For a class of complex interconnected nonlinear disturbed systems, a proportional integral (PI) decentralized observer-based feedback robust decentralized controller technique is proposed, relying on ...H∞ synthesis for disturbance mitigation and linear matrix inequality (LMI) tools to achieve asymptotic stabilization and stability analysis within the Lyapunov framework. The proposed design method draws on a prominent optimization problem that can be tackled in terms of LMI constraints to evaluate the decentralized controller and PI observer gain matrices jointly, to maximize the nonlinearity coverage tolerated by the system without destabilization and to improve the robustness of the proposed control strategy by minimizing an H∞ criterion despite exogenous disturbances and strong nonlinear interconnections affecting the subsystems. The efficacy and high performance of the proposed control approach, compared with a renowned decentralized guaranteed cost control strategy from the literature, are validated by numerical simulations on a greatly interconnected three-machine power system.
This paper proposes developing a
H
∞
dynamic output-feedback decentralized control design method for nonlinear interconnected systems subject to time-varying parameters and external disturbances. The ...designed controller is formulated as an optimization problem subject to linear matrix inequalities (LMIs) for the concurrent computation of the decentralized observation and control gains, and for the external disturbance mitigation by means of a
H
∞
performance criterion minimization. The propounded optimization problem, designed in LMI conditions, is expeditiously resolved by a one-step procedure to override the conservatism generated by using many step-based procedures often used in the analysis and synthesis of interconnected systems. The effectiveness of the developed control scheme is demonstrated through simulation results of multimachine power systems.
The characterization of organic matter (OM) composition, physico-chemical, geochemical, and mineralogical studies of sedimentary core can help to better understand the paleoclimates and the ...depositional environments. The purpose of this work is to identify the factors monitoring the mineralogical composition and the sedimentation of sebkha Mhabeul sediments (southeastern Tunisia), during the Holocene. A 100.5 cm core (Mh 1) collected from this sebkha was analyzed for the determination of chemical composition by X-ray fluorescence (XRF), carbonate content by Bernard calcimetry, grain-sized sediments by AFNOR sieves, OM content by Rock-Eval 6 Pyrolysis, and mineralogical composition by X-ray diffraction (XRD), scanning electronic microscope (SEM), and infrared spectroscopy (IR). The sedimentary fillings of this sebkha, constituted by fine fractions, are characterized by the dominance of the detrital minerals (72–96 %) with high quartz percentages (42.2–91.5 %). The mineralogical composition of the studied sediments included detrital minerals (clay minerals, quartz, and feldspars), carbonate minerals (ankerite, dolomite, and calcite), and evaporitic minerals (halite, bassanite). The clay minerals (11–14%) are composed of a mixture of kaolinite, illite and palygorskite. Fourier transform infrared (FTIR) absorption spectra of all sediment samples confirm the mineralogical composition obtained by XRD and the existence of OM, by defining the band assignments for OM and different minerals as quartz, feldspar, clay, and carbonate minerals. The Rock Eval pyrolysis shows that the OM is immature and has a mixed origin (terrestrial and aquatic). The statistical analyses prove the results of geochemical and mineralogical studies. Indeed, the principal component analysis (PCA) of geochemical and mineralogical data and the depth help to prove the relationships between minerals and chemical elements. Moreover, the negative correlation between the Rock Eval Pyrolysis parameters and the depth shows a homogenous statistical group.
Paleoenvironmental and climate changes along the Thapsus coast over the last 4000 years were recorded in lagoonal sediments. These variations were analysed by geochemistry, sedimentology and ...paleontology data. Grain size and sediment texture as well as organic matter richness and biotas were assessed in sediment samples. Terrigenous influence was reconstructed via the following proxies: Si/Al, Ti/Al and Zr/Al ratios for aeolian dust input and fluvial input were accounted for via Mg/Al, K/Al and Rb/Al ratios. Other element ratios (Cl/Al, Ca/Al, Na/Al and S/Al) have provided reliable reconstructions of open ocean influence. The computation of the grain size parameters was herein adopted in order to comprehend the factors that controlled the sedimentary facies. The new data reveal the development of Thapsus coast and captured sensitive changes during the following periods: (i) towards 3993 cal years BP, during Bronze Age, the dominance of gravelly and clastic materials, poorly sorted fine-grained sand and reduced values of K/Al, Rb/Al and Mg/Al element ratios indicated a period of aridity and high energy condition. In addition, the presence of shallow-water foraminifera (
Ammonia
, elphidiids, small miliolids, rosaliniids) records the first marine transgression; (ii) the interval between 3993 and 2203 cal years BP records high values of marine and fluvial element ratios suggesting a humid period and an inflow of oxygenated water during the Iron Age (IA) and the Roman Humid Period (RHP); (iii) towards 1242 cal years BP, the increase of aeolian input proxies suggests a reduction of fluvial input and a reduction of circulation intensity related to the Dark Age (DA) and the Medieval Climate Anomaly (MCA). Increased abundances of ammoniid foraminifera (20%), the lack of epiphytic peneroplids and lower species richness and abundance indicated the development of a semi-closed lagoon environment; (iv) the decrease of aeolian input proxies as well as the moderate increase of proxies related to fluvial input indicate humid conditions during the Little Ice Age (LIA).
