scholarly journals Physical modelling of the interaction between powder avalanches and defence structures

2002 ◽  
Vol 2 (3/4) ◽  
pp. 193-202 ◽  
Author(s):  
F. Naaim-Bouvet ◽  
M. Naaim ◽  
M. Bacher ◽  
L. Heiligenstein
Keyword(s):  
Vertical Velocity ◽  
Three Dimensional ◽  
Physical Modelling ◽  
Front Velocity ◽  
Small Scale ◽  
Water Tank ◽  
A Value ◽  
Physical Experiments ◽  
Scale Models ◽  
Increasing Function

Abstract. In order to better understand the interaction between powder snow avalanches and defence structures, we carried out physical experiments on small-scale models. The powder snow avalanche was simulated by a heavy salt solution in a water tank. Quasi two-dimensional and three-dimensional experiments were carried out with different catching dam heights. For the reference avalanche, the velocity just behind the nose in the head was greater than the front velocity. For the 2-D configuration, the ratio Umax/Ufront was as high as 1.6, but it depends on the height. For the 3-D configuration, this ratio differed slightly and was even greater (up to 1.8). The vertical velocity rose to 106% of the front velocity for the 3-D simulation and 74% for the 2-D simulation. The reduction in front velocity due to the presence of dams was an increasing function of the dam height. But this reduction depended on topography: dams were more effective on an open slope avalanche (3-D configuration). The ratio Umax/Ufront was an increasing function of the dam’s height and reached a value of 1.9. The obstacle led to a reduction in vertical velocity downstream of the vortex zone.

Heat-flow experiments in liquid 4He with a variable cylindrical geometry

1987 ◽  
Vol 174 ◽  
pp. 209-231 ◽  
Author(s):  
H. Gao ◽  
G. Metcalfe ◽  
T. Jung ◽  
R. P. Behringer
Keyword(s):  
Cylindrical Geometry ◽  
Small Scale ◽  
Onset Of Convection ◽  
Aspect Ratios ◽  
A Value ◽  
Prandtl Numbers ◽  
Convection Rolls ◽  
Flow Experiments ◽  
Increasing Function ◽  
Good Agreement

This paper first describes an apparatus for measuring the Nusselt number N versus the Rayleigh number R of convecting normal liquid 4He layers. The most important feature of the apparatus is its ability to provide layers of different heights d, and hence different aspect ratios [Gcy ]. The horizontal cross-section of each layer is circular, and [Gcy ] is defined by [Gcy ] = D/2d where D is the diameter of the layer. We report results for 2.4 [les ] [Gcy ] [les ] 16 and for Prandtl numbers Pr spanning 0.5 [lsim ] Pr [lsim ] 0.9 These results are presented in terms of the slope N1 = RcdN/dR evaluated just above the onset of convection at Rc. We find that N1 is only a slowly increasing function of [Gcy ] in the range 6 [lsim ] [Gcy ] [lsim ] 16, and that it has a value there which is quite close to 0.72. This value of N1 is in good agreement with variational calcuations by Ahlers et al. (1981) pertinent to parallel convection rolls in cylindrical geometry. Particularly for [Gcy ] [lsim ] 6, we find additional small-scale structure in N1 associated with changes in the number of convection rolls with changing [Gcy ]. An additional test of the linearzied hydrodynamics is given by measurements of Rc. We find good agreement between theory and our data for Rc.

Propagation of Buckles in Sandwich Pipes Under External Pressure

2005 ◽  
Author(s):  
I. P. Pasqualino ◽  
M. I. Lourenc¸o ◽  
T. A. Netto
Keyword(s):  
Three Dimensional ◽  
Nonlinear Behavior ◽  
Element Model ◽  
External Pressure ◽  
Core Material ◽  
Small Scale ◽  
Ongoing Research ◽  
Scale Models ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

Sandwich pipes have been considered feasible conceptions for ultra deepwater pipelines, since they are capable to work at low temperatures and withstand high hydrostatic pressures. Sandwich pipelines are composed by inner and outer metallic pipes and a suitable core material which must provide high compression strength and good thermal insulation. The aim of this ongoing research is to study the quasi-static propagation of buckles in sandwich pipes. In this paper, a three-dimensional finite element model considering material and geometric nonlinear behavior is presented. The mesh discretization is determined through a detailed mesh sensitivity analysis. Some experiments with small scale models combining aluminum pipes and polypropylene as core material were carried out to calibrate the numerical model. The propagation pressure is evaluated under different bonding conditions between pipe layers.

