Moderate Wind Conditions Research Articles

Performance enhancement of a rotational energy harvester utilizing wind-induced vibration of an inclined stay cable

In this paper, an innovative strategy for improving the performance of a recently developed rotational energy harvester is proposed. Its performance can be considerably enhanced by replacing the electromagnetic induction part, consisting of moving permanent magnets and a fixed solenoid coil, with a moving mass and a rotational generator (i.e., an electric motor). The proposed system is easily tuned to the natural frequency of a target structure using the position change of a proof mass. Owing to the high efficiency of the rotational generator, the device can more effectively harness electrical energy from the wind-induced vibration of a stay cable. Also, this new configuration makes the device more compact and geometrically tunable. In order to validate the effectiveness of the new configuration, a series of laboratory and field tests are carried out with the prototype of the proposed device, which is designed and fabricated based on the dynamic characteristics of the vibration of a stay cable installed in an in-service cable-stayed bridge. From the field test, it is observed that the normalized output power of the proposed system is 35.67 mW (m s−2)−2, while that of the original device is just 5.47 mW (m s−2)−2. These results show that the proposed device generates much more electrical energy than the original device. Moreover, it is verified that the proposed device can generate sufficient electricity to power a wireless sensor node placed on a cable under gentle–moderate wind conditions.

The Dance of MaleAnopheles gambiaein Wild Mating Swarms

An important element of mating in the malaria vector Anopheles gambiae Giles in nature is the crepuscular mating aggregation (swarm) composed almost entirely of males, where most coupling and insemination is generally believed to occur. In this study, we mathematically characterize the oscillatory movement of male An. gambiae in terms of an established individual-based mechanistic model that parameterizes the attraction of a mosquito toward the center of the swarm using the natural frequency of oscillation and the resistance to its motion, characterized by the damping ratio. Using three-dimensional trajectory data of ten wild mosquito swarms filmed in Mali, Africa, we show two new results for low and moderate wind conditions, and indicate how these results may vary in high wind. First, we show that in low and moderate wind the vertical component of the mosquito motion has a lower frequency of oscillation and higher damping ratio than horizontal motion. In high wind, the vertical and horizontal motions are similar to one another and the natural frequencies are higher than in low and moderate wind. Second, we show that the predicted average disagreement in the direction of motion of swarming mosquitoes moving randomly is greater than the average disagreement we observed between each mosquito and its three closest neighbors, with the smallest level of disagreement occurring for the nearest neighbor in seven out of 10 swarms. The alignment of the direction of motion between nearest neighbors is the highest in high wind. This result provides evidence for flight-path coordination between swarming male mosquitoes.

Analysis of tree sway and crown collisions for managed Pinus resinosa in southern Maine

In this experimental analysis, we attempt to determine if and how the oscillation frequencies of trees in a real forest stand vary. We examined the oscillation dynamics of trees in a red pine plantation before and after the stand was thinned from an initial density of approximately 1400trees/ha to a final density of approximately 200trees/ha. The prescribed thin effectively prevented collisions from occurring in the post-thin canopy under low and moderate wind conditions. A comparison of the pre-thin and post-thin canopies suggests that crown collisions increased the oscillation frequencies of individual trees in the stand by an average of 12.0%. We used several scaling relationships to estimate that collisions reduced tree sway amplitudes by an average of 32%. These findings are consistent with theoretical predictions from an elastic collision model of crown interactions which predicts that oscillation frequencies should increase as the wind speed increases. However, we did not find conclusive evidence of this latter behavior in the real stand, perhaps because of the limited range of wind speeds occurring during our trial.

