On Variational Ensemble Kalman Filtering

The Extended Kalman Filter (EKF) and four dimensional assimilation variational method (4D-VAR) are both advanced data assimilation methods. The EKF is impractical in large scale problems and 4D-VAR needs much effort in building the adjoint model. In this work we have formulated a data assimilation method that will tackle the above difficulties. The method will be later called the Variational Ensemble Kalman Filter (VEnKF). The method has been tested with the Lorenz95 model. Data has been simulated from the solution of the Lorenz95 equation with normally distributed noise. Two experiments have been conducted, first with full observations and the other one with partial observations. In each experiment we assimilate data with three-hour and six-hour time windows. Different ensemble sizes have been tested to examine the method. There is no strong difference between the results shown by the two time windows in either experiment. Experiment I gave similar results for all ensemble sizes tested while in experiment II, higher ensembles produce better results. In experiment I, a small ensemble size was enough to produce nice results while in experiment II the size had to be larger. Computational speed is not as good as we would want. The use of the Limited memory BFGS method instead of the current BFGS method might improve this. The method has proven succesful. Even if, it is unable to match the quality of analyses of EKF, it attains significant skill in forecasts ensuing from the analysis it has produced. It has two advantages over EKF; VEnKF does not require an adjoint model and it can be easily parallelized.

Power line communication in motor cables of variable-speed electric drives − analysis and

Data transmission between an electric motor and a frequency converter is required in variablespeed electric drives because of sensors installed at the motor. Sensor information can be used for various useful applications to improve the system reliability and its properties. Traditionally, the communication medium is implemented by an additional cabling. However, the costs of the traditional method may be an obstacle to the wider application of data transmission between a motor and a frequency converter. In any case, a power cable is always installed between a motor and a frequency converter for power supply, and hence it may be applied as a communication medium for sensor level data. This thesis considers power line communication (PLC) in inverter-fed motor power cables. The motor cable is studied as a communication channel in the frequency band of 100 kHz−30 MHz. The communication channel and noise characteristics are described. All the individual components included in a variable-speed electric drive are presented in detail. A channel model is developed, and it is verified by measurements. A theoretical channel information capacity analysis is carried out to estimate the opportunities of a communication medium. Suitable communication and forward error correction (FEC) methods are suggested. A general method to implement a broadband and Ethernet-based communication medium between a motor and a frequency converter is proposed. A coupling interface is also developed that allows to install the communication device safely to a three-phase inverter-fed motor power cable. Practical tests are carried out, and the results are analyzed. Possible applications for the proposed method are presented. A speed feedback motor control application is verified in detail by simulations and laboratory tests because of restrictions for the delay in the feedback loop caused by PLC. Other possible applications are discussed at a more general level.

Cumulative Costs of Caries Prevention and Treatment in Children - with Special Reference to Work Division and Cohort Effect

