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1.
Numerical analysis of fluid flow in a vial
Žiga Časar, 2019, master's thesis

Abstract: Lyophilization or freeze-drying is a widely used process in the pharmaceutical and food industry. In the process the solvent will be removed under extreme conditions of low temperature and low system pressures, whereby sublimation happens, the transition from the solid phase to the gas phase, with skipping the liquid phase, which happens bellow the triple point. This study focuses on numerical modeling at the start of the process, the so called primary drying. For this stage the highest mass flow rates of vapor are typical, since the driving force of the process is the pressure difference between the sublimation front and surrounding area. In this stage the non-bonded solvent is removed. Because of the extreme conditions the typical computational fluid dynamics approach is not suitable anymore and has to be corrected. One way to do this is to use additional models for fluid behavior at the solid wall. The study focuses on the influence of different boundary conditions on the solid wall, No-Slip, Free Slip and Maxwell Slip, and their effect on fluid flow inside the vial. A quantitative and qualitative comparison of the results is presented.
Keywords: Lyophilization, Knudsen number, computational fluid dynamics, fluid flow, numerical modeling, slip boundary condition
Published: 09.07.2019; Views: 720; Downloads: 119
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2.
Nonlinear control of a one-dimensional self-balancing system with an inertia wheel
Marko Boršić, 2019, master's thesis

Abstract: The master’s thesis describes the development of a one-dimensional self-balancing system with an inertia wheel. The plan was to establish all the theoretical knowledge that was gathered throughout the process of studying at the University and to finish the practical model which has the ability to balance in one dimension. The paper contains a description of constructing the mechanical part of the pendulum, developed in SolidWorks software. It also contains the execution of the mathematical model of the inverted pendulum. The simulation was conducted in Matlab/Simulink software. Based on the results of the simulation, the design of the controller for the EC motor was made. Designed controllers and measured data required for the active balance of the system were implemented on the microcontroller STM32F4. To measure the angle and angle velocity, the gyroscope and accelerometer on the MPU6050 sensor were used. The results of the simulation and of the practical model are presented in this paper.
Keywords: modeling, inertia wheel, backstepping, state space, sliding mode
Published: 29.03.2019; Views: 1216; Downloads: 214
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3.
Modeling of a geocell-reinforced pavement
Samo Peter Medved, Bojan Žlender, Stanislav Lenart, Primož Jelušič, 2016, original scientific article

Abstract: This article details how the serviceability of a flexural pavement structure is improved by incorporating the Cellular Confinement System (geocells). For this purpose, two different pavement structures, with and without embedded geocells, were manufactured in a laboratory and an accelerated traffic type of loading was applied. The vertical and horizontal cyclic loads were applied simultaneously to simulate the effect of principal stress rotation. A comparative study between the conventional flexible pavement and the geocell-reinforced flexible pavement is presented. Additionally, numerical models of the laboratory tests were built and the results were compared. The simulation of the experimental tests using the Traffic Load Simulator (TLS) are carried out using the FEM and advanced models that describe the permanent strain behavior of the unbound granular material. The development of permanent deformation within the pavement structure, with and without the geocells, is also presented through the numerical model, which was verified by the experimental results.
Keywords: flexible pavement, reinforcement, geocell, traffic load simulator, permanent deformation, numerical modeling
Published: 18.06.2018; Views: 533; Downloads: 56
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4.
Constitutive modeling and computer methods in geotechnical engineering
Chandrakant Desai, 2010, original scientific article

