Fengrong Bi

Aero-engine Blade Fatigue Analysis Based on Nonlinear Continuum Damage Model Using Neural Networks

Fatigue life and reliability of aero-engine blade are always of important significance to flight safety. The establishment of damage model is one of the key factors in blade fatigue research. Conventional linear Miner’s sum method is not suitable for aero-engine because of its low accuracy. A back propagation neutral network (BPNN) based on the combination of Levenberg-Marquardt (LM) and finite element method (FEM) is used to describe process of nonlinear damage accumulation behavior in material and predict fatigue life of the blade. Fatigue tests of standard specimen made from TC4 are carried out to obtain material fatigue parameters and S-N curve. A nonlinear continuum damage model (CDM), based on the BPNN with one hidden layer and ten neurons, is built to investigate the nonlinear damage accumulation behavior, in which the results from the tests are used as training set. Comparing with linear models and previous nonlinear models, BPNN has the lowest calculation error in full load range. It has significant accuracy when the load is below 500 MPa. Especially, when the load is 350 MPa, the calculation error of the BPNN is only 0.4%. The accurate model of the blade is built by using 3D coordinate measurement technology. The loading cycle in fatigue analysis is defined from takeoff to cruise in 10 min, and the load history is obtained from finite element analysis (FEA). Then the fatigue life of the compressor blade is predicted by using the BPNN model. The final fatigue life of the aero-engine blade is 6.55×104 cycles (10 916 h) based on the BPNN model, which is effective for the virtual design of aero-engine blade.

Source Separation of Diesel Engine Vibration Based on the Empirical Mode Decomposition and Independent Component Analysis

Vibration signals from diesel engine contain many different components mainly caused by combustion and mechanism operations, several blind source separation techniques are available for decomposing the signal into its components in the case of multichannel measurements, such as independent component analysis (ICA). However, the source separation of vibration signal from single-channel is impossible. In order to study the source separation from single-channel signal for the purpose of source extraction, the combination method of empirical mode decomposition (EMD) and ICA is proposed in diesel engine signal processing. The performance of the described methods of EMD-wavelet and EMD-ICA in vibration signal application is compared, and the results show that EMD-ICA method outperforms the other, and overcomes the drawback of ICA in the case of single-channel measurement. The independent source signal components can be separated and identified effectively from one-channel measurement by EMD-ICA. Hence, EMD-ICA improves the extraction and identification abilities of source signals from diesel engine vibration measurements.

Diesel engine noise source identification based on EEMD, coherent power spectrum analysis and improved AHP

As the essential foundation of noise reduction, many noise source identification methods have been developed and applied to engineering practice. To identify the noise source in the board-band frequency of different engine parts at various typical speeds, this paper presents an integrated noise source identification method based on the ensemble empirical mode decomposition (EEMD), the coherent power spectrum analysis, and the improved analytic hierarchy process (AHP). The measured noise is decomposed into several IMFs with physical meaning, which ensures the coherence analysis of the IMFs and the vibration signals are meaningful. An improved AHP is developed by introducing an objective weighting function to replace the traditional subjective evaluation, which makes the results no longer dependent on the subject performances and provides a better consistency in the meantime. The proposed noise identification model is applied to identifying a diesel engine surface radiated noise. As a result, the frequency-dependent contributions of different engine parts to different test points at different speeds are obtained, and an overall weight order is obtained as oil pan > left body > valve chamber cover > gear chamber casing > right body > flywheel housing, which provides an effectual guidance for the noise reduction.

Analysis of thermoelastohydrodynamic performance of journal misaligned engine main bearings

To understand the engine main bearings’ working condition is important in order to improve the performance of engine. However, thermal effects and thermal effect deformations of engine main bearings are rarely considered simultaneously in most studies. A typical finite element model is selected and the effect of thermoelastohydrodynamic(TEHD) reaction on engine main bearings is investigated. The calculated method of main bearing’s thermal hydrodynamic reaction and journal misalignment effect is finite difference method, and its deformation reaction is calculated by using finite element method. The oil film pressure is solved numerically with Reynolds boundary conditions when various bearing characteristics are calculated. The whole model considers a temperature-pressure-viscosity relationship for the lubricant, surface roughness effect, and also an angular misalignment between the journal and the bearing. Numerical simulations of operation of a typical I6 diesel engine main bearing is conducted and importance of several contributing factors in mixed lubrication is discussed. The performance characteristics of journal misaligned main bearings under elastohydrodynamic(EHD) and TEHD loads of an I6 diesel engine are received, and then the journal center orbit movement, minimum oil film thickness and maximum oil film pressure of main bearings are estimated over a wide range of engine operation. The model is verified through the comparison with other present models. The TEHD performance of engine main bearings with various effects under the influences of journal misalignment is revealed, this is helpful to understand EHD and TEHD effect of misaligned engine main bearings.

Psychoacoustic study on contribution of fan noise to engine noise

There are more researches on engine fan noise control focusing on reducing fan noise level through optimizing fan structure, and a lot of research achievements have been obtained. However, researches on the effect of fan noise to engine noise quality are lacking. The influences of the effects of fan structure optimization on the engine noise quality are unclear. Thus, there will be a decline in fan noise level, but the deterioration of engine noise quality. Aiming at the above problems, in consideration of fan structure design and engine noise quality, an innovative method to analyze the contribution of fan noise to engine noise quality using psychoacoustic theory is proposed. The noises of diesel engine installing different cooling fans are measured by using the acoustic pressure method. The experiment results are regarded as analysis samples. The model of sensory pleasantness is used to analyze the sound quality of a diesel engine with different cooling fans. Results show that after installing 10-blade fan in medium diameter the sensory pleasantness at each test point is increased, and the increase is 13.53% on average, which indicate the improvement of the engine noise quality. In order to verify the psychoacoustical analysis, the subjective assessment is carried out. The test result shows the noise quality of engine installed 10-blade fan in medium diameter is most superior. 1/3 octave frequency spectrum analysis is used to study the reason of the improvement of engine noise quality. It is found that after installing proper cooling fan the sound pressure level below 400 Hz are obviously increased, the frequency assignment and spectral envelope are more reasonable and a proper cooling fan can optimize the spectrum structure of the engine noise. The psychoacoustic study is applied in the contribution of fan noise to engine noise, and the idea of engine sound quality improvement through the structure optimization is proposed.