År 2004 infördes EU:s ramdirektiv för vatten i svensk lagstiftning vilket har inneburit att vattendragets funktion som vandringsväg för fisk behöver upprätthållas eller säkras, även efter att dammar byggts. För vattenkraftverksdammar kan detta ske genom att dammarna rivs eller förses med olika typer av anordningar för passage upp- och nedströms dammen. Vid Sikfors vattenkraftverk finns en ledarm för att leda smolten till ett utskov för passage nedströms dammen. Studier har dock visat att smolten dör i för stor utsträckning vid passage via utskovet, och projektets syfte har därför varit att ta fram en modell för flödet över utskovet. Modellen har ställts upp för tre volymflöden, 18, 30 och 59 m3/s och vattendjup, vattenhastighet och flödesbeteende har analyserats för volymflödena.  Geometrin en bit uppströms dammen, luckan och skibordet byggdes upp i Designmodeler utifrån ritningar. För att underlätta simuleringarna delades geometrin i två delar, där den första delen innefattar geometrin en bit uppströms dammen samt luckan medan den andra geometrin innefattar skibord och uppkastare och nedslagsplats. Simuleringen gjordes i ANSYS CFX och vattenytan modellerades som en fri yta med luft och vatten som fluider i modellen. Luckans öppning varierades med volymflödet, utifrån data från vattenkraftverket.  Det lägsta vattendjupet över luckan blev 5 cm vid slutet av luckan för ett volymflöde på 18 m3/s, medan för 30 m3/s blev det lägsta vattendjupet 10 cm vid slutet av luckan. Den högsta vattenhastigheten över luckan blev 8,5 m/s för 30 m3/s i mitten av luckan medan samma hastighet blev 8,3 och 8,9 m/s för volymflöde på 18 respektive 59 m3/s.  För skibordet blev det lägsta vattendjupet 15 cm och 30 cm för 18 respektive 30 m3/s. Vattenhastigheten för samtliga volymflöden för skibordet överstiger 12 m/s, vilket är den högsta rekommenderade hastigheten för nedströmspassage. För 30 och 59 m3/s kastas vattnet över ingången till fisktrappan, medan för 18 m3/s påverkas flödet vid ingången utav flödet från utskovet. Vattendjupet för 30 m3/s borde vara tillräckligt för att smolten inte ska få skrapskador, medan 18 m3/s kan vara för lågt volymflöde. Ingen tendens för virvlar eller turbulens syns för luckan eller skibordet för något volymflöde, så flödesbeteendet borde inte vara ett problem för smolten. Vattenhastigheten för skibordet överskrider den högsta rekommenderade hastigheten, men hastigheten är inte mycket högre än rekommenderat och under en kort period, så det borde inte vara den enskilda orsaken till smoltens låga överlevnadsgrad.    Den numeriska modellen har ställts upp för tre volymflöden, och kontrollerats mot teoretiska beräkningar och mot parametrar för meshkvalitet, som visar att modellen är bra uppställd. Analysen har visat att vattendjup och vattenhastighet är beroende av volymflödet över utskovet, och att skillnaden är större för vattendjupet. Flödesbeteendet visar ingen tendens till turbulens eller virvlar, och flödesbeteendet följer ett typiskt beteende för kanalströmning.

