Hasil untuk "River protective works. Regulation. Flood control"

Fuyuan Chen, Jian Zeng, Zhiyong Zhang et al.

In tidal estuarine regions, toe scour and deposition at seawalls, which are influenced by runoff and tidal flow, present complexities not found in inland rivers and wave-dominated coasts. Existing methods for predicting toe scour at seawalls are often inaccurate in estuarine environments and can be computationally demanding, limiting their practical application. Hence, there is a need for a simplified, reliable approach tailored to these dynamic settings. This study investigated the characteristics of toe scour and deposition through a case study in the Qiantang River Estuary on the basis of field data. We analyzed continuous monthly riverbed topography data from five cross-sections collected between 2011 and 2018 to examine riverbed profiles and their temporal variations in front of the seawall. In addition, we elucidated the underlying scour and deposition mechanisms. The results indicate that the riverbed slope at the seawall toe ranges from 14° to 27° over 50 m, whereas the riverbed flattens and significantly fluctuates between 50 and 100 m. Toe scour frequently occurs when the maximum daily average runoff discharge exceeds 5000 m3/s or when the average daily runoff discharge surpasses 2200 m3/s. Conversely, deposition is primarily observed with larger tidal ranges and lower runoff conditions. Furthermore, we developed a process-based prediction method (PPM) based on the sediment transport capacity to predict scour depths during various flood events. This method achieves a relative error within 20 %, showing improved accuracy over existing approaches. This study provides a reliable method to predict toe scour at seawalls in tidal estuaries, supporting safer seawall design and more effective maintenance strategies.

Max H. Cohen, Pio Ong, Aaron D. Ames

Guaranteeing safety in the presence of unmatched disturbances -- uncertainties that cannot be directly canceled by the control input -- remains a key challenge in nonlinear control. This paper presents a constructive approach to safety-critical control of nonlinear systems with unmatched disturbances. We first present a generalization of the input-to-state safety (ISSf) framework for systems with these uncertainties using the recently developed notion of an Optimal Decay CBF, which provides more flexibility for satisfying the associated Lyapunov-like conditions for safety. From there, we outline a procedure for constructing ISSf-CBFs for two relevant classes of systems with unmatched uncertainties: i) strict-feedback systems; ii) dual-relative-degree systems, which are similar to differentially flat systems. Our theoretical results are illustrated via numerical simulations of an inverted pendulum and planar quadrotor.

Rukai Wang, Ximin Yuan, Fuchang Tian et al.

ABSTRACT Floods are major natural disasters that present considerable challenges to socioeconomic and ecological systems. Flash floods are highly nonlinear and exhibit rapid spatiotemporal variability. Existing methods struggle to capture these features, leading to suboptimal long‐term and peak flood prediction accuracy. This study proposes a hierarchical flood prediction model based on clustering to enhance forecasting accuracy in the Heshengxi watershed. We employ STGCN and GWN models with the spatiotemporal attention mechanism. Enhanced loss functions further refine flood prediction accuracy. Results show that the hierarchical prediction method is an effective means of extracting flood features by addressing the variability of prediction parameters for different flood magnitudes. The integration of Graph Convolutional and Time Aware models enables the model to recognize the spatiotemporal flood characteristics, overcoming limitations of prevailing methods and ensuring long‐term forecast accuracy. The optimized loss function further improves the prediction performance, resulting in a significant improvement in the accuracy of flood peak prediction, with a reduction of 0.26% in the relative error of the peak prediction by the GWN model. This framework provides an effective solution for flood warning, emergency response, and optimal scheduling. It also demonstrates the potential of deep learning models in the field of intelligent hydrological forecasting.

Kenichiro Kobayashi, Atsushi Tamura, Riku Misato et al.

