| 1. |
- Ademuyiwa, Adesoji O., et al.
(författare)
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Determinants of morbidity and mortality following emergency abdominal surgery in children in low-income and middle-income countries
- 2016
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Ingår i: BMJ Global Health. - : BMJ Publishing Group Ltd. - 2059-7908. ; 1:4
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Tidskriftsartikel (refereegranskat)abstract
- Background: Child health is a key priority on the global health agenda, yet the provision of essential and emergency surgery in children is patchy in resource-poor regions. This study was aimed to determine the mortality risk for emergency abdominal paediatric surgery in low-income countries globally.Methods: Multicentre, international, prospective, cohort study. Self-selected surgical units performing emergency abdominal surgery submitted prespecified data for consecutive children aged <16 years during a 2-week period between July and December 2014. The United Nation's Human Development Index (HDI) was used to stratify countries. The main outcome measure was 30-day postoperative mortality, analysed by multilevel logistic regression.Results: This study included 1409 patients from 253 centres in 43 countries; 282 children were under 2 years of age. Among them, 265 (18.8%) were from low-HDI, 450 (31.9%) from middle-HDI and 694 (49.3%) from high-HDI countries. The most common operations performed were appendectomy, small bowel resection, pyloromyotomy and correction of intussusception. After adjustment for patient and hospital risk factors, child mortality at 30 days was significantly higher in low-HDI (adjusted OR 7.14 (95% CI 2.52 to 20.23), p<0.001) and middle-HDI (4.42 (1.44 to 13.56), p=0.009) countries compared with high-HDI countries, translating to 40 excess deaths per 1000 procedures performed.Conclusions: Adjusted mortality in children following emergency abdominal surgery may be as high as 7 times greater in low-HDI and middle-HDI countries compared with high-HDI countries. Effective provision of emergency essential surgery should be a key priority for global child health agendas.
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| 2. |
- Al Maliki, Ali, et al.
(författare)
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Comparison between inductively coupled plasma and X-ray fluorescence performance for Pb analysis in environmental soil samples
- 2017
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Ingår i: Environmental Earth Sciences. - : Springer. - 1866-6280 .- 1866-6299. ; 76:12
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Tidskriftsartikel (refereegranskat)abstract
- Comparison of two conventional analytical techniques such as X-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP-MS) for measuring Pb concentrations in soil samples was achieved using field and laboratory work. Seventy-three samples were collected from urban areas surrounding the large lead smelter at South Australia, as an indicator of the environment impact of smelter activity. Soil Pb concentrations were determined using hand-held XRF analyser under laboratory conditions. ICP-MS analysis on digested soils (using a microwave-assisted nitric acid digestion-extraction) was applied to validate p-XRF data. The analysis showed that Pb concentrations determined by XRF correlated with high linearity with Pb concentrations determined by ICP-MS measurements (R2 = 0.89). Statistical test (t test) was applied to the data of both methods applied without any significant difference between the two techniques. These results indicated that ICP-MS corroborated XRF for Pb soil measurements and suggests that XRF was a reliable and quick alternative to traditional analytical methods in studies of environmental health risk assessment, allowing for much larger sampling regimes in relatively shorter times and could be applied in the field.
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| 3. |
- Alhelfi, Ali Kadhim Hadi, et al.
(författare)
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A Condition Monitoring for Collapsing Bubble Mechanism for Sonoluminescence and Sonochemistry
- 2015
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Ingår i: Journal of Thermal Science and Engineering Apllications. - : ASME International. - 1948-5093 .- 1948-5085. ; 7:2, s. 8-021014
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- The acoustic cavitation phenomenon is a source of energy for a wide range of applications such as sonoluminescence and sonochemistry. The behavior of a single bubble in liquids is an essential study for acoustic cavitation. The bubbles react with the pressure forces in liquids and reveal their full potential when periodically driven by acoustic waves. As a result of extreme compression of the bubble oscillation in an acoustic field, the bubble produces a very high pressure and temperature during collapse. The temperature may increase many thousands of Kelvin, and the pressure may approach up to hundreds of bar. Subsequently, short flashes can be emitted (sonoluminescence) and the high local temperatures and pressures induce chemical reactions under extreme conditions (sonochemistry). Different models have been presented to describe the bubble dynamics in acoustic cavitation. These studies are done through full numerical simulation of the compressible Navier–Stokes equations. This task is very complex and consumes much computation time. Several features of the cavitation fields remain unexplained. In the current model, all hydrodynamics forces acting on the bubble are considered in the typical solution. Bubble oscillation and its characteristics under the action of a sound wave are presented in order to improve and give a more comprehensive understanding of the phenomenon, which is considered to have a significant role in different areas of science and technology.