Dynamic response of surface water‐groundwater exchange to currents, tides, and waves in a shallow estuary

In shallow, fetch‐limited estuaries, variations in current and wave energy promote heterogeneous surface water‐groundwater mixing (benthic exchange), which influences biogeochemical activity. Here, we characterize heterogeneity in benthic exchange within the subtidal zone of the Delaware Inland Bays by linking hydrodynamic circulation models with mathematical solutions for benthic exchange forced by current‐bedform interactions, tides, and waves. Benthic fluxes oscillate over tidal cycles as fluctuating water depths alter fluid interactions with the bed. Maximum current‐driven fluxes (~1–10 cm/d) occur in channels with strong tidal currents. Maximum wave‐driven fluxes (~1–10 cm/d) occur in downwind shoals. During high‐energy storms, simulated wave pumping rates increase by orders of magnitude, demonstrating the importance of storms in solute transfer through the benthic layer. Under moderate wind conditions (~5 m/s), integrated benthic exchange rates due to wave, current, and tidal pumping are each ~1–10 m3/s, on the order of fluid contributions from runoff and fresh groundwater discharge to the estuary. Benthic exchange is thus a significant and dynamic component of an estuary's fluid budget that may influence estuarine geochemistry and ecology.

Feasibility Study of Micro-Wind Turbines for Powering Wireless Sensors on a Cable-Stayed Bridge

In this study, the feasibility of using micro-wind turbines to power wireless sensors on a cable-stayed bridge is comprehensively investigated. To this end, the wind environment around a bridge onto which a turbine is installed is examined, as is the power consumption of a wireless sensor. Feasible alternators and rotors are then carefully selected to make an effective small wind generator (known as a micro-wind turbine). Using the three specially selected micro-wind turbines, a series of experiments was conducted to find the turbine best able to generate the largest amount of power. Finally, a horizontal-axis micro-wind turbine with a six-blade rotor was combined with a wireless sensor to validate experimentally its actual power-charging capability. It is demonstrated that the micro-wind turbine can generate sufficient electricity to power a wireless sensor under moderate wind conditions.

Fade and recovery process of algae-induced black bloom in Lake Taihu under different wind conditions

The duration time of the black bloom is a major index which would determine weather the disaster of the black bloom is severe or not. Wind-induced reoxygenation is the main factor which can disrupt the stability of the black bloom. In this study, laboratory simulation, visual comparison, and analysis of oxidation and reduction methods were employed to investigate the stability of algae-induced black bloom and the recovery processes of the water characteristics under different levels of wind conditions. Results showed that under the controlled calm condition, the black bloom system remained at a stable state in the entire experiment period, in which the DO was continuously1.5 mg/L. Under slow wind (S, the wind speed was about 2 m/s) and moderate wind (M, the wind speed was about 4 m/s) conditions, the black bloom disappeared after 2 d and the DO increased to about 6 mg/L when the black color of the water faded. Under high wind (H, the wind speed was about 8 m/s) condition, the black bloom totally disappeared in only 14 h. The results indicated that the black bloom did not re-occur after disappears while the wind conditions were maintained in the left experiment time. It was also shown that the concentrations of water soluble nutrients (NH+4-N and PO34 -P) were significantly responded to the wind levels. The research results would provide decision basis on the emergency control of the algae-induced black bloom.

Influence of Local Wind Conditions on the Flight Speed of the Great CormorantPhalacrocorax carbo

In seabirds, the relationship between flight speed and wind direction/speed is thought to be particularly important for studying energy-saving strategy and foraging habitat selection. In this study, we examined whether the ground and calculated air speeds of four great cormorants (Phalacrocorax carbo) were affected by wind conditions using high-resolution GPS data loggers. The birds increased their ground flight speed in tailwinds, decreased it in headwinds, and changed their air speed in relation to wind components. However, they did not change their foraging sites according to the wind conditions. They were likely to respond to moderate wind conditions by adjusting their air speed without changing their foraging sites.

