Survey strategies to quantify and optimize detecting probability of a CO2 seep in a varying marine environment

AbstractDesigning a marine monitoring program that detects CO2 leaks from subsea geological storage projects is challenging. The high variability of the environment may camouflage the anticipated anisotropic signal from a leak and there are a number of leak scenarios. Marine operations are also costly constraining the availability of measurements. A method based on heterogeneous leak scenarios and anisotropic predictions of chemical footprint under varying current conditions is presented. Through a cost function optimal placement of sensors can be given both for fixed installations and series of measurements during surveys. Ten fixed installations with an optimal layout is better than twenty placed successively at the locations with highest leakage probability. Hence, optimal localizations of installations offers cost reduction without compromising precision of a monitoring program, e.g. quantifying and reduce probabilities of false alarm under control. An optimal cruise plan for surveys, minimizing transit time and operational costs, can be achieved

Assessing Model Uncertainties Through Proper Experimental Design

This paper assesses how parameter uncertainties in the model for rise velocity of CO2 droplets in the ocean cause uncertainties in their rise and dissolution in marine waters. The parameter uncertainties in the rise velocity for both hydrate coated and hydrate free droplets are estimated from experiment data. Thereafter the rise velocity is coupled with a mass transfer model to simulate the fate of dissolution of a single droplet. The assessment shows that parameter uncertainties are highest for large droplets. However, it is also shown that in some circumstances varying the temperature gives significant change in rise distance of droplets.publishedVersio

Layout of CCS monitoring infrastructure with highest probability of detecting a footprint of a CO2 leak in a varying marine environment

Monitoring of the marine environment for indications of a leak, or precursors of a leak, will be an intrinsic part of any subsea CO2 storage projects. A real challenge will be quantification of the probability of a given monitoring program to detect a leak and to design the program accordingly. The task complicates by the number of pathways to the surface, difficulties to estimate probabilities of leaks and fluxes, and predicting the fluctuating footprint of a leak. The objective is to present a procedure for optimizing the layout of a fixed array of chemical sensors on the seafloor, using the probability of detecting a leak as metric. A synthetic map from the North Sea is used as a basis for probable leakage points, while the spatial footprint is based on results from a General Circulation Model. Compared to an equally spaced array the probability of detecting a leak can be nearly doubled by an optimal placement of the available sensors. It is not necessarily best to place the first in the location of the highest probable leakage point, one sensor can monitor several potential leakage points. The need for a thorough baseline in order to reduce the detection threshold is shown.publishedVersio

A SAT Approach to Clique-Width

Clique-width is a graph invariant that has been widely studied in combinatorics and computer science. However, computing the clique-width of a graph is an intricate problem, the exact clique-width is not known even for very small graphs. We present a new method for computing the clique-width of graphs based on an encoding to propositional satisfiability (SAT) which is then evaluated by a SAT solver. Our encoding is based on a reformulation of clique-width in terms of partitions that utilizes an efficient encoding of cardinality constraints. Our SAT-based method is the first to discover the exact clique-width of various small graphs, including famous graphs from the literature as well as random graphs of various density. With our method we determined the smallest graphs that require a small pre-described clique-width.Comment: proofs in section 3 updated, results remain unchange

Den døande kreftpasienten i heimen: litteraturstudie

Bakgrunn og hensikt: kreft er ein verdskjend sjukdom. Kvart år døyr mange av kreft, det er allmennkjend og akseptert at desse personane skal få lov å døy i heimen. Det å skulle pleie ein døande kreftpasient i heimen vert sett på som ei krevjande oppgåve, og dei fleste pasientane døyr på ein institusjon eller i eit sjukehus. Hensikta med denne studien er å finne ut kva som må være til stades for at pasienten skal få den best moglige pleie i heimen fram til sin død. Metode: metoden som er brukt er litteraturstudie. Ved denne typen metode finner ein fram relevant litteratur ut i frå bøker, godkjende nettstader og artiklar som omhandlar lindring av smerter hos kreftpasientar. For å finne svar på problemstillinga har det gjennom heile oppgåva vert lest litteratur som har gitte relevanskriteria, der urelevant litteratur har blitt luka bort. Det er også blitt lest fleire forskingsartiklar som er relevant for temaet. Resultat: Å pleie ein døande kreftpasienten i heimen er svært samansatt. Det kan oppstå mange komplikasjonar som sjukepleiaren må ta omsyn til, men det er likevel gjennomførlig. Det som må være til stades er engasjerte, motiverte og dyktige sjukepleiarar. Ein sjukepleiar skal ikkje være redd for og gå inn i vanskelige situasjonar, dei kan heller ikkje være redd for å kjenne på eigne avgrensingar. Best mulig pleie er også at sjukepleiaren ser på kvar enkeltpasient som eit individ og behandlar det der etter. Håpet viser seg også å være viktig for den døande, sjukepleiaren må også ivareta dette hos disse pasientane. Individualitet er med på og gjere kvart enkelt menneskje til ein person. Ein må alltid hugse på at god pleie til ein pasient ikkje synonymt med god pleie for ein annan. Det er også viktig å ta med pasienten i si eiga behandling

Monotonicity Conditions for Discretization of Parabolic Conservation Laws

In the recent years monotonicity of control volume methods for elliptic equations has been studied. A discrete maximum principle is established in Keilegavlen et al. [18], and a set of monotonicity conditions on general quadrilateral grids has been derived in Nordbotten et al. [23]. Monotonicity criteria for parabolic equations have not yet been studied. We will therefore in this thesis extend the already existing monotonicity conditions for elliptic equations to a set of conditions for parabolic equations. These conditions is derived under the assumption that the discrete maximum principle for parabolic equations is the same as the principle for elliptic problem. It turns out that these conditions are stricter than the elliptic conditions. Since the maximum principle for the time discrete parabolic equation is different from the principle for the elliptic equation, it may be necessary to reformulate the discrete maximum principle. It is not obvious how this shall be done. We will therefore discuss various formulations of time discrete maximum principles together with numerical examples

Assessing Model Uncertainties Through Proper Experimental Design

This paper assesses how parameter uncertainties in the model for rise velocity of CO2 droplets in the ocean cause uncertainties in their rise and dissolution in marine waters. The parameter uncertainties in the rise velocity for both hydrate coated and hydrate free droplets are estimated from experiment data. Thereafter the rise velocity is coupled with a mass transfer model to simulate the fate of dissolution of a single droplet. The assessment shows that parameter uncertainties are highest for large droplets. However, it is also shown that in some circumstances varying the temperature gives significant change in rise distance of droplets