scholarly journals KAJIAN NUMERIK FENOMENA UNDULAR TIDAL BORES DALAM MEMPENGARUHI PROSES EROSI PADA DAERAH ALIRAN SUNGAI (Numerical study of undular tidal bores phenomenon in influencing erosion processes of watersheds)

2021 ◽  
Vol 5 (1) ◽  
pp. 51-68
Author(s):  
Yoga Satria Putra ◽  
◽  
Mentari Yuniar ◽  
Arie Antasari Kushadiwijayanto ◽  
Keyword(s):  
Flow Velocity ◽  
Froude Number ◽  
Shear Force ◽  
River Flow ◽  
Numerical Study ◽  
Dissipation Energy ◽  
Shear Coefficient ◽  
Erosion Processes ◽  
Tidal Bores ◽  
Riverbank Erosion

Riverbank erosion is one indication of watershed damage. One of the causes is the phenomenon of tidal bores waves that occur in a river channel.The strength of tidal bores wave's can be measured based on its shear force parameter and dissipation energy. Wave shear force and dissipation energy are the parameters that play a role in a riverbank erosion process. Both of them are characterized by the Froude number (Fr) which is a function of the upstream river flow velocity (V0), the tidal bores flow velocity from the estuary (Vb), the river depth (h1), and the gravity acceleration (g). A numerical study of the phenomenon of undular tidal bores has been carried out in this article. Five undular bores simulations have been built using the open-source Computational Fluid Dynamics (CFD) software, OpenFOAM. This study aims to analyze the effect of the Froude number variations (Fr) on the magnitude of the wave shear coefficient (ϵ) and dissipation energy ( ) on undular bores cases. Five simulations of undular bores have been generated based on five Froude's numbers, Fr = 1.0, 1.1, 1.2, 1.3, and 1.4. The validation has been performed by comparing the experimental and numerical results from the scientific literature. The analysis results show that the increase in Fr has a significant effect on the increase in the ϵ and .These results indicate that the Froude number variations have influenced the wave shear coefficient and dissipation energy on the undular bores cases. Increasing the Fr values have triggered an increase in the value of ϵ linearly and exponentially. Thus, the erosion that occurs on the riverbank in the undular tidal bores phenomenon could be determined based on Froude's number.

Numerical study of the aerodynamic and power characteristics of the cycloidal rotor, under incoming flow

2019 ◽  
pp. 25-34
Author(s):  
Александр Анатольевич Дектерев ◽  
Артем Александрович Дектерев ◽  
Юрий Николаевич Горюнов
Keyword(s):  
Flow Velocity ◽  
Numerical Study ◽  
Lift Coefficient ◽  
Simulation Method ◽  
Aerodynamic Characteristics ◽  
Incoming Flow ◽  
Ansys Fluent ◽  
Energy Characteristics ◽  
Power Characteristics ◽  
Calculation Results

Исследование направлено на разработку и апробацию методики численного моделирования аэродинамических и энергетических характеристик циклоидального ротора. За основу взята конфигурация ротора IAT21 L3. Для нее с использованием CFD-пакета ANSYS Fluent построена математическая модель и выполнен расчет. Проанализировано влияние скорости набегающего потока воздуха на движущийся ротор. Математическая модель и полученные результаты исследования могут быть использованы при создании летательных аппаратов с движителями роторного типа. This article addresses the study of the aerodynamic and energy characteristics of a cycloidal rotor subject to the influence of the incoming flow. Cycloidal rotor is one of the perspective devices that provide movement of aircrafts. Despite the fact that the concept of a cycloidal rotor arose in the early twentieth century, the model of a full-scale aircraft has not been yet realized. Foreign scientists have developed models of aircraft ranging in weight from 0.06 to 100 kg. The method of numerical calculation of the cycloidal rotor from the article [1] is considered and realized in this study. The purpose of study was the development and testing of a numerical simulation method for the cycloidal rotor and study aerodynamic and energy characteristics of the rotor in the hovering mode and under the influence of the oncoming flow. The aerodynamic and energy characteristics of the cycloidal rotor, rotating at a speed of 1000 rpm with incoming flow on it with velocities of 20-80 km/h, were calculated. The calculation results showed a directly proportional increase of thrust with an increase of the incoming on the rotor flow velocity, but the power consumed by the rotor was also increased. Increase of the incoming flow velocity leads to the proportional increasing of the lift coefficient and the coefficient of drag. Up to a speed of 80 km/h, an increase in thrust and power is observed; at higher speeds, there is a predominance of nonstationary effects and difficulties in estimating the aerodynamic characteristics of the rotor. In the future, it is planned to consider the 3D formulation of the problem combined with possibility of the flow coming from other sides.

