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1
Liu, Bao Guo, Hai Feng Hua, Long Wang Yue e Xiao Ding Xu. "Design of the Post-Processor for Rotors Dynamics Based on the STEP Standard". Advanced Materials Research 706-708 (giugno 2013): 1871–76. http://dx.doi.org/10.4028/www.scientific.net/amr.706-708.1871.
Testo completoAbstract (sommario):
The STEP standard is an international standard for data expressing and exchanging during the whole life cycle of the product, the neutral file is an universal data exchange form for the data exchanging. In order to develop a STEP post-processer for the rotor dynamics analysis software-Rotors Dynamics, the author elaborates the lexical analysis module and data mapping module, studies the rotor model parameter extraction based on STEP neutral file, and realizes the seamless connectivity between the Rotors Dynamics and the rotor’s CAD model.
2
Jalal, Sara, Fernando Ponta, Apurva Baruah e Anurag Rajan. "Dynamic Aeroelastic Response of Stall-Controlled Wind Turbine Rotors in Turbulent Wind Conditions". Applied Sciences 11, n. 15 (27 luglio 2021): 6886. http://dx.doi.org/10.3390/app11156886.
Testo completoAbstract (sommario):
With the current global trend of the wind turbines to be commissioned, the next generation of state-of-the-art turbines will have a generating capacity of 20 MW with rotor diameters of 250 m or larger. This systematic increase in rotor size is prompted by economies-of-scale factors, thereby resulting in a continuously decreasing cost per kWh generated. However, such large rotors have larger masses associated with them and necessitate studies in order to better understand their dynamics. The present work regarding the aeroelastic behavior of stall-controlled rotors involves the study of the frequency content and time evolution of their oscillatory behavior. A wide range of experiments were conducted to assess the effects of rapid variations on the rotor’s operational conditions. Various gust conditions were tested at different wind speeds, which are represented by pulses of different intensities, occurring suddenly in an otherwise constant wind regime. This allowed us to observe the pure aero-elasto-inertial dynamics of the rotor’s response. A reduced-order characterization of the rotor’s dynamics as an oscillatory system was obtained on the basis of energy-transfer principles. This is of fundamental interest for researchers and engineers working on developing optimized control strategies for wind turbines. It allows for the critical elements of the rotor’s dynamic behavior to be described as a reduced-order model that can be solved in real time, an essential requirement for determining predictive control actions.
3
Zaytsev, Nikolay, Denis Zaytsev, Andrey Makarov e Dmitriy Mineev. "NUMERICAL SIMULATION OF THE DYNAMICS OF A FLEXIBLE ROTOR WITH TWO BALL AUTO-BALANCERS". Perm National Research Polytechnic University Aerospace Engineering Bulletin, n. 62 (2020): 31–44. http://dx.doi.org/10.15593/2224-9982/2020.62.04.
Testo completoAbstract (sommario):
Ball auto-balancing devices can to compensate changes of unbalance "on the move" only for rotors operating at supercritical speeds. For automatic balancing of such rotors, classified as flexible rotors, several auto-balancers located in different cross sections of the shaft are necessary. This makes it necessary to account bending fluctuations on studies of dynamics of the rotor with auto-balancers, that is especially important in the design of the real rotors. In view of the complexity of experimental studies of such rotors in the article the method of direct numerical simulation of the dynamics of the flexible rotor system – supports – auto-balances is considered. The methodological basis of this method is the use of a discrete multi-mass rotor model, which is equivalent in dynamic characteristics to a real rotor, and also the equations of dynamics of the system discrete rotor – supports – auto-balancers, obtained in the direct form of recording. For definition of discrete masses and a matrix of coefficients of influence of stiffness of rotor cross-sections it is supposed to use calculations for finite-element model of a real rotor by existing software complexes of the engineering analysis. The mathematical model of the system dynamics obtained by the Lagrange method takes into account the non-stationarity of the rotor rotation speed, the influence of gravity and the rolling friction of the balls in the auto-balancer cages. Verification of the mathematical model was performed by reproducing the published data using a computational model for a two-support single-disk three-mass rotor with a two-ball auto-balancer. For a four-mass rotor with two two-ball auto-balancers, the results of numerical simulation of dynamics for the modes of acceleration, steady-state rotation and deceleration are presented. It is shown that for the system under consideration, only partial auto-balancing takes place in the steady rotation mode, including after a stepwise increase of the imbalance.
4
Pacholczyk, Michał, e Dariusz Karkosiński. "Parametric Study on a Performance of a Small Counter-Rotating Wind Turbine". Energies 13, n. 15 (29 luglio 2020): 3880. http://dx.doi.org/10.3390/en13153880.
Testo completoAbstract (sommario):
A small Counter-Rotating Wind Turbine (CRWT) has been proposed and its performance has been investigated numerically. Results of a parametric study have been presented in this paper. As parameters, the axial distance between rotors and a tip speed ratio of each rotor have been selected. Performance parameters have been compared with reference to a Single Rotor Wind Turbine (SRWT). Simulations were carried out with Computational Fluids Dynamics (CFD) solver and a Large Eddy Scale approach to model turbulences. An Actuator Line Model has been chosen to represent rotors in the computational domain. Summing up the results of simulation tests, it can be stated that when constructing a CRWT turbine, rotors should be placed at a distance of at least 0.5 D (where D is rotor outer diameter) or more. One can then expect a noticeable power increase compared to a single rotor turbine. Placing the second rotor closer than 0.5 D guarantees a significant increase in power, but in such configurations, dynamic interactions between the rotors are visible, resulting in fluctuations in torque and power. Dynamic interactions between rotor blades above 0.5 D are invisible.
5
Fan, Ye Sen, San Min Wang e Zhen Yang. "Dynamic Characteristics of the Coupled System of the High Pressure Rotor and the Radial Driveshaft of a Turbofan Engine". Advanced Materials Research 44-46 (giugno 2008): 127–34. http://dx.doi.org/10.4028/www.scientific.net/amr.44-46.127.
Testo completoAbstract (sommario):
In a turbofan engine, the high pressure rotor and the radial driveshaft, which transmit the power from the internal gear-box to the external gear-box, are geared by a spiral bevel gear pair. In this paper, a reasonably simplified dynamic model of the coupled rotors system is established, and then, the coupled stiffness matrix and coupled damping matrix of the spiral bevel gear pair are deduced. A shaft element method is proposed to investigate the lateral-torsional coupled vibration equations of the gear-rotor system. Furthermore, the mode shapes and unbalance responses of this two rotors coupled system are simulated. The results indicate that the system derives many new modes and the exciting forces on a rotor of the system would be passed to the other rotor for the gears meshing. When the rotor dynamics of a turbofan engine is being analyzed, the high pressure rotor and the radial drive shaft must be viewed as a whole. The dynamic balance precision of the rotors should be qualified properly, in order to improve the dynamic quality of the turbofan engine.
6
Pacholczyk, Michał, Krzysztof Blecharz e Dariusz Karkosiński. "Numerical investigation on the performance of a small counter-rotating wind turbine". E3S Web of Conferences 116 (2019): 00055. http://dx.doi.org/10.1051/e3sconf/201911600055.
