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.

Efficient image mosaicing for multi-robot visual underwater mapping

Robotic platforms have advanced greatly in terms of their remote sensing capabilities, including obtaining optical information using cameras. Alongside these advances, visual mapping has become a very active research area, which facilitates the mapping of areas inaccessible to humans. This requires the efficient processing of data to increase the final mosaic quality and computational efficiency. In this paper, we propose an efficient image mosaicing algorithm for large area visual mapping in underwater environments using multiple underwater robots. Our method identifies overlapping image pairs in the trajectories carried out by the different robots during the topology estimation process, being this a cornerstone for efficiently mapping large areas of the seafloor. We present comparative results based on challenging real underwater datasets, which simulated multi-robot mapping

Estimation of surface area and pore volume of activated carbons by methylene blue and iodine numbers

Data of methylene blue number and iodine number of activated carbons samples were calibrated against the respective surface area, micropore volume and total pore volume using multiple regression. The models obtained from the calibrations were used in predicting these physical properties of a test group of activated carbon samples produced from several raw materials. In all cases, the predicted values were in good agreement with the expected values. The method allows extracting more information from the methylene blue and iodine adsorption studies than normally obtained with this type of material.

A comparison of electricity spot prices simulation using ARMA-GARCH and mean-reverting models

The aim of this work is to compare two families of mathematical models for their respective capability to capture the statistical properties of real electricity spot market time series. The first model family is ARMA-GARCH models and the second model family is mean-reverting Ornstein-Uhlenbeck models. These two models have been applied to two price series of Nordic Nord Pool spot market for electricity namely to the System prices and to the DenmarkW prices. The parameters of both models were calibrated from the real time series. After carrying out simulation with optimal models from both families we conclude that neither ARMA-GARCH models, nor conventional mean-reverting Ornstein-Uhlenbeck models, even when calibrated optimally with real electricity spot market price or return series, capture the statistical characteristics of the real series. But in the case of less spiky behavior (System prices), the mean-reverting Ornstein-Uhlenbeck model could be seen to partially succeeded in this task.

Porvoon jalostamon haihtuvien orgaanisten yhdisteiden päästömääritysmenetelmät

Työssä käytiin läpi Porvoon jalostamon haihtuvien orgaanisten yhdisteiden päästömääritysmenetelmiä ja arvioitiin nykyisin käytössä olevien sekä uusien menetelmien soveltuvuutta Porvoon jalostamon päästömääritykseen. Nykyisten menetelmien arviointia tehtiin käymällä läpi eri alueiden 2000-luvun päästömäärät sekä vertaamalla päästömääriä muiden jalostamojen vastaaviin päästömääriin. Haihtuvista orgaanisista yhdisteistä puhuttaessa jätetään yleisesti metaani määritelmän ulkopuolelle ja käytetään termiä NMVOC-yhdisteet. Työssä laskettiin arvio Porvoon jalostamon metaanin päästömäärälle ja arvioitiin sen vaikutusta NMVOC-kokonaispäästömäärään. Metaanin kokonaispäästömäärien havaittiin olevan noin kymmenen kertaa haihtuvien orgaanisten yhdisteiden päästömääriä pienempiä, ja näin ollen niiden lisäämisellä NMVOC-päästöihin ei ole juuri vaikutusta. Myös menetelmien investointi- ja käyttökustannuksia, sekä pidemmän aikavälin kustannuksia arvioitiin. Kustannuksiltaan tällä hetkellä Porvoon jalostamolla käytössä olevat menetelmät ovat kustannustehokkaita. Uusista menetelmistä DIAL, SOF ja OGI ovat kustannuksiltaan huomattavasti kalliimpia, myös pitkän aikavälin vertailulla. Nykyisten menetelmien vuosittaiset kustannukset aiheutuvat mittausten vaatimista henkilötyötunneista. Uusista menetelmistä SOF ja DIAL vaativat ulkopuolisten mittaajien käyttämistä. Massavirran määrityksen suhteen vielä kehitysvaiheessa olevalla OGI-kameralla mitatessa voidaan käyttää mittaajina omaa henkilökuntaa. Toisin kuin DIAL- ja SOF-menetelmien laitteistot, OGI-kamera ostetaan omaksi ja näin ollen sitä voidaan käyttää tarpeen vaatiessa vuoden ympäri esimerkiksi suurien vuotajien paikallistamiseen ja LDAR-kiristysohjelman tukena. Tarkastelun perusteella olisi suositeltavaa tarkastaa nykyisin käytettävistä laskentamenetelmistä erityisesti prosessi- ja säiliöalueen sekä jätevesijärjestelmä päästömäärät käyttäen tarkempia DIAL-, SOF- tai myöhemmin OGI-menetelmiä ja muokata laskentamenetelmiä vastamaan näillä määritettyjä päästömääriä.

