Modification Of Surface Roughness Research Articles

Effects of material type and surface roughness of settlement tiles on macroalgal colonisation and early coral recruitment success

Sexual propagation of corals is a promising strategy for coral restoration, but one of the main challenges is the high mortality of coral spat due to competitive interactions with macroalgae during the early life history stages. Optimising the properties of settlement substrates such as material types and surface roughness has the potential to improve the survival of spat by limiting the recruitment and growth of macroalgae. In this study, we assessed the effects of modifying surface roughness across three different tile materials (alumina-based ceramic, calcium carbonate (CaCO3), and concrete) on the settlement success and post-settlement survivorship of Acropora kenti coral larvae in six mesocosm tanks, each with different established macroalgal communities. The macroalgal community compositions on the tiles were significantly different among material types, but not surface roughness, although the type and abundance of macroalgal species were heavily influenced by the established tank communities. Increasing surface roughness did not affect larval settlement success or spat survivorship. Substantially higher larval settlement density was found on concrete tiles (1.92 ± 0.10 larvae cm−2), but spat survival was the highest on CaCO3 tiles (73.4 ± 4.2% survived). Very strong competitive interactions were observed between spat and macroalgae, with overgrowth by the crustose coralline alga Crustaphytum sp. and the brown alga Lobophora sp. being the primary cause of spat mortality. Overall, when taking into account both settlement and survival rates, concrete was the best performing among the tile types tested here.

Laser Machining at High ∼PW/cm2 Intensity and High Throughput

Laser machining by ultra-short (sub-ps) pulses at high intensity offers high precision, high throughput in terms of area or volume per unit time, and flexibility to adapt processing protocols to different materials on the same workpiece. Here, we consider the challenge of optimization for high throughput: how to use the maximum available laser power and larger focal spots for larger ablation volumes by implementing a fast scan. This implies the use of high-intensity pulses approaching ∼PW/cm2 at the threshold where tunneling ionization starts to contribute to overall ionization. A custom laser micromachining setup was developed and built to enable high speed, large-area processing, and easy system reconfiguration for different tasks. The main components include the laser, stages, scanners, control system, and software. Machining of metals such as Cu, Al, or stainless steel and fused silica surfaces at high fluence and high exposure doses at high scan speeds up to 3 m/s were tested for the fluence scaling of ablation volume, which was found to be linear. The largest material removal rate was 10 mm3/min for Cu and 20 mm3/min for Al at the maximum power 80 W (25 J/cm2 per pulse). Modified surfaces are color-classified for their appearance, which is dependent on surface roughness and chemical modification. Such color-coding can be used as a feedback parameter for industrial process control.

Leakage Retardation of Static Seals via Surface Roughness and Wettability Modification.

In this paper, the effects of surface roughness and wettability on the leakage performance of static seals were highlighted. The results show that the leakage rate is negatively correlated with the contact pressure and positively correlated with surface roughness. Surface wettability affects leakage performance. Leakage retardation is achieved by modifying the roughness and wettability at the interface. The seal interface consists of two oleophobicity surfaces and exhibits an excellent seal performance, of which the leakage reduction is approximately 64%. A theoretical model based on wettability is established to predict the leakage rates under varying wettability conditions, and its validity is confirmed. This research result is expected to be applied in the field of seals and predict the leakage performance of interfaces with different wettabilities to minimize and reduce the leakage of oil in static sealing systems.

Rainband‐Occurrence Probability in Northern Hemisphere Tropical Cyclones by Synthetic Aperture Radar Imagery

AbstractRainbands are essential to tropical cyclones (TCs), significantly affecting TC structure and intensity change. High‐resolution synthetic aperture radar (SAR) imagery can capture the footprints of rainbands caused by rain‐induced sea surface roughness modification. Using 464 SAR TC images, we investigated the rainband‐occurrence probability of TCs under different hemispheres, local times (LTs), intensities, and ocean basins. Results show that the rainband‐occurrence probability is highest in the downshear‐left quadrant for Northern Hemisphere TCs (downshear‐right quadrant for Southern Hemisphere TCs). For Northern Hemisphere TCs, the rainband‐occurrence probability is overall higher in the early morning (LT), and the peak region of rainband‐occurrence probability appears farther from the TC center in the evening (LT). Compared with weak TCs, the rainband‐occurrence probability becomes higher for strong TCs in the Northern Hemisphere. Furthermore, TCs have a higher rainband‐occurrence probability in the Northwest Pacific than in the North Atlantic and Northeast Pacific.

