Papers by Keyword: Physical Model

Abstract: Erosion and sedimentation generally occur in river channels. Erosion impacts reducing the walls and bottom of the channel due to shear stress between the moving fluid particles and the channel particles. Sedimentation causes a buildup of sediment particles resulting from erosion in an area of the river which results in shallowing. In efforts to overcome erosion on river walls, especially at river bends, the river “groynes” is usually used. In this research, we tested the effectiveness of river “groynes” spacing in reducing erosion on river walls. We carried out numerical simulations to prove the effectiveness of river “groynes” in reducing flow velocity. Based on the results of this research, it is proven that with the presence of a river “groynes”, there is a decrease in flow velocity on the river wall where the river “groynes” are installed. The closer or smaller the distance between the river “groynes”, the smaller the impact of erosion that will occur.

Abstract: Digitalisation of the construction sector is one of the priorities in the European Union and one of the main technologies used for this purpose is Building Information Modelling (BIM). An important advantage of BIM is that it enables management of information about the built environment through all phases of the asset lifecycle: procurement, design, construction, operation and maintenance. Major promotion for the use of BIM in construction projects in EU member countries comes from the EU directive on Public Procurement and many public investments are related to infrastructure projects, including bridges. Indeed, in some countries, for certain public projects it is now mandatory to use BIM. This paper focuses on the implementation of BIM for bridges, which was overall much slower than for buildings. Some of the differences between BIM for bridges and BIM for buildings are pointed out, as well as what is identified as major barriers for implementation of BIM in bridge projects. At the same time, there are significant advancements with respect to openness and standardization on the international level, which are essential for widespread and effective use. Several software developers have taken on the challenge to provide bridge BIM solutions, some with the intention of using a single model for both physical representation of a bridge in blueprints and analytical calculations to design and verify mechanical resistance of the structure. This paper uses one such example to discuss current possibilities, some of the great advantages this technology offers, but also potential problems in the bridge BIM modelling procedure, when BIM model is used for structural analysis.

Abstract: We discuss the quantification of the secondary electron doping contrast in the scanningelectron microscope on 4H-SiC. It has been observed and studied at length mostly on silicon, but noconclusive theoretical model has been proposed yet. Therefore, we propose a simple physical modelthat allows for a quantification of the doping contrast. It is based on the changes in effective ionizationenergy for different doping concentrations and types. For a better agreement between our model andthe experiment, a locally increased temperature of the electron system or separate quasi Fermi levelsfor electrons and holes have to be assumed. A line profile of the sample under investigation is comparedwith a SRIM simulation of the corresponding implant and shows very good agreement.

Abstract: New type of plan curved structure has been developed within the research of arch footbridges at Faculty of Civil Engineering of Brno University of Technology. Structural arrangement came out of study of behaviour of plan curved upper deck arch structures of various radii of curvature. The design method of such structures with ideal shape of arch was the outcome of the research. Results of numerical analysis were verified on physical model in scale 1:10, which has been built and tested. The model has been mounted with gauges – 41 strain gauges at various positions on concrete and steel part of the structure and 5 deflection sensors. Then the structure has been subjected to loads in various positions corresponding with load positions of variable loads in calculation model. The paper describes evaluation of measurement of stresses and deformations of physical model of plan curved structure supported by an arch. Obtained values of stresses and deformations were compared with values derived from FE calculation model.

Abstract: The process of nucleation of fatigue defects in metal alloys with different structural morphology is considered. A physical model was built, calculation expressions were presented, a numerical experiment was performed to determine the moment of nucleation of the critical-size defect in Fe-based alloys during high-speed droplet impacts. The physical model is based on the theory of dislocations. It is shown that the determining factor in the process of wear nucleation under dynamic cyclic loading has a structural factor. Depending on the structure and properties of the material, as well as on the nature of the loads, the critical fatigue defect develops in the form of cracks, pores or microcraters. Comparative data of calculations and bench tests for droplet impingement erosion were presented. The contribution of the nucleation stage during the incubation period of erosive wear of the materials studied was evaluated. Due to the fact that rigorous instrumental methods for determining the duration of the nucleation stage are absent, the usage of the proposed analytical model is recommended for this purpose.