Small-Scale Models for Testing Masonry Structures

2010 ◽  
Vol 133-134 ◽  
pp. 497-502 ◽  
Author(s):  
Alvaro Quinonez ◽  
Jennifer Zessin ◽  
Aissata Nutzel ◽  
John Ochsendorf
Keyword(s):  
Large Scale ◽  
Low Cost ◽  
Three Dimensional ◽  
Model Testing ◽  
Scale Model ◽  
Small Scale ◽  
Material Strength ◽  
Masonry Structures ◽  
Scale Models ◽  
Set Up

Experiments may be used to verify numerical and analytical results, but large-scale model testing is associated with high costs and lengthy set-up times. In contrast, small-scale model testing is inexpensive, non-invasive, and easy to replicate over several trials. This paper proposes a new method of masonry model generation using three-dimensional printing technology. Small-scale models are created as an assemblage of individual blocks representing the original structure’s geometry and stereotomy. Two model domes are tested to collapse due to outward support displacements, and experimental data from these tests is compared with analytical predictions. Results of these experiments provide a strong understanding of the mechanics of actual masonry structures and can be used to demonstrate the structural capacity of masonry structures with extensive cracking. Challenges for this work, such as imperfections in the model geometry and construction problems, are also addressed. This experimental method can provide a low-cost alternative for the collapse analysis of complex masonry structures, the safety of which depends primarily on stability rather than material strength.

scholarly journals Numerical Simulation of a Lee Wave Case over Three-Dimensional Mountainous Terrain under Strong Wind Condition

2013 ◽  
Vol 2013 ◽  
pp. 1-13 ◽  
Author(s):  
Lei Li ◽  
P. W. Chan ◽  
Lijie Zhang ◽  
Fei Hu
Keyword(s):  
Mesoscale Model ◽  
Three Dimensional ◽  
Wave Structure ◽  
Energy Utilization ◽  
Small Scale ◽  
Mountainous Terrain ◽  
Water Tank ◽  
Wind Condition ◽  
Strong Wind ◽  
Lee Wave

This study of a lee wave event over three-dimensional (3D) mountainous terrain in Lantau Island, Hong Kong, using a simulation combining mesoscale model and computational fluid dynamics (CFD) model has shown that (1) 3D steep mountainous terrain can trigger small scale lee waves under strong wind condition, and the horizontal extent of the wave structure is in a dimension of few kilometers and corresponds to the dimension of the horizontal cross-section of the mountain; (2) the life cycle of the lee wave is short, and the wave structures will continuously form roughly in the same location, then gradually move downstream, and dissipate over time; (3) the lee wave triggered by the mountainous terrain in this case can be categorized into “nonsymmetric vortex shedding” or “turbulent wake,” as defined before based on water tank experiments; (4) the magnitude of the wave is related to strength of wind shear. This study also shows that a simulation combining mesoscale model and CFD can capture complex wave structure in the boundary layer over realistic 3D steep terrain, and have a potential value for operational jobs on air traffic warning, wind energy utilization, and atmospheric environmental assessment.

scholarly journals Large Scale Experimental Study of the Scour Protection Damage Around a Monopile Foundation Under Combined Wave and Current Conditions

2020 ◽  
Vol 8 (6) ◽  
pp. 417 ◽  
Author(s):  
Minghao Wu ◽  
Leen De Vos ◽  
Carlos Emilio Arboleda Chavez ◽  
Vasiliki Stratigaki ◽  
Tiago Fazeres-Ferradosa ◽  
...  
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Static Stability ◽  
Future Research ◽  
Small Scale ◽  
Flume Experiments ◽  
Wave Flume ◽  
Scale Models ◽  
Damage Data ◽  
Scour Protection

