Vertical Rotor Research Articles

Numerical Analysis of Vibration Patterns in Hydropower Units

AbstractEvery manufactured hydropower rotor shows some degree of unbalance and other imperfections that cause vibrations. In this contribution, a non‐linear dynamic model is used to calculate the lateral vibrations of vertical rotors in hydropower units due to generator unbalance and coupling misalignment. The vibrations are analyzed and distinguishing features are identified. Using the identified features, it is possible to diagnose the vibration cause from vibrational data for the described model. This can be done even when some model parameters like bearing properties are not known with high accuracy.

Nonlinear free vibrations analysis of overhung rotors under the influence of gravity

In this paper, nonlinear free vibration of a cantilever flexible shaft carrying a rigid disk at its free end (overhung rotor) is investigated. The Rayleigh beam model is used and the rotor has large amplitude vibrations. With the assumption of inextensibility, the effect of nonlinear curvature and inertia is considered. The effect of disk mass on the dynamical behavior of the system is studied in the presence and absence of gravity (horizontal and vertical rotors). By using perturbation technique (method of multiple scales), the main focus is on the influence of gravity on equations of motion and on quantities such as amplitude and damped natural frequency. Here, a different behavior is observed due to the rotor weight. Indeed, the combination effects of gyroscopic term, nonlinearity and gravity are studied on the modal behavior of the system. It is shown that the static deflection creates second order nonlinear terms and changes the nonlinear damped natural frequency. With considering of gravity, both beat and high frequency in beat phenomenon increase. With increasing of the rotor weight, the minimum value of amplitude is extremely amplified in the direction of gravity but in the other transverse direction, amplitude of vibrations decreases. In addition, it is found that the weight has directly influence on beat frequency, while the mass ratio between disk and beam affects the high frequency.

A method to obtain the linear dynamic coefficients for journal bearing in vertical rotors

PurposeThe infinitesimal perturbation (IP) method is commonly used in calculating stiffness and damping of journal bearing in horizon rotor systems. The boundary condition (BC) for the perturbed pressure is assumed being zero at leading edge of film, although it is usually not zero because of nonzero pressure gradient. This assumption is sufficiently accurate for most purpose in horizon rotors. However, for journal bearing in vertical rotor-bearing systems, the BC with the assumption in IP method will bring in significant errors in calculating linear dynamic coefficients. This paper aims to propose a method to obtain the dynamic coefficients of journal bearing in vertical rotors.Design/methodology/approachThe stiffness and damping are approached based on IP method and the modified BC of perturbed pressure. As it is difficult to predict perturbed pressure at leading edge at a fixed coordinate system using IP method, a dynamic coordinate system is introduced in this method, of which the origin on circumferential direction is defined as the leading edge of film.FindingsThe effectiveness and accuracy of proposed IP method in dynamic coordinate (IPMDC) system are verified by comparing the obtained results with analytical solutions. The comparison shows that the results from IPMDC present a good agreement with the analytic solutions.Originality/valueThe proposed method can be applied in obtaining linear dynamic coefficients of journal bearing in vertical rotors with high precisions. Instead of the usual nonlinear analysis of vertical rotors, this method provides a feasibility of predicting the instability threshold of vertical rotor-bearing systems via linear models.

Numerical analysis of a vertical rotor rub system partially immersed in inviscid incompressible fluid

Two-dimensional linearized Navier-Stokes equations have been used to model the inviscid fluid forces acting on a vertical rotor-cylindrical stator system partially immersed in an inviscid incompressible fluid. The response of the fluid-stator-system subjected to subsequent fault feature extraction. The influences of parameters of the fluid system, among them, fluid density, and mass ratio on the unstable contact zones are analyzed. It is shown that for an effective prediction of rub-impact in a submerged rotor system, the influence of the fluid mass on the stability of the system is an important dynamic factor. It is revealed, that the fluid forces increase the amplitude of vibration, while the frequency of oscillation is reduced, phenomena that stabilise the isotropic vertical rotor-stator system.

Performance Evaluation of Projected Seed Cell Vertical Rotor Device for Pelleted Rice

Performance Evaluation of Projected Seed Cell Vertical Rotor Device for Pelleted Rice

Nonlinear dynamic performance of tilting-pad journal bearing with adjustable elastic pivot design

Abstract To improve the security and reliability of a traditional rigid-pivot tilting-pad journal bearing (RPTPJB), a kind of elastic-pivot tilting-pad journal bearing (EPTPJB), which is an adjustable-pivot TPJB that can realize self-adaptive preload factors, is proposed for vertical rotors. The nonlinear movement performance and film load performance of a water-lubricated four-pad EPTPJB are investigated by journal displacements, journal center orbits, minimum film thicknesses, tilting angles and radial displacements of pads using an analytical turbulent hydrodynamic model. The results show a safer film thickness of an EPTPJB and reveal the dynamic performance adjustment mechanism adjusted by pivot stiffness, pre-tightening force and preload factors. This study contributes to the reduction of impact and rubbing between the journal and the pads.