Abstract: This thesis aims to contribute to the development of the isobaric combustion engines by exploring multiple injection strategies, by means of computational simulations using a commercial software Converge. A single injection case validated with experimental data in terms pressure trace and heat release rate was used as a baseline reference. The adjustment of the turbulent kinetic energy dissipation constant is found to have the most significant influence in reproducing the pressure and heat release rate histories observed in the experiment. As a first attempt to achieve isobaric combustion, a multiple injection strategy using a single injector was explored with up to four consecutive injections. Considering that the computational simulations were unable to reproduce the experimental data due to a number of uncertainties in the implemented models, the present study attempted to identify the main causes of the discrepancies through various parametric studies. First, different liquid fuel properties were examined and it was found that, while the physical properties of the fuels have a notable effect in terms of evaporation and atomization, such variations were not sufficient to reproduce the experimentally observed heat release cycle. Next, the effects of the uncertainties in the kinetic mechanisms were assessed by the reaction multiplier, an artificial adjustment of the rate constants, and it was found that the reaction multiplier affected the ignition of the first injection, but not the subsequent injection events. As such, the use of reaction multipliers to reproduce the experimental data was found to be unsuccessful. The effect of thermodynamics properties was also examined by employing real-gas equations of state, such as Redlich-Kwong and Peng-Robinson, and the results showed little difference at the conditions under consideration. Finally, advancing the start of injection was found to have the most significant effect on pressure trace and heat release rate to lead to a substantial improvement in the numerical prediction. The results suggest that the key uncertainties in modeling of the present engine combustion are likely the accurate timing of the start of injection combined with the exact injection rate shape profile.

Väderstad AB develops and sells agricultural machines in large parts of the world. Their segment includes many different types of machines, several of them being seed drills. The machine that this project focuses on is a seed drill that can plant numerous kinds of seeds, wheat and colza being among them. This machine is named Spirit. The seed drill Spirit uses air currents to transport seeds from a container to the ground via a hose system. The velocity of the air must be high enough to eliminate the risk of seed getting trapped in the hose system. However, the high air velocity introduces the risk of seed bouncing out or being blown out of the furrow they are supposed to grow in. Therefore, this project’s purpose has been to solve this problem and thus improve the seed placement the seed drill possesses. This paper consists of the theories and methods used to find a solution to this problem. A product development-process laid the foundation to this project in order to plan the project and generate solutions in a systematic way. After a problem analysis and analyzing competitors it became clear that a geometry in the end of the hose system could be used to separate air and seeds to reduce the seeds velocity and improve the seed placement. Several concepts have been modeled in CAD programs (Computer Aided Design) to later be analyzed in CFD programs (Computational Fluid Design), where air flows can be studied. Concepts has also been manufactured with 3D-printers in order to be evaluated with air currents and different kinds of seeds. The usage of a product development process resulted in a final concept that uses the Coandă effect and the momentum of the seed in order to separate air and seed in an efficient way. Results from tests shows that the velocity of the seed are being reduced and that the air is being evacuated before the seed reaches the ground.

The Computational Fluid Dynamics General Notation System provides a unified way in which computational fluid dynamics data can be stored, but does not support the parallel I/O capabilities now available from version five of the Hierarchical Data Format library which serves as a back end for he standard. To resolve this deficiency, a new parallel extension library has been written and benchmarked for this work which can write files compliant with the standard using parallel file access modes. When using this new library, the write performance shows an increase of four-fold in some cases when compared to the same hardware operating in serial. Additionally, the use of parallel I/O allows much larger cases to be written since the problem is scattered across many nodes of a cluster, whose aggregate memory is much greater than that found on a single machine. These developments will allow computational fluid dynamics simulations to execute faster, since less time will be spent waiting for each time step to finish writing, as well prevent the need for lengthy reconstruction of data after the completion of a simulation.

The dangerous hydraulic conditions that can form downstream of a low-head dam were investigated. These dangerous hydraulic conditions have been the cause of hundreds of drowning incidents since the construction of the first low-head dams. Two primary objectives were identified for this study, each of which were primarily performed using the Computational Fluid Dynamics software, Flow-3D®, with physical models used to verify the numerical results. The first objective was the identification of a risk factor made up of easily measured parameters that could accurately predict when the dangerous hydraulic conditions are present at a low-head dam. The risk factor that was found to achieve this objective was calculated as (hu - hd)/P, where hu and hd are the upstream and downstream water depths, respectively, and P is the dam height. For the flat-topped dams tested, the dangerous condition was present within the range of risk factors from 0.343 to 0.708. For the ogee-crested dams tested, the dangerous conditions were present between risk factors of 0.093 and 0.798. The second objective was to identify possible remediation options that would be capable of eliminating the dangerous hydraulic conditions, therefore reducing risk to the public. It was also desired to keep the options easily and inexpensively implemented. Two different remediation options were found to this end, and consisted of either upstream facing ramps spaced along the width of the channel below a low-head dam, or spaced platforms protruding from the downsteam face of the dam slightly below its crest. Three different designs of each configuration were tested, with those for the ramp configuration being identified as R1, R2, and R3. The platform designs were identified as P1, P2, and P3. The options were evaluated based on how long it took for human dummies introduced into the flow to pass through the high risk region of the simulations, with the maximum allowed time being 50 seconds. Any test in which a dummy remained in the danger region for longer than 50 seconds was deemed ineffective. The option found to perform the best was the P2 design, which had an overall performance time of about 17.4 seconds.

