Apparent Wind Research Articles

Ship speed power performance under relative wind profiles in relation to sensor fault detection

Statistical data analysis and visualization approaches to identify ship speed power performance under relative wind (i.e. apparent wind) profiles are considered in this study. Ship performance and navigation data of a selected vessel are analyzed, where various data anomalies, i.e. sensor related erroneous data conditions, are identified. Those erroneous data conditions are investigated and several approaches to isolate such situations are also presented by considering appropriate data visualization methods. Then, the cleaned data are used to derive various relationships among ship performance and navigation parameters that have been visualized in this study, appropriately. The results show that the wind profiles along ship routes can be used to evaluate vessel performance and navigation conditions by assuming the respective sea states relate to their wind conditions. Hence, the results are useful to derive appropriate mathematical models that represent ship performance and navigation conditions. Such mathematical models can be used for weather routing type applications (i.e. voyage planning), where the respective weather forecast can be used to derive optimal ship routes to improve vessel performance and reduce fuel consumption. This study presents not only an overview of statistical data analysis of ship performance and navigation data but also the respective challenges in data anomalies (i.e. erroneous data intervals and sensor faults) due to onboard sensors and data handling systems. Furthermore, the respective solutions to such challenges in data quality have also been presented by considering data visualization approaches.

Low-cost mobile air pollution monitoring in urban environments: a pilot study in Lubbock, Texas

ABSTRACTThe complex nature of air pollution in urban areas prevents traditional monitoring techniques from obtaining measurements representative of true human exposure. The current study assessed the capability of low-cost mobile monitors to acquire useful data in a city without a monitoring network in place (Lubbock, Texas) using a bicycle platform. The monitoring campaign resulted in 30 days of data along a 13.4 km fixed concentric route. Due to high sensitivities to airflow, the apparent wind velocity was accounted for throughout the route. The data were also normalized into percentiles in order to visualize spatial patterns.The highest estimated pollution levels were located near frequently busy intersections and roads; however, sensor issues resulted in lower confidence. Additional research is needed concerning the appropriate use of low-cost metal oxide sensors for citizen science applications, as measurements can be misleading if the user is unaware of sensors specifications. The simultaneous use of several low-cost mobile platforms, rather than a single platform, as well as the use of high-end cases, are recommended to create a more robust spatial analysis. The issues addressed from this research are important to understand for accurate and beneficial application of low-cost gaseous monitors for citizen science.

Vehicle Aerodynamic Stability Analysis under High Crosswinds

In a strong crosswind, wind direction change may result in vehicle stability loss. This paper presents a numerical study of vehicle aerodynamic stability in a high crosswind situation. We start with a model explanation and introduce the complete computational fluid dynamics (CFD) framework used in the study. Important CFD parameters such as mesh type, turbulence model, and boundary conditions are exposed and discussed in detail. We demonstrate and discuss the flow structure around a simplified truck model. Results of the CFD analysis are compared to experimental data, showing an almost perfect match. The final CFD outcomes are functions of aerodynamic coefficients that depend on the apparent wind angle. Then, CFD results are used in the application of an aerodynamic stability analysis for the truck model. Finally, the critical stability bounds are calculated, showing the marginal crosswind driving properties of the vehicles.

A methodical and taxonomic study of dispersed oak pollen (Fagaceae) from the Holocene of Rolla, Missouri, USA

Oak pollen has great potential to be used in reconstructing paleovegetation and paleoclimate. Pollen grains from Holocene sediments of Rolla, Missouri, USA were studied. The goal of this study was to evaluate the morphology of dispersed oak pollen using light and electron microscopy. Three types of oak pollen were recognized: Group 1, Group 2, and Group 3. They occurred in the sample in the following approximate percentage: 52, 32 and 16% respectively. Pollen of Group 1 corresponds to that of white oaks, pollen of Group 2 to that of red oaks. Pollen of Group 3 differs from oak pollen known for the studied region. While electron microscopy shows a good prospect for a detailed interpretation of dispersed oak pollen, many factors should be taken into account when assessing past vegetation: the paleo-forest density, location of sampling, apparent wind direction during pollination, and the “resolving ability” of pollen morphology for different oak species. The intensity of flowering and direction of the pollen transport can significantly influence the quantity of pollen of a particular species in the spectrum. The possibility of medium or long-distance transport of a small quantity of oak pollen from other regions should also be considered in the interpretations of fossil spectra.