scholarly journals Artisanal Mining Practice and Physical Impacts on the Environment in the Ity-Floleu Gold Region, Côte d'Ivoire

2021 ◽  
pp. 17-31
Author(s):  
Sandotin Lassina Coulıbaly ◽  
Franck Michaël Zahui ◽  
Lydie Clarisse Mangoua-Allali ◽  
Awa Cherif ◽  
Lacina Coulibaly
Keyword(s):  
Flow Velocity ◽  
Cote D'ivoire ◽  
Côte D’Ivoire ◽  
River Flow ◽  
Agricultural Land ◽  
River Sediments ◽  
Cote D’Ivoire ◽  
Water Flow Velocity ◽  
Artisanal Mining ◽  
Côte D'ivoire

This paper describes artisanal gold mining practices and environmental impacts around the Ity-Floleu gold mine, in western Côte d'Ivoire. Interviews and field observations as well as measurements of turbidity and water flow velocity in the section of the river (Cavally) watering the study area, made it possible to identify 13 artisanal mining sites, housing 247 artisans, operating in groups made up mainly of 5 to 10 people. The activity is dominated by local populations from the villages of Ity and Floleu and the surrounding communities. Gold mined comes from alluvial and vein ores, with a predominance of alluvial ore, extracted in the sediments of the bed and the banks of the river and in the soils, inside forests. In the bed of the river, sediments are dredged using machines placed on boats, from where they are washed in mats and then dumped into the watercourse. On the other hand, on the banks of the river and in the forests, the material used consists of picks, dabas, mats, and shovels. In all cases, gold is recovered as a concentrate of gold powder. As regards vein ores, they are also extracted along with the soils of cultivable land, but in the form of blocks of stone which are crushed and washed. The gold is then recovered using mercury, followed by cyanidation. The techniques used lead to the silting up and the fall of the banks of the river, reduction of agricultural land, and the degradation of the environment by the tailings. The Cavally River appears to be strongly impacted in the midstream part of the Ity-Floleu axis, marked by a decrease in the bed and the river flow velocity (0.19 m/s) and higher turbidity (255.3 NTU). More effective policies are urgently needed to restore degraded ecosystems, both aquatic and terrestrial.

Numerical study of surface thermal signatures of lee waves excited by moving underwater sphere at low Froude number

2021 ◽  
pp. 109314
Author(s):  
Cheng-An Wang ◽  
Duo Xu ◽  
Ji-Peng Gao ◽  
Jian-Yu Tan ◽  
Zhi-Quan Zhou
Keyword(s):  
Froude Number ◽  
Numerical Study ◽  
Lee Waves ◽  
Low Froude Number

Average Quantifying the snowmelt dominant river erosion in Afghanistan between 2004-2020

2021 ◽  
Author(s):  
Abdul Basir Mahmoodzada ◽  
Divyesh Varade ◽  
Sawahiko Shimada ◽  
Hiromu Okazawa ◽  
Chembolu Vinay
Keyword(s):  
River Flow ◽  
Empirical Relationship ◽  
Temporal Analysis ◽  
Reanalysis Data ◽  
Data Availability ◽  
Landsat 8 ◽  
Western Himalayas ◽  
Stream Power ◽  
Riverbank Erosion ◽  
Erosion Area

