Rough Strips Research Articles

Wind-induced vibration response of supertall sightseeing tower evaluation during construction through wind tunnel test of aeroelastic models

Four construction phases of an ultra-high sightseeing tower with a cable-barrel composite structure and their wind-induced vibration response were studied. The first-order natural vibration characteristic of the structure in four different construction phases was calculated through finite element models, and associated aeroelastic models were also designed. Meanwhile, rough strips are applied uniformly on the surface of the model to compensate the Reynolds number of the wind tunnel test. The performance of this method was investigated utilizing the pressure test of rigid segment models. The wind-induced vibration response under four construction conditions, and the effects of wind direction angle, wind speed and structural damping ratio were investigated through the wind tunnel test of aeroelastic models. The results show that sticking rough strips on the surface can effectively improve the Reynolds number of wind tunnel tests. As the wind speed during construction increases, the structural wind-induced vibration response intensifies. A large vortex-induced resonance occurs in the construction phase of a cable-barrel composite structure with the Strouhal number around 0.12 under turbulent conditions in this study. Furthermore, the crosswind-induced vibration response of the structure at a wind deflection angle of 0° is greater than 45° and 90°. Specifically, the mean value of downwind displacement and the maximum value of standard deviation (STD) of downwind and crosswind displacements on the prototype tower top at 0° during construction phases are 1.21 m, 0.35 m, and 0.25 m respectively. Thus, the risk of large wind-induced vibration should be fully considered during construction. Implementing corresponding damping measures to improve the damping ratio of the structure proves effective in restraining its vibration.

Origination of Cellular Secondary Cells in Wide Open-Channel Turbulent Unsteady Flows over Spanwise-Oriented Alternate Rough and Smooth Bed Strips

Origination of Cellular Secondary Cells in Wide Open-Channel Turbulent Unsteady Flows over Spanwise-Oriented Alternate Rough and Smooth Bed Strips

Flow resistance over heterogeneous roughness made of spanwise-alternating sandpaper strips

The Reynolds number dependent flow resistance of heterogeneous rough surfaces is largely unknown at present. The present work provides novel reference data for spanwise-alternating sandpaper strips as one idealised case of a heterogeneous rough surface. Experimental data are presented and analysed in direct comparison with drag measurements of homogeneous sandpaper surfaces and numerical simulations. Based on the homogeneous roughness data, the related challenges and sensitivities for the evaluation of roughness functions from experiments and simulations are discussed. A hydraulic channel height is suggested as an alternative measure for the drag impact of rough surfaces in internal flows. For the investigated heterogeneous roughness, it is found that turbulent flow does not exhibit a fully rough flow behaviour, indicating that the assignment of an equivalent sand grain height as commonly applied for homogeneous roughness is not possible. A prediction of the drag behaviour of rough strips based on an average between rough and smooth drag curves appears promising, but requires further refinement to capture the impact of turbulent secondary flows and spatial transients linking smooth and rough surface parts. While turbulent secondary flow induced by the roughness strips yield significant spanwise variation of the mean velocity profile for the investigated rough strips, we show that the spanwise averaged velocity profiles collapse reasonably well with a smooth or homogeneous rough wall flow. This allows to extract a global roughness function from the spanwise averaged flow field in good agreement with the one deduced from global pressure drop measurements.

Enhancement of energy capture by flow induced motion of a circular cylinder using passive turbulence control: Decoupling strip thickness and roughness effects

Passive turbulence control of flow induced motion of a cylinder using strips has been practiced for over 30 years. The two distinct physical characteristics of strips: thickness and roughness, can have coupled effects on altering the flow induced motion. The experimental work discussed here decouples these two effects for augmented energy extraction. Tests with cylinders attached with strips of roughness varying from 0% to 100%, and thickness varying from 0.8% to 8.2% of the cylinder diameter, were performed (5000 < Re < 35600). The dynamic response of the configurations with rough strips was compared to that with smooth strips of same thickness. Mechanical power and energy transfer efficiencies were evaluated to analyze the power extraction potential of different configurations. Power generated by the smooth strip configurations was 1.25–5 times higher depending on the roughness ratio and flow velocity. Smooth strips also provided more operational stability, characterized by smaller values of the coefficient of variation of power and concentrated non-dimensional force-velocity states. These devices are the more efficient adaptation from an energy harvesting perspective at low velocities (<1.0 m/s), a range below the cut-in speed for most hydrokinetic turbines, thereby making energy extraction feasible from shallow rivers and slow-flowing streams.

