scholarly journals Flume Experiments on Flow Analysis and Energy Reduction through a Compound Tsunami Mitigation System with a Seaward Embankment and Landward Vegetation over a Mound

Geosciences ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 90
Author(s):  
Md Abedur Rahman ◽  
Norio Tanaka ◽  
A. H. M. Rashedunnabi
Keyword(s):  
Laboratory Experiments ◽  
Flow Analysis ◽  
Maximum Energy ◽  
Energy Reduction ◽  
Coastal Vegetation ◽  
Vegetation Density ◽  
Flow Conditions ◽  
Flume Experiments ◽  
Tsunami Inundation ◽  
Tsunami Mitigation

As a countermeasure against tsunami inundation, the present study conducted a series of laboratory experiments using a compound mitigation system in which a seaward embankment (E) followed by landward coastal vegetation (V) over a mound (M) (EMV) was investigated in supercritical flow conditions. The changes of flow around the mitigation system and energy reduction were clarified under varying conditions of mound height and vegetation density. Cases of an embankment followed by only a mound (EMNV) were also considered for comparison. Experimental results showed that three basic types of flow structures were observed within the mitigation system in EMV cases. A water cushion was created within the mitigation system mainly due to the combined effects of the mound and vegetation. It significantly reduced the maximum total energy in EMV cases by approximately 41–66%, whereas in EMNV cases, the maximum energy reduction was found to be 23–65%. Increments in both mound height and vegetation density increased the intensity of the water cushion within the mitigation system by offering more drag and reflecting the flow, and hence, significantly reduced the energy of the flow.

Characteristics of a Hydraulic Jump Formed on Upstream Vegetation of Varying Density and Thickness

2020 ◽  
Vol 14 (03) ◽  
pp. 2050012
Author(s):  
Ghufran Ahmed Pasha ◽  
Norio Tanaka
Keyword(s):  
Energy Loss ◽  
Froude Number ◽  
Hydraulic Jump ◽  
Variable Density ◽  
Maximum Energy ◽  
Coastal Vegetation ◽  
Critical Flow ◽  
Vegetation Density ◽  
Sparse Vegetation ◽  
Upstream Flow

The effectiveness of coastal vegetation as a barrier to mitigate a tsunami greatly depends on the magnitude of tsunami and vegetation structure. This paper summarizes a series of laboratory experiments that investigated the upstream flow structure and energy loss due to a hydraulic jump in a steady super-critical flow. The characteristics of the jump were determined against vegetation of variable density ([Formula: see text], where [Formula: see text] of each cylinder in cross-stream direction, [Formula: see text] of cylinder), thickness (dn, where [Formula: see text] of cylinder, [Formula: see text] of cylinders in the stream-wise direction per unit of cross-stream width), and initial Froude number (Fro, where Froude number is obtained from a model without vegetation in the flume). In super-critical flow ([Formula: see text]–1.83), a weak hydraulic jump formed on upstream side of vegetation. The height of the jump, its location, and the resulting energy loss were increased by increasing both the vegetation density and thickness. Due to reduced reflection at vegetation front, the drag force against sparse vegetation ([Formula: see text]/[Formula: see text]) was higher compared to intermediate ([Formula: see text]/[Formula: see text]) and dense ([Formula: see text]/[Formula: see text]) vegetation. Under these conditions, the maximum energy reduction due to a weak hydraulic jump reached 9.4% for dense vegetation while it was 8.1% and 7.8% for intermediate and sparse vegetation, respectively.

scholarly journals Laboratory data on wave propagation through vegetation with following and opposing currents

2021 ◽  
Vol 13 (10) ◽  
pp. 4987-4999
Author(s):  
Zhan Hu ◽  
Simei Lian ◽  
Huaiyu Wei ◽  
Yulong Li ◽  
Marcel Stive ◽  
...  
Keyword(s):  
Drag Coefficient ◽  
Wave Height ◽  
Wind Waves ◽  
Model Development ◽  
Laboratory Data ◽  
Coastal Vegetation ◽  
Vegetation Density ◽  
Wave Dissipation ◽  
Flume Experiments ◽  
Key Factor