Abstract: Computer methods are in the forefront of the procedures for analysis and design for geotechnical problems. Constitutive models that characterize the behavior of geologic materials and interfaces/joints play a vital role in the solutions obtained by using computer methods or any other solution procedure. The literature on both constitutive and computer models is wide; attention in this paper is devoted to the disturbed state concept (DSC) for constitutive modeling and the finite element method for computer solutions. The disturbed state concept, a unified and hierarchical approach, provides a unified framework for characterization of the behavior of geologic materials and interfaces/joints. Important factors such as elastic, plastic and creep responses, stress paths, volume change (contraction and dilation), disturbance (softening and damage or stiffening), thermal effects, partial saturation and liquefaction can be included in the same DSC framework. Because of its hierarchical nature, simplified models for specific applications can be derived from the DSC. It has been applied successfully for defining behavior of many geologic materials and interfaces/joints. Procedures for the determination of parameters for the DSC models based on laboratory tests have been developed. Various models from the DSC have been validated at the specimen level with respect to laboratory test data. They have been validated at the practical boundary value problem level by comparing observed behavior in the field and/or simulated problems in the laboratory with predictions using computer (finite element) procedures in which DSC has been implemented; these have been presented in various publications by Desai and coworkers, and are listed in the References. Three typical examples of such validations at the practical problem level are included in this paper. It is believed that the DSC can provide unified and powerful models for a wide range of geomechanical and other engineering materials, and interfaces/joints.
Keywords: constitutive modeling, disturbed state concept, DSC, geologic materials, interfaces/joints
Published: 11.06.2018; Views: 343; Downloads: 42
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5.
Modeling of the stress-strain behavior in hard soils and soft rocks
Vladimir Vukadin, 2007, original scientific article

Abstract: The paper begins with a definition of hard soils and soft rocks (HSSR); this is followed by a short overview of the typical stress-strain behavior of HSSR. It is shown that in spite of the differences in the origin, type and strength of materials, similar stress-strain behaviors can be observed for different materials, ranging from soils to rocks. Based on this observed similarity a theoretical framework can be postulated, with which an appropriate constitutive model for HSSR can be formulated. This model includes the concepts of structure and destructurization as intrinsic material properties. A model named S_BRICK that takes into account the structure and destructurization has been developed and a comparison of this model’s predictions with laboratory results is presented.
Keywords: geomechanics, soft rocks, hard soils, stress-strain behaviour, constitutive modeling, structure, destructurization, numerical modeling
Published: 18.05.2018; Views: 658; Downloads: 61
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6.
New trends in rock mass characterisation for designing geotechnical structures
Drago 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: 16.05.2018; Views: 618; Downloads: 32
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7.
Development of a conceptual material model for structured materials - S_BRICK
Vladimir Vukadin, Jakob Likar, Vojkan Jovičić, 2005, original scientific article

Abstract: Materials known in literature as Soft Rocks & Hard Soils such as claystones, siltstones, flysh, hard soils, marls, etc. received a lot of attention in research community in recent years. It was demonstrated that some of these materials can be described through general theoretical framework (Cotecchia & Chandler [1]), which takes into account the structure as an intrinsic material property that is present in all natural geological materials. The influence of the structure is manifested as an increase in strength and stiffness in a material. Based on a laboratory results and existent theoretical frameworks, a further step was taken with the development of a conceptual constitutive model for structured materials. A model formulated in strain space named BRICK (Simpson [2]) was chosen as a base model and was further developed with the inclusion of structure and destructuring. The new model was named S_BRICK and was tested on a conceptual level where the results of numerical tests on structured and structure less (reconstituted) materials at different stress paths were compared. The results showed that S_BRICK was able to capture stress-strain behavior typical for structured material and could be potentially used for the modeling of Soft Rocks and Hard Soils.
Keywords: geomechanics, soft rocks, hard soils, constitutive material models, structure, destructuring, numerical modeling
Published: 15.05.2018; Views: 687; Downloads: 43
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8.
Understanding the structural complexity of induced travel demand in decision-making
Juan Angarita-Zapata, Jorge Parra-Valencia, Hugo Andrade-Sosa, 2016, original scientific article