Improvement of Global Forecast of Tropical Cyclone Intensity by Spray Heat Flux and Surface Roughness

AbstractIn global forecasting systems, tropical cyclone (TC) intensity is usually underestimated, which is one of the major challenges for TC forecasting. One possible reason is the deficiency of physical parameterizations associated with ocean surface waves. To improve the TC intensity forecast, effects of two powerful wave‐related processes, the spray‐mediated heat flux and surface roughness, are considered in a global coupled ocean‐atmosphere‐wave system (CFSv2.0‐WW3). Serial 24 hr forecasting experiments for all TCs from May to October 2019 are conducted, and comparisons are made against the International Best Track TC data. The results show that for strong TCs the underestimation of TC intensity in CFSv2.0‐WW3 is significantly improved by the modified surface roughness parameterization and the accelerated spray heat flux parameterization based on Gaussian Quadrature. For major hurricanes with initial wind speeds above 30 m/s, the error of TC maximum wind speed decreases by about 34.4%. To understand the associated dynamic and thermodynamic processes, a series of 120 hr simulations for major hurricane Hagibis is conducted. The effect of spray‐mediated heat flux accounts for 91.7% of the TC intensity improvement. The increased heat fluxes offset the negative contributions of vertical advection and ventilation, leading to enhanced entropy. The low‐level pressure is then decreased, resulting in enhanced convergence of absolute vorticity, which overpowers the negative effects of frictional dissipation and vertical momentum advection. The study indicates that the application of these two wave‐related parameterizations can potentially improve the global forecast and reanalysis of TC intensity.

Effect of acid corrosion on the surface roughness and floatability of magnesite and dolomite

To modify surface roughness and improve flotation performance, hydrochloric acid etching pretreatment was performed on magnesite and dolomite. Flotation tests disclosed that acid corrosion improved the flotation kinetics and flotation recovery rates of magnesite and dolomite. Under pulp pH 10 and sodium oleate (NaOl) concentration 20 mg·L−1, the flotation recovery rates of magnesite and dolomite after acid etching increased by 31.05% and 29.20%, respectively, compared with those before acid etching. Adsorption density tests proved that the adsorption density of NaOl on magnesite and dolomite was higher after acid etching than before acid etching, implying that acid etching drives NaOl adsorption. Zeta potential analysis revealed that acid etching reduces the point of zero charge of magnesite and dolomite. Atomic force microscopy and X-ray photoelectron spectroscopy results demonstrated that acid corrosion modified the surface roughness of magnesite and dolomite, increasing the magnesium (Mg) content on the magnesite surface and the calcium and Mg contents on the dolomite surface. Contact angle measurements indicated that acid corrosion slightly reduced the contact angle between magnesite and dolomite. With NaOl present on the surface, the contact angles of magnesite and dolomite after acid etching significantly increased compared with those before acid etching. Therefore, acid etching is effective in improving the floatability of magnesite and dolomite.

Catalytic thermoelectric hydrogen sensor with CoSb3 thermopile by single-step deposition on bare/textured glass

Hydrogen sensors are required due to the flammability of hydrogen in air. Catalytic thermoelectric hydrogen sensors show promise because they provide direct voltage output from a temperature difference generated by the catalytic combustion of hydrogen. CoSb3 is a good thermoelectric material for energy harvesting and sensing. However, conventional CoSb3 thermopiles require the separate deposition of p- and n-type thermoelectric elements. This study proposes the surface roughness modification of a soda-lime glass substrate through the development of a textured glass surface to prepare a CoSb3 thermopile by single-step deposition. A Co-In-Sb stack with a SiO2 capping layer is deposited by an e-beam evaporator on bare/textured glass and thermally activated under room conditions, which produces a thermoelectric pair due to the partial release of volatile Sb from cracks developed in the rough layer formed on textured glass. A thermoelectric pair consists of a CoSb3 layer with a deficiency of Sb (n-type) on textured glass and that with an excess of Sb (p-type) on bare glass. A hydrogen sensor is made with CoSb3 thermopile with 41 thermoelectric pairs and a catalyst reservoir coated with hydrogen oxidation catalyst. The sensor shows a sensitivity of 13 mV for 1 % H2 in air at room temperature.

