1,721,386 research outputs found
Comment on “Effects of different tillage practices on the hydraulic resistance of concentrated flow on the loess plateau in China” by J. Sun et al
No full textFor concentrated flows, which are characterized by small water depth and steep sloping beds, hydraulic conditions different from those typical of streams and rivers occur. In this study a new theoretically deduced flow resistance equation was tested using the experimental data by Sun et al. for three different tilled surfaces (Manual Dibbling, MD, Manual Hoeing, MH, and Contour Drilling, CD). At first, the profile parameter-relationship, which is the relationship between the velocity profile parameter Γ, the channel slope and the flow Froude number, was calibrated using rill flow data by Di Stefano et al. Then, the applicability of this relationship was tested by the measurements of Sun et al. The calculated Darcy–Weisbach friction factor values were generally lower than those measured by Sun et al. and this result was justified taking into account that the rill measurements used for calibrating the profile parameter-relationship simply correspond to grain resistance conditions. For taking into account both grain resistance and tillage induced surface roughness, the profile parameter-relationship was calibrated by the measurements by Sun et al. This calibration was carried out for each tillage practice (MD, MH and CD) and using all the measurements carried out during each 20 min – experimental run. This study was also developed using exclusively the data concerning the beginning of the experiment (0–4 min), in order to state the effect of the initial roughness, and those regarding the end of the experiment (16–20 min) to estimate the influence of the temporal evolution of roughness on the friction factor. The study proved that the Darcy–Weisbach friction factor due to grain resistance and tillage induced roughness can be accurately estimated using the proposed theoretical approach. A temporal variation of the Darcy–Weisbach friction factor was also recognized. Finally, the data were supportive of the slope independence hypothesis of flow velocity stated by Govers
Comment on “Rill erosion processes on steep colluvial deposit slope under heavy rainfall in flume experiments with artificial rain by F. Jiang et al.”
No full textSince rill flows are characterized by small water depths and steeply sloping channels, the corresponding hydraulic conditions are very different to those which are typically found in channels of streams and rivers. Furthermore, limited information is currently available on the effect of rainfall on flow resistance. The objective of this comment was to investigate the applicability of a recently theoretically deduced rill flow resistance equation, based on a power-velocity profile, using measurements carried out by Jiang et al. for both different slope steepness conditions and rainfall intensity. The relationship between the velocity profile parameter Γ, the channel slope and the flow Froude number was calibrated using the data by Jiang et al. The theoretical approach and the measurements carried out in the investigated conditions allowed to state that a) the Darcy-Weisbach friction factor can be accurately estimated using the proposed theoretical approach, b) the data were supportive of the slope independence hypothesis of rill velocity stated by Govers and c) the Darcy-Weisbach friction factor varies with rainfall intensity
A new approach for deducing the stage-discharge relationship of a triangular broad-crested device
No full textIn this paper, the outflow process of a triangular broad-crested device is examined using the dimensional analysis and the incomplete self-similarity theory. A new theoretical stage-discharge relationship is proposed, and its applicability is verified using measurements available in literature. The proposed power equation is characterized by a coefficient depending on device apex angle and a constant value of the exponent
Flow resistance due to shrubs and woody vegetation
Full text linkIn this paper, a theoretical open channel flow resistance equation was verified using flow depth and discharge measurements carried out by Freeman et al. in a large channel, 2.44 m wide, for ten different types of uniform-sized plants (shrubs and woody vegetation). The plants, which are broadleaf deciduous vegetation commonly found in floodplains and riparian zones, were placed in staggered rows inside the channel whose bed was constructed to accept plants with their root systems. For each species, the available measurements were carried out by Freeman et al. with plants having different values of plant density, height, and bending stiffness. The available literature database (87 measurements) was divided into two groups which were separately used to calibrate and test the theoretical approach. In particular, 46 measurements were used to calibrate the relationship between the scale factor Γ of the velocity profile, the Froude number, and the channel slope. This relationship was calibrated using the entire available dataset or varying the scaling coefficient a with the investigated vegetation type. The measured values of the Darcy-Weisbach friction factor, obtained by the measured flow velocity, water depth and slope values, were compared with those calculated by the theoretical flow resistance law, coupled with the relationship for estimating the Γ function having a scaling coefficient different for each investigated vegetation type. This comparison allowed to demonstrate that an accurate estimate of the Darcy-Weisbach friction factor (errors less than or equal to ±10% for 87% of the investigated cases) can be obtained. However, for the investigated vegetation species, that are characterized by a large range of bending stiffness, also a mean value of the scaling coefficient a equal to 0.3283 allows an accurate estimate of the Darcy-Weisbach friction factor
