scholarly journals The Maximum Height and Attenuation of Impulse Waves Generated by Subaerial Landslides

2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Baoliang Wang ◽  
Lingkan Yao ◽  
Haixin Zhao ◽  
Cong Zhang
Keyword(s):  
Influencing Factors ◽  
Wave Height ◽  
Water Waves ◽  
High Speed ◽  
Transient Flow ◽  
Evaluation Criteria ◽  
Maximum Height ◽  
Flume Experiments ◽  
Orthogonal Experiments ◽  
Wave Height Attenuation

High-speed landslides that flow into reservoirs can cause impulsive water waves. To study the characteristics of the maximum impulse wave’s height and its attenuation, 25 sets of flume experiments were conducted using orthogonal theory and 6 main influencing factors were considered. Taking the impulse wave heights as the evaluation criteria and analyzing the 6 influencing factors at 5 different levels, the characteristics of the maximum impulse wave’s height and its attenuations were obtained. Then, statistical relationships between the maximum wave height and the controlling factors were proposed. Then, by combining the continuity equation and the hydrodynamic open channel transient flow movement equation, the process of landslide wave height attenuation was studied, and it was found that the attenuation of the wave is consistent with exponential attenuation. Then, combined with the data obtained from the orthogonal experiments, an attenuation equation for the surge was derived. Finally, the proposed equation was validated by applying it to the landslides that took place along the shore of the Zipingpu reservoir, which were triggered by the Wenchuan earthquake, and the results indicate that the calculated results are very close to the observed results.

Theory of the almost-highest wave. Part 2. Matching and analytic extension

1978 ◽  
Vol 85 (4) ◽  
pp. 769-786 ◽  
Author(s):  
M. S. Longuet-Higgins ◽  
M. J. H. Fox
Keyword(s):  
Phase Velocity ◽  
Wave Height ◽  
Water Waves ◽  
Phase Speed ◽  
Wave Crest ◽  
Analytic Extension ◽  
Radius Of Curvature ◽  
Maximum Height ◽  
Branch Points ◽  
Method Of Calculation

Most methods of calculating steep gravity waves (of less than the maximum height) encounter difficulties when the radius of curvature R at the crest becomes small compared with the wavelength L, or some other typical length scale. This paper describes a new method of calculation valid when R/L is small.For deep-water waves, a parameter ε is defined as equal to q/2½c0, where q is the particle speed at the wave crest, in a frame of reference moving with the phase speed c. Hence ε is of order (R/L)½. Three zones are distinguished: (1) an inner zone of linear dimensions ε2L near the crest, where the flow is described by the inner solution found previously by Longuet-Higgins & Fox (1977); (2) an outer zone of dimensions O(L) where the flow is given by a perturbed form of Michell's solution for the highest wave; and (3) a matching zone of width O(L). The matching procedure involves complex powers of ε.The resulting expression for the square of the phase velocity is found to be \[ c^2 = (g/k)\{1.1931-1.18\epsilon^3\cos(2.143\ln \epsilon + 2.22)\} \] (see figures 5a, b), which is in remarkable agreement with independent calculations based on high-order series. In particular, the existence of turning-points in the phase velocity as a function of wave height is confirmed.Similar expressions, valid to order ε3, are found for the wave height, the potential and kinetic energies and the momentum flux or impulse of the wave.The velocity field is extended analytically across the free surface, revealing the existence of branch-points of order ½, as predicted by Grant (1973).

Bulk drag coefficient of a subaquatic vegetation subjected to irregular waves: Influence of Reynolds and Keulegan-Carpenter numbers

2020 ◽  
pp. 34-42
Author(s):  
Thibault Chastel ◽  
Kevin Botten ◽  
Nathalie Durand ◽  
Nicole Goutal
Keyword(s):  
Drag Coefficient ◽  
Wave Height ◽  
Wave Attenuation ◽  
Empirical Relationship ◽  
Breaking Waves ◽  
Irregular Waves ◽  
Geometrical Parameters ◽  
Flume Experiments ◽  
Seagrass Meadows ◽  
Artificial Vegetation