Kuituvuoto reikäsihdillä massan syöttövaiheessa

Diplomityön tarkoituksena oli kehittää tutkimuslaite, jolla pystyttäisiin tutkimaan sellumassan syöttötapahtumaa reikäsihdillä ja tarkastelemaan syöttöhetkellä tapahtuvaa kuituhäviötä. Laitteen suunnittelun ja valmistuksen tavoitteena oli myös saada tutkimuslaite mahdollisim-man modifioitavaksi (syöttöaukon koko, muoto ja erityyppiset reikäsihdit ja näiden vaikutukset sellukuitujen hävikkiin). Haluttiin myös mahdollisuus syöttötapahtuman kuvaamiseen esim. suurnopeuskameroin, joka otettiinkin huomioon laiteosia valittaessa (läpinäkyvä akryyli). Tutkimuslaitteen kestävyyttä erilaisissa prosessiolosuhteissa haluttiin korostaa (voidaan operoida laajalla pH ja lämpötila-alueilla, sekä syöttöpainetta voidaan muunnella). Diplomityön kirjallisuusosassa käsitellään kuituvuodon aiheuttamia haittoja, joista tärkein on taloudellinen menetys. Näiden lisäksi kirjallisuusosassa tarkastellaan pääpirteittäin pesume-netelmiä ja käydään läpi kuitusulpun suotautumiseen vaikuttavia tekijöitä. Diplomityöhön sisältyi tutkimuslaitteen suunnittelun ja valmistuksen lisäksi myös laitteen toi-mivuuden testaus. Testit suoritettiin pohjoismaisella koivusellulla. Koivusellu otettiin happi-vaiheen jälkeisen pesurin poistosta. Massalle suoritettiin KAPPA-luvun, SR-luvun, viskositee-tin ja syrjäytys -määritykset, sekä kuituanalyysi. Laitteella suoritettiin 7 %, 10 % ja 12 % sakeuksisten massojen koeajotestit. Suodokset otettiin talteen jatkotutkimuksiin, jossa niistä mitattiin kuituvuoto. 10 % suodokselle suoritettiin myös kuituanalyysi. Tuloksista nähtiin, että 7 % sakeuksinen massa antoi lähes nelinkertaisen kuituvuotomäärän 10 % sakeuksiseen massan syöttöön nähden.

Bayesian methods for estimation, optimization and experimental design

Mathematical models often contain parameters that need to be calibrated from measured data. The emergence of efficient Markov Chain Monte Carlo (MCMC) methods has made the Bayesian approach a standard tool in quantifying the uncertainty in the parameters. With MCMC, the parameter estimation problem can be solved in a fully statistical manner, and the whole distribution of the parameters can be explored, instead of obtaining point estimates and using, e.g., Gaussian approximations. In this thesis, MCMC methods are applied to parameter estimation problems in chemical reaction engineering, population ecology, and climate modeling. Motivated by the climate model experiments, the methods are developed further to make them more suitable for problems where the model is computationally intensive. After the parameters are estimated, one can start to use the model for various tasks. Two such tasks are studied in this thesis: optimal design of experiments, where the task is to design the next measurements so that the parameter uncertainty is minimized, and model-based optimization, where a model-based quantity, such as the product yield in a chemical reaction model, is optimized. In this thesis, novel ways to perform these tasks are developed, based on the output of MCMC parameter estimation. A separate topic is dynamical state estimation, where the task is to estimate the dynamically changing model state, instead of static parameters. For example, in numerical weather prediction, an estimate of the state of the atmosphere must constantly be updated based on the recently obtained measurements. In this thesis, a novel hybrid state estimation method is developed, which combines elements from deterministic and random sampling methods.