ABSTRACT The authors present an attempt to reproduce a flash flood in the steep mountainous Myohoujigawa River, Japan, using a physics‐based distributed rainfall‐runoff/flood‐inundation model (DRRFI). The Myohoujigawa River is located in Kobe city. The length is 6.975 km and the area is 11.81 km2. The authors aimed to simulate a 4 m rise in the water level within 40 min in the catchment. Man‐made open‐channel rainwater drainages were added to the river network which could collect more rainwater faster. Likewise, the flux difference splitting (FDS) scheme was used for 1D dynamic wave modeling of steep river flow because it can simulate sub‐ and super‐critical flow regimes. Moreover, the X‐band rainfall data of 250 m and 1 min spatiotemporal resolution, currently the highest‐resolution product in Japan, served as input for the rainfall‐runoff‐inundation model. Consequently, a level of reproducibility was achieved via runoff simulation using the X‐band rainfall data. Subsequently, 21 forecast ensemble rainfalls under the operation of the Japan Meteorological Agency were used for the feasibility study of ensemble flood forecasting. This ensemble flood simulation aimed to determine that the 5 km and 1 h spatiotemporal resolution of the ensemble rainfall currently best product available to the general public in Japan were sufficient to reproduce the flash flood that occurred within 40 min. The 21 ensemble flood simulations exhibited qualitatively acceptable results as the water level rise timings are similar; however, quantitatively the simulated water levels were lower than those of the observed water.

Saba Soori, Hojat Karami

ABSTRACT The position of bridge piers relative to abutments plays a critical role in controlling large wood (LW) accumulation and the resulting local scour, which are among the leading causes of bridge instability. Previous studies have mainly examined isolated piers or abutments using simplified, solid debris shapes, overlooking the interactive effects of pier–to–abutment distance, and the natural porosity of wood accumulations. To address this gap, a comprehensive series of flume experiments was conducted, systematically varying pier–to–abutment distance, log length, flow intensity ratio, bed condition (fixed, movable‐static, movable‐dynamic), and temporal evolution of scour. The results show that LW accumulation probability (LW AP) is primarily controlled by relative log length, bed mobility, and pier–to‐abutment distance. Accumulation reached up to 98% for longer logs at large pier–abutment distances, as these positions aligned the piers with the main LW transport path. While flow intensity ratio and pier placement significantly influenced scour depth and geometry, porous, and transient LW accumulations produced only minor additional scour effects (< 6.5%) compared to solid accumulations reported in earlier studies. This study, by highlighting pier–to–abutment distance as a governing factor in LW accumulation and scour, simulating realistic LW with variable porosity instead of idealized debris shapes, and comparing LW AP under fixed, static, and dynamic bed conditions, provides novel insights into flow–structure–wood interactions and demonstrates that strategic pier placement can offer more effective risk mitigation than conservative design assumptions based on non‐representative debris models.

Layla Poubel Tunala, Frederico Tapajós de Souza Tâmega, Ricardo Coutinho

Sediment is highly related to coral reef degradation worldwide, and sedimentation is considered a critical cause of stress for coral communities. The current study focused on the Arraial do Cabo Marine Extractive Reserve (ACMER), recognized as a coralline oasis in the southwest Atlantic, which is facing multiple environmental pressures. Among them, mass tourism stands out, which enhances sedimentation. To address the scientific question of how sediment characteristics and rates vary across different sites, local sedimentation was monitored for about one year through sedimentation rates, granulometric composition, and the percentage of calcium carbonate (%CaCO3) at five sampling sites, each exposed to varying levels of natural and anthropogenic activities. The results revealed distinct patterns linked to these activities and natural agents. For instance, Forno's Cove exhibited the highest percentage of fine sediment (about 70%) among all the other sampled points, suggesting the sedimentation to be strongly related to anthropogenic action. Although the overall sedimentation rates in Arraial do Cabo Bay were not high, the current findings highlight the sedimentation related to the increase in tourist activities and the need for continuous monitoring of ACMER. Such vigilance is crucial for ensuring the environmental health of coral environments and supporting the local human community's livelihoods.

Meysam Nouri, Rasoul Ilkhanipour, Amir Hossein Azimi

This paper presents the results of experimental investigation on the local erosion and mound formation induced by slurry turbulent circular wall jets in crossflow and with the presence of a secondary current. The trajectory of the slurry jets with different intensities on the bed formation was measured with an accurate laser scanner with a resolution of ±1 mm. Other data such as scour, and mound areas and volumes were measured to study the effects of sediment concentration and jet’s intensity on deformation of erodible bed at the vicinity and downstream of the crossflow. Experimental results indicated that the mass flux of sediment in slurry wall jets increased the width and spreading rate of sediment mound while increasing the intensity of the jet reduced the mound width and stretched it along the flow direction. The correlation between non-dimensional geometry parameters with the jet’s Reynolds number indicated a distinct behavior on the development and direction of mounds with a threshold Reynolds number of approximately 36,000. For turbulent slurry wall jets with Reynolds number smaller than the threshold value, most of the sediments settled at the vicinity of the nozzle and reduced the scour depth while for stronger jets, sediment dunes were formed in the curved region of the flume and scour depth was almost the same as the scour depth formed by the corresponding clear water turbulent wall jets. A linear correlation was found between the peak scour depth and jet’s Reynolds number, while peak scour depth, area, and volume decreased with increasing the initial sand concentration of slurry jets. Empirical formulas were proposed for prediction of bed deformation and jet’s trajectory, the accuracies of the proposed models were evaluated using statistical analysis, and the performance of the proposed models were compared with the existing models from the literature.

