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Understanding the aerodynamic characteristics of landfalling typhoons is of great importance for both wind engineering and meteorology. This study comparatively investigated the near‐surface wind profiles and aerodynamic parameters over coastland and coastal sea areas using typhoon observational data collected by Doppler wind lidars and wind tower anemometers during the passage of 15 typhoons that made landfall over China during 2009–2020. Specifically, the three surface aerodynamic parameters of roughness length, friction velocity, and drag coefficient (Cd) were obtained using the logarithmic law wind profile method. Results showed that the near‐surface wind profiles became much closer to the power law wind profile with increase in wind speed. The values of roughness length and friction velocity over the coastal sea were found to exceed those over coastland areas when the 10‐m wind speed (U(10)) was larger than 18 m s−1. The critical wind speed at which Cd peaks over the coastal sea was found to be 24 m s−1. There are two peaks in the variation of Cd with U(10) under the condition of onshore wind over the sea, which has never been reported in previous observational studies. Finally, a formula for Cd was proposed to describe the variation in Cd with U(10) under the condition of onshore wind over land, which is expected to be applied in the typhoon surface layer scheme to improve numerical simulation of landfalling typhoons. Plain Language Summary: Typhoons are one of the most destructive natural disasters that cause severe economic losses and human casualties in many parts of the world. Understanding the typhoon wind field is important for designing high‐rise buildings and improving weather forecast. In order to understand how the near‐surface wind field change in coastal regions, we measure it using specialized observation instruments during the passage of 15 typhoons that made landfall over China and analyze the results of the measurements. We find that the aerodynamic characteristics of typhoons over coastland are very different from those over the coastal sea. A specialized surface aerodynamic parameter called drag coefficient, which represents the momentum transport efficiency on the sea/land surface, is found to reach its maximum value when the 10‐m wind speed is 24 m s−1 over the coastal sea. Interestingly, two peaks are observed in the plot of drag coefficient as a function of 10‐m wind speed under the condition of onshore wind over the coastal sea, which has not been reported before in any other related studies. Further development of the typhoon numerical models should take these results into account. Key Points: Values of roughness length and friction velocity over the coastal sea were found to exceed those over the coastland for U(10) > 18 m s−1Critical wind speed at which Cd peaks over the coastal sea was found to be 24 m s−1There are two peaks in the variation of Cd with U(10) under the condition of onshore wind over the coastal sea [ABSTRACT FROM AUTHOR]

The shoal area of the lower Yellow River in China is not flooded with water during the dry season, so various plants can grow. When floods overflow the plains in the flood season, the complexity of water resistance is increased due to the resistance to water flow by vegetation, which directly affects flood discharge in the beach area. The drag force coefficient (CD), Manning's roughness coefficient (n), and Darcy-Weisbach resistance coefficient (f) are commonly used to characterize vegetation drag force. Such studies are commonly conducted in clear water, but flood water in the lower Yellow River is generally muddy. In order to study the effect of the same sediment content and different sedimentation thicknesses on the resistance of muddy waters containing vegetation, this study conducted experiments in a flume (length = 28 m, width = 0.5 m, and height = 0.5 m) under different deposition thicknesses. The results showed that the vegetation drag force coefficient (CD), vegetation roughness (nb), and Darcy-Weisbach drag coefficient (f) all decreased logarithmically with increasing Reynolds number (Re) and Froude number (Fr). When Re > 30,000, under the conditions of different siltation thicknesses of vegetation, the vegetation roughness tended to stabilize near its minimum value. When the Reynolds number of the water flow is large (Re > 20,000), the variation of the Darcy-Weisbach drag coefficient f slows down with the Reynolds number Re. Logarithmic functions were established for the above resistance coefficients and flow coefficients, and the corresponding correlation coefficients were high, indicating that the conclusions were reliable. [ABSTRACT FROM AUTHOR]

