Research on the Critical Buckling Pressure of Bucket Foundations with Inner Compartments for Offshore Wind Turbines

In the process of suction penetration of bucket foundations with inner compartments for offshore wind turbines,most researches focus on soil seepage failure and soil plugs,while the buckling of foundations is rarely investigated.Therefore,theoretical calculation methods for critical buckling pressures of the skirt and bulkheads of the bucket foundation are first presented according to the stability theory of a cylindrical shell and the small deflection theory of a thin plate,respectively.Furthermore,two types of models with and without considering the skirt-soil interaction are developed for the calculation of critical buckling pressure of the bucket foundation.Taking a practical project as an example,theoretical and numerical methods are used to obtain the critical buckling pressures of a bucket foundation.In this work,the theoretical method and the finite element model considering the skirt-soil interaction for calculating the critical buckling pressure of bucket foundations are firstly proposed.The results can help to optimize the design process of offshore wind turbine foundations and improve the safety of offshore wind power systems.

Effect of ambient wind on pressure wave generated by high-speed train entering a tunnel

Using three-dimensional, unsteady N-S equations and k-ε turbulence model, the effect of ambient wind on the pressure wave generated by a high-speed train entering a tunnel was studied via numerical simulation. Pressure changes of the train surface and tunnel wall were obtained as well as the flow field around the train. Results show that when the train runs downwind, the pressure change is smaller than that generated when there is no wind. When the train runs upwind, the pressure change is larger. The pressure change is more sensitive in the upwind condition than in the downwind condition. Compared with no wind condition, when the wind velocity is 10 m/s and 30 m/s, the pressure amplitude on the train head is reduced by 2.8% and 10.5%, respectively. The wall pressure amplitude at 400 m away from the tunnel entrance is reduced by 2.4% and 13.5%, respectively. When the wind velocity is-10 m/s and-30 m/s, the pressure amplitude on the train head increases by 3.0% and 17.7%, respectively. The wall pressure amplitude at 400 m away from the tunnel entrance increases by 3.6% and 18.6%, respectively. The pressure waveform slightly changes under ambient wind due to the influence of ambient wind on the pressure wave propagation speed.

Integrated Design of D.D.I., Filament Winding and Curing Processes for Manufacturing the High Pressure Vessel(Type Ⅱ)

As energy crisis and environment pollution all around the world threaten the widespread use of fossil fuels,compressed natural gas(CNG)vehicles are explored as an alternative to the conventional gasoline powered vehicles.Because of the limited space available for the car,the composite pressure vessel(TypeⅡ)has been applied to the CNG vehicles to reach large capacity and weight lightening vehicles.High pressure vessel(TypeⅡ)is composed of a composite layer and a metal liner.The metal liner is formed by the deep drawing and ironing(D.D.I.)process,which is a complex process of deep drawing and ironing.The cylinder part is reinforced by composite layer wrapped through the filament winding process and is bonded to the liner by the curing process.In this study,an integrated design method was presented by establishing the techniques for FE analysis of entire processes(D.D.I.,filament winding and curing processes)to manufacture the CNG composite pressure vessel(TypeⅡ).Dimensions of the dies and the punches of the 1 st(cup drawing),2 nd(redrawing-ironing 1-ironing 2)and 3 rd(redrawing-ironing)stages were calculated theoretically,and shape of tractrix die to be satisfied with the minimum forming load was suggested for life improvement and manufacturing costs in the D.D.I.process.Thickness of the composite material was determined in the filament winding process,finally,conditions of the curing process(number of heating stage,curing temperature,heating rate and time)were proposed to reinforce adhesive strength between the composite layers.

Effect of change in large and fast solar wind dynamic pressure on geosynchronous magnetic field

We present a comparison of changes in large and sharp solar wind dynamic pressure, observed by several spacecraft, with fast disturbances in the magnetospheric magnetic field, measured by the geosynchronous satellites. More than 260 changes in solar wind pressure during the period 1996-2003 are selected for this study. Large statistics show that an increase （a decrease） in dynamic pressure always results in an increase （a decrease） in the magnitude of geosynchronous magnetic field. The amplitude of response to the geomagnetic field strongly depends on the location of observer relative to the noon meridian, the value of pressure before disturbance, and the change in amplitude of pressure.

