Influence of Suction Dredging on the Failure Mechanism of Sandy Submarine Slopes: Revisited With a Coupled Numerical Approach

2019 ◽  
Author(s):  
Manuela Kanitz ◽  
Juergen Grabe
Keyword(s):  
Failure Mechanism ◽  
High Speed ◽  
Particle Interaction ◽  
Discrete Element ◽  
Shallow Foundation ◽  
Offshore Wind ◽  
Scale Model ◽  
Small Scale ◽  
Failure Behavior ◽  
Submarine Slope

Abstract The installation of shallow foundation systems for offshore wind turbines like gravity foundations requires the excavation of the weak top soil of the seabed to place the structure on more stable ground. This excavation can be done through suction dredging resulting in a pit. Different slope angles of this pit can be realized using this technique. As the failure mechanisms of artificial submarine slopes using suction dredging are barely investigated, relatively small final slope angles of max. 10 degree are reached to guarantee stability. Nevertheless, small-scale experiments show that submarine slopes with overcritical slope inclinations can be stable for a while when prepared with suction dredging. Steeper inclinations would significantly reduce the disturbance of the marine fauna and the amount of sand to be removed and therefore meet both economic and ecological interests. The investigations of the failure mechanism in the submarine slope during suction dredging are carried out with a coupled Euler-Lagrange approach, namely the combination of the Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM). This method enables the computation of particle-particle as well as the fluid-particle interaction forces and hence their influence on the investigated submarine slope behavior. The calculations are carried out with the open source software package CFDEM® coupling, which combines the discrete element code LIGGGHTS® with CFD solvers based on OpenFOAM®. Additionally, small scale model tests of suction dredging of sandy submarine slopes are carried out. The displacement of the soil grains is monitored with a high-speed camera. To take into account effects of contractancy and dilatancy, a loosely and a densely packed sand are investigated and the influence of the packing density on the failure mechanism is evaluated. The experimentally gained results will be compared to the numerical ones to evaluate the capability of the coupled CFD-DEM method to depict the failure behavior of submarine slopes during suction dredging.

scholarly journals Failure Mechanism of Rock Bridge Based on Acoustic Emission Technique

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
Guoqing Chen ◽  
Yan Zhang ◽  
Runqiu Huang ◽  
Fan Guo ◽  
Guofeng Zhang
Keyword(s):  
Acoustic Emission ◽  
Failure Mechanism ◽  
High Speed ◽  
Large Scale ◽  
Small Scale ◽  
Failure Behavior ◽  
Long Distance ◽  
Rock Bridge ◽  
Rocky Slope ◽  
Landslide Model

Acoustic emission (AE) technique is widely used in various fields as a reliable nondestructive examination technology. Two experimental tests were carried out in a rock mechanics laboratory, which include (1) small scale direct shear tests of rock bridge with different lengths and (2) large scale landslide model with locked section. The relationship of AE event count and record time was analyzed during the tests. The AE source location technology and comparative analysis with its actual failure model were done. It can be found that whether it is small scale test or large scale landslide model test, AE technique accurately located the AE source point, which reflected the failure generation and expansion of internal cracks in rock samples. Large scale landslide model with locked section test showed that rock bridge in rocky slope has typical brittle failure behavior. The two tests based on AE technique well revealed the rock failure mechanism in rocky slope and clarified the cause of high speed and long distance sliding of rocky slope.

Experimental Study on Cavitation Motion of Underwater Vehicle With Protrusions

2020 ◽  
Author(s):  
Zhaoyu Qu ◽  
Ning Gan ◽  
Yingyu Chen ◽  
Nana Yang
Keyword(s):  
High Speed ◽  
Underwater Vehicle ◽  
Test Method ◽  
Scale Model ◽  
Small Scale ◽  
Reduced Pressure ◽  
Local Flow ◽  
Bubble Generation ◽  
Scale Characteristics ◽  
Motion Characteristics

Abstract For underwater vehicles with protrusions (external structure), the geometric shape of the protrusions is bound to affect the local flow field of the vehicles during the moving process of the vehicles, thus affecting the generation, development and collapse of cavitation around the vehicles. The cavitation may break, fall off and collapse randomly, and other local movements may affect the motion attitude of the underwater vehicle. It is an effective method to study fluid dynamics to simulate prototype cases with small scale models. In this paper, we mainly use the small scale model test method to explore the cavitation motion characteristics of the vehicle in water with protrusions. Through the establishment of a set of vehicle motion test equipment under reduced pressure, a series of experiments were conducted on this basis to explore the motion characteristics of vehicle cavitation under different bump shapes. In this study, two high-speed cameras were used to simultaneously record cavitation generation, development, collapse and other characteristics, to analyze the bubble generation mechanism and scale characteristics caused by the bulge, and then to study the influence of cavitation induced by the bulge on the motion attitude of the vehicle.

