Inaug.-Diss.--Leipzig. / Lebenslauf. Literatur-Angabe": p. [2-3].

Compositional simulation is a complex task that involves solving several equations simultaneously for all grid blocks representing a petroleum reservoir. Usually, these equations are separated into two groups: primary and secondary equations. Similarly, the unknowns of the system are also separated into primary and secondary variables. Considering the large number of unknowns, there are many ways to separate such variables in order to deal with the primary variables. This work aims at comparing a number of formulations for compositional reservoir simulation. It also aims at enhancing the formulations with new features not provided in the original publications. To accomplish these objectives, various formulations prevailing in the literature are implemented in The University of Texas at Austin in-house fully implicit simulator named GPAS (General Purpose Adaptive Simulator) and their performances were compared. Subsequently, some of the formulations were enhanced and tested for various applications. The comparison of the formulations studied indicated differences in efficiency for each approach. These differences come from the fact that when one is solving for a different set of primary variables, the manipulation of the equations is analogous to the use of a preconditioner applied to a linear system of equations. Furthermore, unlike a preconditioner, changing the primary variables affects the non-linear solver. Therefore, differences in terms of the number of Newton-Raphson iterations, used for solution of nonlinear equations resulting from discretization of nonlinear partial differential equations representing fluid flow in the reservoir, are expected. In addition to these differences in the non-linear solver, many formulations explore the fact that a reduced number of equations need to be solved implicitly, thus considerably reducing the CPU time dedicated to the linear solver. Finally, new features not provided in the original published formulations such as three-phase flash calculation, physical dispersion, and unstructured grid were implemented and verified. Additionally, it was demonstrated that, in certain situations, these enhancements are essential to properly model the physical phenomena occurring in oil and gas reservoirs. / text

Skiftarbetare löper hög risk att utsättas för hälsorisker och dåliga arbetsförhållanden från bland annat negativ påverkan på dygnsrytm, kost samt oregelbundna och obekväma tider. Syftet med studien var att beskriva upplevelser av aktivitet och delaktighet i förhållande till skiftarbete bland vårdpersonal.  En kvalitativ metod med bekvämlighets- och snöbollsurval samt semistrukturerade intervjuer har använts. Nio informanter som jobbade treskift inom vården intervjuades på fyra vårdavdelningar på två olika sjukhus. En kvalitativ innehållsanalys genomfördes. Resultatet visade att informanter upplevde en påverkan på aktivitet och delaktighet i samband med treskiftarbete. Orsaken till detta var oregelbundna arbetstider och rutiner, skiftande dygnsrytm och svårigheter att ställa om mellan arbetspass. Informanterna beskrev positiva likaså negativa upplevelser av aktivitet och delaktighet i förhållande till skiftarbete. Slutsatsen visade att informanter upplevde en förändring i aktivitetsutförandet och delaktighet i samband med treskiftarbete. De upplevde att de hade mer fritid men att tröttheten och svårigheter att ställa om mellan olika skift bidrog till negativt påverkad delaktighet. Informanterna upplevde även att en förändrad dygnsrytm hade en påverkan på aktivitetsutförandet och delaktighet i vardagen. / Shift workers are at high risk of being exposed to health risks and poor working conditions from, among other things, a negative impact on the circadian rhythm, diet and irregular and uncomfortable working hours. The purpose of the study was to describe experiences of activity and participation in relation to shift work among care staff. A qualitative method with convenience and snowball selection as well as semi-structured interviews was used. Nine informants working three-shifts in health care were interviewed in four care units at two different hospitals. Qualitative content analysis was performed. The results showed that informants, due to irregular working hours and routines, varying circadian rhythms and difficulties in switching between shifts, experienced an impact on activity and participation. They described positive as well as negative experiences of activity and participation in relation to shift work. The conclusion showed that informants experienced a change in activity performance and participation in connection with three-shift work. They felt that they had more free time but that the fatigue and difficulties to switch between different shift contributed to negatively affected participation. Informants also experienced that a changed circadian rhythm had an impact on activity performance and participation in everyday life.