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Search Results: 1 - 10 of 138 matches for " Eirik Kaarstad "
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Theory and Application of Buoyancy in Wells
Eirik Kaarstad,Bernt Sigve Aadnoy
Modern Applied Science , 2011, DOI: 10.5539/mas.v5n3p15
Abstract: The paper presents a generalized buoyancy model for application in wells, called the generalized Archimedes’ principle. There exists confusion in the oil industry about buoyancy effects as related to the force-area method (also known as piston force method) or the Archimedes’ principle, the stability force in buckling and axial forces during well intervention operations. This paper will present a general model called the generalized Archimedes’ principle, which is valid for all cases. The paper presents examples of application to ordinary drilling operations, deviated wells and different fluid densities inside and outside the pipe. For well intervention scenarios, the effects of wellhead shut-in pressures on buoyancy are demonstrated. This simple model, not requiring use of a “stability force”, can also analyze buckling. Two field cases are presented to demonstrate the use of the generalized Archimedes’ principle in torque and drag analysis. When the drill string is run in hole having a float valve installed, the buoyancy factor changes depending on how much air is in the drill string. The generalized Archimedes’ principle may simply be applied to the torque and drag model for accurate lowering force calculations. Using the generalized Archimedes’ principle, a correct assessment of the real axial load of the pipe is obtained, a critical factor for tubular work in petroleum wells. The model is also significant as it is simple and can be applied to all well operations.
Improvement of Torque-and-Drag Modeling in Long-Reach Wells
Seyed Ahmad Mirhaj,Eirik Kaarstad,Bernt Sigve Aadnoy
Modern Applied Science , 2011, DOI: 10.5539/mas.v5n5p10
Abstract: Torque and drag modeling is regarded as an invaluable process to assist in well planning and to predict and prevent drilling problems. It discusses how to use torque and drag calculations and measurements to plan long-reach well profiles, to execute drilling operations that minimize torque and drag effects and to monitor hole cleaning. In this study a general overview on most of the available literature on the subject is presented. Different models that have been developed for torque and drag predictions along with pros and cons of the models will be discussed. The application of our new fully 3-dimensional analytical friction model will be presented. Moreover a new criterion has been implemented into the new model in order to capture the effect of weight in the horizontal section especially when BHA is dragged into/out of the wellbore. The model validity will be checked by applying the model for two field cases of ERD wells in North Sea. Field cases also demonstrate the importance of buoyancy effects, tripping speed, hydraulic piston force, pipe stiffness as well as well path effects.
Indo-European syntax and pragmatics: contrastive approaches
Eirik Welo
Oslo Studies in Language , 2011,
Abstract: This volume presents papers from the International Workshop on Indo-European Syntax held at the University of Georgia in Athens,Georgia in May 2009. The workshop was a cooperative effort between the Pragmatic Resources in Old Indo-European Languages (PROIEL) project at the University of Oslo and the University of Georgia. The papers in the volume study the interaction between syntax and discourse structure in various old Indo-European languages, in most cases with an explicitly contrastive focus.
Introduction
Eirik Welo
Oslo Studies in Language , 2011,
Abstract: An introduction to the papers in the volume and a short presentation of the PROIEL project.
An invariant bayesian model selection principle for gaussian data in a sparse representation
Eirik Fossgaard
Mathematics , 2005,
Abstract: We develop a code length principle which is invariant to the choice of parameterization on the model distributions. An invariant approximation formula for easy computation of the marginal distribution is provided for gaussian likelihood models. We provide invariant estimators of the model parameters and formulate conditions under which these estimators are essentially posteriori unbiased for gaussian models. An upper bound on the coarseness of discretization on the model parameters is deduced. We introduce a discrimination measure between probability distributions and use it to construct probability distributions on model classes. The total code length is shown to equal the NML code length of Rissanen to within an additive constant when choosing Jeffreys prior distribution on the model parameters together with a particular choice of prior distribution on the model classes. Our model selection principle is applied to a gaussian estimation problem for data in a wavelet representation and its performance is tested and compared to alternative wavelet-based estimation methods in numerical experiments
On the Minimum Distance of Array-Based Spatially-Coupled Low-Density Parity-Check Codes
Eirik Rosnes
Mathematics , 2015,
Abstract: An array low-density parity-check (LDPC) code is a quasi-cyclic LDPC code specified by two integers $q$ and $m$, where $q$ is an odd prime and $m \leq q$. The exact minimum distance, for small $q$ and $m$, has been calculated, and tight upper bounds on it for $m \leq 7$ have been derived. In this work, we study the minimum distance of the spatially-coupled version of these codes. In particular, several tight upper bounds on the optimal minimum distance for coupling length at least two and $m=3,4,5$, that are independent of $q$ and that are valid for all values of $q \geq q_0$ where $q_0$ depends on $m$, are presented. Furthermore, we show by exhaustive search that by carefully selecting the edge spreading or unwrapping procedure, the minimum distance (when $q$ is not very large) can be significantly increased, especially for $m=5$.