No description available.

Dual fuel combustion is one strategy to achieve low oxides of nitrogen and soot emissions while maintaining the fuel conversion efficiency of IC engines. However, it also suffers from high engine-out carbon monoxide and unburned hydrocarbon emissions, and the incidence of knock at high loads. The present work focused on CFD simulation of diesel-methane dual fuel combustion in a single-cylinder research engine (SCRE). For pure diesel combustion, a load sweep of 2.5 bar brake mean effective pressure (BMEP) to 7.5 bar BMEP was performed at a constant engine speed of 1500 rpm and a diesel injection pressure of 500 bar. For diesel-methane dual fuel combustion, a methane percent energy substitution sweep was performed from 30% to 90 % at 1500 rpm, 3.3 bar BMEP, 500 bar Pinj, and 355 crank angle degrees (CAD) diesel injection timing. Combustion, performance, and emissions results are presented and compared with experimental data where possible.

Nanoluids are colloidal solutions made up of particles of the nanometric scale suspended in a fluid. This type of solution has widespread great interest since the discovery of their particular properties. The Poisson-Nernst Planck system of equations (PNP) is one of the known models for the description of ion transport. This thesis aims to develop a method to solve the PNP equations in space and time for these nanoluids. Additionally, a simulation platform (C++) is developed using an iterative scheme to solve the nonlinear equations resulting from the discretization of the system. After an overview of the literature on the subject, a discussion on the validity of the results obtained through the simulation platform through its comparison with literature and a commercial software package, COMSOL.

The use of solar heated attic air is an area of increasing interest in commercial poultry production. Attic inlets satisfy the demand for alternative heating while being simple to implement in an existing poultry house. However, little attention has been given to the configuration of the attic space and its influence on thermal energy extraction. This issue was approached in a threefold manner: i.) test case experimental data for the operation of attic inlets in an east-west oriented commercial broiler house was recorded, ii.) a two-dimensional computational fluid dynamics (CFD) attic inlet ventilation model (AIVM) was developed and verified using the experimental data, and iii.) the simulation was used to investigate the efficiency of attic inlet system improvements. The simulation demonstrated that the strategic placement of a simple diverter and an inlet riser may increase thermal energy extraction by 40% over the measured attic inlet system.

Coarctation of the aorta (CoA) is a congenital heart disease in which the aorta witnesses localized obstruction. CoA can be fatal if left untreated. Endovascular stenting of CoA is an attractive treatment of choice in adolescents and adults; however, it can be associated with problems like stent malapposition and inappropriate stent expansion. The main objective of this study is to investigate the effects of stent implantation on the hemodynamic factors in a patient with mild coarctation. Computational fluid dynamics was utilized to illustrate the hemodynamic factors like velocity distribution, wall shear stress, and trans-coarctation pressure drop in pre- and post-intervention states. These factors were used to assess the success of stent deployment in this patient. Large Eddy Simulation (LES) model is employed in this work to provide detailed information on hemodynamics in patient-specific preand post-intervention geometries of the aorta. The results of an in-house lumped parameter code, in which its input parameters are obtained from patient-specific clinical data, were applied as the boundary conditions in this study. / Thesis / Master of Applied Science (MASc)