Dynamic analysis of wind turbine tower structures in complex ocean environment

Studying and analyzing the dynamic behavior of offshore wind turbines are of great importance to ensure the safety and improve the efficiency of such expensive equipments.In this work,a tapered beam model is proposed to investigate the dynamic response of an offshore wind turbine tower on the monopile foundation assembled with rotating blades in the complex ocean environment.Several environment factors like wind,wave,current,and soil resistance are taken into account.The proposed model is ana-lytically solved with the Galerkin method.Based on the numerical results,the effects of various structure parameters including the taper angle,the height and thickness of the tower,the depth,and the diameter and the cement filler of the monopile on the funda-mental natural frequency of the wind turbine tower system are investigated in detail.It is found that the fundamental natural frequency decreases with the increase in the taper angle and the height and thickness of the tower,and increases with the increase in the diameter of the monopile.Moreover,filling cement into the monopile can effectively im-prove the fundamental natural frequency of the wind turbine tower system,but there is a critical value of the amount of cement maximizing the property of the monopile.This research may be helpful in the design and safety evaluation of offshore wind turbines.

Concurrent multi-scale design optimization of composite frame structures using the Heaviside penalization of discrete material model

This paper deals with the concurrent multi-scale optimization design of frame structure composed of glass or carbon fiber reinforced polymer laminates. In the composite frame structure, the fiber winding angle at the micro-material scale and the geometrical parameter of components of the frame in the macro-structural scale are introduced as the independent variables on the two geometrical scales. Considering manufacturing requirements, discrete fiber winding angles are specified for the micro design variable. The improved Heaviside penalization discrete material optimization interpolation scheme has been applied to achieve the discrete optimization design of the fiber winding angle. An optimization model based on the minimum structural compliance and the specified fiber material volume constraint has been established. The sensitivity information about the two geometrical scales design variables are also deduced considering the characteristics of discrete fiber winding angles. The optimization results of the fiber winding angle or the macro structural topology on the two single geometrical scales, together with the concurrent two-scale optimization, is separately studied and compared in the paper. Numerical examples in the paper show that the concurrent multi-scale optimization can further explore the coupling effect between the macro-structure and micro-material of the composite to achieve an ultralight design of the composite frame structure. The novel two geometrical scales optimization model provides a new opportunity for the design of composite structure in aerospace and other industries.

NUMERICAL SIMULATION ON THE WIND FIELD STRUCTURE OF A MOUNTAINOUS AREA BESIDE SOUTH CHINA SEA DURING THE LANDFALL OF TYPHOON MOLAVE

Leveraging the commercial CFD software FLUENT,the fine-scale three-dimensional wind structure over the Paiya Mountains on the Dapeng Peninsula near Shenzhen,a city on the seashore of South China Sea,during the landfall of Typhoon Molave has been simulated and analyzed.Through the study,a conceptual wind structure model for mountainous areas under strong wind condition is established and the following conclusions are obtained as follows:(1)FLUENT can reasonably simulate a three-dimensional wind structure over mountainous areas under strong wind conditions;(2)the kinetic effect of a mountain can intensify wind speed in the windward side of the mountain and the area over the mountain peak;and(3)in the leeward side of the mountain,wind speed is relatively lower with relatively stronger wind shear and turbulence.

Modulation of the Wind Field Structure of Initial Vortex on the Relationship between Tropical Cyclone Size and Intensity

This study investigates the modulation of initial wind field structure on the relationship between the size and intensity of a simulated vortex.A series of idealized experiments are conducted by varying the radius of maximum wind(RMW)and shape parameter of the initial vortices.The size–intensity relationship is quantified by the linear regression coefficient of the azimuthally-averaged gale-force wind radius against the maximum wind during the development stage,reflecting the degree of size expansion at the same intensity increment.The regression coefficient increases with increased RMW and decreased,with the RMW being the primary constraint.The effect of lowering on the elevation of the regression coefficient gradually stands out when the initial RMW is large.Enlarging the RMW leads to a secondary circulation with a horizontally elongated structure,which retards the intensification while promoting size expansion,thus substantially enhancing size expansion as the vortex intensifies.Broadening the wind field outside the RMW by reducing results in abounding convection in the outer region,which promotes size expansion.Based on the axisymmetric tangential wind tendency and Sawyer–Eliassen equations,when the RMW is large,the active convection in the outer region can weaken the radial inflow induced by the eyewall heating in the inner region,thus retarding the intensification by reducing the radial imports of vorticity near the RMW.