Afshin Amiri, Silvio Jose Gumiere, Bahram Gharabaghi et al.

Hiroshi Takebayashi, Masaharu Fujita

ABSTRACT On August 9–10, 2021, the Koakagawa Bridge in Mutsu, Aomori Prefecture, Japan, collapsed owing to the flood caused by a tropical cyclone. In this study, the cause of the collapse was examined. The characteristics of flood inundation with bypassing flows and countermeasures for bank erosion due to channel blockage by driftwood were investigated based on field surveys and numerical simulations. The scouring of the bed around the bridge pier was found to be the cause leading to bridge failure. Channel blockage owing to driftwood would have caused flood inundation and damage to the left bank, the top of the bank is bare of sediment, by forming a bypassing flow. However, the surface of the right bank on which the bypassing flow with high velocity formed was covered with concrete; therefore, bank erosion did not occur. These results indicate that to prevent bank erosion caused by bypassing flows during floods, it is important to protect banks downstream of the bridge using non‐erosive materials. Only a small area, where bypassing flows form and non‐dimensional shear stress is larger than 0.05, is sufficient for protection. It is also important to predict bed degradation characteristics around piers and banks, especially when the bed material is small.

Panagiotis Rousseas, Haejoon Lee, Dimos V. Dimarogonas et al.

Control synthesis under constraints is at the forefront of research on autonomous systems, in part due to its broad application from low-level control to high-level planning, where computing control inputs is typically cast as a constrained optimization problem. Assessing feasibility of the constraints and selecting among subsets of feasible constraints is a challenging yet crucial problem. In this work, we provide a novel theoretical analysis that yields necessary and sufficient conditions for feasibility assessment of linear constraints and based on this analysis, we develop novel methods for feasible constraint selection in the context of control of autonomous systems. Through a series of simulations, we demonstrate that our algorithms achieve performance comparable to state-of-the-art methods while offering improved computational efficiency. Importantly, our analysis provides a novel theoretical framework for assessing, analyzing and handling constraint infeasibility.

Marco Peruzzo, Giacomo Baggio, Francesco Ticozzi

We consider a network of identical, first-order linear systems, and investigate how replacing a subset of the systems composing the network with higher-order ones, either taken to be generic or specifically designed, may affect its controllability. After establishing a correspondence between state controllability in networks of first-order systems with output controllability in networks of higher-order systems, we show that adding higher-order dynamics may require significantly fewer subsystem modifications to achieve structural controllability, when compared to first-order heterogeneous subsystems. Furthermore, we characterize the topology of networks (which we call X-networks) in which the introduction of heterogeneous local dynamics is not necessary for structural output controllability, as the latter can be attained by suitable higher-order subsystems with homogeneous internal dynamics.

Hee Won Jee, Seung Beom Seo, Kyeong‐Moon Ko et al.

Abstract Adaptation policies are being increasingly implemented to cope with the increased frequency of natural disasters due to climate change. However, it is crucial to quantitatively evaluate the mitigating effects of these policies, as this allows for their assessment and prioritization. Therefore, this study sought to develop a nonlinear flood damage function for each administrative region of South Korea to quantify the potential damage caused by extreme rainfall events. Afterward, a power function was nested to model the coefficient of the flood damage function with regional factors characterizing each region's flood mitigation capacity. Here, regional factors were selected based on their linkage to two potential adaptation policies: enhancing retention reservoir and pumping capacity and enhancing river dike construction. The proposed evaluation framework was tested in 15 administrative districts in South Korea and the flood damage reduction effects of the two policy scenarios were estimated. The enhancement of retention reservoir and pumping capacity showed a 6.7% reduction effect, whereas enhancing river dike construction showed a 29.2% reduction effect. The implementation of both policies yielded a 34.3% reduction effect. Despite the limitations of this study, our findings still provide a quantitative comparison of the long‐term effects of national climate change adaptation measures. Additionally, accumulating more damage records would allow for the development of damage functions at a finer scale.