Evaluating the effects of sediment transport on pipe flow resistance
Full text linkIn this paper, the applicability of a theoretical flow resistance law to sediment-laden flow in pipes is tested. At first, the incomplete self-similarity (ISS) theory is applied to deduce the velocity profile and the corresponding flow resistance law. Then the available database of measurements carried out by clear water and sediment-laden flows with sediments having a quasi-uniform sediment size and three different values of the mean particle diameter Dm (0.88 mm, 0.41 mm and 0.30 mm) are used to calibrate the Γparameter of the power-velocity profile). The fitting of the measured local velocity to the power distribution demonstrates that (i) for clear flow the exponent δ) can be estimated by the equation of Castaing et al. and (ii) for the sediment-laden flows δ is related to the diameter Dm. A relationship for estimating the parameter Гv obtained by the power-velocity profile) and that Гf of the flow resistance law) is theoretically deduced. The relationship between the parameter Гv, the head loss per unit length and the pipe flow Froude number is also obtained by the available sediment-laden pipe flow data. Finally, the procedure to estimate the Darcy–Weisbach friction factor is tested by the available measurements
Model predictive control of cyber-physical systems
No full textCyber-Physical Systems (CPS) represent a groundbreaking technological advancement that integrates physical processes with computational resources and networking capabilities, heralding a significant leap in efficiency, functionality, and adaptability across various applications. From revolutionizing transportation through self-driving cars to enhancing energy distribution via smart grids, CPS are poised to be pivotal in the fourth industrial revolution, fundamentally altering daily life and work in a manner akin to the transformative impacts of the internet and the World Wide Web.
Originating from the concept of merging digital and physical realms, CPS aim to create systems that are inherently intelligent, adaptive, and resilient, extending beyond traditional embedded systems by leveraging advancements in computing, communication, and control.
These systems are characterized by a core architecture comprising physical components (sensors and actuators), cyber elements (computational and communication infrastructure), and control mechanisms (algorithms and software), working in unison through a feedback loop to dynamically interact with and respond to their environment. In this respect, the work done in this thesis is the application of Model Predictive Control (MPC) framework to CPS with the aim to an increase in operational efficiency, an increase in optimality with respect to resource allocation, and an increase in general responsiveness and adaptability of such systems to ambient variability. This thesis attempts to manifest the future implications in applying MPC to transform the management and control of these sophisticated cyber-physical systems within their crucial sectors via theoretical development and practical implementation of case studies.
The control methodology discussed in this thesis regards the application of MPC in three case studies: in the frame of Power Systems, Smart Cities and Industry 4.0 in the space sector.
The first work deals with the emerging complexities in modern transmission and distribution grids that arise through integration with distributed energy resources such as electric energy storage systems, renewable energy plants, and plug-in electric vehicles. The new issues are the intermittency in power generation from renewable sources and in the demand from electric vehicles present a new challenge to grids requiring advancement in grid control and optimization. Considering these challenges, in this work the candidate proposes a novel reconfiguration algorithm based on MPC for the dynamic configuration and re-configuration (topology) of the grid to minimize losses and to improve operational resilience in the presence of adverse events like faults or (cyber-)attacks. The algorithm progresses over the existing methods by removing the necessity of constantly connected grids to let autonomous grid islands be formed that can dynamically get connected and disconnected from the main grid. This research provides a critical review of existing network reconfiguration strategies, spanning between classic optimization-based methods, heuristics ((meta)heuristics), and machine learning-based solutions with their respective advantages and limits. It is hence observed that while the classic optimization methods actually give optimum solutions, they are afflicted by high computational costs. (Meta)heuristics are computationally efficient, though void of guarantees about the optimality of solutions. Machine learning based approaches, in particular Reinforcement Learning, promise policies that are near optimal but come at an enormously high demand for computational resources during training and also offer serious concerns about safety. In such a way, the proposed MPC-based solution combines the features of optimal control at a lower computational cost and adaptability for real-time applications. This means to be the breakthrough approach in network reconfiguration, bridging the gaps that exist within today's available methodologies and thereby offering a powerful, robust, efficient, flexible solution to meet challenges posed by today's modern, dynamic grid environment.