Testo completoAbstract (sommario):
The article presents results of the investigation on the performance of a small counter-rotating wind turbine. Wind turbine has been simulated using Computational Fluid Dynamics methods. Actuator Line Model has been successfully used to represent rotors in computational domain. Parametric study has been carried out, taking into account changes in the tip speed ratio of the rotors while maintaining a constant distance between upwind and downwind rotor. Study results revealed noticeable increase in power coefficient for optimal configuration. Dynamic interaction between rotors has been investigated exposing no significant interference in both torque and power.
7
Mimmi, G., e P. Pennacchi. "Analytical model of a particular type of positive displacement blower". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 213, n. 5 (1 maggio 1999): 517–26. http://dx.doi.org/10.1243/0954406991522743.
Testo completoAbstract (sommario):
Many papers exist in the literature that deal with the twin-screw compressor. This usually has two different rotors, a male and a female, and is commonly used to produce compressed gas for industrial uses. However, a different type of positive displacement rotary compressor with two screws is sometimes used, one of its typical applications being in car engine supercharging. The present paper deals with the latter type, which is defined as a two-screw blower. This blower has two identical helical rotors, each with three lobes. The kinematics and the geometry of the rotors are analysed here, and a complete mathematical model for the rotor is defined. Moreover, different possible shapes of the rotors, depending on the design parameters, are analysed and the limitations in the choice of the design parameters are presented. Finally, an analysis of the theoretical specific slipping of the rotors is presented, showing which zones of the profile are the most stressed. This model will be useful for further studies on rotor pressure loads and blower dynamics.
8
Kaleta, Jiří, Josef Michl, Cécile Mézière, Sergey Simonov, Leokadiya Zorina, Pawel Wzietek, Antonio Rodríguez-Fortea, Enric Canadell e Patrick Batail. "Gearing motion in cogwheel pairs of molecular rotors: weak-coupling limit". CrystEngComm 17, n. 41 (2015): 7829–34. http://dx.doi.org/10.1039/c5ce01372k.
Testo completoAbstract (sommario):
Investigation of the rotor dynamics by X-ray diffraction, spin–lattice relaxation, and DFT modelling of the two rotational barriers in arrays of rod-like molecules with 1,3-bis(ethynyl)bicyclo[1.1.1]pentane rotators conclude to gearing motion between two rotors in a pair.
9
Muszynska, Agnes, Charles T. Hatch e Donald E. Bently. "Dynamics of Anisotropically Supported Rotors". International Journal of Rotating Machinery 3, n. 2 (1997): 133–42. http://dx.doi.org/10.1155/s1023621x97000134.
Testo completoAbstract (sommario):
The paper discusses dynamic effects occurring in machinery rotors supported in bearings and pedestals with laterally different characteristics. In the considered rotor model the anisotropy of radial stiffness and tangential (“cross”) stiffness components are included. Within certain ranges of the rotative speed the support anisotropy leads to the specific, excited-by-unbalance rotor lateral synchronous vibrations in a form of backward (reverse) precession. In addition, one section of the rotor may precess backward, while the other section simultaneously precesses forward. Experimental results illustrate this phenomenon. The analytical model of the system is based on multimode modal approach. It is also shown in this paper that greatly enhanced information for machine malfunction diagnostics can be obtained by simulated rotation of the XY transducer system observing rotor lateral vibration. This simulated rotation can be accomplished by the machine diagnostic data acquistion and processing system. The data processing also includes extraction of forward and backward components of elliptical orbits filtered to one frequency, and the filtered orbit major axis magnitude and its angular orientation.Numerical examples, field data, and experimental results performed on a rotor rig illustrate applications.
10
Mimmi, Giovanni, e Paolo Pennacchi. "Compression Load Dynamics in a Special Helical Blower: A Modeling Improvement". Journal of Mechanical Design 123, n. 3 (1 ottobre 1999): 402–7. http://dx.doi.org/10.1115/1.1377016.
Testo completoAbstract (sommario):
The instantaneous variation of pressure loads acting on the rotors of positive displacement rotary blowers may produce vibrations and noise that in some case produce the failure of the machine and of the piping. In a previous paper the authors determined the pressure loads acting on the rotors, starting from the geometry of the chambers that are formed during the rotor meshing and the thermodynamic transformation of the working fluid. The calculation of the loads has been made in a quasi-static manner. In this paper the model has been improved by taking into account the effects due to a closed volume chamber at the discharge. This assumption better reproduces the real cases and allows the researchers to perform more efficient calculations and more reliable predictions.
11
Smalley, Anthony J. "Jørgen Lund: A Perspective on His Contributions to Modern Rotor Bearing Dynamics". Journal of Vibration and Acoustics 125, n. 4 (1 ottobre 2003): 434–40. http://dx.doi.org/10.1115/1.1605765.
Testo completoAbstract (sommario):
This paper presents a perspective on the work of Dr. J. W. Lund, in the field of rotor-bearing dynamics. It traces his most influential work in published journals, software, data published in various manuals, government reports, and course notes. It addresses his work in oil bearings, gas bearings, unbalance response of flexible rotors, stability of flexible rotors, squeeze-film dampers, rotor balancing, and modal testing of rotors. It provides a road map for those who would revisit the knowledge base. It shows how Dr. Lund’s work has permeated the practice of today’s suppliers and users of turbomachinery, and industry consultants.
12
Park, J. S., e S. N. Jung. "Comprehensive multibody dynamics analysis for rotor aeromechanics predictions in descending flight". Aeronautical Journal 116, n. 1177 (marzo 2012): 229–49. http://dx.doi.org/10.1017/s0001924000006813.
Testo completoAbstract (sommario):
AbstractThis paper studies the rotor aeromechanics in descending flight using a nonlinear flexible multibody dynamic analysis code, DYMORE. A freewake model is included in DYMORE to improve the rotor wake modelling. The wind-tunnel test data of the Higher-harmonic Aeroacoustics Rotor Test (HART) II rotor, with and without higher harmonic pitch control (HHC), and the flight test data of the full-scale utility helicopter rotor in descent are used for the aeromechanics correlation at an advance ratio of 0·15. The blade-vortex interaction (BVI) airloads are reasonably predicted for both the HART II and utility helicopter rotors, although some BVI peaks are missed on the advancing sides for both the rotors. The flap deflections and elastic torsion deformations at the blade tip are fairly correlated against the measured data of the HART II rotor. The correlation of blade structural moments for both HART II and utility helicopter rotors are not as good as the lift predictions; however, a reasonable prediction is obtained for the utility helicopter rotor.
13
Sawicki, Jerzy T., Asok K. Sen e Grzegorz Litak. "Multiresolution Wavelet Analysis of the Dynamics of a Cracked Rotor". International Journal of Rotating Machinery 2009 (2009): 1–8. http://dx.doi.org/10.1155/2009/265198.
