P.S. Heyns

Vibration isolation of a mounted engine through optimization

Abstract This paper is concerned with the minimization of the transmission of engine vibration in the case of a mounted four cylinder engine. This problem can profitably be studied from the point of view of optimization theory. For this purpose a mathematical model is constructed, which describes the motion of the mounted engine. The individual balancing masses and associated phase angles are chosen as the design variables. The objective function to be minimized relates to the minimization of the motion at the engine mounting positions. An optimization algorithm may be employed that allows for a systematic adjustment of the variables in order to minimize the objective function. Because of difficulties encountered in the application of standard optimization methods, Snymans dynamic optimization algorithm LFOP1B, which is a proven robust method, was applied to the problem. This method is successful in minimizing the objective function.

Multiple-criterion method for determining structural damage

A new multiple-criterion updating method that minimizes the Euclidean norm of the error vector obtained by adding the normalized eigenproblem equation and equation of motion with equal weighting functions is proposed. The method is applied to detecting damage in structures and is tested on an unsymmetrical H-shaped structure. It is found that the multiple-criterion updating method predicts the presence, the position, and the extent of damage. The multiple-criterion method is compared to the frequency-response function method and the modal property-based method by using the coordinate modal assurance criterion and the modal assurance criterion. The multiple-criterion method was found to give better results than the other two methods. This is because it was better able to detect damage on the structure than the modal property method (which failed to detect multiple-damage cases) and gave results that were less noisy, i.e., less updating to undamaged elements, than the frequency-response method.

Vold-Kalman Filter Order Tracking in Vibration Monitoring of Electrical Machines

This paper presents a simplified simulation model of electrical rotating machinery and an experimental test rig for applying the Vold-Kalman filter order tracking technique (VKF-OT). The effectiveness and advantages of VKF-OT for condition monitoring are demonstrated on both the simulation model and the experimental test rig through time domain analysis, using crest factor and kurtosis. The choice of the Vold-Kalman filter bandwidth is considered in the context of the simulation model, based on two different damping ratios. Several observations are made regarding the choice of Vold-Kalman filter bandwidth for the different damping ratios. Three different filter bandwidths are subsequently considered in a study of the experimental data, to confirm the conclusions made during the simulation study.

Consistent haul road condition monitoring by means of vehicle response normalisation with Gaussian processes

Suboptimal haul road management policies such as routine, periodic and urgent maintenance may result in unnecessary cost, both to roads and vehicles. A recent idea is to continually access haul road condition based on measured vehicle response. However the vehicle operating conditions, such as its instantaneous speed, may significantly influence its dynamic response resulting in possibly ambiguous road classifications. This paper proposes vehicle response calibration by means of Gaussian process regression, so that a severity metric which is more robust to fluctuating operating conditions may be obtained.

A Comparison Between Three Blade Tip Timing Algorithms for Estimating Synchronous Turbomachine Blade Vibration

Blade Tip Timing (BTT) is a non-intrusive condition monitoring technique used to measure blade vibration in turbomachinery. The method is suited for industrial implementation due to its low cost and ability to measure vibrations of all blades in a single blade row. The signals captured by a BTT system is however aliased which makes determining the vibration characteristics of the blades non-trivial. This article is concerned with comparing the accuracies in estimating blade vibration frequency and amplitude of three different data processing algorithms namely, the Auto-Regressive, Circumferential Fourier Fit and a new Bayesian regression approach. This is done using numerically simulated BTT data for different blade vibration conditions.

Condition monitoring of tapered roller bearings: a photogrammetric approach

The study evaluated damage detection of a tapered roller bearing using a non-contact photogrametric approach. Customized round tape was pasted on the bearing housing and GOM Pontos was used to measure the radial accelerations from the bearing housing. The data obtained from the the photogrammetric techniques was processed to detect damage of the bearing using statistical tools such as RMS, kurtosis. It was established that the phogrammetric approach detects bearing damage excellently.

Seeded Damage Detection on Self-aligning Ball Bearings with Acoustic Emission

Acoustic emission (AE) has evolved as one of the much used techniques for condition monitoring and diagnosis of rotating machinery. Major research has been carried out in the attempt to comprehend the prospects of AE in condition monitoring of bearings. However, this has been mainly applied to other types of bearings. This study investigates the usefulness of the AE approach in the seeded damage detection on self-aligning ball bearings.

Reducing Vibratory Screen Structural Loading Using a Vibration Absorber

Publisher Summary In the nature of their operation, vibratory screens are subject to high levels of acceleration and may impart significant dynamic loads on plant buildings, especially in cases, where large numbers of these screens are employed in process applications. To avoid premature failure and reduce plant building construction costs in critical cases, a variety of techniques are applied in practice. Most of these require substantially increased system mass, which is undesirable. With this work, the use of a liquid inertia tuned vibration absorber to reduce the structural input loading without significantly affecting the screen acceleration is investigated. A mathematical model is developed and applied to the design of an experimental vibration absorber. This absorber was built and tested on a Schenck Hydropuls machine, and the mathematical model was validated. The model was subsequently employed in a design study on typical sand washing plant screen. Different absorber configurations are considered, and substantial benefits may be realized using a vibration absorber for reducing structural input loading in such applications.

An Optimization Approach to Vibration Isolation of Rigid Bodies

The conventional single-degree-of-freedom approach to isolator design dealt with in most undergraduate curricula, is not always adequate for the design of practical isolator systems. In this article, an optimization approach to the design problem is presented and the viability of the approach demonstrated. It is, however, also shown that multiple local minima may exist and that due care should be exercised in the application of the method.