Design and calibration of a semi-active control logic to mitigate structural vibrations in wind turbines

Nicola Caterino,Christos T. Georgakis,Mariacristina Spizzuoco,Antonio Occhiuzzi 국제구조공학회 2016 Smart Structures and Systems, An International Jou Vol.18 No.1

The design of a semi-active (SA) control system addressed to mitigate wind induced structural demand to high wind turbine towers is discussed herein. Actually, the remarkable growth in height of wind turbines in the last decades, for a higher production of electricity, makes this issue pressing than ever. The main objective is limiting bending moment demand by relaxing the base restraint, without increasing the top displacement, so reducing the incidence of harmful \"p-delta\" effects. A variable restraint at the base, able to modify in real time its mechanical properties according to the instantaneous response of the tower, is proposed. It is made of a smooth hinge with additional elastic stiffness and variable damping respectively given by springs and SA magnetorheological (MR) dampers installed in parallel. The idea has been physically realized at the Denmark Technical University where a 1/20 scale model of a real, one hundred meters tall wind turbine has been assumed as case study for shaking table tests. A special control algorithm has been purposely designed to drive MR dampers. Starting from the results of preliminary laboratory tests, a finite element model of such structure has been calibrated so as to develop several numerical simulations addressed to calibrate the controller, i.e., to achieve as much as possible different, even conflicting, structural goals. The results are definitely encouraging, since the best configuration of the controller leaded to about 80% of reduction of base stress, as well as to about 30% of reduction of top displacement in respect to the fixed base case.

Aerodynamics and rain rivulet suppression of bridge cables with concave fillets

Burlina, Celeste,Georgakis, Christos T.,Larsen, Soren V.,Egger, Philipp Techno-Press 2018 Wind and Structures, An International Journal (WAS Vol.26 No.4

In this paper, the aerodynamic performance of two new cable surfaces with concave fillets (strakes) is examined and compared to plain, dimpled and helically filleted surfaces. To this end, an extensive wind-tunnel campaign was undertaken. Different samples with different concave fillet heights for both new surfaces were tested and compared to traditional surfaces in terms of aerodynamic forces (i.e. drag and lift reduction) and rain-rivulet suppression. Furthermore, flow visualization tests were performed to investigate the flow separation mechanism induced by the presence of the concave fillet and its relation to the aerodynamic forces. Both new cable surfaces outperformed the traditional surfaces in terms of rain-rivulet suppression thanks to the ability of the concave shape of the fillet to act as a ramp for the incoming rain-rivulet. Furthermore, both new surfaces with the lowest tested fillet height were found to have drag coefficients in the supercritical Reynolds range that compare favorably to existing cable surfaces, with an early suppression of vortex shedding.

Using the design of dynamic experiments to optimize photosynthetic cyanophycin production by Synechocystis sp.

Giulia Trentin,Alberto Bertucco,Christos Georgakis,Eleonora Sforza,Elena Barbera 한국공업화학회 2023 Journal of Industrial and Engineering Chemistry Vol.117 No.-

The production of cyanophycin by photosynthetic microorganisms, as a high-value bio-based compound,is getting increasing interest. The aim of this work is to maximize the production of this compound by thecyanobacterium Synechocystis sp. in semi-batch cultivation systems, by applying a data-driven modelingapproach based on the Design of Dynamic Experiments (DoDE) and Response Surface Model (RSM)methodologies. A first set of experiments, carried out inside an initially defined domain, was used to finda preliminary RSM model describing cyanophycin concentration as a function of incident light intensityprofile, temperature, and phosphorus supply profile. The model was then improved, according to an evolutionaryoptimization approach, by carrying out additional experiments in a modified domain, exploitinginformation derived by the initial model. The updated model was used to identify the optimaloperating conditions resulting in maximum cyanophycin concentration at the end of the batch. The cyanophycinconcentration found experimentally (228.2 ± 20.0 mg/L) in these conditions fell within the confidenceinterval of the model prediction. Remarkably, this experimentally obtained value represents asignificant (about 20 %) increase in the cyanophycin production with respect to the highest value foundin the experiments before the optimization step (184.3 ± 0.8 mg/L).