Numerical Investigations of Aerodynamics Characteristics of Main Rotors in Helicopter UAV Used for Pesticide Spraying in Agriculture

In the last several decades past, Helicopters UAVs (Unmanned Aerial Vehicles) have quickly developed and day by day, they play an important role in human life. As it is well-known, helicopters UAV make some outstanding characteristics such as light weight, flexibility and particularly automatically controlled. By applying these characteristics, we research and manufacture Helicopter UAV using for spraying pesticide in agriculture. One of the most important components is main rotor because main rotor generated thrust, drag and momentum. Helicopters UAV efficient changed depending on main rotor. The research works focus on aerodynamics characterization of main rotor in helicopter UAV. This work uses CFD tool in ANSYS CFX software to calculate the aerodynamics parameters generated by main rotor using in UAV. The aim is to characterize the aerodynamics characteristics such as thrust, drag, pressure, aerodynamics quality on the different flight modes (hover, vertical and forward flight). Firstly, the simulations are carried out in hover flight mode with different blade pitch angles. The results are compared to experiment date in another research to validate numerical results. Then, the simulations are carried out in vertical flight mode and forward flight mode. The results showed that thrust and drag coefficient creased with increasing blade pitch angle. When blade pitch angle started from 1800, thrust coefficient decreased but drag coefficient increased sharply. The rotor performance was measured by aerodynamics quality and numerical results showed that the best rotor performance was at 900. In the vertical flight mode, the thrust and drag coefficient decreased with increasing vertical velocity but rotor performance increased slightly. The best vertical velocity for vertical flight is around 2 m/s and 3 m/s. Finally, in forward flight mode, the aerodynamics characterizations of rotors depended on azimuthal angular position of blade or time. Our helicopter operates in environment with light gust. The results showed the change of aerodynamics coefficient to time. Both thrust and drag coefficient changed but the rotor performance did not change much.

The impact of an elastic rotor suspender and the size of the compensating mass on the acceleration of the automatic balancer

The researches of a vertical rotor with a ball-type automatic balancer with a torus-shaped body have shown its efficiency in the reduction of vibrations of an unbalanced rotor. At the same time, there is a problem of the acceleration of compensating masses of the automatic balancer till the working rotor velocity, for which the initial movement velocity is to be provided. The work has shown that the value of the initial velocity of compensating masses is influenced by the rigidity of a rotor elastic suspender and their size. The authors have carried out the analysis of the mutual impact of the given factors on the acceleration of the automatic balancer. The suggestions for the selection of parameters of a rotor suspender and the size of compensating masses in an automatic balancer have been given.

The role of centrifugation process in the preparation of therapeutic blood concentrates: Standardization of the protocols to improve reproducibility

Investigations of endogenous blood-derived growth factors have increased in the past two decades. The initial protocols for blood concentrates, such as platelet-rich-plasma, utilized anticoagulants followed by bovine thrombin to catalyze fibrin polymerization. Subsequently, platelet-rich-fibrin (PRF) protocol was developed to eliminate anticoagulants and thrombin. The PRF production was described in a vertical rotor centrifuge with an angle of ~33°. Many commercial enterprises have attempted to replicate this protocol with a multitude of different centrifuges. These attempts have utilized revolutions per minute (RPM) to develop their protocol to generate PRF. However, RPM is a variable parameter, as it depends on the design and radius of the centrifuge. The separation of blood components is highly dependent on the relative centrifugal force (RCF) generated, which is based on the applied centrifugal force, expressed as multiples of earth's gravitation (g) field. RCF is a function of the acceleration due to the gravity of the earth, g = 9.81 m/s2 RCF, not RPM, is the key factor for the sedimentation of the cells and proteins within blood concentrates. RCF is determined using the maximum centrifuge radius for calculation. The initial PRF was generated by applying an RCF of 700 ×g. Accordingly, so far, a large number of studies existing about PRF are not comparable, as they were technically prepared with different RCFs. In addition, due to the nonstandardized measurement methods, in some published studies, incorrect RCF values are published as the authors did not know how to calculate the RCF correctly. This is the case for a widespread blood concentrate called leukocyte-PRF, which is commercially available. Recently, we introduced the low-speed centrifugation concept (LSCC) for the production for solid and liquid PRF matrices. This concept is based on the above-mentioned initial PRF protocols, which represents a relatively high RCF. It shows that a systematic reduction of 700 ×g to 44 ×g can significantly increase the cells and growth factors within the same blood concentrates. The LSCC concept was established initially for a fixed rotor centrifuge with a radius of ~110 mm. The present narrative review highlights the necessity of standardization in the generation of blood concentrates, which utilizes RCF, rather than commercial protocols.