Performance of 4 mm impact sprinklers at different spacing within acceptable pressure ranges (250-350 kPa)

Irrigation Engineers in Zimbabwe use the 12 m x 18 m spacing for the design of the sprayline, using 4 mm nozzle sprinklers. A study was conducted to determine performance and cost effectiveness of other spacings that can be used in sprinkler irrigation systems design. The main targeted spacings were a square layout of 15 m x 15 m and a rectangular layout of 15 m x 18 m. Water application uniformity and wetted diameter tests were done using the single line catch can layout method at 250 kPa, 300 kPa and 350 kPa using two locally manufactured (Toronto and Non Ferrous) and two imported (Rainbird and an Irriline) sprinklers. Highest coefficient of uniformity (CU) of 97 % and distribution uniformity (DU) of 95 % were obtained from a Rainbird sprinkler at 300 kPa. The lowest CU of 66 % and DU of 46 % were obtained from a Toronto sprinkler at 250 kPa. Highest wetted diameter (WD) of 32 m was obtained at 300 kPa from a Toronto sprinkler while lowest wetted diameter of 24 m was recorded at 250 kPa from a Toronto sprinkler. The results of CU, DU and wetted diameter showed that the 15 m x 15 m sprinkler spacing can be used in Zimbabwe under moderate wind conditions at 300 kPa, using preferably imported sprinklers for best application uniformity results.   

An energy harvesting system using the wind-induced vibration of a stay cable for poweringa wireless sensor node

This paper proposes an electromagnetic energy harvesting system, which utilizes thewind-induced vibration of a stay cable, and investigates its feasibility for powering awireless sensor node on the cable through numerical simulations as well as experimentaltests. To this end, the ambient acceleration responses of a stay cable installed in anin-service cable-stayed bridge are measured, and then they are used as input excitationsin cases of both numerical simulations and experimental tests to evaluate theperformance of the proposed energy harvesting system. The results of the feasibility testdemonstrate that the proposed system generates sufficient electricity for operation of awireless sensor node attached on the cable under the moderate wind conditions.

Coastal circulation in the absence of wind in the Gulf of Tehuantepec, Mexico: High-frequency radar observations

Using high-frequency radars, ocean surface currents were mapped every hour over an area of ≈5000 km2 in the inner Gulf of Tehuantepec (Mexico). The coastal circulation patterns (≈100 km offshore) were studied during spring, summer, and autumn 2006. The spring circulation was similar to the typical winter circulation, when the circulation is forced by outbursts of northerly winds (>8 m s–1) known locally as Tehuanos. Although Tehuano events are less common in spring than in winter, they are perfectly capable of modifying the sea surface by triggering cyclonic and anticyclonic eddies (≈50–200 km in diameter). Under moderate wind conditions, the ocean circulation showed a quasipermanent westward coastal current (≈50 cm s–1). Though the Tehuano winds were absent in summer, cyclonic eddies were observed and likely linked to the westward coastal current. Autumn was influenced by steady northerly winds with speeds of ≈12 m s–1 that remained over the region for almost 15 days. These conditions allowed us to study the competition between the wind-induced circulation and the more intense (≈100 cm s–1) westward coastal current during this period. The origin of this coastal current could be related to a warm coastal-trapped flow, composed of tropical low-salinity waters. The northwestward excursion of the observed coastal current is discussed, and the three-dimensional implications of surface current fields are studied by the Ekman theory and vorticity conservation.

Identification of ocean oil spills in SAR imagery based on fuzzy logic algorithm

Ocean oil spills cause serious damage to the marine environment, especially around coastal waters. Synthetic aperture radar (SAR) has been proven to be a useful tool for oil spill detection under low to moderate wind conditions. SAR operates in the microwave band and the data is not affected by the cloud cover and day/night conditions. However, the operational application of SAR for oil spill detection in the ocean is limited by false alarm targets or lookalike phenomena such as low wind speed, natural films, etc. In this study, we develop analysis of variance (ANOVA) to extract the features based on their characteristic geometry, grey level and texture features in the SAR images. We further analysed a fuzzy logic algorithm to separate oil spills features from lookalikes. We trained this algorithm using 38 SAR images (11 ENVISAT-Advanced Synthetic Aperture Radar (ASAR) and 27 European Remote Sensing (ERS)-2 SAR images) with 120 known oil spills and 80 lookalikes to generate an oil spill probability of a dark pixel in a SAR image. An independent set of 26 SAR images were used to validate the algorithm and it was found that 80.9% of the oil spills were correctly classified, and 20.0% of the lookalikes were wrongly classified as oil spills. The complete algorithmic procedure was coded in Matlab7.0 using its Fuzzy Logic Toolbox.