Influence of Wind Vector Structure Variation of Typhoon "Catfish" Circulation on Its Pathway Mutation

[Objective] The research aimed to study the wind vector structure variation of No.1013 strong typhoon 'catfish',and its influence on typhoon pathway mutation.[Method] According to the theory that the asymmetric structure of typhoon vortex had influence on typhoon movement,the center of No.1013 super typhoon 'catfish' was as the coordinate origin,and 850,500 hPa tangential rotation speeds within 300-500 km were decomposed into u and v components.The composite force movement tendency of typhoon was analyzed.The wind vector structure variation of No.1013 strong typhoon 'catfish' and its influence on typhoon pathway mutation were discussed.[Result] At the quick movement stage of No.1013 strong typhoon,the wind vector had obvious asymmetric structure.When the typhoon rotated in situ,the wind vector presented symmetric structure.When ΔU,ΔV and composite wind vector had obvious variations,the composite force of typhoon changed,and the moved direction also would change.The asymmetric structure of wind speed near 300-500 km around 500 and 850 hPa typhoon centers was favorable for tendency of moved pathway.The pointed directions of ΔU,ΔV and composite wind vector could be as the direction of composite force movement of typhoon.[Conclusion] The research provided reference basis for typhoon prevention.

Alfvn Waves in the Solar Wind

Alfvn waves are found to be ubiquitous in the solar wind.Recent progress in observational studies of the waves is reviewed to formulate a microscopic picture for the Alfvenic fluctuations. The main aspects of the observational properties of these waves,including the wave intervals, propagation,evolution,origin and generation,are presented.Then Alfven wave heating and acceleration of the solar wind plasma are briefly introduced.The relation of the waves to rotational and tangential discontinuities,magnetic decreases,and other relatively large-scale structures such as flux tubes/ropes,magnetic clouds and interplanetary coronal mass ejections in the solar wind is particularly investigated.Finally,some remaining open questions are also indicated due to their fundamental importance of understanding of the physical nature of Alfven waves and the role of the waves in heating and accelerating the solar wind.

Wind Structure in an Intermediate Boundary Layer Model Based on Ekman Momentum Approximation

A quasi three–dimensional, intermediate planetary boundary layer (PBL) model is developed by including inertial acceleration with the Ekman momentum approximation, but a nonlinear eddy viscosity based on Blackadar’s scheme was included to improve the theoretical model proposed by Tan and Wu (1993). The model could keep the same complexity as the classical Ekman model in numerical, but extends the conventional Ekman model to include the horizontal accelerated flow with the Ekman momentum approximation. A comparison between this modified Ekman model and other simplified accelerating PBL models is made. Results show that the Ekman model overestimates (underestimates) the wind speed and pumping velocity in the cyclonic (anticyclonic) shear flow due to the neglect of the acceleration flow, however, the semi–geostrophic Ekman model overestimates the acceleration effects resulting from the underestimating (overestimating) of the wind speed and pumping velocity in the cyclonic (anticyclonic) shear flow. The Ekman momentum approximation boundary layer model could be applied to the baroclinic atmosphere. The baroclinic Ekman momentum approximation boundary layer solution has both features of classical baroclinic Ekman layer and the Ekman momentum approximate boundary lager.

The Wind Structure in Planetary Boundary Layer

The investigations on the dynamies of the PBL have been developed in recent years. Some authors emphasized macro-dynamics and others emphasized micro-structure of the PBL. In this paper, we study and review some main characteristics of the wind field in the PBL from the view point connecting the macro-dynamics and micro-stucture of the PBL, thus providing the physical basis for the further research of the dynamics and the parameterization of the PBL.