Full-scale flying shape measurement of offwind yacht sails with photogrammetry

Yacht downwind sails are complex to study due to their non-developable shape with high camber and massively detached flow around thin and flexible membranes. Numerical simulations can now simulate this strong Fluid-Structure Interaction, but need experimental validation. It remains complex to measure spinnaker flying shapes partly because of their inherent instability, like luff flapping. This work presents full-scale experimental investigation of spinnaker shapes with simultaneous measurement of aerodynamic loads on the three sail corners, with navigation and wind data. The experimental set-up and photogrammetric method are presented. Results are analysed in the whole range of apparent wind angle for this sail. The spinnaker shape shows dramatic variations and high discrepancies with the design shape. The photogrammetric measurement produces the full 3D flying shape with a satisfactory accuracy. Even if only steady state results are given here, this new system enables time-resolved measurement of flying shapes and thus flapping of spinnakers to be investigated, which is valuable for yacht performance optimisation. On top of sailing yacht applications, the method is useful in any application where a non-developable 3D shape is to be determined, and particularly when it results from the Fluid Structure Interaction of a flexible structure with a complex flow.

“APEC Blue” association with emission control and meteorological conditions detected by multi-scale statistics

The term “APEC Blue” has been created to describe the clear sky days since the Asia-Pacific Economic Cooperation (APEC) summit held in Beijing during November 5–11, 2014. The duration of the APEC Blue is detected from November 1 to November 14 (hereafter Blue Window) by moving t test in statistics. Observations show that APEC Blue corresponds to low air pollution with respect to PM2.5, PM10, SO2, and NO2 under strict emission-control measures (ECMs) implemented in Beijing and surrounding areas. Quantitative assessment shows that ECM is more effective on reducing aerosols than the chemical constituents. Statistical investigation has revealed that the window also resulted from intensified wind variability, as well as weakened static stability of atmosphere (SSA). The wind and ECMs played key roles in reducing air pollution during November 1–7 and 11–13, and strict ECMs and weak SSA become dominant during November 7–10 under weak wind environment. Moving correlation manifests that the emission reduction for aerosols can increase the apparent wind cleanup effect, leading to significant negative correlations of them, and the period-wise changes in emission rate can be well identified by multi-scale correlations basing on wavelet decomposition. In short, this case study manifests statistically how human interference modified air quality in the mega city through controlling local and surrounding emissions in association with meteorological condition.

Is there a Hispanic Health Paradox in sensitivity to air pollution? Hospital admissions for asthma, chronic obstructive pulmonary disease and congestive heart failure associated with NO2 and PM2.5 in El Paso, TX, 2005–2010

Study objectiveLinkages between pollution and morbidity have been observed in numerous studies. But race/ethnicity has been underemphasized as a modifier of that association, and few studies have tested for a Hispanic Health Paradox in sensitivity to air pollution. MethodsDaily asthma, chronic obstructive pulmonary disease (COPD) and congestive heart failure (CHF) hospital admissions in El Paso, Texas were studied in age groups and insurance groups. Daily PM2.5 and NO2 were calculated from pollution monitors and all models adjusted for apparent temperature and wind speed. Conditional logistic regression for the case-crossover design was used for a between-group comparison and for a within-group comparison for Hispanics. ResultsHispanics were at lower risk than non-Hispanic whites and non-Hispanics of other races for NO2-associated admissions, but at greater risk for PM2.5-associated admissions. While Hispanics were generally protected with regards to NO2, Hispanic children (vs. Elderly) faced increased risk for asthma and uninsured Hispanics (vs. Private) faced increased risk for COPD admissions. While Hispanics were at increased risk of PM2.5-associated admissions, certain characteristics heightened their risks: being a Hispanic child (vs. Elderly) for asthma; being a Hispanic with Medicare (vs. Private) for asthma; and being a Hispanic with private insurance (vs. all other insurance types) for CHF. The main effect of pollution on admissions was more significant for asthma and CHF than for COPD, which had the fewest cases. ConclusionsThere was heterogeneity in sensitivity to air pollution based on social characteristics and moderate evidence for a Hispanic Health Paradox in sensitivity to NO2.