Vuokamallisten kartonkipakkausten laadunvarmistuslaitteiston kehittäminen

Diplomityön tavoitteena oli kehittää vuokamallisille kartonkipakkauksille laadunvarmistuslaitteisto. Kirjallisen osan alussa esiteltiin vuokamallisten kartonkipakkausten valmistusprosessia. Tästä siirryttiin laatuasioihin, jossa tärkeimmät asiat olivat kartonkivuokien valmistuksessa esiintyvät laatupoikkeamat ja konenäkö. Tutkimusosan alussa esitellään Lappeenrannan teknillisessä yliopistossa kehitetty kartonkivuokien valmistuslinjasto. Tämän jälkeen vaatimuslistan pohjalta suunnitellaan kyseiseen linjastoon sopiva automaattinen laadunvalvontalaite, johon sisältyy myös kartonkivuokien siirtolaite. Suunnitteluprosessi aloitettiin koekuvaamalla kartonkivuokia erilaisilla kameroilla ja valaistusmenetelmillä. Koekuvausten perusteella valittiin konenäkölaitteisto. Tämän jälkeen toiminnoista luotiin periaatepiirroksia, joista kehitettiin varsinainen suunnitelma. Työn tuloksena saatiin suunnitelma konenäköön perustuvan automaattisen laadunvalvontalaitteen rakentamiselle.

Development of capacitive sensor for measuring soil water content

The irrigation management based on the monitoring of the soil water content allows for the minimization of the amount of water applied, making its use more efficient. Taking into account these aspects, in this work, a sensor for measuring the soil water content was developed to allow real time automation of irrigation systems. This way, problems affecting crop yielding such as irregularities in the time to turn on or turn off the pump, and excess or deficit of water can be solved. To develop the sensors were used stainless steel rods, resin, and insulating varnish. The sensors measuring circuit was based on a microcontroller, which gives its output signal in the digital format. The sensors were calibrated using soil of the type “Quartzarenic Neosoil”. A third order polynomial model was fitted to the experimental data between the values of water content corresponding to the field capacity and the wilting point to correlate the soil water content obtained by the oven standard method with those measured by the electronic circuit, with a coefficient of determination of 93.17%, and an accuracy in the measures of ±0.010 kg kg-1. Based on the results, it was concluded that the sensor and its implemented measuring circuit can be used in the automation process of irrigation systems.

Estimation of transpiration of the 'Valencia' orange young plant using thermal dissipation probe method

Most studies on measures of transpiration of plants, especially woody fruit, relies on methods of heat supply in the trunk. This study aimed to calibrate the Thermal Dissipation Probe Method (TDP) to estimate the transpiration, study the effects of natural thermal gradients and determine the relation between outside diameter and area of xylem in 'Valencia' orange young plants. TDP were installed in 40 orange plants of 15 months old, planted in boxes of 500 L, in a greenhouse. It was tested the correction of the natural thermal differences (DTN) for the estimation based on two unheated probes. The area of the conductive section was related to the outside diameter of the stem by means of polynomial regression. The equation for estimation of sap flow was calibrated having as standard lysimeter measures of a representative plant. The angular coefficient of the equation for estimating sap flow was adjusted by minimizing the absolute deviation between the sap flow and daily transpiration measured by lysimeter. Based on these results, it was concluded that the method of TDP, adjusting the original calibration and correction of the DTN, was effective in transpiration assessment.

Using an aerial system of remote sensing to detect different nutritional status in Brachiaria decumbens

The aim of this study was to use digital images acquired by cameras attached to a helium balloon to detect variation of the nutritional status in Brachiaria decumbens. The treatments consisted of five doses of nitrogen (0, 50, 100, 150 e 200kg ha-1) with six replications each, evaluated in a completely randomized statistical design. A remote sensing system composed of digital cameras and microcomputers was used for image acquisition, and a helium balloon lifted the cameras to the heights of 15, 20, 25 and 30m. A portable chlorophyll meter and analyses of leaf nitrogen content were used to make comparisons with data obtained by the remote sensing system. Data was acquired in two phases, in different climatic conditions. At the end of each phase, dry matter production was measured. Three vegetation indices were used to evaluate the detection of different nutritional status. The three indices were able to detect the effects of N doses. The indices constructed with the Green spectral band showed to be more efficient.