Analysis and validation of mathematical models of secondary velocities along vertical and transverse directions in wide open-channel turbulent flows

Cellular secondary flows are inevitably present in turbulent flows through ducts, natural or artificial channels, and compound channels. Secondary currents significantly modify the characteristics of turbulent quantities, the pattern of primary flow velocity by causing dip-phenomenon. To understand the detailed mechanism and hidden cause, modelling of secondary flow velocities is crucial. In this study, proper mathematical models of secondary flow velocities along vertical and transverse directions are proposed for steady and uniform turbulent flow through wide open channels with equal smooth and rough bed strips. Starting from the continuity and the Reynolds averaged Navier–Stokes equations, governing equation for secondary velocity is derived first and then using appropriate boundary conditions (no-slip boundary conditions at channel bottom and free surface, and maximum vertical velocity in magnitude at the interface of two cellular secondary cells and at mid-depth of the channel. All these conditions are consistent with several experimental observations). A new model of the streamwise Reynolds shear stress is proposed for the entire cross-sectional plane and using it, the analytical solutions are obtained. Proposed models include the effects of viscosity of the fluid and the eddy viscosity model of turbulence. All suggested models are validated with existing experimental data in rectangular open-channel flows, compound open channel flows, and duct flows, and satisfactory results are obtained. Furthermore, models are also compared with existing empirical models from literature to show the effectiveness and superiority of proposed models. Apart from these, the obtained results from this study are used to investigate the effects of vertical and transverse secondary flow velocities on the settling velocity vector in a cross-sectional plane. Effective alternative models for the settling velocity vector are suggested. The model of settling velocity vector is also compared with the existing model. Finally, all results are justified from physical viewpoints.

Performance of Thermally Insulated Reinforced Concrete Beams Strengthened with Near-Surface Mounted-Carbon Fiber Reinforced Polymer Strips under Elevated Temperature

This paper investigated the performance of reinforced concrete beams strengthened with near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) smooth and rough strips using cement based adhesive and insulated with plasterboards for protection the beams subjected to high temperature. An experimental work was carried out on ten large scale RC strengthened beams and strengthened insulated beams. The experimental program subject the strengthened beams to high temperature degrees up to 600 °C in electric furnace and observe changes after beams been heated. Results showed that the plasterboards provided excellent protection and decreased the CFRP temperature of about 42-24%. The insulated beams behaved as good as that of strengthened beams prior to expose to 600°C.

The effect of spanwise wavelength of surface heterogeneity on turbulent secondary flows

We examine the behaviour of turbulent boundary layers over surfaces composed of spanwise-alternating smooth and rough strips, where the width of the strips $S$ varies such that $0.32\leqslant S/\overline{\unicode[STIX]{x1D6FF}}\leqslant 6.81$ , where $\overline{\unicode[STIX]{x1D6FF}}$ is the boundary-layer thickness averaged over one spanwise wavelength of the heterogeneity. The experiments are configured to examine the influences of spanwise variation in wall shear stress over a large $S/\overline{\unicode[STIX]{x1D6FF}}$ range. Hot-wire anemometry and particle image velocimetry (PIV) reveal that the half-wavelength $S/\overline{\unicode[STIX]{x1D6FF}}$ governs the diameter and strength of the resulting mean secondary flows and hence the observed isovels of the mean streamwise velocity. Three possible cases are observed: limiting cases (either $S/\overline{\unicode[STIX]{x1D6FF}}\ll 1$ or $S/\overline{\unicode[STIX]{x1D6FF}}\gg 1$ ), where the secondary flows are confined near the wall or near the roughness change, and intermediate cases ( $S/\overline{\unicode[STIX]{x1D6FF}}\approx 1$ ), where the secondary flows are space filling and at their strongest. These secondary flows, however, exhibit a time-dependent behaviour which might be masked by time averaging. Further analysis of the energy spectrogram and fluctuating flow fields obtained from PIV show that the secondary flows meander in a similar manner to that of large-scale structures occurring naturally in turbulence over smooth walls. The meandering of the secondary flows is a function of $S/\overline{\unicode[STIX]{x1D6FF}}$ and is most prominent when $S/\overline{\unicode[STIX]{x1D6FF}}\approx 1$ .