Abstract: A physical model studying the diffusion of interstitial atoms has been used in the study of hydrogen redistribution, in order to predict the risk of hydrogen damage in a range of manufacturing processes. In this work, conditions representative of hydrogen storage and some scenarios in the nuclear or chemical industries are considered. A singular advantage of this model is that, contrary to some simplified commercial and academic models, it contemplates diffusion in its most comprehensive description, i.e., with the driving force for atom diffusion being the gradient in chemical activation instead of simply considering it occurs down a composition gradient. Because the model also incorporates thermal history, microstructure, matrix solubility, multiple trapping distributions, interaction with the atmosphere and others, it is ideally suited to study real industrial applications. In this work, several simulations of hydrogen permeation are considered. Hydrogen permeation in industrial applications may introduce damage within the metal structure, leading to delayed failure. In the cases studied hydrogen is transported through a metal wall separating one volume with high hydrogen pressure and/or high temperature from another volume with low hydrogen pressure and temperature. By using such comprehensive physical model, it is possible to study the effects of hydrogen pressure and temperature gradient, wall thickness, metal microstructure and trap distribution on the flux across the wall and on the accumulation of hydrogen within the metal. Furthermore, it makes possible to estimate the embrittlement risk and when necessary the time to fracture. Keywords: hydrogen, steel, permeation, physical model, hydrogen storage, nuclear industry

Abstract: This paper describes the physical model, experimental setup and tests performed at the Portuguese Civil Engineering Laboratory (LNEC), to study the motions and forces of a moored ship at the Leixões port, for different sea states in irregular waves. The tests were carried out at one of the wave tanks of LNEC, where the Leixões port layout was implemented at scale 1:80 with the detailed model similar to the prototype bathymetry and surrounding structures. The moored ship is a 3.43 m long scale model of the well-known “Esso Osaka” tanker and is moored to the pier A of the oil terminal at 0.135 m draft. Several types of measurements were recorded in this study. The free-surface elevation and wave direction were measured with a set of resistive wave gauges. The wave velocities at the entrance of the harbour were measured with an acoustic Doppler velocimeter. Motions of the moored ship were measured with the OptiTrackTM motion capture system whereas forces on fenders and mooring lines were measured with load cells attached to a complex spring system developed at LNEC. Several tests were carried out for a number of incident sea states characterized by a JONSWAP spectrum, with different significant wave heights and peak periods. The measurement, analysis and results obtained for the incident wave conditions characterized by a significant wave height of 6 m and a peak wave period of 14 s are presented and discussed in this paper.

Abstract: A set of scale-model tests carried out to enlarge the range of wave steepness values analysed in run-up, overtopping and armour layer stability studies, focusing on oblique extreme wave conditions and on their effects on a gentler slope breakwater’s trunk armour and roundhead, is presented in this paper. A stretch of a rubble mound breakwater (head and part of the adjoining trunk, with a slope of 1(V):2(H)) was built in a wave basin at the Leibniz University Hannover to assess, under extreme wave conditions (wave steepness of 0.055) with different incident wave angles (from 40º to 90º), the structure behaviour in what concerns wave run-up, wave overtopping and damage progression of the armour layer. Two types of armour elements (rock and Antifer cubes) were tested. Non-intrusive methodologies including a new application of laser scanning technique for the assessment of both armour layer damage and wave run-up and overtopping were used. It is expected that such work will contribute also with data to improve empirical formulas as well as to validate complex numerical model for wave-structure interaction.

Abstract: Semi-submersible permeable tetrahedron is a new wave consumption structure. The design concept of the model structure is that on the premise of ensuring the natural landscape are not destroyed. Structure completely infiltrate below sea level is called semi-submersible wave structure. In this paper, based on the physical model, the transmission coefficient of this wave consumption structure under regular wave were got, and the effect of the wave period, wave height, model height, rows’ number of layout and other factors on the attenuation characteristics of Semi-submersible permeable tetrahedron were investigated. The research results show that Semi-submersible permeable tetrahedron performs better wave dissipation on both long-period waves and short-period waves, which has wide prospect in application.

Abstract: A set of physical model tests was run in to characterize the ship’s response to different wave conditions going from frequently-occurring conditions up to extreme ones. Several wave heights, periods and directions were generated. The waves around the ship were measured with probes and the movements of the ship were measured with a fiber-optic gyrocompass. Transfer functions are established and compared with numerical ones obtained with the WAMIT model.