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15 results on '"Wilhelmsen, Nils"'

10. Minimum Time Bilateral Observer Design for 2x2 Systems of Linear Hyperbolic PDEs - With Application to Oil Well Drilling State Estimation for Improved Kick Handling

Author

Wilhelmsen, Nils Christian Aars and Aamo, Ole Morten

Subjects
Kybernetikk og robotikk
Abstract

We consider state estimation of 1D systems of 2x2 linear first-order coupled hyperbolic PDEs, consisting of two distributed states propagating information in opposite directions but interacting across the spatial domain. These types of systems can be used to model various technical and physical phenomena. In most practical situations only measurements from boundary points are available, and the interior states must from these be deduced. We derive a bilateral boundary observer, utilizing sensing at both boundaries of the spatial domain, to provide state estimates of the 2x2 system which are correct within a finite and theoretically minimal amount of time. This optimal convergence time is smaller than the corresponding lowest possible convergence time for unilateral boundary observers, being observers only using measurements from a single boundary point. As a first step in the derivation of the 2x2 bilateral observer, we derive for a 1D system of 2+2 linear first-order coupled hyperbolic PDEs, consisting of four distributed states coupled point-wise across the domain, of which two transmit information leftwards and the other two information rightwards, a boundary observer which relies on measurements from a single boundary that is collocated with actuation. The design is achieved by using infinite dimensional backstepping through applying a Volterra integral transformation composed with a Fredholm integral transformation. We show that this observer converges within the theoretical lower bound for convergence time of unilateral boundary observers for 2+2 systems. Next, we split the spatial domain of the 2x2 system at an interior point, and transform it to a 2+2 system by re-scaling of the sub-domains and redefining boundary conditions. A bilateral observer for the 2x2 system is subsequently derived from the previously derived minimum time unilateral observer for the 2+2 system. How the splitting point should be chosen to achieve minimum time convergence for the bilateral 2x2 observer is shown. To demonstrate the efficiency of the 2x2 bilateral observer, we implement 2x2 systems and their corresponding minimum time bilateral observers in simulations. These are bench-marked against 2x2 unilateral boundary observers only sensing a single boundary point, and it is found that the bilateral observers have superior performance to the unilateral observers. As an application of the theory derived, it is next shown how the 2x2 system can be used to model the pressure and flow dynamics of drilling fluid during oil well drilling. A scenario where the observers are used for state estimation during kick handling is considered. The scenario is simulated and it is shown that an observer using both topside and downhole measurements during drilling has a more efficient response with respect to correctly estimating the states of the drilling fluid than an observer only utilizing topside measurements, something that can contribute to safer kick handling.

Published
2018

12. Minimum time observer designs for n+mlinear hyperbolic systems with unilateral, bilateral or pointwise in-domain sensing

Author

Wilhelmsen, Nils Christian A., Anfinsen, Henrik, and Aamo, Ole Morten

Abstract

In this paper we derive minimum time convergent observers for n+m1systems of linear coupled first-order 1-D hyperbolic PDEs, that use either unilateral (single boundary measured), bilateral (both boundaries measured) or pointwise in-domain sensing. First, a Volterra integral transformation is combined with a Fredholm integral transformation to derive a minimum time unilateral observer for n+msystems. Then, it is shown that an n+msystem with bilateral sensing can be transformed to an (n+m)+(n+m)system with unilateral sensing via an invertible coordinate transformation. The n+mbilateral observer is subsequently obtained from the (n+m)+(n+m)minimum time unilateral observer, and it is shown that it converges in a theoretical minimum time for bilateral sensing. In a similar fashion, the observer using pointwise in-domain measurement is derived using the same techniques. The performances of the n+mbilateral and unilateral observers are demonstrated in simulations.

Published
2021
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14. Radiation doses to Norwegian heart-transplanted patients undergoing annual coronary angiography.

