排序方式： 共有9条查询结果，搜索用时 62 毫秒
1
1.
Jing Shi Ahmed Al-Durra Rachid Errouissi Igor Boiko 《Journal of The Franklin Institute》2019,356(4):2031-2059
Artificial gas-lift (AGL) is one of the most widely used methods in oil production to maintain acceptable oil flow to the processing equipment and sales when the reservoir pressure is not high enough. In spite of its popularity, the AGL process is prone to casing-heading instability, which is revealed as significant flow oscillation. This is undesirable as it results in production losses and unstable behavior that has negative impact on the downstream equipment. Controller design for such a process is very challenging as it exhibits highly nonlinear dynamics. In this work, the predictive generalized minimum variance control (NPGMV) is employed to derive a robust controller based on the state estimation to stabilize AGL process when casing-heading phenomenon occurs. A closed-form optimal control law is obtained based on the Taylor series approximation. Further, a nonlinear state observer is produced and combined with the controller to ensure closed-loop control through variables that are most beneficial to the system performance, which are unmeasurable and can be obtained only via estimation. Through simulation studies, the effectiveness of the proposed controller is demonstrated. 相似文献
2.
Mohamad Sleiman Rachid Bouyekhf Adbellah El Moudni 《Journal of The Franklin Institute》2019,356(1):351-381
The paper explores the application of thermodynamic formalism to model and control transportation networks. Specifically, by considering the vehicles as the abstract energy supplied to the system, we show in certain circumstances that certain thermodynamic concepts such as temperature, thermal capacity and thermal equilibrium can have the corresponding notions in transportation context. In addition, despite the lack of a natural principle in transportation context that corresponds to the second law of thermodynamic as we will show, the most important thermodynamic notion, which is the entropy, can be also defined in order to measure the disorder of transportation systems. It is then shown that the state when all lanes have the same occupancy corresponds to the thermal equilibrium arising in isolated thermodynamic system. This equilibrium occupancy leads to a minimum entropy corresponding to a minimal disorder. Besides, by taking the transportation entropy as the storage function, a robust dissipativity based control strategy is presented to reduce the disorder and render the system better organized. Finally, an example is worked out to illustrate the results. 相似文献
3.
Oscillating electrowetting on dielectrics (EWOD) with coplanar electrodes is investigated in this paper as a way to provide efficient stirring within a drop with biological content. A supporting model inspired from Ko et al. [Appl. Phys. Lett. 94, 194102 (2009)] is proposed allowing to interpret oscillating EWOD-induced drop internal flow as the result of a current streaming along the drop surface deformed by capillary waves. Current streaming behaves essentially as a surface flow generator and the momentum it sustains within the (viscous) drop is even more significant as the surface to volume ratio is small. With the circular electrode pair considered in this paper, oscillating EWOD sustains toroidal vortical flows when the experiments are conducted with aqueous drops in air as ambient phase. But when oil is used as ambient phase, it is demonstrated that the presence of an electrode gap is responsible for a change in drop shape: a pinch-off at the electrode gap yields a peanut-shaped drop and a symmetry break-up of the EWOD-induced flow pattern. Viscosity of oil is also responsible for promoting an efficient damping of the capillary waves which populate the surface of the actuated drop. As a result, the capillary network switches from one standing wave to two superimposed traveling waves of different mechanical energy, provided that actuation frequency is large enough, for instance, as large as the one commonly used in electrowetting applications (f ∼ 500 Hz and beyond). Special emphasis is put on stirring of biological samples. As a typical application, it is demonstrated how beads or cell clusters can be focused under flow either at mid-height of the drop or near the wetting plane, depending on how the nature of the capillary waves is (standing or traveling), and therefore, depending on the actuation frequency (150 Hz–1 KHz). 相似文献
4.
A numerical modeling of natural convection under the influence of either axial (Bz) or radial (Br) magnetic field in a cylindrical configuration filled with a low-Prandtl number electrically conducting fluid, is studied. The finite volume method is used to discretize the equations of continuity, Navier Stokes and energy. A computer program based on the SIMPLER algorithm is developed. The flow and temperature fields are presented by stream function and isotherms, respectively. Stability diagrams are established according to the numerical results of this investigation. These diagrams put in evidence the dependence of the critical Grashof number, Grcr with the increase of the Hartmann number, Ha. The strongest stabilization of the convective flows occurs when the magnetic field is applied in the radial direction. This study confirms the possibility of stabilization of a liquid metal flow in natural convection by application of a radial magnetic field. 相似文献
5.