Richard Pates, Anders Rantzer

An optimal control problem on finite-dimensional positive cones is stated. Under a critical assumption on the cone, the corresponding Bellman equation is satisfied by a linear function, which can be computed by convex optimization. A separate theorem relates the assumption on the cone to the existence of minimal elements in certain subsets of the dual cone. Three special cases are derived as examples. The first one, where the positive cone is the set of positive semi-definite matrices, reduces to standard linear quadratic control. The second one, where the positive cone is a polyhedron, reduces to a recent result on optimal control of positive systems. The third special case corresponds to linear quadratic control with additional structure, such as spatial invariance.

Erik van den Eshof, Jorn van Kampen, Mauro Salazar

This paper presents an energy and thermal management system for electric race cars, where we tune a lift-off-throttle signal for the driver in real-time to respect energy budgets and thermal constraints. First, we compute the globally optimal state trajectories in a real-time capable solving time, optimizing a 47-kilometer horizon in 2.5 seconds. Next, for safe operation with a human driver, we simplify it to a maximum-power-or-coast operation in full-throttle regions (straights). Thereby, both the positions from which the vehicle should start coasting and the optimal throttle map are subject to tuning. To this end, we define the coasting sections with a threshold on the co-state trajectory of the kinetic energy from the optimal solution. We devise an online implementable bisection algorithm to tune this threshold and adapt it using PI feedback. Finally, we validate the proposed approach for an electric endurance race car and compare three variants with varying implementation challenges: one re-optimizing and updating the kinetic co-state trajectory online, one applying only the bisection algorithm online, and one relying exclusively on feedback control. Our results show that, under typical racing disturbances, our energy management can achieve stint times ranging from less than 0.056\% to 0.22\% slower compared to offline optimization with a priori knowledge of disturbances, paving the way for on-board implementations and testing.

رضا چمنی, مهدی وفاخواه, سیدحمیدرضا صادقی

امروزه خشکسالی به یکی از موضوعات داغ مورد توجه جهان تبدیل شده است اما تاثیر آن بر ارائه خدمات و سلامت حوزه آبخیزها در مواجه با این بلای طبیعی کمتر مورد ارزیابی قرار گرفته است. بر همین اساس، در این پژوهش سعی شده است تا تاثیر خشکسالی در دوره 1384 تا 1398 بر سلامت حوزه آبخیز افین مبتنی بر تغییرات پایایی (Rel)، تاب‌آوری (Res) و آسیب‌پذیری (Vul) مورد ارزیابی قرار گیرد. لذا، داده‌های بارندگی سه ایستگاه باران‌سنجی با روش عکس فاصله وزنی برای حوزه آبخیز و زیرحوضه­‌ها میان‌یابی شد. سپس، شاخص بارش استاندارد شده (SPI) بر اساس میانگین و انحراف معیار داده‌­های ماهانه تعیین شد و برای محاسبه شاخص‌های Rel ،Res و Vul مورد استفاده قرار گرفت. در انتها، با محاسبه مقدار میانگین هندسی این شاخص‌ها وضعیت کلی سلامت آبخیز تعیین شد. نتایج سالانه پژوهش نشان داد، آبخیز افین به لحاظ شاخص‌­های Rel ،Res و Vul به‌­ترتیب مقادیری بین 0.92-0.83، 0.33-0.17 و 0.54-0.24 را دارا است. شاخص RelResVul نیز مقادیری بین 0.53-0.37 را به خود اختصاص داده است. همچنین، متوسط شاخص سلامت حوزه آبخیز در این دوره 0.42 محاسبه شد که نشان‌دهنده قرارگیری سلامت حوزه آبخیز در گروه متوسط است. تغییرات مکانی سلامت آبخیز نیز نشان داد، شاخص‌های Rel ،Res و Vul در زیرحوضه­‌های مختلف به‌­ترتیب مقادیری بین 0.86-0.85، 0.24-0.21 و 0.78-0.76 را دارا هستند. نتایج تحلیل بارندگی منطقه حاکی از آن است که با توجه به ثبات نسبی بارندگی، تاثیر دخالت­‌های انسانی و تشدید عوامل تهدیدکننده سلامت آبخیز، بیش از پیش بر وضعیت موجود تاثیرگذار بوده است و در صورت عدم توجه به آن تاثیرات زیان‌باری در پی خواهد داشت.