This paper presents a series of large-scale wave flume experiments on the scour protection damage around a monopile under combined waves and current conditions with model scales of 1:16.67 and 1:8.33. The main objective is to compare the damage data obtained from these large-scale models with existing monopile scour protection design approaches, which were proposed based on small scale wave flume experiments, and to study the applicability of the existing approaches. The static stability (onset of motion and bed shear stress) and the dynamic stability (three-dimensional damage numbers) of the scour protection are investigated. Both results show that the existing design approaches can be conservative when applied to large scale models, which highlights the need of further investigations on scale and model effects. In addition, this paper also analyses the scour protection damage depth. It is observed that damage depths of the scour protection layer under low Keulegan–Carpenter number (KC) conditions are smaller than predictions. The study provides valuable large scale experimental data for future research on the monopile scour protection design.

A Basic Study on Influence of Airchamber Volume on OWC Models to Power Conversion Performance

2019 ◽  
Author(s):  
Tomoki Ikoma ◽  
Yoshiyuki Kihara ◽  
Shota Hirai ◽  
Yasuhiro Aida ◽  
Koichi Masuda ◽  
...  
Keyword(s):  
Forced Oscillation ◽  
Scale Effects ◽  
Power Conversion ◽  
Air Pressure ◽  
Hydrodynamic Performance ◽  
Small Scale ◽  
Water Tank ◽  
Basic Study ◽  
Scale Models ◽  
Water Elevation

Abstract Oscillating water column (OWC) types of wave energy converters have still several issues to be studied because system including wave-air-turbine interaction is complex. Besides, scale effects between small scale models and full scale models have not been definite. Although the effect in initial design of OWC devices might been able to be ignored, it is important to understand its characteristics exactly. The present study carried out forced oscillation tests in a water tank corresponding to the radiation problem. Three models whose scale are 1/1, 1/2 and 1/4 were used. In the forced oscillation test, we measured mean water elevation in an airchamber to predict the air flow rate and air pressure inside of the airchamber. From the mean water elevation and the air pressure, the primary power conversion was calculated. As a result, the pressure and the elevation were affected by not only the scale reduction but also the difference of airchamber volume. Variation of the volume of an airchamber affected on hydrodynamic performance sensitively.

scholarly journals On the Accuracy of Three-Dimensional Actuator Disc Approach in Modelling a Large-Scale Tidal Turbine in a Simple Channel

Energies ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 2151 ◽  
Author(s):  
Anas Rahman ◽  
Vengatesan Venugopal ◽  
Jerome Thiebot
Keyword(s):  
Large Scale ◽  
Source Term ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Small Scale ◽  
Structured Grid ◽  
Scale Models ◽  
Actuator Disc ◽  
Tidal Turbine ◽  
Swept Area

To date, only a few studies have examined the execution of the actuator disc approximation for a full-size turbine. Small-scale models have fewer constraints than large-scale models because the range of time-scale and length-scale is narrower. Hence, this article presents the methodology in implementing the actuator disc approach via the Reynolds-Averaged Navier-Stokes (RANS) momentum source term for a 20-m diameter turbine in an idealised channel. A structured grid, which varied from 0.5 m to 4 m across rotor diameter and width was used at the turbine location to allow for better representation of the disc. The model was tuned to match known coefficient of thrust and operational profiles for a set of validation cases based on published experimental data. Predictions of velocity deficit and turbulent intensity became almost independent of the grid density beyond 11 diameters downstream of the disc. However, in several instances the finer meshes showed larger errors than coarser meshes when compared to the measurements data. This observation was attributed to the way nodes were distributed across the disc swept area. The results demonstrate that the accuracy of the actuator disc was highly influenced by the vertical resolutions, as well as the grid density of the disc enclosure.

