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The hammer mill exhibits strong vibration during operation, and the dynamic characteristics of its rotor are an important factor affecting the overall vibration state of the machine. This study focuses on the vibration characteristics of the rotor in the self-developed hammer mill, utilizing a combined approach of impact testing and numerical simulation based on finite element analysis. A more accurate finite element simulation model was obtained when the error between the experimental and simulation results was less than 5%. The natural vibration frequencies and modes of the rotor at various orders were studied, revealing that the lower-order modes of the rotor exhibit a single vibration pattern, while the higher-order modes display a combination of torsional and bending vibrations. It was found that the steady-state vibration of the mill is not caused by rotor resonance, providing a theoretical basis for the vibration reduction design of the hammer mill. [ABSTRACT FROM AUTHOR]

The issues related to the design features and operating conditions of turbochargers are addressed briefly. In addition to long-established technical solutions, new, more advanced options that are intended for further scientific research and practical application in turbocharger bearings are revealed. [ABSTRACT FROM AUTHOR]

The results of research into the properties of grain and development of a crushing method that ensures effective grain milling by optimizing the parameters of the grain grinder are presented. The main characteristics of the structural and mechanical properties of barley grain harvested on the plain of Belgorod oblast of the Central Federal District of the Russian Federation and the methods of its milling are studied. Recommendations based on a mathematical model are given for obtaining the required quality of finished products of grain crops processed in conical mills. An installation reproducing real processes of grain grinding in conical mills, with the ability to adjust the process accurately and to output the obtained data to a computer, is proposed. [ABSTRACT FROM AUTHOR]

Many bacteria swim in liquids and move over solid surfaces by rotating flagella. The bacterial flagellum is a supramolecular protein complex that is composed of about 30 different flagellar proteins ranging from a few to tens of thousands. Despite structural and functional diversities of the flagella among motile bacteria, the flagellum commonly consists of a membrane-embedded rotary motor fueled by an ion motive force across the cytoplasmic membrane, a universal joint, and a helical propeller that extends several micrometers beyond the cell surface. The flagellar motor consists of a rotor and several stator units, each of which acts as a transmembrane ion channel complex that converts the ion flux through the channel into the mechanical work required for force generation. The rotor ring complex is equipped with a reversible gear that is regulated by chemotactic signal transduction pathways. As a result, bacteria can move to more desirable locations in response to environmental changes. Recent high-resolution structural analyses of flagella using cryo-electron microscopy have provided deep insights into the assembly, rotation, and directional switching mechanisms of the flagellar motor complex. In this review article, we describe the current understanding of the structure and dynamics of the bacterial flagellum. [ABSTRACT FROM AUTHOR]

Copyright of Machine Tool & Hydraulics is the property of Guangzhou Mechanical Engineering Research Institute (GMERI) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Rotor structure has a great influence on the gas backflow in a screw vacuum pump. The characteristics of the gas main flow along the spiral groove of the screw rotor and the gas reverse flow along the tooth-shaped, tooth side, radial, and circumferential clearances are investigated. A new mathematical model of the pumping flow and backflow involved in a flow balance model is proposed to investigate the actions of the shearing force and pressure difference force. The calculated backflow is verified by comparing the experimental measured results. The relationships of the structural parameters of the screw rotor are established. The effects of the rotor parameters, such as pitch, diameter, and compression ratio, on backflow are revealed. The results show that the rotor diameter and compression ratio remain constant and that the influence of pitch on the backflow is slightly weak, with backflow variations of less than 3%, whereas the pitch, rotor length, and compression ratio are constant and the rotor addendum diameter is directly proportional to the backflow. The addendum diameter of rotor #4 is the largest, and its backflow is about 1.5 times larger than that of rotor #1. When the rotor radial sizes and the pitch of the suction end are constant, the compression ratio is inversely proportional to the backflow in the low-pressure region and proportional to the backflow in the high-pressure regions. Therefore, for a vacuum pump operating in low-pressure areas, the use of the compression ratio of 2.2 or higher is favorable for the reduction in backflow. [ABSTRACT FROM AUTHOR]