scholarly journals Effect of Specimen Placement on Model Rock Blasting

2021 ◽  
Author(s):  
Zong-Xian Zhang ◽  
Li Yuan Chi ◽  
Qingbin Zhang
Keyword(s):  
Kinetic Energy ◽  
High Speed ◽  
Rock Specimen ◽  
Base Material ◽  
Scale Model ◽  
Small Scale ◽  
High Speed Photography ◽  
Rock Blasting ◽  
Ground Material ◽  
Very High

AbstractSmall-scale model blasting plays an important role in understanding mechanism of rock fragmentation by blasting and improving blast technology in rock and mining engineering. Because a specimen (or model) often needs to be placed on either a ground or another material in model blasting, an additional interface appears between the specimen and the ground (or material), compared with an engineering blast that does not have such an interface. In this paper, four model blasts with high-speed photography were presented. The results showed that: (1) as the impedance of a rock specimen was smaller than that of the ground material, the specimen was thrown up and a certain amount of kinetic energy was brought with such a bounce. Thus, this placement should be avoided in model blasts. (2) As a rock specimen was placed on three blocks of the same type of rock as the specimen the specimen was not bounced up during blasting. Correspondingly, no kinetic energy was induced by specimen bounce. Therefore, this placement is recommended for model blasting. If very high specific charge must be used in model blasting, the above-recommended method will not work well due to possible breakage of the base material during blasting. In this case, the rock specimen can be placed on a material with smaller impedance than that of the rock specimen so that specimen bounce can be reduced. Accordingly, such a possible specimen bounce should be estimated by stress wave analysis.

scholarly journals Ultimate lateral pressures exerted on buried pipelines by the initiation of submarine landslides

Landslides ◽  
2021 ◽  
Author(s):  
Weiyuan Zhang ◽  
Amin Askarinejad
Keyword(s):  
High Speed ◽  
Imaging System ◽  
Hybrid Approach ◽  
Scale Model ◽  
Small Scale ◽  
Shear Strain Rate ◽  
Submarine Landslides ◽  
Fluid Inertia ◽  
Buried Pipelines ◽  
Slope Instabilities

AbstractSubmarine slope instabilities are considered one of the major threats for offshore buried pipelines. This paper presents a novel method to evaluate the ultimate pressure acting on a buried pipeline during the liquefaction of an inclined seabed. Small-scale model tests with pipes buried at three different embedment ratios have been conducted at an enhanced centrifugal acceleration condition. A high-speed, high-resolution imaging system was developed to quantify the soil displacement field of the soil body and to visualize the development of the liquefied zone. The measured lateral pressures were compared with the hybrid approach proposed for the landslide–pipeline interaction in clay-rich material by Randolph and White (2012) and Sahdi et al. (2014). The hybrid approach is proved to be able to predict later pressures induced by the movement of (partially) liquefied sand on buried pipelines. It is found that the fluid inertia (fluid dynamics) component plays an important role when the non-Newtonian Reynolds number >~2 or the shear strain rate > 4.5 × 10−2 sec−1.

Aerodynamic and Vibration Analysis of the Morphing Wings of a Hypersonic Vehicle

2020 ◽  
Author(s):  
Mohammad Khairul Habib Pulok ◽  
Uttam K. Chakravarty
Keyword(s):  
Vibration Analysis ◽  
High Speed ◽  
Thermal Loading ◽  
Hypersonic Vehicle ◽  
Vibration Characteristics ◽  
Scale Model ◽  
Small Scale ◽  
Hypersonic Vehicles ◽  
Morphing Wings ◽  
Wing Morphing

Abstract Hypersonic vehicles are receiving great attention in recent years due to their high speed and long-range capabilities. The shock waves come into consideration as a propagating disturbance for any aircraft when it exceeds the speed of sound. Complex environment and flight requirements of the hypersonic vehicles are leading the researchers to focus on several design considerations. Adaptive shape deformation is one of the prospective areas among them which has an impact on thermal loading, global and local load factors, vehicle acceleration, total energy dissipation, and fuel consumption. The wings play a key role in the aerodynamic performances of a flying machine; therefore, the overall performance of the hypersonic vehicle can be improved by applying morphing technologies on the wing. Morphing can help with reducing wave drag, increasing lift-to-drag ratio as well as enhancing flight endurance, and extending the range for a hypersonic vehicle. In this study, the telescopic wing morphing profile is considered for the aerodynamics and vibration analysis. The experimental validations of the aerodynamics and vibration characteristics are conducted by a wind-tunnel experiment and a vibration-testing arrangement, respectively, using a small-scale model of the wing. The computational analysis of the aerodynamics and vibration characteristics of the morphing wings are conducted and compared. Thus, a comprehensive study including the comparison between morphing modes can establish a standard to choose the appropriate morphing technique for the hypersonic vehicles.