Responses of wind-induced internal pressure in a two-compartment building with a dominant opening and background porosity Part 1:Theoretical formulation and experimental verification

The equations governing wind-induced internal pressure responses for a two-compartment building with a dominant opening and background porosity were derived.The unsteady form of the Bernoulli equation,the law of mass conservation,and adiabatic equation were used for the derivation.The precision of the governing equations was verified by a wind tunnel test on a rigid model of a low-rise building.The results show that the governing equations can effectively analyze the wind-induced internal pressure responses.The internal pressure responses in both compartments are suppressed due to the additional damping provided by background porosity.The responses of internal pressure in both compartments,especially in the compartment without an external opening,decrease with increased lumped leakage area.

Research on reasonable winding angle of ribbons of Flat Steel Ribbon Wound Pressure Vessel

Flat Steel Ribbon Wound Pressure Vessels (FSRWPVs) are used in many important industry areas. There is no such kind of pressure vessel exploding on operation for its reasonable structure design. Many explosion experiments on Flat Steel Ribbon Wound Pressure Vessel showed that their limited load pressure is related to the winding angle of the steel ribbons. FSRWPVs with reasonable winding angle have better security and lower cost. Reasonable angels given at the end of this paper facilitate engineering design.

The Analysis of the Line Pattern of Nonlinear Winding Filament on FRP Composite Air Vessel Resisting High Pressure

The FW process is a prefect method of manufacturing FRP composite air vessel resisting high pressure and aerial press vessel.In this paper FW pattern of FRP composite air vessel resisting high pressure was analyzed in a nutshell.The stability of FW patterns on end head is very sensitive to changing of pattern parameter.Consequently,its FW pattern was based on geodesic track.The FW angles and on equators depend on the dimension of end part and the condition of geodesic FW.Generally speaking, the polar holes of rocket engine shell are disproportional.Therefore,the FW angles of the shell column are changeable.The feasi- bility of nongeodesic FW of the shell column was discussed in this paper.Furthermore,it expounded the indispensable condition be- tween the length of shell column and the FW friction coefficient.At the same time,the general mathematic models of the movement control of nongeodesic FW were deduced.

Multivariate stationary non-Gaussian process simulation for wind pressure fields

Stochastic simulation is an important means of acquiring fluctuating wind pressures for wind induced response analyses in structural engineering. The wind pressure acting on a large-span space structure can be characterized as a stationary non-Gaussian field. This paper reviews several simulation algorithms related to the Spectral Representation Method （SRM） and the Static Transformation Method （STM）. Polynomial and Exponential transformation functions （PSTM and ESTM） are discussed. Deficiencies in current algorithms, with respect to accuracy, stability and efficiency, are analyzed, and the algorithms are improved for better practical application. In order to verify the improved algorithm, wind pressure fields on a large-span roof are simulated and compared with wind tunnel data. The simulation results fit well with the wind tunnel data, and the algorithm accuracy, stability and efficiency are shown to be better than those of current algorithms.

Pressure Distribution Induced by Ionic Wind in Needle-to-water Corona Discharge

The negative DC corona discharge in air at atmospheric pressure was investigated in a needle-to-water system to obtain the pressure distribution of corona ionic wind.The deformation of water surface was measured and the distribution of wind pressure over the water surface was calculated.The effects of varying discharge parameters,such as applied voltage,gap spacing,tip radius of needle,and the shape of grounded electrode,on the wind pressure were studied.The measured wind pressure ranges from several Pa to several tens of Pa and up to 33 Pa over a small area;the pressure is comparatively large in the center and decreases quickly outwards.In the experiment system,a higher voltage on a 3 mm gap resulted in a stronger pressure of the ionic wind;around the onset voltage,using a needle with tip radius of 50μm obtained a larger wind pressure than using a needle with 100μm tip radius,but the latter one can produce larger pressure at higher voltages.Plus,the shape of the grounded electrode only influences the wind pressure a little.

Wind-induced internal pressure fluctuations of structure with single windward opening

A frequency domain method for estimating wind-induced fluctuating internal pressure of structure with single windward opening is presented in this paper and wind tunnel tests were carried out to verify the theory. The nonlinear differential equation of internal pressure dynamics and iteration algorithm were applied to calculate fluctuating internal pressure and time domain analysis was used to verify the accuracy of the proposed method. A simplified estimation method is also provided and its scope of application is clarified. The mechanism of internal pressure fluctuation is obtained by using the proposed method in the frequency domain and a new equivalent opening ratio is defined to evaluate internal pressure fluctuation. A series of low-rise building models with various openings and internal volumes were designed for wind tunnel tests with results agreeing well with analytical results. It is shown that the proposed frequency domain method based on Gaussian distribution of internal pressure fluctuations can be applied to predict the RMS internal pressure coefficient with adequate accuracy for any opening dimensions, while the simplified method can only be used for structure with single dominant opening. Helmholtz resonance is likely to occur when the equivalent opening ratio is adequately high, and controlling individual opening dimension is an effective strategy for avoiding Helmholtz resonance in engineering.