Lamps attached on the stay cable can change the stable circular cross-section of the stay cable, which is easy to cause galloping vibration. Stay cables of the Kuipu bridge in the Fuzhou City of China were equipped with damper and helical fillets. After the installation of rectangular lamps on this bridge, no obvious vibration of the stay cables was observed. This is totally different from another bridge, the Kuimen bridge in the Chongqing City of China, which has been recently reported by the authors. The purpose of this study is to clarify the effects of the helical fillets and the structural damping on galloping vibration. The features of galloping vibration of the stay cable attached to a rectangular lamp were carefully studied, and the effectiveness of damping and helical fillets in reducing the galloping vibration was evaluated. First, the force measurement wind tunnel tests on the segmental test model were carried out, and the lift and drag coefficients of the stay cable attached to the rectangular lamp were measured. The dangerous wind attack angle of galloping vibration was predicted by the galloping force coefficient. Second, 3-dimensional vibration measurement wind tunnel tests were carried out to measure the wind-induced response of the cable-lamp test models. The variation of wind-induced response of stay cable with yaw angle and wind velocity was measured for test models with and without helical fillets. In the test, the features of wind-induced vibration were studied at the damping level of 0.1%, 0.6%, 0.7%, 0.8%, and 1.0%. According to Den Hartog's theory, the minimum coefficient of galloping force is about −9.8. The experimental results of 3-dimensional vibration measurement wind tunnel tests show that the helical fillets wrapped on the cable surface can enhance the critical wind velocity to a certain extent, but the critical wind velocity is still far lower than the design wind velocity. When the damping ratio of the stay cable is up to 1.0% (S C = 35.1), the galloping vibration of the stay cable attached to a rectangular lamp on the Kuipu Bridge can be effectively mitigated. [ABSTRACT FROM AUTHOR]

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In this study, a longline aquaculture facility with lantern nets off the coast of northern China was modelled to conduct hydrodynamic tests starting from the culture unit to the entire facility under various current and wave conditions. The experimental results indicated that the drag coefficients of the lantern net model with weights of 0.5, 0.75, and 1.0 kg were 0.75, 0.83, and 0.91, respectively, in the Reynolds number range of 1 × 104–1 × 106. The current-driven upstream mooring line was more dominant than the wave-driven tension, and a simplified model of the longline facility accurately predicted the mooring line tension under the current conditions. The scope of the mooring line (defined as the length of the mooring line related to the water depth) played an important role in eliminating an order of magnitude difference in mooring tension under the wave conditions. The amplitudes of the vertical movement of the longline facility were smaller than the wave height when L/Lm was less than 1.5. Therefore, detailed information is needed to better understand the hydrodynamic characteristics and motion response of longline aquaculture facilities for the safe operation of longline structures in offshore environments, in order to process high-quality oyster products. [ABSTRACT FROM AUTHOR]

Accurate prediction of tropical cyclone (TC) intensity is important but challenging. In this study, a physically based algebraic decay model for predicting TC weakening after landfall over China is introduced, which assumes the TC weakening rate is proportional to the square of the TC maximum near‐surface wind speed. In this algebraic decay model, a decay parameter including the topographic effect by modifying the surface drag coefficient with the normalized terrain height is determined by minimizing the forecast errors for all landfalling TCs over mainland China during 1980–2020. Results show that the algebraic decay model with topographic effect considered performs better than the commonly used exponential decay model for TCs after landfall over mainland China, especially when TCs move further inland. This new model has a time‐dependent decay parameter along the TC track due to the topographic variation, which is different from the previous exponential decay model. Plain Language Summary: Previous exponential decay models of tropical cyclone (TC) weakening after landfall assume the TC weakening rate after landfall being proportional to TC intensity at the time of landfall. In recent years, a physically based algebraic decay model of TCs after landfall is also evaluated based on idealized numerical simulations and observations. The algebraic decay model assumes the TC weakening rate is proportional to the square of the TC maximum near‐surface wind speed. In this study, the topographic effect on enhancing surface drag coefficient and thus TC weakening in such a physically based algebraic decay model is introduced by minimizing the forecast errors for all landfalling TCs over mainland China using the best track data during 1980–2020. Different from earlier decay models, the newly constructed decay model has a time‐dependent decay parameter along the TC track due to the topographic variation. Results show that the newly constructed model performs better for TCs after landfall over China than the commonly used exponential decay model without considering the topographic effect. Key Points: The weakening of a tropical cyclone (TC) after landfall can be modeled with a physically based algebraic decay modelThe orographic effect on the weakening of landfalling TCs can be included using a terrain height‐dependent surface drag coefficientA physically based algebraic decay model with orographic effect has been developed for predicting TC weakening after landfall over China [ABSTRACT FROM AUTHOR]

