Ratio Of Gap Width Research Articles

Mathematical model of wave diffraction for partially reflecting breakwaters

This study derived analytical solutions for wave diffraction by a semi-infinite breakwater or collinear, symmetrical, and asymmetrical double breakwaters with partial reflection. The diagrams of the diffraction coefficient distribution for double breakwaters are presented. The analytical results of this study are compared to those of other analytical diffraction solutions in detail, and the effects of the reflection coefficient and layout of the breakwaters on the wave heights are analyzed. The results reveal that the reflection coefficient of the breakwaters mainly affects the wave heights in the reflection area in front of the breakwaters, and somewhat affects the wave heights in the shielding area behind the breakwaters. The reflection coefficients’ effect on the shielding area is closely related to the breakwater layout. In addition, the layouts of asymmetrically diverging double breakwaters are closely related to their shielding effects. The main factors that affect the wave heights in the shielding area are the inclination angles of breakwaters, the ratio of gap width to wavelength and the position of right breakwater head. The impact of those factors is not independent, but interrelated; the above factors, rather than just one of them, should be considered comprehensively when the breakwater layout is designed.

A simulation study on stress-seepage characteristics of 3D rough single fracture based on fluid-structure interaction

This paper expounds on the process of deformation and seepage field change of single coarse fracture under normal stress and puts forward a numerical simulation framework based on fluid-structure coupling method to reasonably link contact deformation of fracture surface with seepage field change. The geometric model of a three-dimensional rough single fracture surface with controllable JRC is established based on the random surface generation method. The numerical test model of radiation flow of single fracture in rough rock is constructed, which is consistent with the laboratory test. Through carrying out numerical simulation tests of different JRC and normal stress conditions, this paper discusses the phenomenon and intrinsic nature of the influence of JRC on fracture seepage characteristics. The increase in eddy current intensity and eddy current area ratio is the inherent characteristics of the seepage field characteristics after JRC increases. With the rise of energy loss, the macroscopic seepage flow decreases. In addition, with the advantage of the fluid-structure interaction method, the fracture deformation characteristics under different normal stresses are reflected by the ratio of the contact area. The correlation among fracture surface deformation, velocity vector, and seepage pressure are analyzed. Finally, the cubic polynomial correlation between gap width ratio and contact area ratio is established and verified. It is of positive significance to quantify the influence of coarse single fracture contact ratio on deformation-seepage coupling characteristics under normal stress.

Numerical investigation of flow structures and aerodynamic interference around stationary parallel box girders

Many parallel bridges have been recently designed and built around the world to accommodate the ever-increasing volumes of vehicle and rail traffic. Accordingly, the aerodynamic interference around the parallel girders becomes important to investigate for a more accurate estimation of wind-induced effects on bridges. In this study, a wide range of gap-width ratios (0–15) for parallel box girders are selected to investigate the aerodynamic interference using three-dimensional large eddy simulation at zero wind attack angle. Specific aerodynamic characteristics, including the flow structures, pressure distributions, mean values and standard deviations of the force coefficients, Strouhal number as well as spanwise correlations of the aerodynamic coefficients are examined with various gap-width ratios. The detailed comparison work demonstrates a good agreement with the experimental work. The simulation results reveal that all the aerodynamic characteristics are significantly influenced by the gap-width ratio. The three regions are bounded by critical gap-width ratios of G/B = 0.25 and G/B = 5. There are large changes in behavior at G/B = 0.25, whereas, for G/B > 5, interference effects are not evident. The interference effects on both mean and fluctuating aerodynamic coefficients of parallel box girders are also quantified and summarized.

Study of solar air heater with discrete arc ribs geometry: Experimental and numerical approach

In design of Solar Air Heaters (Sol-AHs) duct, the most efficient way to enhance the heat transfer is by providing artificial roughness on the absorber plate. In the present paper, experimental analyses perform on solar air heater (Sol-AHs) with novel discrete symmetrical arc rib geometry. The studied parameters are ratio of gap width to rib element diameter (g/e) of 2, 3, 4 and 5, ratio of rib diameter height to hydraulic diameter (e/Dh) as 0.045, ratio of rib pitch to rib element diameter as 10, air flow angle of attack as 30°, number of gaps 3 and Re in range of 3000–14000. The performance of novel discrete arc rib solar air heater has been compared with existing staggered V-rib geometry. Maximum enhancement in Nusselt number achieves at g/e equal to 4, which is 3.88 times more compared to the smooth plate, while the highest increment in the thermo-hydraulic performance also observes at g/e of 4. Correlations have been developed for ratio of gap width to rib element diameter and flow parameters. The mathematical model has been developed using a MATLAB code and validates with an experimental study, which further use to design the Solar Air Heater (Sol-AHs) under various operating parameters. Moreover, the new discrete symmetrical arc rib geometry has better performance than the existing best novel V-rib geometry.