Testo completoAbstract (sommario):
We examine the dynamics of a healthy rotor and a rotor with a transverse crack, which opens and closes due to its self weight. Using discrete wavelet transform, we perform a multiresolution analysis of the measured vibration signal from each of these rotors. In particular, the measured vibration signal is decomposed into eight frequency bands, and the rms amplitude values of the healthy and cracked rotors are compared in the three lowest-frequency bands. The results indicate that the rms vibration amplitudes for the cracked rotor are larger than those of the healthy rotor in each of these three frequency bands. In the case of externally applied harmonic force excitation to the rotor, the rms values of the vibration amplitude of the cracked rotor are also found to be larger than those of a healthy rotor in the three lowest-frequency bands. Furthermore, the difference in the rms values between the healthy and cracked rotors in each of the three lowest-frequency bands is more pronounced in the presence of external excitation than that with no excitation. The obtained results suggest that the present multiresolution approach can be used effectively to detect the presence of a crack in a rotor.
14
Dai, Yuting, Linpeng Wang, Chao Yang e Xintan Zhang. "Dynamic Gust Load Analysis for Rotors". Shock and Vibration 2016 (2016): 1–12. http://dx.doi.org/10.1155/2016/5727028.
Testo completoAbstract (sommario):
Dynamic load of helicopter rotors due to gust directly affects the structural stress and flight performance for helicopters. Based on a large deflection beam theory, an aeroelastic model for isolated helicopter rotors in the time domain is constructed. The dynamic response and structural load for a rotor under the impulse gust and slope-shape gust are calculated, respectively. First, a nonlinear Euler beam model with 36 degrees-of-freedoms per element is applied to depict the structural dynamics for an isolated rotor. The generalized dynamic wake model and Leishman-Beddoes dynamic stall model are applied to calculate the nonlinear unsteady aerodynamic forces on rotors. Then, we transformed the differential aeroelastic governing equation to an algebraic one. Hence, the widely used Newton-Raphson iteration algorithm is employed to simulate the dynamic gust load. An isolated helicopter rotor with four blades is studied to validate the structural model and the aeroelastic model. The modal frequencies based on the Euler beam model agree well with published ones by CAMRAD. The flap deflection due to impulse gust with the speed of 2m/s increases twice to the one without gust. In this numerical example, results indicate that the bending moment at the blade root is alleviated due to elastic effect.
15
Buranarote, Jirarote, Yutaka Hara, Masaru Furukawa e Yoshifumi Jodai. "Method to Predict Outputs of Two-Dimensional VAWT Rotors by Using Wake Model Mimicking the CFD-Created Flow Field". Energies 15, n. 14 (18 luglio 2022): 5200. http://dx.doi.org/10.3390/en15145200.
Testo completoAbstract (sommario):
Recently, wind farms consisting of clusters of closely spaced vertical-axis wind turbines (VAWTs) have attracted the interest of many people. In this study, a method using a wake model to predict the flow field and the output power of each rotor in a VAWT cluster is proposed. The method uses the information obtained by the preliminary computational fluid dynamics (CFD) targeting an isolated single two-dimensional (2D) VAWT rotor and a few layouts of the paired 2D rotors. In the method, the resultant rotor and flow conditions are determined so as to satisfy the momentum balance in the main wind direction. The pressure loss of the control volume (CV) is given by an interaction model which modifies the prepared information on a single rotor case and assumes the dependence on the inter-rotor distance and the induced velocity. The interaction model consists of four equations depending on the typical four-type layouts of selected two rotors. To obtain the appropriate circulation of each rotor, the searching range of the circulation is limited according to the distribution of other rotors around the rotor at issue. The method can predict the rotor powers in a 2D-VAWT cluster including a few rotors in an incomparably shorter time than the CFD analysis using a dynamic model.
16
Bartlett, H., e R. Whalley. "Distributed rotor dynamics". Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering 212, n. 4 (1 giugno 1998): 249–65. http://dx.doi.org/10.1243/0959651981539442.
Testo completoAbstract (sommario):
The modelling, simulation and analysis of powered rotors with ‘long’ thin shells is investigated. General results enabling the prediction of the torsional vibrational signature of high-speed assemblies under acceleration or braking conditions are outlined. It is demonstrated that simulated response characteristics can be easily obtained and the effect of varying the rotor geometry can be routinely accommodated. Finally, a rotor for a high-speed paper manufacturing unit is investigated and the torsional behaviour of the assembly is computed. The volatile transient conditions presented are commented upon.
17
Liu, Yi, e Heng Liu. "Dynamic behaviors of three-dimensional rod-disk rotor rolling bearing system". Proceedings of the Institution of Mechanical Engineers, Part K: Journal of Multi-body Dynamics 232, n. 1 (20 aprile 2017): 21–31. http://dx.doi.org/10.1177/1464419317705987.
Testo completoAbstract (sommario):
A typical rod-disk rotor is meshed by three-dimensional solid elements. The stability features, whirling motions and frequency spectrums of 3D rod-disk rotor rolling bearing system are investigated by combining nonlinear analysis method and finite element method. Meanwhile, an identical 1D rod-disk rotor system is introduced for comparison. With the support of the ball bearing, the stability region of 1D and 3D rod-disk rotors shows good consistency at lower speed and has obvious differences at higher speed. However, 3D rotor has smaller bending deformation because 3D solid elements can restrict large deflection but the equivalent springs in 1D model do not have this function. When cylindrical roller bearings are applied, both rotors also have the same frequency spectrums which consist of rotating frequency, variable compliance frequency and their linear combinations. Moreover, 3D rotor dynamics have the advantage of analyzing dynamic stress. In short, this paper proposes a numerical way to investigate the dynamic behaviors of 3D rod-disk rotor rolling bearing system.
18
Fletcher, T. M., e R. E. Brown. "Modelling the interaction of helicopter main rotor and tail rotor wakes". Aeronautical Journal 111, n. 1124 (ottobre 2007): 637–43. http://dx.doi.org/10.1017/s0001924000004814.
Testo completoAbstract (sommario):
Abstract The mutual interaction between the main rotor and tail rotor wakes is central to some of the most problematic dynamic phenomena experienced by helicopters. Yet achieving the ability to model the growth and propagation of helicopter rotor wakes with sufficient realism to capture the details of this interaction has been a significant challenge to rotorcraft aerodynamicists for many decades. A novel computational fluid dynamics code tailored specifically for rotorcraft applications, the vorticity transport model, has been used to simulate the interaction of the rotors of a helicopter with a single main rotor and tail rotor in both hover and low-speed quartering flight, and with the tail rotor rotating both top-forward and top-aft. The simulations indicate a significant level of unsteadiness in the performance of both main and tail rotors, especially in quartering flight, and a sensitivity to the direction of rotation of the tail rotor. Although the model thus captures behaviour that is similar to that observed in practice, the challenge still remains to integrate the information from high fidelity simulations such as these into routine calculations of the flight dynamics of helicopters.
19
Wang, Aiming, Yujie Bi, Yun Xia, Xiaohan Cheng, Jie Yang e Guoying Meng. "Continuous Rotor Dynamics of Multi-Disc and Multi-Span Rotor: A Theoretical and Numerical Investigation on the Continuous Model and Analytical Solution for Unbalance Responses". Applied Sciences 12, n. 9 (25 aprile 2022): 4351. http://dx.doi.org/10.3390/app12094351.
