Papers by Keyword: Torsional Vibration

Abstract: Torsional vibration analysis of the axially functionally graded carbon nanotubes has been carried out. Nonlocal stress gradient elasticity theory has been used in continuum mechanics model of the carbon nanotube. Variation of the material properties of the axially graded nanostructure has been assumed in exponential form. Differently from the majority of literature works, viscous damping and nonlocal parameters have been assumed in grading form. Energy functional for the carbon nanotube has been achieved with minimum potential energy principle and weak form solution has been obtained with the Ritz Method. Effects of material grading, nonlocality and viscoelasticity to the torsional dynamics of axially graded carbon nanotube have been investigated. Results of the present work could be useful in modeling and production of axially functionally graded nanostructures.

Abstract: The results of crankshaft forced vibration calculations, including the dry friction force which can be formed in the viscous damper bearing sliding, were presented. This problem concerns the big dampers used in the marine engines. The friction force influence is presented using the function {sign}. Low values of friction coefficient, corresponding to the conditions similar to the real ones, were assumed. In the range of tested value, it was found that the vibration increases linearly, and system free vibration frequency doesn’t change practically.

Abstract: In the torque converter, a damper with a piecewise-linear spring is used to reduce the forced vibration, and the subharmonic vibration occurs when the spring restoring torque characteristics approach the switching point. This research analyzed the effect of stiffness ratio between the neighboring piecewise-linear springs on the occurrence of the subharmonic nonlinear vibration in automatic transmission powertrain. The powertrain is modeled with multi degree-of-freedom nonlinear system as an actual vehicle. The result shows higher value of the stiffness ratio between the neighboring springs creates larger value of the subharmonic vibration.

Abstract: The problem of damping of torsional vibrations of the crankshaft in a multi-cylinder engine is very important from the point of view of durability and reliability of the drive unit of the vessel or ship. Mostly dependent on the technical state of the torsional vibration damper that is located at the free end of the crankshaft. The paper presents selected results of the research that led to the acceptance criterion for assessing the technical condition of the viscous torsion damper.

Abstract: The paper presents an estimation analysis methopd for the natural mode and frequency of the torsional vibrations of a marine power transmission system. A typical merchantman marine propulsion system is made up of a slow speed main engine connected to a directly driven propeller by a relatively short shaft line. Although all classification societies require calculating the operating parameters of the propulsion system, however, they have no simplified formulas. The torsional vibrations of the marine power transmission system are usually the most dangerous for the shaft line and crankshaft. Numerical algorithms based mostly on the Finite Element Method (FEM) are unobtainable and not useful for a ship crew. The chief of marine engineers should have checked a possibility of the analysis and measurements of torsional vibrations. The authors have investigated an estimation method of the torsional vibrations of the system. The article deals with a simulation method for more difficult parameters of the propulsion system like propeller water added mass moment of inertia. The paper also briefly describes the advantages and disadvantages of the undercritical and overcritical propulsion system and discusses calculation results included in the final part of the work. The introduced calculation method has been verified comparing detailed FEM estimations and the measurements of real ships.

Abstract: A single pile in soil is modeled as a vertical circular elastic prismatic bar, and the soil around the pile is regarded as transversely isotropic medium. The relationship between stress and displacement of the soil is described by fractional derivative viscoelastic model. Ignoring the radial and vertical displacement, the torsional vibration equation of the soil is built. It is solved by using the method of separation of variables and the boundary conditions of the soil. The torsional vibration of the single pile is also obtained. The torsional complex stiffness at pile head is investigated in particular. The results indicate that anisotropic parameters and model parameters of the soil have effects on the torsional complex stiffness, and the influence rules are different with the homogeneous soil.

Abstract: Through the establishment of motor electromechanical coupling vibration model, torsional vibration characteristics of motor is analyzed in starting process. With 1000T lubricating oil ship electric propulsion shafting as the object of study, the free vibration and the forced vibration characteristics are analyzed. In two cases of considering the electromagnetic excitation torque and without considering the electromagnetic excitation torque, the responded vibration of electric propulsion shafting is calculated. The low noise design of the motor and propulsion shafting provides a theoretical basis.

Abstract: In this paper, a model predictive controller for the position tracking of flexible robot joints with harmonic drive gears is presented. The control methodology enables the drive's safety and physical constraints on torque and speed variables while guaranteeing the stability of the system. The effect of the predictive horizon on the drive performance is examined. Moreover, the influence of parameter changes is tested in this paper. Experimental results demonstrate the proposed controller is very effective in tracking position references while meeting the demanding drive constraints requirements during operation.

Abstract: The cutting processes of drill rod under different surge pressures, rotate pressures and propulsion forces were recorded by the high-speed camera in the hydraulic percussive rotary cutting tests of deep-ocean cobalt-rich crusts. Meanwhile, the curves of impact vibration, torsional vibration and frame vibration during the cutting processes were plotted by digital picture processing technique. The impact frequency, torsional vibration frequency, torsional vibration amplitude, vibration amplitude of drill rod and the frame were calculated. The photogrammetry results are generally in agreement with the traditional test results. High-speed photogrammetry is a non-contact, wide range application, and high precision measurement, and the cutting process can be described visually and adequately.

Abstract: The torsional vibration problems of turbo-generator shafts are increasing widespread and sever under the coupled action between the turbo-generator unit and the power grid because of the complicated power grid structure. Thus, the accurate solution of torsional vibration inherent characteristics of the shafts is of great significance to do the safety evaluation. The finite element method (FEM) with higher accuracy is adopted to calculate the torsional vibration inherent characteristics in this paper. A 1000 MW turbo-generator shaft is taken as a studying object and its torsional vibration finite element (FE) model and solving process are introduced, using ANSYS software as implementation platform of the FEM. The simulation results show that the torsional vibration characteristics calculated by FEM are accurate and reliable.