Variation of Pressure Coefficient Along Bottom of Dam Vertical Lift Gates

The vertical lift gates are exposed to hydrodynamic forces that arise as a result of pressurized flow established by the large-scale effect of the water levels in the dam reservoirs. The most influential forces are those that are applied on the gate vertically upward due to the intensity of the flow under the gate and downward as a result of passage flow above the gate. The difference between these two forces generates a downpull force that is the most important gate stability indicator. In this research, an arbitrary hydraulic model was constructed to investigate the effects of many gate lip shapes with and without extensions on the magnitudes and distribution of bottom pressure coefficient when the values of flow and shaft gap width ratio (b2/bl) are constant. The results indicate that the bottom pressure coefficient appears to vary uniformly with gate openings and seem to be influenced effectively by the gate lip geometry. So, for the given value of (b2/bl), the top pressure coefficient regarding the downward force will mostly be with uniform changes and hence the downpull coefficient depends on the magnitudes and distribution of bottom pressure coefficient. An attempt by using the correlation coefficient of Statistical Package of Social Sciences was made to determine whether the pressure fluctuation is significantly shown at the bottom pressure distribution curve, which in turn is considered as appropriate indicator for the vibration occurrence. Full range of maximum bottom pressure coefficients in a matrix form is made to assist in design purposes. The results are analyzed and many conclusions are obtained.

Experimental investigation of solar air heater with new symmetrical GAP ARC GEOMETRY and staggered element

The paper presents experimental analysis of air flowing in solar air heater having new symmetrical gap arc geometry and staggered element. The roughness parameters are arc angle (α), relative staggered rib pitch (p'/p), number of gap on half arc (Ng), ratio of gap width to rib height (g/e) and relative staggered rib length (r/e) as 300, 0.4, 3, 4 and 4, respectively for rib diameter of 2 mm. Reynolds number and relative rib pitch were varied as 3000–15000 and 6–14, respectively. Five rib roughened plates having new symmetrical gap arc geometry and staggered element with relative rib pitch of 6, 8, 10, 12 and 14 were tested. Performance of new symmetrical gap arc geometry and staggered element has been compared with broken arc rib with staggered element and smooth duct. In new symmetrical gap arc geometry and staggered element the maximum increase in friction factor and Nusselt number corresponded to relative rib pitch of 10 and it is 3.88 and 2.18 times as compared to smooth plate. Also new symmetrical gap arc geometry and staggered element has better performance than existing best arc geometry namely broken arc rib with staggered element.

Laminar natural convection of yield stress fluids in annular spaces between concentric cylinders

This paper aims to investigate the laminar natural convection of Bingham fluids between horizontal concentric cylinders. The governing equations are solved numerically by using the Galerkin’s weighted residuals scheme of finite element method with a non-uniform unstructured triangular grid. The effects of various parameters such as the Rayleigh number (103≤Ra≤106), yield number (0≤Y≤Ymax), ratio of gap width to inner cylinder radius (0.5≤L/Ri≤5) and fixed Prandtl number (Pr=100 since results are not sensitive to Pr in the tested range) on the flow and temperature profiles as well as on the heat transfer and morphology of yielded/unyielded regions are presented and discussed. The heat transfer rate shows a positive dependence on the Rayleigh number and L/Ri, however, there is an optimum value for L/Ri which maximizes the heat transfer rate. The results also show that the yield number has a significant impact on the flow and temperature fields and the heat transfer performance. In fact, the heat transfer rate decreases with the rise of the yield number and above a certain value of Y, the convection does not occur, and heat transfer is only due to conduction. It is found that while the enhancement of the Rayleigh number augments the heat transfer, it is not necessarily associated with a decrease in the size of the unyielded zones.