Seagrass meadows are essential for protection of coastal erosion by damping wave and stabilizing the seabed. Seagrass are considered as a source of water resistance which modifies strongly the wave dynamics. As a part of EDF R & D seagrass restoration project in the Berre lagoon, we quantify the wave attenuation due to artificial vegetation distributed in a flume. Experiments have been conducted at Saint-Venant Hydraulics Laboratory wave flume (Chatou, France). We measure the wave damping with 13 resistive waves gauges along a distance L = 22.5 m for the “low” density and L = 12.15 m for the “high” density of vegetation mimics. A JONSWAP spectrum is used for the generation of irregular waves with significant wave height Hs ranging from 0.10 to 0.23 m and peak period Tp ranging from 1 to 3 s. Artificial vegetation is a model of Posidonia oceanica seagrass species represented by slightly flexible polypropylene shoots with 8 artificial leaves of 0.28 and 0.16 m height. Different hydrodynamics conditions (Hs, Tp, water depth hw) and geometrical parameters (submergence ratio α, shoot density N) have been tested to see their influence on wave attenuation. For a high submergence ratio (typically 0.7), the wave attenuation can reach 67% of the incident wave height whereas for a low submergence ratio (< 0.2) the wave attenuation is negligible. From each experiment, a bulk drag coefficient has been extracted following the energy dissipation model for irregular non-breaking waves developed by Mendez and Losada (2004). This model, based on the assumption that the energy loss over the species meadow is essentially due to the drag force, takes into account both wave and vegetation parameter. Finally, we found an empirical relationship for Cd depending on 2 dimensionless parameters: the Reynolds and Keulegan-Carpenter numbers. These relationships are compared with other similar studies.

Shock Tube Simulation of the Transient Surge Phase Inside an Axial Compressor

2018 ◽  
Author(s):  
Paul Xiubao Huang ◽  
Robert S. Mazzawy
Keyword(s):  
Shock Wave ◽  
Shock Tube ◽  
High Speed ◽  
Transient Flow ◽  
Pressure Ratio ◽  
Axial Compressor ◽  
Dynamic Effect ◽  
Initiation Site ◽  
Flow Reversal ◽  
Expansion Waves

This paper is a continuing work from one author on the same topic of the transient aerodynamics during compressor stall/surge using a shock tube analogy by Huang [1, 2]. As observed by Mazzawy [3] for the high-speed high-pressure (HSHP) ratio compressors of the modern aero-engines, surge is an event characterized with the stoppage and reversal of engine flow within a matter of milliseconds. This large flow transient is accomplished through a pair of internally generated shock waves and expansion waves of high strength. The final results are often dramatic with a loud bang followed by the spewing out of flames from both the engine intake and exhaust, potentially damaging to the engine structure [3]. It has been demonstrated in the previous investigations by Marshall [4] and Huang [2] that the transient flow reversal phase of a surge cycle can be approximated by the shock tube analogy in understanding its generation mechanism and correlating the shock wave strength as a function of the pre-surge compressor pressure ratio. Kurkov [5] and Evans [8] used a guillotine analogy to estimate the inlet overpressure associated with the sudden flow stoppage associated with surge. This paper will expand the progressive surge model established by the shock tube analogy in [2] by including the dynamic effect of airflow stoppage using an “integrated-flow” sequential guillotine/shock tube model. It further investigates the surge formation (characterized by flow reversal) and propagation patterns (characterized by surge shock and expansion waves) after its generation at different locations inside a compressor. Calculations are conducted for a 12-stage compressor using this model under various surge onset stages and compared with previous experimental data [3]. The results demonstrate that the “integrated-flow” model closely replicates the fast moving surge shock wave overpressure from the stall initiation site to the compressor inlet.

scholarly journals Wave energy dissipation in the mangrove vegetation off Mumbai, India

2017 ◽  
Author(s):  
Samiksha S. Volvaiker ◽  
Ponnumony Vethamony ◽  
Prasad K. Bhaskaran ◽  
Premanand Pednekar ◽  
MHamsa Jishad ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Drag Coefficient ◽  
Wave Height ◽  
Wave Attenuation ◽  
Coastal Region ◽  
Measured Data ◽  
Vegetation Density ◽  
Mangrove Vegetation ◽  
Wave Height Attenuation ◽  
Set Up

Abstract. Coastal regions of India are prone to sea level rise, cyclones, storm surges and human induced activities, resulting in flood, erosion, and inundation. The primary aim of the study is to estimate wave attenuation by mangrove vegetation using SWAN model in standalone mode, as well as SWAN nested with WW3 model for the Mumbai coastal region. To substantiate the model results, wave measurements were carried out during 5–8 August 2015 at 3 locations in a transect normal to the coast using surface mounted pressure level sensors under spring tide conditions. The measured data presents wave height attenuation of the order of 52 %. The study shows a linear relationship between wave height attenuation and gradual changes in water level in the nearshore region, in phase with the tides. Model set-up and sensitivity analyses were conducted to understand the model performance to vegetation parameters. It was observed that wave attenuation increased with an increase in drag coefficient (Cd), vegetation density, and stem diameter. For a typical set-up for Mumbai coastal region having vegetation density of 0.175 per m2, stem diameter of 0.3 m and drag coefficient varying from 0.4 to 1.5, the model reproduced attenuation, ranging from 49 to 55 %, which matches well with the measured data. Spectral analysis performed for the cases with and without vegetation very clearly portrays energy dissipation in the vegetation area as well as spectral changes. This study has the potential of improving the quality of wave prediction in vegetation areas, especially during monsoon season and extreme weather events.

