Globvs terraqvevs ecclesiastico politicvs Esinimiö. Frontispiece

Viduae 1703, Leonhard Heckenauer sculpsit

A Practical Micro Mechanical Model Based Local Approach Methodology for the Analysis of Ductile Fracture of Welded T-Joints

This thesis concentrates on developing a practical local approach methodology based on micro mechanical models for the analysis of ductile fracture of welded joints. Two major problems involved in the local approach, namely the dilational constitutive relation reflecting the softening behaviour of material, and the failure criterion associated with the constitutive equation, have been studied in detail. Firstly, considerable efforts were made on the numerical integration and computer implementation for the non trivial dilational Gurson Tvergaard model. Considering the weaknesses of the widely used Euler forward integration algorithms, a family of generalized mid point algorithms is proposed for the Gurson Tvergaard model. Correspondingly, based on the decomposition of stresses into hydrostatic and deviatoric parts, an explicit seven parameter expression for the consistent tangent moduli of the algorithms is presented. This explicit formula avoids any matrix inversion during numerical iteration and thus greatly facilitates the computer implementation of the algorithms and increase the efficiency of the code. The accuracy of the proposed algorithms and other conventional algorithms has been assessed in a systematic manner in order to highlight the best algorithm for this study. The accurate and efficient performance of present finite element implementation of the proposed algorithms has been demonstrated by various numerical examples. It has been found that the true mid point algorithm (a = 0.5) is the most accurate one when the deviatoric strain increment is radial to the yield surface and it is very important to use the consistent tangent moduli in the Newton iteration procedure. Secondly, an assessment of the consistency of current local failure criteria for ductile fracture, the critical void growth criterion, the constant critical void volume fraction criterion and Thomason's plastic limit load failure criterion, has been made. Significant differences in the predictions of ductility by the three criteria were found. By assuming the void grows spherically and using the void volume fraction from the Gurson Tvergaard model to calculate the current void matrix geometry, Thomason's failure criterion has been modified and a new failure criterion for the Gurson Tvergaard model is presented. Comparison with Koplik and Needleman's finite element results shows that the new failure criterion is fairly accurate indeed. A novel feature of the new failure criterion is that a mechanism for void coalescence is incorporated into the constitutive model. Hence the material failure is a natural result of the development of macroscopic plastic flow and the microscopic internal necking mechanism. By the new failure criterion, the critical void volume fraction is not a material constant and the initial void volume fraction and/or void nucleation parameters essentially control the material failure. This feature is very desirable and makes the numerical calibration of void nucleation parameters(s) possible and physically sound. Thirdly, a local approach methodology based on the above two major contributions has been built up in ABAQUS via the user material subroutine UMAT and applied to welded T joints. By using the void nucleation parameters calibrated from simple smooth and notched specimens, it was found that the fracture behaviour of the welded T joints can be well predicted using present methodology. This application has shown how the damage parameters of both base material and heat affected zone (HAZ) material can be obtained in a step by step manner and how useful and capable the local approach methodology is in the analysis of fracture behaviour and crack development as well as structural integrity assessment of practical problems where non homogeneous materials are involved. Finally, a procedure for the possible engineering application of the present methodology is suggested and discussed.

Separation of Gas Bubbles from Circulation Waters and Pulp Suspensions in Open Channel Flow

The objective of this thesis was to study the removal of gases from paper mill circulation waters experimentally and to provide data for CFD modeling. Flow and bubble size measurements were carried out in a laboratory scale open gas separation channel. Particle Image Velocimetry (PIV) technique was used to measure the gas and liquid flow fields, while bubble size measurements were conducted using digital imaging technique with back light illumination. Samples of paper machine waters as well as a model solution were used for the experiments. The PIV results show that the gas bubbles near the feed position have the tendency to escape from the circulation channel at a faster rate than those bubbles which are further away from the feed position. This was due to an increased rate of bubble coalescence as a result of the relatively larger bubbles near the feed position. Moreover, a close similarity between the measured slip velocities of the paper mill waters and that of literature values was obtained. It was found that due to dilution of paper mill waters, the observed average bubble size was considerably large as compared to the average bubble sizes in real industrial pulp suspension and circulation waters. Among the studied solutions, the model solution has the highest average drag coefficient value due to its relatively high viscosity. The results were compared to a 2D steady sate CFD simulation model. A standard Euler-Euler k-ε turbulence model was used in the simulations. The channel free surface was modeled as a degassing boundary. From the drag models used in the simulations, the Grace drag model gave velocity fields closest to the experimental values. In general, the results obtained from experiments and CFD simulations are in good qualitative agreement.

Dissertatio historica de vrbe Vloa, : cujus partem priorem, adprobante amplissima facultate philosophicae in regia ad Auram universitate, praeside ... Algotho A. Scarin, ... Publicae censurae, qua par est modestia, sistit Johannes Joh. Snellmann, scholae triv. Vloënsis collega superior. In auditorio superiori & maximo, ad diem XXVI. Martii, anni repar. salutis MDCCXXXVII. Horis ante meridiem solitis.