CFD analysis of an innovative combined lift and drag (CLD) based modified Savonius water turbine

Savonius water turbine is a popular turbine that can be used for energy extraction from free stream flows in rivers or manmade channels and also from tidal and ocean currents. The present study aims at developing a new combined lift-drag (CLD) based blade design for a conventional two-bladed Savonius water turbine. The semicircular blade is replaced with a straight blade section starting from the turbine axis and ending with an airfoil blade section at the leading edge. The blade lengths are adjusted within the overall diameter of an established conventional Savonius water turbine, taken from available literature. This innovative design is considered as the base model. The base model is then gradually modified and optimized using ANSYS Fluent 14 CFD software by considering design parameters – gap width ratio and overlap ratio. The evolved optimal design is then further studied for two more turbine diameters, one of which is taken from another prominent literature. All the performance analyses are carried out through flow physics study of the turbines. It has been found that the maximum coefficient of power Cp obtained for the CLD Savonius turbine is 0.284 obtained at a tip speed ratio 0.6 for an overall turbine diameter 260 mm, gap width ratio 8.45%, and overlap ratio 46.9%. The contributions of the individual blade sections on the CLD turbine performance have also been appreciated. Finally, the CLD design is compared with an established Savonius turbine design to highlight the significant importance of the present design.

Effect of yarn cross-sectional shape on resin flow through inter-yarn gaps in textile reinforcements

Axial flow through gaps between aligned straight yarns with realistic cross-sectional shapes, described by power-ellipses, was analysed numerically. At a given fibre volume fraction, equivalent gap permeabilities have a maximum at minimum size of elongated tapering parts of the gap cross-section and a ratio of gap width to height near 1. When the yarn spacing is given in addition to the fibre volume fraction, calculated maximum and minimum values for the equivalent permeability of inter-yarn gaps, which occur at near-rectangular and lenticular cross-sections, differ by factors of up to 3.3. Novel approximations for the shape factor and the hydraulic diameter in Poiseuille flow were derived as a function of the fibre volume fraction, the yarn cross-sectional aspect ratio and the geometrical parameter describing the shape of the power-elliptical yarn cross-section. This allows the equivalent gap permeability to be predicted with good accuracy for any fibre volume fraction and yarn cross-section.

Excitation Condition for Self-Sustained Oscillation in Flow Past a Louvered Cavity

AbstractLouvered cavities are extensively employed in engineering applications. In the configurations of flow past these cavities, self-sustained oscillations will be excited. This can give rise to structure vibrations or noise. Numerical models are established to analyze excitation condition for of these oscillations. Computational results reveal that the excitation condition can be quantitatively described by the ratio of gap width G to the boundary layer thickness δ at the separation edge. When G/δ exceeds a certain critical value G/δc, self-sustained oscillations are excited. Otherwise, disturbances will dissipate and the flow configuration along the louver will be like a parallel plate flow. The critical value G/δc decreases with the ratio of G to the thickness of the louver plate H. This suggests that the excitation condition is more easily satisfied for a louver with sparse fins. The bottom boundary of the cavity restricts the feedback flow and then suppresses the excitation of self-sustained oscillations. With an increasing cavity height Hc, which reflects the distance between the louver and the bottom boundary, the critical value G/δc decreases and the decreasing rate reduces gradually. In contrast, because G/δc is relatively insensitive to the cavity length Lc, the side boundaries have no obvious influence on the excitation condition.

Interference Effect on Stationary Aerodynamic Performance between Parallel Bridges

During the operation stage, parallel bridges may become nonparallel as a result of unequal load distribution between two parallel bridges and other special conditions. Aerodynamic performance could change significantly under nonparallel positions and become different from that under parallel positions. In this paper, the stationary aerodynamic performance of two parallel bridges under various nonparallel positions during operation stage is studied through a series of wind tunnel tests. This includes the investigation of two horizontal gap distances (HGDs), five relative vertical displacements (RVD) and five relative torsional displacements (RTD). First, sectional models of two closed box girders were tested in smooth flow for stationary aerodynamic force coefficients. An optimum iteration method was then used to calculate the structural displacements and torsional divergence critical wind velocities ([Formula: see text]) of two assumed suspension bridges under stationary aerodynamic force. The research outcomes demonstrated that the changes of stationary aerodynamic force coefficients are dependent on the relative displacements of two girders and wind attack angles. In addition, it was revealed that interference effects are detrimental to stationary aerodynamic instability of two bridges with a larger gap-width ratio (i.e. D/B [Formula: see text] 1), which is related to the aerodynamic shape of girders and bridge structures. Further, the [Formula: see text] of the leeward bridge significantly decline when the vertical position of the leeward bridge become higher that of the windward bridge. Most importantly, it showed that the combination of RVD and RTD (e.g. RVD [Formula: see text][Formula: see text]mm and RTD [Formula: see text]) could potentially lead to the worst stationary aerodynamic performance by decreasing [Formula: see text] of the windward and leeward bridge with 12.03% and 7.89%, respectively.