Generation and propagation of 21-day bottom pressure variability driven by wind stress curl in the East China Sea

Between June 2015 and June 2017,two pressure-recording inverted echo sounders(PIESs)and five current and pressure-recording inverted echo sounders(CPIESs)deployed along a section across the Kerama Gap acquired a dataset of ocean bottom pressure records in which there was significant 21-day variability(Pbot21).The Pbot21,which was particularly strong from July-December 2016,was coherent with wind stress curl(WSC)on the continental shelf of the East China Sea(ECS)with a squared coherence of 0.65 for a 3-day time lag.A barotropic ocean model demonstrated the generation,propagation,and dissipation of Pbot21.The modeled results show that the Pbot21 driven by coastal ocean WSC in the ECS propagated toward the Ryukyu Island Chain(RIC),while deep ocean WSC could not induce such variability.On the continental shelf,the Pbot21 was generated nearly synchronously with the WSC from the coastline to the southeast but dissipated within a few days due to the effect of bottom friction.The detection of Pbot21 by the moored array was dependent on the 21-day WSC patterns on the continental shelf.The Pbot21 driven southeast of the Changjiang Estuary by the WSC was detected while the Pbot21generated northeast of the Changjiang Estuary was not.

Analogy Theory and Application of Pressure Difference of Wind Turbine Blade Profile

This paper aims to design an optimized blade for Horizontal Axis Wind Turbine(HWAT).Since airfoil is a basic component of blade design,an optimized airfoil(referred as SJX)was proposed based on the line theory through the weight analogy to pressure distribution of air flow.Its lift,drag,lift⁃to⁃drag ratio were compared with those NACA2409⁃34,NACA2410,and RK40 airfoils by using Profili software at fixed wind velocity and under different angles of attack.The NACA2409⁃34 airfoil was found to be greatly similar with the SJX airfoil.Based on the Wilson method,blades using SJX and NACA2490⁃34 airfoils were developed and different performance parameters such as velocity distribution,pressure distribution,and power were compared under variable wind velocities and different angles of attack ranging from-4°to 6°at different radius from the center of rotor using computational fluid dynamics(CFD)in ANSYS FLUENT.Results of the study suggested that the performance of the SJX based airfoil and blade was much more optimized.

Design and Application of a New Splitter Plate Pressure Probe for Wind Tunnel Flow Measurements

A new siplitter plate presure probe was developed for flow field measurements on an airfoil with slotted flap in a low speed wind tunnel with 7 by 10 ft test section. Wind tunnel tests were conducted at a Reynolds number of 2.2 million and Mach number of 0.13. The splitter plate was made of aluminum and had pressure taps on its one side. The probe can make many measurements in the plane of the plate simultaneously by using these pressure tabs. It was supported by a traversing strut in the wind tunnel and surveyed the flow field on the airfoil upper surface. Measured pressures were presented by isobars of coefficients. These isobars were connected with the pressure coefficients distributed over the airfoil. Results of splitter plate pressure probe compare well with other single-point measuring probes. However, results show that no matter how small the probe, its presence in the flow causes a disturbance, especially in the highly time-dependent separated flow regions.

Wind tunnel testing of wind pressures on a large gymnasium roof

A wind tunnel test was conducted for a large steel gymnasium structure. Simultaneous pressure measurements were made on its entire ellipsoidal roof in a simulated suburban boundary layer flow field. Special attention is paid to the characteristics of fluctuating wind pressures in different zones on the roof. Some selected results are presented:1) correlations between fluctuating wind pressures on both roof surfaces,2) eigenvalues and eigenvectors of covariance matrices of the fluctuating wind pressures,3) probability distributions of the fluctuating wind pressures,and 4) statistical characteristics of peak factor. Furthermore,the applicability of the quasi-steady approach is discussed in detail. Based on the results,an empirical formula for estimating the minimum pressure coefficients,using a peak factor approach,is presented. Comparison of the minimum pressure coefficients determined by the proposed formula and those obtained from the wind tunnel tests is made to examine the applicability and accuracy of the proposed formula.

