School of Engineering (SoE)

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Browsing School of Engineering (SoE) by Author "Addali, Abdulmajid"

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    Condition Monitoring of Helical Gears Using Acoustic Emission (AE) Technology
    (Cranfield University, 2013-07) Hamel, Mhmod A. A.; Mba, David; Addali, Abdulmajid
    Techniques such as vibration monitoring, thermal analysis and oil analysis are well established as means to have been used to improve reliability of gearboxes and extend time-to-failure. In this area Acoustic Emission (AE) technology is still in its infancy but the attention shown by researchers towards this method has increased dramatically because several studies have shown the AE offers the important advantage of improved sensitivity over more conventional monitoring tools for the early detection and prediction of gear failure. Helical gear lubrication is critically important for maintaining the integrity of operating gears and the oil also prevents asperity contact at the gear mesh thereby protecting the gears from a deterioration process and surface failures. In gear systems, there are three types of lubrication regimes: Dry Running, Boundary Lubrication (BL), Hydrodynamic Lubrication (HL) and Elastohydro-dynamic Lubrication (EHL). The last regime is associated with the normal operating running condition of gears. Acoustic emissions were acquired from gears and analysed for different lubrication regimes (dry, BL, HL and EHL regimes at different temperatures), and corresponding specific film thicknesses (λ) levels. The results showed an inverse relationship between AE signal levels and specific film thickness (λ) of the oil. This relation was used to determine the lubrication regime from the measured AE signals. For instance, dry running had the highest AE levels which were attributed to the metal-to-metal contact of the gear mesh. The BL regime had relatively high AE levels which also attributed to the level of asperity contact is greater than the oil film thickness. The HL regime was characterized by the lowest AE levels due to the lubricant oil completely separating the teeth during gear meshing. Finally, the EHL regime showed intermediate AE levels compared to the BL and HL regimes because the oil film was less than for the HL regime but greater than for the BL regime. It is shown that the application of advanced signal processing methods is necessary for monitoring helical gears; Kurtosis and Spectral Kurtosis were used to investigate the AE signatures and found to be effective in de-noising (spectral kurtosis) acquired signals. Acoustic Emission proved to be a powerful tool to detect the oil regime for both defective and non-defective conditions. It is concluded that the experimental findings of this research programme will provide the foundations for significant advancement in the application of AE for the determining the lubrication regime present within a helical gearbox and for the detection of developing gear faults. This should give a new impetus in the field of maintenance and prevention of human and material catastrophes. Several papers presenting the findings of this research have been published in international journals and given at conferences.
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    Defect source location of a natural defect on a high speedrolling element bearing with Acoustic Emission
    (PHM Society, 2011-09-25) Eftekharnejad, Babak; Addali, Abdulmajid; Mba, David
    The application of Acoustic Emission (AE) technology for machine health monitoring is gaining ground as powerful tool for health diagnosis of rolling element bearings. The successful application of AE to life prognosis of bearings is very dependent on the ability of the technology to identify and locate a defect at its earliest stage. Determining source locations of AE signals originating in real time from materials under load is one of the major advantages of the technology. This paper presents results which highlight the ability of AE to locate naturally initiated defects on high-speed roller element bearing in-situ. To date such location has only be successfully demonstrated at rotational speeds of less than 100 rpm.