Simulation of natural convection heat transfer using nanofluid in a concentric annulus

In the present study, natural convection of nanofluids in a concentric horizontal annulus enclosure has been numerically simulated using the lattice Boltzmann method. A water-based nanofluid containing Al2O3 nanoparticle has been studied. Simulations have been carried while the Rayleigh number ranges from 103 to 105 and solid volume fraction varies between 0 and 0.04. The effects of solid volume fraction of nanofluids on hydrodynamic and thermal characteristics such as average and local Nusselt numbers, streamlines, and isotherm patterns for different values of solid volume fraction, annulus gap width ratio and Rayleigh number are investigated and discussed in detail.

Determination of failure mechanism of very soft clay behind L-pile wall with physical model tests

This paper presents physical model tests to verify the failure mechanism of soil behind the gap of contiguous L-pile retaining wall used to support the excavation in soft clay. The ratio of pile gap to pile width (Sg /B) of 0.1, 0.3, 0.5, 0.7, 1.2, 1.6, 2.0, and 3.0 was used. The undisturbed soft clay samples were obtained from an open cut in Samutprakarn province. The physical model tests were conducted in the vanity of the soil sampling area to avoid the effect of sample disturbance. The pressures were applied to the physical model using screw jack until the failure of soil between the L-piles was observed. The digital photos of soil movement were recorded during the test to monitor the failure mechanism. The test results show that the normalized failure pressures reduce as the gap width ratio (Sg /B) increases. The failure pressure of L-pile is lower than that of circular pile proposed by Winit [9] due to soil arching size. The failure arches are clearly observed in the model with Sg /B of 0.1–1.2, but not with Sg /B of 1.6–3.0.

Mixed convection in cylindrical annulus with rotating outer cylinder and constant magnetic field with an effect in the radial direction

In the present study, mixed convection of a fluid in the fully developed region in a horizontal concentric cylindrical annulus with different uniform wall temperatures, is numerically investigated in both steady and unsteady states in the presence of radial MHD force, as well as in consideration of heat generation due to viscous dissipation. Also, cylinder length is assumed to be infinite. Moreover, radiation heat transfer from the hot surface is assumed to be negligible. Buoyancy effects are also considered, along with Boussinesq approximation. The forced flow is induced by the cold rotating outer cylinder at slow constant angular velocity, with its axis at the center of the annulus. Investigations are made for various combinations of non-dimensional group numbers; Reynolds number (Re), Rayleigh number (Ra), Hartmann number (Ha), Eckert number (Eck) and annulus gap width ratio (σ0). These dimensionless parameters used in the present study will be investigated over a wide range to present the basic flow patterns and isotherms in a concentric cylindrical annulus. A finite volume scheme, consisting of the Tri-Diagonal Matrix Algorithm (TDMA), is used to solve governing equations, which are continuity, two-dimensional momentum and energy, by the SIMPLE algorithm. The numerical results reveal that the flow and heat transfer are suppressed more effectively by imposing an external magnetic field. Furthermore, it is found that the external magnetic field causes the fluid velocity and temperature to be suppressed more effectively. Moreover, it will be shown that viscous dissipation terms have significant effects in situations with high values of Eckert and Prandtl number and low values of Reynolds number.

Local measurements of turbulent angular momentum transport in circular Couette flow

We report on velocity fluctuations and the fluctuation-driven radial transport of angular momentum in turbulent circular Couette flow. Our apparatus is short (cylinder height to gap width ratio Γ ~ 2) and of relatively high wall curvature (ratio of cylinder radii η ~ 0.35). Fluctuation levels and the mean specific angular momentum are found to be roughly constant over radius, in accordance with previous studies featuring narrower gaps. Synchronized dual beam Laser Doppler Velocimetry (2D LDV) is used to directly measure the r − θ Reynolds stress component as a function of Reynolds number (Re), revealing approximate scalings in the non-dimensional angular momentum transport that confirm previous measurements of torque in similar flows. 2D LDV further allows for a decomposition of the turbulent transport to assess the relative roles of fluctuation intensity and r − θ cross-correlation. We find that the increasing angular momentum transport with Re is due to intensifying absolute fluctuation levels accompanied by a slightly weakening cross-correlation.