The article aims to contribute to the ongoing study of damage to steam turbine rotors resulting from asynchronous connection of electric generators to the unified power system. At the present time, the assessment of the residual life of steam turbine equipment is based on the study of the degradation of the mechanical properties of steels and the analysis of the thermal stress state. The aim of this work was to determine the impact of such vibrations on the mechanical proper-ties of rotors and their damage. This goal was achieved by solving the following tasks: develop-ing a 3D model of the K-1000-60/3000 LMZ turbine unit shaft based on design documentation; calculating the stress-strain state of the shaft resulting from asynchronous connections using fi-nite element analysis; and evaluating the level of metal damage in the rotors due to torsional vi-brations. The developed mathematical model used a classical approach, replacing the working blades and bandage fastenings with concentrated masses and moments of inertia. The most im-portant results are the calculated rotor damages that occur due to asynchronous connection of the turbogenerator to the unified power system with a synchronization angle of 30°. The greatest damage to the rotor metal was found in the shaft section between the steam turbine and the elec-tric generator. The significance of the results obtained is that the use of this data will improve methods for assessing the remaining life of turbogenerators. This, in turn, will improve the relia-bility and safety of power plant operations.

Various processes take place in rotor systems with tilting pad bearings. It is important not only to control but also to manage these processes. Due to the instability of the oil film layer in a bearing with inclined pads, oil whirl/whip can occur. Such whirl/whip destabilize the operation of the rotor system. Additional elastic elements between the tilt pads suppress oil whirl/whip and thus reduce rotor vibration excitation. By identifying the working zones of such bearings where oil whirl and whip occur, the problems of rotor rotation instability can be solved. In order to determine the effectiveness of the elastic elements between the tilting pads, research was conducted. A special stand with diagnostic equipment was used for the tests. The clearance between the rotor and the bearing was 50 μm. During the research, the rotor rotation speed was varied from 0 to 5000 rpm. After conducting the research, stable and unstable rotor working zones were determined (Zone I: 0 to 1938 rpm; Zone II: 1938–3923 rpm; Zone III: 3923–5000 rpm). Based on the obtained research results, it is possible to control the working process of the rotor system. [ABSTRACT FROM AUTHOR]

Copyright of Karaelmas Science & Engineering Journal / Karaelmas Fen ve Mühendislik Dergisi is the property of Karaelmas Science & Engineering Journal and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Compound-wing unmanned aerial vehicles (UAVs) are highly valued for their performance. However, during the transition from vertical take-off to the cruise phase, the rotor wake can be coupled with the fixed wing. In this study, the aerodynamic effects of a DJI 9450 rotor on a NACA2415 fixed wing during transition were investigated using the computational fluid dynamics (CFD) method. The rotor-to-wing distances (R/L = 0.25, 0.5, and 0.9) were varied to analyze their impact on aerodynamic performance. The results show that increasing the distance between the front rotor and the fixed wing enhances the lift and drag of the fixed wing, while increasing the distance between the rear rotor and the fixed wing decreases the lift and drag of the fixed wing. During the rotor's rotation, the fluctuation in the lift and drag of the fixed wing changes periodically due to the rotor wake, and the smaller the distance between the rotor and the fixed wing, the larger the fluctuation. When R/L = 0.25, the fluctuation of the fixed wing is minimized. Compound-wing UAVs with rotors mounted at R/L = 0.25 during the design stage can improve the flight stability during the transition phase in UAVs. [ABSTRACT FROM AUTHOR]

