Jan Černetič

Bio: Jan Černetič is an academic researcher from University of Ljubljana. The author has contributed to research in topics: Centrifugal pump & Noise (radio). The author has an hindex of 3, co-authored 5 publications receiving 88 citations.

The use of noise and vibration signals for detecting cavitation in kinetic pumps

Abstract: Cavitation in a kinetic pump reduces delivery head and efficiency of the pump. It also causes mechanical damage and an increase of vibrations and noise. Therefore, it is important to detect inception and development of a cavitation phenomenon in the pump. This article deals with signals of vibration and noise, which will be used for detection and monitoring of the cavitation in kinetic pumps, and also to prevent the effect of the cavitation in the pump and pumping system. When the cavitation is increasing, the flowing conditions are changing, which leads to an increase of vibrations of the pump and emitted noise in the surroundings. Because vibrations and noise are transferred from the pump through its casing, the signal is non-uniformly distorted due to transfer losses and structure of the casing surfaces. Noise and vibrations are increasing steadily, but in some specific frequency ranges the signal is more pronounced than in other parts of the spectrum. Experimental results have shown that vibra...

Use of noise and vibration signal for detection and monitoring of cavitation in kinetic pumps

Abstract: Cavitation in kinetic pumps causes lowering performance, mechanical damage and increase of vibrations and noise. Therefore, it is important to detect inception and development of cavitation phenomenon in the pump. This paper deals with signals of vibrations and noise, which will be used for detection and monitoring of cavitation in kinetic pumps, and also to prevent the effect of cavitation in the pump and pumping system. When the cavitation is increasing, the flowing conditions are changing, which leads to an increase of vibrations of the pump and emitted noise in the surroundings. Because vibrations and noise are transferred from the pump through its casing, the signal is non‐uniformly distorted due to transfer losses and structure of the casing surfaces. Even so, it is possible to determine development of cavitation phenomena from the measured signal. Noise and vibrations are increasing steadily, but in some specific frequency ranges the signal is more pronounced than in other part of the spectrum. Experimental results have shown that when the cavitation is fully developed, the measured signals at a characteristic frequency or range of frequencies start to decrease. This characteristic frequency or band of frequency is discussed in this paper, and also comparison between theoretical expectations and measurement results was performed.

Simple Feedback Structure of Active Noise Control in a Duct

Abstract: An active noise control is usually constructed with the use of electronic filters. For sufficient noise attenuation, electronic filters are not always needed. In this case, the electronic controller and appropriate software is not required so the system can be much easier. This paper deals with the use of a feedback structure of active noise control in an experimental ventilation duct. Simulation was performed to investigate the efficiency of a simple analoguous system for active noise control without incorporating electronic filters. The transfer function of the entire analogous system can be used to predict the maximum attenuation level. Tests were made to verify the simulation and to show what noise attenuation level can be achieved in an experimental duct. It has been shown that in a specific frequency range this kind of a system is efficient enough for use in some ventilation ducts.

Detection of Cavitation Phenomenon within a Centrifugal Pump Based on Vibration Analysis Technique in both Time and Frequency Domains

Abstract: Cavitation is an important problem that occurs in any pump and contributes highly towards the deterioration in the performance of the pump. In industrial applications, it is vital to detect and decrease the effect of cavitation in pumps. In this study therefore, focus is on detecting and diagnosing the cavitation phenomenon within a centrifugal pump using vibration technique. The results obtained for vibration signal in time and frequency domains have been analysed in order to achieve a better understanding regarding detection of cavitation within a pump. The effect of different operating conditions, including various flow rates related to the cavitation have been investigated in this work using different statistical features in time domain analysis (TDA). Moreover, Fast Fourier Transform (FFT) technique for frequency domain analysis (FDA) has also been applied.

Experimental analysis of cavitation in a centrifugal pump using acoustic emission, vibration measurements and flow visualization

Abstract: The continuously increasing industrial productivity has resulted in a great breakthrough in the field of maintenance on centrifugal pumps in order to ensure their optimum operation under different operating conditions. One of the important mechanisms that affect the steady and dynamic operation of a pump is cavitation, which appears in the low static pressure zone formed at the impeller entrance region. This paper investigates the inception and development of cavitation in three different impellers of a laboratory centrifugal pump with a Plexiglas casing, using flow visualization, vibration and acoustic emission measurements. The aim of this study is the development of an experimental tool that detects cavitation in different impellers and the further understanding of the effects of blade geometry in cavitation development. The results show that the geometrical characteristics of the impeller affect cavitation development and behavior, while an acoustic emission sensor and an accelerometer can be applied for successfully detecting the onset of this mechanism.

Research on vibration suppression method of alternating current motor based on fractional order control strategy

Abstract: At present, the changing structure, material and increasing device are used to suppress the vibration of motor in general. These methods increase system complexity in the different degree. So a novel vibration suppression method based on fractional order Proportional-Integral-Derivative (PID) controller is proposed in this article. First, the digital realization process of fractional order PID controller is illustrated in detail. Then the integer order PID controller and fractional order PID controller are, respectively, used to adjust the input current of inverter to control the 1.5 kW alternating current motor. The vibration frequency spectrums and stator current frequency spectrums in low-frequency and carrier frequency band are, respectively, studied by using the comparison and analysis methods. At the same time, the vibration frequency spectrum and stator current frequency spectrum of 15 kW alternating current motor are compared and analyzed. And the frequency spectrums near the rotating frequency of...

A vibration cavitation sensitivity parameter based on spectral and statistical methods

Abstract: Octave band analysis and PCA used on RMS velocity to obtain key indicators.Mahalanobis distance is used to set thresholds since data is normally distributed.Pump health separated into no cavitation, incipient, and fully formed condition.Method works on a range of types and sizes of centrifugal pumps. Cavitation is one of the main problems reducing the longevity of centrifugal pumps in industry today. If the pump operation is unable to maintain operating conditions around the best efficiency point, it can be subject to conditions that may lead to vaporisation or flashing in the pipes upstream of the pump. The implosion of these vapour bubbles in the impeller or volute causes damaging effects to the pump. A new method of vibration cavitation detection is proposed in this paper, based on adaptive octave band analysis, principal component analysis and statistical metrics. Full scale industrial pump efficiency testing data was used to determine the initial cavitation parameters for the analysis. The method was then tested using vibration measured from a number of industry pumps used in the water industry. Results were compared to knowledge known about the state of the pump, and the classification of the pump according to ISO 10816.