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1.
In the present paper, results of a parametric study conducted on the Local Joint Flexibility (LJF) of two-planar tubular DK-joints under In-Plane Bending (IPB) loads are presented. DK-joints are among the most common joint types in jacket substructure of Offshore Wind Turbines (OWTs). A total of 324 finite element (FE) analyses were carried out on 81 FE models under four types of IPB loading in order to investigate the effect of the DK-joint’s geometrical parameters on the LJF factor (fLJF). Based on the results of parametric study, the factors leading to the LJF reduction were introduced. Generated FE models were verified using the existing experimental data, FE results, and parametric equations. The effect of the weld profile was also considered. The fLJF in two-planar DK- and uniplanar K-joints were compared. Results indicated that the effect of multi-planarity on the LJF is quite significant and consequently the use of the equations already available for uniplanar K-joints to calculate the fLJF in two-planar DK-joints may lead to highly under-/over-predicting results. To handle this issue, the FE results were used to derive a set of parametric equations for the prediction of the fLJF in IPB-loaded two-planar DK-joints. The proposed equations were checked against the acceptance criteria recommended by the UK DoE and can be reliably used for the analysis and design of tubular joints in OWTs. 相似文献
2.
MASNUM海浪数值模式业务化预报与检验 总被引：2，自引：2，他引：0
介绍了MASNUM(Key Laboratory of Marine Science and Numerical Modeling)海浪数值预报系统,并利用全球和西北太平洋的Jason-1卫星数据和NDBC浮标数据中的海浪波高观测,对该预报系统进行了自2007年8月1日-2007年12月31日5个月的24,48和72 h预报结果的比较检验.模式校验结果表明,有效波高预报与观测的绝均差在0.5 m左右,从夏季到冬季,预报精度不断提高,与风场冬季预报精度较高吻合. 相似文献
3.
Verification of an operational ocean circulation-surface wave coupled forecasting system for the China's seas 总被引：3，自引：2，他引：1
An operational ocean circulation-surface wave coupled forecasting system for the seas off China and adjacent areas(OCFS-C) is developed based on parallelized circulation and wave models. It has been in operation since November 1, 2007. In this paper we comprehensively present the simulation and verification of the system, whose distinguishing feature is that the wave-induced mixing is coupled in the circulation model. In particular, with nested technique the resolution in the China's seas has been updated to(1/24)° from the global model with(1/2)°resolution. Besides, daily remote sensing sea surface temperature(SST) data have been assimilated into the model to generate a hot restart field for OCFS-C. Moreover, inter-comparisons between forecasting and independent observational data are performed to evaluate the effectiveness of OCFS-C in upper-ocean quantities predictions, including SST, mixed layer depth(MLD) and subsurface temperature. Except in conventional statistical metrics, non-dimensional skill scores(SS) is also used to evaluate forecast skill. Observations from buoys and Argo profiles are used for lead time and real time validations, which give a large SS value(more than 0.90). Besides, prediction skill for the seasonal variation of SST is confirmed. Comparisons of subsurface temperatures with Argo profiles data indicate that OCFS-C has low skill in predicting subsurface temperatures between 100 m and 150 m. Nevertheless, inter-comparisons of MLD reveal that the MLD from model is shallower than that from Argo profiles by about 12 m, i.e., OCFS-C is successful and steady in MLD predictions. Validation of 1-d, 2-d and 3-d forecasting SST shows that our operational ocean circulation-surface wave coupled forecasting model has reasonable accuracy in the upper ocean. 相似文献
4.
This paper aims to investigate the local joint flexibility (LJF) of tubular X-joints with collar plates subjected to axial load. A total number of 136 FE models were generated and analyzed to investigate the effect of collar plate size and joint geometry (η, τc, β, γ, and τ) on the local joint flexibility factor (fLJF). Also, the weld profiles and the contact between the chord wall and the collar plates were modeled in the numerical simulations. Results showed that the increase of the collar plate thickness and length results in the decrease of the fLJF. Despite the difference between the fLJF of unreinforced and collar plate reinforced X-joints, there has not been any study on the fLJF of the X-joints reinforced with collar plate. Also, there is no design equation for determining the fLJF of the collar plate reinforced X-joints. Thus, the results of the parametric study were used to develop a design formula, to determine the fLJF of X-joints reinforced with collar plates under axial load. 相似文献
5.
