Influence of surface treatments on fatigue life of a two-stroke free piston linear engine component using random loading

This paper describes the finite element (FE) analysis technique to predict fatigue life using the narrow band frequency response approach. The life prediction results are useful for improving the component design methodology at the very early development stage. The approach is found to be suitable for a periodic loading but requires very large time records to accurately describe random loading processes. This paper is aimed at investigating the effects of surface treatments on the fatigue life of the free piston linear engine’s components. Finite element modelling and frequency response analysis were conducted using computer aided design and finite element analysis commercial codes, respectively. In addition, the fatigue life prediction was carried out using finite element based fatigue analysis commercial code. Narrow band approach was specially applied to predict the fatigue life of the free piston linear engine cylinder block. Significant variation was observed between the surface treatments and untreated cylinder block of free piston engine. The obtained results indicated that nitrided treatment yielded the longest life. This approach can determine premature products failure phenomena, and therefore can reduce time to market, improve product reliability and customer confidence.

Research on Real-time Monitoring of Abnormal Seismic Noise

The noise data in vertical component records of 85 seismic stations in Fujian Province during 2012 is used as the research object in this paper. The noise data is divided into fiveminute segments to calculate the power spectra. The high reference line and low reference line of station are then identified by drawing a probability density function graph( PDF)using the power spectral probability density function. Moreover, according to the anomalies of PDF graphs in 85 seismic stations,the abnormal noise is divided into four categories: dropped packet, low noise, high noise, and median noise anomalies.Afterwards,four selection methods are found by the high or low noise reference line of the stations,and the system of real-time monitoring of seismic noise is formed by combining the four selection methods. Noise records of 85 seismic stations in Fujian Province in July2013 are selected for verification,and the results show that the anomalous noise-recognition system could reach a 90% success rate at most stations and the effect of selection are very good. Therefore,it could be applied to the seismic noise real-time monitoring in stations.

Use of probabilistic and deterministic measures to identify unfavorable earthquake records

This study introduces measures to identify resonant (concentration of energy in a single or a few frequencies) or unfavorable earthquake ground motions. Probabilistic measures based on the entropy rate and the geometric properties of the power spectral density function (PSDF) of the ground acceleration are developed first. Subsequently, deterministic measures for the frequency content of the ground acceleration are also developed. These measures are then used for identifying resonance and criticality in stochastic earthquake models and 110 acceleration records measured at rock, stiff, medium and soft soil sites. The unfavorable earthquake record for a given structure is defined as the record having a narrow frequency content and dominant frequency close to the structure fundamental natural frequency. Accordingly, the measures developed in this study may provide a basis for selecting records that are capable of producing the highest structural response. Numerical verifications are provided on damage caused to structures by identified resonant records.