Diagnostic Wind Model Initialization over Complex Terrain Using the Airborne Doppler Wind Lidar Data~!2010-03-01~!2010-04-29~!2010-08-07~!

An initialization method using airborne Doppler wind lidar data was developed and evaluated for a mass- consistent diagnostic wind model over complex terrain. The wind profiles were retrieved from the airborne lidar using a conical scanning scheme and a signal processing algorithm specifically designed for the airborne lidar system. An objective data analysis method in complex terrain was then applied to those wind profiles to produce a three-dimensional wind field for model initialization. The model results using the lidar data initialization were compared with independent surface weather observational data and profiles from a microwave radar wind profiler. The model was previously run for a small domain with simple terrain where comparisons with a surface observation array showed that the model performed well in a strong wind condition. For the more complex terrain in the Salinas valley, the model evaluation with a limited number of observations indicated that the diagnostic wind model with airborne Doppler lidar data also produced a reasonably good wind field in moderate to strong wind conditions. However, caution must be stressed for weak wind conditions in which the flow is thermally driven as the mass-consistent diagnostic wind model is not equipped to handle such cases. The effect of the lidar wind profile density over a simulation domain was also investigated for practical applications. The results indicate that about a half dozen lidar wind profiles would be adequate for a 20 by 20 km complex terrain domain with fairly uniform and moderate wind conditions.

Protection Against Cold in Prehospital Care—Thermal Insulation Properties of Blankets and Rescue Bags in Different Wind Conditions

In a cold, wet, or windy environment, cold exposure can be considerable for an injured or ill person. The subsequent autonomous stress response initially will increase circulatory and respiratory demands, and as body core temperature declines, the patient's condition might deteriorate. Therefore, the application of adequate insulation to reduce cold exposure and prevent body core cooling is an important part of prehospital primary care, but recommendations for what should be used in the field mostly depend on tradition and experience, not on scientific evidence. The objective of this study was to evaluate the thermal insulation properties in different wind conditions of 12 different blankets and rescue bags commonly used by prehospital rescue and ambulance services. The thermal manikin and the selected insulation ensembles were setup inside a climatic chamber in accordance to the modified European Standard for assessing requirements of sleeping bags. Fans were adjusted to provide low (< 0.5 m/s), moderate (2-3 m/s) and high (8-9 m/s) wind conditions. During steady state thermal transfer, the total resultant insulation value, Itr (m2 C/Wclo; where C = degrees Celcius, and W = watts), was calculated from ambient air temperature (C), manikin surface temperature (C), and heat flux (W/m2). In the low wind condition, thermal insulation of the evaluated ensembles correlated to thickness of the ensembles, ranging from 2.0 to 6.0 clo (1 clo = 0.155 m2 C/W), except for the reflective metallic foil blankets that had higher values than expected. In moderate and high wind conditions, thermal insulation was best preserved for ensembles that were windproof and resistant to the compressive effect of the wind, with insulation reductions down to about 60-80% of the original insulation capacity, whereas wind permeable and/or lighter materials were reduced down to about 30-50% of original insulation capacity. The evaluated insulation ensembles might all be used for prehospital protection against cold, either as single blankets or in multiple layer combinations, depending on ambient temperatures. However, with extended outdoor, on-scene durations, such as during prolonged extrications or in multiple casualty situations, the results of this study emphasize the importance of using a windproof and compression resistant outer ensemble to maintain adequate insulation capacity.