A Practical Decision Making on Design of Fixed Offshore Wind Turbine Support Structure Considering Socio-economic Impact

Wind energy is considered one of the most promising alternative energy sources against the conventional fossil fuels.However,the deployment of these structures in deep-water for better power production is considered as a complex task.This also has raised the issue regarding selection of appropriate support structures for various sea conditions by considering environmental impact and carbon footprint.This paper considers a jacket like support structure as a case study for an intermediate water depth(50m).The jacket is considered to be located in North of Dutch Sea,and 100-extreme wave is applied as load condition.Here,the presented methodology provides an insight towards environmental/social impact made by the optimized designs in comparison with reference design.

Wind tunnel simulation of wind loading on a solid structure of revolution

The wind tunnel simulations of wind loading on a solid structure of revolution with one smooth and five rough surfaces were conducted using wind tunnel tests. Timemean and fluctuating pressure distributions on the surface were obtained, and the relationships between the roughness Reynolds number and pressure distributions were analyzed and discussed. The results show that increasing the surface roughness can significantly affect the pressure distribution, and the roughness Reynolds numbers play an important role in the change of flow patterns. The three flow patterns of subcritical, critical and supercritical flows can be classified based on the changing patterns of both the mean and the fluctuating pressure distributions. The present study suggests that the wind tunnel results obtained in the supercritical pattern reflect more closely those of full-scale solid structure of revolution at the designed wind speed.

NUMERICAL STUDY ON THE LOCAL WIND STRUCTURES FORCED BY THE COMPLEX TERRAIN OF QINGDAO AREA

In this paper, some 2-D features of the down- and up-slope winds and sea-land-breeze generated over the com- plex terrain of the Qingdao area and the interaction between them are numerically analysed by use of a 2-D non-hydrostatic mesoscale model. The simulated results in the west-east vertical cross-section show that (1) when the large-scale wind is a southerly gentle one, the generated easterly down-slope wind is much stronger than with an oppo- site background wind, and the down-slope wind can trigger and intensify the land breeze corresponding to the eastern coast of Jiaozhou Bay; (2) a gentle westerly background wind will reduce the eastward sea breeze and up-slope wind during the daytime due to a cold advection, but shows a little effect on the mesoscale circulation formed in the nighttime.

The Effect of Asymmetric Wind Structures of Tropical Cyclones on Their Tracks

A model is proposed relating a variety of factors of tropical cyclones (TCs)to their tracks, and attentions are paid to the influence of the asymmetric wind structures of TCs.Ideal numerical calculation shows that the asymmetric wind structures of TCs have conspicuousinfluence on their motion tracks. When moving due westward initially, an axisymmetric TC willdeflect right, and the overall trend is eastward. When it is asymmetric but the asymmetry is notsharp, wherever the area of maximum wind is, the TC deflects northwest first, and then, to variousareas depending on the positions of the areas of maximum wind, i.e. for the area of maximum wind inQuadrant Ⅰ, to the southeast; for in Quadrant Ⅱ, to the northeast; for in Quadrant Ⅲ, to thenorthwest; for in Quadrant IV, to the southwest. And in the above four cases, the TC tracks are allaccompanied by clockwise looping motions. With the asymmetry of the TC intensifiying, the track ofthe TC motion will be stretched further. For the area of maximum wind in Quadrants Ⅰ and Ⅱ, the TCtracks are still accompanied by clockwise looping motions; for the area of maximum wind inQuadrants Ⅲand Ⅳ, the TC tracks become oscillatory, without clockwise looping motions.

Three-dim ensional MHD simulation for the solar wind structure observed by Ulysses

Ulysses has been the first spacecraft to explore the high latitudinal regions of the heliosphere till now. During its first rapid pole-to-pole transit from September 1994 to June 1995, Ulysses observed a fast speed flow with magnitude reaching 700—800 km/s at high latitudinal region except 20°area near the ecliptic plane where the velocity is 300—400 km/s. The observations also showed a sudden jump of the velocity across the two regions. In this note, based on the characteristic and representative observations of the solar magnetic field and K-coronal polarized brightness, the large-scale solar wind structure mentioned above is reproduced by using a three-dimensional MHD model. The numerical results are basically consistent with those of Ulysses observations. Our results also show that the distributions of magnetic field and plasma number density on the solar source surface play an important role in governing this structure. Furthermore, the three-dimensional MHD model used here has a robust ability to simulate this kind of large-scale wind structure.

