1. Measurements of material heat transfer properties : master study programmeMiha Donša, 2022, master's thesis Abstract: An experimental setup was created to observe temperature change at two points inside the experimental body. Such an experimental setup created data that was used as an anchor point of optimization that was coupled with numerical models to find unknown variables of heat conductivity and specific heat of the materials. Two numerical models were created. A 1D numerical model was created for possibilities of fast optimization ignoring the insulation and heat transfer through it. Such a model did not manage to describe the experimental setup accurately. Therefore, a 3D numerical model was created simulating the whole experimental setup and yielded much more promising results. Problems with the model were soon seen when experimental data was compared to the numerical solution where variables that were initially not taken into the account showed a much greater effect than first anticipated. Therefore, the 3D numerical model was adjusted to describe the experimental setup as accurately as possible. The experiment was done with two different materials. The materials were picked based on their heat conductivity (high and low). High heat conductivity material was easy to understand and to find a solution to it. With low conductivity material, some problems were quickly observed and as such created a lot of questions as to why and how to find the unknown variables of the material. It was then shown that the masses of the materials in the experiment and the length of the experiment played the most important role in the experiment and quickly explained why and how the experimental setup should be modified to obtain better results.
Keywords: heat transfer, material heat transfer properties, specific heat, heat conductivity, optimization, numerical simulation of heat transfer
Published in DKUM: 07.07.2022; Views: 834; Downloads: 47
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2. Design of geometry and numerical simulation of the operating characteristic of the rotor of the wind turbine : diplomsko deloaljaž Janič, 2018, undergraduate thesis Abstract: The diploma thesis consists of design and numerical simulation of the wind turbine. Geometries are designed according to two theories, the Betz theory and the Schmitz theory. I used Solidworks for 3D modeling of the both rotors. Using Ansys software package, we performed numerical simulations of a rigid body for two different wind speed regimes. We were interested in the angular velocity of the spinning blades, which in combination with moment give us power.
Keywords: Renewable energy, wind energy, numerical simulation, wind turbine, blade design, Betz and Schmitz theory
Published in DKUM: 09.08.2018; Views: 1692; Downloads: 190
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3. Reinforced piled embankment for a high-speed railway over soft soil : a numerical and analytical investigationYan Zhuang, Xiaoyan Cui, 2015, original scientific article Abstract: A geosynthetic, reinforced, piled embankment is an effective and economic method to solve the problems of possible bearing failure, unacceptable settlement and slope instability for an embankment built over soft soil; this has led to its widespread use, especially for high-speed railway embankments. Some design methods have been developed to assess the performance of these reinforced structures, which are mainly based on the results from small-scale models and numerical simulations. However, the reliability of these methods needs to be validated under full-scale field tests. This paper presents a numerical and analytical study for a full-scale field test of the Fengyang high-speed railway embankment. The results were analyzed and discussed in terms of the settlement of subsoil, the stressconcentration ratio (SCR), the axial force and the frictional stress of the pile. They showed that the settlement of the subsoil, from both the finite-element method (FEM) and the analytical method, were in good agreement with the measurement, and thus was a reliable parameter to assess the performance of the piled embankment with reasonable accuracy. The SCR was overestimated by the modified Terzaghi method, with a difference of 25%, while it was underestimated by the FEM, with a difference of approximately 20%. It was also shown that the tensile force in the reinforcement could be effectively assessed using the proposed analytical method, while it was overestimated by the FEM with a difference of 44%.
Keywords: reinforced piled embankment, high-speed railway, numerical simulation, analytical method
Published in DKUM: 15.06.2018; Views: 1746; Downloads: 221
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4. The geo-mechanics behaviour of soft marine silts under a nearshore rubble-mound breakwaterLien-Kwei Chien, Feng Tsung-Shen, Tsung-Ching Chen, 2009, original scientific article Abstract: In this study, the soft marine silts under a rubble-mound breakwater in Ma-Zu of west Taiwan are adopted as a test sample. The specimens were prepared by a new, remolded method at dry density and consolidated stresses. Tri-axial shear-strength tests were performed to evaluate the pore-water pressure and the shear strength. The test results show that the pore-water pressure increases gradually and is close to the critical values as the axial strain increases. In addition, under isotropic and K0 consolidation, both the c and c' of the soft marine silts were 0 kPa, which means that the silts do not have any shear resistance, just like fluid under a rubble-mound breakwater. Based on the linear-elasticity and the one-dimensional consolidation theory, the model of the settlement and stability was evaluated in SIGMA/W. The results show that the soft marine silts at the breakwater induced a displacement, greatly increasing with the filling rubble-mound loading. The figures and results can be referenced for a stability evaluation of the silt soil deposits under the rubble-mound breakwater. The results are useful for marine silts mechanics and a stability analysis for the planning, design, and related research on near-shore engineering.