On slope instability induced by seepage erosion

1999 ◽  
Vol 36 (6) ◽  
pp. 1056-1073 ◽  
Author(s):  
G Crosta ◽  
C di Prisco
Keyword(s):  
Unsaturated Soils ◽  
Soil Layer ◽  
Three Dimensional ◽  
Experimental Tests ◽  
Slope Instability ◽  
Small Scale ◽  
Fluvial Terrace ◽  
Seepage Erosion ◽  
Concentrated Flow ◽  
Scale Models

This paper is focused on seepage erosion causing liquefaction processes and rapid slope failures. One case history, which occurred along an old fluvial terrace in the Po Plain (northern Italy), is presented. The failure was the final consequence of a concentrated flow induced by the incisions due to tractor edged-blade-wheels cutting through the soil layer sealing the bottom of a flooded rice field. To clarify the evolution of the seepage and the erosion phenomena which preceded and characterized the collapse, numerical analyses and some experimental tests on small-scale models have been performed. The problems associated with the hydraulic and mechanical description of localized water flows in unsaturated soils, the three-dimensional conditions of the failure mechanism, and the liquefaction phenomenon are discussed.

Values Underlying Preferences for Adaptive Governance in a Chilean Small-Scale Fishing Community

2020 ◽  
Author(s):  
Sarah A. Ebel ◽  
Christine M. Beitl ◽  
Michael P. Torre
Keyword(s):  
Environmental Change ◽  
Environmental Governance ◽  
Small Scale ◽  
Adaptive Governance ◽  
Fishing Community ◽  
A Value ◽  
Ways Of Life ◽  
Value Frames

Environmental change requires individuals and institutions to facilitate adaptive governance. However, facilitating adaptive governance may be difficult because resource users’ perceptions of desirable ways of life vary. These perceptions influence preferences related to environmental governance and may stem from the ways individuals subjectively value their work and their connections to their environment. This paper uses a value-based approach to examine individual and institutional preferences for adaptive governance in Carelmapu, Chile. We show that two groups had different value frames rooted in divergent ontologies which influenced their actions related to adaptive governance, creating conflict.

Extrusion-Based 3D Printing for Pharmaceuticals: Contemporary Research and Applications

2019 ◽  
Vol 24 (42) ◽  
pp. 4991-5008 ◽  
Author(s):  
Mohammed S. Algahtani ◽  
Abdul Aleem Mohammed ◽  
Javed Ahmad
Keyword(s):  
Cosmetic Surgery ◽  
Fused Deposition Modeling ◽  
Personalised Medicine ◽  
Organ Transplant ◽  
Three Dimensional ◽  
Dosage Forms ◽  
Release Profile ◽  
Small Scale ◽  
Drug Release Profile ◽  
Fused Deposition

Three-dimensional printing (3DP) has a significant impact on organ transplant, cosmetic surgery, surgical planning, prosthetics and other medical fields. Recently, 3 DP attracted the attention as a promising method for the production of small-scale drug production. The knowledge expansion about the population differences in metabolism and genetics grows the need for personalised medicine substantially. In personalised medicine, the patient receives a tailored dose and the release profile is based on his pharmacokinetics data. 3 DP is expected to be one of the leading solutions for the personalisation of the drug dispensing. This technology can fabricate a drug-device with complicated geometries and fillings to obtain the needed drug release profile. The extrusionbased 3 DP is the most explored method for investigating the feasibility of the technology to produce a novel dosage form with properties that are difficult to achieve using the conventional industrial methods. Extrusionbased 3 DP is divided into two techniques, the semi-solid extrusion (SSE) and the fused deposition modeling (FDM). This review aims to explain the extrusion principles behind the two techniques and discuss their capabilities to fabricate novel dosage forms. The advantages and limitations observed through the application of SSE and FDM for fabrication of drug dosage forms were discussed in this review. Further exploration and development are required to implement this technology in the healthcare frontline for more effective and personalised treatment.

Sign in / Sign up

Export Citation Format

Share Document