In the face of the increasing risk of Maritime accidents caused by global climate change, it is necessary to improve the accuracy of drift model of the dropped containers at seas for Maritime Search and Rescue (SAR). Sensitivity test on the classic drift model illustrates that immersion ratio (I r) of container plays a dominate role in the drift trajectory of container compared to the drag coefficients. Inspired from it, a new scheme of variable I r is proposed to improve the model by considering the water entering process of container in the study. Based on the stability analysis of four floating attitudes of intact empty container under strong wind condition, the variable I r is estimated according to the orifice inflow theory and the Archimedes' principle of buoyancy. The new scheme is compared with the fixed I r scheme from the simulation of the drift trajectory of the dropped container at Xiamen Bay of China. The result shows that error arisen from the fixed I r would be accumulated as the time integral, but the new scheme of variable I r can obviously improve the model accuracy for the long-time prediction of SAR. In addition, the drag coefficients of wind and water in the drift model of the dropped container are suggested to be 0.8 and 1.2, respectively. • Extended-Fourier amplitude sensitivity test (E-FAST) is applied to the drift model of dropped container at sea for the first time. • A new scheme of variable immersion ratio is proposed to the model basing on the stability analysis of dropped container. • New scheme can obviously improve the trajectory accuracy of the long-time prediction for maritime search and rescue. [ABSTRACT FROM AUTHOR]

Aerodynamic resistance, also called the aerodynamic drag, can greatly affect the movements of athletes during high-speed sports. In terms of skiing, the wind environment of the venue creates pushing force or dragging force on the body of skiers during their skiing process in the ski resort. The sliding velocity and the work against resistance are greatly affected by wind, so how to reduce the work against wind resistance is a research focus of sports science. This study conducted wind tunnel experiment on physical skier models. At first, non-contact 3D measurement was carried out to measure the body of a certain skier and several skier models were scanned and printed; then, for the typical movement postures made by the skier in the Yabuli Ski Training Base which is located in the Heilongjiang province of China, wind tunnel experiment was conducted to study the relationship between the air drag coefficient and the wind speed during the skiing process. The results show that the drag coefficient does not change with wind speed during the skiing process. Parameters such as the skier’s height, posture, and frontal area on the windward side have a certain impact on the drag coefficient. The greater the height of the skier, the larger the drag coefficient. The laws summarized in this paper could be used by athletes to adopt rational tactics and optimize their postures during training, thereby improving their competition performance. [ABSTRACT FROM AUTHOR]

Long-term and high-frequency observing of the oceanic bottom boundary layer was implemented using a seabed-mounted tripod equipped with multiple high-frequency instruments in a semidiurnal tide-dominated channel around the Zhoushan Islands, China. The estimated turbulent parameters, e.g., turbulent intensity, friction velocity, and bottom drag coefficient, varied with quarter-diurnal frequency. The amplitudes of turbulent intensity, bottom stress, and friction velocity were larger in spring tide than those in neap tide. As the Reynolds number increased from 103 to 105, the measured bottom drag coefficient initially increased, peaked at a Reynolds number of approximately 1.4 × 105, and then decreased. The observed drag reduction is similar to the variations of drag coefficient of cross-flow around a circular cylinder and the fluid friction of the pipe flow in the transitional state, which can provide a necessary and important proof for further theoretical and experimental investigations. Several plausible explanations are raised for this reduction: the stratification caused by the gradient of salinity or sediment suspension and the occurrence of recirculation vortices generated by seabed topography. [ABSTRACT FROM AUTHOR]

The rivers connecting oceans generally carry sediment due to water and soil losses in China. Additionally, the maximum sediment concentration is 300 g/L, which is much higher than that of other countries. It is unknown whether seawater with sand particles will affect the power of tidal current turbine blades. It is therefore necessary to study the capture power of tidal current turbines in the water-sediment environment. In this study, the blade was divided into a number of transversal airfoil elements based on the blade element theory. The CFD-DPM model was employed to study the lift and drag coefficients of airfoil under multiphase flow, and the fluid–particle interaction was considered. The accuracy of this presented model was assessed using the experimental data of a 120 kW tidal current turbine in a water-sediment environment. Good agreement between the predictions and experimental data was observed. The effect of particle properties on the lift coefficient and the drag coefficient of airfoil were investigated in detail. Furthermore, the 120 kW tidal current turbine power was calculated based on the Blade Element Momentum theory under different particle concentrations. The results show that small diameter particles can improve the tidal current turbine power and the large diameter particle can reduce the power. [ABSTRACT FROM AUTHOR]