Analysis of flux footprints in fragmented, heterogeneous croplands

An accurate quantification of fluxes from heterogeneous sites and further bifurcation into contributing homogeneous fluxes is an active field of research. Among such sites, fragmented croplands with varying surface roughness characteristics pose formidable challenges for footprint analysis. We conducted two flux monitoring experiments in fragmented croplands characterized by two dissimilar surfaces with objectives to: (i) evaluate the performance of two analytical footprint models in heterogeneous canopy considering aggregated roughness parameters and (ii) analyze the contribution of fluxes from individual surfaces under changing wind speed. A set of three eddy covariance (EC) towers (one each capturing the homogenous fluxes from individual surfaces and a third, high tower capturing the heterogeneous mixed fluxes) was used for method validation. High-quality EC fluxes that fulfill stationarity and internal turbulence tests were analyzed considering daytime, unstable conditions. In the first experiment, source area contribution from a surface is gradually reduced by progressive cut, and its effect on high-tower flux measurements is analyzed. Two footprint models (Kormann and Meixner ‘KM’; analytical solution to Lagrangian model ‘FFP’) with modified surface roughness parameters were applied under changing source area contributions. FFP model has consistently over predicted the footprints (RMSEFFP = 0.31 m−1, PBIASFFP = 19.00), whereas KM model prediction was gradually changed from over prediction to under prediction towards higher upwind distances (RMSEKM = 0.02 m−1, PBIASKM = 8.50). Sensitivity analysis revealed that the models are more sensitive to turbulent conditions than surface characteristics. This motivated to conduct the second experiment, where the fractional contribution of individual surfaces (α and β) to the heterogeneous fluxes measured by the high tower (T3) was estimated using the principle of superposition (FT3 = α FT1 + β FT2). Results showed that α and β are dynamic during daylight hours and strongly depend on mean wind speed (U) and friction velocity (u*). The contribution of fluxes from adjoining fields [1 − (α + β)] is significant beyond 80% isopleth. Our findings provide guidelines for future analysis of fluxes in heterogeneous, fragmented croplands.

Effect of surface engineering methods on refrigerant evaporating flow characteristics in annular tubes: Experimental approach

Techniques such as mechanical, electrochemical, and chemical etching are recognized as functional strategies for modifying surface roughness, which in turn manipulates surface energy. This research aims to delve into the influence of these factors on the heat transfer and pressure drop characteristics of two-phase R134a refrigerant flow during boiling inside horizontal annular concentric tubes with internal heat flux. The study scrutinizes the heat transfer coefficient and frictional pressure drop for R134a evaporating flow in an annular tube featuring an inner diameter of 28.6 mm and an outer diameter of 42 mm. The exploration spans a broad range of parameters, which include vapor quality from 0.15 to 0.8, mass flux from 6.72 to 20.16 kg/m2s, internal heat flux from 0.608 to 2.432 kW/m2, and varying surface characteristics. The results show that escalating surface roughness via mechanical techniques introduces greater resistance to flow shear stress in comparison to other methods. Moreover, an increase in surface roughness contributes to a reduction in contact angle and an expansion of the heating area, thereby enhancing both heat transfer coefficient and pressure drop. However, the implementation of low-energy coating holds an insignificant influence on R134a heat transfer characteristics, potentially due to its diminutive surface tension. This results in minor variations in the refrigerant contact angle in relation to the coatings. Performance evaluation criteria have been employed to assess the optimal thermal performance of the surface engineering method, with peak performance achieved at a mass flux of 20.16 Kg/m2s and an internal heat flux of 2.432 kW/m2. Ultimately, the study corroborates the experimental procedure by comparing the observed outcomes with established empirical correlations for R134a flow boiling.

