia Mauro , Schurig Michael , Schlums Hartmut , Zerbst Uwe 
Published: November 2022

Abstract
Aero-engine turbine disks are safety-relevant components which are operated under high thermal and mechanical stress conditions. The actual part qualification and certification procedures make use of spin-tests conducted on production-similar disks. While these tests provide, on the one hand, a reliable definition of the critical conditions for real components, on the other hand they represent a relevant cost item for engine manufacturers. The aim of this work is to present part of a fracture mechanics-based procedure under development which aims at replacing the tests on production-similar disks with lab tests on fracture mechanics specimens. In particular, the rim-peeling failure mode is considered as case study. A semi-circular surface crack is modelled at the most stressed region at the diaphragm of a turbine disk, with the crack plane perpendicular to the radial direction. The crack is therefore subjected to a biaxial stress state and grows under increasing rotational speed until it triggers the rim-peeling failure. The finite element simulation of the cracked disk considers the real thermal and mechanical loading conditions. In order to design a lab representative specimen, beside the crack driving force, expressed in terms of J-integral, also the constraint to plastic deformation e.g., stress triaxiality, at the crack-tip must be similar for the same crack in the specimen and in the disk. This has been achieved and as expected, both the highest J-integral and constraint factor are calculated at the same location along the crack front for both disk and specimen. The results of the structural integrity assessment in the form of a Failure Assessment Diagram (FAD) show good agreement between designed specimen and disk both in terms of expected failure mode and value of the critical speed. Probabilistic aspects are also considered in the calculations.
Quantification of the Impact of the Crack Shape Constraint Assumption Onto Predicted Remaining Useful Life
Authors: Loghin Adrian 
Published: November 2022

Abstract
Today, different LEFM based reduced order modeling and 3D FEA based crack propagation life assessment tools are available to the end user. For a benchmark problem where solutions from different tools are compared, numerical variability can be observed [1]. One source of variability is related to the crack shape definition since reduced order models make use of elliptical representations during crack propagation modeling procedure while a 3D FEA based simulation can eliminate this shape constraint. Using a classical corner crack at a hole geometry, the impact of the crack front shape assumption on the computed remaining useful life is addressed. The same 3D FEA based explicit crack growth software application is used to obtain the two solutions and therefore limiting other sources of error in this comparison. The accuracy of the mode I stress intensity factor solution for initial crack and convergence of the fatigue crack growth solutions are also addressed since numerical error accumulation can impact the conclusion reached in the study.
Morton Effect Calculation and Analysis of Shop Test Results for Single-Shaft Multistage Centrifugal Compressors
Authors: Takahashi Naohiko , Magara Yohei , Hemmi Makoto , Sato Motoki 
Published: November 2022

Abstract
In the manufacturing process of single-shaft multistage centrifugal compressors for process gases, factory tests are conducted to confirm that the lateral vibration satisfies the allowable limits. One of the problems that must be taken care of during the test is the increase in vibration due to the Morton Effect. The Morton Effect is a thermal bending vibration caused by the non-uniformity of the oil film temperature of the bearing, and many troubles have been reported in overhung rotors. However, there are few reports of the Morton Effect in single-shaft multistage compressors. This is thought to be because even if the Morton Effect did occur, it was often only a minor problem. Although it is a minor problem, it is necessary to predict and evaluate the Morton Effect in order to prevent a prolonged test process and costly countermeasures. In this study, a calculation method for the Morton Effect has been developed for a single-shaft multistage centrifugal compressor, and an evaluation index for the Morton Effect is proposed. The developed method is verified and the validity of the proposed evaluation index of the Morton Effect is checked using cases of increased vibration that occurred in factory tests.
Condition Monitoring Insight Using Bayesian Inference and Rotor Dynamics Modelling for Rotating Machinery
Authors: Nelson Greg , Palmer Iain 
Published: November 2022

Abstract
Rotor dynamics modelling can be used to predict vibration levels for given inputs, such as unbalance levels and location, which may be of interest for condition monitoring or diagnosis. However, given measured vibration, using rotor dynamics models to find the corresponding root cause inputs is not straightforward.
In the method presented in this paper, Gaussian Process models are developed as surrogates for the rotor dynamics finite element models, and are used with Bayesian Inference to determine the probability distributions of model inputs for a given vibration response. This method allows parameters describing the machine condition, such as unbalance location and magnitude, and bearing clearances, to be determined as well as the confidence in these predictions.
The method is demonstrated by simulating the vibration response of a compressor rotor, adding noise to it, and then using the technique to accurately infer useful information such as the unbalance magnitude and location, and the clearance in each bearing.
This technique can be applied as a risk-based approach to condition monitoring of rotating machinery. Further development of this approach as part of a digital twin which uses in-service measurements would provide operators with insight into the likelihood of different root causes of vibration, and the corresponding machine condition.
Short-Time Creep Deformation of the Coarse-Grained Nickel-Base Alloy 247 and Its Implications on the High-Cycle Fatigue Behavior
Authors: Jordan Oliver , Lion Philipp , Beck Tilmann 
Published: November 2022