Effect of Polyethylene Strips Surface Roughness on Its Efficiency for Enhancement of Wastewater Treatment

This study aimed to determine the effect of roughness surface for polyethylene strips on its quality for enhancement the characteristics of wastewater treatment plant effluent as a very cheap method. The study was applied at Abu Rawash WWTP effluent channel using the smooth and rough polyethylene strips where a biofilm layer forms above its surface. The removal ratio for smooth polyethylene strips for BOD and TSS was 4.45 and 4.33% respectively, while for the rough polyethylene strips was 14.10 and 13.37 respectively. This shows the success of the polyethylene strips even smooth or rough to remove both the BOD and TSS from treated wastewater. The results show that the material roughness affected the treatment efficiency with proportional effect. And the rough surface has a good removal efficiency that makes it more applicable for such purpose of enhancing the treated wastewater with very low cost technique.

Flexural Behavior of RC Beams Strengthened by NSM-CFRP Laminates or Bars

The strengthening and enhancing the structures represents an important aspect in the construction industry due to the growing need to increase the tolerability of origin to a specific level and within the required rehabilitation and maintenance work. This paper assessed the performance and effectiveness of the Near Surface Mounted (NSM) strengthening technique for the reinforced concrete beams. Three (140x260x2700 mm) reinforced concrete beams were strengthened in flexure with NSM strengthening systems using Carbon Fiber Reinforced Polymer (CFRP) strips, bars, and cement-based adhesive as a binding materials. The flexural behaviour of the beams was evaluated by testing the specimens under three-point loading to failure. The structural performance, deflection, ductility, stiffness, and modes of failure of the tested beams are presented and discussed in this paper. The test results indicate that using NSM-CFRP strips and bars is practical and significantly improves the stiffness and increases the flexural capacity of reinforced concrete beams. The strength increments were 48, 42, and 15 percent recorded with CFRP bars, rough strips, and smooth strips respectively. The deflection of the strengthened beams was reduced by about 66, 48, and 58 percent for CFRP smooth strips, rough strips, and CFRP bars respectively, compared with the control beam due to the increased stiffness of the strengthened beams.

Fatigue performance of NSM CFRP strips embedded in concrete using innovative high-strength self-compacting cementitious adhesive (IHSSC-CA) made with graphene oxide

The efficiency of strengthening reinforced concrete (RC) structures using the near-surface mounted (NSM) fibre reinforced polymer (FRP) technique depends on the bond between the NSM FRP and the concrete substrate. This paper presents the results of an experimental study of NSM carbon FRP strips bonded to concrete substrate with innovative high-strength self-compacting cementitious adhesive (IHSSC-CA) under fatigue loading using single-lap shear tests. Graphene oxide and cementitious materials were used to synthesise the IHSSC-CA. The test variables were: CFRP strip dimensions (1.4×10mm, 1.4×20mm) and CFRP strip surface conditions (smooth, rough). 61 specimens were tested under different fatigue load ranges to develop the load range (LR)-fatigue life (N) relationships. Finally, equations were developed to predict fatigue lives based on the experimental results. It was found that the rough surface CFRP strips 1.4×20mm in dimensions showed the best fatigue life under different fatigue load levels. Moreover, the test results confirm the effectiveness of using IHSSC-CA to bond NSM CFRP strips to the concrete substrate. Furthermore, the proposed equations can predict fatigue life reasonably well and can be used in the design of NSM CFRP-strengthened RC members.

Fatigue performance of NSM CFRP strips embedded in concrete using epoxy adhesive

Strengthening of reinforced concrete (RC) structures using the near-surface mounted (NSM) fibre reinforced polymer (FRP) technique is becoming an attractive system for upgrading these structures. The efficiency of this method depends on the bond between the concrete and the NSM FRP. Although different experimental and analytical studies on the bond of NSM FRP to concrete substrate under monotonic loading have been carried out, very few studies have been conducted under fatigue loading conditions. This paper presents the results of an experimental study of NSM carbon FRP bonded to concrete with epoxy adhesive under fatigue loading using single-lap shear tests. The test variables were: CFRP strip dimensions (1.4×10mm, 1.4×20mm), and CFRP strip surface conditions (smooth, rough). 52 specimens were tested under different fatigue load ranges to develop the load range (LR)-fatigue life (N) relationships. Finally, equations were developed to predict fatigue lives based on the experimental results. It was found that the rough surface CFRP strips 1.4×20mm in dimensions showed the best fatigue life under different fatigue load levels. Moreover, the proposed equations can predict fatigue life reasonably well and can be used in the design of NSM CFRP-strengthened RC members.