Liquid transportation and distribution during (re)wetting : impact on coated papers in printing

In many industrial applications, such as the printing and coatings industry, wetting of porous materials by liquids includes not only imbibition and permeation into the bulk but also surface spreading and evaporation. By understanding these phenomena, valuable information can be obtained for improved process control, runnability and printability, in which liquid penetration and subsequent drying play important quality and economic roles. Knowledge of the position of the wetting front and the distribution/degree of pore filling within the structure is crucial in describing the transport phenomena involved. Although exemplifying paper as a porous medium in this work, the generalisation to dynamic liquid transfer onto a surface, including permeation and imbibition into porous media, is of importance to many industrial and naturally occurring environmental processes. This thesis explains the phenomena in the field of heatset web offset printing but the content and the analyses are applicable in many other printing methods and also other technologies where water/moisture monitoring is crucial in order to have a stable process and achieve high quality end products. The use of near-infrared technology to study the water and moisture response of porous pigmented structures is presented. The use of sensitive surface chemical and structural analysis, as well as the internal structure investigation of a porous structure, to inspect liquid wetting and distribution, complements the information obtained by spectroscopic techniques. Strong emphasis has been put on the scale of measurement, to filter irrelevant information and to understand the relationship between interactions involved. The near-infrared spectroscopic technique, presented here, samples directly the changes in signal absorbance and its variation in the process at multiple locations in a print production line. The in-line non-contact measurements are facilitated by using several diffuse reflectance probes, giving the absolute water/moisture content from a defined position in the dynamic process in real-time. The nearinfrared measurement data illustrate the changes in moisture content as the paper is passing through the printing nips and dryer, respectively, and the analysis of the mechanisms involved highlight the roles of the contacting surfaces and the relative liquid carrier properties of both non-image and printed image areas. The thesis includes laboratory studies on wetting of porous media in the form of coated paper and compressed pigment tablets by mono-, dual-, and multi-component liquids, and paper water/moisture content analysis in both offline and online conditions, thus also enabling direct sampling of temporal water/moisture profiles from multiple locations. One main focus in this thesis was to establish a measurement system which is able to monitor rapid changes in moisture content of paper. The study suggests that near-infrared diffuse reflectance spectroscopy can be used as a moisture sensitive system and to provide accurate online qualitative indicators, but, also, when accurately calibrated, can provide quantification of water/moisture levels, its distribution and dynamic liquid transfer. Due to the high sensitivity, samples can be measured with excellent reproducibility and good signal to noise ratio. Another focus of this thesis was on the evolution of the moisture content, i.e. changes in moisture content referred to (re)wetting, and liquid distribution during printing of coated paper. The study confirmed different wetting phases together with the factors affecting each phase both for a single droplet and a liquid film applied on a porous substrate. For a single droplet, initial capillary driven imbibition is followed by equilibrium pore filling and liquid retreat by evaporation. In the case of a liquid film applied on paper, the controlling factors defining the transportation were concluded to be the applied liquid volume in relation to surface roughness, capillarity and permeability of the coating giving the liquid uptake capacity. The printing trials confirmed moisture gradients in the printed sheet depending on process parameters such as speed, fountain solution dosage and drying conditions as well as the printed layout itself. Uneven moisture distribution in the printed sheet was identified to be one of the sources for waving appearance and the magnitude of waving was influenced by the drying conditions.