Abstract. Coastal vegetation has been increasingly recognized as an effective buffer against wind waves. Recent laboratory studies have considered realistic vegetation traits and hydrodynamic conditions, which advanced our understanding of the wave dissipation process in vegetation (WDV) in field conditions. In intertidal environments, waves commonly propagate into vegetation fields with underlying tidal currents, which may alter the WDV process. A number of experiments addressed WDV with following currents, but relatively few experiments have been conducted to assess WDV with opposing currents. Additionally, while the vegetation drag coefficient is a key factor influencing WDV, it is rarely reported for combined wave–current flows. Relevant WDV and drag coefficient data are not openly available for theory or model development. This paper reports a unique dataset of two flume experiments. Both experiments use stiff rods to mimic mangrove canopies. The first experiment assessed WDV and drag coefficients with and without following currents, whereas the second experiment included complementary tests with opposing currents. These two experiments included 668 tests covering various settings of water depth, wave height, wave period, current velocity and vegetation density. A variety of data, including wave height, drag coefficient, in-canopy velocity and acting force on mimic vegetation stem, are recorded. This dataset is expected to assist future theoretical advancement on WDV, which may ultimately lead to a more accurate prediction of wave dissipation capacity of natural coastal wetlands. The dataset is available from figshare with clear instructions for reuse (https://doi.org/10.6084/m9.figshare.13026530.v2, Hu et al., 2020). The current dataset will expand with additional WDV data from ongoing and planned observation in natural mangrove wetlands.

scholarly journals Influence of Rigid Emerged Vegetation in a Channel Bend on Bed Topography and Flow Velocity Field: Laboratory Experiments

Water ◽  
2019 ◽  
Vol 12 (1) ◽  
pp. 118 ◽  
Author(s):  
Hossein Hamidifar ◽  
Alireza Keshavarzi ◽  
Paweł M. Rowiński
Keyword(s):  
Laboratory Experiments ◽  
Flow Characteristics ◽  
Maximum Velocity ◽  
Flow Conditions ◽  
Mean Flow ◽  
Bed Topography ◽  
Channel Bend ◽  
Bed Erosion ◽  
Flow Hydraulics ◽  
The Mean

Trees have been used extensively by river managers for improving the river environment and ecology. The link between flow hydraulics, bed topography, habitat availability, and organic matters is influenced by vegetation. In this study, the effect of trees on the mean flow, bed topography, and bed shear stress were tested under different flow conditions. It was found that each configuration of trees produced particular flow characteristics and bed topography patterns. The SR (single row of trees) model appeared to deflect the maximum velocity downstream of the bend apex toward the inner bank, while leading the velocity to be more uniformly distributed throughout the bend. The entrainment of sediment particles occurred toward the area with higher values of turbulent kinetic energy (TKE). The results showed that both SR and DR (double rows of trees) models are effective in relieving bed erosion in sharp ingoing bends. The volume of the scoured bed was reduced up to 70.4% for tests with trees. This study shows the effectiveness of the SR model in reducing the maximum erosion depth.

Energetics of a Circular Membrane Subjected to a Sudden Eccentric Circular Areal Constraint

2012 ◽  
Author(s):  
Assaad AlSahlani ◽  
Ranjan Mukherjee
Keyword(s):  
Total Energy ◽  
Active Control ◽  
Small Area ◽  
Outer Boundary ◽  
Maximum Energy ◽  
Energy Reduction ◽  
Physical Interaction ◽  
Circular Membrane ◽  
Time Of Application ◽  
Simulation Results

We investigate the energetics of a freely vibrating circular membrane subjected to a sudden eccentric circular areal constraint. The membrane is assumed to be fixed at its outer boundary and the constraint is assumed to be applied at an arbitrary time during the motion of the membrane. The constraint is applied instantaneously such that immediately after application of the constraint, the geometry of the membrane outside the area of the constraint remains unchanged and the constrained area comes to rest. The change in total energy after constraint application is investigated for different sizes and locations of the constraint and time of application of the constraint. The results show that the energy can decrease or increase depending on the time of application of the constraint. The condition for maximum energy reduction is presented and simulation results based on this condition show that sequential application and removal of the constraint reduces the total energy rapidly. This provides the opportunity for active control of membrane vibration through direct physical interaction with a small area of the membrane.

scholarly journals Debris-flow velocities and superelevation in a curved laboratory channel

2015 ◽  
Vol 52 (3) ◽  
pp. 305-317 ◽  
Author(s):  
Christian Scheidl ◽  
Brian W. McArdell ◽  
Dieter Rickenmann
Keyword(s):  
Debris Flow ◽  
Flow Velocity ◽  
Correction Factor ◽  
Debris Flows ◽  
Laboratory Experiments ◽  
Flow Conditions ◽  
Vortex Equation ◽  
Flow Surface ◽  
Sediment Mixture ◽  
Sediment Mixtures