Direct Flux Measurements from Mobile Platforms at Sea: Motion and Airflow Distortion Corrections Revisited

AbstractShip-based measurements of wind speed and direct fluxes are affected by airflow distortion that can lead to a tilt of the wind vector as well as acceleration or deceleration of the wind speed. Direct flux measurements are additionally affected by the fluctuating velocity of the platform. The classic approach is to first correct the wind speed for angular and translational platform velocities and thereafter rotate the wind vector into the mean flow. This study finds that for ships under way, this leads to an overestimation of the vector tilt and biased flux estimates. This may explain the common observation that flux estimates from ships in transit have lower quality than measurements taken on station. Here an alternative approach is presented, where the flow-distortion-induced tilt of the wind vector is estimated from the 3D wind speed measurements and applied to the apparent wind vector. The tilt correction is carried out after correction for the fluctuating part of the platform velocity but before removing the ship’s mean translational velocity. This new method significantly improved the agreement of direct momentum flux measurements made from a ship under way with the parameterization of the COARE3.5 bulk model. The sensitivity of the eddy covariance measurements of momentum and scalar fluxes to the choice of the tilt-motion correction method is analyzed, and this study proposes that a reanalysis of previous direct flux measurements with the new method discussed here can improve researchers’ understanding of air–sea interaction.

D-4 風洞実験によるウィングセールの各種パラメータに関する空気力学的研究(流体特性)

Following the 33rd America's Cup which featured a trimaran versus a catamaran, and the recent 34th America's Cup in 2013 featuring AC72 catamarans with multi-element wing sail yachts sailing at unprecendented speeds, interest in wing sail technology has increased substantially. Unfortunately there is currently very little open peer-reviewed literature available with a focus on multi-element wing design for yachts. The limited available literature focuses primarily on the structures of wings and their control, rather than on the aerodynamic design. While there is substantial available literature on the aerodynamic properties of aircrafy wings, the differences in the flow domains between aeroplanes and yachts is significant. A yacht sail will operate in a Reynolds number range of 0.2 to 8 million while aircraft operate regularly in excess of 10 million. Furthermore, yachts operate in the turbulent atmospheric boundary layer and require high maximum lift coefficients at many apparent wind angles, and minimizing drag is not so critical. This paper reviews the literature on wing sail design for high performance yachts and discusses the results of wind tunnel testing. Two wings with different symmetrical profiles have been tested at low Reynolds number with surface pressure measurements to measure the effect of gap geometry, angle of attack and camber on a wing sail's performance characteristic. It has been found that for the two element wing studied, the gap size and pivot point of the rear element have only a weak influence on the lift and drag coefficients. Reynolds number has a strong effect on separation for highly cambered foils.

Wind-tunnel pressure measurements on model-scale rigid downwind sails

This paper describes an experiment that was carried out in the Twisted Flow Wind Tunnel at The University of Auckland to measure a detailed set of pressure distributions on a rigid 1/15th scale model of a modern asymmetric spinnaker. It was observed that the pressures varied considerably up the height of the spinnaker. The fine resolution of pressure taps allowed the extent of leading edge separation bubble, pressure recovery region, and effect of sail curvature to be observed quite clearly. It was found that the shape of the pressure distributions could be understood in terms of conventional aerodynamic theory. The sail performed best at an apparent wind angle of about 55°, which is its design angle, and the effect of heel was more pronounced near the head than the foot. Analysis of pressure time histories allows the large scale vortex shedding to be detected in the separation region, with a Strouhal number in the range 0.1–0.3, based on local sail chord length.