<p>Flooding of rivers is one of the major causes of soil erosion leading to significant changes in the geomorphological environment. Particularly, in countries such as Afghanistan, where the transboundary are designated according to the Amu River shorelines, are significantly affected by riverbank erosions. Amu River is driven by streamflow from the Pir Pranjal ranges of Afghanistan and Tajikistan. Numerical analysis of the river flow dynamics in such regions is subject to the scarce data availability on ground stations. Thus, ERA5 Reanalysis data provides a significant means for the temporal analysis of the geomorphological changes in such multi-national watersheds.</p><p>In this study, we propose a framework to quantify the Amu riverbank erosion in the Kaldar District of the Balkh Province of Afghanistan. The proposed framework is based on establishing an empirical relationship between the riverbank erosion area based on the discharge intensity and the specific stream power. To determine these two parameters, the river discharge is modeled using the ERA5 Reanalysis hydrological parameters based on multivariate regression. The river width is determined using the Normalized Difference Water Index-based (NDWI) derived from the Landsat-7 and Landsat-8 datasets. The riverbank erosion area is determined using shoreline analysis carried out using these datasets. The shoreline analysis indicates that Afghanistan is losing precious land due to the riverbank erosion over the past two decades (2004-20) amounting to as much as 86 sq. km and on average 5.4 sq. km every year. According to the ERA5 Reanalysis data, the water contribution from snowmelt in the spring and the summer was significantly dominant compared to the precipitation, which is consistent with several other watersheds in the north-western Himalayas. The river width and the discharge are observed to follow a power-law relation with an r<sup>2 </sup>of 0.7. Additionally, the discharge intensity and the specific stream power showed significant relation (r<sup>2 </sup>of 0.84 both) corresponding to the riverbank erosion area, where the peak flood events were observed to be outliers.</p>

scholarly journals Improving the Blast Resistance of Large Steel Gates—Numerical Study

Materials ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2121 ◽  
Author(s):  
Hasan Al-Rifaie ◽  
Wojciech Sumelka
Keyword(s):  
Positive Impact ◽  
Numerical Study ◽  
Blast Resistance ◽  
Critical Factor ◽  
Induced Response ◽  
Dissipation Energy ◽  
Auxetic Structures ◽  
Explicit Solver ◽  
Supporting Frame ◽  
Energy Absorbing

Blast resistant gates/doors are essential for sensitive infrastructure, such as embassies, ministries, or parliaments. Lightweight gates equipped with ‘energy absorbing systems’ have better operational performance than the traditional costly and bulky design. Graded auxetic structures have not yet been used as potential passive damping systems in the supporting frame of blast resistant gates. Consequently, this study tries to test if a uniaxial graded auxetic damper (UGAD) proposed by the authors in a recent article, namely the development of a new shock absorbing UGAD, could maintain a 3000 mm × 4500 mm steel gate operable after high blast peak reflected overpressure of 6.6 MPa, from 100 kg TNT at 5 m stand-off distance. The blast-induced response of the gate was assessed, with and without the proposed UGAD, using Abaqus/Explicit solver. Results showed that the attachment of the proposed UGAD to the gate led to a dramatic decrease in permanent deformations (a critical factor for gate operability after a blast event). Hence, a lighter, more economical gate (with 50% reduction in mass) was required to satisfy the operability condition. In addition, 49% of peak reaction forces were diminished, that have a direct impact on the supporting frame. Moreover, the results revealed that, in the numerical model, 56% of the achieved plastic dissipation energy was from the UGADs, and 44% from the gate. The outcomes of this research may have a positive impact on other sectors beyond academia, such as industry, economy, and public safety.

scholarly journals A numerical study of pumping effects on flow velocity distributions in Mosul Dam reservoir using the HEC-RAS model

2020 ◽  
Vol 25 (1) ◽  
pp. 72-83
Author(s):  
Mohammad E. Mohammad ◽  
Nadhir Al-Ansari ◽  
Sven Knutsson ◽  
Jan Laue
Keyword(s):  
Flow Velocity ◽  
Numerical Study ◽  
Dam Reservoir