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    Diagnosis of low-speed bearing degradation using acoustic emission techniques
    (Cranfield University, 2017-01) Alshimmeri, Fiasael; Addali, Abdulmajid; Amaral Teixeira, Joao
    It is widely acknowledged that bearing failures are the primary reason for breakdowns in rotating machinery. These failures are extremely costly, particularly in terms of lost production. Roller bearings are widely used in industrial machinery and need to be maintained in good condition to ensure the continuing efficiency, effectiveness, and profitability of the production process. The research presented here is an investigation of the use of acoustic emission (AE) to monitor bearing conditions at low speeds. Many machines, particularly large, expensive machines operate at speeds below 100 rpm, and such machines are important to the industry. However, the overwhelming proportion of studies have investigated the use of AE techniques for condition monitoring of higher-speed machines (typically several hundred rpm, or even higher). Few researchers have investigated the application of these techniques to low-speed machines (<100 rpm), This PhD addressed this omission and has established which, of the available, AE techniques are suitable for the detection of incipient faults and measurement of fault growth in low-speed bearings. The first objective of this research program was to assess the applicability of AE techniques to monitor low-speed bearings. It was found that the measured statistical parameters successfully monitored bearing conditions at low speeds (10-100 rpm). The second objective was to identify which commonly used statistical parameters derived from the AE signal (RMS, kurtosis, amplitude and counts) could identify the onset of a fault in either race. It was found that the change in AE amplitude and AE RMS could identify the presence of a small fault seeded into either the inner or the outer races. However, the severe attenuation of the signal from the inner race meant that, while AE amplitude and RMS could readily identify the incipient fault, kurtosis and the AE counts could not. Thus, more attention needs to be given to analysing the signal from the inner race. The third objective was to identify a measure that would assess the degree of severity of the fault. However, once the defect was established, it was found that of the parameters used only AE RMS was sensitive to defect size. The fourth objective was to assess whether the AE signal is able to detect defects located at either the centre or edge of the outer race of a bearing rotating at low speeds. It is found that all the measured AE parameters had higher values when the defect was seeded in the middle of the outer race, possibly due to the shorter path traversed by the signal between source and sensor which gave a lower attenuation than when the defect was on the edge of the outer race. Moreover, AE can detect the defect at both locations, which confirmed the applicability of the AE to monitor the defects at any location on the outer race.
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    An experimental investigation into the correlation between Acoustic Emission (AE) and bubble dynamics
    (Cranfield University, 2011-08) Husin, Shuib; Mba, David; Addali, Abdulmajid
    Bubble and cavitation effects phenomena can be encountered in two-phase gas-liquid systems in industry. In certain industries, particularly high-risk systems such as a nuclear reactor/plant, the detection of bubble dynamics, and the monitoring and measurement of their characteristics are necessary in controlling temperature. While in the petro-chemical engineering industry, such as oil transportation pipelines, the detection and monitoring of bubbles/cavitation phenomena are necessary to minimise surface erosion in fluid carrying components or downstream facilities. The high sensitivity of Acoustic Emission (AE) technology is feasible for the detection and monitoring of bubble phenomena in a two phase gas-liquid system and is practical for application within the industry. Underwater measurement of bubble oscillations has been widely studied using hydrophones and employing acoustic techniques in the audible range. However, the application of Acoustic Emission (AE) technology to monitor bubble size has hitherto not been attempted. This thesis presents an experimental investigation aimed at exploring AEs from gas bubble formation, motion and destruction. AE in this particular investigation covers the frequency range of between 100 kHz to 1000 kHz. The AE waveform analysis showed that the AE parameter from single bubble inception and burst events, i.e. AE amplitude, AE duration and AE energy, increased with the increase of bubble size and liquid viscosity. This finding significantly extends the potential use of AE technology for detecting the presence of bubbles in two-phase flow. It is concluded that bubble activity can be detected and monitored by AE technology both intrusively and non-intrusively. Furthermore, the bubble size can be determined by measurement of the AE and this forms the significant contribution of this thesis.
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    Heat removal in axial flow high pressure gas turbine
    (Cranfield University, 2016) Alhajeri, Hamad; Amaral Teixeira, Joao; Addali, Abdulmajid
    The demand for high power in aircraft gas turbine engines as well as industrial gas turbine prime mover promotes increasing the turbine entry temperature, the mass flow rate and the overall pressure ratio. High turbine entry temperature is however the most convenient way to increase the thrust without requiring a large change in the engine size. This research is focused on improving the internal cooling of high pressure turbine blade by investigating a range of solutions that can contribute to the more effective removal of heat when compared with existing configuration. The role played by the shape of the internal blade passages is investigated with numerical methods. In addition, the application of mist air as a means of enhanced heat removal is studied. The research covers three main area of investigation. The first one is concerned with the supply of mist on to the coolant flow as a mean to enhancing heat transfer. The second area of investigation is the manipulation of the secondary flow