Jérôme Antoni

A comprehensive study of the bias and variance of frequency-response-function measurements: Optimal window selection and overlapping strategies

This paper investigates the measurement errors involved in measuring frequency response functions from weighted-overlapped segment averaging, a technique that has become a standard in modern spectral analysers due to its computational advantages. A particular attention is paid to leakage errors, for which this procedure has been frequently criticised. Exact and asymptotic expressions for the bias and variance are provided, whose minimisation enables the derivation of the optimal settings to be used with this procedure. Our main finding is that a Half-sine or Diff window with 23 overlap achieves the best compromise to reduce leakage errors, and this is independently of the system frequency response function. This conclusion is to be contrasted with the customary habit of using a Hanning window with 12 overlap.

Detection of Surface Ships From Interception of Cyclostationary Signature With the Cyclic Modulation Coherence

This paper addresses the problem of passive detection of surface ships from radiated propeller noise in the far field. This is traditionally accomplished by means of envelope analysis, a largely empirical technique. The first contribution of the paper is to give a formal justification why this approach is sound based on the cyclostationary modeling of propeller noise. Pursuing along similar lines, the paper proposes a new statistical test based on the recently introduced cyclic modulation coherence (CMC), which is close to optimal in detecting cyclostationary noise, while at the same time being easy and extremely fast to compute. Detection capability is thoroughly investigated as a function of the blade pass frequency and other parameter settings. Finally, the cyclostationarity framework makes possible the proposal of a closed-form statistical threshold that opens the way to automatic detection.

H/sub /spl alpha// - a consistent estimator for frequency response functions with input and output noise

Nonparametric estimators of frequency response functions are usually biased when the system to be identified has unknown, possibly correlated, additive noise on both the inputs and outputs. In this paper, it is shown how the use of a specific type of input force (random with periodic second-order statistics) leads to a simple, but unbiased, estimator, even in the presence of high levels of additive stationary noise at the inputs and the outputs. No other a priori information on the noise sources is required and these are even allowed to be mutually correlated. The statistical performance of the proposed H/sub /spl alpha// estimator is analyzed and a nontrivial formula is established for its variance. In turn, this analytical result is used for designing a suboptimal input signal. Finally, the predicted performance of the proposed estimator is validated with the aid of experimental results.

FRF measurements with the weighted overlapped segment averaging technique

Abstract This paper investigates the measurement errors involved in estimating frequency response functions from weighted overlapped segment averaging, a technique that has become a standard in modern data analysers due to its computational advantages. A particular attention is paid to leakage errors, for which this technique has been frequently criticised. Our main result is that a Half-sine or Diff window with 67% overlap achieves the best compromise to reduce leakage errors, and this is independently of the system frequency response function. This conclusion is to be contrasted with the customary habit of using a Hanning window with 50% overlap.

Detection of cylinder unbalance from Bayesian inference combining cylinder pressure and vibration block measurement in a Diesel engine

In the automotive industry, the necessary reduction of pollutant emission for new Diesel engines requires the control of combustion events. This control is efficient provided combustion parameters such as combustion occurrence and combustion energy are relevant. Combustion parameters are traditionally measured from cylinder pressure sensors. However this kind of sensor is expensive and has a limited lifetime. Thus this paper proposes to use only one cylinder pressure on a multi‐cylinder engine and to extract combustion parameters from the other cylinders with low cost knock sensors. Knock sensors measure the vibration circulating on the engine block, hence they do not all contain the information on the combustion processes, but they are also contaminated by other mechanical noises that disorder the signal. The question is how to combine the information coming from one cylinder pressure and knock sensors to obtain the most relevant combustion parameters in all engine cylinders. In this paper, the issue is ...