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| 4. |
- Alhelfi, Ali Kadhim Hadi
(författare)
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Development and Assessment of Methods for the Prediction of Hydrodynamic and Ultrasound induced Cavitation
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The cavitation phenomenon has today become a keystone for different areas of science and technology including various industrial processes and medicine. Recently increasing interest and much attention have been paid to study this phenomenon. The last two decades have witnessed the development of numerous devices for different important applications of considerable practical interest, and the range of these applications is in continuous increase. This thesis aims to gain more knowledge about the mechanisms and dynamics of the cavitation phenomenon. In the present study, various techniques are developed and investigated. The major principal parameters associated with these phenomena are all presented in order to improve and give more comprehensive understanding of the phenomenon. The study presents enhanced numerical models to analyze the cavitation phenomenon and simulated results of formation and collapse of a single bubble in a liquid are provided. A convenient model is applied and its enhancements are examined numerically. The validity and comparison with the available experimental data were found favorable. The model is employed to deduce the bubble dynamics in flow domains for the following situations, 1. Bubble dynamics in an acoustic field. The sound waves create pressure variations through the medium and cause regions of rarefaction and compression. These pressure variations can set a tiny bubble into radial motions, i.e., expansion and compression. The bubble in an acoustic field grows as the pressure associated with the sound waves gives rarefaction. When the pressure turns to compression, the bubble is compressed and may reach an unstable size and then collapse violently. During this process, the nonlinear motion of the bubble is a complicated process. Despite many efforts, the demand of creating more suitable models with a realistic applicability calls for numerical calculations of the bubble motion in an acoustic field. This will provide improved knowledge about the real situation and the main results associated with this phenomenon. 2. Bubble dynamics close to a rigid boundary. In fact, the simulation of non-spherical bubble dynamics and its interaction with solid boundaries has received much less attention due to the complexity of the problem. A main reason of the structural damages in the cavitation phenomenon is due the formation of micro jets generated due to the bubble collapse and impingement on the solid surfaces or boundaries. The boundary integral method (BIM) is employed to compute the bubble motion and explosion of a cavitation bubble close to a rigid boundary. The liquid is considered to be incompressible, inviscid, and irrotational around the bubble. These assumptions satisfy the conditions for the Laplacian equation.
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| 5. |
- Alhelfi, Ali Kadhim Hadi, et al.
(författare)
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Simulations of Cryogenic Cavitation of Low Temperature Fluids with Thermodynamics Effects
- 2015
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Ingår i: International Journal of Mechanical, Aerospace, Industrial and Mechatronics Engineering. ; 9:1, s. 65-69
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Cavitation in cryogenic liquids is widely present in contemporary science. In the current study, we re-examine a previously validated acoustic cavitation model which was developed for a gas bubble in liquid water. Furthermore, simulations of cryogenic fluids including the thermal effect, the effect of acoustic pressure amplitude and the frequency of sound field on the bubble dynamics are presented. A gas bubble (Helium) in liquids Nitrogen, Oxygen and Hydrogen in an acoustic field at ambient pressure and low temperature is investigated numerically. The results reveal that the oscillation of the bubble in liquid Hydrogen fluctuates more than in liquids Oxygen and Nitrogen. The oscillation of the bubble in liquids Oxygen and Nitrogen is approximately similar.
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| 6. |
- Alhelfi, Ali Kadhim Hadi, et al.
(författare)
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THE BOUNDARY INTEGRAL METHOD APPLIED TO NON-SPHERICAL CAVITATION BUBBLE GROWTH AND COLLAPSE CLOSE TO A RIGID BOUNDARY
- 2015
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Ingår i: ASME 2015 International Mechanical Engineering Congress and Exposition. - 9780791857496 ; 8A
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Konferensbidrag (refereegranskat)abstract
- Recently much attention has been paid to studies concerning bubble dynamics in the cavitation phenomena and this topic has been the subject of many research works. In fact, the simulation of non-spherical bubble dynamics and its interaction with solid boundaries have received much less attention due to the complexity of the problem. One of the main reasons of the structural damages in the cavitation phenomenon is due to the formation of micro jets generated due to the bubble collapse and impinging on the solid surfaces or boundaries. The boundary integral method (BIM) based on Green’s function is used to model the oscillation and collapse of a cavitation bubble close to a rigid boundary. The liquid is considered to be incompressible, inviscid, and irrational around the bubble. These assumptions satisfy the conditions for the Laplacian equation. The theory permits one to predict correctly the interaction between the bubble and the rigid boundary, which is of great importance in the study of cavitation damage due to a bubble collapsing close to the boundaries. The results reveal that the amplitude of bubble oscillation depends on the bubble location away from a rigid surface. Also, the theory for the cavitation bubble dynamics presented in this study has many advantages in various situations and might be helpful to understand effects of the cavitation phenomenon such as generation of excessive vibration, surface erosion and undesirable acoustic emission.