Major bridge development in Hong Kong,China—past,present and future

The first"modern"type of vehicular bridge was built in Hong Kong China in the 1920s.The need for an efficient transportation system to cope with population growth and enable economic development has demanded the construction of more and more bridges since the middle of the 20th century.By 2007,Hong Kong had a total of about 1300 vehicular bridges.Four of these bridges,including the Tsing Ma Bridge,Kap Shui Mun Bridge,Ting Kau Bridge,and the cable-stayed bridge on the Hong Kong-Shenzhen Western Corridor,are considered to be major bridges supported by cables.Currently,the Stonecutters Bridge on Route No.8 is under construction and is expected to be completed in late 2009.At the same time,the Hong Kong-Zhuhai-Macao Bridge will be in its detailed design stage soon.While efforts have been made by bridge builders to construct these giant structures,the upkeeping of these valuable assets at a high standard and ensuring their continuous functioning and performance during their intended lifespans will be another important task for bridge engineers.Wind and structural health monitoring system(WASHMS)will play a key role in this respect.

A REVIEW OF THE STORM CHARACTERISTICS OF TYPHOON KALMAEGI (1415) AND RELATED FORECASTING CONSIDER ATIONS IN HONG KONG

Kalmaegi(1415)required the issuance of Gale or Storm Wind Signal No.8 in Hong Kong in 2014,even though it passed by at a distance of 370 km from Hong Kong during its closest approach.Storm surges triggered by Kalmaegi caused backflow of sea water in some low lying areas in both Hong Kong and Macao.This paper reviews the use of observational data in monitoring the cyclone characteristics and studies the synoptic factors leading to its fast movement and extensive circulation.The combined analysis of multi-platform satellite wind retrieval,in-situ surface observations and aircraft reconnaissance data over the northern part of the South China Sea is found to be useful in depicting the cyclone structure.Synoptic analysis suggests that the relatively large size of Kalmaegi may be attributed to monsoon shear pattern during its formation stage and the subsequent strengthening of southwesterlies over the northern part of the South China Sea.A strong subtropical ridge north of Kalmaegi not only provides strong steering and thus its high translational speed,but also leads to extensive gale force wind distribution over its northern semi-circle.The performance of various numerical prediction models in forecasting the movement,intensity change and wind structure of Kalmaegi,as well as the storm surge triggered,is assessed and presented.

Verification of tropical cyclones(TC)wind structure forecasts from global NWP models and ensemble prediction systems(EPSs)

Forecasting wind structure of tropical cyclone(TC)is vital in assessment of impact due to high winds using Numerical Weather Prediction(NWP)model.The usual verification technique on TC wind structure forecasts are based on grid-to-grid comparisons between forecast field and the actual field.However,precision of traditional verification measures is easily affected by small scale errors and thus cannot well discriminate the accuracy or effectiveness of NWP model forecast.In this study,the Method for Object-Based Diagnostic Evaluation(MODE),which has been widely adopted in verifying precipitation fields,is utilized in TC’s wind field verification for the first time.The TC wind field forecast of deterministic NWP model and Ensemble Prediction System(EPS)of the European Centre for Medium-Range Weather Forecasts(ECMWF)over the western North Pacific and the South China Sea in 2020 were evaluated.A MODE score of 0.5 is used as a threshold value to represent a skillful(or good)forecast.It is found that the R34(radius of 34 knots)wind field structure forecasts within 72 h are good regardless of DET or EPS.The performance of R50 and R64 is slightly worse but the R50 forecasts within 48 h remain good,with MODE exceeded 0.5.The R64forecast within 48 h are worth for reference as well with MODE of around 0.5.This study states that the TC wind field structure forecast by ECMWF is skillful for TCs over the western North Pacific and the South China Sea.