Using survey responses from 1300 full-time employees in the Australian Telecommunications Industry, this paper explores the relative effects of task characteristics and sub-unit structure on aspects of information processing. Results of multiple regressions revealed that task characteristics have a greater impact on amounts and timeliness of information. In contrast, structural characteristics have greater effects on the degree of openness and accuracy of information. More specifically: (a) variety and task analyzability were found to increase the amount and timeliness of information; (b) greater sub-unit size tends to reduce openness and accuracy of information, while greater participation and formalization tend to increase these. Further scrutiny of these effects revealed that (a) the impact of structural characteristics on information accuracy and openness (i.e., section-level information processing) were strongly moderated by sub-unit size and (b) the effects of task characteristics on amounts and timeliness of information (i.e., individual-level information processing) were strongly moderated by the nature of the job, as strong differences between administrative, managerial, technical, and engineering positions were discovered in this regard. 相似文献
6.
Fadi Motawej Rachid Bouyekhf Abdellah El Moudni 《Journal of The Franklin Institute》2011,348(4):703-717
In this paper, using the energy concept, the control of traffic flow by traffic lights on an over-saturated single intersection is addressed. By regarding the flow entry of vehicles as the energy stored in the system, we show that the dissipative system theory can be applied. As a result, a state feedback control law is found in terms of the solution of an associated dissipation equation that renders the system non-accumulative, i.e., to get out of the over-saturation situation. The results of the simulations indicate that our control strategy guarantees a high degree of control benefit. 相似文献
7.
Rachid El Hour 《Al-Masaq: Islam & the Medieval Mediterranean》2014,26(3):288-298
The Berber language has historically been a key element in the socio-cultural and ethnic fabric of the Maghrib. Consequently, in recent years there have been several initiatives to recover and interpret the information Arabic sources provide on the Berber language and the role played by Berber peoples in the consolidation of Islam in this area.Studies of the Berber language and peoples have primarily centred on chronicles and geographical sources, but scholars have devoted less attention to other sources, especially hagiographies. With the exception of some specific work, the role of the Berber language and peoples in hagiographic literature has not been systematically analysed. The analysis presented in this article suggests that some hagiographic sources, especially those written by Berber authors, while avoiding an open defence of Berber identity, in fact hid it behind comments and quotes of a linguistic nature. This study, although it includes some additional references to the Mārinid, Wa??āsid and Sa?did periods, concentrates on the Almohads, and deals with written sources, both Andalusi and Maghribi. 相似文献
8.
How learners can build their own knowledge, which is precisely tailored to their needs and background? This is precisely the question to which this paper attempts to answer by providing a framework for a flexible object-based e-learning environment. The paper recognizes that the general learner modeling alternative is an intractable problem. However, it suggests learning objects construct used as building blocks to root out individual learning deficiencies. The paper also provides an algorithm to construct individual learning routes that are adjusted to learners' profile as well as an open implementation to accommodate the integration of various learning sources. 相似文献
9.
Rachid El Hour 《Al-Masaq: Islam & the Medieval Mediterranean》2012,24(3):265-278
This article examines the nature of the wrath of Abū Marwān al-Yu[hdot]ānisī, a thirteenth-century Andalusi saint, and the protagonist of the Tu?fat al-mughtarib of al-Qashtālī. I have divided the study into two main parts. The first sets out and analyses various occasions on which the saint committed violent acts against Christians. Two of them died as a consequence of these aggressions. All the cases in this first part took place in the Muslim East during the saint's stay in this area. The second part examines cases of violence committed against Muslim people from al-Andalus. The victims suffered the consequences of the wrath of the saint, although he was not directly involved in the aggressions themselves. The stories are narrated by al-Yu[hdot]ānisī himself, and we do not know whether they really took place. Regarding these manifestations of violence, the hagiographic sources not only justify all the violent acts committed by the saint, murder included, but they present the saint to society as an “example” to follow, and indeed as a “hero”. 相似文献
1