Dedicated to: Carl Cronstedt, Carl Gustaf Tessin, Theodor Ankarkrona, Otto Reinhold Wrangel, Olof Sandberg, Jacob von Hökerstedt, Carl von Groot, Carl Friedrich Piper, Olof von Törne, Petter Drufwa, Johan Löwen, Swen Cederström, Johan Maurits Klinkowström, Leonhard Klinkowström, Reinholdt Berndt Hauswolff, Christopher Christopherssen, Johan Williamsson, Olof Malmer, Johan Adam Petersson, Gustaf Kierman, Anders Plomgren.

Liikesodankäynti Julian S. Corbettin kirjoituksissa

Tämän strategian perustutkimukseen kuuluvan tutkimuksen tarkoituksena on selvittää liikesodan periaatteiden kuvautumista merisodan teoreetikon Sir Julian S. Corbettin kirjoituksissa. Tutkimuksen näkökulma on luonteeltaan teoreettinen ja perustuu Merivoimien tarpeeseen tutkia liikesodankäyntiä merisodassa. Tutkimuksen pääongelmana on: miten liikesodankäynnin periaatteet kuvautuvat J. S. Corbettin kirjoituksissa? Tutkimuksen alaongelmat ovat: mitä tarkoittaa liikesodankäynti? Mitkä ovat liikesodankäynnin keskeiset periaatteet ja teoriat? Mitkä ovat Corbettin merisodan teorian keskeisimmät opit? Mitä merisota on Corbettin mukaan? Tutkimuksen päälähteenä on Julian Corbettin merisodan teorian pääteos ”Some Principles of Maritime Strategy” vuodelta 1911. Liikesodan teorian päälähteenä on Robert Leonhardin teos ”The Art of Maneuver – Maneuver-Warfare Theory and AirLand Battle” vuodelta 1991. Tutkimusmenetelmänä on kuvaileva kvalitatiivinen tapaustutkimus. Tutkimuksessa kuvaillaan tutkimuskohteena olevan merisotateoreetikon, J. S. Corbettin merisodan teoriaa ja tarkastellaan sitä liikesodankäynnin teorian näkökulmasta. Liikesodankäynnin erottaa muista sodankäynnin muodoista sillä, miten liikesodassa määritetään voittoon tähtäävät keinot. Liikesodan teorian keskeisiin periaatteisiin kuuluvat vihollisen vahvuuksien välttäminen, vihollisen harhauttaminen, vihollisen haavoittuvuuksien tunnistaminen ja niitä vastaan hyökkääminen. Leonhard on jalostanut nämä edelleen kolmeksi toimintamalliksi: ennakoinniksi, dislokaatioksi sekä hajaannukseksi. Merisota on Corbettin mukaan taistelua meren ja meriyhteyksien hallinnasta. Laivaston tavoitteena tulee olla merenherruuden saavuttaminen. Saavuttamalla ja ylläpitämällä merenherruus kyetään toteuttamaan muut merivoimien tehtävät. Corbettia voidaan pitää yhteisoperaatio-ajattelun edelläkävijänä, sillä Corbettin mukaan sodassa operaatioihin tulee käyttää sekä maa- että merivoimia yhdessä. Corbett luokittelee merelliset operaatiot kolmeen kategoriaan: 1) merenherruuden varmistaminen, 2) merenherruuden kiistäminen, 3) merenherruuden hyödyntäminen. Tutkimuksen johtopäätöksenä havaittiin, että Sir Julian Stafford Corbettin kirjoituksissa esiintyvät näkemykset merisodasta ja merisodan teoriasta noudattavat pitkälti liikesodankäynnin periaatteita. Liikesodan perusperiaatteet vihollisen vahvuuksien välttämisestä, harhautukseen pyrkimisestä sekä vihollisen haavoittuvuuksien tunnistamisesta ja niitä vastaan hyökkäämisestä ovat voimakkaasti läsnä corbettiaanisessa merisodan teoriassa.