Wave-dependence of friction velocity, roughness length, and drag coefficient over coastal and open water surfaces by using three databases

The parameterization of friction velocity, roughness length, and the drag coefficient over coastal zones and open water surfaces enables us to better understand the physical processes of air-water interaction. In context of measurements from the Humidity Exchange over the Sea Main Experiment (HEXMAX), we recently proposed wave-parameter dependent approaches to sea surface friction velocity and the aerodynamic roughness by using the dimensional analysis method. To extend the application of these approaches to a range of natural surface conditions, the present study is to assess this approach by using both coastal shallow (RASEX) and open water surface measurements (Lake Ontario and Grand Banks ERS-1 SAR) where wind speeds were greater than 6.44 m s−1. Friction velocities, the surface aerodynamic roughness, and the neutral drag coefficient estimated by these approaches under moderate wind conditions were compared with the measurements mentioned above. Results showed that the coefficients in these approaches for coastal shallow water surface differ from those for open water surfaces, and that the aerodynamic roughness length in terms of wave age or significant wave height should be treated differently for coastal shallow and open water surfaces.

A comparison of global models for the solar wind interaction with Mars

We present initial results from the first community-wide effort to compare global plasma interaction model results for Mars. Seven modeling groups participated in this activity, using MHD, multi-fluid, and hybrid assumptions in their simulations. Moderate solar wind and solar EUV conditions were chosen, and the conditions were implemented in the models and run to steady state. Model output was compared in three ways to determine how pressure was partitioned and conserved in each model, the location and asymmetry of plasma boundaries and pathways for planetary ion escape, and the total escape flux of planetary oxygen ions. The two participating MHD models provided similar results, while the five sets of multi-fluid and hybrid results were different in many ways. All hybrid results, however, showed two main channels for oxygen ion escape (a pickup ion ‘plume’ in the hemisphere toward which the solar wind convection electric field is directed, and a channel in the opposite hemisphere of the central magnetotail), while the MHD models showed one (a roughly symmetric channel in the central magnetotail). Most models showed a transition from an upstream region dominated by plasma dynamic pressure to a magnetosheath region dominated by thermal pressure to a low altitude region dominated by magnetic pressure. However, calculated escape rates for a single ion species varied by roughly an order of magnitude for similar input conditions, suggesting that the uncertainties in both the current and integrated escape over martian history as determined by models are large. These uncertainties are in addition to those associated with the evolution of the Sun, the martian dynamo, and the early atmosphere, highlighting the challenges we face in constructing Mars’ past using models.

On the co‐polarized phase difference for oil spill observation

In this study dual‐polarized synthetic aperture radar (SAR) measurements were used to enhance oil spill observation. The co‐polarized phase difference (CPD) was modelled and used to characterize the scattering return from oil spills and biogenic slicks. The model predicts, under low to moderate wind conditions, a larger CPD standard deviation (σ) for oil with respect to the sea, while for biogenic slicks a σ value similar to that for the sea is obtained. Experiments accomplished with multilook complex (MLC) C‐ and L‐band SAR data show that the model predictions are confirmed and that the C‐band is, as expected, to be preferred to the L‐band.

Recent advances in ocean-circulation research on the Yellow Sea and East China Sea shelves

Recent advances in ocean-circulation research on the Yellow Sea and East China Sea shelves are summarized. Observations using acoustic Doppler current profilers (ADCPs) suggest that the connectivity of mean-volume-transports is incomplete between the Tsushima (2.6 Sverdrups; 1 Sv = 106 m3/s) and Taiwan Straits (1.2 Sv). The remaining 1.4-Sv transport must be supplied by onshore Kuroshio intrusion across the East China Sea shelf break. The Yellow Sea Warm Current is not a persistent ocean current, but an episodic event forced by northerly winter monsoon winds. Nevertheless, the Cheju Warm Current is detected clearly regardless of season. In addition, the throughflow in the Taiwan Strait may be episodic in winter when northeasterly winds prevail. The throughflow strengthens (vanishes) under moderate (severe) northeasterly wind conditions. Using all published ADCP-derived estimates, the throughflow transport (V) in the Taiwan Strait is approximated as $$ V = V_0 + V_1 \cos [2\pi (t - K)/T], $$ where V 0, V 1, K are 1.2 Sv, 1.3 Sv, and 157 days, respectively, t is yearday, and T is 365.2422 days (i.e., 1 year). The difference between the throughflow transports in the Tsushima and Taiwan Straits suggests that the onshore Kuroshio intrusion across the shelf break increases from autumn to winter. The China Coastal Current has been observed in winter, but shelf currents are obscure in summer.

