Phase difference and stability of a shaft mounted a dry friction damper: Effects of viscous internal damping and gyroscopic moment

This study investigates the stability and phase difference of a shaft mounted a dry friction damper with effects of viscous internal damping and gyroscopic moment. The equations of the system with the vibration reduction effect of the dry friction damper on the shaft are derived in the form of the rectangular coordinate and polar coordinate in the vicinity of critical speed. The phase difference characteristics in the rub-impact process and its physical mechanism are analyzed by mathematical derivation. The characteristic equation is studied to investigate the stability of the periodic solution. Effects of different parameters of the system, especially viscous internal damping of the composite shaft and gyroscopic moment on the phase difference and stability regions are presented in detail by analytical and numerical simulation based on a helicopter tailrotor driveline. The experimental investigation is conducted in a test rig to validate theoretical formulas and simulation analysis. The analysis results show that rub impact delays the change of phase difference, viscous internal damping improves the stability of synchronous full annual rub solution, and gyroscopic moment affects the increase of the phase difference.

Оscillations of closed conical shells with complex rotation

The paper consider a system of two closed conical shells connected by a central rigid insert rotating in opposite directions in a central force field with a constant angular velocity around the axis of symmetry of the system. The shell element is subjected to a load consisting of gravitational and inertial forces, but at large values of the angular velocity of the system, the gravitational loads can be neglected. The gyroscopic interaction between the rotational portable motion of the system and the relative elastic oscillations of the elements is a source of excitation of precession oscillations, which may be resonant or unstable. Occurring when changing the axis of orientation of the system gyroscopic moment causes the appearance of alternating stresses, which significantly affect the strength and reliability of the shells. Such problems arise in construction engineering, mechanical engineering, aircraft construction, space engineering and other sectors of the economy. The main load acting on the elements of such systems are significant centrifugal forces of inertia, which significantly affect the strength characteristics of structures. Taking into account the periodicity of the right-hand side and the coefficients of the system of resolving equations, with the help of the projection method it is possible to reduce the resolving equations to the system of ordinary differential equations, which approximately replaces the original one. The solution of the obtained system of equations makes it possible to determine the forms of oscillations and forces in a composite conical shell at various parameters of the shell and the ratios of the velocities of the shell's own rotation and the rotation of its center of mass.

DIGITAL AND PULSE-WIDTH CONTROL OF A SPACE ROBOT WHEN APPROACHING A GEOSTATIONARY SATELLITE

The control problems on a space robot during its approach to an information geostationary satellite are considered. The robot motion control system uses an electric propulsion system with 8 engines at the pulse-width modulation of their thrust values and a gyroscopic moment cluster based on 4 gyrodines with digital control. Numerical results are presented that demonstrate the effectiveness of the developed discrete guidance and control algorithms.

Effects of Four Moon Pools on a Floating System Installed With Twin-VAWTs

This paper describes characteristics of motion responses and tether tensions of a floating structure with four moon pools, on which one or two vertical axis wind turbine models are installed. Effects of several moon pools founded in a floating structure on motion characteristics have been unclear. In this study, the authors proposed a twin-VAWT installed floating system, which was a pontoon based structure. However four moon pools were set on. The study conducted model experiments in a wave tank using regular waves with 0.6 to 2.0 seconds in wave periods and 0.02 and 0.04 m in wave height. The model had four moon pools and was installed with one or two vertical axis turbine models. From it, gyroscopic moment effects were investigated. Besides, the study performed numerical calculations with the linear potential theory based method which were a Green function method. As a results, responses of the twin-turbine model are not affected by gyroscopic moment. The study discusses motion responses and tether tensions with nonlinear behaviours from mainly the experimental results. Also the effect of moon pools were investigated from the calculations. From comparisons of motion results on calculation models with same displacement but different draft, the results suggested that not only heave motion but also roll motion could be reduced because of the moon pools if the size of the moon pools were optimized.

