Arkistoluettelo 676: Felix Iversen

Luettelo Kansalliskirjastossa olevan Felix Iversenin arkiston sisällöstä

Herra Apteekkari Horst Atzinger 18/10 1971

Kirje 18.10.1971

CFD simulation of complex phenomena containing suspensions and flow throughporous media

There is an increasing reliance on computers to solve complex engineering problems. This is because computers, in addition to supporting the development and implementation of adequate and clear models, can especially minimize the financial support required. The ability of computers to perform complex calculations at high speed has enabled the creation of highly complex systems to model real-world phenomena. The complexity of the fluid dynamics problem makes it difficult or impossible to solve equations of an object in a flow exactly. Approximate solutions can be obtained by construction and measurement of prototypes placed in a flow, or by use of a numerical simulation. Since usage of prototypes can be prohibitively time-consuming and expensive, many have turned to simulations to provide insight during the engineering process. In this case the simulation setup and parameters can be altered much more easily than one could with a real-world experiment. The objective of this research work is to develop numerical models for different suspensions (fiber suspensions, blood flow through microvessels and branching geometries, and magnetic fluids), and also fluid flow through porous media. The models will have merit as a scientific tool and will also have practical application in industries. Most of the numerical simulations were done by the commercial software, Fluent, and user defined functions were added to apply a multiscale method and magnetic field. The results from simulation of fiber suspension can elucidate the physics behind the break up of a fiber floc, opening the possibility for developing a meaningful numerical model of the fiber flow. The simulation of blood movement from an arteriole through a venule via a capillary showed that the model based on VOF can successfully predict the deformation and flow of RBCs in an arteriole. Furthermore, the result corresponds to the experimental observation illustrates that the RBC is deformed during the movement. The concluding remarks presented, provide a correct methodology and a mathematical and numerical framework for the simulation of blood flows in branching. Analysis of ferrofluids simulations indicate that the magnetic Soret effect can be even higher than the conventional one and its strength depends on the strength of magnetic field, confirmed experimentally by Völker and Odenbach. It was also shown that when a magnetic field is perpendicular to the temperature gradient, there will be additional increase in the heat transfer compared to the cases where the magnetic field is parallel to the temperature gradient. In addition, the statistical evaluation (Taguchi technique) on magnetic fluids showed that the temperature and initial concentration of the magnetic phase exert the maximum and minimum contribution to the thermodiffusion, respectively. In the simulation of flow through porous media, dimensionless pressure drop was studied at different Reynolds numbers, based on pore permeability and interstitial fluid velocity. The obtained results agreed well with the correlation of Macdonald et al. (1979) for the range of actual flow Reynolds studied. Furthermore, calculated results for the dispersion coefficients in the cylinder geometry were found to be in agreement with those of Seymour and Callaghan.

De usu montium ad aqvationem terrae

Invocatio: Deo Duce.

På berget

Melartinin käsikirjoitusluettelon tunnus Mel 23:676 (ks. http://lib.siba.fi/fi/kokoelmat/kasikirjoitusarkisto/melartin_erkki/).

Kirkkonummen Syväjärven perustila : Kirkkonummen järvikohtainen järvikunnostusohjelma

Kirkkonummen kunta on ollut mukana Uudenmaan ympäristökeskuksen aloittamassa kuntakohtaisessa järvikunnostusohjelmassa vuodesta 2006 asti, jolloin tehtiin Kalljärven perustilan selvitys. Tämän jälkeen Uudenmaan ELY-keskuksen ja Kirkkonummen kunnan neuvotteluiden seurauksena päätettiin selvittää myös Djupströmin eli Syväjärven perustila. Syväjärvi on kerättyjen tietojen valossa matala ja rehevä järvi. Käyttökelpoisuusluokituksessa 2000–2003 se oli luokassa 4 välttävä. Järven suurimmat ongelmat näyttäisivät kohdistuvan veden korkeisiin ravinnepitoisuuksiin ja talviaikaisiin happivajeisiin tai suoranaisiin happikatoihin. Järvi luokitellaan nykyisten ravinnepitoisuuksien perusteella erittäin reheväksi. Toisaalta korkeat fosfori- ja typpitasot eivät näy suoraan leväkukintojen määrissä. Syväjärvellä särki oli sekä biomassaosuudeltaan että lukumäärältään selkeästi yleisin laji. Särjen osuus saaliin painosta oli 48 ja lukumäärästä 60 prosenttia. Ahvenkalojen osuus saaliin biomassasta oli 18 % ja yksilömäärästä 35 %. Särkikalojen biomassaosuus, 82 %, saaliista oli hyvin korkea, mikä kyllä kuvaa Syväjärven tyyppisten, matalien ja rehevien järvien kalakannan rakennetta. Matalassa ja ravinteikkaassa järvessä, jossa auringon valo pääsee kasvukaudella tunkeutumaan järven pohjaan asti, on vesikasvien runsastumiselle hyvät olosuhteet. Tämän vuoksi Syväjärvessä on paikoin erittäin tiheää vesikasvillisuutta, jonka seurauksena on ollut vesialueiden umpeenkasvua. Syväjärveen kohdistuu melko paljon virkistyskäyttöpaineita. Järven valuma-alueella ja sen läheisyydessä on viime vuosina ollut paljoin uudisrakentamista ja lisäksi järvellä on vilkas uimaranta. Vedenlaatutulosten perusteella järven vedenlaatu näyttäisi kuitenkin heikentyneen vuosien mittaan. Jotta järven virkistyskäyttöarvoa saataisiin parannettua, tulisi järvelle aloittaa kunnostussuunnittelu.

Minimizing Circulating Current in Parallel-Connected Photovoltaic Inverters

Parallel-connected photovoltaic inverters are required in large solar plants where it is not economically or technically reasonable to use a single inverter. Currently, parallel inverters require individual isolating transformers to cut the path for the circulating current. In this doctoral dissertation, the problem is approached by attempting to minimize the generated circulating current. The circulating current is a function of the generated common-mode voltages of the parallel inverters and can be minimized by synchronizing the inverters. The synchronization has previously been achieved by a communication link. However, in photovoltaic systems the inverters may be located far apart from each other. Thus, a control free of communication is desired. It is shown in this doctoral dissertation that the circulating current can also be obtained by a common-mode voltage measurement. A control method based on a short-time switching frequency transition is developed and tested with an actual photovoltaic environment of two parallel inverters connected to two 5 kW solar arrays. Controls based on the measurement of the circulating current and the common-mode voltage are generated and tested. A communication-free method of controlling the circulating current between parallelconnected inverters is developed and verified.

Kirjallisuushistorian varjoista valoon

Kirjallisuusarvostelu

Meat inspection and control in the slaughterhouses

Kirjallisuusarvostelu