In recent years, unmanned aerial vehicle (UAV) formation flight has become an effective strategy for urban air mobility (UAM). However, close rotor separation during formation flight leads to complex aerodynamic interference between rotors, significantly affecting UAV flight performance and operational safety. This study systematically examines the effects of axial and lateral rotor separation on the rotor's thrust performance through wind tunnel experiments. The tests simulate horizontal, vertical, and hovering states by generating relative airflow in the wind tunnel, focusing primarily on the thrust coefficient changes of the bottom rotor at various separations. The results are compared with a single rotor operating under the same conditions without wake interference. Additionally, computational fluid dynamics (CFD) simulations using the Fluent software were conducted to investigate the effect of wake interactions by analyzing the velocity flow field between the two rotors in different separations. Both the experimental and simulation results demonstrate that rotor aerodynamic performance is notably influenced by wake interactions. Under hovering and vertical states, substantial aerodynamic interference occurs in the region directly beneath the top rotor, within 1D ≤ Z ≤ 3D. This interference gradually diminishes as the rotor separation increases. Additionally, the thrust coefficient of the bottom rotor decreases with increasing flight speed due to the wake, and at higher flight speeds, the wake tends to contract. When the lateral separation is X = 0D, the mid-sectional flow field of the two rotors exhibits symmetry; however, with lateral separation, the symmetry of the bottom rotor's wake velocity field is disrupted. During the horizontal flight, the rotor wake tilts backward due to the relative airflow, and the extent of this influence is governed by both rotor rotational speed and flight velocity. Therefore, when UAVs operate in formation, it is crucial to account for these factors affecting aerodynamic performance, and rotor separation must be optimized to enhance flight safety and efficiency. [ABSTRACT FROM AUTHOR]

In order to ensure the vibration safety of rotor systems in the next generation of aero-engines and reduce the impact of misalignment faults, the effect of support misalignment on the vibration characteristics of rotor systems under ultra-high operating speeds is investigated in this paper. Firstly, an analytical excitation model of the rotor systems under ultra-high operating speeds is established, considering the impact of the support misalignment. Then, based on the model of the misaligned combined support system, the dynamic model of the flexible discontinuous rotor support system with the support misalignment is presented. Subsequently, based on the established model, the effects of support parameters and support misalignment amounts on the vibration characteristics of the rotor support system are analyzed. Finally, experimental validation of the research findings is conducted. The research result shows that the support misalignment increases the vibration response of the rotor, reduces the vibration reduction efficiency of the combined support system, and consequently decreases the vibration safety of the rotor support system. [ABSTRACT FROM AUTHOR]

The study discusses the opportunities for producing geothermal energy, which is a renewable resource providing a continuous supply of heat from the Earth's interior. Unlike fossil fuels, which are non-renewable and cause environmental degradation, geothermal energy is of great interest to researchers, particularly in the context of sustainable development principles. The authors demonstrate the advantages of a new hydro-steam turbine (HST) using the heat of water from geothermal springs and heating boilers for power generation. The HST is designed as a Segner wheel with a steam-water mixture flowing out of a Laval nozzle, the resulting reactive force driving the turbine rotor and the power generator. The features of the HST thermodynamic process are analyzed in the form of a case study describing the design of a 20 kW plant and providing the technical specifications of the installation for a heating boiler plant: hot water flow rate of 7 kg/s, temperature of 130°C, and inlet pressure of 0.6 MPa. The authors present the thermal schemes of the HST in two variants (at a boiler house and as a part of a geothermal power plant). The study concludes that the main advantages of the HST are the absence of elements subject to erosion under the action of steam and water flow and the simplicity of the design increasing the availability of geothermal energy for power generation. Among the limitations of the HST is its low economic efficiency narrowing down its application to conditions where geothermal fields are available for local power supply. [ABSTRACT FROM AUTHOR]

As the advancement of brushless direct current (BLDC) motor is rising, it has been an advantage to use the motor for a wide range of applications. Its robustness and torque development have benefited small applications, such as the agriculture cutter. However, dropping performances of conventional BLDC are affected by the shape of the rotor that has unused magnetic flux. Therefore, this research aimed to analyze the electromagnetic torque by reducing the unused flux from an electromagnetic point of view. Two BLDC models with different slot-pole numbers and rotor types were modeled and simulated with equal permanent magnet volume, and magnetomotive force (MMF). Finite element method (FEM) software was used to compute backelectromotive force (BEMF), cogging torque, electromagnetic torque, and magnetic flux density of the BLDC models. As a result, 9/8 slot-pole with zero ferromagnetic underneath the permanent magnet had the highest BEMF and torque produced compared to the conventional type, with a percentage difference of 27%. In conclusion, this research presents the motor that had an improvement of electromagnetic torque for electrical cutter application. [ABSTRACT FROM AUTHOR]