Flow and Heat Transfer of Natural Convection in Horizontal Annulus With a Heating Element on Inner Cylinder

Experiments have been performed to study natural convection flow and heat transfer in a horizontal annulus when a square heating element is positioned at different locations on the inner insulated cylinder. The annulus is filled with water and has cylinder to cylinder diameter ratio of 3. The square heating element is small and has the width to annulus gap width ratio of 1/6. The range of Rayleigh number studied is approximately from 1.9×106 to 3.3×107. It has been found that the flow pattern, the temperature distribution around the inner cylinder wall, and the local heat transfer rate around the outer cylinder are very sensitive to the location of the heating element. The heating element Nusselt numbers at various locations on the inner cylinder are obtained and well correlated against the Rayleigh number to the 1/3 powers. A maximum in the correlation parameter C is obtained when the heating element is placed 90 deg from the bottom.

Propagation of Lamb Waves in Phononic-Crystal Plates

AbstractIn this paper, the band structures of Lamb waves in the two-dimensional phononic-crystal plates are calculated and analyzed based on the plane wave expansion method. The phononic-crystal plates are composed of an array of circular crystalline iron cylinders embedded in the epoxy matrix. Square lattice and triangular lattice are analyzed and discussed, respectively. For the square lattice, two complete band gaps exist, and a narrow pass band between the complete band gaps separates them apart. For the triangular lattice, a wide complete band gap existing with the ratio of gap width to midgap frequency Δω/ωm equal to 72% is found. Furthermore, the influence of the plate thickness is crucial for band structures of Lamb waves. Tuning plate thickness can shift the pass bands effectively, and band shifting causes the variation of the width of complete band gap and its opening and closure.

Combined Forced- and Natural-Convection Heat Transfer in Horizontally CounterRotating Eccentric and Concentric Cylinders

The present investigation focuses on the numerical simulation of mixed-convection heat transfer in a horizontal annulus configuration. The flow is set to operate in the laminar regime under steady-state condition. A counterrotating cylinder arrangement is considered while the inner cylinder is heated. A nonuniform grid size is employed in the radial direction to capture the velocity and temperature distributions near the walls. Furthermore, discretization of the governing equations is achieved using a finite-element scheme based on the Galerkin method of weighted residuals. The flow and thermal characteristics are explored for a pertinent range of dimensionless velocity ratio, gap-width ratio, and Rayleigh number given by 0 ≤ κ ≤ 5, 0.5 ≤ σ ≤ 5.0, and 103 ≤ Ra ≤ 105 while eccentricity factor ϵ(r, φ) is varied over various radial and angular positions. The local Nusselt number distributions along the cylinders are documented over a range of operating conditions.

Design of triangular lattice photonic crystals using genetic algorithms

Genetic Algorithms (GAs) were used to design triangular lattice photonic crystals with large absolute band-gap. Considering fabricating issues, the algorithms represented the unit cell with large pixels and took the largest absolute band-gap under the fifth band as the objective function. By integrating Fourier transform data storage mechanism, the algorithms ran efficiently and effectively and optimized a triangular lattice photonic crystal with scatters in the shape of ‘dielectric-air rod'. It had a large absolute band gap with relative width (ratio of gap width to midgap) 23.8%.

Theoretical and Experimental Studies of Longitudinal Guided Wave Generation in Hollow Cylinders by Multielement Transducers

Numerical simulation and experimental investigation on defect detection in pipes using ultrasonic guided waves are carried out in the paper. In theoretical analysis, normal mode expansion method is used to quantify the coupling between the applied boundary loadings and acoustic field. The general results are specialized to the loading configuration of multielement transducers. Several important conclusions can be drawn about the design of transducers to generate guided wave modes in pipes. The importance of design parameters such as the number of elements, the ratio of gap width to element width, and the length of each element is discussed in detail. The experimental study demonstrates the use of practical axisymmetric loading in generating axisymmetric longitudinal guided waves, which is particularly useful in the inspection of tubing or piping.