Surface Severe Plastic Deformation for Improved Mechanical/Corrosion Properties and Further Applications in the Bio-Medical and Hydrogen Sectors

Various techniques enabling surface severe plastic deformation (SSPD) have been developed or optimised over the past years. This manuscript presents a broad overview of recent developments in the field of SSPD and its application that take advantages of having a deformed gradient surface with both (i) higher strength and (ii) an improved "reactivity". First, the principle and technological advantages/disadvantages of several SSPD technologies, involving either guided or non-directional mechanical impacts, are recalled. Then, after a short recall on the nature of the structure the modified surface formed under SSPD, the effects of the processing parameters and temperature of deformation on the surface roughness and subsurface microstructure modifications are illustrated with a particular emphasis on the surface mechanical attrition treatment (SMAT) and ultrasonic shot peening (USP) techniques deriving from the traditional pre-strain shot peening. The effect of these surface and sub-surface modifications on the mechanical properties, and in particular the fatigue response, are recalled with a special emphasis on the surface integrity and potential over shot peening. Then, the manuscript concentrates on the effect of the surface enhanced diffusion of chemical species induced by the presence of structural defects to modify the corrosion behaviour and enhance the potential assisted SSPD + thermo-chemically “duplex” treatments. In these cases, in addition to induce grain refinement and dislocations, the importance of controlling some potential surface contamination is stressed. Finally, the manuscript terminates by illustrating some new research studies on potential applications for the challenges in the hydrogen sector for its solid-state storage and the protection of mechanical infrastructures as well as for bio-medical applications with biocompatible Ti-based alloys and biodegradable Mg-based ones.

Significantly enhanced flashover voltage of epoxy in vacuum by graded surface roughness modification

AbstractThe flashover strength of epoxy (EP) insulations in the High voltage direct current applications of future energy grids can be improved by tailoring their surface condition. This work aims to improve the DC surface flashover characteristics of EP after being treated with sandpaper of different gradings. Samples with virgin EP and homogenously modified EP considering varying surface roughness (Ra = 0.54, 3.16, 5.24, and 8.35 μm) are prepared. Different experimental characterisations, such as water contact angle, surface intrinsic conductivity, surface voltages, flashover strength, and trap distributions are conducted and evaluated to analyse the difference between virgin and treated EP. Moreover, based on the obtained experimental results of homogenously treated EP and theoretical analysis, the concept of surface functionally graded materials (SFGMs) is put forward. The flashover voltages of homogenously treated EP are augmented significantly compared to virgin EP regardless of the voltage polarity and enhanced by enhancing the surface roughness. The sample TModel‐C with SFGM design shows a 45.02% and 43.75% improvement in the negative and positive flashover voltages than that of the virgin EP. In the end, COMSOL simulations are conducted to justify the experimental findings and to analyse the difference between virgin and modified samples in terms of electric field distribution.

Improved corrosion resistance of 42CrMo4 steel by reconstructing surface integrity using ultrasonic surface rolling process

The ultrasonic surface rolling process (USRP) was adopted to improve the corrosion resistance of 42CrMo4 steel by reconstructing the surface integrity in terms of surface roughness, microhardness, residual stress, and microstructures. The corrosion behaviors of 42CrMo4 steel were studied by salt spray corrosion, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The results indicated that the surface integrity of 42CrMo4 steel was restructured after USRP with the surface roughness reduced to 0.052 µm, the surface microhardness improved to 305 HV0.1, the residual compressive stress achieved up to − 274 MPa at 0.6 mm depth, and the average grain diameter minimized to 2.02 µm in the zone of 5–150 µm depth. Owing to the modified surface roughness, hardened layer, and induced residual compressive stress, the corrosion resistance of 42CrMo4 steel was enhanced by USRP with the annual corrosion rate of 2.972 mm/a reduced about 5.2 %, the corrosion current density of 2.748 μA·cm−2 decreased up to 45.2 %, and the charge transfer resistance of 1809 Ω·cm2 increased up to 19.6 %.

A novel magnetic field assisted diamond turning of Ti-6Al-4 V alloy for sustainable ultra-precision machining

Titanium alloys play a crucial role in the advanced industries due to their high strength, resilience, rigidity, and low density, as well as their excellent corrosion resistance, which makes them suitable for a variety of engineering applications. Nonetheless, they have poor performance when machined. In this study, magnetic field diamond turning (MFDT) was used to increase the thermal conductivity and thus the machinability of machined Ti-6Al-4 V alloy parts, as well as the lifetime of the diamond cutting tool. The thermal properties of the work material under a magnetic field were investigated using ABAQUS software. The simulation results were validated by the cutting experiments, which demonstrated improved machining performance, increased tool life, and enhanced thermal properties of the machined parts. The surface morphology such as surface defects and surface roughness and microstructure modifications were investigated as evidence. This study demonstrates the effectiveness of the MFDT on the machinability of titanium alloys as the thermal conductivity increases, resulting in increased tool life and improved machined surface quality reached to more than 60% for achieving sustainable diamond machining.