through cross-section variation as a means to augment heat transfer. Lastly a combination of a number of geometrical features in the passage is investigated. A promising technique to significantly improve heat transfer is to inject liquid droplets into the coolant flow. The droplets which will evaporate after travelling a certain distance, act as a cooling sink which consequently promote added heat removal. Due to the promising results of mist cooling in the literature, this research investigated its effect on a roughened cooling passage with five levels of mist mass percentages. In order to validate the numerical model, two stages were carried out. First, one single-phase flow case was validated against experimental results available in the open literature. Analysing the effect of the rotational force, on both flow physics and heat transfer, on the ribbed channel was the main concern of this investigation. Furthermore, the computational results using mist injection were also validated against the experimental results available in the literature. Injection of mist in the coolant flow helped achieve up to a 300% increase in the average flow temperature of the stream, therefore in extracting significantly more heat from the wall. The Nusselt number increased by 97% for the rotating leading edge at 5% mist injection. In the case of air only, the heat transfers decrease in the second passage, while in the mist case, the heat transfer tends to increase in the second passage. Heat transfer increases quasi linearly with the increase of the mist percentage when there is no rotation. However, in the presence of rotation, the heat transfers increase with an increase in mist content up to 4%, thereafter the heat transfer whilst still rising does so more gradually. The second part of this research studies the effect of non-uniform cross- section on the secondary flow and heat transfer in order to identify a preferential design for the blade cooling internal passage. Four different cross-sections were investigated. All cases start with square cross-section which then change all the way until it reaches the 180 degree turn before it changes back to square cross-section at the outlet. All cases were simulated at four different speeds. At low speeds the rectangle and trapezoidal cross-section achieved high heat transfer. At high speed the pentagonal and rectangular cross-sections achieved high heat transfer. Pressure loss is accounted for while making use of the thermal performance factor parameter which accounts for both heat transfer and pressure loss. The pentagonal cross-section showed high potential in terms of the thermal performance factor with a value over 0.8 and higher by 33% when compared to the rectangular case. In the final section multiple enhancement techniques are combined in the sudden expansion case, such as, ribs, slots and ribbed slot. The maximum heat enhancement is achieved once all previous techniques are used together. Under these circumstances the Nusselt number increased by 60% in the proposed new design.
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    Monitoring Gas Void Fraction In Two-Phase Flow With Acoustic Emission
    (Cranfield University, 2010-04) Addali, Abdulmajid; Mba, David
    The two-phase gas/liquid flow phenomenon can be encountered over a range of gas and liquid flow rates in the chemical engineering industry, particularly in oil and gas production transportation pipelines. Monitoring and measurement of their characteristics, such as the gas void fraction, are necessary to minimise the disruption of downstream process facilities. Thus, over the last decade, the investigation, development and use of multiphase flow metering system have been a major focus for the industry worldwide. However, these meters suffer from several limitations in some flow conditions such as Slug flow regime. This research presents experimental results correlating Acoustic Emission measurements with Gas Void Fraction (GVF) in a two-phase air / water flow. A unique experimental facility was modified to accommodate an investigation into the applicability of the Acoustic Emission (AE) technology in monitoring two-phase gas\liquid flow. The testing facility allowed for investigations over a range of superficial liquid velocities (0.3 to 2.0 ms-1) and superficial gas velocities (0.2 to 1.4 ms-1). The influence of several variables such as temperature, viscosity and surface roughness were also investigated. Measurements of AE for varying gas void fractions were compared to conductive probe measurements and results showed a direct correlation between the AE energy and the gas void fraction. It is concluded that the GVF can be determined by measurement of Acoustic Emission and this forms the major contribution of this thesis.
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    Slug Velocity Measurement and Flow Regime Recognition Using Acoustic Emission Technology
    (Cranfield University, 2013-07) Alssayh, Muammer Ali Ahmed; Mba, David; Addali, Abdulmajid
    Slug velocity measurement and flow regime recognition using acoustic emission technology are presented. Two non-intrusive and three intrusive methods were employed to detect the slug regime and measure its velocity using AE sensors. For the non-intrusive methods, AE sensors were placed directly on the exterior of the steel pipe section of the test rig with and without clamps. The intrusive method involved using different waveguide configurations with the AE sensors flush with the inner wall of the pipe. The experimental study presented investigated the application of Acoustic Emission (AE) technology for detecting slug velocity in addition to differentiating flow regime in two-phase (gas/liquid) flow in horizontal pipes. It is concluded that the slug velocity can be determined with acoustic emission (AE) sensors. The results were compared to slug velocities measured using high speed camera (HSC) and Ultrasound Transit Time (UST) techniques with good agreement between the three techniques at low gas void fraction (GVF). However, at high GVF (up to 95%) where the UST technique has limitations in application, the AE and HSC offered a good agreement. Flow regimes were also differentiated by using a combination of AE technology and Kolmogorov–Smirnov test technique. Stratified, slug and bubble regimes were recognised differentiated.