Yizhong Xu

Factors Influencing the Performance of Porous Wind Shields

Porosity, porosity distribution, porous shape, porous size, thickness of shield, shield height &width, and shield orientation are the factors that influence the performance of porous wind shields. Among them, porosity is the most important factor in determining the performance of porous shields. However shield height & width have major impacts on the performance of shields. The remaining factors play less significant influences on the performance of the shield, but they remain researching interests to be further studied.

3D CFD Investigation of Air Flow Behind a Porous Fence Using Different Turbulence Models

Even after many years of the application of numerical CFD techniques to flow through porous fences, still there is disagreement between researchers regarding the best turbulence model to be implemented in this field. Moreover, different sources claim to have achieved good agreement between numerical results and experimental data; however, it is not always possible to compare numerical and experimental results due to the lack of information or variations in test conditions. In this paper, five different turbulence models namely; K-e models (standard, RNG and Realizable) and K-ω models (Standard and SST), have been applied through a 3D CFD model to investigate air flow behind a porous panel, under the same conditions (boundary conditions and numerical schemes). Results are compared with wind tunnel experiments. Comparison is based on the vertical velocity profile at a location 925 mm downstream of the fence along its center line. All models were capable of reproducing the velocity profile, however, some turbulence models over-predicted the reduction of velocity while it was under-predicted by other models, however, discrepancy between CFD modelling and experimental results was kept around 20%. Comprehensive description of the turbulence structure and the streamlines highlight the fact that the criterion for selecting the best turbulence model cannot rely only on the velocity comparison at one location, it must also include other variables.Copyright

Application of numerical analysis in the design and small-scale intelligent manufacturing process of porous fences

This paper presents an application of Computational Fluid Dynamics (CFD) technique for designing of protective fences for shelter from snow and winds commonly used on offshore rigs and other facilities in cold regions. The CFD simulation of real situations provided detailed information about the flow characteristics behind the fence and the effective shelter zone. Such flow details are usually very expensive, time consuming and difficult to obtain by physical experiments. The numerical simulations found that the shape of pores and surface shear stress has significant impact on the reattachment length and the size of effective fence zone. The effective shelter distance can be increased by avoiding sharp angular corners in the porous pores and reducing surface shear stress. The 3D modelling and CFD simulation provide detailed aerodynamics flow characteristics and stress distributions that allow evaluating a number of designs cost effectively. The technique can be integrated with small-scale intelligent manufacturing system (SIMS) for flexible design and manufacturing of fences.

Effect of Corrugation on the Performance of Porous Baffles Used as Weather Shelters on Oil and Gas Platforms

Porous baffles are usually used for weather protection on onshore and offshore oil installations in order to provide a sheltered area for personnel to operate. Corrugated fences are more favourable than flat fences in large installations, due to their increased stiffness; however, the performance of those fences is expected to differ from flat fences due to changes in porosity and flow structure. In this work, the experimental and numerical studies of the influence of corrugated fence on the flow characteristics are presented. The tri-dimensional effect imposed by the angle of corrugation and the depth of the fence influences the windward and leeward flow characteristics with respect to the fence. Velocity coefficient is used as one important parameter for measuring the performance of porous fences. It was found that, under similar conditions, the total obstruction produced by the corrugated fence varies significantly from that of the flat fence. Hence, velocity reduction for a corrugated fence system is expected to be smaller. A complete description of the physics of the fluid mechanics around the fence is given. Furthermore, the behaviour of the stream lines close to the fences in both cases; corrugated and non-corrugated, were studied using CFD techniques. Through observation of local pressure distribution, it was possible to reveal how velocity variations were concentrated around the inclined sections of the corrugated fence. In performing the numerical simulations, a two dimensional approach was initially implemented to capture the flow behaviour in the vicinity of the inclined sections. Subsequently, a tri-dimensional simulation on a section of the fence was undertaken and compared with experimental data. The results of the simulations were in good agreement with experimental data obtained from wind tunnel tests.Copyright

Mathematical representation of snow transport

The model of snow transport is based on the resolution of a set of governing equations which are a differential mass balance equation, momentum balance equation and energy balance equation for the air as well as for the snow. The interaction between the snow and the air must also be included in this set of equations. The complete set is a complex system that will need a closure relation to be solved in order to reproduce the real situation in the best possible way. Mathematical structure of this system is far too complicated even for the powerful resources currently available. So, some simplifications are needed in order to succeed in the resolution process. This simplification is derived from considerations of the physics involved in the particular problem to be solved. In this work, the performance of a porous panel used in winterization of offshore platforms under snowing condition is studied. A comprehensive discussion of the mathematical representation of the total resolution process used to perform ...

Numerical Simulation of Crack Tip Behavior under Fatigue Loading

Fatigue damage is a localized phenomenon controlled by the near-tip crack behavior. This paper presents an application of a dislocation distribution technique to the simulation of crack tip behavior under fatigue loading. A centre-cracked tension specimen under uni-axial fatigue loading is used in the study. Crack opening and plastic deformation around the crack tip are simulated by distributions of dislocation dipoles in crack plane and four inclined planes ahead of the crack tip. Climb dislocation dipole is used to model the opening and closing of the crack while glide dislocation dipole is used to simulate the backward and forward slip in the inclined planes during loading and unloading of the fatigue cycle. Stress field around the crack tip is obtained by the superposition of the contributions of the applied external load and the distributed dislocation dipoles. Correct boundary conditions of the model are achieved by employing a quadratic programming technique to minimize a properly constructed non-negative object function. It is found that the simulated crack closure variations under the constant amplitude fatigue load agree well with the result of a previously developed modified strip yield model with an appropriate constraint factor.

Delamination Threshold Load of Composite Laminates under Low-Velocity Impact

A key factor affecting the use of carbon fibre reinforced composite laminates is the low velocity impact damage which may be introduced accidentally during manufacture, operation or maintenance of the component. Among the several barely visible impact damages, interlaminar delamination is the dominant failure mode and may reduce the post-impact compressive strength of the component significantly. This paper focuses on the study of the delamination threshold load (DTL) above which significant increase of delamination and thus large reduction of the residual compressive strength of the component may occur. Instrumented drop weight tests were carried out under various impact energy levels to determine the delamination threshold load. Efforts are directed to the study of the laminate thickness effect on the reliability of the detection of the DTL. The validity of the concept of DTL has been investigated and possible implications on the measurement of the DTL has been discussed. It is demonstrated that DTL exists but its detection requires proper testing conditions.