Houssine Zine, El Mehdi Lotfi, Delfim F. M. Torres et al.

Using the recent weighted generalized fractional order operators of Hattaf, a general fractional optimal control problem without constraints on the values of the control functions is formulated and a corresponding (weak) version of Pontryagin's maximum principle is proved. As corollaries, necessary optimality conditions for Caputo-Fabrizio, Atangana-Baleanu and weighted Atangana-Baleanu fractional dynamic optimization problems are trivially obtained. As an application, the weighted generalized fractional problem of the calculus of variations is investigated and a new more general fractional Euler-Lagrange equation is given.

Yujie Wang, Xiangru Xu

When the disturbance input matrix is nonlinear, existing disturbance observer design methods rely on the solvability of a partial differential equation or the existence of an output function with a uniformly well-defined disturbance relative degree, which can pose significant limitations. This note introduces a systematic approach for designing an Immersion and Invariance-based Disturbance Observer (IIDOB) that circumvents these strong assumptions. The proposed IIDOB ensures the disturbance estimation error is globally uniformly ultimately bounded by approximately solving a partial differential equation while compensating for the approximation error. Furthermore, by integrating IIDOB into the framework of control barrier functions, a filter-based safe control design method for control-affine systems with disturbances is established where the filter is used to generate an alternative disturbance estimation signal with a known derivative. Sufficient conditions are established to guarantee the safety of the disturbed systems. Simulation results demonstrate the effectiveness of the proposed method.

Brooks A. Butler, Philip E. Paré

As modern systems become ever more connected with complex dynamic coupling relationships, developing safe control methods becomes paramount. In this paper, we discuss the relationship of node-level safety definitions for individual agents with local neighborhood dynamics. We define a collaborative control barrier function (CCBF) and provide conditions under which sets defined by these functions will be forward invariant. We use collaborative node-level control barrier functions to construct a novel \edit{decentralized} algorithm for the safe control of collaborating network agents and provide conditions under which the algorithm is guaranteed to converge to a viable set of safe control actions for all agents. We illustrate these results on a networked susceptible-infected-susceptible (SIS) model.

Yiting Chen, Liliaokeawawa Cothren, Jorge Cortes et al.

This paper considers the problem of regulating a dynamical system to equilibria that are defined as solutions of an input- and state-constrained optimization problem. To solve this regulation task, we design a state feedback controller based on a continuous approximation of the projected gradient flow. We first show that the equilibria of the interconnection between the plant and the proposed controller correspond to critical points of the constrained optimization problem. We then derive sufficient conditions to ensure that, for the closed-loop system, isolated locally optimal solutions of the optimization problem are locally exponentially stable and show that input constraints are satisfied at all times by identifying an appropriate forward-invariant set.

Gabriel Melun, Frédéric Liébault, Guillaume Piton et al.

On October 2nd, 2020, under the combined effect of the winter Alex storm formed off the Brittany coast, and a strong Mediterranean episode, very intensive rainfalls affected in the south eastern France, both Roya and V{é}subie catchments (locally up to 600 mm in 24h). This paroxysmal event with a heavy human toll (10 dead, 8 missing) generated extreme flash floods over a large part of the hydrographic network. The result is an almost generalized fluvial metamorphosis of rivers, from sinuous single-thread channels to braided channels. The characterization of morphological effects of these floods is based on a diachronic aerial picture analysis highlighting a strong increase of the active channel width (up to 900%) reaching -- or even pushing back in few sectors -- front limits of the valley bottom. In the V{é}subie, the 2D morphological effect of the Alex storm was 10 times higher than that of the 100-yrs return period flood of November 1997. Comparison of digital terrain models (DEM) before- and after-flood also allows us to foresee the altitudinal variations (erosion/deposition) that affected beds and their riverine margins. The analysis of the impacts caused by these floods changes the perception of the ``freedom space'' of these alpine rivers, which now must be taken into account in the perspective of resilient reconstruction.