Winds, wind waves, and turbulence are essential variables and playing critical role in regulating a series of physical and biogeochemical processes in large shallow lakes. However, parameterizing winds, waves, currents and turbulence and simulating the interaction between them in large shallow lakes haven't been evaluated strictly because of a lack of field observations of lake hydrodynamics process. To address this problem, two process-based field observations were conducted to record the development of summer and winter wind-driven currents in Lake Taihu, a large shallow lake in China. Based on these observations and numerical experiments, a wave-current coupled model (WCCM) is developed by rebuilding expression of wind drag coefficient, introducing wave-induced radiation stress, and adopting a simple turbulence scheme, and then used to simulate wind-driven currents in Lake Taihu. The results show that, the WCCM can accurately simulate the upwelling process resulting from the wind-driven currents during the field observations. Comparing with other model, there is a 42.9 % increase of WCCM-simulated current speed which is mainly attributed to the new expression of wind drag coefficient. Meanwhile WCCM-simulated current direction and field are also improved due to the introduction of wave-induced radiation stress. Furthermore, the use of the simple turbulent scheme in the WCCM makes the simulation of the upwelling processes more efficient. The WCCM provides a sound basis for simulating shallow lake ecosystems. [ABSTRACT FROM AUTHOR]

Wind load is the designed control load for super-large cooling tower (SLCT) structures. Studies on wind resistance of those structures have focused mainly on normal winds, not on the influence of strong typhoons, or in particular the values of suction. To study the suction distribution and action mechanism of flow fields in an SLCT in typhoon conditions, in this study a high temporal–spatial resolution simulation of Typhoon Megi was done using a mesoscale weather research and forecasting (WRF) model with a multiple nesting structure. The wind velocity profile in the simulated region was gained through least squares fit. The research object was the world's highest cooling tower (220 m) at the Lu'an power plant in Shanxi Province, China. Three-dimensional (3D) computational fluid dynamics (CFD) wind field simulations of this tower in normal-wind and typhoon conditions were done based on a mesoscale–microscale nesting technology. A comparative analysis on the 3D effect of wind loads on the internal surface of an SLCT in a typhoon was also done, as was a summary of the meridian and circumferential distribution laws of the internal pressure coefficients. Differences on flow field characteristics, pressure coefficients, drag coefficients, and wind resistance in the tower structure in normal-wind and typhoon conditions and relative causes were investigated. Finally, the recommended values of suction in an SLCT in typhoon conditions are proposed. Results demonstrate that a WRF–CFD coupling model can effectively simulate the near-surface 3D wind field of an SLCT in typhoon conditions. Compared with a normal wind, the high wind velocity and strong turbulence of a typhoon causes larger-scale vortices inside the cooling tower, a more turbulent airflow on the leeward side, and a longer development area of vortices. In typhoon conditions, the internal pressure coefficient of the tower increased when the ventilation rate of the louver was 15%, 30%, and 100%. The overall internal pressure coefficient was found to be −0.61 , −0.36 , −0.34 , and −0.42 when the ventilation rates of the louver are 0%, 15%, 30%, and 100%, respectively. [ABSTRACT FROM AUTHOR]

Use of mangrove ecosystems for coastal flood protection requires reliable predictions of mangrove wave attenuation, especially if this capacity lessens due to storm‐induced forest damage. Quantifying and understanding the variation in drag forces and mechanical properties of mangrove vegetation can improve assessment of mangrove protective capacity. We studied five mangrove species common in the subtropical Pearl River Delta, south China. The studied species range from typically landward‐occurring to more seaward‐occurring pioneer species. We sampled across seven sites in the delta to study the impact of salinity on mechanical properties. We quantified strength and flexibility of branches (branch strength and flexibility related to branch diameter, modulus of rupture and modulus of elasticity), leaf strength (leaf attachment strength related to leaf size, and leaf mass per area) and drag properties (drag force related to surface area and drag coefficient). For all tested species, larger branch diameters resulted in higher mechanical strength. Larger leaf size resulted in larger peak pulling forces and larger branch surface area resulted in stronger drag forces. Notably, species that generally occur lower in the intertidal zone, where exposure to wind and waves is higher, had relatively stronger branches but more easily detachable leaves. This may be regarded as a damage‐avoiding strategy. Across the seven field sites, we found no clear effect of salinity on mangrove mechanical properties. This study provides a mechanistic insight in the storm damage process for individual mangrove trees and a solid base for modeling storm (surge) damage at the forest scale. [ABSTRACT FROM AUTHOR]