Testo completoAbstract (sommario):
Continuous rotor dynamics remains stagnant. In this paper, aim at multi-span and multi-disc rotor-bearing system, the continuous rotor dynamic analysis method (CRDAM) is proposed. The force acting on the shaft by the rotating eccentric disc is simulated as a point force. The counterforce of bearing is also considered as a point force. The shaft is considered free-ended. A continuous rotor dynamic model is obtained and an analytical solution is proposed to express the unbalance response as function of the position, unbalance, support stiffness and damping. The proposed method is validated by numerical experiments in which unbalance responses obtained by it are compared with that obtained by the two classical methods the finite element method (FEM) and Ricatti method. The results indicate that the proposed method is applicable to calculating unbalance response of multi-disc and multi-span rotor. Moreover, it is closer to FEM than Ricatti and can be applied to actual high speed rotors. Among the three methods, the calculating speed of Ricatti is the fastest, CRDAM is the second fastest and FEM is the slowest. The proposed method, which solves the forward problems of the continuous rotor dynamics for the multi-disc and multi-span rotors, can provide theoretical basis for further studies on inverse problems such as identification of rotor unbalance and bearing stiffness and damping coefficients without test runs and external excitations.
20
Wang, Aiming, Yujie Bi, Yun Xia, Xiaohan Cheng, Jie Yang e Guoying Meng. "Continuous Rotor Dynamics of Multi-Disc and Multi-Span Rotor: A Theoretical and Numerical Investigation on the Continuous Model and Analytical Solution for Unbalance Responses". Applied Sciences 12, n. 9 (25 aprile 2022): 4351. http://dx.doi.org/10.3390/app12094351.
Testo completoAbstract (sommario):
Continuous rotor dynamics remains stagnant. In this paper, aim at multi-span and multi-disc rotor-bearing system, the continuous rotor dynamic analysis method (CRDAM) is proposed. The force acting on the shaft by the rotating eccentric disc is simulated as a point force. The counterforce of bearing is also considered as a point force. The shaft is considered free-ended. A continuous rotor dynamic model is obtained and an analytical solution is proposed to express the unbalance response as function of the position, unbalance, support stiffness and damping. The proposed method is validated by numerical experiments in which unbalance responses obtained by it are compared with that obtained by the two classical methods the finite element method (FEM) and Ricatti method. The results indicate that the proposed method is applicable to calculating unbalance response of multi-disc and multi-span rotor. Moreover, it is closer to FEM than Ricatti and can be applied to actual high speed rotors. Among the three methods, the calculating speed of Ricatti is the fastest, CRDAM is the second fastest and FEM is the slowest. The proposed method, which solves the forward problems of the continuous rotor dynamics for the multi-disc and multi-span rotors, can provide theoretical basis for further studies on inverse problems such as identification of rotor unbalance and bearing stiffness and damping coefficients without test runs and external excitations.
21
Shad, Muhammad Rizwan, Guilhem Michon e Alain Berlioz. "Nonlinear Dynamics of Rotors due to Large Deformations and Shear Effects". Applied Mechanics and Materials 110-116 (ottobre 2011): 3593–99. http://dx.doi.org/10.4028/www.scientific.net/amm.110-116.3593.
Testo completoAbstract (sommario):
An analysis of linear and nonlinear dynamics of rotors is presented taking into account the shear effects. The nonlinearity arises due to the consideration of large deformations in bending. The rotor system studied is composed of a rigid disk and a circular shaft. In order to study the combined effect of rotary inertia and shear effects the shaft is modeled as a Timoshenko beam of circular cross section. A mathematical model is developed consisting of 4th order coupled nonlinear differential equations of motion. Method of multiple scales is used to solve these nonlinear equations. Linear and nonlinear dynamic behavior is studied numerically for different values of slenderness ratio r. Resonant curves are plotted for the nonlinear analysis. Due to nonlinearity these curves are of hard spring type. This spring hardening effect is more visible for lower values of r. Also the nonlinear response amplitude is higher when shear deformations are taken into account.
22
Su, Jianmin, Chengyue Su, Sheng Xu e Xiaoxing Yang. "A Multibody Model of Tilt-Rotor Aircraft Based on Kane’s Method". International Journal of Aerospace Engineering 2019 (16 aprile 2019): 1–10. http://dx.doi.org/10.1155/2019/9396352.
Testo completoAbstract (sommario):
A tilt-rotor aircraft can switch between two flight configurations (the helicopter configuration and the fixed-wing plane configuration) by tilting its rotors. In the process of rotor tilting, the nacelles which drive the rotors tilt together with the rotors. Because the mass of the nacelles cannot be ignored compared to the mass of the whole aircraft, the tilting of the nacelles is a coupling motion of the body and the nacelles. In order to better character the aircraft dynamics during the nacelle tilting, a multibody model is established in this paper. In this multibody model, Kane’s method is used to build a dynamic model of a tilt-rotor aircraft. The generalized rates are used to describe the movement of the body and the nacelles (with rotors). The generalized active forces and generalized inertial forces of both the body and the nacelles (with rotors) are obtained, respectively, and the first-order differential equations of the generalized rates are obtained. The longitudinal trim of the XV-15 aircraft is calculated according to the single-body model and our multibody model, in this paper, and the results verify the correctness of the multibody model. In the process of nacelle inclination angle command tracking, the multibody model can provide more information about the disturbance torque of the nacelle than the single-body model, and model inversion control based on the proposed multibody model can obtain a better tracking result than a PID control method only using nacelle angle feedback information.
23
Das, Suma R., Pashupati Dhakal e Abhilash J. Chandy. "Comparison of Three Rotor Designs for Rubber Mixing Using Computational Fluid Dynamics". Tire Science and Technology 45, n. 4 (1 ottobre 2017): 259–87. http://dx.doi.org/10.2346/tire.17.450402.
Testo completoAbstract (sommario):
ABSTRACT In recent years, there has been an increasing demand for efficient mixers with high-quality mixing capabilities in the rubber product industry, with the focus of producing fuel-efficient tires. Depending on the functional characteristics of the tire and thus the compounding ingredients, different types of mixers can be used for the rubber mixing process. Hence, the choice of an appropriate mixer is critical in achieving the proper distribution and dispersion of fillers in rubber and a consistent product quality, as well as the attainment of high productivity. With the availability of high-performance computing resources and high-fidelity computational fluid dynamics tools over the last two decades, understanding the flow phenomena associated with complex rotor geometries such as the two- and four-wing rotors has become feasible. The objective of this article is to compare and investigate the flow and mixing dynamics of rubber compounds in partially filled mixing chambers stirred with three types of rotors: the two-wing, four-wing A, and four-wing B rotors. As part of this effort, all the 3D simulations are carried out with a 75% fill factor and a rotor speed of 20 rpm using a computational fluid dynamics (CFD) code. Mass flow patterns, velocity vectors, particle trajectories, and other mixing statistics, such as cluster distribution index and length of stretch, are presented here. All the results showed consistently that the four-wing A rotor was superior in terms of dispersive and distributive mixing characteristics compared with the other rotors. The results also helped to understand the mixing process and material movement, thereby generating information that could potentially improve productivity and efficiency in the tire manufacturing process.