Stability of vertical rotor supported with self-acting gas bearings with air supply and exhaust holes

Stability of vertical rotor supported with self-acting gas bearings with air supply and exhaust holes

A review of wind energy literature: alternative technologies for Central America

Wind energy has proven to be one of the most viable sources of renewable energy. In this sense, although wind power generation systems have evolved considerably in size, capacity and design, it has not been possible to build an ideal system, due to the behaviour of the wind, which varies temporarily, being something uncontrollable that depends of its direction and affects the efficiency of a wind system. Specifically, this paper focuses on making a first literature review that identifies the best technologies that can be implemented in Central America (CA). Although the types of wind turbines most used in CA are three-blade horizontal axis, since they take advantage of the variability of the winds, this review shows there are other technologies in developed countries for obtaining kinetic energy, by means of vertical Rotors that can be implemented. The results obtained have practical implications in the adoption of alternative technologies for developing countries in CA.

Model of a vertical rotor with an automatic balancer with two compensating masses

The use of automatic balancing devices in unbalanced rotor systems has proven their ability to reduce rotor vibrations in the super resonance zone of velocities. At the same time, the creation of efficient automatic balancing devices with a torus-shaped body and a circular cross-section is associated with the multimodal motion of the compensating masses, which makes the device unsuitable for operation. To ensure the acceleration of the compensating masses from the rest state to the working speed of the rotor, they need to be provided with some initial velocity. The magnitude of this velocity is influenced by the parameters of the elastic suspension of the rotor, the geometric parameters of the automatic balancing device, the rolling friction coefficient between the body and the compensating mass, etc. The work is devoted to the description of the vertical rotor model with an automatic balancer with two compensating masses. It also considers the effect of the rolling friction coefficient on the value of their initial velocity.

Pareto Optimal Decentralized Control of a Rotor in Electromagnetic Bearings

The problem of the optimal stabilization of a vertical rigid rotor rotating in two electromagnetic bearings is considered. A quantitative estimate of transient processes is based on the maximal deviation of the rotor from the equilibrium state and the maximal value of the current intensity in the windings of electromagnets. The use of linear matrix inequalities allow synthesizing the Pareto optimal control laws in the form of linear state-feedback, as well as decentralized control laws, which are defined by the displacements of the rotor in each electromagnetic bearing. The Pareto optimal criteria for centralized and decentralized control laws are compared. It is shown that utilization of simple easily realizable decentralized control laws only slightly worsens transient processes.

The Impact of Design Deviations on Dynamic Characteristics of a Flexible Multispan Rotor on Complete Electromagnetic Suspension

The paper presents a study of dynamics of rotors on complete electromagnetic suspension, a characteristic feature of which is a relatively low stiffness of the support system. The experience of balancing the rotors of this type shows that deviations of geometrical parameters, although the latter are within design tolerance limits, may have a significant impact on the rotor dynamics. The analysis of the impact of design deviations caused by the nonorthogonality of the disk plane of the axial active magnetic bearings (AMBs) to the rotation axis and noncoaxiality of the rotor shafting in the elastic clutch section on the dynamics of the flexible multispan rotors was made. The model of the dynamics of the rotor was refined considering the above deviations. The resulting model of the dynamics of a rotor on the complete electromagnetic suspension comprises a mechanical model, models of forces of different physical nature, and a model of the AMB control system. The model takes into consideration the effects of forces in the radial and axial active magnetic bearings, imbalance, gyroscopic forces, the force of gravity, and the frequency-independent inner damping; it also describes circulation impacts and tension forces caused by electromagnetic interactions in the generator and exciter as well as gas-dynamic forces in turbines, compressors, and labyrinth seals of their shafts. It is shown in the paper that the considered design deviations caused by nonorthogonality of the disk plane of the axial AMB to the rotation axis and noncoaxiality of the rotor shafting in the elastic clutch section lead to amplitude- constant harmonic influences on the rotor, whose frequency coincides with the rotational speed of the rotor. The verification of the refined computer model was conducted on a scale-modeling test bench for the vertical flexible rotor of a high-temperature gas-cooled reactor. The testing of the model demonstrated qualitative identity of the numerical and experimental results that describe the rotor dynamics in the running- down mode. The proposed mathematical model of the flexible rotor allows for enhancing the precision of the method for identification of unknown parameters, in particular, the residual imbalance, based on solving the inverse dynamics problem.