On the noise sources of the unsuppressed high-speed jet

1971 ◽  
Vol 50 (1) ◽  
pp. 21-31 ◽  
Author(s):  
K. A. Bishop ◽  
J. E. Ffowcs Williams ◽  
W. Smith
Keyword(s):  
Reynolds Number ◽  
High Speed ◽  
Large Scale ◽  
Jet Noise ◽  
Jet Flow ◽  
Scale Model ◽  
Small Scale ◽  
Noise Sources ◽  
Supersonic Transport ◽  
Scale Turbulence

The paper describes an interpretation of jet-noise theory and scale-model experiments to highlight physical properties of jet-noise sources at very high speed. The study is prompted by current efforts to suppress the noise of supersonic transport aircraft.The principal noise sources are shown to be very large-scale wave-like undulations of the jet flow that travel downstream at supersonic speed for a distance of several jet diameters. These motions are relatively well ordered and are probably more akin to recognizable instabilities of a laminar flow than the confused small-scale turbulence. Because of this we postulate a model of the noise generating motions as the instability products of a jet flow of low equivalent Reynolds number. This Reynolds number is based on an eddy viscosity and can be further reduced by artificially increasing the small-scale turbulence level. This step would tend to stabilize the flow and inhibit the formation of large-scale noise producing eddies.

Characterization of Particle and Heat Losses From Falling Particle Receivers

2019 ◽  
Author(s):  
Clifford K. Ho ◽  
Sean Kinahan ◽  
Jesus D. Ortega ◽  
Peter Vorobieff ◽  
Andrea Mammoli ◽  
...  
Keyword(s):  
Convective Heat ◽  
High Speed ◽  
Field Tests ◽  
Heat Losses ◽  
Image Correlation ◽  
Scale Model ◽  
Small Scale ◽  
Small Particles ◽  
Bench Scale ◽  
Particle Velocities

Abstract Camera-based imaging methods were evaluated to quantify both particle and convective heat losses from the aperture of a high-temperature particle receiver. A bench-scale model of a field-tested on-sun particle receiver was built, and particle velocities and temperatures were recorded using the small-scale model. Particles heated to over 700 °C in a furnace were released from a slot aperture and allowed to fall through a region that was imaged by the cameras. Particle-image, particle-tracking, and image-correlation velocimetry methods were compared against one another to determine the best method to obtain particle velocities. A high-speed infrared camera was used to evaluate particle temperatures, and a model was developed to determine particle and convective heat losses. In addition, particle sampling instruments were deployed during on-sun field tests of the particle receiver to determine if small particles were being generated that can pose an inhalation hazard. Results showed that while there were some recordable emissions during the tests, the measured particle concentrations were much lower than the acceptable health standard of 15 mg/m3. Additional bench-scale tests were performed to quantify the formation of particles during continuous shaking and dropping of the particles. Continuous formation of small particles in two size ranges (< ∼1 microns and between ∼8–10 microns) were observed due to de-agglomeration and mechanical fracturing, respectively, during particle collisions.

A Reduced-Order Mathematical Model for the Current-Induced Motion of a Floating Offshore Wind Turbine

2021 ◽  
Author(s):  
Éverton L. de Oliveira ◽  
Celso P. Pesce ◽  
Bruno Mendes ◽  
Renato M. M. Orsino ◽  
Guilherme R. Franzini
Keyword(s):  
Mathematical Model ◽  
Wind Turbine ◽  
Horizontal Plane ◽  
Offshore Wind ◽  
Scale Model ◽  
Offshore Wind Turbine ◽  
Small Scale ◽  
Floating Offshore Wind Turbine ◽  
Reduced Order ◽  
Induced Motion

Abstract Floating offshore platforms motions induced by currents are quite complex phenomena, in general. In particular, VIM, Vortex-Induced Motion, is a type often encountered in platforms with circular columns. Recently, VIM has been observed in towing tank tests with a small-scale model of a Floating Offshore Wind Turbine (FOWT), the OC4 Phase II floater, a 3+1 columns platform. The present paper proposes a reduced-order mathematical model (ROM) to assess VIM of a FOWT. The ROM is derived on the horizontal plane, including yaw motions and nonlinear mooring forces. Current forces are represented through ‘wake variables’, adapting phenomenological models firstly used for VIM of mono-column platforms. The ROM is built upon a set of eleven generalized coordinates, three for the rigid body motion on the horizontal plane and a pair of wake variables for each column, resulting in a system of eleven nonlinear second-order ODEs. The pairs of wake variables obey van der Pol equations, and use hydrodynamic coefficients and parameters obtained from previous experiments with small draught cylinders. Hydro-dynamic interferences among columns or heave plates effects on the flow are not considered, for simplicity. The validity of the proposed model is assessed having the mentioned small-scale experimental campaign as a case study. The simulations are carried out at three different current incidence angles, 0, 90 and 180 degrees, spanning a large range of reduced velocities. The simulations reproduce well the oscillations observed in the experimental tests. A good agreement in transverse oscillations is found, including lock-in regions. The simulations also depict a possibly important phenomenon: a resonant yaw motion emerging at high reduced velocities.

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