Main Source Of Vibration Research Articles

A Literature Review of Diesel Engine Noise with Emphasis on Piston Slap

The noise radiated from an ICE is ultimately caused by its external surface vibration, which is excited by internal sources. These vibrations excite the ICE boundary surface and radiate noise into the air. To control ICE noise, generated by mechanical impacts, it is important to understand the behaviour and to have accurate measurements of piston slap. Since piston slap is generated by a complex mechanism, which involves many factors. Taking into account that the noise and vibration generated in an ICE are the sums of many different sources, it is important to know and understand the possible techniques available for separating and measuring these. This review is presented as follows: a review with the definition of the main ICE vibration and noise sources, and the principal methodologies used for their determination and the most common assessment techniques for piston slap.

Active damping of vibrations in elevator cars

AbstractThe goal of this dissertation was to develop an active vibration damping system for high‐speed elevator cars to achieve a ride comfort not reached before by passive means. The system developed comprises eight actuators, six accelerometers, eight position sensors, a signal conditioning unit, and power electronics. It is controlled by a real‐time computer utilizing a digital signal processor. A laboratory test rig was designed and constructed to allow testing the active damping system fitted to a full‐scale high‐speed elevato car. The unevennes of the two guide rails, which is the main source of vibrations, is emulated using eight hydraulic cylinders. A multivariable system identification procedure in the frequency domain was developed to obtain a linear time‐invariant system model. A first controller loop utilizes the acceleration outputs to suppress the vibrations. Due to asymmetric load distributions in the cabin, the orientation of the car with respect to the guide rails may change to the extent that for one or more actuators there may not be enough actuation distance. To correct the car orientation, a second controller loop utilizing position outputs is used. However, since the position measurements are taken between the car and the guide rails, nulling the position error signals means forcing the car to follow an average line of the two rail profiles which is the main source of vibrations. To avoid a conflict between the two loops, a frequency domain separation of the bandwidths of the two controllers is achieved. The two multivariable controllers are designed using the H∞ robust design method and employing the plant non‐inverting GS/T weighting scheme. The effectiveness of the active system was tested using rail profiles previously measured in a real building and emulated by the hydraulic excitation system. The vibration reduction factor achieved is around 5 as to a passive damping system. Meanwhile, the controller is capable of correcting the car orientation caused by asymmetric loads.

The main sources of helicopter vibration and noise emissions and adaptive concepts to reduce them

AbstractThis paper deals with the sources of helicopter vibration and noise emissions. It shows and evaluates adaptive concepts to reduce them. The main reasons for these emissions are aerodynamic effects such as blade‐vortex‐inter action (BVI), aerodynamic hysteresis, and local transonic effects at the forward moving blade.After a review of conventional control concepts to reduce the vibrations and/or sound emissions, the possibilities to realise an adaptive rotorblade are explained.The understanding of the interaction between the aerodynamic sources and the resulting vibrations and noise is the basis of the design of optimal control concepts.

Wind-induced Dynamics Of A Deep Space Network Antenna

Accurate spacecraft tracking by the NASA Deep Space Network (DSN) antennas must be assured during changing weather conditions. Wind disturbances are the main source of antenna vibrations, and consequently tracking errors. A wind force model is developed, and simulation results of wind-induced vibrations and pointing errors of the DSN antennas are presented. The antenna model includes the antenna structure, the elevation and azimuth servos, and the tracking controller. Simulation results show that pointing errors due to wind gusts are of the same order as errors due to wind steady state pressure, and that (similarly to steady state wind pressure) these errors satisfy the velocity quadratic law. The methodology presented is next used for wind disturbance estimation and for design of an antenna controller with wind disturbance rejection properties.

Analysis of the dynamic characteristics of the model of an energy cumulation system with composite flywheel. 4. Forced vibrations

1. We conclude the examination of the dynamic properties of the model of an energy cumulation system [1-3] by an analysis of its forced vibrations. The main source of such vibration are linear and angular eccentricities of the flywheel shaft and rim. As before we will regard the rim as absolutely rigid. This is based, in addition to its being massive, on the circumstance that on account of eccentricity it is impossible to excite in the rim vibrations other than the first form (as a rigid whole) since they all are symmetric [4] and yield a zero resultant of interaction with the shaft through a symmetric joint. Therefore, like in [1-3], we deal with a system of two masses consisting of a vertically arranged rigid rim and shaft in which the rim is connected with the shaft by an elastic joint, and the shaft runs in elastic damping bearings. A special trait of the system is that for technical considerations external damping can be effected solely in relation to the shaft. The effectiveness of its influence on the vibrations of the rim is determined by the parameters of the system which to some extent can be controlled, in particular: the mass and moment of inertia of the shaft and of the rigid supports. An analysis of the influence of these parameters on the amplitudes of the damped resonance vibrations, the forces in the supports, and the loads in the joint of rim and shaft is the aim of the present work. 2. When we complement the system of equations from [3] with the load induced by the radial and angular eccentricity of the rim and shaft, we obtain the system of dimensionless equations in complex form z~ + (C:l~ - io~a~) ~ +/~ (1 + K) Z~ -/2 Z2 = ~2 (1 - a,) r~ e ~' ; }, - i a2 ~ Z2 + Z2 - Zl = ~2 (1 - a2) r2 e' (~' + e)