Dynamic responses of a floating tidal turbine with 6-DOF prescribed floater motions

This study aims to reveal the dynamic response and power output characteristics of a floating tidal turbine with prescribed motions in six degrees of freedom. Floater motions were calculated in the time domain based on linear potential theory. Both wave-induced inflow fields and floater motions are considered in a modified blade element momentum theory model for rotor load simulation. Generator power production and loads on a reference tidal turbine system were investigated. The torque and thrust response spectra are found to be dominated by floater-motion-induced contributions, and two response peaks can be clearly identified. A cancellation effect occurs between direct wave effects and floater-motion-induced loads, and horizontal and vertical rotor positions can significantly affect the dynamic responses of the blade loads; the rotor should be placed close to the floater centre to avoid large floater-motion-induced velocity on the blade section. Sensitivity studies are carried out with varying significant wave heights and peak periods. These results may contribute to a general understanding of floater-induced dynamic loads on floating tidal turbines in a random sea.

On the issue of impact of anisotropy of the rotor elastic suspension on the performance of the automatic balancer

Experimental researches of a vertical rotor with a ball-type automatic balancer with a circular cross-section of the body have proved its efficiency in the reduction of vibrations of an out-of-balance rotor, however for acceleration of compensating masses till the rotor working velocity it is necessary to set initial velocity. A value of the initial velocity of compensating masses depends on the stiffness of the elastic rotor suspension. At the same time, real elastic suspensions of rotors possess nonhomogeneous elastic dissipative characteristics in directions. The research is aimed at determining the influence of anisotropy of the elastic rotor suspension on the acceleration of compensating masses. The authors give recommendations on the selection of parameters of a rotor suspension.

Nonlinear Control of a Vertical Rotor Orientation System

The rotor position control is the core issue of the active magnetic bearing (AMB) control. Aiming to the rotor position control during the rotor spinning launching period, this paper presents a nonlinear control approach based on the feed-back linearization technique. Theoretical derivation and simulation results are provided to illustrate the feasibility of this approach. The work in this paper may provide new thought of the vertical rotor position control problem.

The impact of rotor elastic suspension settings on the acceleration of the automatic balancer compensating mass

Experimental studies of the vertical rotor with the automatic balancer ball type with a torus-shaped body with a cross section of the round form showed that the compensating masses are not accelerated to its operating speed at the each start of the rotor. The work is devoted to clarify the effect of the stiffness of the rotor elastic suspension on the acceleration process of compensating mass.

Nonlinear Analysis and Characteristic Variation of Self-Excited Vibration in the Vertical Rotor System Due to the Flexible Support of the Journal Bearing

Various vibration problems occur in rotating machinery. Specifically, the large amplitude vibration may occur in the vertical pump using a journal bearing. In an actual vertical pump, the stator's structure supporting the pump shaft may be relatively flexible. In such a case, rotor's motion such as amplitude of the self-excited vibration is not able to be predicted accurately without considering the nonlinear fluid film force reacting in the relative motion between the shaft and the flexibly supported bearing stator. However, the vibration characteristics in such situations have not been explained theoretically so far. In this paper, the vibration characteristics of a vertical rotating shaft with journal bearing are investigated. The nonlinear steady-state vibration analysis of the self-excited vibration is demonstrated, and the influences of the parameters, such as fluid viscosity, radial clearance, and stiffness and damping coefficients of the flexible support of bearing stator, on the vibration characteristics of the system are explained. Moreover, these theoretical results of the self-excited vibration in the vertical rotating shaft with journal bearing are verified both numerically and experimentally.

Dynamic Analysis for the Rotor Drop Process and Its Application to a Vertically Levitated Rotor/Active Magnetic Bearing System

Active magnetic bearings (AMBs) have been utilized widely to support high-speed rotors. However, in the case of AMB failure, emergencies, or overload conditions, the auxiliary bearing is chosen as the backup protector to provide mechanical supports and displacement constraints for the rotor. With lack of support, the auxiliary bearing will catch the dropping rotor. Accordingly, high contact forces and corresponding thermal generation due to mechanical rub are applied on the dynamic contact area. Rapid deterioration may be brought about by excessive dynamic and thermal shocks. Therefore, the auxiliary bearing must be sufficiently robust to guarantee the safety of the AMB system. Many approaches have been put forward in the literature to estimate the rotor dynamic motion, nonetheless most of them focus on the horizontal rotor drop and few consider the inclination around the horizontal plane for the vertical rotor. The main purpose of this paper is to predict the rotor dynamic behavior accurately for the vertical rotor drop case. A detailed model for the vertical rotor drop process with consideration of the rotating inclination around x- and y-axes is proposed in this paper. Additionally, rolling and sliding friction are distinguished in the simulation scenario. This model has been applied to estimate the rotor drop process in a helium circulator system equipped with AMBs for the 10 MW high-temperature gas-cooled reactor (HTR-10). The HTR-10 has been designed and researched by the Institute of Nuclear and New Energy Technology (INET) of Tsinghua University. The auxiliary bearing is utilized to support the rotor in the helium circulator. The validity of this model is verified by the results obtained in this paper as well. This paper also provides suggestions for the further improvement of auxiliary bearing design and engineering application.