Physical processes behind flow‐topography interactions and turbulent transitions are essential for parameterization in numerical models. We examine how the Kuroshio cascades energy into turbulence upon passing over a seamount, employing a combination of shipboard measurements, tow‐yo microstructure profiling, and high‐resolution mooring. The seamount, spanning 5 km horizontally with two summits, interacts with the Kuroshio, whose flow speed ranges from 1 to 2 m s−1, modulated by tides. The forward energy cascade process is commenced by forming a train of 2–3 nonlinear lee waves behind the summit with a wavelength of 0.5–1 km and an amplitude of 50–100 m. A train of Kelvin‐Helmholtz (KH) billows develops immediately below the lee waves and extends downstream, leading to enhanced turbulence. The turbulent kinetic energy dissipation rate is O (10−7–10−4) W kg−1, varying in phase with the upstream flow speed modulated by tides. KH billows occur primarily at the lee wave's trailing edge, where the combined strong downstream shear and low‐stratification recirculation trigger the shear instability, Ri < 1/4. The recirculation also creates an overturn susceptible to gravitational instability. This scenario resembles the rotor, commonly found in atmospheric mountain waves but rarely observed in the ocean. A linear stability analysis further suggests that critical levels, where the KH instability extracts energy from the mean flow, are located predominantly at the strong shear layer of the lee wave's upwelling portion, coinciding with the upper boundary of the rotor. These novel observations may provide insights into flow‐topography interactions and improve physics‐based turbulence parameterization. Plain Language Summary: A thorough grasp of the physics driving flow‐topography interactions and turbulent transition is crucial for precise parameterization in numerical models. This study explores energy transformation into turbulence as the Kuroshio encounters a seamount based on direct field observations and theoretical examination. We found that the Kuroshio affected by the seamount kick starts a series of processes wherein the Kuroshio transfers its energy into turbulence through the formation of lee waves and shear instability. As the flow reverses beneath the trailing edge of lee waves, a recirculation rotor is formed, enhancing the vertical shear and weakening the stratification. The strong vertical shear exceeds the limitations imposed by water column stratification, promoting the development of shear instability and ultimately leading to water roll‐ups and turbulence generation, which could dissipate the Kuroshio energy and mix the Kuroshio water. Our findings could help improve physics‐based turbulence parameterization skills for flow‐topography interaction processes in numerical models. Key Points: Prominent nonlinear lee waves are formed as the Kuroshio interacts with the seamount east of TaiwanThe enhanced shear related to the lee wave and the weakened stratification related to the rotor generate a shear unstable regionThe shear instability grows by extracting the mean flow energy at the upwelling portion of the lee wave, where ε O(10−7−10−4) W kg−1 [ABSTRACT FROM AUTHOR]

The primary electrophysiological mechanism of atrial fibrillation (AF) maintenance is poorly defined. AF mapping studies readily record focal activations (defining them as focal sources or breakthroughs) and “incomplete reentries” (defining them as reentries or would-be-reentries) but do not or rarely detect complete circular activations. Electrophysiological alterations induced by anti-AF drugs before AF cardioversion may help delineate the mechanism of AF maintenance. Cardioversion of AF by antiarrhythmic drugs is associated with prolongation of the AF cycle length and temporal excitable gap (t-EG), resulting in improvement in AF organization (AF-org), and with or without alterations in the refractory period, conduction velocity and wavelength. Such electrophysiological pattern is conceivable with termination of a single focal source but not a single reentry (Class III agents do not increase reentrant t-EG). Yet, a single focal source and multiple focal sources are plausible as the primary mechanism of AF maintenance prior drug administration. Improvement in AF-org caused by anti-AF agents before AF cardioversion is coherent with simultaneous multiple random reentries and wavelets. However, simultaneous multiple reentries are unlikely to occur regularly (most of the contemporary AF mapping studies report either a single reentry at a time or no reentry at all), and the ability of random wavelets to maintain AF is speculative. The conducted analysis inclines toward the focal source as the primary mechanism of AF maintenance.