Two-dimensional computational modeling of high-speed transient flow in gun tunnel

Shock Waves ◽  
2017 ◽  
Vol 28 (2) ◽  
pp. 335-348 ◽  
Author(s):  
A. M. Mohsen ◽  
M. Z. Yusoff ◽  
H. Hasini ◽  
A. Al-Falahi
Keyword(s):  
Computational Modeling ◽  
High Speed ◽  
Transient Flow ◽  
Two Dimensional

scholarly journals High Speed Shadowgraphy of Transparent Nozzles as an Evaluation Tool for In-Nozzle Cavitation Behavior of GDI Injectors

2017 ◽  
Author(s):  
Dmitrii Mamaikin ◽  
Tobias Knorsch ◽  
Philipp Rogler ◽  
Philippe Leick ◽  
Michael Wensing
Keyword(s):  
High Speed ◽  
Gasoline Engine ◽  
Transient Flow ◽  
Direct Injection ◽  
Ambient Air ◽  
Gasoline Direct Injection ◽  
Fuel Injector ◽  
Evaluation Tool ◽  
Long Distance ◽  
Cavitation Behavior

Gasoline Direct Injection (GDI) systems have become a rapidly developing technology taking up a considerableand rapidly growing share in the Gasoline Engine market due to the thermodynamic advantages of direct injection. The process of spray formation and propagation from a fuel injector is very crucial in optimizing the air-fuel mixture of DI engines. Previous studies have shown that the presence of some cavitation in high-pressure fuel nozzles can lead to better atomization of the fluid. However, under some very specific circumstances, high levels of cavitation can also delay the atomization process; spray stabilization due to hydraulic flip is the most well-known example. Therefore, a better understanding of cavitation behavior is of vital importance for further optimization of next generation fuel injectors.In contrast to the abundance of investigations conducted on the inner flow and cavitation patterns of diesel injectors, corresponding in-depth research on the inner flow of gasoline direct-injection nozzles is still relatively scarce. In this study, the results of an experiment performed on real-size GDI injector nozzles made of acrylic glass are presented. The inner flow of the nozzle is visualized using a high-power pulsed laser, a long-distance microscope and a high- speed camera. The ambiguity of dark areas on the images, which may represent cavitation regions as well as ambient air drawn into the nozzle holes, is resolved by injecting the fuel both into a fuel or gas filled environment. In addition, the influence of backpressure on the transient flow characteristics of the internal flow is investigated. In good agreement with observations made in previous studies, higher backpressure levels decrease the amount of cavitation inside the nozzles. Due to the high temporal and spatial resolution of the experiment, the transient cavitation behavior during the opening, quasi-steady and closing phases of the injector needle motion can be analyzed. For example, it is found that cavitation patterns oscillate with a characteristic frequency that depends on the backpressure. The link between cavitation and air drawn into the nozzle at the beginning of injection is alsorevealed.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4639

scholarly journals MACH-REFLECTION AS A DIFFRACTION PROBLEM

1976 ◽  
Vol 1 (15) ◽  
pp. 45 ◽  
Author(s):  
Udo Berger ◽  
Soren Kohlhase
Keyword(s):  
Wave Height ◽  
Incident Wave ◽  
Water Waves ◽  
Gas Dynamics ◽  
Mach Reflection ◽  
Diffraction Problem ◽  
Vertical Wall ◽  
Oblique Wave ◽  
Wave Heights ◽  
The Waves

As under oblique wave approach water waves are reflected by a vertical wall, a wave branching effect (stem) develops normal to the reflecting wall. The waves progressing along the wall will steep up. The wave heights increase up to more than twice the incident wave height. The £jtudy has pointed out that this effect, which is usually called MACH-REFLECTION, is not to be taken as an analogy to gas dynamics, but should be interpreted as a diffraction problem.

Field test measurement of the dynamic tightness performance of high-speed trains and study on its influencing factors

Measurement ◽  
2019 ◽  
Vol 138 ◽  
pp. 602-613 ◽  
Author(s):  
Tanghong Liu ◽  
Mingyang Chen ◽  
Xiaodong Chen ◽  
Shengen Geng ◽  
Zhenhua Jiang ◽  
...  
Keyword(s):  
Influencing Factors ◽  
Field Test ◽  
High Speed ◽  
Test Measurement ◽  
High Speed Trains
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