Detached Eddy Simulation of a sailing yacht

Wind tunnel experiments on a 1:15th model-scale yacht were modelled with Detached Eddy Simulations, which allowed drawing the topology of the turbulent structures in the sail wake discovering new flow features. Simulations were performed with two different grids and three different time steps. It was found that a leading edge vortex grows from the foot to the head of the spinnaker (foresail), where it deflects downstream forming the tip vortex. The twist of the spinnaker leads to a mid-span helicoidal vortex, which has a horizontal axis almost parallel to the apparent wind and rotates in the same direction of the tip vortex. Vortical spanwise tubes are released from the trailing edge of the mainsail (aftsail) and the spinnaker and roll around the tip and the mid-span vortex of the spinnaker. Vortical tubes are also detached intermittently from the sails׳ feet and these break down into smaller and smaller structures while convecting downstream. For comparison, we also performed a Reynolds-averaged Navier–Stokes simulation. The comparison between forces and pressure distributions computed with different grids and time resolutions, different turbulence models, and measured with flexible and rigid sails showed similar trends; differences between numerical results were smaller than those between experimental results.

Storm time response of the midlatitude thermosphere: Observations from a network of Fabry‐Perot interferometers

AbstractObservations of thermospheric neutral winds and temperatures obtained during a geomagnetic storm on 2 October 2013 from a network of six Fabry‐Perot interferometers (FPIs) deployed in the Midwest United States are presented. Coincident with the commencement of the storm, the apparent horizontal wind is observed to surge westward and southward (toward the equator). Simultaneous to this surge in the apparent horizontal winds, an apparent downward wind of approximately 100 m/s lasting for 6 h is observed. The apparent neutral temperature is observed to increase by approximately 400 K over all of the sites. Observations from an all‐sky imaging system operated at the Millstone Hill observatory indicate the presence of a stable auroral red (SAR) arc and diffuse red aurora during this time. We suggest that the large sustained apparent downward winds arise from contamination of the spectral profile of the nominal thermospheric 630.0 nm emission by 630.0 nm emission from a different (nonthermospheric) source. Modeling demonstrates that the effect of an additional population of 630.0 nm photons, with a distinct velocity and temperature distribution, introduces an apparent Doppler shift when the combined emissions from the two sources are analyzed as a single population. Thus, the apparent Doppler shifts should not be interpreted as the bulk motion of the thermosphere, calling into question results from previous FPI studies of midlatitude storm time thermospheric winds. One possible source of contamination could be fast O related to the infusion of low‐energy O+ ions from the magnetosphere. The presence of low‐energy O+ is supported by observations made by the Helium, Oxygen, Proton, and Electron spectrometer instruments on the twin Van Allen Probes spacecraft, which show an influx of low‐energy ions during this period. These results emphasize the importance of distributed networks of instruments in understanding the complex dynamics that occur in the upper atmosphere during disturbed conditions.

A comparison of downwind sail coefficients from tests in different wind tunnels

This paper contains results from five different tests on model sailing yacht rigs and sails. The tests were conducted by the author in four different wind tunnels over a fifteen year period between 1991 and 2007. The tests were conducted as part of development programmes for Whitbread 60 and America׳s Cup Class yachts and for particular racing teams. They were originally subject to commercial confidentiality so have not been published previously.Although the aim of the original tests was to compare sail designs and develop the performance of the individual yachts the aim of this study is somewhat different and uses the data to compare wind tunnels. The paper describes features of the wind tunnels that affect the results together with the test requirements for investigation of downwind sailing performance. A large number of individual results are presented from tests over a range of apparent wind angles and curves of maximum lift and drag coefficients from each tunnel are then compared.Although the original tests were not designed for benchmarking wind tunnels the lift coefficients from the different tests showed broad similarity within a 10% tolerance band and the drag coefficients within 20%. The difference between the tolerance bands being partly attributed to the dependence of induced drag on the square of lift. These together with similarities in the trends of the coefficients with apparent wind angle help validate the technique of wind tunnel testing of sailing yacht rigs. Conclusions have also been drawn from the results about the effect of lift on the drag of downwind sails and the overall accuracy of wind tunnel tests on rigs.