In the present study, iron-pillared clay was prepared using ferrous nitrate Fe(NO
3
)
3
. The removal of Reactive Blue (RB4) dye by ultrasound-assisted sorption onto the synthesized pillared Tunisian ...clay in aqueous solutions was studied. The natural and modified clay samples were characterized using XRD, FTIR TEM, and nitrogen adsorption measurement methods. Mineralogical data show that smectites are the main minerals of clay samples. FTIR spectra indicate that the stretching vibration bands of the structural hydroxyl groups are broad after treatments. A new band appears at 1570 cm
−1
, after the sorption of RB4 dye, attributed to aromatic C = C stretching vibration, which suggests the adsorption of RB4. A remarkable decrease was detected in the BET surface after sono-adsorption indicating that the sites of modified clay are almost occupied by the dye. The maximum Reactive Blue 4 quantity was removed at pH 8. Meanwhile, more active Fe–C surface sites were available for both adsorption and sono-adsorption with increasing RB4 concentration, thereby increasing the removal efficiency. Monolayer adsorption capacity via the sono-assisted method also showed a high removal amount of 46.51 mg/g. Langmuir’s model describes the experimental data better than Freundlich’s. A comparative study confirmed that RB4 sono-adsorption by a Tunisian clay sample was higher than others used in other relevant studies, highlighting that these clay deposits may be applied to the dyes’ elimination from wastewaters.
Purpose
This paper aims to focus on the design of a decentralized observation and control method for a class of large-scale systems characterized by nonlinear interconnected functions that are ...assumed to be uncertain but quadratically bounded.
Design/methodology/approach
Sufficient conditions, under which the designed control scheme can achieve the asymptotic stabilization of the augmented system, are developed within the Lyapunov theory in the framework of linear matrix inequalities (LMIs).
Findings
The derived LMIs are formulated under the form of an optimization problem whose resolution allows the concurrent computation of the decentralized control and observation gains and the maximization of the nonlinearity coverage tolerated by the system without becoming unstable. The reliable performances of the designed control scheme, compared to a distinguished decentralized guaranteed cost control strategy issued from the literature, are demonstrated by numerical simulations on an extensive application of a three-generator infinite bus power system.
Originality/value
The developed optimization problem subject to LMI constraints is efficiently solved by a one-step procedure to analyze the asymptotic stability and to synthesize all the control and observation parameters. Therefore, such a procedure enables to cope with the conservatism and suboptimal solutions procreated by optimization problems based on iterative algorithms with multi-step procedures usually used in the problem of dynamic output feedback decentralized control of nonlinear interconnected systems.
This study investigates the problem of robust tracking control for interconnected nonlinear systems affected by uncertainties and external disturbances. The designed H∞ dynamic output-feedback model ...reference tracking controller is parameterized in terms of linear matrix inequalities (LMIs), which is formulated within a convex optimization problem readily implementable. The resolution of such a problem, guarantying not only the quadratic stability but also a prescribed performance level of the resulting closed-loop system, enables to calculate concurrently the robust decentralized control and observation gain matrices. The established LMI conditions are computed in a single-step resolution to obtain all the controller/observer parameters and therefore to overcome the problem of iterative algorithm based on a multi-stage resolution leading in most cases to conservative and suboptimal solutions. Numerical simulations on diverse applications ranging from a numerical academic example to coupled inverted double pendulums and a 3-strongly interconnected machine power system are provided to corroborate the merit of the proposed control scheme.
This study concerns the purification of Tunisian phosphoric acid produced by the Tunisian Chemical Group (TCG), using raw and activated clays materials from Southern Tunisia. The Gafsa basin clays ...samples (Jebel Hamadi (JHM); Jebel Stah (JS) and the El Hamma sample (Jebel Aïdoudi (JAD)) were activated with 3 M, HCl solution. Phosphoric acid purification was performed on raw and activated clays. Mineralogical characterisation was carried out using the X-ray powder diffraction method and infrared absorption spectroscopy. Textural changes between raw and activated clays were identified using SEM observations and specific surface analysis. Jebel Hamadi clays were almost dominated by smectite associated with kaolinite and illite traces, while Jebel Stah and Jebel Aïdoudi clays were composed of the association of smectite, illite and kaolinite. It is worth noting that the position of the smectite (001) reflection increased after the acidic activation in all studied samples, indicating the relaxation of the smectite structure along the c-axis. This was corroborated by the increasing specific surface area of the clay particles with the activation process. The specific surface area was close to 50 m2/g and 200 m2/g, for raw and activated materials, respectively. The maximum phosphoric acid purification was obtained by using activated clays with 3 N HCl for 4 h. This performance correlated with the maximum of the external specific surface area which generated strong acid sites. Furthermore, the best results of phosphoric acids purification from TCG were obtained at a specific consumption equivalent to 30 Kg of clay/ton of P2O5. These results showed that the best phosphoric acid purification was yielded by Jebel Aïdoudi clay. In all cases, the highest organic carbon reduction rates in the phosphoric acid after filtration were obtained at 90°C.
Activation of smectitic clays:•Induces relaxation of the structure in the c direction.•Decreases specific surface area.•Improves textural parameters (specific surface area and density).•Gives a good purification of raw phosphoric acid.
In this paper, we investigate the problem of H(infinity) decentralized tracking control design with a decentralized observer for interconnected nonlinear systems which are characterized by the ...interconnection of N subsystems. Each subsystem is modeled by a linear constant part perturbed by an additive nonlinearity which is illustrated by the interconnection terms. The proposed feedback control scheme is developed to ensure the asymptotic stability of the augmented system, to reconstruct the non-measurable state variables of each subsystem, to maximize the nonlinearity domain, and to improve the performance of the model reference tracking control by using the H(infinity) criterion despite the external disturbances. The proposed control approach is formulated in a minimization problem and derived in terms of linear matrix inequalities (LMIs) whose resolution yields the decentralized control and observation gain matrices. The effectiveness of the proposed control scheme is demonstrated through numerical simulations on a power system with three interconnected machines.