Author

Seierstad, Therese, Friberg, Eva Godske, Lervåg, Christoffer, Widmark, Anders, Wilhelmsen, Nils, and Stranden, Erling

Subjects
HEART transplantation, TRANSPLANTATION of organs, tissues, etc., ANGIOGRAPHY, RADIATION
Abstract

Heart-transplanted patients in Norway undergo annual coronary angiography (CA). The aims of this study were to establish a conversion factor between dose-area product and effective dose for these examinations and to use this to evaluate the accumulated radiation dose and risks associated with annual CA. An experienced cardiac interventionist performed a simulated examination on an Alderson phantom loaded with thermoluminescence dosemeters. The simulated CA examination yielded a dose-area product of 17 Gy cm2 and an effective dose of 3.4 mSv: the conversion factor between dose-area product and effective dose was 0.20 mSv Gy cm−2. Dose-area product values from 200 heart-transplanted patients that had undergone 906 CA examinations between 2001 and 2008 were retrieved from the institutional database. Mean dose-area product from annual CA was 25 Gy cm2, ranging from 2 to 140 Gy cm2. Mean number of CA procedure was 8 (range, 1–23). Mean accumulated effective dose for Norwegian heart-transplanted patients between 2001 and 2008 was 34 mSv (range, 5–113 mSv). Doses and radiation risks for heart-transplanted patients are generally low, because most heart transplantations are performed on middle-aged patients with limited life expectancy. Special concern should however be taken to reduce doses for young heart-transplanted patients who are committed to lifelong follow-up of their transplanted heart. [ABSTRACT FROM PUBLISHER]

Published
2012
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15. Assessment of wasted myocardial work: a novel method to quantify energy loss due to uncoordinated left ventricular contractions.

Author

Russell K, Eriksen M, Aaberge L, Wilhelmsen N, Skulstad H, Gjesdal O, Edvardsen T, and Smiseth OA

Subjects
Aged, Animals, Biomechanical Phenomena, Bundle-Branch Block diagnosis, Bundle-Branch Block physiopathology, Cardiac Resynchronization Therapy, Disease Models, Animal, Dogs, Female, Heart Failure diagnosis, Heart Failure physiopathology, Heart Failure therapy, Humans, Male, Middle Aged, Models, Cardiovascular, Time Factors, Ventricular Dysfunction, Left diagnosis, Ventricular Dysfunction, Left physiopathology, Ventricular Dysfunction, Left therapy, Ventricular Pressure, Bundle-Branch Block metabolism, Energy Metabolism, Heart Failure metabolism, Myocardial Contraction, Myocardium metabolism, Ventricular Dysfunction, Left metabolism, Ventricular Function, Left
Abstract

Left ventricular (LV) dyssynchrony reduces myocardial efficiency because work performed by one segment is wasted by stretching other segments. In the present study, we introduce a novel noninvasive clinical method that quantifies wasted energy as the ratio between work consumed during segmental lengthening (wasted work) divided by work during segmental shortening. The wasted work ratio (WWR) principle was studied in 6 anesthetized dogs with left bundle branch block (LBBB) and in 28 patients with cardiomyopathy, including 12 patients with LBBB and 10 patients with cardiac resynchronization therapy. Twenty healthy individuals served as controls. Myocardial strain was measured by speckle tracking echocardiography, and LV pressure (LVP) was measured by micromanometer and a previously validated noninvasive method. Segmental work was calculated by multiplying strain rate and LVP to get instantaneous power, which was integrated to give work as a function of time. A global WWR was also calculated. In dogs, WWR by estimated LVP and strain showed a strong correlation (r = 0.94) and good agreement with WWR by the LV micromanometer and myocardial segment length by sonomicrometry. In patients, noninvasive WWR showed a strong correlation (r = 0.96) and good agreement with WWR using the LV micromanometer. Global WWR was 0.09 ± 0.03 in healthy control subjects, 0.36 ± 0.16 in patients with LBBB, and 0.21 ± 0.09 in cardiomyopathy patients without LBBB. Cardiac resynchronization therapy reduced global WWR from 0.36 ± 0.16 to 0.17 ± 0.07 (P < 0.001). In conclusion, energy loss due to incoordinated contractions can be quantified noninvasively as the LV WWR. This method may be applied to evaluate the mechanical impact of dyssynchrony.

Published
2013
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