Settling velocity of bioclastic particles in coastal and shallow marine environments is essential for interpreting depositional facies and processes. There is, however, a paucity of accurate formulae for predicting the settling velocities and drag coefficients of platy biogenic particles in particular. This study provides experimental settling data based on 320 platy shell fragments from a sediment core recovered in Li'an Lagoon, south‐eastern Hainan Island, China. The results indicate that the settling velocities of platy shell fragments are strongly correlated with nominal diameters and Corey shape factors (ranging from 0.02 to 0.20 in this study). On this basis, a practical equation of acceptable accuracy was established for platy particles, relating dimensionless settling velocities to dimensionless diameters and Corey shape factors. Similarly, another empirical formula for quickly calculating the equivalent diameter of platy shell fragments in practice was proposed as well. Regarding the strong dependence of the drag coefficients using equivalent spherical diameters to Corey shape factors, the drag coefficient based on the diameter of the equivalent maximum projected area remains almost constant and is hence physically well‐suited for the definition of grain drag coefficients. The settling data of this study has extended the lower Corey shape factors limit of bioclastic particles, and the equations presented here can be used for quantitative interpretations of sedimentary records, modelling of depositional processes and investigations of other platy particles. [ABSTRACT FROM AUTHOR]

In this study, the Weather Research and Forecasting (WRF) model is used to quantify the effects of land use and cover change (LUCC) on the near-surface wind speed (SWS). The simulated results show that the SWS based on land use cover data for the 2010s (LUC10) is lower than that based on land use cover data for the 1980s (LUC80) by a difference of 0.17 m s−1; the LUCC effects also result in a decrease of 9.0% of the probability of strong wind. The LUCC effects induce significant alteration of the roughness length, causing changes in the drag coefficient and friction velocity, and thereby decrease SWS. A 0.1 m increase in roughness length could cause a 0.003 increase in drag coefficient and a 0.015 m s−1 increase in friction velocity. The contributions of LUCC to the SWS changes vary among different regions. The increase of SWS in Northeastern China is caused by the changes from deciduous broadleaf to deciduous needleleaf forests, mixed forests and croplands, and these changes decrease the surface roughness length, drag coefficient and friction velocity. The significant decrease of SWS over the middle reaches of the Yangtze River is induced by the changes from closed shrubland and cropland/natural vegetation mosaic to evergreen broadleaf and deciduous broadleaf forest. The slowdown of SWS over the Shandong Peninsula, the Beijing–Tianjin–Hebei region, the Yangtze River Delta, and the Pearl River Delta can be attributed to the extension of urban and built-up areas and the decrease of croplands and the cropland/natural vegetation mosaic. The slowdown in SWS caused by LUCC is also revealed by the friction wind model (FWM); however, the FWM presented more significant effects of LUCC on decrease in SWS. [ABSTRACT FROM AUTHOR]

Our research targets a subway foundation pit construction project in Nanning, a city in southwestern China. The foundation pit was excavated in the water-rich round gravel stratum. The theoretical calculation was combined with finite-element analysis, which is based on drag coefficient method, to derive the relevant seepage parameters of the stratum. The complex seepage surface was solved through the meshing of virtual grids with fixed nodes. The 3D seepage field around the ground-connecting wall in the pit (hereinafter referred to as the wall) was investigated through finite-element analysis on midas GTS NX. In this way, the author identified the features and law of soil seepage around the wall in the water-rich gravel stratum. The results show that the middle and lower part of the wall were within the sand layer and the gravel layer, both of which are strongly permeable; the seepage rate around the wall peaked in the middle of the wall (0.156 m/sec); there was an obvious seepage effect in the pit; the waterrich gravel stratum had greater seepage water inflow than any other stratum; the pore water migration features could be described accurately by the seepage control equation of the heterogeneous anisotropic porous medium. [ABSTRACT FROM AUTHOR]