A METHOD OF ESTIMATING TYPHOON CENTRAL WIND BASED ON SEA LEVEL PRESSURE OF THE TYPHOON YEARBOOK OF CHINA

Based on the Typhoon Yearbook data(1980-2000),some wind-pressure fitting relationships were established for different typhoon intensity at the different latitudes of the western North Pacific.As shown in validations with the 2001-2005 data,the relationships(namely,those between minimum sea level pressure(SLP) and maximum sustained wind near a typhoon center) are stable.They may be applied to correct the overestimated typhoon wind speeds in earlier years(1950-1979).Statistical analysis showed that the stronger the typhoon,the more stable this wind-pressure relationship is.Moreover,it is more stable at the lower latitude belt(10°N-30°N).On the basis of this result,a methodology of correcting typhoon's wind speeds and frequency in these years was put forward,and the climatological series were reconstructed of yearly total typhoon frequencies over the western North Pacific in 1950-1979 and indices were determined of destructive power of typhoons in the offshore regions of China.

Determination of Wind Pressure Coefficients for Arc-Shaped Canopy Roof with Numerical Wind Tunnel Method

In this paper,the wind load on an arc-shaped canopy roof was studied with numerical wind tunnel method(NWTM) .Three-dimensional models were set up for the canopy roof with opened or closed skylights.The air flow around the roof under wind action from three directions was analysed respectively.Wind pressure coefficients on the canopy roof were determined by NWTM.The results of NWTM agreed well with those of wind tunnel test for the roof with opened skylights,which verified the applicability and rationality of NWTM.The effect of the closure of skylights was then investigated with NWTM.It was concluded that the closure of the skylights may increase the wind suction on the top surface of the roof greatly and should be considered in the structure design of the canopy roof.

Characteristics of wind pressure pulse on large-span flat roofs

The wind pressure pulse events, among the most important characteristics of wind pressure fluctuations on large-span flat roofs, were investigated by wind tunnel tests in this paper. Incorporating the formation mechanism of wind pressure pulse events, the peak over threshold method was employed to study properties of this kind of events. The event duration time, the energy contribution, the number of the pulse events, and the distribution of average peak pressure were calculated. Probability density functions of some typical samples in separation region were also given. Results show that the non-Gaussian roof pressure is strong in the flow separation region owing to the wind pressure pulse events. Evaluations of the extreme peak pressures, which can be determined by the peak over threshold method effectively, are important to the design of building cladding.

Joint observations of the large-scale ULF wave activity from space to ground associated with the solar wind dynamic pressure enhancement

This study reports the rare ultralow-frequency(ULF) wave activity associated with the solar wind dynamic pressure enhancement that was successively observed by the GOES-17(Geostationary Operational Environmental Satellite) in the magnetosphere, the CSES(China Seismo-Electromagnetic Satellite) in the ionosphere, and the THEMIS ground-based observatories(GBO) GAKO and EAGL in the Earth's polar region during the main phase of an intense storm on 4 November 2021. Along with the enhanced-pressure solar wind moving tailward, the geomagnetic field structure experienced a large-scale change. From dawn/dusk sides to midnight, the GAKO, EAGL, and GOES-17 sequentially observed the ULF waves in a frequency range of0.04–0.36 Hz at L shells of ~5.07, 6.29, and 5.67, respectively. CSES also observed the ULF wave event with the same frequency ranges at wide L-shells of 2.52–6.22 in the nightside ionosphere. The analysis results show that the ULF waves at ionospheric altitude were mixed toroidal-poloidal mode waves. Comparing the ULF waves observed in different regions, we infer that the nightside ULF waves were directly or indirectly excited by the solar wind dynamic pressure increase: in the area of L-shells~2.52–6.29, the magnetic field line resonances(FLRs) driven by the solar wind dynamic pressure increase is an essential excitation source;on the other hand, around L~3.29, the ULF waves can also be excited by the outward expansion of the plasmapause owing to the decrease of the magnetospheric convection, and in the region of L-shells ~5.19–6.29, the ULF waves are also likely excited by the ion cyclotron instabilities driven by the solar wind dynamic pressure increase.

Back Pressure Characteristics for Turbine Channel of External-Parallel TBCC Inlet

For investigating the back pressure characteristics of turbine channel of an external-parallel turbine-based combined cycle(TBCC)inlet during the mode transition with the freestream air Mach number of 1.8,wind tunnel tests and numerical simulations are carried out.The results show that the critical back pressure of the turbine channel decreases linearly with the decrease of the open degree of splitter plate.The turbine channel has self-starting capacity when the open degree of the turbine channel is 100%.The total pressure recovery coefficient increases with the increase of back pressure when turbine channel is at supercritical and critical state.The mass capture ratio,total pressure recovery coefficient and outlet pressure ratio decrease obviously when turbine channel is at subcritical state.Results of the research would provide scheme reference and technology storage for TBCC propulsion evolution.