24
Kahraman, A., H. Nevzat Ozguven, D. R. Houser e J. J. Zakrajsek. "Dynamic Analysis of Geared Rotors by Finite Elements". Journal of Mechanical Design 114, n. 3 (1 settembre 1992): 507–14. http://dx.doi.org/10.1115/1.2926579.
Testo completoAbstract (sommario):
A finite element model of a geared rotor system on flexible bearings has been developed. The model includes the rotary inertia of shaft elements, the axial loading on shafts, flexibility and damping of bearings, material damping of shafts and the stiffness and the damping of gear mesh. The coupling between the torsional and transverse vibrations of gears were considered in the model. A constant mesh stiffness was assumed. The analysis procedure can be used for forced vibration analysis of geared rotors by calculating the critical speeds and determining the response of any point on the shafts to mass unbalances, geometric eccentricities of gears, and displacement transmission error excitation at the mesh point. The dynamic mesh forces due to these excitations can also be calculated. The model has been applied to several systems for the demonstration of its accuracy and for studying the effect of bearing compliances on system dynamics.
25
Wang, Guangding, Xiaole Wang, Chuanliu Xie e Huiqun Yuan. "Whirl dynamics of an axially functionally graded liquid-filled rotor considering shear deformation and rotary inertia". AIP Advances 12, n. 6 (1 giugno 2022): 065303. http://dx.doi.org/10.1063/5.0094880.
Testo completoAbstract (sommario):
In this study, whirl characteristics and stability of an axially functionally graded (AFG) liquid-filled rotor are investigated. The rotor is modeled based on the spinning Timoshenko beam theory. The governing equations for flexural vibration are derived via Hamilton’s principle. For pinned–pinned AFG liquid-filled rotor, the analytical solutions are derived for both the exact whirl frequency equation and the stability model. To validate the present formulations, comparative studies by numerical solutions available in the literature are conducted. Some numerical examples are performed to investigate the effects of gradient parameter, mass ratio, cavity ratio, rotary inertia, and shear deformation on the whirl speed, the critical spinning speed, and the stability of the AFG liquid-filled rotor system. The results show that these parameters have noticeable influences on dynamic behavior and stability of the rotor system. In particular, the rotary inertia and shear deformation play an important role in the stability analysis for different length rotors.
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Shchur, Ihor, Volodymyr Klymko, Shengbai Xie e David Schmidt. "Design Features and Numerical Investigation of Counter-Rotating VAWT with Co-Axial Rotors Displaced from Each Other along the Axis of Rotation". Energies 16, n. 11 (2 giugno 2023): 4493. http://dx.doi.org/10.3390/en16114493.
Testo completoAbstract (sommario):
In this paper, dual-rotor counter-rotating (CR) configurations of vertical axis wind turbines (VAWTs) are briefly inspected and divided into three types. This investigation was focused on one of these types—the CR-VAWT with co-axial rotors, in which two equal rotors are placed on the same shaft, displaced from each other along it and rotated in opposite directions. For this CR-VAWT with three-blade H-Darrieus rotors, the properties of the design in terms of aerodynamics, mechanical transmission and electric generator, as well as control system, are analyzed. A new direct-driven dual-rotor permanent magnet synchronous generator was proposed, in which two built-in low-power PM electric machines have been added. They perform two functions—starting-up and overclocking of the rotors to the angular velocity at which the lifting force of the blades is generated, and stabilizing the CR-VAWT work as wind gusts act on the two rotors. Detailed in this paper is the evaluation of the aerodynamic performance of the CR-VAWT via 3D computational fluid dynamics simulations. The evaluation was conducted using the CONVERGE CFD software with the inclusion of the actuator line model for the rotor aerodynamics, which significantly reduces the computational effort. Obtained results show that both rotors, while they rotate in opposite directions, had a positive impact on each other. At the optimal distance between the rotors of 0.3 from a rotor height, the power coefficients of the upper and lower rotors in the CR-VAWT increased, respectively, by 5.5% and 13.3% simultaneously with some increase in their optimal tip-speed ratio compared to the single-rotor VAWT.
27
Thirumaleshwar Hegde, Navya, V. I. George, C. Gurudas Nayak e Kamlesh Kumar. "Transition flight modeling and robust control of a VTOL unmanned quad tilt-rotor aerial vehicle". Indonesian Journal of Electrical Engineering and Computer Science 18, n. 3 (1 giugno 2020): 1252. http://dx.doi.org/10.11591/ijeecs.v18.i3.pp1252-1261.
Testo completoAbstract (sommario):
<span>The development of fully autonomous Unmanned Aerial Vehicles (UAV) plays a major contribution towards reducing the risk to human life in various applications including rescue teams, border patrol, police and inspection of buildings, pipelines, coasts, and terrains. Tiltrotor hybrid UAV exhibit special application value due to its unique rotor structure. The variation in the model dynamics and aerodynamics due to the tilting rotors are the major key issues and challenges which attracted the attention of many researchers. This vehicle combines the hovering capabilities of a helicopter along with the high-speed cruise capabilities of a conventional airplane by tilting its four rotors. In the present research work, the authors attempt to model a quad tilt rotor UAV using Newton-Euler formulation. A dynamic model of the vehicle is derived mathematically for horizontal, vertical and transition flight modes. A robust H-infinity control strategy is proposed, evaluated and analyzed through simulation to control the flight dynamics of the different modes of the UAV. Simulation results shows that the tiltrotor UAV achieves transition successfully.</span>
28
Gislén, Lars, Carsten Peterson e Bo Söderberg. "Rotor Neurons: Basic Formalism and Dynamics". Neural Computation 4, n. 5 (settembre 1992): 737–45. http://dx.doi.org/10.1162/neco.1992.4.5.737.
Testo completoAbstract (sommario):
Rotor neurons are introduced to encode states living on the surface of a sphere in D dimensions. Such rotors can be regarded as continuous generalizations of binary (Ising) neurons. The corresponding mean field equations are derived, and phase transition properties based on linearized dynamics are given. The power of this approach is illustrated with an optimization problem—placing N identical charges on a sphere such that the overall repulsive energy is minimized. The rotor approach appears superior to other methods for this problem both with respect to solution quality and computational effort needed.
29
Rezaee, Mousa, Mir Mohammad Ettefagh e Reza Fathi. "Dynamics and Stability of Non-Planar Rigid Rotor Equipped with Two Ball-Spring Autobalancers". International Journal of Structural Stability and Dynamics 19, n. 02 (febbraio 2019): 1950001. http://dx.doi.org/10.1142/s0219455419500019.