Öljynjalostamon vetyverkon PINCH-analyysi

Tässä diplomityössä on tarkasteltu Porvoon öljynjalostamon vetyverkkoa ja pohdittu keinoja, joilla vedyn käyttöä jalostamolla voitaisiin tehostaan sekä polttokaasuverkkoon menevän vedyn määrä pienentää. Tarkastelun lähtökohtana toimii vetytaseen pohjalta laadittu vetypinch-analyysi. Kirjallisuusosassa on esitelty jalostamon vetyverkkoon kuuluvat yksiköt sekä käsitelty lyhyesti niiden toimintaa. Lisäksi on käsitelty vetypinch-analyysin periaate, sekä kuinka todelliset prosessirajoitteet voidaan huomioida sitä toteutettaessa. Kirjallisuusosan lopussa on esitetty miten vetyverkon vaiheittainen optimointi etenee. Työn soveltavassa osassa laadittiin vetyverkon virtauskaavio, jolla saatiin luotua kattava käsitys jalostamon vedynjakelusta. Virtauskaaviosta tehtiin yksinkertaistettu versio, jonka perusteella laadittiin vetytase. Vetytaseen pohjalta suoritettiin vetypinch-analyysi, jonka mukaan jalostamolla tuotettiin tasehetkellä ylimäärin vetyä. Vedyn käytön tehostamiseksi jalostamolla tulee rikkivedyn talteenottoyksikkö 2:n polttokaasuvirta pyrkiä minimoimaan tai hyödyntämään. Lisäksi virtausmittareiden mitoituspisteiden molekyylimassat tulisi muuttaa vastaamaan paremmin nykyistä ajotilannetta, sekä seurata niitä jatkossa säännöllisesti. Myös vetypitoisuutta mittaavien online-analysaattoreiden kalibroinnista tulee huolehtia, ja ottaa riittävästi kenttänäytteitä vetyverkosta. On huomattava, että öljynjalostamon vedyn tuotannon minimointi ei ole aina automaattisesti taloudellisin ratkaisu. Joissain tapauksissa vedyn osapaineen nostaminen vetyä kuluttavan yksikön reaktorissa voi lisätä yksikön tuottavuutta niin paljon, että se kompensoi lisääntyneestä vedyn tuotannosta aiheutuvat kustannukset.

Elever syns på nätet : multimodala texter och autentiska mottagare

This study is based on the notion that all students are likely to have a computer of some kind as their primary tool at school within a few years. The overall aim is to contribute to the knowledge of what this development of computer-assisted multimodal text production and communication on and over the net may entail in a school context. The study has an abductive approach drawing on theory from Media and Communication studies and from Pedagogy - particularly on media peda-gogy, multimodality, storytelling, conversation research and deliberative democracy – and is based on a DBR project in three schools. The empirical data are retrieved from four school classes, school years 4 and 5, with good access to computers and digital cameras. The classes have used the class blogs to tell the blog visitors about their school work and Skype to communicate with other classes in Sweden and Tanzania. A variety of research methods was employed: content analysis of texts, observations with field notes and camera documentation, interviews with individual students, group interviews with teachers and students, and a small survey. The study is essentially qualitative, focusing on students’ different perceptions. A small quantitative study was conducted to determine if any factors and variables could be linked to each other and to enable comparisons of the surveyed group with other research results. The results suggest that more computers at school offer more opportunities for real-life assignments and the chance to secure an authentic audience to the students’ production; primarily the students’ parents and relatives, students in the same class and at other schools. A theoretical analysis model to determine the degree of reality and authenticity in various school assignments was developed. The results also indicate that having access to cameras for documenting various events in the classes and to an authentic audience can create new opportunities for storytelling that have not been practiced previously at school. The documentary photo invites a viewer into the present tense of the image and the location where the picture was taken, whoever took the picture. It is used by the students and here too, a model has been developed to describe this relationship. The study also focuses on the freedom of expression and democracy. One of the more unexpected findings is that the students in the study did not see that they can influence other people’s perceptions or change various power structures through communication on the web, neither in nor outside of school.

Weed mapping using a machine vision system

Weed mapping is a useful tool for site-specific herbicide applications. The objectives of this study were (1) to determine the percentage of land area covered by weeds in no-till and conventionally tilled fields of common bean using digital image processing and geostatistics, and (2) to compare two types of cameras. Two digital cameras (color and infrared) and a differential GPS were affixed to a center pivot structure for image acquisition. Sample field images were acquired in a regular grid pattern, and the images were processed to estimate the percentage of weed cover. After calculating the georeferenced weed percentage values, maps were constructed using geostatistical techniques. Based on the results, color images are recommended for mapping the percentage of weed cover in no-till systems, while infrared images are recommended for weed mapping in conventional tillage systems.