Abstract As an innovative, low-power consuming, and low-stiffness suspension approach, the diamagnetic levitation technique has attracted considerable interest because of its potential applicability in miniaturized mechanical systems. The foundation of a diamagnetic levitation system is mathematical modeling, which is essential for operating performance optimization and stability prediction. However, few studies on systematic mathematical modeling have been reported. In this study, a systematic mathematical model for a disc-shaped diamagnetically levitated rotor on a permanent magnet array is proposed. Based on the proposed model, the magnetic field distribution characteristics, diamagnetic levitation force characteristics (i.e., levitation height and stiffness), and optimized theoretical conditions for realizing stable levitation are determined. Experiments are conducted to verify the feasibility of the proposed mathematical model. Theoretical predictions and experimental results indicate that increasing the levitation height enlarges the stable region. Moreover, with a further increase in the rotor radius, the stable regions of the rotor gradually diminish and even vanish. Thus, when the levitation height is fixed, a moderate rotor radius permits stable levitation. This study proposes a mathematical modeling method for a diamagnetic levitation system that has potential applications in miniaturized mechanical systems.

The effect of helicopter rotor blade tip shape on overall aircraft noise level is analyzed, in forward flight conditions. The infamous HART-II experimental data is used as a base for validations. Commercially available CFD software Ansys/Fluent is used to model the flow field over rotor-body interaction with movingdeforming meshes. The blades are modelled individually to match the actual physical blade geometry and blade movement. The acoustics calculations are performed via FW-H modelling of the software. HART-II blade has a rectangular blade tip planform. Four different tip shapes are modeled and analyzed in addition to the original blade planform. Baseline case of HART-II experiment is used for the predictive calculations. The predictions show that the least sound pressure level obtained by %10 c notched tip shape having 10-degree anhedral angle with 2,23 dB(A) difference amongst other four tip shapes.

A rotor fault identification method integrating symbolic entropy and evidence theory was proposed for the problem of the difficulty to accurately identify the fault state caused by the nonlinearity and nonstationarity of the rotor vibration signal. Firstly, the fluctuation sequence was obtained by processing the recorded data of the rotor system by de-averaging and difference. Secondly the binary sequence was obtained by binary processing. Thirdly the symbol sequence was obtained by encoding to calculate the symbol entropy. In this paper, the code length in the calculation of symbol entropy was determined by an indicator of the relative growth rate of the mean value of symbol entropy. Through experimental analysis, the symbol entropy of the four channels of the rotor was used as the identification vector, and then compared with the identification standard vector obtained from the historical data to obtain the recognition probability of each state, and finally the results of two tests were fused through D-S evidence theory to obtain the final discriminatory result. Compared with the traditional fault identification method based on symbolic entropy, the proposed method can accurately identify the common states of the rotor system, providing a solution to the rotor fault state identification problem when the vibration signals are in nonlinear and nonstationary conditions.

