Wyniki wyszukiwania - BazTech

1

Modeling total surface current in the Persian Gulf and the Oman Sea by combination of geodetic and hydrographic observations and assimilation with in situ current meter data

Pirooznia Mahmoud, Naeeni Mehdi Raoofian, Tourian Mohammad J.

Acta Geophysica

|

2023

|

Vol. 71, no. 6

2839--2863

EN

Surface currents in oceanic environment are of vital importance from economical, biological and environmental aspects. Modelling ocean currents has generally been performed using numerical ocean circulation models as a solution to initial-boundary value problems in oceanic domain. Due to lack of knowledge about model parameters as well as initial and boundary values, they need to be externally calibrated for accurate local and regional applications. In this study, an alternative approach is proposed to incorporate spaceborne geodetic observations as well as hydrographic data to estimate the total surface current in the Persian Gulf and the Oman Sea. Being the data-driven approach, the method is comparable to numerical ocean models and regionally it is more accurate and simpler in application. The proposed method focuses on the computation of dynamic topography (DT) by least squares variance component estimation combining two different schemes. They are (1) DT estimation via direct observations of sea surface height from satellite altimetry and (2) steric and non-steric modeling of sea level anomaly using temperature and salinity data for the steric component; and Gravity Recovery and Climate Experiment observations for the non-steric component. Ultimately, the total surface current is obtained by computing the horizontal gradient of DT using geostrophic equation and adding the components of the Ekman current. Moreover, the estimated total surface current is further improved by assimilating with in situ current meter data using 3D-Variational data assimilation method and it is validated against two control stations. This assimilation leads to improvement of about 3 to 15 cm/s in total surface current computed using geostrophic equation and Ekman current. Besides, to illustrate the significance of the proposed approach, the estimated total surface current is externally validated and compared with the output of Copernicus Marine Environment Monitoring Service (CMEMS), as a numerical ocean model developed for oceanographic applications. Our comparison reveals that the proposed method is more accurate and reliable than CMEMS products. As for the circulation and current pattern, the estimated surface velocities reveal the existence of eddies in the region of the Persian Gulf and the Oman Sea, indicating the occurrence of cyclonic and anti-cyclonic circulations. Moreover, they elucidate that the velocities are lower in spring and summer and higher in autumn and winter.

2

An inverse backward problem for degenerate two-dimensional parabolic equation

Atifi Khalid, Essoufi El-Hassan, Khouiti Bouchra

Opuscula Mathematica

|

2020

|

Vol. 40, no. 4

427--449

EN

This paper deals with the determination of an initial condition in the degenerate two-dimensional parabolic equation [formula], where Ω is an open, bounded subset of R2, a [formula] with a ≥0 everywhere, and [formula], with initial and boundary conditions [formula] from final observations. This inverse problem is formulated as a minimization problem using the output least squares approach with the Tikhonov regularization. To show the convergence of the descent method, we prove the Lipschitz continuity of the gradient of the Tikhonov functional. Also we present some numerical experiments to show the performance and stability of the proposed approach.

3

A data assimilation approach for estimating strength of steel pipes reinforced with composite sleeves under unsteady pressure-flow conditions

Witek Maciej, Uilhoorn Ferdinand

Archives of Thermodynamics

|

2020

|

Vol. 41, no 4

3--22

EN

The aim of this paper is twofold: to estimate the unsteady pressure-flow variations in gas transmission pipelines using the ensemblebased data assimilation approach and to analyse the strength of steel tubes reinforced with composite sleeves containing localized part-wall thickness loss caused by corrosion while taking into consideration a safe operating pressure of the pipeline. For a steel thin-walled cylinder containing a partwall metal loss, a flexible wrap of fibreglass as well as carbon glass with epoxy resin are determined. The strength of the repaired pipeline with two kinds of materials for sleeves is investigated taking into consideration the internal pressure at the defect location. For the case study, a section of the Yamal transit pipeline on the Polish territory is selected. The results enable pipeline operators to evaluate the strength of corroded steel pipelines and develop optimal repair activities, which are of vital importance for the maintenance and operation of underground steel networks.

4

Hyperbolic model of fluid flow under Bayesian paradigm

Uilhoorn F. E.

