In multiscale molecular dynamics simulations the accuracy of detailed models is combined with the efficiency of a reduced representation. For several applications - namely those of sampling enhancement - it is desirable to combine fine-grained (FG) and coarse-grained (CG) approaches into a single hybrid approach with an adjustable mixing parameter. We present a benchmark of three algorithms that use a mixing of the two representation layers using a Lagrangian formalism. The three algorithms use three different approaches for keeping the particles at the FG level of representation together: 1) addition of forces, 2) mass scaling, and 3) temperature scaling. The benchmark is applied to liquid hexadecane and includes an evaluation of the average configurational entropy of the FG and CG subsystems. The temperature-scaling scheme achieved a 3-fold sampling speedup with little deviation of FG properties. The addition-of-forces scheme kept FG properties the best but provided little sampling speedup. The mass-scaling scheme yielded a 5-fold speedup but deviated the most from FG properties.

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The paper presents a numerical study regarding the mechanical response of the body of a freight wagon to the usual loads encountered during service. The main goal of the present research is to investigate the possibility to replace the steel walls of the wagon with walls made of laminated composites. In this way, the total mass of the wagon can be decreased, leaving room for supplementary load of goods. Finite element analyses of the wagon with steel walls is presented first, in order to show that most of the load is taken by the structure of the wagon, while the stresses in the walls are low. Further, composite plates with different thickness are studied to find the minimum value of thickness for which the displacements have values below a certain range. These thicknesses are further considered in the finite element analyses of the entire wagon with composite walls to investigate if the new walls significantly change the stresses in the vehicle structure. It was concluded that the replacement does not alter the stress state in the structure, and, consequently, it is a good solution for diminution of the total mass of the vehicle.

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