Verhopäällystyspastojen analyysimenetelmät

Diplomityön tarkoitus oli selvittää verhopäällystyspastoille sopivia analyysimenetelmiä. Verhopäällystyksessä onnistunut päällystystapahtuma vaatii venymäviskositeetin ja pintajännityksen hyvää hallintaa. Kirjallisuusosassa käsiteltiin verhopäällystystä, verhopäällystyspastojen koostumusta, reologiaa ja pintajännitystä. Kirjallisuusosassa käsiteltiin lisäksi verhopäällystyspastojen reologian ja pintajännityksen mittaamiseen soveltuvia mittausmenetelmiä. Verhopäällystyksen luonteen vuoksi kirjallisuusosassa syvennyttiin venymäviskositeetin ja dynaamisen pintajännityksen mittaamiseen tarkoitettuihin menetelmiin. Kokeellisessa osassa tutkittiin päällystyspastasarjojen reologiaa ja pintajännitystä verhopäällystystä varten. Osaan päällystyspastoista luotiin venymäviskositeettia ja osasta laskettiin pintajännitystä. Venymäviskositeetin mittaamista varten työssä käytettiin ACAV A2 -reometriin liitettyjä teräsreikälevyjä. Dynaamisen pintajännityksen mittaamista varten työssä käytettiin KSV BPA-800P -pintajännitysmittaria. ACAV A2 -reometriin liitettyjen teräsreikälevyjen (reiän sisähalkaisija 0,5 tai 0,7 mm) avulla mitattiin venymäviskositeettia kuvaavia Eulerin lukuarvoja onnistuneesti suurilla kiintoainepitoisuuksilla (50, 60 tai 65 p %). Erikoispaksuntajan määrää lisäämällä onnistuttiin luomaan huomattavaa venymäviskositeettia. Kiintoainepitoisuuden kasvaessa kasvoi myös venymäviskositeetti. Tavanomaisille paksuntajille mitattiin hieman kohonneita venymäviskositeetteja verrattuna referenssipäällystyspastaan. Pigmenttikoostumuksella (kalsiumkarbonaatti/kaoliini) ei näyttänyt olevan vaikutusta venymäviskositeettiin, tai vaikutus oli suhteellisen pieni. Dynaamisen pintajännityksen mittaamista varten käytössä ollut KSV BPA-800P -pintajännitysmittari ei toiminut luotettavasti, vaikka näytteitä laimennettiin. Kiintoainepitoisuudessa 10 p-% olleilla laimennoksilla saavutettiin analysoinnin kannalta parhaat tulokset. Tuloksista saatiin kuitenkin viitteitä, että kyseinen mittari voisi olla potentiaalinen menetelmä dynaamisen pintajännityksen mittaamiseksi.

A multibody dynamic model of the cross-country ski-skating technique

The objective of this thesis is the development of a multibody dynamic model matching the observed movements of the lower limb of a skier performing the skating technique in cross-country style. During the construction of this model, the formulation of the equation of motion was made using the Euler - Lagrange approach with multipliers applied to a multibody system in three dimensions. The description of the lower limb of the skate skier and the ski was completed by employing three bodies, one representing the ski, and two representing the natural movements of the leg of the skier. The resultant system has 13 joint constraints due to the interconnection of the bodies, and four prescribed kinematic constraints to account for the movements of the leg, leaving the amount of degrees of freedom equal to one. The push-off force exerted by the skate skier was taken directly from measurements made on-site in the ski tunnel at the Vuokatti facilities (Finland) and was input into the model as a continuous function. Then, the resultant velocities and movement of the ski, center of mass of the skier, and variation of the skating angle were studied to understand the response of the model to the variation of important parameters of the skate technique. This allowed a comparison of the model results with the real movement of the skier. Further developments can be made to this model to better approximate the results to the real movement of the leg. One can achieve this by changing the constraints to include the behavior of the real leg joints and muscle actuation. As mentioned in the introduction of this thesis, a multibody dynamic model can be used to provide relevant information to ski designers and to obtain optimized results of the given variables, which athletes can use to improve their performance.

Numerical Simulation of Stochastic Di erential Equations

Stochastic differential equation (SDE) is a differential equation in which some of the terms and its solution are stochastic processes. SDEs play a central role in modeling physical systems like finance, Biology, Engineering, to mention some. In modeling process, the computation of the trajectories (sample paths) of solutions to SDEs is very important. However, the exact solution to a SDE is generally difficult to obtain due to non-differentiability character of realizations of the Brownian motion. There exist approximation methods of solutions of SDE. The solutions will be continuous stochastic processes that represent diffusive dynamics, a common modeling assumption for financial, Biology, physical, environmental systems. This Masters' thesis is an introduction and survey of numerical solution methods for stochastic differential equations. Standard numerical methods, local linearization methods and filtering methods are well described. We compute the root mean square errors for each method from which we propose a better numerical scheme. Stochastic differential equations can be formulated from a given ordinary differential equations. In this thesis, we describe two kind of formulations: parametric and non-parametric techniques. The formulation is based on epidemiological SEIR model. This methods have a tendency of increasing parameters in the constructed SDEs, hence, it requires more data. We compare the two techniques numerically.

Excessive functions, Appell polynomials and optimal stopping

The main topic of the thesis is optimal stopping. This is treated in two research articles. In the first article we introduce a new approach to optimal stopping of general strong Markov processes. The approach is based on the representation of excessive functions as expected suprema. We present a variety of examples, in particular, the Novikov-Shiryaev problem for Lévy processes. In the second article on optimal stopping we focus on differentiability of excessive functions of diffusions and apply these results to study the validity of the principle of smooth fit. As an example we discuss optimal stopping of sticky Brownian motion. The third research article offers a survey like discussion on Appell polynomials. The crucial role of Appell polynomials in optimal stopping of Lévy processes was noticed by Novikov and Shiryaev. They described the optimal rule in a large class of problems via these polynomials. We exploit the probabilistic approach to Appell polynomials and show that many classical results are obtained with ease in this framework. In the fourth article we derive a new relationship between the generalized Bernoulli polynomials and the generalized Euler polynomials.

De fide salvifica

Variantti A.

De urbe Uloa 1

Variantti C.