Prace Naukowe Politechniki Warszawskiej. Inżynieria Środowiska

|

2017

|

z. 73

3--104

PL

Teoretyczne i numeryczne modelowanie przebiegów nieustalonych płynów w systemach rurociągowych jest wyzwaniem w dziedzinie badań. Równania rządzące przepływami stanowią system hiperbolicznych nieliniowych równań różniczkowych cząstkowych opartych na zasadach zachowania masy, pędu i energii. Stosowanie takich modeli matematycznych może być ograniczone ze względu na brak pełnej wiedzy o zjawiskach fizycznych i niepewnościach. Wiedzę o początkowych i brzegowych warunkach zazwyczaj otrzymuje się z pomiarów. Istnienie szumów i niedokładności pomiarów, jak również niedokładność modelu przepływu płynu i aproksymacji do rozwiązywania pełnego systemu matematycznego, może prowadzić do przewidywań, które znacznie różnią się od rzeczywistości. W obszarze naszych zainteresowań jest problem uzyskania informacji o stanach i/lub parametrach systemu w czasie rzeczywistym z pomiarów zawierających szum. Badaliśmy skuteczność różnych metod, asymilacji danych nieliniowych w ramach Bayesa stosowanych do quasi-liniowego niejednorodnego hiperbolicznego układu równań różniczkowych cząstkowych pierwszego rzędu, opisującego przebieg nieustalony płynu. Te metody scalają dane w modele numeryczne w celu optymalizacji przewidywań oraz zmniejszenia niepewności modelowanych zmiennych stanu. Oceniliśmy skuteczność rozszerzonego filtru Kalmana, bezśladowego filtru Kalmana i dwóch filtrów cząsteczkowych, a mianowicie klasycznego algorytmu filtru cząsteczkowego oraz jego wariantu - pomocniczego filtru cząsteczkowego. Numeryczne eksperymenty zostały przeprowadzone dla izotermicznego i nieizotermicznego pola przepływu. Model izotermicznego przepływu płynu w postaci zachowawczej w sensie matematycznym został rozwiązany z dwustopniowego schematu Laxa-Wendroffa oraz semidyskretnej metody objętości skończonych używając ograniczników strumienia (flux limiters). Ta ostatnia metoda została zastosowana do estymowania przepływu przebiegu nieustalonego, za pomocą filtru Kalmana i dopuszcza rozwiązania, które zawierają nieciągłości, takie jak fale uderzeniowe. Nieizotermiczny model przepływu w postaci niezachowawczej został rozwiązany metodą linii za pomocą pięciopunktowego centralnego schematu różnicowego czwartego rzędu. Całkowanie układu równań różniczkowych zwyczajnych zostało zrobione poprzez klasyczną metodę Rungego-Kutty. W odniesieniu do dokładności estymacji, odporności i czasu obliczeń algorytmów Bayesa omówiony został wpływ przestępstwa odwrotności (inverse crime), ilości cząsteczek i algorytmu repróbkowania stosowanych w filtrach cząstek staIh, przestrzennej i czasowej siatki odczytów czujników; statystyk szumów i stromości warunków brzegowych przepływu. Symulacje zostały wykonane dla płynów w gęstej fazie ciekłej lub gazowej. Ogólnie, można stwierdzić, że w większości sytuacji bayesowskie podejście jest skuteczne w estymacji przebiegów nieustalonych płynów. Biorąc pod uwagę czas obliczania bezśladowego filtru Kalmana, kwestie odporności filtrów cząstek i efektywności numerycznej obliczania macierzy Jacobiego, wykorzystanie rozszerzonego filtru Kalmana byłoby lepszym wyborem dla estymacji stanu w czasie rzeczywistym.