Ice adhesion to hydrotechnical structures

Mitigating ice adhesion on offshore and port structures is crucial for ensuring their safety and operational efficiency in cold climates. Ice adhesion, the molecular attraction between ice and a surface, can lead to increased structural loads, reduced stability, and restricted functionality. This work provides an overview of the different concepts, including the nature of ice adhesion, its consequences on structures, and effective strategies to minimize it. The strategies include surface coatings, surface roughness modifications, heating systems, de-icing and anti-icing systems, structural design considerations, and regular maintenance. These approaches aim to reduce ice adhesion, facilitate ice shedding, and enhance the resilience of offshore and port structures. By implementing these strategies, the integrity and performance of these critical infrastructures can be maintained, ensuring safe operations and supporting transportation and energy production in cold regions.

Toward an Improved Surface Roughness Parameterization Model for Soil Moisture Retrieval in Road Construction

In passive microwave remote sensing, the estimation of the surface roughness parameter is a significant obstacle for soil moisture (SM) retrieval. For a given SM content, the geometric soil surface roughness has been shown to have a large impact on the surface emission at L-band frequency, which affects the SM retrieval success when using the information observed from the radiometer and is represented through the so-called the surface roughness parameter ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H_{R}$ </tex-math></inline-formula> ). Moreover, no previous study has examined the effect of this factor in the context of road construction, where the geometric soil surface roughness is affected by the compaction process, resulting in a substantial change in roughness before and after compaction. Accordingly, a series of experiments at various compaction levels and SM contents was performed for a sand subgrade material in order to identify their effects on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H_{R}$ </tex-math></inline-formula> . The soil brightness temperature (TB) was measured using an L-band radiometer at different incidence angles and a laser profiler was used to measure the surface roughness standard deviation ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma$ </tex-math></inline-formula> ) before and after compaction. The results of this article have demonstrated that the incidence angle ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta$ </tex-math></inline-formula> ) and SM both affect <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H_{R}$ </tex-math></inline-formula> and its relation to the geometric soil surface roughness. Importantly, these factors are not accounted for by existing models. Consequently, a modified surface roughness parameter ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H_{R}$ </tex-math></inline-formula> ) model, based on the traditional Choudhury model, was developed to include the contribution of these two factors, and its impact on the accuracy of SM retrieval results tested. Specifically, it was shown that it is possible to obtain SM retrieval results with an accuracy of 0.04 cm3/cm3 at almost all incidence angles using either dual-polarization [both horizontal (H) and vertical polarization (V)] or only vertical polarization observations. The modified surface roughness parameter ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H_{R}$ </tex-math></inline-formula> ) model has improved the performance of the SM retrieval model to achieve an accuracy of 0.04 cm3/cm3, whereas the traditional Choudhury model achieved an accuracy of only 0.05 cm3/cm3.

Enhanced corrosion resistance of laser additive manufactured 316L stainless steel by ultrasonic surface rolling process

The ultrasonic surface rolling process (USRP) was adopted to strengthen the surface corrosion resistance of laser additive manufactured 316L stainless steel (LAMed 316L), and the strengthening mechanism of USRP on corrosion resistance was studied with various static pressures. The surface integrity and corrosion behaviors of LAMed 316L were analyzed by the tests of surface roughness, microhardness, residual stress, electron backscatter diffraction (EBSD), Xray diffraction (XRD), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), Mott-Schottky (M-S), Xray photoelectron spectroscopy (XPS), and three-dimensional microscope, respectively. The results indicated that the LAMed 316L after USRP obtained the reduced surface roughness up to 95 %, the improved microhardness up to 53 %, the introduced residual compressive stress up to −212 MPa, and the decreased grain diameter about 16 %. The LAMed 316L treated by USRP under the static pressure of 200 N presented the supreme corrosion resistance with the corrosion current density decreased up to 41 %, the polarization resistance increased up to 34 %, and the donor and acceptor densities reduced about 51 % and 81 %, respectively. The corrosion resistance of LAMed 316L was strengthened by USRP, benefiting from the modified surface roughness, grain refinement, increased Cr2O3 content in the passive film, work hardening, and residual compressive stress.