Secondary Currents and Turbulence over a Non-Uniformly Roughened Open-Channel Bed

Large-eddy simulations (LES) of the flow over a non-uniformly roughened channel bed are carried out to study the effect of non-uniform bed roughness on turbulence driven secondary currents and turbulence statistics. The channel bed is comprised of alternating rough and smooth strips, the width of which corresponds to the water depth. The Reynolds number based on hydraulic radius and bulk velocity is 34,000. The LES are successfully validated using experimental data. The secondary flow and bed roughness have a significant effect on the streamwise velocity and second order turbulence statistics. Turbulence is enhanced over rough strips and suppressed over smooth strips. Significant lateral momentum transfer takes place due to both advection and turbulence. The bed shear stresses over the smooth strips are approximately four times less than over the rough strips a result of near bed low momentum fluid being transported from the rough strips to the smooth strips and high momentum fluid being convected from the surface towards the bed. The most significant terms in the streamwise momentum equation are quantified and discussed with regard to momentum transfer.

Roughness’s shapes comparative analysis of some reinforced earth elements under monotonous loading

This paper presents and analyzes the experimental and numerical results of a series of pullout tests under monotonous loading performed on five steel strips presenting various forms of roughness (smooth, ribbed, punched, W-shaped, chain) and embedded in the same dry sand massif constituting the backfill. The pullout tests were conducted by means of a small-scale model and the calculations carried out by using a finite elements computer program. Obtained results show a good agreement between the experimental and numerical data. They show in addition that the rough strips are more advantageous than the smooth strip. Among the rough strips considered, chain is most relevant.

A Survey of Soil-Reinforcement Interface Friction

The most important aspect of reinforced earth is the sliding shear resistance between the soil and reinforcements expressed in terms of a sliding friction angle or a coefficient of friction. A number of different procedures have been followed in order to quantify this physical property and as a result there is a wide range of reported values. In the present paper, the friction coefficient values of smooth and rough brass strips as determined by modified direct shear tests and by pull out and wall rotation tests in a model box are given and interpreted. For smooth strips, it is found that direct shear and pull out tests give comparable results and the friction coefficients are not influenced by the density. For rough strips, however, pull out tests may give much higher friction values than the direct shear tests as density increases. In wall rotation tests which are an attempt to represent the friction mobilization mechanism in reinforced earth, the friction coefficient values appear to be limited by the values obtained from direct shear tests for both smooth and rough strips, irrespective of density

Micromagnetic analysis of current-driven DW dynamics along rough strips with high perpendicular anisotropy at room temperature

Domain-wall motion along thin ferromagnetic strips with high perpendicular magnetocrystalline anisotropy driven by spin-polarized currents is theoretically analyzed by means of full micromagnetic simulations and one-dimensional model, both including surface roughness and thermal effects. At finite temperature, the results show a current dependence of the domain wall velocity in good qualitative agreement with available experimental observations, depicting a low-current, low velocity creep regime, and a high-current, linear regime separated by a smeared depinning region. The analysis points out the relevance of both thermal fluctuations and surface roughness on the domain wall dynamics, and confirms that these effects are essential to get a better understanding on the origin, the role and the magnitude of the non-adiabaticity by direct comparison with experiments.

Self-imaging of gratings with rough strips

We analyze the self-imaging process produced by a transmission grating whose strips present two different roughness levels. This kind of grating periodically modulates the transmitted light owing only to the different microtopographic properties of the strips. In spite of the fact that the grating is not purely periodic, it produces a kind of self-image at Talbot distances. These self-images gradually appear as light propagates, but they are not present just after the grating, as occurs in amplitude or phase gratings. There exists a distance from the grating, which depends on the stochastic properties of roughness, from which the contrast of the self-images becomes stable. Important cases are analyzed in detail, such as low- and high-roughness limits. We assume for the calculations that the grating can be used in a mobile system. Simulations using the Rayleigh-Sommerfeld regime have been performed, which confirm the validity of the theoretical approach proposed in this work.