Numerical study of a flexible sail plan submitted to pitching: Hysteresis phenomenon and effect of rig adjustments

A numerical investigation of the dynamic fluid structure interaction (FSI) of a yacht sail plan submitted to harmonic pitching is presented to analyse the system׳s dynamic behaviour and the effects of motion simplifications and rigging adjustments on aerodynamic forces. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces presented as a function of the instantaneous apparent wind angle show hysteresis loops. It is shown that the hysteresis phenomenon dissipates some energy and that the dissipated energy increases strongly with the pitching reduced frequency and amplitude. The effect of reducing the real pitching motion to a simpler surge motion is investigated. Results show significant discrepancies with underestimated aerodynamic forces and no more hysteresis when a surge motion is considered. However, the superposition assumption consisting in a decomposition of the surge into two translations normal and collinear to the apparent wind is verified. Then, simulations with different dock tunes and backstay loads highlight the importance of rig adjustments on the aerodynamic forces and the dynamic behaviour of a sail plan. The energy dissipated by the hysteresis is higher for looser shrouds and a tighter backstay.

Time variations of O2(a1Δ) nightglow spots on the Venus nightside and dynamics of the upper mesosphere

The dynamical regime of the Venus upper atmosphere is mainly decomposed into three regions. The first one, located below 65km of altitude is governed by the retrograde superrotational zonal (RSZ) circulation. The second region above 130km is dominated by the subsolar to antisolar (SS–AS) circulation. The dynamics of the transition region in between are still not fully understood. However, the O2(a1Δ) nightglow emission at 1.27μm, whose emitting layer is located at ∼96km, can be used as a tracer of the dynamics in this transition region and the imaging spectrometer VIRTIS-M on board Venus Express, orbiting Venus since April 2006, acquired a large amount of nadir observations at this wavelength.Several previous studies showed that the O2(a1Δ) nightglow emission is statistically located near the antisolar point. In this study, individual VIRTIS-M nadir observations have been analyzed to investigate the variability of the phenomenon. Bright patches of 1.27μm airglow have been extracted from every observation. It appears that the location of the bright patch is highly variable, even though the brightest patches occur near the antisolar point.Nadir observations have also been divided into time series, allowing generating animations to follow the intensity and the displacement of bright patches over time. Apparent wind velocities and characteristic decay/rise times and have been deduced from these time series. The speed of the displacements varies from ∼0 up to 213ms−1, with a mean value of 54ms−1. Owing to the high variability of the direction of the displacements both in the short and the long terms, no clear trend of a global motion at ∼96km can be deduced from these observations. The mean decay time is ∼750min while the mean rise time is ∼1550min. The decay time can be explained as a combination of radiative decay and atomic oxygen transport.

The Flutterwing WindPumps: Design, NonLinearities, & Measurements

A preceding linear stability analysis showed that the pitch and roll flutter of a wing can stop in high winds. The built-in protection and variable stroke motivated development of a flutterwing windpump, because rotors pumping with a fixed stroke usefully convert only 10% of the Betz limit of the wind's annual power. Here the stroke has to be negligible at small roll not to stiffle the start of flutter in the lightest of winds, but ultimately must increase fast to safely limit the roll amplitude by absorbing all the power of the strongest oscillation. It must be largely single-acting, just as for a piston pump down a deep well, to allow a suddenly-becalmed wing to return to vertical and then restart with a new wind. The more non-linear the pump's stroke, the larger its stiffening side effect. Other non-linearities at large amplitude include the apparent wind, the centrifuging effects of roll speed and the saturation of pitch. Smoke observation of light wind flow at full +/−90° tangent pitch shows remarkable stall delay until at the end of the roll swing the leading edge sheds a massive vortex to completely reverse the wing circulation. Such a wide vortex street maximises the swept area in the actuator limit where tangent blades of constant chord keep the circulation constant between stalls. Runaway of frequency and amplitude with wind speed is avoided by static gravity imbalance replacing some dynamic imbalance and the inertia and softening of a gravity pendulum, both as favoured by large scale and low design wind speed. Also helpful are not too high pitch inertia centrifuging and an aircushion on the output pipeline which reduces the stresses and pipe frictional loss as well as the pump stiffening. Then in moderate winds, the pitch can unsaturate and the wing start to feather at lower reduced frequency, containing the power and especially the downwind bending moment. In higher wind the wing then becomes stable just leaning with the wind veer. The niche is pumping as much as the prairie rotary windpumps of diameter equalling the wing length, but with only 1/2 of the mean wind or 1/8 the mean windpower density, and with much less material. Both floating and well bases and pumps have been developed for the same pendulum, wing, and nonlinear pump winch.

