Yazar "Valyrakis, Manousos" seçeneğine göre listele

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    A numerical study of the flow patterns around midchannel islands in lowland rivers and their possible biogeomorphological impacts
    (2023) Heıdarı, Naghmeh; Heidari, Naghmeh; Yagcı, Oral; Valyrakis, Manousos
    Midchannel islands (MCIs) are instream geomorphic units generally emerge in lowland rivers. Despite their significant ecomorphological services in the river ecosystem, the flow patterns around these self-forming riparian landforms and their impacts on aquatic life are not fully understood yet. Understanding the flow pattern around these formations enables practitioners to produce cost-effective, sustainable, and eco-friendly river management projects and strategies, forming the motivation of this study. Herein, the secondary flow pattern around MCIs was analyzed by employing a RANS-based numerical model. Flow around the simplified bodies was simulated to give a more precise analysis regarding flow-island interactions. Once the numerical validation process was completed for the cylinder using an experimental dataset, the validated model was implemented for islands (streamlined island, vertically sloped island (VSI), and realistically sloped island (RSI)). Analysis of the model results revealed the following key findings: 1) the RSI acted like a streamlined object and produced weaker lee-wake vortices with a longer recovery distance compared to the streamlined island and the VSI, 2) the RSI gained a better-streamlined form near the bed than near the water surface due to enhanced elongation, 3) this situation in the RSI case generated highly variable flow patterns along the depth behind the MCI, and 4) due to the three-dimensional geometry of the RSI, the generated large-scale vortices propagated asymmetrically towards the sides of the channel rather than remaining around the centerline.
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    Flow Structures around a Sphere Attached to the Bottom of a Prismatic Sloshing Tank: Problem-oriented basic research
    (Nan Yang Academy of Sciences Pte. Ltd, 2024) Aksel, Murat; Yagci, Oral; Valyrakis, Manousos; Kirca, V. S.Ozgur
    This study aimed to investigate the spatiotemporal variation of hydrodynamic variables around a sphere rigidly fixed to the bottom of a sloshing tank. The experimental measurement of the variations of dynamic variables around a body in a sloshing tank requires non-intrusive measurements that are usually expensive and sometimes inapplicable. Therefore, the numerical model could serve as a cost-effective tool for such problems. A two-stage analysis was con-ducted. In the first stage, an experimental study was carried out in a testing system comprising a water tank with uniaxial freedom of movement constructed on a monorail operated by a computer-controlled step motor. The primary objective of the experiments was to generate reliable data for calibrating the numerical model. During the experiments, the tank’s movements were recorded using an accelerometer and ultrasonic sensors with a sampling frequency of 200 Hz for each. The accelerometer and ultrasonic sensor data were used to impose the motion of the sloshing tank into a Reynolds-Averaged Navier-Stokes (RANS)-based numerical model. The video recordings, which comprised temporal fluctuations of the water surface, were used to calibrate the Model 1. Once the first numerical model was calibrated based on water surface level records using image processing methods, the second numerical model was constructed to accommodate a rigid spherical body with a 17 mm diameter connected to the bottom of the sloshing tank. The initial and boundary conditions used in the second numerical model were identical to those used in the first model to measure the spatiotemporal fluctuations of the surrounding spherical body’s kinematic and dynamic variables, respectively. The findings revealed that sloshing motion exerts a significant impact on the boundary layer separation process around the sphere. It was also witnessed that the stage of the sloshing motion controls the temporal lag between the pressure, velocity and water surface level. © 2024 by the author(s). Published by Nan Yang Academy of Sciences Pte. Ltd.
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    Morphodynamic Controls on Thermal Plume Dispersion at River Mouths: Insights from Field Data and Numerical Modeling
    (Mdpi, 2025) Heidari, Naghmeh; Aksel, Murat; Yagci, Oral; Erbisim, Mehmet Yusuf; Cokgor, Sevket; Valyrakis, Manousos
    Thermal discharge from power plants causes significant concerns in aquatic environments. The purpose of this study is to evaluate how river mouth morphodynamics, particularly spit development and removal, influence the dispersion of thermal plumes. To achieve this, a case study was carried out at a coastal power plant in southwest T & uuml;rkiye, where thermal effluent is conveyed to the sea through a low-flow river. Field measurements combined with numerical modeling were used to analyze plume dynamics under varying spit configurations. Results revealed that the evolution of a spit on one side of the river mouth influences plume dispersion and redirects the mixing zone toward the opposite shoreline. Numerical simulations demonstrated that spit development reduces dispersion efficiency (by over 75%), while the physical removal of the spit significantly improves it, reducing temperature excess from 4-5 degrees C to 0-1 degrees C within the mixing zone, meeting safe environmental standards. The findings highlight the pivotal role of morphological changes in governing thermal discharge behavior and emphasize the importance of continuous monitoring and management strategies, such as periodic dredging, to ensure compliance with environmental regulations.