Transcritical flow over two obstacles: forced Korteweg–de Vries framework

2016 ◽  
Vol 809 ◽  
pp. 918-940 ◽  
Author(s):  
Roger H. J. Grimshaw ◽  
Montri Maleewong
Keyword(s):  
Froude Number ◽  
Numerical Study ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Control Flow ◽  
Main Concern ◽  
Undular Bore ◽  
Second Stage ◽  
Third Stage ◽  
De Vries

We consider free-surface flow over two localised obstacles using the framework of the forced Korteweg–de Vries equation in a suite of numerical simulations. Our main concern is with the transcritical regime when the oncoming flow has a Froude number close to unity. The flow behaviour can be characterised by the Froude number and the maximum heights of the obstacles. In the transcritical regime at early times, undular bores are produced upstream and downstream of each obstacle. Our main aim is to describe the interaction of these undular bores between the obstacles, and to find the outcome at very large times. We find that the flow development can be defined in three stages. The first stage is described by the well-known development of undular bores upstream and downstream of each obstacle. The second stage is the interaction between the undular bore moving downstream from the first obstacle and the undular bore moving upstream from the second obstacle. The third stage is the very large time evolution of this interaction, when one of the obstacles controls criticality. For equal obstacle heights, our analytical and numerical results indicate that either one of the obstacles can control flow criticality, that being the first obstacle when the flow is slightly subcritical and the second obstacle otherwise. For unequal obstacle heights the larger obstacle controls criticality. The results obtained here complement a recent numerical study using the fully nonlinear, but non-dispersive, shallow water equations.

Numerical Study on the Migration of Two Spheres in Upward Pipe Flow

2018 ◽  
Author(s):  
Lei Liu ◽  
Haining Lu ◽  
Jianmin Yang ◽  
Xinliang Tian ◽  
Tao Peng ◽  
...  
Keyword(s):  
Flow Velocity ◽  
Poiseuille Flow ◽  
Pipe Flow ◽  
Deep Sea ◽  
Numerical Study ◽  
Critical Value ◽  
Dynamic Responses ◽  
Phase Flow ◽  
Two Phase ◽  
Offshore Engineering

Migration of particles in pipe flow is commonly seen in offshore engineering, such as vertical transport of ores in deep sea mining. As the basis of the investigation on fluid-particle two-phase flow, the interaction of two spheres in upward pipe flow is studied by direct numerical simulations in this paper. The pipe flow is set as Poiseuille flow; the Reynolds number is no more than 1250. The dynamic responses of the spheres and the flow pattern are analyzed at different flow velocity. When compared to the sedimentation of two spheres in quiescent flow, the trailing sphere in Poiseuille flow will never surpass the leading one in Poiseuille flow. As the flow velocity increases in the pipe, the spheres are easier to separate after collision. When the flow velocity exceeds a critical value, the spheres will never collide.

A numerical study on the blow-off limit of premixed hydrogen/air flames in a cylindrical micro-combustor

2020 ◽  
pp. 095441002097144
Author(s):  
Saeed Naeemi ◽  
Seyed Abdolmehdi Hashemi
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Flow Velocity ◽  
Equivalence Ratio ◽  
Numerical Study ◽  
Flame Stability ◽  
Convection Coefficient ◽  
Inlet Flow ◽  
Micro Combustor ◽  
Emissivity Coefficient

In the current work, a numerical study on combustion of premixed H2–air in a micro-cylindrical combustor was carried out and the critical velocity of inlet flow that causes the blow-off was obtained. Furthermore, the effects the equivalence ratio, wall thickness, geometry of combustor and thermal properties of walls on the critical blow-off velocity were studied. The numerical results showed that, increasing the equivalence ratio results in higher critical blow-off velocity. A micro combustor with thicker wall had better flame stability. As the combustor dimeter is decreased the blow-off occur in lower inlet flow velocity. Higher thermal conductivity of walls increases the critical blow-off velocity. In addition, with varying heat convection coefficient (h) and emissivity coefficient [Formula: see text] of the walls from 1 to 60 W/m2.K and 0.2 to 0.8 respectively, the critical blow-off velocity is reduced and shows the importance of wall thermal properties in the design and operation of micro-combustors.

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