• How to model the hydrodynamic drag of cultivation activities is our major concern. • Surface and bottom shear stress were simultaneously used for hydrodynamic drag. • Tidal prism & half-life time were used for quantifying water exchange capability. This study mainly addressed the methodology issue of how to model the hydrodynamic drag effects of aquaculture facilities and activities. Here, firstly, surface shear stress was determined by roughness height for characterizing the drag from floating aquaculture activities, while bottom shear stress was determined by the Manning number for characterizing the drag caused by bottom fixed aquaculture activities. Then, by taking Qinzhou Bay as a typical case, the two-dimensional model was established by integrating the multiple drag coefficients to quantify the impacts of the oyster cultivation activities on the water exchange capability (tidal prism and half-life time). The results showed that: (1) Cultivation activities would reduce the average tidal prism by 6.4% in Qinzhou Bay; (2) 10 averages longer day of half-life time was estimated to be resulting from the cultivation drag. [ABSTRACT FROM AUTHOR]

Long-term changes in surface wind speed (SWS) are influenced by both large-scale circulation and relative resistance. The effects of large-scale circulation are embodied by the pressure-gradient force (PGF), which is mostly a natural factor, whereas the resistance is due to the drag between the air and the surface as well as in the different boundary layers, which is mainly caused by the anthropogenic land use and cover change (LUCC). We performed experiments using a simple dynamical method in which a balance among the PGF, Coriolis force, and drag is reached to separate the effects of the PGF and LUCC on the SWS, and then, to quantitatively estimate the influence of the LUCC on the SWS over the East China Plain (ECP) during the period 1980-2011. The results show a distinct decrease in the SWS in the station observation data with a rate of −0.13 m s (10 year), but there is no statistically significant long-term trend in the reanalysis data. At the same time, the drag coefficient induced by the LUCC shows an increasing trend, which is consistent with the 30 % increase in the rate of urbanization during the study period. In addition, the PGF fluctuates with distinct seasonal and interannual changes, and it has an insignificant long-term increasing trend during the period 1980-2011. At the same time, the spatial distribution of the linear trend coefficient of the normalized PGF is inconsistent with that of the SWS, but the linear trend coefficient of the normalized drag coefficient shows a similar spatial distribution as the SWS. Therefore, the increase in the drag coefficient induced by the LUCC should account for the long-term decrease in the SWS. The difference between the model wind speed, in which the drag coefficient is constrained to its value in the year 1980, and the observed wind speed at each station (SWSD) can reflect the influence of the LUCC on the SWS. Furthermore, the long-term changes in East Asian monsoons may not completely account for the observed wind speed decrease near the surface in the ECP region, but it is an important factor in the SWS. [ABSTRACT FROM AUTHOR]

The statistics of momentum exchange in the urban roughness sublayer are investigated. The analysis focuses on the characteristics of the dimensionless friction velocity, $${u_{*}}/U$$ , which is defined as the square root of the drag coefficient. The turbulence observations were made at a height of 47 m above the ground on the 325-m meteorological tower, which is located in a very inhomogeneous urban area in Beijing. Under neutral conditions, the dependence of the drag coefficient on wind speed varies with wind direction. When the airflow is from the area of densely built-up buildings, the drag coefficient does not vary with wind speed, while when the airflow is from the area covered by vegetation, the drag coefficient appears to decrease with increasing wind speed. Also, the drag coefficient does not vary monotonically with the atmospheric stability. Both increasing stability and increasing instability lead to the decrease of the drag coefficient, implying that the roughness length and zero-plane displacement may vary in urban areas. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the flow restructure and resistance in vegetal flow under wind shear action in shallow lakes. A special racetrack-style flume with two sets of driving devices installed on the top was designed to simulate the wind-driven current. Two typical types of live vegetation, Vallisneria natans and Acorus calamus of Taihu Lake in China, were planted in the system. The results revealed that the velocity distribution of vegetal flow under wind action differed from that in open channels. The velocity distribution can be described as logarithmic-curve shaped and contained a compensation current in the lower layer. The area within the effective height of vegetation in which the velocity was obviously affected comprised an effective friction region. When compared with V. natans, A. calamus displayed better resisting capacity. Based on measured data, a new empirical relationship between drag coefficient and wind speed was presented, which indicated the resistance ability of vegetation under different intensities of wind action. Variations in the equivalent roughness coefficient were also discussed. [ABSTRACT FROM AUTHOR]