Testo completoAbstract (sommario):
Recently, a new type of automatic ball balancer (ABB), called the ball-spring autobalancer (AB), has been proposed, which substantially eliminates the drawbacks of the traditional ABBs. In previous studies, the dynamics of the Jeffcott planar rotor equipped with ball-spring AB has been investigated. In the Jeffcott model, it is assumed that the ABB is located on the plane of the unbalance disk. However, for the non-planar rigid rotor with distributed imbalances, out-of-plane motions may occur, and the Jeffcott model becomes unreliable as the tilting motion cannot be explained. To this end, the aim of this paper is to analyze the capability of the ball-spring AB in balancing non-planar rotors and to reconfirm its pre-claimed advantages over the traditional ABBs for balancing non-planar rotors. To start, the mathematical model of the rigid rotor with two ball-spring ABs is established, based on which the nonlinear equations of motion are derived. Then, the system time responses are computed numerically and the balanced stable regions are acquired by the Lyapunov’s first method. The results of this study show that the ball-spring ABs can balance the non-planar rotors and the tilting motion does not impair the pre-claimed advantages of the ball-spring AB.
30
Kliem, W. "The dynamics of viscoelastic rotors". Dynamics and Stability of Systems 2, n. 2 (gennaio 1987): 424–29. http://dx.doi.org/10.1080/02681118708806031.
Testo completo
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Palma, Carlos-Andres, Jonas Björk, Francesco Rao, Dirk Kühne, Florian Klappenberger e Johannes V. Barth. "Topological Dynamics in Supramolecular Rotors". Nano Letters 14, n. 8 (31 luglio 2014): 4461–68. http://dx.doi.org/10.1021/nl5014162.
Testo completo
32
Gorbenko, A. N., S. Kh Shmelev e G. Strautmanis. "The Effect of Unbalance Mass on the Necessary Conditions of the Double-Support Rotor Autobalancing Stability". Herald of the Bauman Moscow State Technical University. Series Mechanical Engineering, n. 2 (125) (aprile 2019): 71–82. http://dx.doi.org/10.18698/0236-3941-2019-2-71-82.
Testo completoAbstract (sommario):
The analysis of necessary conditions for autobalancing stability of rotor, which performs spatial oscillations, was carried out in this paper taking into account the influence of unbalance and autobalancer masses. It was found that the using of traditional models, where unbalance and autobalancer masses are assumed small, could lead to significant errors in the dynamics analysis of spatially moving rotor. The influence of this factor leads to the doubling of the critical rotational speeds spectrum. Moreover, the system motion between the split critical frequencies is unstable. There may be one or two onset areas of autobalancing mode motion depending on the dynamic rotor type, its location relative to the supports, the unbalance mass and other system parameters. It was found that rotors, that are long type or close to the spherical type, are the most sensitive to this factor. On the other hand, rotors of the short type are weakly sensitive. It is shown that the most preferred case is when the unbalance and autobalancer location plane passes through the common mass center of the composite rotor. The quantitative criterion is formulated for the necessity of taking into account (or not taking into account) the influence of this factor when analyzing the system dynamics
33
Hansen, Morten Hartvig. "Modal dynamics of structures with bladed isotropic rotors and its complexity for two-bladed rotors". Wind Energy Science 1, n. 2 (30 novembre 2016): 271–96. http://dx.doi.org/10.5194/wes-1-271-2016.
Testo completoAbstract (sommario):
Abstract. The modal dynamics of structures with bladed isotropic rotors is analyzed using Hill's method. First, analytical derivation of the periodic system matrix shows that isotropic rotors with more than two blades can be represented by an exact Fourier series with 3/rev (three per rotor revolution) as the highest order. For two-bladed rotors, the inverse mass matrix has an infinite Fourier series with harmonic components of decreasing norm; thus, the system matrix can be approximated by a truncated Fourier series of predictable accuracy. Second, a novel method for automatically identifying the principal solutions of Hill's eigenvalue problem is introduced. The corresponding periodic eigenvectors can be used to compute symmetric and antisymmetric components of the two-bladed rotor motion, as well as the additional forward and backward whirling components for rotors with more than two blades. To illustrate the use of these generic methods, a simple wind turbine model is set up with three degrees of freedom for each blade and seven degrees of freedom for the nacelle and drivetrain. First, the model parameters are tuned such that the low-order modal dynamics of a three-bladed 10 MW turbine from previous studies is recaptured. Second, one blade is removed, leading to larger and higher harmonic terms in the system matrix. These harmonic terms lead to modal couplings for the two-bladed turbine that do not exist for the three-bladed turbine. A single mode of a two-bladed turbine will also have several resonance frequencies in both the ground-fixed and rotating frames of reference, which complicates the interpretation of simulated or measured turbine responses.
34
Castillo-Rivera, Salvador, e Maria Tomas-Rodriguez. "Description of a Dynamical Framework to Analyse the Helicopter Tail Rotor". Dynamics 1, n. 2 (12 ottobre 2021): 171–80. http://dx.doi.org/10.3390/dynamics1020010.
Testo completoAbstract (sommario):
In this work, a tail rotor is modelled with the aid of a multibody software to provide an alternative tool in the field of helicopter research. This advanced application captures the complex behaviour of tail rotor dynamics. The model has been built by using VehicleSim software (Version 1.0, Mechanical Simulation Corporation, Ann Arbor, MI, USA) specialized in modelling mechanical systems composed of rigid bodies. The dynamic behaviour and the control action are embedded in the code. Thereby, VehicleSim does not need an external link to another software package. The rotors are articulated, the tail rotor considers flap and feather degrees of freedom for each of the equispaced blades and their dynamic couplings. Details on the model’s implementation are derived, emphasising the modelling aspects that contribute to the coupled dynamics. The obtained results are contrasted with theoretical approaches and these have displayed to agree with the expected behaviour. This rotorcraft model helps to study the performance of a tail rotor under certain dynamic conditions.
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Hajžman, Michal, Miroslav Balda, Petr Polcar e Pavel Polach. "Turbine Rotor Dynamics Models Considering Foundation and Stator Effects". Machines 10, n. 2 (22 gennaio 2022): 77. http://dx.doi.org/10.3390/machines10020077.
Testo completoAbstract (sommario):
The paper deals with the modelling of turbine rotors, including a foundation and stator parts, and with their dynamic analysis. The dynamics of turbines can be strongly influenced by the effects of a rotor foundation, and therefore suitable modelling approaches should be developed to obtain proper analysis tools. The standard methods for the modelling of rotating shafts are summarized in the paper, and two approaches to including foundation effects into dynamic models are introduced. The approach based on the dynamic compliance of the foundation with respect to the rotor angular velocity is compared with the approach based on the modal synthesis of rotor and foundation models. The calculation of modal properties is then demonstrated, and the characteristics of both presented methods are discussed. A comparison of the steady-state dynamic response calculated using both methods is shown. It can be concluded that both approaches can be advantageously used for several analyses, and our final recommendations are given in the conclusions.
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Asdaque, P. M. G. Bashir, e R. K. Behera. "Vibration Analysis of Hollow Tapered Shaft Rotor". Advances in Acoustics and Vibration 2014 (28 aprile 2014): 1–14. http://dx.doi.org/10.1155/2014/410851.
Testo completoAbstract (sommario):
Shafts or circular cross-section beams are important parts of rotating systems and their geometries play important role in rotor dynamics. Hollow tapered shaft rotors with uniform thickness and uniform bore are considered. Critical speeds or whirling frequency conditions are computed using transfer matrix method and then the results were compared using finite element method. For particular shaft lengths and rotating speeds, response of the hollow tapered shaft-rotor system is determined for the establishment of dynamic characteristics. Nonrotating conditions are also considered and results obtained are plotted.