Research on Prediction of Dam Seepage and Dual Analysis of Lag-Sensitivity of Influencing Factors Based on MIC Optimizing Random Forest Algorithm

Yongtao Liu,Dongjian Zheng,Xin Wu,Xingqiao Chen,Christos T. Georgakis,Jianchun Qiu 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.2

The seepage of the dam is an important representation of the operation characteristics of thedam, and there are many factors affecting the seepage with a certain lag. It is still difficult topredict its change and sensitivity because of complex operating conditions. At present, the lagsensitivityof influence factors of the dam seepage has not been studied. The time seriesinfluence factors of seepage are determined by HTRT (hydrostatic-thermal-rainfall-time)model in this paper. To avoid the pseudo fitting of conventional methods, HTRT model nestedrandom forest algorithm is used to establish the predicting model of the dam seepage. AndMIC algorithm is used to achieve the dual purposes of time lag and sensitivity analysis. Firstly,the time lag of relationship between seepage and its influencing factors is characterized, andthe most appropriate lag time of the HTRT model factors is determined. Secondly, independentcorrelation analysis on all influencing factors is carried out and the sensitivity of each factor isanalyzed by MIC. Meanwhile, the sensitivity of the factors to seepage is quantitatively analyzedby the two parameters of %IncMSE and IncNodePurity of RF algorithm. The sensitivity ofinfluencing factors is analyzed by comparing MIC results with RF results. Combined with thecase, taking the error of fitting prediction as the evaluation index of seepage prediction, theprediction accuracy of MIC-RF model, RF model and MIC-BPNN (Back Propagation neuralnetwork) model is calculated and compared. Case study showed that MIC- RF monitoringmodel has high prediction accuracy, strong adaptability and high robustness in dam seepage,and the sensitivity and time lag of influencing factors can be quantitatively analyzed. Thewater pressure and rainfall of the lag time are 14 days and 16 days respectively. The sensitivitystudy of the time series influencing factors of seepage showed that the water pressurecomponent is the main controlling factor of seepage, and rainfall component is more sensitiveto later stage. The MIC-RF model can be used as a new dam seepage safety monitoringmodel.

Integrating operations and control: A perspective and roadmap for future research

Daoutidis, Prodromos,Lee, Jay H.,Harjunkoski, Iiro,Skogestad, Sigurd,Baldea, Michael,Georgakis, Christos Elsevier 2018 Computers & chemical engineering Vol.115 No.-

<P><B>Abstract</B></P> <P>This “white paper” is a concise perspective based on a session during FIPSE 3, held in Rhodes, Greece, June 20–23, 2016. This was the third conference in the series “Future Innovation in Process Systems Engineering” (http://fi-in-pse.org), which takes place every other year in Greece, with a limited number of participants and just three topics/sessions whose objective is to pose and discuss open research challenges in Process Systems Engineering. This specific session comprised invited talks by Sigurd Skogestad and Iiro Harjunkoski, followed by short presentations by the participants and extensive discussions. The paper does not intend to provide a comprehensive review on the subject, or a detailed exposition of the concepts and problems. Its aim is to highlight open problems and directions for future research.</P> <P><B>Highlights</B></P> <P> <UL> <LI> This white paper is a concise perspective based on a session during FIPSE 3, held in Rhodes, Greece, June 20–23, 2016. </LI> <LI> Its aim is to highlight open problems and directions for future research on the integration of control and operations. </LI> <LI> It discusses such problems on control and optimization of plants with frequent transitions, on the integration of scheduling and control, and on the impact of big data on control and operations. </LI> <LI> Case studies on the design and operation of microgrids are also discussed. </LI> </UL> </P>