Vibration isolating coupling

A vibration isolating coupling ideally suited for coupling the bobbin (31) of a linear actuator (23) to a flexure supported printer carriage (11) is disclosed. The two main sources of vibration in a system that includes a flexure (13, 15) supported carriage coupled to a linear actuator (23) are low-frequency vibration resulting from the pivot arc motion of the flexures (13, 15), and high frequency vibration resulting from the change in bobbin shape occurs as AC energy is applied to the bobbin (31). The first source of vibration is reduced by configuring the interface plane between the linear actuator and the flexure supported carriage such that contact occurs at spaced apart points located on either side of the flexure movement plane. Preferably, four contact points equally spaced from the flexure motion plane are used. The region between the contact points and the flexure motion plane is cut out so that no contact occurs in and on either side of the flexure motion plane. It is the absence of contact that reduces the first source of vibration. The second source of vibration is reduced by mounting a damping plate (61), preferably comprising a layer of viscoelastic material sandwiched between two layers of steel or some other rigid material, at the interface plane between the linear actuator (23) and the flexure supported carriage (11).

An Investigation of the Origins of Vibration of an Automobile Rear Axle

SUMMARY An investigation was carried out to determine the origins of vibration of an automobile rear axle with the object of establishing the significance of road-surface-induced vibratory inputs. This was achieved by measuring the vibratory acceleration of the rear axle of an automobile as it traverses straight sections of typically paved roads, at uniform speeds, then comparing the results with those obtained by laboratory simulation. The investigation revealed significant levels of vertical, longitudinal and, to a much lesser extent, lateral vibrations. The main source of vertical vibrations is shown to be induced mainly by vertical displacements imposed by the road-surface irregularities on the vehicle tyres. The longitudinal and lateral components are shown to be induced mainly by the engine and the drive-line (including tyre/wheel assemblies) as well as due to coupling between the vertical, longitudinal and lateral motions of the rear axle imposed by the geometry of the rear axle suspension.

Criminal evidence : by Jon R. Waltz. Nelson-Hall Company (325 West Jackson Boulevard, Chicago, Illinois 60606), 1975, 424 pp., hardcover—$14.00.

When designing helical gears, the goal is to optimize gear weight, efficiency, and noise while simultaneously achieving the required strength. In this study, the macro geometry of a helical gear pair was optimized for low weight, high efficiency, and low noise; further, trends of optimal solutions for five combinations of the three objectives were analyzed. The gear mass and efficiency were directly used as the design objectives. However, since the calculation of the gear noise is generally very complicated and time-consuming, the gear noise has not been directly used as the design objective, and the peak-to-peak static transmission error (PPSTE), which is the main source of the gear vibration, was selected as the design objective for the gear noise in the optimization. The objectives exhibited a trade-off relation between each other in the optimal space. If one of them was omitted, the objective considerably deteriorated. To analyze the results, the objectives were normalized and scored. As a result, most of the top ranks were from the optimal solutions considering the mass, efficiency, and PPSTE. Therefore, all three objectives should be considered in the gear optimization for low weight, high efficiency, and low noise.

City vibration and its threshold limits

House vibration is one of the public problems in Japan. An interview survey with 186 persons disclosed that the main source of house vibration was traffic vehicles such as trucks. Actual measurement of house vibration revealed that vertical vibrational intensity with the houses was below 35 cm/second 2 in acceleration and ranged 4–30 cps in frequency. Relationship between the vibrational intensity and its perception by inhabitants was explored and the upper limit of 95% confidence interval of “not perceptible” response was 2.48 cm/second 2 in acceleration and 0.2 mm/second in velocity. Finally, a criterion for threshold limits of vibrational nuisance was proposed by three types of habitation.

Paper 11: Variation of Hydraulic Pressure in Annular Space between Guide Vanes and Impeller of a Francis Turbine

One of the main sources of vibration in Francis turbines is thought to be pressure-wave disturbances generated from the impeller and interference impulses between impeller vanes and guide vanes. A theory is developed which explains the occurrence of severe vibrations caused by the elasticity of the water as a resonance phenomenon between the disturbing impulses and normal modes of vibration in the space between the impeller and the guide wheel. The wave propagation in the fluid, which is assumed to be uniform with no steady flow, is thought to satisfy the well-known sound-wave differential equation without any damping effects. The natural frequencies for one- and two-dimensional pressure-wave oscillations are calculated. The calculations, based on prior knowledge of the velocity of sound-wave propagation, show that a simple theory of one-dimensional oscillations interpreted as rotating sound waves in the annular space is sufficient to predict critical speeds of the turbine. Measurements carried out on a laboratory model Francis turbine for a head of 4.5 m and a capacity of about 1.0 m3/s confirmed the presence of free oscillations and indicated the occurrence of a resonance phenomenon in the annular space.