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| 7. |
- Castaño Arranz, Miguel, et al.
(författare)
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On Guided and Automatic Control Configuration Selection : Application on a Secondary Heating System
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This technical report provides supplementary materialto the research paper entitled ”On Guided and AutomaticControl Configuration Selection”, presented at the ETFA 2017.In that paper, different Control Configuration Selection (CCS)tools are reviewed and integrated into guided and automaticCCS methodologies. The guided CCS is a heuristic step-by-stepmethodology to be applied by practitioners, while the automaticCCS methodologies target the adaptation of such heuristicsinto algorithms which can be run in a computer and assist thepractitioners in the decision making. This report summarizesthe results of applying the introduced methodologies to a reallifeprocess: the Secondary Heating System. For an introductorybackground, preliminaries, and details on the methodologies,the reader is referred to the original research paper.
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| 8. |
- Castaño Arranz, Miguel, et al.
(författare)
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On Guided and Automatic Control Configuration Selection
- 2018
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Ingår i: IEEE International Conference on Emerging Technologies and Factory Automation (ETFA). - Piscataway, Nj : Institute of Electrical and Electronics Engineers (IEEE). - 9781509065059
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Konferensbidrag (refereegranskat)abstract
- This paper discusses the guided and automatic control configuration selection in large scale complex systems. Due to the trend of increasesd level of automation and connectedness which is promoted by the Industry 4.0 strategy and supported by technologies relating to cyber-physical systems and the industrial internet of things, selecting appropriate control strategies becomes increasingly important and complex. This is especially important as a control strategies will limit the achievable performance of the process system, and there are trade-offs between complexity of the control strategies, achievable performance, vulnerability and maintainability.The paper reviews the state of the art of methodologies that support the practitioners in taking decisions on control strategies, where two main approaches are considered, the guided one and a fully automatic one. It is shown how both approached can be conducted and examples are used to clarify the selection process.
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| 9. |
- Kadhim, Ali, et al.
(författare)
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Automated Control Configuration Selection Considering System Uncertainties
- 2017
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 56:12, s. 3347-3359
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Tidskriftsartikel (refereegranskat)abstract
- This paper proposes an automated pairing approach for configuration selection of decentralized controllers which considers system uncertainties. Following the Relative Interaction Array (RIA) pairing rules, the optimal control configuration, i.e. the configuration that fits best the pairing rules, is obtained automatically by formulating the control configuration selection problem as an Assignment Problem (AP). In this AP, the associated costs related to each input-output pairing are given by the RIA coefficients. The Push-Pull algorithm is used to solve the AP for the nominal system and to obtain the set of costs for which the resulting configuration remains optimal, also called the perturbation set. The introduction of uncertainty bounds on the RIA-based costs enables the testing of the possible violation of the optimality conditions. Examples to illustrate the proposed approach for a 3×3 system and 4×4 gasifier plant are given.
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| 10. |
- Kadhim, Ali, et al.
(författare)
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Dynamic Relative Gain Array Estimation using Local Polynomial Approximation Approach
- 2016
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Ingår i: Modeling, Identification and Control. - : Norwegian Society of Automatic Control. - 0332-7353 .- 1890-1328. ; 37:4, s. 247-259
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Tidskriftsartikel (refereegranskat)abstract
- This article presents a procedure that utilizes the local polynomial approximation approach in the estimation of the Dynamic Relative Gain Array (DRGA) matrix and its uncertainty bounds for weakly nonlinear systems. This procedure offers enhanced frequency resolution and noise reduction when random excitation is used. It also allows separation of nonlinear distortions with shorter measuring time when multisine excitation is imposed. The procedure is illustrated using the well-known quadruple tank process as a case study in simulation and in real life. Besides, a comparison with the pairing results of the static RGA, nonlinear RGA and DRGA based on linearized quadruple tank model for different simulation cases is performed.