The vortex equation is often used to estimate the front velocity of debris flows using the lateral slope of the flow surface through a channel bend of a given radius. Here we report on laboratory experiments evaluating the application of the vortex equation to channelized debris flows. Systematic laboratory experiments were conducted in a 8 m long laboratory flume with a roughened bed, semi-circular cross section (top width 17 cm), and two different bend radii (1.0 and 1.5 m) with a common bend angle of 60°, and two channel inclinations (15° and 20°). Four sediment mixtures were used with systematic variations in the amount of fine sediment. In the experiments, 12 kg of water-saturated debris were released in a dam-break fashion, and multiple experiments were conducted to verify the repeatability for a given sediment mixture. Data are available for 69 experimental releases at a channel inclination of 20° and 16 releases at an inclination of 15°. Flow velocity was determined with high-speed video, and flow depth and the lateral inclination of the flow surface (superelevation) were measured using laser sensors. In general, the results from an individual sediment mixture are repeatable. We found that the channel slope as well as centerline radius have a significant influence on the correction factor k used in the vortex equation. Relatively coarse-grained sediment mixtures have larger superelevation angles than finer-grained mixtures. We found a statistically significant relation between the correction factor and Froude number. Correction factors of 1 < k < 5 were found for supercritical flow conditions. However, for subcritical flow conditions the correction factor shows a larger value as a function of the Froude number, which leads to an adaption of the forced vortex formula considering active and passive earth pressures. Finally, based on our experimental results, we present a forced vortex equation for debris-flow velocity estimation without a correction factor.

Tsunami mitigation by coastal vegetation considering the effect of tree breaking

2011 ◽  
Vol 16 (1) ◽  
pp. 111-121 ◽  
Author(s):  
Nguyen Ba Thuy ◽  
Norio Tanaka ◽  
Katsutoshi Tanimoto
Keyword(s):  
Coastal Vegetation ◽  
Tsunami Mitigation

scholarly journals Morphodynamics and sedimentary structures of bedforms under supercritical-flow conditions: New insights from flume experiments

Sedimentology ◽  
2013 ◽  
Vol 61 (3) ◽  
pp. 712-748 ◽  
Author(s):  
Matthieu J.B. Cartigny ◽  
Dario Ventra ◽  
George Postma ◽  
Jan H. van Den Berg
Keyword(s):  
Flow Conditions ◽  
Flume Experiments ◽  
Supercritical Flow ◽  
Sedimentary Structures

scholarly journals Modeling Physiological Flow in Fontan Models With Four-Dimensional Flow Magnetic Resonance Imaging, Particle Image Velocimetry, and Arterial Spin Labeling

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
David R. Rutkowski ◽  
Rafael Medero ◽  
Timothy A. Ruesink ◽  
Alejandro Roldán-Alzate
Keyword(s):  
Arterial Spin Labeling ◽  
Phase Contrast ◽  
Particle Image ◽  
Flow Analysis ◽  
Patient Specific ◽  
Resonance Imaging ◽  
Flow Conditions ◽  
4D Flow ◽  
Image Velocimetry ◽  
Flow Mri

Abstract The Fontan procedure is a successful palliation for single ventricle defect. Yet, a number of complications still occur in Fontan patients due to abnormal blood flow dynamics, necessitating improved flow analysis and treatment methods. Phase-contrast magnetic resonance imaging (MRI) has emerged as a suitable method for such flow analysis. However, limitations on altering physiological blood flow conditions in the patient while in the MRI bore inhibit experimental investigation of a variety of factors that contribute to impaired cardiovascular health in these patients. Furthermore, resolution and flow regime limitations in phase contrast (PC) MRI pose a challenge for accurate and consistent flow characterization. In this study, patient-specific physical models were created based on nine Fontan geometries and MRI experiments mimicking low- and high-flow conditions, as well as steady and pulsatile flow, were conducted. Additionally, a particle image velocimetry (PIV)-compatible Fontan model was created and flow was analyzed with PIV, arterial spin labeling (ASL), and four-dimensional (4D) flow MRI. Differences, though nonstatistically significant, were observed between flow conditions and between patient-specific models. Large between-model variation supported the need for further improvement for patient-specific modeling on each unique Fontan anatomical configuration. Furthermore, high-resolution PIV and flow-tracking ASL data provided flow information that was not obtainable with 4D flow MRI alone.

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