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Chen, Yue, Jiwen Cui e Xun Sun. "A Vibration Suppression Method for the Multistage Rotor of an Aero-Engine Based on Assembly Optimization". Machines 9, n. 9 (5 settembre 2021): 189. http://dx.doi.org/10.3390/machines9090189.
Testo completoAbstract (sommario):
The assembly quality of the multistage rotor is an essential factor affecting its vibration level. The existing optimization methods for the assembly angles of the rotors at each stage can ensure the concentricity and unbalance meet the requirements, but it cannot directly ensure its vibration responses meet the indexes. Therefore, in this study, we first derived the excitation formulas of the geometric and mass eccentricities on the multistage rotor and introduced it into the dynamics model of the multistage rotor system. Then, the coordinate transfer model of the geometric and mass eccentricities errors, including assembly angles of the rotors at all stages, was established. Moreover, the mathematical relationship between the assembly angles of the rotors at all stages and the nodal vibration responses was established by combining the error transfer model with the dynamics model of the multistage rotor system. Furthermore, an optimization function was developed, which takes the assembly angles as the optimization variables and the maximum vibration velocity at the bearings as the optimization objective. Finally, a simplified four-stage high-pressure rotor system was assembled according to the optimal assembly angles calculated in the simulations. The experimental results showed that the maximum vibration velocity at the bearings under the optimal assembly was reduced by 69.6% and 45.5% compared with that under the worst assembly and default assembly. The assembly optimization method proposed in this study has a significant effect on the vibration suppression of the multistage rotor of an aero-engine.
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Barkat, Ibtissem, Abdelouahab Benretem, Fawaz Massouh, Issam Meghlaoui e Ahlem Chebel. "Modeling and simulation of forces applied to the horizontal axis wind turbine rotors by the vortex method coupled with the method of the blade element". International Journal of Power Electronics and Drive Systems (IJPEDS) 12, n. 1 (1 marzo 2021): 413. http://dx.doi.org/10.11591/ijpeds.v12.i1.pp413-420.
Testo completoAbstract (sommario):
This article aims to study the forces applied to the rotors of horizontal axis wind turbines. The aerodynamics of a turbine are controlled by the flow around the rotor, or estimate of air charges on the rotor blades under various operating conditions and their relation to the structural dynamics of the rotor are critical for design. One of the major challenges in wind turbine aerodynamics is to predict the forces on the blade as various methods, including blade element moment theory (BEM), the approach that is naturally adapted to the simulation of the aerodynamics of wind turbines and the dynamic and models (CFD) that describes with fidelity the flow around the rotor. In our article we proposed a modeling method and a simulation of the forces applied to the horizontal axis wind rotors turbines using the application of the blade elements method to model the rotor and the vortex method of free wake modeling in order to develop a rotor model, which can be used to study wind farms. This model is intended to speed up the calculation, guaranteeing a good representation of the aerodynamic loads exerted by the wind.
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Hattori, T., H. Ohnishi e M. Taneda. "Optimum Design Technique for Rotating Wheels". Journal of Engineering for Gas Turbines and Power 110, n. 1 (1 gennaio 1988): 41–44. http://dx.doi.org/10.1115/1.3240084.
Testo completoAbstract (sommario):
Compressor rotors and turbine rotors are subject to centrifugal and thermal loads. These loads increase proportionally with tip speed, pressure ratio, and gas temperature. On the other hand, the rotor weight must be lessened to improve rotor dynamics and restrict bearing load. Thus, an optimum design technique is required, which offers the lightest possible wheel shape under the stress limit restriction. This paper introduces an optimum design system developed for turbomachinery rotors, and discusses several application results. The sequential linear programming method is used in the optimizing process, and centrifugal and thermal stress analyses of variable thickness rotating wheels are performed using Donath’s method. This system’s validity is confirmed by application to uniform-strength rotating disk problems and comparison with analytical results. This optimum design program is then applied to the design of axial flow compressor wheels.
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Halder, B., A. Mukherjee e R. Karmakar. "Theoretical and Experimental Studies on Squeeze Film Stabilizers for Flexible Rotor-Bearing Systems Using Newtonian and Viscoelastic Lubricants". Journal of Vibration and Acoustics 112, n. 4 (1 ottobre 1990): 473–82. http://dx.doi.org/10.1115/1.2930131.
Testo completoAbstract (sommario):
A combination of a squeeze film damper and a plane journal bearing is studied as a stabilizing scheme. The damper is made to play the role of a stabilizer to postpone the instability threshold speeds of flexible rotors. Both Newtonian and viscoelastic fluids are used in the rotor-bearing system. Dynamics of the system is theoretically analyzed using bond graphs. Analysis reveals that the use of a Newtonian fluid in the stabilizer largely improves the high speed stability range. However, viscoelastic stabilizing fluid has a detrimental effect on highly flexible rotors. Experimental investigations, conducted on a flexible rotor (natural frequency, 30 Hz), confirm the theoretical findings. In addition, experiments indicate that though the use of viscoelastic stabilizing fluids leads to instability in flexible rotors, the growth of large amplitude whirl is postponed to very high speeds.
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de Carvalho Michalski, Miguel Angelo, Moysés Zindeluk e Renato de Oliveira Rocha. "Influence of Journal Bearing Axial Grooves on the Dynamic Behavior of Horizontal Rotors". Shock and Vibration 13, n. 4-5 (2006): 285–300. http://dx.doi.org/10.1155/2006/785823.
Testo completoAbstract (sommario):
Journal bearing design and the lubricant characteristics are very influential in a rotating machine behaviour. The bearing geometry can drastically affect the lubricant flow and also the rotor dynamics. Approaching that issue, this paper presents an experimental study of the dynamic behavior of a horizontal rotor suported by journal bearings with semi-circular axial grooves. The journal bearings were manufactured with a varied number of axial grooves and a versatile test rig is used, making possible the analysis of different configurations. The acquired signals are analyzed with classical and non-linear tools and the differences among the rotors’ configurations can be shown.
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Singh, Puneet, e Peretz P. Friedmann. "Dynamic Stall Modeling Using Viscous Vortex Particle Method for Coaxial Rotors". Journal of the American Helicopter Society 66, n. 1 (1 gennaio 2021): 1–16. http://dx.doi.org/10.4050/jahs.66.012010.
Testo completoAbstract (sommario):
Dynamic stall is an important source of vibrations on a rotor at high advance ratios. The periodic flow separation and reattachment during dynamic stall generates large unsteady loads. In this study, the flow separation is modeled as the shedding of concentrated vorticity from the leading edge of the airfoil. The viscous vortex particle method is used to calculate the evolution of the rotor wake. Blade loads are calculated using a reduced order model obtained from computational fluid dynamics, and dynamic stall loads are calculated using the ONERA dynamic stall model. Results are presented for single main rotor and coaxial rotors at advance ratios of μ = 0.3–0.4. The separated wake modifies the angle of attack distribution on the rotor and hence impacts the hub loads. The results indicate that the separated wake modifies the vibratory hub loads by 5–10% for a single main rotor at μ = 0.3. The vibratory hub loads for the coaxial rotor are modified by 10–20% at μ = 0.4 with the inclusion of the separated wake. The upper and lower rotor tip path planes are tilted such that the blade and wake interaction is greater on the retreating side of the upper rotor and decreased on the advancing side.