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| 11. |
- Kadhim, Ali
(författare)
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Estimation of the Dynamic Relative Gain Array for Control Configuration Selection
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The control of multi-input multi-output systems (MIMO) is more difficult than for single-input single-output systems (SISO) due to the multitude of input-output couplings. Coupling, simply means that a change in any input leads to changes in many outputs. Nevertheless, in many cases, a simple decentralised controller is usually sufficient to achieve desired performance goals. However, there is a need for systematic techniques that can suggest the most promising configurations or pairings for the decentralized controller.The relative gain array (RGA) has proven itself to be an efficient tool to solve the pairing problem. It is easily calculated and does not depend on input-output scaling. However, it gives misleading results in some cases where system dynamics are involved and hence Dynamic Relative Gain Array (DRGA) used instead. The commonplace procedure to estimate DRGA values from the input-output data is to identify a parametric system model. Thus, the user needs to decide a model structure and a model order to calculate the system frequency response. Eventually, DRGA values are obtained based on that system frequency response over the frequency range of interest. In this work, a method which requires less user interaction is proposed. The system frequency response, and subsequently the DRGA, is directly estimated from the input-output data by employing a non-parametric identification approach. Such an approach reduces the uncertainties arising from incorrect user decisions by avoiding the parametric model identification. However, DRGA values obtained by the nonparametric identification are subject to different uncertainty sources such as system nonlinearity and noise. In this thesis various strategies are presented to reduce the effect of these uncertainties. In that direction, RGA (DRGA) of linear systems is first analysed using a random excitation signal. Due to the nonperiodic nature of the random signal, the frequency response is susceptible to leakage. To reduce the leakage effect, data is divided into sub-records and the frequency response was averaged over these sub-records. Although the data division proved to be efficient in limiting the leakage effect it has a drawback of reducing the frequency resolution. Moreover, RGA (DRGA) of weakly nonlinear systems is analysed using a multisine excitation signal. The multisine excitation is used to distinguish between the nonlinear distortion and the output noise. It is very difficult to make such distinction using the random excitation. However, long experimental time is needed in returns. To overcome the shortcomings represented by low frequency resolution and the experiment running time, local polynomial approximation approach (LPA) is investigated using both random and multisine excitation.In that direction, RGA (DRGA) of linear systems is first analysed using a random excitation signal. Due to the nonperiodic nature of the random signal, the frequency response is susceptible to leakage. To reduce the leakage effect, data is divided into sub-records and the frequency response was averaged over these sub-records. Although the data division proved to be efficient in limiting the leakage effect it has a drawback of reducing the frequency resolution. Moreover, RGA (DRGA) of weakly nonlinear systems is analysed using a multisine excitation signal. The multisine excitation is used to distinguish between the nonlinear distortion and the output noise. It is very difficult to make such distinction using the random excitation. However, long experimental time is needed in returns. To overcome the shortcomings represented by low frequency resolution and the experiment running time, local polynomial approximation approach (LPA) is investigated using both random and multisine excitation.It can be concluded that the proposed approach achieves quite accurate RGA values with the advantage of exempting the user from deriving a complete parametric model of the plant. Hence, efforts of identifying the parameters of all MIMO subsystems can be saved by finding the parameters of the most significant subsystems of a multivariable system.
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| 12. |
- Kadhim, Ali, et al.
(författare)
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Relative Gain Array Estimation Based on Non-parametric Process Identification for Uncertain Systems
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Since the introduction of the Relative Gain Array (RGA) by Bristol in 1966, it has become awidely used practical tool for solving the input-output pairing problems in decentralized control. In order to remove the dependency of this tool on a parametric description and accurate knowledge of a nominal model, this work proposes a method to estimate the RGA directly from a non-parametric frequency response matrix (FRM) derived from a frequency domain system identification approach. The proposed method reduces the influence of model uncertainties on the calculation of the RGA and derives the RGA at frequencies of interest. The results are exemplified using a 2x3 LTI systems and a 2x2 uncertain system.
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| 13. |
- Kadhim, Ali, et al.
(författare)
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Relative Gain Array of Weakly Nonlinear Systems using a Nonparametric Identification Approach
- 2015
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Ingår i: 2015 IEEE International Conference on Control Applications (CCA 2015). - Piscataway, NJ : IEEE Communications Society. - 9781479977871 ; , s. 1612-1617
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Konferensbidrag (refereegranskat)abstract
- This article presents a procedure to estimate the relative gain array (RGA) matrix for weakly nonlinear systems by means of nonparametric identification of the frequency response matrix (FRM). Specifically, the best linear approximation of nonlinear systems and the covariance of the nonlinear distortions are used in the relative gain array estimation. For the estimation neither process model nor model structure need to be known which is an advantage over methods that require accurate knowledge of a parametric process model. The proposed approach is compared with the original RGA and a nonlinear RGA calculation using the well-known quadruple tank process as a case
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| 14. |
- Kadhim, Ali, et al.
