Propeller Inertia Research Articles

Nonlinear dynamic modeling for a diesel engine propeller shafting used in large marines

Longitudinal vibration, torsional vibration and their coupled vibration are the main vibration modes of the crankshaft-sliding bearing system. However, these vibrations of the propeller-crankshaft-sliding bearing system generated by the fluid exciting force on the propeller are much more complex. Currently, the torsional and longitudinal vibrations have been studied separately while the research on their coupled vibration is few, and the influence of the propeller structure to dynamic characteristics of a crankshaft has not been studied yet. In order to describe the dynamic properties of a crankshaft accurately, a nonlinear dynamic model is proposed taking the effect of torsional-longitudinal coupling and the variable inertia of propeller, connecting rod and piston into account. Numerical simulation cases are carried out to calculate the response data of the system in time and frequency domains under the working speed and over-speed, respectively. Results of vibration analysis of the propeller and crankshaft system coupled in torsional and longitudinal direction indicate that the system dynamic behaviors are relatively complicated especially in the components of the frequency response. For example, the 4 times of an exciting frequency acting on the propeller by fluid appears at 130 r/min, while not yield at 105 r/min. While the possible abnormal vibration at over-speed just needs to be vigilant. So when designing the propeller shafting used in marine diesel engines, strength calculation and vibration analysis based only on linear model may cause great errors and the proposed research provides some references to design diesel engine propeller shafting used in large marines.

プロペラ軸系ねじり振動実験装置の製作

The torsional vibration of the shafting driven by the marine main engine is a mater of the utmost importance. When the frequency of periodic torque is equal to the natural frequency of the shafting, the amplitude of the torsional vibration increases. This frequency is called critical speed. In order to calculate the critical speed of a propeller shaft, it is necessary to know propeller inertia.This paper describes the production of the experimental equipment excited by periodic torque. Propeller inertia could be calculated from the experimental results.Propeller inertia obtained from the experimental results is compared with it from the measurement of dimension.

Evaluation of the K-Gill Propeller Vane

Abstract Dynamic properties of the K-Gill propeller vane (k vane) are assessed from perturbation theory, wind tunnel, and field comparison experiments. Measurement errors for average wind speed are negligible. The dynamic response of the k vane can be described with a single response length that is the propeller’s distance constant at a 45° angle of attack. Measurement errors in longitudinal and vertical wind speed variances and the momentum flux due to propeller inertia can be described and corrected for as if the k vane were a simple first-order system. Standard spectra as well as spectra measured by the k vane itself can be used to calculate correction coefficients. In the latter case no information on atmospheric stability and boundary layer height is necessary. Transfer of lateral wind speed variance can be described as if the k vane were a damped harmonic oscillator. Measurement errors in lateral wind speed variance, however, are usually negligible because loss of high-frequency variance is compensa...

Corrections for Response Errors in a Three-Component Propeller Anemometer

Abstract Methods of eliminating or reducing three types of errors found in the Gill UVW anemometer have been investigated by utilizing field experiments comparing this sensor with a three-component sonic anemometer. The non-cosine response of each of the three orthogonal propellers to a wind which is not parallel to the propeller axis was adequately corrected during computer processing of the data, using the manufacturer's wind-tunnel-measured calibrations. The accepted theory describing a propeller as a first-order system with a time constant τ = L/ū (where L is a distance constant characterizing the propeller inertia and ū is the mean wind) was found to be only a fair description of the frequency response, probably due to dependence of L on properties of the flow, but was used to qualitatively delineate proper applications for this sensor. The threshold response was improved for the U and V components by orienting the anemometer so that the mean wind direction bisects the angle between the horizontal ax...

Rotary Flow Meter as Turbulence Transducer

Two factors prevent the direct determination of the point spectrum of axial turbulence from a spectrum of the fluctuations in rpm values of the analog output of a rotary flow meter. The first of these is the effect of the finite size of the flow meter propeller, the second is the effect of its inertia. The finite size effect depends on the local turbulence structure and is characterized by an efficiency factor which in general can only be estimated. The effect of propeller inertia can be evaluated by linearizing the equation of motion of the propeller. From the resulting linear ordinary differential equation with constant coefficients, a transfer function for the linear system can be calculated. This transfer function makes it possible to calculate a spectrum of axial turbulence in which the velocity is averaged over the area of the propeller. Experiments in which propellers were oscillated sinusoidally while being towed through still water showed that the amplitude response function is approximately equal to that of a first-order system, while the phase function appeared to be independent of the natural frequency of the system.

Virtual Moment of Inertia of Marine Propellers

In order to culculate the critical speed of propeller shaft, the accurate value of virtual moment of inertia of marine propeller should be estimated.Virtual moment of inertia consists of the mass moment of inertia of propeller I and the additional moment of inertia by entrained water Δ I.It is usual to estimate Δ I by making a percentage additon to I, varying from some 20 percent to 30 percent, but this estimate is sometimes accompanies by risk, The auther introduced the theoreitcal formula by application of two dimensional, and three dimensional potential flow theory, and by the test results for series model propeller the coefficient of the theoretical formula were added some correction the simple practical formula for Δ I were obtained. The availability of this practical formula was also prove by the test results of torsional vibration of propulsion at sea trial,