This paper describes an innovative approach, based on the instrinsic mode functions (IMFs), to characterize the nature of mechanical vibration encountered in transport vehicles. The paper highlights the importance of understanding the nature of transport vibration and shows that their accurate characterization is essential for the optimization of protective packaging. Although there have been numerous studies aimed at characterizing random vibration during transport, the majority of those have been limited to applying relatively conventional signal analysis techniques, such as the average power spectral density (PSD). This paper investigates the benefits offered by the recently introduced Hilbert–Huang transform when characterizing non‐stationary random vibration in comparison with more traditional Fourier analysis‐based techniques. The paper describes the operation of the Hilbert–Huang transform, which was developed to assist in the analysis of non‐Gaussian and non‐stationary random data. The Hilbert–Huang transform is based on the empirical mode decomposition (EMD) technique used to produce a finite number of IMFs, which, as a set, provide a complete description of the process. It is shown how these IMFs are well suited to the application of the Hilbert–Huang transform to determine the magnitude and instantaneous frequency of each IMF. The technique is applied to various records of random vibration data collected from transport vehicles in order to illustrate the benefits of the method in characterizing the nature of non‐stationarities present in transport vibration. Copyright © 2004 John Wiley & Sons, Ltd.

This paper deals with the dynamic behaviour of stacked packaging units when subjected to vertical vibrational inputs as experienced in transport vehicles. Although the vibrational performance of single-unit packaging systems has been thoroughly studied, the behaviour of stacked packaging units is not fully understood. The complexity of the problem is compounded when the effects of vertical restraints are taken into account. The paper presents the development of a numerical computer model designed to predict the dynamic response of stacked package systems when subjected to vertical vibrational excitation. Provisions have been made to account for the effects of vertical restraint tension and stiffness. In addition, a physical model representative of a generic stacked packaging system has been developed to assist in validating the numerical model. The paper includes results from preliminary experiments in which the frequency response functions of the models were evaluated and compared. The validity of the numerical model in the time domain was tested using random burst excitation signals. These preliminary experiments reveal that, when the effects of frictional damping are taken into account, the numerical model can be used to generate reasonably accurate predications of the dynamic behaviour of the equivalent physical system. Copyright (C) 2004 John Wiley Sons, Ltd.

This paper describes a method to predict the vertical vibrations of road vehicles from measured pavement profiles. It discusses the limitations Of current methods used for analysing and simulating vehicle vibrations and shows that more accurate characterization and simulation of the transport environment must take into account the non-stationary nature of road vehicle vibrations. Vertical vibrations for typical transport vehicles under various operating conditions and pavement profiles are predicted using a computer model of the vehicle characteristics and analysed to produce the spectral and statistical characteristics. The paper also presents an improved method to compute the vibration intensity by using a dynamic segmentation data reduction technique. The effectiveness of the procedure to characterize the non-stationarity of random vehicle vibrations is demonstrated. Finally, the paper deals with the statistical distribution of the vibration intensity and demonstrates how it can be adapted to a technique for the simulation the non-stationary nature Of random vehicle vibrations. Copyright (C) 2002 John Wiley Sons, Ltd.

This paper introduces a new method for the analysis and simulation of non-stationary random vibrations. The method pays particular attention to the non-stationary nature of vibrations generated by transport vehicles. The limitations of current methods used for analysing and simulating non-stationary random vehicle vibrations are demonstrated. The paper shows how the Hilbert transform can be used to compute the vibration intensity (VI) and offers substantial data reduction advantages. It is shown how the statistical distribution of VI can be combined with the spectral characteristics of the vibration signal to enable more realistic simulations of non-stationary transport vibrations.

This paper presents a novel technique for the simulation of shock and vibrations related to road surface irregularities. The technique is based on a recently developed universal road profile classification scheme, which is one of the main outcomes of a project aimed at better understanding the statistical nature of road surfaces and their interactions with road vehicles. The method, which focuses on the nonstationary and non-Gaussian nature of road profiles, is described along with an analysis procedure developed and implemented to automatically detect and extract transient events from the road spatial acceleration data as well as identify stationary segments of similar roughness (RMS). The paper shows how the concept of treating road surface irregularities as two fundamental components, namely, steady-state road surface irregularities and transient events, can be employed for classification and simulation purposes. The simulation technique is based on a universal statistical model of road surface profiles that characterizes the power spectral density of the underlying irregularities, the probability distribution function of the RMS level using the offset Raleigh distribution function, and the transient density. The transient events are generated with random amplitudes according to the Gaussian distribution, the mean and standard deviation of which are functions of the underlying RMS level. This paper shows how these two components can be combined to numerically synthesize a process that faithfully represents the nonstationary, transient-laden nature of road surface profiles. The synthesized process can be physically realized on a vibration shaker to simulate road profiles.

When a package undergoes progressive damage during a sine dwell vertical vibration test, its dynamic characteristics, such as stiffness and damping, will change. This will result in variation of its resonance frequency during a test. This paper demonstrates that tracking the resonance by feedback control of the excitation frequency during resonance dwell tests is essential. Furthermore, this paper shows the differences in the results obtained from dwell tests with uncontrolled and controlled excitation frequencies. A computer-based resonance tracking system was developed and used together with a commercial vibration table to experimentally verify the benefits of such a technique. Copyright (C) 2000 John Wiley & Sons, Ltd.

A new method for the measurement of shock-absorbing characteristics of cushioning materials and determination of 'cushion curves' is discussed in this paper The method not only significantly reduces testing time but also improves the accuracy of the estimate of a cushion curve. Cushion curves are determined from the material's static compression characteristics and the impact data (static load/peak acceleration) obtained from a small number of impacts on a cushion tester. However, the method is capable of producing a cushion curve from the measurement of just a single impact. The process involves an iterative least mean squares (ILMS) minimisation of the discrepancy between peak acceleration values predicted from a theoretical model and measured in the impact tests. The algorithm of the ILMS method, examples demonstrating its application and the dynamic effect in impacts of various materials such as the EPU; the EPS and corrugated fibreboard are presented. Copyright (C) 2000 John Wiley & Sons, Ltd.

This paper introduces a new method to analyse and simulate vibrations of transport vehicles. The method pays particular attention to the non-stationary nature of vibrations, especially during road transport. The limitations of current methods used for analysing and simulating vehicle vibrations are demonstrated. The paper shows how the Hilbert transform can be used to compute the vibration intensity and offers substantial data reduction advantages. It is shown how statistical characteristics of the vibration intensity can be combined with spectral characteristics to enable more realistic simulations of transport vibrations. Finally, it is shown how the processed data is well suited for use with modern telemetry techniques integrated with web browser technologies. Copyright © 2000 John Wiley & Sons, Ltd.