Improved low-temperature mechanical properties of FH36 marine steel after ultrasonic surface rolling process

The ultrasonic surface rolling process (USRP) was adopted to improve the low- temperature mechanical properties of FH36 marine steel for strengthening the service performance of marine steel in the low-temperature environment between − 30 °C and − 60 °C, such as polar regions. The results indicated that the surface integrity of FH36 marine steel was restructured as a result of the severe plastic deformation induced by USRP. The surface average grain diameter was refined from 10.92 µm to 5.86 µm with the number of nanoscale grains increased significantly and a nanostructured surface layer formed. The surface roughness decreased greatly with Ra not more than 0.074 µm. The surface residual compressive stress with an affected layer depth of not less than 2.6 mm was produced. The surface microhardness increased significantly with a large-depth work hardening layer of not less than 580 µm. The yield strength and ultimate tensile strength of FH36 marine steel after USRP at room temperature and low temperatures were enhanced. The combined effects of fine grain strengthening, dislocation strengthening, modified surface roughness, induced residual compressive stress, work hardening, and changed heat transfer performance caused by USRP were the main reasons for the improved low-temperature mechanical properties of FH36 marine steel.

IMPROVING CORROSION RESISTANCE OF MAGNESIUM NANOCOMPOSITES BY USING ELECTROLESS NICKEL COATINGS

The present study aims at improving corrosion resistance of magnesium nanocomposites through autocatalytic Ni-P coating. Electroless Ni-P coatings with different concentration of sodium hypophosphite are deposited on 2% WC incorporated magnesium nanocomposites (AZ31-2WC) and the coated samples are further heat-treated. Basic characterizations and compositional analyses are done by using scanning electron microscope (SEM), energy dispersive x-ray analysis (EDAX), and X-ray diffraction analysis (XRD). Microhardness values of the developed materials are also evaluated. The attempt is made to improve corrosion resistance of AZ31-2WC by modifying surface roughness. Corrosion characteristics of Ni-P coated AZ31-2WC nanocomposites are examined by performing potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS). Corrosion resistance improves with enhancement of surface quality. Corrosion resistance of AZ31-2WC nanocomposite also improves due to application of Ni-P coating. Finally, corrosion morphologies are scrutinized by SEM micrographs of corroded surface.

Knowledge transfer between liquid- and gas-fed CO2 electrolysis

In this issue of Chem Catalysis , Corral and Lee et al. suggest that bridging the knowledge gap between liquid- and gas-fed CO 2 electrolyzers reveals a better understanding of the local CO 2 reduction reaction environment. A generalized strategy to reduce overpotential and improve catalyst selectivity by modifying surface roughness is offered. In this issue of Chem Catalysis , Corral and Lee et al. suggest that bridging the knowledge gap between liquid- and gas-fed CO 2 electrolyzers reveals a better understanding of the local CO 2 reduction reaction environment. A generalized strategy to reduce overpotential and improve catalyst selectivity by modifying surface roughness is offered.

Along-Wind Aerodynamic Damping of Wind Turbine Towers: Determination by Wind Tunnel Tests and Impact on Tower Lifetime

As wind turbines become larger and their towers more slender, aeroelastic effects play a bigger role in the wind turbine’s dynamic behavior. This study focuses on the along-wind aerodynamic damping of wind turbine towers, which has been determined by wind tunnel experiments using the forced oscillation method according to Steckley’s approach. Reynolds number scale effects have been considered through surface roughness modifications using sand paper and a dimple pattern, which have been described in detail. The wind tunnel measurements are performed in sub-critical, critical and trans-critical flow regimes, as well as in low- and high-turbulence conditions, which allows for an accurate description of the required relative roughness and Reynolds numbers for achieving trans-critical conditions. The resulting along-wind aerodynamic damping values according to Steckley’s and Holmes’ approaches are compared, and an analytical relation between them is established. Both approaches are then used in aeroelastic multi-body-simulations of an onshore 6 MW reference wind turbine and their impact on the wind turbine lifetime is evaluated through fatigue proofs at the tower base section. Holmes’ approach seems more appropriate for the application in aeroelastic multi-body simulations. A lifetime extension for the wind turbine tower of approximately 0.4% is achieved for the reference wind turbine tower, which roughly corresponds to 1 to 2 months for 20 years of operation. An analytical expression is given for the estimation of the tower’s aerodynamic damping in parked and operating conditions.