Keywords: geo-mechanics behavior, soft marine silt, rubble-mound breakwater, settlement, numerical simulation mode
Published in DKUM: 06.06.2018; Views: 1322; Downloads: 170
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5. New trends in rock mass characterisation for designing geotechnical structuresDrago Ocepek, 2005, original scientific article Abstract: The investigation on designing supporting measures for geotechnical structures consists of the proper selection of the input data for the stress – strain analysis of the excavation process and the selection of retaining measures. In the preliminary phase of investigation the area must be geologically mapped in detail, and discontinuities precisely measured, boreholes and their “in situ” tests listed and samples for laboratory examinations taken. The new method allows rock mass classification for different rock quality, from soft rocks to mixed rock masses, as well as determination of the geological strength index GSI. The limits for using the suggested method are persistent discontinuities in rock mass which lead to translation or rotation failure mechanisms, either in a single plane or as a wedge. In all cases where discontinuities play a significant role, the rock mass structure must be considered and kinematical analyses performed. In other circumstances, a rock may be uniform and reasonably isotropic due to the geometry of discontinuities and their mutual intersections. The value range of GSI is first determined in the beginning of investigation and later in the excavation phase by considering the disturbance factor D, which expresses disturbances caused by excavation methods and rock mass relaxation. The strength and deformability parameters of rocks of different quality are determined by the generalized Hoek-Brown failure criterion and applied to shallow and deep tunnels or slopes. Before the start of excavations work and after establishing the retaining measures, the analysis results are checked by monitoring. New methods include the determination of post peak strength parameters of rock mass after relaxation, and routine measurements. The newest measurement system however allows direct readings of displacements of the rock mass in both the elastic and post-peak states. With back analyses we determine the softening behavior of the rock mass and a possible need for increasing retaining measures. Such a design method enables the optimization of retaining measures and the reduction of investment costs.
Keywords: geological strength index – GSI, simulation of a triaxial large scale »in situ« test, numerical modeling, retaining measures, rock reinforcement, monitoring, back analyses, strain softening, rock mass relaxation
Published in DKUM: 16.05.2018; Views: 1325; Downloads: 68
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6. Experimental and numerical evaluation of the mechanical behavior of strongly anisotropic light-weight metallic fiber structures under static and dynamic compressive loadingOlaf Andersen, Matej Vesenjak, Thomas Fiedler, Jehring, Lovre Krstulović-Opara, original scientific article Abstract: Rigid metallic fiber structures made from a variety of different metals and alloys have been investigated mainly with regard to their functional properties such as heat transfer, pressure drop, or filtration characteristics. With the recent advent of aluminum and magnesium-based fiber structures, the application of such structures in light-weight crash absorbers has become conceivable. The present paper therefore elucidates the mechanical behavior of rigid sintered fiber structures under quasi-static and dynamic loading. Special attention is paid to the strongly anisotropic properties observed for different directions of loading in relation to the main fiber orientation. Basically, the structures show an orthotropic behavior; however, a finite thickness of the fiber slabs results in moderate deviations from a purely orthotropic behavior. The morphology of the tested specimens is examined by computed tomography, and experimental results for different directions of loading as well as different relative densities are presented. Numerical calculations were carried out using real structural data derived from the computed tomography data. Depending on the direction of loading, the fiber structures show a distinctively different deformation behavior both experimentally and numerically. Based on these results, the prevalent modes of deformation are discussed and a first comparison with an established polymer foam and an assessment of the applicability of aluminum fiber structures in crash protection devices is attempted.
Keywords: aluminum fiber, fiber structure, orthotropy, sintering, compression, static loading, dynamic loading, energy absorption, numerical simulation
Published in DKUM: 21.06.2017; Views: 1148; Downloads: 561
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8. A numerical simulation of metal injection mouldingBoštjan Berginc, Miran Brezočnik, Zlatko Kampuš, Borivoj Šuštaršič, 2009, original scientific article Abstract: Metal injection moulding (MIM) is already a well-established and promising technology for the mass production of small, complex, near-net-shape products. The dimensions and mechanical properties of MIM products are influenced by the feedstock characteristics, the process parameters of the injection moulding, as well as the debinding and the sintering. Numerical simulations are a very important feature of the beginning of any product or technology development. In the article two different techniques for measuring the rheological properties of MIM feedstocks are presented and compared. It was established that capillary rheometers are more appropriate for MIM feed stocks, while on the other hand, parallel-plate rheometers are only suitable for shear rates lower than 10 s[sup]{-1}. Later on we used genetic algorithms to determine the model coefficients for some numerical simulation software. The results of the simulation of the filling phase and a comparison with the experimental results are presented in the article.
Keywords: metal injection moulding, numerical simulation, genetic algorithms
Published in DKUM: 14.03.2017; Views: 1311; Downloads: 168
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10. Numerical modelling of micro-pitting of gear teeth flanksGorazd Fajdiga, Jože Flašker, Srečko Glodež, Trevor K. Hellen, 2003, original scientific article Abstract: A two-dimensional computational model for simulation of contact fatigue of gear teeth flanks is presented. In the model, it is assumed that the initial crack of length 0.015 mm is initiated at the surface due to previous mechanical or heat treatment of the material as well as a consequence of the running in process. The discretized model with the initial crack is then subjected to normal contact pressure, which takes into account the elasto-hydro-dynamic (EHD) lubrication conditions, and tangential loading due to friction between contacting surfaces. The model also considers the moving contact of gear flanks, fluid trapped in the crack and residual stresses due to heat treatment of the material on crack propagation. The virtual crack extension (VCE) method, implemented in the finite element method, is then usedfor simulating the fatigue crack growth from the initial crack up to the formation of the surface pit. The computational results show that the initial surface crack of length 15 m and the considered boundary conditions lead to the appearance of very small surface pits, which can be termed as micro-pitting on gear teeth flanks. The numerical results correspond well withavailable experimental data.
Keywords: machine elements, gearing, fracture mechanics, numerical analysis, micro pitting, pitting simulation, matematical model, fatigue, contact mechanics, crack propagation
Published in DKUM: 01.06.2012; Views: 2660; Downloads: 0 |