• Aerodynamic characteristics of five surfaces undergoing wind erosion differ. • Pulsation intensity, turbulence intensity, and drag coefficient increase with z 0. • Consumption of roughness elements on wind force affects the surface stability. • τ R /τ increases with increasing wind speed for flexible roughness elements but decreases for rigid roughness elements. Aerodynamic characteristics is a crucial factor influencing soil wind erosion, which is closely related to the properties of surface roughness elements. In the expansive arid and semi-arid northern China, grassland, farmland, mobile sandy land, and gobi are the main land surface types that suffer wind erosion to varying degrees. To investigate the aerodynamic characteristics of different surfaces, we used three-dimensional ultrasonic anemometers to observe the near-surface wind speed above grassland, farmland, mobile sand, and two types of gobi surfaces in areas of northern China (a total of five observation sites). We compared the aerodynamic characteristics of the five surfaces and their causes (i.e., the surface roughness length, wind speed pulsation, turbulence intensity, and drag coefficient), and analyzed how surface roughness elements weakened the airflow. The roughness length was greatest for grassland, followed by farmland, sand, fine gobi, and black gobi. The pulsation intensity of near-surface wind speed increased linearly with increasing wind speed at all sites. At a given wind speed, increasing roughness length increased the pulsation intensity of wind speed. The probability distributions for the drag coefficient and turbulence intensity of the five surfaces followed a positively skewed distribution. The drag coefficient and turbulence intensity were greatest for grassland, followed by farmland, sand, fine gobi, and black gobi surfaces. The drag force exerted on the roughness elements increased with increasing wind speed, but the ratio of drag force exerted on the roughness elements to the total drag force (τ R / τ) for flexible roughness elements (i.e., plants) increased as the wind speed increased; for rigid roughness elements, τ R / τ decreased with increasing wind speed. This confirms that the shelter capability of flexible roughness elements against soil wind erosion increases with the increase of wind speed, while that of rigid roughness elements is opposite. [ABSTRACT FROM AUTHOR]

Turbulent flux measurements at Qamdo site over the Tibetan Plateau during TIPEX from May 18 to June 30, 1998 are presented. Sensible heat dominated, accounting for about 66% of the available energy (the sum of net radiation and soil heat flux) prior to the monsoon (dry period), reducing to about 31%, with latent heat increased to about 56% of available energy, in the monsoon season (wet period). Surface energy budget closure on average was about 0.80 (0.85) prior to the monsoon and 0.89 (0.76) during the monsoon using eddy correlation (profile) methods. The sum of latent and sensible heat fluxes calculated from the flux-profile method was smaller by about 15% than that from eddy correlation. Martano's method is used to estimate the surface aerodynamic roughness length z0 and zero plane displacement d from single level sonic anemometer data, giving d = 0.12 m and z0 = 0.08 m. The overall neutral drag coefficient (CDN) and scalar coefficient (CHN) were found to be CDN = 0.0055 and CHN = 0.0059 in the southeastern area of Tibet. Their variations with the mean wind speed at 10 m are discussed. [ABSTRACT FROM AUTHOR]

Recently, a new structure type of a vertical truncated dumbbell-shaped cylinder has been widely used in bridge cofferdams in many sea-crossing bridges in China. Wave-only and wave-current interactions with this new structure type are studied experimentally and numerically. The modified Morison equation is applied to derive the drag coefficients C D and inertia coefficients C M. The influence of the incident flow directions, current velocity, static wave height and wave periods on the hydrodynamic coefficients is explored. The study shows that the hydrodynamic coefficients are strongly correlated with the sine values of the incident flow directions. In addition, a 3D numerical model using a multilayer σ-coordinate model and an immersed boundary method based on the Navier-Stokes equations (Kang et al., 2015) is established. Based on the validated numerical model, flow patterns around the structure, including the free surface and 3D vorticity distributions, are analyzed numerically. The results presented herein provide important guidance to better understand the hydrodynamic performance of this new structure type. • Wave-current interactions with a new structure type of a dumbbell-shaped bridge cofferdam are studied experimentally and numerically. •.The modified Morison equations are applied to derive hydrodynamic coefficients on the dumbbell-shaped cylinder. •.The influence of the incident flow directions, current velocity, static wave height and wave periods on hydrodynamic coefficients is explored in this study. •.The developed numerical model of wave-current-body interactions is verified by the wave flume tests results. •.The flow patterns including the free surface and 3D vorticity distributions around the cylinder are analyzed. [ABSTRACT FROM AUTHOR]

