# Measurement and Analysis of Vibration Levels for Truck Transport Environment in Korea
## 1 Introduction  
All products are transported between the production site and the consumer and are subject to vibration during transport, which shortens the product life and reduce the commodity value. Vibration during transport has large and small impacts from simple abrasion of the package to the collapse of the palletized unit-load owing to pallet destruction [1]. Therefore, products in distribution should include protective packaging for adequate protection from vibration during transport [2]. Both under-packaging and over-packaging are costly because the former increases the occurrence of damage incidents, and the latter increases the volume and weight of packages. Therefore, to reduce these costs, optimal packaging design should be developed to achieve product protection while minimizing the weight and size of the cushioning material [3]. The first step in the development of product packaging is to simulate the physical stresses of vibration that occur during transport. However, both severe and moderate simulations are costly. The former guarantee the product's integrity but leads to increased logistics expenses owing to excessive use of cushioning materials, and the latter cause economic losses to the enterprise due to product damage caused by insufficient protection of the product. Therefore, this simulation should be able to reproduce the vibrations produced by the vehicle accurately. Because the vehicle speed and road pavement roughness vary throughout the journey, the vehicle vibration is non-stationary, in which statistical values such as the mean and root-mean-square acceleration (standard deviation; rms G or Grms) of the events are not maintained over time. The non-stationarity of vehicle vibration causes the non-Gaussian distribution of vehicle vibration events [4; 5]. However, vibration signals measured in a vehicle are characterized such that their average values remain relatively constant even if the vibration values for a particular frequency in the signal continue to change. This characteristic enables the vibration test equipment to reproduce the vibration behavior of the vehicle in a laboratory [6]. Therefore, in the vibration analysis of the vehicle, the random vibration of the vehicle is a Gaussian distribution, and it is assumed that all measured events exist within three standard deviations (\(\pm 3\sigma\); Figure 1). Power spectral density (PSD) is measured vibration signals using the Fast Fourier Transform (FFT) algorithm, which represents the average intensity of the vibration. Some researchers [4; 7; 8] have reported that the Gaussian distribution used in FFT at vibration test excludes values outside the normal distribution such as high-amplitude events in the vibration signal, which can have a significant effect on product damage. Therefore, reproducing actual vehicle vibrations through PSD-based simulation is limited [5]. Because high-amplitude events owing to shocks during transport are included in the vibration signal, transport vibrations are not considered random vibration. Therefore, in research separating shock and vibration in the simulation of vehicle transport vibration, [PERSON] et al. [9] reported that when shock events more significant than 0.1 G were removed from the vibration data measured during truck transport, vibration level was close to a normal distribution. Such shock events are caused chiefly by road unevenness conditions such as roughness, metal joints, and sewer hole covers. Several researchers [7; 10; 11; 12] developed PSD profiles for each by decomposing the signal into low-amplitude and high-amplitude events based on a rank of rms G. This method is based on the hypothesis that the low-level PSD profile represents the vehicle response to random variations in the road profile and that the high-level profile represents the response to transient events such as speed bumps, cracks, and potholes [7]. [PERSON] et al. [10] and [PERSON] et al.