Sails trim optimisation using CFD and RBF mesh morphing

The study is focused on the use of mesh morphing to explore different trims of yachts sails. In particular, four trims of the fore and aft sail of a model-scale sailing yacht were modelled leading to 16 configurations in total. Sail pressure distributions were validated with wind-tunnel measurements for all the 16 configurations, and full verification and validation was performed for one of these conditions. The 16 configurations were modelled with two different approaches: generating a new mesh for each trim condition (standard method) and using a morphed version of the baseline condition. This second novel method, based on the use of radial basis functions to morph the mesh, allows the computational time of exploring different geometries with computational fluid dynamics to be significantly decreased. Good agreement is observed between the pressure distributions computed with new meshes and morphed meshes. In order to show an example of trim optimisation, a metamodel approach is defined for the estimation of the response surface using radial basis function interpolation in the parameter space. Thanks to the continuum nature of morphing approach, the optimal trim angles for the given flow condition could be verified using new full computational fluid dynamic simulations. The original full factorial map of 16 points was replaced with a new map of 9 points with an optimal space filling approach to understand the faithfulness of a reduced metamodel. In both cases optimal point is evaluated using a fine design of experiment table built using the metamodel (41 levels for each parameter). The maximum thrust is achieved at the same trim for both metamodels.Proposed method can be easily extended to a wide number of parameters. Such flexibility is demonstrated in the present paper showing the sensitivity of results with respect to apparent wind angle and heeling angle.

A wind tunnel investigation of the aerodynamics of sailing dhows

This paper presents the results of experimental tests conducted to study the aerodynamic performance of sailing dhows. The investigation emerged from the interest shown by designers and sail-makers to understand how these sails perform, since they have never been studied before. The 43ft/13.1m and 60ft/18m classes have been tested in a wind tunnel where the effects of varying several parameters were investigated. These parameters were: heel angle, apparent wind angle, bending and stiffness of the yard, optimisation of the trimming and the influence of the mizzen on the mainsail. This is the first investigation where the aerodynamic performance of the lateen sails on sailing dhows has been investigated in a wind tunnel study.

Direct detection of classically undetectable dark matter through quantum decoherence

Although various pieces of indirect evidence about the nature of dark matter have been collected, its direct detection has eluded experimental searches despite extensive effort. If the mass of dark matter is below 1 MeV, it is essentially imperceptible to conventional detection methods because negligible energy is transferred to nuclei during collisions. Here I propose directly detecting dark matter through the quantum decoherence it causes rather than its classical effects such as recoil or ionization. I show that quantum spatial superpositions are sensitive to low-mass dark matter that is inaccessible to classical techniques. This provides new independent motivation for matter interferometry with large masses, especially on spaceborne platforms. The apparent dark matter wind we experience as the Sun travels through the Milky Way ensures interferometers and related devices are directional detectors, and so are able to provide unmistakable evidence that decoherence has galactic origins.

Dynamic behaviour of a flexible yacht sail plan

A numerical investigation of the dynamic Fluid–Structure Interaction (FSI) of a yacht sail plan submitted to harmonic pitching is presented to address both issues of aerodynamic unsteadiness and structural deformation. The FSI model – Vortex Lattice Method fluid model and Finite Element structure model – have been validated with full-scale measurements. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces presented as a function of the instantaneous apparent wind angle show hysteresis loops, suggesting that some energy is exchanged by the system. The area included in the hysteresis loop increases with the motion reduced frequency and amplitude. Comparison of rigid versus soft structures shows that FSI increases the energy exchanged by the system and that the oscillations of aerodynamic forces are underestimated when the structure deformation is not considered. Dynamic loads in the fore and aft rigging wires are dominated by structural and inertial effects. This FSI model and the obtained results may be useful firstly for yacht design, and also in the field of auxiliary wind assisted ship propulsion, or to investigate other marine soft structures.