Further Results on Quadratic Permutation Polynomial-Based Interleavers for Turbo Codes
Eirik Rosnes
Mathematics , 2011,
Abstract: An interleaver is a critical component for the channel coding performance of turbo codes. Algebraic constructions are of particular interest because they admit analytical designs and simple, practical hardware implementation. Also, the recently proposed quadratic permutation polynomial (QPP) based interleavers by Sun and Takeshita (IEEE Trans. Inf. Theory, Jan. 2005) provide excellent performance for short-to-medium block lengths, and have been selected for the 3GPP LTE standard. In this work, we derive some upper bounds on the best achievable minimum distance dmin of QPP-based conventional binary turbo codes (with tailbiting termination, or dual termination when the interleaver length N is sufficiently large) that are tight for larger block sizes. In particular, we show that the minimum distance is at most 2(2^{\nu +1}+9), independent of the interleaver length, when the QPP has a QPP inverse, where {\nu} is the degree of the primitive feedback and monic feedforward polynomials. However, allowing the QPP to have a larger degree inverse may give strictly larger minimum distances (and lower multiplicities). In particular, we provide several QPPs with an inverse degree of at least three for some of the 3GPP LTE interleaver lengths giving a dmin with the 3GPP LTE constituent encoders which is strictly larger than 50. For instance, we have found a QPP for N=6016 which gives an estimated dmin of 57. Furthermore, we provide the exact minimum distance and the corresponding multiplicity for all 3GPP LTE turbo codes (with dual termination) which shows that the best minimum distance is 51. Finally, we compute the best achievable minimum distance with QPP interleavers for all 3GPP LTE interleaver lengths N <= 4096, and compare the minimum distance with the one we get when using the 3GPP LTE polynomials.
Alternative Local Discriminant Bases Using Empirical Expectation and Variance Estimation
Eirik Fossgaard
Computer Science , 1999,
Abstract: We propose alternative discriminant measures for selecting the best basis among a large collection of orthonormal bases for classification purposes. A generalization of the Local Discriminant Basis Algorithm of Saito and Coifman is constructed. The success of these new methods is evaluated and compared to earlier methods in experiments.
Fast Computational Algorithms for the Discrete Wavelet Transform and Applications of Localized Orthonormal Bases in Signal Classification
Eirik Fossgaard
Computer Science , 1999,
Abstract: We construct an algorithm for implementing the discrete wavelet transform by means of matrices in SO_2(R) for orthonormal compactly supported wavelets and matrices in SL_m(R), m > = 2, for compactly supported biorthogonal wavelets. We show that in 1 dimension the total operation count using this algorithm can be reduced to about 50% of the conventional convolution and downsampling by 2-operation for both orthonormal and biorthogonal filters. In the special case of biorthogonal symmetric odd-odd filters, we show an implementation yielding a total operation count of about 38% of the conventional method. In 2 dimensions we show an implementation of this algorithm yielding a reduction in the total operation count of about 70% when the filters are orthonormal, a reduction of about 62% for general biorthogonal filters, and a reduction of about 70% if the filters are symmetric odd-odd length filters. We further extend these results to 3 dimensions. We also show how the SO_2(R)-method for implementing the discrete wavelet transform may be exploited to compute short FIR filters, and we construct edge mappings where we try to improve upon the degree of preservation of regularity in the conventional methods. We also consider a two-class waveform discrimination problem. A statistical space-frequency analysis is performed on a training data set using the LDB-algorithm of N.Saito and R.Coifman. The success of the algorithm on this particular problem is evaluated on a disjoint test data set.
Determinants of Egyptian Agricultural Exports: A Gravity Model Approach  [PDF]
Assem Abu Hatab, Eirik Romstad, Xuexi Huo
Modern Economy (ME) , 2010, DOI: 10.4236/me.2010.13015
Abstract: In this paper, a gravity model approach was employed to analyze the main factors influencing Egypt’s agricultural exports to its major trading partners for the period 1994 to 2008. Our findings are that a one percent increase in Egypt’s GDP results in roughly a 5.42 percent increase in Egypt’s agricultural export flows. In contrast, the increase in Egypt’s GDP per capita causes exports to decrease, which is attributed to the fact that an increase in economic growth, besides the increasing population, raises the demand per capita for all normal goods. Hence, domestic growth per se leads to reduced exports. The exchange volatility has a significant positive coefficient, indicating that depreciation in Egyptian Pound against the currencies of its partners stimulates agricultural exports. Transportation costs, proxied by distance, are found to have a negative influence on agricultural exports. These results are important for trade policy formulation to promote Egyptian agricultural exports to the world market.
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