Abstract
Cast polycrystalline nickel-base superalloys are typically used for critical high temperature aerospace and automotive components, such as turbine blades or turbocharger wheels. These high temperature components can undergo creep damage caused by, e.g., centrifugal forces on the turbine rotor blades, as well as high-cycle fatigue (HCF) from, for instance, vibrations of the rotor blade. Therefore, both, creep resistance and fatigue strength, are important mechanical properties of these materials. The study presented here addresses the introduction of creep damage and its influence on the high-cycle fatigue behavior. For this purpose, fatigue specimens of coarse-grained Alloy 247 LC CC blade root material were pre-stressed on a pneumatic creep test rig to achieve creep-induced microstructural damage. The isothermal 900°C short-time creep investigations below 1000 h test duration were performed at different tensile stresses which result in different strain rates. After the creep tests, scanning electron- and light microscopy investigations of metallographic cross-sections of selected specimens were performed to determine the creep-induced grain boundary damage such as pore count, pore size, and coarsening of the γ′ structure. This was followed by uniaxial, stress-controlled isothermal 850°C high-cycle fatigue tests on undamaged and pre-damaged specimens at a frequency of 10 Hz and a load ratio of R = −1. Subsequently, fractographic and cross-section investigations, which provide information on the fatigue cracking, the failure initiating defects, and the pore morphology were performed. The results of this study show that the degree of creep induced porosity is a dominant structural parameter for the HCF behavior of the investigated nickel-base superalloy.
Feasibility Analysis of the Rotor Elastic Support With Piezoelectric Damping
Authors: Hu Yu , Li Lin , Wu Yaguang , Fan Yu 
Published: November 2022

Abstract
The squirrel cage is a widely-used elastic support in aeroengine. The combination of the squirrel cage and damping structures, such as squeeze film dampers, can effectively suppress rotor vibration. The squeeze film damper, although providing significant damping, requires a specific auxiliary lubricant supply system, which occupies space and brings additional weight. Piezoelectric materials have the advantages of light weight, high energy density, and wide bandwidth. The electromechanical coupling effect ensures that they can be used as energy transducers, and the corresponding piezoelectric damping has attracted extensive attention. In this study, we propose an elastic support-piezoelectric damper system for rotors by integrating the piezoelectric damping to the squirrel cage. The purpose of this study is to demonstrate the feasibility of the piezoelectric squirrel cage to suppress the vibration of the low pressure rotor of aero-engine from both the aspects of vibration and strength. To do that, the finite element model of a dummy rotor with elastic support-piezoelectric damper system is established first. The polarization direction and the network topology are optimized to reduce the amount of circuit impedance under the premise of ensuring the modal electromechanical coupling factor. An in-house code to simulate the dynamic performance of the rotor with the elastic support-piezoelectric damper system is developed in ANSYS/MATLAB environment. To reduce the computational cost, the following acceleration techniques are adopted: 1) the specific modal synthesis method dedicated to piezoelectric structures is implemented to reduce the dimension of the governing equations; 2) the equivalent linearization method is carried out to transfer the synchronized switch damping (SSD) with nonlinear nature to a frequency-dependent impedance, thus the time-consuming nonlinear solver is avoided. The unbalance response of the rotor is analyzed numerically. The damping effects of two promising piezoelectric damping technologies, i.e. the resonant damping and the SSD, are compared and discussed. Results show that the SSD network can reduce the vibration level of the rotor significantly with good robustness; the number of the SSD control circuit is only the half of the number of squirrel cage bars; the failure strength margin is sufficient.
Aerodynamic Damping of Composite UHBR Fans Under the Consideration of Acoustic Intake Reflections
Authors: Gößling Jan , Seume Joerg R. , Flüh Jan Peter , Paletta Nicola , Eggers Torben , Friedrichs Jens , Natale Nunzio 
Published: November 2022

Abstract
Steadily rising regulations and demands on aeroengines require the continuous reduction of CO2 emissions. Among other factors, particularly the weight reduction of the engine as well as synergetic engine-airframe integration are of major concern. Both lead to the application of shorter and more sensitive intakes as well as new materials, such as fiber composites. Fiber composites generally have a considerably lower density but a similar stiffness compared to common fan blade materials resulting in a reduction of the engines’ weight. A further difference from conventional materials is the anisotropic behavior of the stiffness, imposed by the ply orientation. In this paper, the impact of the use of fiber composites for the scaled rotor of an ultra-high bypass ratio (UHBR) fan on the aeroelasticity is investigated numerically. In order to influence the eigenfrequency and mode shape, the ply orientation of the blade lay-up is varied. The influence on the resulting aerodynamic damping is analyzed numerically, using a harmonic balance approach. For an accurate prediction, the aeroacoustic reflection at the intake highlight plane is incorporated in the numerical model and its impact is quantified for different intake lengths. The results are compared to a titanium alloy blade design (Ti-6Al-4V) and show the capability of varying the eigenfrequency with a coupled change in twist-to-plunge ratio due to lay-up variations. This change of the structural dynamics of the rotor blade influences the aerodynamic damping. Additionally, acoustic reflections are found to affect the stability, depending on the lay-up, operating condition, and intake length. A lay-up was found, which stabilizes the fan blade for all investigated conditions operating with a typical short ultra-high bypass ratio (UHBR) intake. A special lay-up generates negative aerodynamic damping of −6.6% (logarithmic decrement) when operated close to stall. This fulfills the present project’s particular need to measure flutter in a wind tunnel.