Far field of gratings with rough strips

In this work, we analyze the far-field pattern produced by a grating made of strips with two different random roughness levels. The efficiency and shape of the diffraction orders is obtained, which are shown to depend on the statistical properties of roughness. We assume for the calculations that the grating can be used in a mobile mechanical system. A preliminary experimental approach which partially corroborates the theoretical results is also performed.

EXPERIMENTAL INVESTIGATIONS ON FLUIDIC CONTROL OVER AN AIRFOIL

This study presents the development of two fluidic actuators − namely, microjets and tangential blowing actuator (TBA), designed for flow separation control. The developed actuators are compact enough to fit inside an ONERA D profiled wing with a chord of 0.35 m. Test bench experiments showed that the microjets (resp. TBA) were able to produce exit velocities up to 330 m/s (resp. 60 m/s). These actuators were placed in the model and were tested in wind tunnels for various blowing rates. The investigations included the use of force balance measurements, on-surface flow visualization with pigmented oil, off-surface flow visualizations with smoke, surface pressure distribution measurements, and Particle Image Velocimetry (PIV). Most of the tests were performed at free-stream velocities between 20 m/s (for PIV) and 40 m/s, corresponding to Reynolds numbers in the range 0.47 × 10^6−0.93 × 10^6 . The angle of attack varied from −2 to 20 degrees. Experiments were conducted using the naturally occurring laminar boundary layer as well as for a turbulent boundary layer. In such a case, rough strips were used in the vicinity of the leading edge. The present tests show the efficiency of these devices to delay separation and improve aerodynamic performances of the wing: for example, a maximum of 30% gain in CL has been reached using the microjets. Both actuators tend to increase the lift coefficient CL after stall and areas of separated flow have been eliminated by applying control, as suggested by flow visualizations and PIV velocity fields.

Secondary flows over artificial bed strips

Characteristics of open channel flows can be significantly modified in the presence of secondary flows. In this study, cellular secondary flows were artificially generated with alternate rough and smooth bed strips, which were aligned longitudinally in an open channel. Flow measurements were conducted with a two-dimensional Laser Doppler Anemometer system. Experimental results show that the distributions of the primary velocity and streamwise Reynolds shear stress that are altered in the presence of the secondary flows clearly deviate from those observed for two-dimensional open channel flows. The modified streamwise velocity can be represented by a function proposed in the log-wake form but varying periodically in the lateral direction. This study also demonstrates that the flow field can be linearized so that a flow quantity can be generally decomposed into two components, one being related to the average base flow and the other symbolizing the perturbation caused by the bed configuration. This perturbation-based approach finally provides an analytical description of the altered Reynolds shear stress distribution that differs from the linear profile used for two-dimensional open channel flows.

Influence of surface texture of polymeric sheets on peripheral nerve regeneration in a two-compartment guidance system

Synthetic guidance channels are useful tools to study the mechanisms underlying peripheral nerve regeneration. In the present study, the lumen of silicone elastomer tubes was divided into two compartments by a polymer strip 10 mm long placed along the tube length. The influence of varying the surface texture of hydrophilic and hydrophobic polymer strips on the morphology of the regenerated neural tissue was analysed. Hydrophilic nitrocellulose (NC) and hydrophobic polyvinylidene fluoride (PVDF) films with smooth (S-NC and S-PVDF) or rough (R-NC, R-PVDF) surface texture were used. Five channels of each type were used to repair transected rat sciatic nerves and analysed after 4 wk. Tissue strips bridged the nerve stumps in all R-NC and R-PVDF tubes, in five of the S-NC and three of the S-PVDF tubes. In R-NC and R-PVDF tubes, bell-shaped tissue adhering to the polymer strip was observed, whereas in S-NC and S-PVDF tubes round, free-floating nerve cables were seen. All the cables contained myelinated and unmyelinated axons and Schwann cells grouped in microfascicles and surrounded by an epineurial layer. For both rough strips, the initial cell layer consisted of macrophages adhering to the polymer surface. The epineurial nerve tissue contacting the rough surface was significantly thinner for PVDF compared with NC strips. No difference in epineurial thickness was observed for nerves facing the silicone tube or for smooth NC and PVDF strips. S-PVDF tubes contained significantly more myelinated axons than S-NC tubes. This study shows that the morphology of regenerated peripheral nerves is significantly influenced by the surface texture of strips placed within guidance channels. Interactions between regenerating neural tissue and polymeric materials used as nerve guidance channels may be useful in controlling patterns and morphologies of regenerating nerves.