Lapsen karieshoidon kustannuskertymän muutokset ja karieshoidon toimintakäytäntöjen yhteys kustannuksiin Tutkimuksen tavoitteena oli mitata terveyskeskuksessa hoidettavien lasten karieshoidon kumulatiivisia kustannuksia ja verrata niitä kahden erilaisen toimintatavan välillä. Lisäksi tarkasteltiin lasten hampaiden terveyttä. Tutkimus tehtiin julkisen palvelutuottajan näkökulmasta. Tutkimusaineisto kerättiin Kemin ja Tornion terveyskeskusten suun terveydenhuollon potilaskertomuksista. Kemin kohortit 1980, 1983 ja 1986 (n = 600) ja Tornion kohortit 1980 ja 1992 (n = 400) edustivat perinteistä ja Kemin kohortit 1989, 1992 ja 1995 (n = 600) uutta toimintatapaa työnjaon ja ehkäisyn ajoituksen suhteen. Kohortteja ja kaupunkeja verrattiin hampaiden terveyden (dmft/DMFT = 0 ja dmft ja DMFT keskiarvot 5 ja 12 vuoden iässä) ja voimavarojen käytön suhteen. Panoskäyttö johdettiin käyntimäärien avulla laskennallisen työajan kautta. Kustannuskertymät muodostettiin käyttämällä henkilöstömenoista laskettuja suorittajakohtaisia yksikkökustannuksia. Panoskäytön ja yksikkökustannusten kautta muodostettiin kustannuskertymät. Kustannusten ja terveysvaikutusten suhteita arvioitiin kustannus-vaikuttavuusanalyysissä. Suuhygienistien työpanosta hyödyntävällä varhaisen ehkäisyn toimintamallilla saavutettiin vähäisemmin kustannuksin alle kouluiässä parempi ja kouluiässä yhtä hyvä hammasterveys kuin perinteisellä, enemmän hammaslääkärien työpanokseen perustuvalla tavalla. Karieksen hoitoon liittyvien käyntien määrä oli nuorimmissa syntymävuosikohorteissa pienempi kuin vanhimmissa kohorteissa. Käynnit hammaslääkärissä vähenivät eniten. Toimintatavalla oli merkittävä vaikutus lapsen karieshoidon kokonaiskustannuksiin. Herkkyysanalyysin mukaan karieshoidon kustannukset olivat työnjakoa hyödyntämällä kolmanneksen pienemmät, kuin jos hoidon suorittajana olisi ollut ainoastaan hammaslääkäri-hoitaja työpari. Lasten karieshoidon kustannusvaikuttavuus kohentui molemmissa terveyskeskuksissa nuoremmissa kohorteissa vanhempiin verrattuna. Suun terveydenhuollon potilaskertomuksia olisi hyödynnettävä toiminnan kehittämisessä. Varhaisen ehkäisyn avulla voitaisiin kaikkien suun terveydenhuollon ammattihenkilöiden työpanos kohdentaa kustannustehokkaasti.

Kalman Filtering in Online Paper Quality Assessment

Controlling the quality variables (such as basis weight, moisture etc.) is a vital part of making top quality paper or board. In this thesis, an advanced data assimilation tool is applied to the quality control system (QCS) of a paper or board machine. The functionality of the QCS is based on quality observations that are measured with a traversing scanner making a zigzag path. The basic idea is the following: The measured quality variable has to be separated into its machine direction (MD) and cross direction (CD) variations due to the fact that the QCS works separately in MD and CD. Traditionally this is done simply by assuming one scan of the zigzag path to be the CD profile and its mean value to be one point of the MD trend. In this thesis, a more advanced method is introduced. The fundamental idea is to use the signals’ frequency components to represent the variation in both CD and MD. To be able to get to the frequency domain, the Fourier transform is utilized. The frequency domain, that is, the Fourier components are then used as a state vector in a Kalman filter. The Kalman filter is a widely used data assimilation tool to combine noisy observations with a model. The observations here refer to the quality measurements and the model to the Fourier frequency components. By implementing the two dimensional Fourier transform into the Kalman filter, we get an advanced tool for the separation of CD and MD components in total variation or, to be more general, for data assimilation. A piece of a paper roll is analyzed and this tool is applied to model the dataset. As a result, it is clear that the Kalman filter algorithm is able to reconstruct the main features of the dataset from a zigzag path. Although the results are made with a very short sample of paper roll, it seems that this method has great potential to be used later on as a part of the quality control system.

Simulating the performance of paper machine control

The topic of this thesis is the simulation of a combination of several control and data assimilation methods, meant to be used for controlling the quality of paper in a paper machine. Paper making is a very complex process and the information obtained from the web is sparse. A paper web scanner can only measure a zig zag path on the web. An assimilation method is needed to process estimates for Machine Direction (MD) and Cross Direction (CD) profiles of the web. Quality control is based on these measurements. There is an increasing need for intelligent methods to assist in data assimilation. The target of this thesis is to study how such intelligent assimilation methods are affecting paper web quality. This work is based on a paper web simulator, which has been developed in the TEKES funded MASI NoTes project. The simulator is a valuable tool in comparing different assimilation methods. The thesis contains the comparison of four different assimilation methods. These data assimilation methods are a first order Bayesian model estimator, an ARMA model based on a higher order Bayesian estimator, a Fourier transform based Kalman filter estimator and a simple block estimator. The last one can be considered to be close to current operational methods. From these methods Bayesian, ARMA and Kalman all seem to have advantages over the commercial one. The Kalman and ARMA estimators seems to be best in overall performance.