The paper is devoted to the study of temperature and stress distribution in the medium-pressure rotor of the K-200-130 turbine, which are of considerable interest when predicting the durability of this equipment and extending its operation beyond the service life. A geometric model of the most loaded part of the rotor – from the middle of the shaft neck in the thrust bearing area to the 5th stage disc – was developed. The study of the thermal and stress-strain state of the rotor during start-up from a cold state was performed in a two-dimensional formulation using the finite element method. The non-stationary problem of heat conduction during start-up was solved. The obtained results indicate a fairly uniform thermal state during variable operating conditions. The largest temperature gradient (1200–2200 K/m) is observed at the time points from the rotor push to the synchronization of the turbine generator with the power system. After the turbine generator is loaded with up to 30 MW of electric power, a decrease in the temperature field irregularity and its gradual stabilization are observed. It was found that when operating at the nominal steam parameters, the maximum metal temperature is 508 °C in the region of the control stage and decreases when the distance from it increases. The stress-strain state of the rotor was evaluated taking into account the unevenness of temperature fields during start-up, stresses from thermal expansion, and centrifugal forces. The highest stresses are characteristic of the moment when the turbine comes to idle in the area of thermal compensation grooves of the rotor and the control gate and amount to 440–472 MPa. It is noted that these areas are the most likely zones of ring crack nucleation during turbine start-up operations. Subsequently, the stress level gradually decreases as the turbine unit reaches its rated power. It has been established that the most stressed area of the rotor during stationary operation is the area of the axial bore under the control stage and its diaphragm seal (121–134 MPa)

Many factors affect the vibration of the hydraulic unit, including the natural oscillation frequencies of the structural elements, which in some cases may contribute to an increase in vibration because of the occurrence of resonance phenomena. In this work, the case of design optimization of the support assemblies of the shaft pipeline of the hydrogenerator-motor was considered, installed at HSPP during its reconstruction in order to improve vibration parameters. The effect of increasing the stiffness of the upper crosspiece and reducing the weight of the rotating parts on the value of the first and second critical rotation frequencies was analyzed. Based on the results of computations, operability of the proposed new reinforced structure of the upper crosspiece of the hydrogenerator-motor with increased rigidity was confirmed. Using this design could increase the first critical rotation frequency from 9 Hz (540 rpm) to 17.6 Hz (1056 rpm). This would lead to the avoidance of resonance phenomena caused by the proximity of the first critical rotation frequency of the rotor to the rated rotation frequency (600 rpm). The computations were performed in a three-dimensional setting in two stages for each of the considered design cases. At the first stage, the supporting elements rigidity of the shaft line of the hydrogenerator-motor were studied by determining the structural element elastic deformations when it was loaded by a transverse force. At the second stage, these determined stiffnesses of the support elements were used as input data for calculating the critical rotation frequencies of the hydraulic unit rotor. [ABSTRACT FROM AUTHOR]

This manuscript proposes a hybrid technique for fault detection and classification in a three-phase induction motor (IM). The proposed hybrid technique combines enhanced ladder spherical evaluation (ELSE) and recurrent neural networks (RNN); hence, it is called the ELSE–RNN method. The main goal of the manuscript is to detect and categorize the faults that occur in the IM. The key objective of the proposed method is to enhance the performance of supercapacitor (SC) storage technology and fuzzy-tuned proportional–integral (PI) supervision over conventional control. The main contribution of this paper is developing an effective fault diagnosis method for three-phase IMs. The presence of stator, rotor, winding, and bearing faults is employed using signal processing techniques, such as the Hilbert transform and SIFT. The proposed ELSE–RNN technique is utilized with the end goal of detecting and classifying faults. Here, the proposed ELSE–RNN technique recognizes motors' healthy or unhealthy conditions in many situations to distinguish faults for protection. The proposed ELSE–RNN technique reduces the complexity of detecting and classifying faults with a validated system and increases the system's accuracy. The ELSE–RNN technique is implemented in MATLAB, and its performance is compared to existing techniques. [ABSTRACT FROM AUTHOR]

Copyright of China Pulp & Paper is the property of China Pulp & Paper Magazines Publisher and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

As an innovative, low-power consuming, and low-stiffness suspension approach, the diamagnetic levitation technique has attracted considerable interest because of its potential applicability in miniaturized mechanical systems. The foundation of a diamagnetic levitation system is mathematical modeling, which is essential for operating performance optimization and stability prediction. However, few studies on systematic mathematical modeling have been reported. In this study, a systematic mathematical model for a disc-shaped diamagnetically levitated rotor on a permanent magnet array is proposed. Based on the proposed model, the magnetic field distribution characteristics, diamagnetic levitation force characteristics (i.e., levitation height and stiffness), and optimized theoretical conditions for realizing stable levitation are determined. Experiments are conducted to verify the feasibility of the proposed mathematical model. Theoretical predictions and experimental results indicate that increasing the levitation height enlarges the stable region. Moreover, with a further increase in the rotor radius, the stable regions of the rotor gradually diminish and even vanish. Thus, when the levitation height is fixed, a moderate rotor radius permits stable levitation. This study proposes a mathematical modeling method for a diamagnetic levitation system that has potential applications in miniaturized mechanical systems. [ABSTRACT FROM AUTHOR]

