Effect Of Period Length Research Articles

Effect of Period Length on Forecasting Maintenance and Repair Costs for Heavy Equipment by the Period Cost Based Methodology

ABSTRACT Substantial economic investments are made by companies in the construction and other processing industries to own and operate heavy equipment fleets. Average total cost minimization models are used by equipment managers to perform a variety of tasks that are largely influenced by the economic performance of the fleet. An important aspect of these models is estimating maintenance and repair costs throughout machine life. The period cost-based (PCB) methodology can be used to model maintenance and repair costs from data collected over a period of time within the life of a machine. The objective of this research was to investigate the effect of the data collection period length on the resulting PCB models and develop recommendations regarding the minimum period length. Data collected from a fleet of excavator-type material handlers were used to construct cost records of varying period lengths, to which the PCB methodology was applied to construct marginal and cumulative cost models. The results show that increasing the period length increases the quality of the marginal cost model and the accuracy of the estimated cumulative costs. However, this is subject to the constraint that the amount of data available for model development does not significantly decrease.

Randomness-Induced Phonon Localization in Graphene Heat Conduction.

Through nonequilibrium molecular dynamics simulations, we report the direct numerical evidence of the coherent phonons participating in thermal transport at room temperature in graphene phononic crystal (GPnC) structure and evaluate their contribution to thermal conductivity based on the two-phonon model. With decreasing period length in GPnC, the transition from the incoherent to coherent phonon transport is clearly observed. When a random perturbation to the positions of holes is introduced in a graphene sheet, the phonon wave-packet simulation reveals the presence of notable localization of coherent phonons, leading to the significant reduction of thermal conductivity and suppressed length dependence. Finally, the effects of period length and temperature on the coherent phonon contribution to thermal conductivity are also discussed. Our work establishes a deep understanding of the coherent phonons transport behavior in periodic phononic structures, which provides effective guidance for engineering thermal transport based on a new path via phonon localization.

The effect of uncertain material properties on free vibrations of thin periodic plates

Thin periodic plates with uncertain properties in a periodicity cell are investigated. To describe dynamics of these plates the non-asymptotic tolerance modelling method, cf. Woźniak and Wierzbicki (Averaging techniques in thermomechanics of composite solids. Wydawnictwo Politechniki Częstochowskiej, Częstochowa, 15), Woźniak et al. (eds.) (Thermomechanics of microheterogeneous solids and structures. Tolerance averaging approach. Wydawnictwo Politechniki Łódzkiej, Łódź, 16), for those plates is applied. The governing equations of tolerance models based on this method take into account the effect of period lengths on the overall behaviour of the plate. Hence, the additional effects of the periodicity can be analysed, as higher order vibrations. Moreover, properties of the plate in the periodicity cell are determined uncertainly. To analyse an influence of random variables of the properties with a fixed probability distribution on vibrations of the plate the Monte Carlo analysis is applied.

On the propagation of elastic waves in a multiperiodically reinforced medium

By a multiperiodically reinforced medium (multiperiodic composite) we mean a composite in which the matrix material is reinforced by two or more families of periodically spaced fibres. Moreover, at least along one direction the periods corresponding to different families are different. An example of this composite is shown in Fig. 1, where along the x 1-axis we deal with two different periods \(l_1^{1}, l_2^{1}\). The aim of the contribution is twofold. First, we propose a macroscopic (averaged) model of a multiperiodic composite, describing the effect of period lengths on the overall dynamic behaviour of the medium, in contrast to the known homogenized models. Second, we apply this model to the analysis of elastic waves propagating across a composite reinforced by two pairs of families of parallel periodically spaced fibres with different periods along certain direction.

Effect of period length of light/dark cycles on the growth rate of young wistar rats

Effect of period length of light/dark cycles on the growth rate of young wistar rats