Response Characteristics of a Floating Structure With Moon Pools Installed With Vertical Axis Wind Turbines

This paper describes characteristics of motion responses and tether tensions of a floating structure with four moon pools, on which one or two vertical axis wind turbines are installed. In this study, the authors proposed a twin-VAWT installed floating system, which was a pontoon based structure. However four moon pools were set on. The study conducted model experiments in a wave tank using regular waves with 0.6 to 2.0 seconds in wave periods and 0.02 and 0.04 m in wave height. The model had four moon pools and was installed with one or two vertical axis turbine models. From it, gyroscopic moment effects were investigated. Besides, the study performed numerical calculations with the linear potential theory based method which were a Green function method. As a results, responses of the twin-turbine model are not affected by gyroscopic moment. The study discusses motion responses and tether tensions with nonlinear behaviours from mainly the experimental results.

Effect of the Gyroscopic Moment, Centrifugal Force and Hydroplaning on the Critical Speed of the Vehicle

Driving vehicles on curved roads is dangerous because of the risk of accidents. This is due to the centrifugal force, gyroscopic moment and hydroplaning of the vehicle, ending with vehicle slipping or tipping. The aim of this research is to find the critical speed under any one of the above mentioned risks. The water pressure under the vehicle tires was calculated using Matlab R2017a in order to find the pressure value that able to lift the vehicle causing slipping and then going out of control. The effect of many parameters, on the vehicle hydroplaning have been studied. These parameters are tire width, wheel load, and water layer thickness. While for vehicle slipping due to the centrifugal force or the gyroscopic moment, the following parameters have been studied. These parameters are height of vehicle gravity center, vehicle width, radius of the circular path and track angle. The results showed that the gyroscopic torque negatively affects the critical velocity of the vehicle, and it reduced it about 0.549%. The centrifugal effect is the has the greatest influence on the gyroscopic effect, and the gyroscopic effect pushes the vehicle outward and increases the radius of the rotation, while the gyroscopic couple effect, at low radius. of low rotation, is very small. Gyroscopic impact is increased by increasing the radius of the rotation path. The result also showed the increase of the road surface angle and surface at the turning the influence positively on the safe speed of the vehicle at all the above variables.

Rotor Dynamic Analysis of Driving Shaft of Dry Screw Vacuum Pump

Rotor dynamics is the study of vibration behavior in axially symmetric rotating structures. Devices such as engines, motors, disk drives and turbines all develop characteristic inertia effects that can be analyzed to improve the design and decrease the possibility of failure. At higher rotational speeds, such as in a gas pumps, the inertia effects of the rotating parts must be consistently represented in order to accurately predict the rotor behavior. An important part of the inertia effects is the gyroscopic moment introduced by the precession motion of the vibrating rotor as it spins. As spin velocity increases, the gyroscopic moment acting on the rotor becomes critically significant. Not accounting for these effects at the design level can lead to bearing and/or support structure damage. The main objective of this project is to study the Rotor Dynamic behavior of the drive rotor shaft of the Dry screw vacuum pump. The design of the pump is considered from the one of the reputed pump manufacturing industry. The operational speed of the pump is 4500 rpm, whereas the maximum capable speed of the pump is 10,000 rpm. Rotating machinery produces vibrations depending on the unbalanced mass and gyroscopic effects. Thus an investigation is to be made on the rotor dynamic properties of the shaft to find the natural frequencies and critical speed. For this rotor dynamic analysis was carried out in ANSYS APDL and Workbench16 to find the natural frequencies and critical speeds in the range of 0 to 10000 rpm. Thus an effort is made to shift the mass moment of inertia of the shaft by varying the design of the shaft and to shift the critical frequency to the higher speeds of the shaft there by increasing the efficiency. The modal analysis is performed to find the natural frequencies and it is extended to harmonic analysis to plot the stresses and deflections at the critical speeds. The design of the rotor shaft is made in NX-CAD.