Abstract: Background and purpose: Induced travel demand (ITD) is a phenomenon where road construction increases vehicles’ kilometers traveled. It has been approached with econometric models that use elasticities as measure to estimate how much travel demand can be induced by new roads. However, there is a lack of “white-box” models with causal hypotheses that explain the structural complexity underlying this phenomenon. We propose a system dynamics model based on a feedback mechanism to explain structurally ITD. Methodology: A system dynamics methodology was selected to model and simulate ITD. First, a causal loop diagram is proposed to describe the ITD structure in terms of feedback loops. Then a stock-flows diagram is formulated to allow computer simulation. Finally, simulations are run to show the quantitative temporal evolution of the model built. Results: The simulation results show how new roads in the short term induce more kilometers traveled by vehicles already in use; meanwhile, in the medium-term, new traffic is generated. These new car drivers appear when better flow conditions coming from new roads increase attractiveness of car use. More cars added to vehicles already in use produce new traffic congestion, and high travel speeds provided by roads built are absorbed by ITD effects. Conclusion: We concluded that approaching ITD with a systemic perspective allows for identifying leverage points that contribute to design comprehensive policies aimed to cope with ITD. In this sense, the model supports decision- making processes in urban contexts wherein it is still necessary for road construction to guarantee connectivity, such as the case of developing countries.
Keywords: induced travel demand, system dynamics, decision-making, dynamic modeling
Published: 23.01.2018; Views: 670; Downloads: 99
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9.
Spatial ability, 3D modelling and styles of thinking in relation to brain hemisphere dominance
Andrej Šafhalter, Srečko Glodež, Karin Bakračevič Vukman, 2013, original scientific article

Abstract: The progress of neuroscience and the understanding of children's styles of thinking are opening up new teaching styles that take into account differences in individual cognitive perception. Students can be classified into three distinctive perceptive types, according to the pronounced activity of one cerebral hemisphere in their thinking and information processing: left-hemisphere, right-hemisphere, and integrative type that does not exhibit a considerable dominance of one particular hemisphere. The purpose of the research was to establish differences in the 3D modeling encouraged progression of spatial ability between the left-hemisphere, right-hemisphere and integrative types of students. Computerized 3D modeling employed during technical extra-curricular activity in lower secondary school (grades 6 to 9) may affect the spatial ability of students, which according to other studies, appears to be predominantly connected with the right brain hemisphere. Research was conducted among a variety of lower secondary school students across Slovenia aged 11 15 years. Data on spatial ability and its development was collected using a hybrid spatial intelligence test conducted on two separate occasions, while assessment of the learning perception type of students depending on hemispheric dominance was obtained using a self-evaluation questionnaire. The 3D modeling of technical objects and objects drawn in orthographic or isometric projection was done with the software Trimble SketchUp.
Keywords: cognitive development, spatial ability, 3D modeling
Published: 19.12.2017; Views: 545; Downloads: 78
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10.
Developing spatial visualization with 3D modeling
Andrej Šafhalter, Srečko Glodež, Karin Bakračevič Vukman, 2012, original scientific article

Abstract: The research was carried out in 20 11 among 22 pupils from 14-15 years old. The purpose of the pilot study was to determine the influence of 3D modeling on the spatial visualization of pupils, as well as the gender difference in the spatial visualization of the tested pupils and the progress of this visualization in individual genders. ln addition, it tried to determine whether the sensory style of the pupils, visual. auditory or kinesthetic, influences spatial perception and the development of spatial visualization. Pupils were divided into two groups, the test group and the control group. Pupils in the test group attended a 3D modeling extra-curricular activity for twelve teaching hours in the second evaluation period of the 2010/2011 school year. Spatial visualization was determined with a modified spatial visualization test. namely before the extra-curricular activity and afterwards. The modified test consisted of different spatial visualization tests: PSVT: R, MeT, MRT, DAT: SR. and tests of rotation within a plane. For 3D modeling exercises pupils used the open-source software Google SketchUp. None of the tested pupils have encountered the mentioned software before. After a second testing, the test group showed greater progress in solving spatial visualization tasks in comparison with the control group, while gender differences were minimal. The results of the spatial visualization test were also compared with the sensory style of pupils, which was filled out by all the pupils included in the study. ln the 2011/2012 school year a broader study is underway, involvlng almost two hundred pupils of various elementary schools in Slovenia.
Keywords: spatial visualization, 3D modeling, perception styles
Published: 15.12.2017; Views: 694; Downloads: 65
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