A Note on the Effect of Wind Waves on Vertical Mixing in Franks Tract, Sacramento–San Joaquin Delta, California

A one-dimensional numerical model that simulates the effects of whitecapping waves was used to investigate the importance of whitecapping waves to vertical mixing at a 3-meter-deep site in Franks Tract in the Sacramento-San Joaquin Delta over an 11-day period. Locally-generated waves of mean period approximately 2 s were generated under strong wind conditions; significant wave heights ranged from 0 to 0.3 m. A surface turbulent kinetic energy flux was used to model whitecapping waves during periods when wind speeds > 5 m s-1 (62% of observations). The surface was modeled as a wind stress log-layer for the remaining 38% of the observations. The model results demonstrated that under moderate wind conditions (5–8 m s-1 at 10 m above water level), and hence moderate wave heights, whitecapping waves provided the dominant source of turbulent kinetic energy to only the top 10% of the water column. Under stronger wind (> 8 m s-1), and hence larger wave conditions, whitecapping waves provided the dominant source of turbulent kinetic energy over a larger portion of the water column; however, this region extended to the bottom half of the water column for only 7% of the observation period. The model results indicated that phytoplankton concentrations close to the bed were unlikely to be affected by the whitecapping of waves, and that the formation of concentration boundary layers due to benthic grazing was unlikely to be disrupted by whitecapping waves. Furthermore, vertical mixing of suspended sediment was unlikely to be affected by whitecapping waves under the conditions experienced during the 11-day experiment. Instead, the bed stress provided by tidal currents was the dominant source of turbulent kinetic energy over the bottom half of the water column for the majority of the 11-day period.

Measurements and inferences of raindrop canting angles

The canting angle distribution of raindrops derived separately from a 2-D video disdrometer and from an S-band advanced polarimetric radar are presented. In the former case, measurements were made in both natural and artificial rain. The canting angles showed a symmetric distribution about 0° with a standard deviation (σβ) of 7°–8° in low wind conditions and 12° in moderate wind conditions. In the radar-based estimates, the histogram of σβ derived from data obtained during a light stratiform rain event with embedded convection shows the mode to be around 7°, with a significant positive skewness. Around 16% of occurrences exceeded 10° and 3.3% exceeded 15°.

Effects of hydrodynamics processes on phosphorus fluxes from sediment in large, shallow Taihu Lake

The turnover of phosphorus (P) in lake sediments, a major cause of eutrophication and subsequent deterioration of water quality, is in need of deep understanding. In this study, effects of resuspension on P release were studied in cylindrical microcosms with Y-shape apparatus. The results indicated that there was a positive correlation between flux of suspended substance across sediment-water interface (Fss) and the wind speed, and an increasing FSS during each wind process followed by a steady state. The maximal FSS under light, moderate, and strong wind conditions were 299.9±41.1, 573.4±61.7, and 2093.8±215.7 g/m2, respectively. However, flux of P across sediment-water interface (FP) did not follow a similar pattern as Fss responding to wind intensity, which increased and reached the maximum in initial 120 min for light wind, then decreased gradually, with maximal flux of 9.4±1.9 mg/m2. A rapid increase of FP at the first 30 min was observed under moderate wind, with maximal flux of 11.2±0.6 mg/m2. Surprisingly, strong wind caused less FP than under light and moderate wind conditions with maximal flux of 3.5±0.9 mg/m2. Fss in water column declined obviously during the sedimentation process after winds, but FP varied with wind regime. No obvious difference was detected on FP after 8 h sedimentation process, compared with the initial value, which means little redundant P left in the water column after winds.