A modified solution to assess the required strength of exposed backfill in mine stopes

2012 ◽  
Vol 49 (8) ◽  
pp. 994-1002 ◽  
Author(s):  
Li Li ◽  
Michel Aubertin
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Material Properties ◽  
Critical Issue ◽  
Underground Mines ◽  
Practical Solution ◽  
Low Aspect Ratio ◽  
Ground Stability ◽  
Stope Design ◽  
Surface Loads

Backfilling contributes to the improvement of ground stability and reduction of ore dilution in underground mines. A critical issue for backfilled stope design is the required strength for the fill material. A practical solution to address this question was proposed by Mitchell and co-workers for stopes with an exposed face and a high aspect ratio (height H over width B). However, this solution is not directly applicable to stopes with a relatively low aspect ratio (H/B). Its application is also restricted by additional limitations on the strength along the fill–rock interfaces and the load applied on top of the backfill. In this note, the model proposed by Mitchell and co-workers is modified to provide an estimate of the required strength of backfill for various geometries, material properties, and surface loads. The modified Mitchell (MM) solution is validated against experimental results. Sample calculations with the MM solution are also presented and discussed.

Wetting Challenges in Cleaning of High Aspect Ratio Nano-Structures

2012 ◽  
Vol 195 ◽  
pp. 235-238 ◽  
Author(s):  
Xiu Mei Xu ◽  
Guy Vereecke ◽  
Erik van den Hoogen ◽  
Jens Smeers ◽  
Silvia Armini ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
New Technology ◽  
Critical Issue ◽  
Silicon Substrates ◽  
Wetting Properties ◽  
Nano Structures ◽  
Wet Processing ◽  
Semiconductor Fabrication ◽  
Technology Nodes

In semiconductor fabrication, pattern collapse of high aspect ratio structures after wet processing has been a critical issue and attracted a lot of interest. On the other hand, very little attention is spent on the potential wetting issues as feature dimensions are continuously scaled down and novel materials with different wetting properties are used in new technology nodes. In this work we investigate the wettability of nanopatterned silicon substrates with different surface modifications.

scholarly journals Strain and Temperature Sensitivities Along with Mechanical Properties of CNT Buckypaper Sensors

Sensors ◽  
2020 ◽  
Vol 20 (11) ◽  
pp. 3067
Author(s):  
Shiuh-Chuan Her ◽  
Wei-Chun Hsu
Keyword(s):  
Mechanical Properties ◽  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Complex Surface ◽  
Thermogravimetric Analyzer ◽  
Low Aspect Ratio ◽  
Four Point Bending ◽  
Thermal Chamber ◽  
Multi Walled Carbon Nanotubes ◽  
Walled Carbon Nanotubes

In this work, buckypaper composed of multi-walled carbon nanotubes (MWCNT) was prepared through a vacuum filtration process. The effect of MWCNT aspect ratio on the buckypaper performance was investigated. The freestanding and highly flexible buckypaper can be used as a sensor to attach on a complex surface monitoring the strain and temperature at the critical area. The mechanical properties of the buckypaper were examined using the tensile and nanoindentation tests. The strain and temperature sensitivities of the buckypaper were evaluated through the four-point bending and thermal chamber tests, respectively. In addition, the microstructure and thermal stability of the buckypaper were studied by scanning electron microscopy (SEM) and thermogravimetric analyzer (TGA), respectively. Experimental results showed that the mechanical properties such as Young’s modulus, tensile strength, fracture strain, and hardness of the buckypaper made of high aspect ratio MWCNTs were significantly superior to the buckypaper consisted of low aspect ratio MWCNTs, while the strain and temperature sensitivities of the buckypaper composed of low aspect ratio MWCNTs were better than that of the buckypaper made of high aspect ratio MWCNTs.

scholarly journals Power reduction and the radial limit of stall delay in revolving wings of different aspect ratio

2015 ◽  
Vol 12 (105) ◽  
pp. 20150051 ◽  
Author(s):  
Jan W. Kruyt ◽  
GertJan F. van Heijst ◽  
Douglas L. Altshuler ◽  
David Lentink
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Angle Of Attack ◽  
Radial Distance ◽  
Leading Edge ◽  
High Angle ◽  
High Angle Of Attack ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Low Aspect Ratio Wings

Airplanes and helicopters use high aspect ratio wings to reduce the power required to fly, but must operate at low angle of attack to prevent flow separation and stall. Animals capable of slow sustained flight, such as hummingbirds, have low aspect ratio wings and flap their wings at high angle of attack without stalling. Instead, they generate an attached vortex along the leading edge of the wing that elevates lift. Previous studies have demonstrated that this vortex and high lift can be reproduced by revolving the animal wing at the same angle of attack. How do flapping and revolving animal wings delay stall and reduce power? It has been hypothesized that stall delay derives from having a short radial distance between the shoulder joint and wing tip, measured in chord lengths. This non-dimensional measure of wing length represents the relative magnitude of inertial forces versus rotational accelerations operating in the boundary layer of revolving and flapping wings. Here we show for a suite of aspect ratios, which represent both animal and aircraft wings, that the attachment of the leading edge vortex on a revolving wing is determined by wing aspect ratio, defined with respect to the centre of revolution. At high angle of attack, the vortex remains attached when the local radius is shorter than four chord lengths and separates outboard on higher aspect ratio wings. This radial stall limit explains why revolving high aspect ratio wings (of helicopters) require less power compared with low aspect ratio wings (of hummingbirds) at low angle of attack and vice versa at high angle of attack.