(författare)
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Relative Gain Array Variation for Norm Bounded Uncertain Systems
- 2015
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Ingår i: IEEE 54th Annual Conference on Decision and Control (CDC). - Piscataway, NJ : IEEE Communications Society. - 9781479978847 ; , s. 5959-5965
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Konferensbidrag (refereegranskat)abstract
- This article proposes computationally tractable, easyto expand and tight relative gain variation bound for uncertain systems. The proposed bound is a further development of previous work, which is summarized anddiscussed. Using several examples, the new method is compared with previous results and the advantages are highlighted. The prediction of sign changes in relative gain array elements due to uncertainties is important for pairing decisions. Based on the proposed bound,a method for the prediction of the uncertainty levels which render sign changes is suggested. The prediction method is currently limited to certain classes of systems.In this prediction method neither prior knowledge of the uncertainty nor numerous calculations are needed.
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| 15. |
- Kadhim, Ali
(författare)
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Selection of Decentralized Control Configuration for Uncertain Systems
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Industrial processes nowadays involve hundreds or more of variables to be maintained within predefined ranges to achieve the production demands. However, the lack of accurate models and practical tools to design controllers for such large processes motivate the engineers/practitioners to break the processes down into smaller subsystems and applying decentralized controllers.In contrast to the centralized controller, the decentralized controller is favourable in large-scale systems due to its robustness against loop failures and model uncertainties as well as being easier to tune and update. Yet, two steps are required prior to synthesizing these single-input single-output (SISO) controllers that comprise the decentralized controller. In the first step, a set of manipulated and the controlled variables need to be selected while the second step deals with pairing these variables to close the SISO control loops in a manner that limits the interaction between the loops. The latter step, called "input-output pairing", is usually performed by means of interaction measures (IM) tools using a nominal system model. Taking model uncertainties into consideration when deciding the pairing selection of the decentralized controller is necessary since adopting the pairing based on the nominal system model might be misleading and resulting in poor system performance or instability. It is therefore essential to have tools indicating the extent to which the pairing based on the nominal model persists against gain variations due to uncertainties.The work in this thesis presents a methodology that determines whether the effect of gain uncertainty would invalidate the selected pairing. This has been done following the definition of the most established IM tool used in the industry, the relative gain array (RGA), and some of its variants. Further, a procedure has been developed to automatically obtain the optimal input-output pairing by formulating the pairing rules of relative interaction array (RIA) method as an \textit{assignment problem} (AP), and thus, simplifying the pairing selection for large-scale systems. Thereafter, uncertainty bounds of the RIA elements are employed to validate the pairing selection under the effect of given variations of the system gain. Moreover, following the RIA pairing rules, a method is proposed to calculate a minimum amount of uncertainty that renders a perturbed system for which the pairing, obtained from the nominal system model, becomes invalid.In the aforementioned methodologies, a parametric system model is assumed to be known. To relax this constraint, an approach is therefore proposed and evaluated which identifies the pairing of the decentralized controller directly from the input-output data. This approach has the advantage of exempting the user from deriving a complete parametric model of the plant to decide the input-output pairing, and hence saves the efforts by finding the parameters of the most significant subsystems in a multivariable system. The frequency response of the system and its covariance, and subsequently the dynamic RGA (DRGA) and corresponding uncertainty bounds, are estimated from the input-output data by employing a nonparametric system identification approach. In short, the work presented in this thesis provides beneficial methodologies for researchers in academia as well as engineers in industry to predict the influence of the system gain uncertainty on the pairing selection of decentralized controllers.
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| 16. |
- Kadhim, Ali, et al.
(författare)
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System Uncertainty Effect on Optimal Control Configuration Selection
- 2016
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- An approach to investigate the effect of system uncertainty on the optimal controlconfiguration selection in multivariable systems is proposed. An optimal control configuration,i.e the configuration which best agrees with input-output pairing rules according to certaininteraction measure (IM) can be obtained automatically by formulating the control configurationselection as a Transportation Problem (TP). The proposed approach then checks whetherthis optimal control configuration is valid for given system uncertainties or if a change in theconguration could be expected.
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