The second work addresses a crucial challenge that urban greenhouse gases (GHG), primarily produced by buildings and transportation, with a focus on optimization of the intelligent traffic light (TL) control systems in mitigating road congestion. Given the global climate change efforts like the 2016 Paris Agreement and the EU 2019 Green Deal, the study would emphasize the need for viable urban traffic management strategies that could lead to significant GHG emission reductions, as a majority of such emissions originate from urban settings. Although an extensive literature on Intelligent TL controls is available today, it is found that there is a gap in adaptability and efficiency, mainly in real-time traffic conditions. A novel model predictive control strategy based on mixed-integer optimization has been proposed in this thesis to enhance the timings of TLs at intersections by an original approach different from classical fixed-timing strategies without any real-time reaction. The main contribution of this thesis lies in proposing an integrated MPC controller which determines both the optimal signal timing for the TLs and optimal trajectories for Automatically Driven Vehicles (ADVs), while modelling also Manually Driven Vehicles (MDVs) dynamics, leading to significant reduction of queue length and waiting times. In these terms the controller is adaptive, allowing it to operate in mixed scenarios. In addition, several innovative constraints that have been introduced within the MPC formulation allow recursive feasibility to be ensured in constraint-activating events, for instance, when a vehicle approaching the TL during red signal could bring the problem towards infeasibility because some constraints cannot be violated.
About Industry 4.0, the most important challenge this thesis tackles is the optimization of task scheduling and controlling in the spaceport within the dynamically changing space industry, which previously limited to governmental entities is now expanding to include private companies. This research was carried out within the framework of the H2020 SESAME project--partnership led by ArianeGroup--that aims to enhance the schedule of assembly operations of space vehicles to maximize the launch throughput at the Guiana space center in Kourou. In the literature they are referred to as Assembly Line Balancing Problems (ALBP) and the key contribution of this work is the development of a scalable MPC algorithm, integrated with a Mixed-Integer Linear Program (MILP) model, to optimize campaign planning in real-time leverages both static and dynamic data, addressing scalability, flexibility and the ability to manage complex constraints, and real-time disturbances. Simulation results confirm the merit of proposed efficient task scheduling algorithm which retains the characteristics of standard MPC and outperforms state-of-the-art optimal scheduling heuristics maintaining similar speed which makes it suitable for real-time implementation
A New Model for Solving Hydrological Connectivity Inside Soils by Fast Field Cycling NMR Relaxometry
Full text linkIn this paper, a new quantitative approach for estimating the structural and functional connectivity inside soil by Fast Field Cycling (FFC) NMR relaxometry is presented, tested by measurements carried out in three samples with different texture characteristics. Measurements by FFC NMR relaxometry have been carried out using water-suspended samples and Proton Larmor frequencies (νL) ranging in the 0.015–35 MHz interval. Two non-degraded soil samples, with different textural characteristics, and a degraded soil collected in a badland area, were analyzed. For a given soil and any applied Proton Larmor frequency, the distribution of the longitudinal relaxation times, T1, (i.e., relaxogram) measured by FFC NMR has been integrated, and the resulting S-shaped curve (i.e., relaxogram integration curve) was represented, for the first time, by Gumbel’s diagram. This new representation of the relaxogram integration curve, transforming the S-shaped curve into a straight line, allowed for distinguishing three linear components, corresponding to three different relaxation time ranges, characterized by three different slopes. Two points, identified by the abrupt slope changes of the relaxogram integration curve plotted in Gumbel’s diagram, are used to identify two characteristic values of relaxation time, T1A and T1B, which define three well-known pore size classes (T1 < T1A micro-pores, T1A < T1 < T1B meso-pores, and T1 > T1B macro-pores). The relaxogram integration curve allowed for calculating the non-exceeding empirical cumulative frequency, F(T1), corresponding to the characteristic T1A and T1B values. The analysis demonstrated that the relaxogram can be used to determine the pore-size ranges of each investigated sample. Finally, using the slope values of the three components of the relaxogram integration curve, a new definition of the Structural Connectivity Index, SCI, and Functional Connectivity Index, FCI, was proposed
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