• Expanding capabilities of Noah-MP model was estimated over subtropical forest. • Nuances of land surface processes could be touched on by using benchmarking metrics. • Soil moisture threshold for transpiration is important for simulate LH & SH fluxes. Accurate estimation of land surface heat fluxes is critical to climate and air quality forecasting, which needs an appropriate parameterization in land surface models. The benchmarking method was applied to search for the optimal combination of the physical parameterization based on Noah land surface model with multi-physics options (Noah-MP). The effect of integrated physical mechanisms on the simulation of land surface energy fluxes in a typical subtropical forest (Dinghushan Forest Ecosystem Research Station) over South China is further investigated. The most sensitive process is the soil moisture threshold for evaporation while there are six processes have little or no effect on heat simulation. The optimal combination options are referred as follow: prescribed table leaf area index (LAI) and vegetation fraction, Jarvis scheme for canopy stomatal resistance, Noah soil moisture scheme, SIMGM model for runoff and groundwater, original Noah consistent scheme for surface layer drag coefficient and two-stream applied to grid-cell scheme for radiation transfer. [ABSTRACT FROM AUTHOR]

In this work, the spatial and temporal sensitivities of the significant wave height (SWH) to ten key parameters in the SWAN model under typhoon conditions are assessed through comprehensive observations at four buoy stations along the eastern coast of China. Experiments were conducted using wind forcing based on Typhoon Chan-hom, which made landfall at Zhujiajian island in 2015. Assessments included wind input and whitecapping, bottom friction, depth-induced wave breaking, and nonlinear quadruplet wave interactions parameterizations. The results show that in shallow water whose depth is less than the threshold depth, depth-induced wave breaking dominates the SWH, and the SWH is most sensitive to the parameter gamma (the ratio of maximum individual wave height to depth) of depth-induced wave breaking. However, beyond a certain threshold depth, the sensitivity of the SWH to depth-induced wave breaking begins to reduce. This threshold depth depends on sea states and ranges from 5 m to 30 m. In deep water, where the water depth is more than the threshold depth, SWH is primarily influenced by wind input and whitecapping. In general, the sensitivity is greater in coastal areas than in the open ocean. With regard to sea state, the higher the sea state, the deeper the threshold depth. The four different numerical procedures of four-wave interactions (so-called quadruplets) mainly affect the distribution of wave energy, not the SWH. In addition, the SWH is most sensitive to the drag coefficient, and bigger wave implies greater sensitivity. The study of spatial and temporal sensitivities of key parameters is of great significance for further application of the SWAN model and wave simulations, especially typhoon wave simulations. • In shallow water, depth-induced wave breaking dominates the significant wave height (SWH). • In deep water whose depth is more than the threshold depth, SWH is primarily influenced by wind input and whitecapping. • This threshold depth depends on sea states and ranges from 5 m to 30 m. • The higher the sea state, the deeper the threshold depth. [ABSTRACT FROM AUTHOR]

In this study, water levels observed at tide stations in the Bohai Sea, Yellow Sea, and East China Sea during Typhoons 7203 and 8509 were assimilated into a numerical assimilation storm surge model combined with regularization technique to study the wind-stress drag coefficient. The Tikhonov regularization technique with different regularization parameters was tested during the assimilation. Using the regularization technique, the storm surge elevations were successfully simulated in the whole sea areas during Typhoons 7203 and 8509. The storm surge elevations calculated with the regularization technique and the elevations calculated with independent point method were separately compared with the observed data. Comparison results demonstrated that the former was closer to the observed data. The regularization technique had the best performance when the regularization parameter was 100. The spatial distribution of the inverted drag coefficient, storm surge elevations, and the wind fields during both typhoons were presented. Simulated results indicated that the change of drag coefficient is more significant in the coastal regions of the Bohai Sea and north of the Yellow Sea. Further analysis showed that the rising water elevation in the Bohai Sea is mostly attributed to the influence of onshore winds, and the negative storm surge in the South Yellow Sea is mainly caused by offshore winds.