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Li, M., e L. He. "The dynamics of a parallel-misaligned and unbalanced rotor system under the action of non-linear oil film forces". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 224, n. 9 (1 settembre 2010): 1875–89. http://dx.doi.org/10.1243/09544062jmes1916.
Testo completoAbstract (sommario):
A mathematical model of a parallel-misaligned rotor system with mass eccentricity that is supported on journal bearings is discussed and its dynamic behaviours are analysed under the action of non-linear oil forces in the present work. First, some assumptions are introduced, such as the long bearing model, small parallel misalignment between rotors and tiny eccentricity of discs, the misaligned displacement constraint between two rotors is taken into account, and the motion equations are deduced by the Lagrange method of undetermined multiplier. Then, the rotor orbits, Poincaré maps, and bifurcation diagrams of the system are studied by a numerical method; the results show that there exists some unrevealed motions and phenomena in the parallel-misaligned and unbalanced rotor system such as period 2, 3, 6, and 7 motions besides chaotic oscillations and so on.
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Berenfeld, Omer. "The Major Role of IK1 in Mechanisms of Rotor Drift in the Atria: A Computational Study". Clinical Medicine Insights: Cardiology 10s1 (gennaio 2016): CMC.S39773. http://dx.doi.org/10.4137/cmc.s39773.
Testo completoAbstract (sommario):
Maintenance of paroxysmal atrial fibrillation (AF) by fast rotors in the left atrium (LA) or at the pulmonary veins (PVs) is not fully understood. This review describes the role of the heterogeneous distribution of transmembrane currents in the PVs and LA junction (PV-LAJ) in the localization of rotors in the PVs. Experimentally observed heterogeneities in IK1, IKs, IKr, Ito, and ICaL in the PV-LAJ were incorporated into models of human atrial kinetics to simulate various conditions and investigate rotor drifting mechanisms. Spatial gradients in the currents resulted in shorter action potential duration, less negative minimum diastolic potential, slower upstroke and conduction velocity for rotors in the PV region than in the LA. Rotors under such conditions drifted toward the PV and stabilized at the less excitable region. Our simulations suggest that IK1 heterogeneity is dominant in determining the drift direction through its impact on the excitability gradient. These results provide a novel framework for understanding the complex dynamics of rotors in AF.
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Zhu, XZ, J. Liu e DP Sun. "Fluid transportation and heat transfer analysis of PP/TiO2 nanocomposites in an internal mixer". Advances in Mechanical Engineering 11, n. 1 (gennaio 2019): 168781401881306. http://dx.doi.org/10.1177/1687814018813068.
Testo completoAbstract (sommario):
The internal mixer is an important devise for processing the polymer nanocomposites acting as a chemical reactor. In this article, based on the computational fluid dynamics method, the fluid transportation and heat transfer analysis of sol–gel reaction processing for Polypropylene (PP)/TiO2 nanocomposites in the internal batch mixers with single-winged and two-winged Cam rotors were simulated. First, the Lagrangian coherent structure analysis was used to understand the fluid transport properties in the mixers. Then the effect of rotational speeds (ratios) and barrel temperatures on the heat transfer characteristics in the mixers with different rotors was analyzed. Also, the changes of viscous heating and torques of rotors with different thermal conditions in the mixers were discussed. Especially, the relationship between the fluid transportation and heat transfer characteristics was explored. The results show that a big rotor speed ratio can induce great fluid transportation in the left and right mixer chambers based on the Lagrangian coherent structure analysis, and the fluid near the horseshoe map has great folding effect and temperature magnitude. The viscous dissipation, viscous heat generation, and rotor torques in the mixers increase with increasing the rotational speeds and decrease with increasing the barrel temperatures. The mixer with two-winged rotors has higher average temperature, viscous dissipation, viscous heat generation and the torques of rotors values of reactive fluid than that with single-winged rotors.
46
Lee, Chong-Won, Jong-Po Park e Kwang-Joon Kim. "Complex Time Series Modeling and Analysis for Rotor Dynamics Identification". Journal of Vibration and Acoustics 119, n. 4 (1 ottobre 1997): 512–22. http://dx.doi.org/10.1115/1.2889753.
Testo completoAbstract (sommario):
A new time series method, directional ARMAX (dARMAX) model-based approach, is proposed for rotor dynamics identification. The dARMAX processes complex-valued signals, utilizing the complex modal testing theory which enables the separation of the backward and forward modes in the two-sided frequency domain and makes effective modal parameter identification possible, to account for the dynamic characteristics inherent in rotating machinery. The dARMAX is superior in nature to the conventional ARMAX particularly in the estimation of the modal parameters for isotropic and weakly anisotropic rotors. Numerical simulations are performed to demonstrate effectiveness of the dARMAX.
47
Wang, Yu, Mao Sun e Chao Yan. "Numerical simulation of hovering flow field and interference characteristics of rotor system". Journal of Physics: Conference Series 2235, n. 1 (1 maggio 2022): 012002. http://dx.doi.org/10.1088/1742-6596/2235/1/012002.
Testo completoAbstract (sommario):
Abstract In order to investigate the aerodynamic interference characteristics of tandem rotor, this paper simulates the hovering flow field of single rotor and tandem rotor based on the dynamic structure overset grid method and unsteady Navier-Stokes equations in computational fluid dynamics (CFD). In the study of hover state of single rotor with twist, the trajectory of the blade vortex and the change pattern are briefly analyzed. Subsequently, the flow field disturbance of tandem rotor, the vortex structure, the pull coefficient and the downwash flow are investigated. The results show that there is obvious blade vortex interference in the overlapping area of the tandem rotor, where the downwash flow reduces the effective angle of attack of the blade and thus has a significantly effect on the pull coefficient. The rotor is less disturbed when it is far from the overlapping area, and the tension coefficient does not change significantly. After integrating the pull coefficient of the upper and lower rotors in one cycle, it was found that the loss of pull coefficient of the two rotors reached 5.7% and 10.7% respectively, which proved that the aerodynamic interference between the tandem rotor in hovering condition had an important effect on the aerodynamic performance of the vehicle.
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Bauer, Wolfgang R., e Walter Nadler. "Dynamics and efficiency of Brownian rotors". Journal of Chemical Physics 129, n. 22 (14 dicembre 2008): 225103. http://dx.doi.org/10.1063/1.3026736.
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Leoni, M., e T. B. Liverpool. "Dynamics and interactions of active rotors". EPL (Europhysics Letters) 92, n. 6 (1 dicembre 2010): 64004. http://dx.doi.org/10.1209/0295-5075/92/64004.
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Schweizer, Bernhard. "Dynamics and stability of turbocharger rotors". Archive of Applied Mechanics 80, n. 9 (28 agosto 2009): 1017–43. http://dx.doi.org/10.1007/s00419-009-0331-0.
Testo completo