The thermal deformation of a flexible rotor system in a high-temperature environment causes changes in the inherent and vibration characteristics. A theoretical model of the flexible rotor was established based on the theory of thermal deformation, the assumed mode method, and the Lagrangian principle. The mode natural frequencies and shapes were explored in detail when the temperature of different nickel-based alloy rotor blades increased gradually (from 0 to 1200°C). The changes in the unstable speed points as the temperature gradually increased were studied based on the rotation speed–frequency diagram. In addition, experimental methods were performed. Mode and steady-state speed tests in a supported state were conducted. Mode experiments were completed on a five-blade rotor test rig with a thermal insulation device, and the acceleration frequency-domain signal showed that the natural frequency decreased with increasing temperature. Through steady-state speed experiments, it was found that the position of the unstable speed points moved forward, and the displacement amplitude increased after local heating. [ABSTRACT FROM AUTHOR]

The effect of helicopter rotor blade tip shape on overall aircraft noise level is analyzed, in forward flight conditions. The infamous HART-II experimental data is used as a base for validations. Commercially available CFD software Ansys/Fluent is used to model the flow field over rotor-body interaction with moving-deforming meshes. The blades are modelled individually to match the actual physical blade geometry and blade movement. The acoustics calculations are performed via FW-H modelling of the software. HART-II blade has a rectangular blade tip planform. Four different tip shapes are modeled and analyzed in addition to the original blade planform. Baseline case of HART-II experiment is used for the predictive calculations. The predictions show that the least sound pressure level obtained by %10 c notched tip shape having 10-degree anhedral angle with 2,23 dB(A) difference amongst other four tip shapes. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agricultural Sciences, Belgrade is the property of University of Belgrade, Faculty of Agriculture and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Bearing is the property of Bearing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Bearing is the property of Bearing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Bearing is the property of Bearing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In urban settings, buildings create complex turbulent conditions, affecting helicopter flight performance during missions and increasing safety risks during takeoff and landing. A numerical study on rotor–building coupled flow field is carried out to address rotor aerodynamic performance under building interferences in natural atmospheric conditions. A high-fidelity atmospheric boundary layer (ABL) model described by an exponential law is established herein. The solution of the coupled flow field is based on the Reynolds-averaged Navier–Stokes (RANS) equations, with the rotor's rotation achieved through the overset grid method. Based on the dominant wind features, the building flow field is distributed into four regions, where the updraft along the headwind side impacts the rotor, bringing about a 76% increase in pitching moment. On the lateral side of the building, distorted rotor wake squeezed upward into the rotor disk, leading to severe blade–vortex interaction (BVI). During low-altitude hovering over rooftops, the mixing of building shed vortices with forward flow wakes causes the formation of a circulation region on the rotor's windward side, resulting in a thrust loss of approximately 7.8%. Meanwhile, the flow environment on the leeward side of the buildings is more stable. Therefore, it is recommended that helicopters adopt a headwind approach during rooftop operations. However, an 11.4% loss in the average hover figure of merit is observed due to consistent thrust losses caused by the recirculation region. [ABSTRACT FROM AUTHOR]

Natural vibrations of multilayer composite beams of an elastic hub and a blade under centrifugal forces are analyzed. Sequence of calculations for the resonance diagram of a blade with a hingeless elastic hub is developed. New results obtained show the possibility of appearance of zones with "zero" dynamic stiffness of the main rotor blade at the start phase. [ABSTRACT FROM AUTHOR]