Assessment of Empirical VIV Analysis Tools and Benchmark With Experiments

2008 ◽  
Author(s):  
Yiannis Constantinides ◽  
Owen H. Oakley
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Full Scale ◽  
Small Scale ◽  
Engineering Practice ◽  
High Current ◽  
Low Aspect Ratio ◽  
Prediction Tools ◽  
High Harmonics ◽  
Current Engineering

In the current engineering practice, riser VIV design is typically based on empirically derived models. These tools have been under development for some time, but are based primarily on small scale rigid cylinder tests and flexible cylinders with relatively low aspect ratio. As high aspect ratio and full scale measurements become available for a wide variety of configurations, an improved understanding of the physics is beginning to emerge. This study employs a design based methodology for benchmarking VIV prediction tools against a comprehensive set of experiments. Configurations with bare, partially and fully straked risers operating at low and high current speeds are used to cover a broader range of validation conditions. Additional work to include the effect of high harmonics over a range of cases is necessary to draw more definitive conclusions. Given the difficulties in predicting VIV response for these small scale experiments the effectiveness in handling full scale risers is in question.

Performance of Low-Aspect-Ratio Diffusers With Fully Developed Turbulent Inlet Flows: Part I—Some Experimental Results

1973 ◽  
Vol 95 (3) ◽  
pp. 385-392 ◽  
Author(s):  
O. J. McMillan ◽  
J. P. Johnston
Keyword(s):  
Experimental Investigation ◽  
Aspect Ratio ◽  
Boundary Layers ◽  
High Aspect Ratio ◽  
Total Pressure ◽  
Turbulent Boundary Layers ◽  
Two Dimensional ◽  
Low Aspect Ratio ◽  
Performance Curves ◽  
Existing Data

An experimental investigation of the effects of incompressible, fully developed, turbulent inlet flow on the performance of straight, two-dimensional rectangular diffusers of low aspect ratio is presented. Results presented include flow regime information, performance curves, and total-pressure loss data for a series of diffusers of moderate non dimensional length and low aspect ratio. The results are compared to existing data and correlations and important differences are noted between the diffusers of this study and diffusers of high aspect ratio with thin to moderately thick turbulent boundary layers at inlet.

scholarly journals The Influence of Dune Aspect Ratio, Beach Width and Storm Characteristics on Dune Erosion for Managed and Unmanaged Beaches

2020 ◽  
Author(s):  
Michael Itzkin ◽  
Laura J. Moore ◽  
Peter Ruggiero ◽  
Sally D. Hacker ◽  
Reuben G. Biel
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Storm Event ◽  
Volume Loss ◽  
Dune Erosion ◽  
Low Aspect Ratio ◽  
Beach Width ◽  
Natural Dune ◽  
Storm Characteristics ◽  
Dune Height

Abstract. Dune height is an important predictor of dune impact during a storm event given that taller dunes have a lower likelihood of being overtopped. However, the temporal dominance of the wave collision regime, wherein significant volume loss (erosion) from the dune will occur through dune retreat without the dune being overtopped, suggests that dune width must also be considered when evaluating the vulnerability of dunes to erosion. We use XBeach, a numerical model that simulates hydrodynamic processes, sediment transport, and morphologic change during a storm, to analyze dune erosion as a function of dune aspect ratio (i.e., dune height versus dune width) for storms of varying intensity and duration. We find that low aspect ratio (low and wide) dunes lose less volume than high aspect ratio (tall and narrow) dunes during longer storms, especially if they are fronted by a narrow beach. During more intense storms, low aspect ratio dunes experience greater erosion as they are more easily overtopped than high aspect ratio dunes. In managed scenarios where sand fences are used to construct a fenced dune seaward of the existing natural dune, we find that the fenced dune effectively prevents the natural dune behind it from experiencing any volume loss until the fenced dune is sufficiently eroded, reducing the magnitude of erosion of the natural dune by up to 50 %. We also find that beach width exerts a significant influence on dune erosion; a wide beach offers the greatest protection from erosion in all circumstances regardless of dune morphology or storm characteristics. These findings suggest that efforts to maintain a wide beach may be effective at protecting coastal communities from dune loss. However, in maintaining wide beaches and dunes, the protection offered in the short-term must be considered against long-term detrimental effects of potentially limiting overwash fluxes, which are critical to maintaining island elevation as sea level rises.

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