EN

Theoretical and numerical modeling of fluid transients in pipeline systems is a challenging field of research. The governing flow equations constitute a system of nonlinear hyperbolic partial differential equations enforcing the conservation laws for mass, momentum and energy. The application of these mathematical models might be limited due to the absence of complete knowledge about the physical phenomena and uncertainties. Knowledge about the initial and boundary conditions is usually obtained from measurements. The presence of noise and inaccuracies in these measurements, as well as inexactness of the fluid flow model and approximations for solving the full mathematical system, can lead to predictions that significantly differ from reality. Our interest is to deal with the problem of extracting information about states, or parameters, or both, of the system in real time given noisy measurements. We investigated the performance of different nonlinear data assimilation methods within the Bayesian framework applied to a quasilinear nonhomogeneous hyperbolic system of partial differential equations of first order describing fluid transients. These methods merge sparse data into numerical models to optimize predictions and reduce uncertainties in the modeled state variables. The performance of the extended Kalman filter, unscented Kalman filter and two particle filters, namely sequential importance resampling and its variant, the auxiliary particle filters, were investigated. Numerical experiments were conducted for an isothermal and nonisothermal flow field. The isothermal fluid flow model in mathematical conservation-law form was solved with the two-step Lax-Wendroff scheme and a semi discrete finite volume scheme using flux limiters. The latter high-resolution technique was applied to estimate flow transients using the extended Kalman filter while allowing for solutions that contain discontinuities, such as shock waves. The non isothermal flow model in non conservative form was solved with the method of lines using a classical five-point, fourth-order finite difference approximation. The semidiscrete approximations were integrated with a multi stage explicit Runge-Kutta scheme. With respect to estimation accuracy, robustness and computation time of the Bayesian algorithms, we discussed the impact of inverse crime, ensemble size and resampling algorithm in the particle filter, spatial and temporal resolution of sensor readings, noise statistics and gradient steepness in the mass flow boundary conditions. Simulations were conducted for fluids in dens liquid or gaseous phase. In general, we can conclude that in most of the situations the Bayesian approach is successful in estimating fluid transients. Taking into account the computation time of the unscented Kalman filter, robustness issues of the particle filters and numerical efficiency of computing the Jacobian matrix, the extended Kalman filter would be a better choice for real-time state estimation.

5

Asymilacja trójwymiarowej odbiciowości radarowej do numerycznego modelu meteorologicznego metodą zespołowego filtru Kalmana : metodyka i eksperyment

Szturc J., Jakubiak J., Jurczyk A., Ośródka K.

Przegląd Geofizyczny

|

2014

|

Z. 1-2

19--38

EN

Assimilation of 3d weather radar reflectivity to nwp model using ensemble Kalman filtering: methodology and experiment

6

Application of Newtonian nudging data assimilation method in hydrodynamic model of flood flow in the Lower Biebrza Basin

Mirosław-Świątek D.

Studia Geotechnica et Mechanica

|

2012

|

Vol. 34, nr 2

91-105

EN

The paper presents a 1D hydrodynamic flood flow model employing a data assimilation procedure based on Newtonian nudging. Data assimilation was used to determine correctly the upstream boundary condition defined as a discharge hydrograph. In the model developed, "nudging to individual observations" method was used. The data chosen for assimilation were water table levels recorded by a D-Diver automatic sensor installed in the river channel c. 1.5 km below a computational cross-section opening the analysed stretch of the river and the adjacent valley. This hydrological model of flood flow containing the data assimilation procedure is based on a one-dimensional Saint-Venant system of equations (dynamic wave model). The calculations were performed for the 2010 spring flood event at a 20-km stretch of the river and the floodplain in the upper part of the Lower Biebrza Basin. Modifying the boundary condition by using data assimilation has dramatically improved the accuracy of water table predictions during floods in the area of the Lower Biebrza Basin.

7

Assimilation experiments in the Gdansk Basin (the south-eastern Baltic): How useful are the sea level data from coastal tide gauges for modelling of hydrophysical fields?

Jankowski A., Jędrasik J.

Oceanological and Hydrobiological Studies

|

2007

|

Vol. 36, No.4

105-128

EN

In the Baltic modelling research, assin.ilation techniques were developed with advance. They were-concerned to model assimilated basic parameters and observed them directly. In present paper, the most important was the assimilation of surface information and its projection deep into temperature and salinity fields. In oceanic investigations altimetry viewed from satellite was the sea level changes projected far inside and predetermined surface-to-subsurface correlations. To obtain improved modelled hydrophysical fields, sea level variations measured at coastal gauges and efficient data assimilation were taken into account. A data assimilation algorithm has been developed and used in conjunction with a three-dimensional baroilinic model of the Baltic Sea. It was based on a time and space weighted nudging technique. The sea level data were inserted continuously by updating the model solution every time step. Several sensitivity experiments with different values of time and spatial weighting scales were performed. In first series of experiments, only sea level data (SL) were assimilated. In the next simulations, seawater temperature (SWT) and seawater salinity (SWS) related directly to SL were assimilated. To evaluate the effectiveness of the assimilation scheme, modelled sea level series and vertical profiles of seawater temperature and salinity in selected coastal gauges in the Gdansk Basin were examined. Evidently low but statistically essential correlation coefficients indicated nonlinear character of vertical mixing and transfer processes. Decreasing errors obtained while comparing the model results to a control case without assimilation confirmed a real transfer of surface information deep and usefulness of such approach in modelling.