6.
The hydrodynamic performance of a dual cylindrical caisson breakwater (DCBW) formed by a row of caissons each of which consisting of a porous outer cylinder circumscribing an impermeable inner cylinder has been theoretically investigated. The theoretical formulation is based on the eigenfunction expansion method proposed by Spring and Monkmeyer (1974) which was further modified by Linton and Evans [Linton, C.M., Evans, D.V., 1990. The interaction of waves with arrays of vertical circular cylinders. Journal of Fluid Mechanics 215, 549–569] for an array of impermeable cylinders. The present formulation is an extension of the work of Wang and Ren [Wang, K.H., Ren, X., 1994. Wave interaction with a concentric porous cylinder system. Ocean Engineering 21(4), 343–360], wherein; the interaction of linear waves with a single concentric porous cylinder system was studied. In the present study, the formulation has been extended to the case of a group of porous dual cylinder system. Parametric studies are carried out to study the influence of porosity (G0) on the outer caisson, width of the doughnut chamber (a/b) and the angle of wave incidence on the variation in the hydrodynamic loading, wave run-up, free-surface elevation in its vicinity as well as the transmission on its lee-side. The importance of the presence of the inner cylinder in achieving the required hydrodynamic performance in terms of either protection or providing tranquility on its lee side keeping higher stability for the breakwater system is highlighted. 相似文献
7.
The deviations of the marine surface slope spectra (measured using an array of wave gauge sensors) from the theoretical estimates obtained using the linear spectral model of the wave field are analyzed. It has been indicated that the average measured full slope spectra (the sum of the slope component spectra in the orthogonal directions) is higher than the theoretical estimates by 6% at frequencies from the surface wave spectral peak (f m ) to 4.5 f m . The difference between the measured and theoretical estimates of the full slope spectrum rapidly increases at frequencies of f < f m . At f m ≈ 0.75 f m , the average measured full slope spectrum is higher than the theoretical estimate by a factor of more than 5. 相似文献
8.
长江口外海域三维水动力模拟结果及与观测的比较 总被引：1，自引：0，他引：1
Base on ECOMSED model, a theree-dimensional hydrodynamic model is developed in the offshore area near the Changjing Estuary in the East China Sea. This model in driven by tide and wind,as well as inflow and outflowcurrents such as Kuroshio,Changjing runoff. The horizontal resolution is 1/20°. There have 11 layers on the verticaldirection. The numerical results of 4 main constituents of tide(M2,S2,K1,O1)and currents are in good agreement with observation data. Compared with 20 gauge stations,the mean absolute erroe between the caluclated M2 tidal amplitude and the observed oned is only 6.72cm; the mean absolute error of phased-lag is 5.23°.For S2,the mean absolute errors of amplitude and phased-lag are 3.67cm and 7.21°,respectively. The mean absolute errors of amplitude and phased-lag for K1 are 3.25cm and 6.63° For O1,the mean absolute error of calculation and observation is relatively small, amwith observation data measured during Aug., 2006 in the East China Sea.The correlation coeffiients of current between simulation and observation are greater than 0.75 generally. The three-dimensional hydrodynamic model develiped by this paper can well describe the characters of elevation and current in the offshore near the Changjiang Estuary and can be used as hydrodynamic background to simulate the suspend sediment transport in this sea area. 相似文献
9.
《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(6):856-870
Yearlong 75 kHz acoustic Doppler current profiler (ADCP) data were obtained well above Reykjanes Ridge (northern extension of the Mid-Atlantic Ridge (MAR)). The area is characterized by relatively large semidiurnal tidal (‘D2’) currents that have (at lunar M2) more than half a decade larger variance than inertial (f) currents. However, despite the relatively weak near-inertial kinetic energy, its vertical current shear shows larger magnitudes than at M2 in an otherwise flat f−D2 band limited between frequencies 0.74 and 1.35f, which equals the inertio-gravity wave bounds [σmin, σmax](N=f). N represents the buoyancy frequency. The shear in this band dominates all shear computed at 20 m effective vertical scale. As the kinetic energy spectrum peaks at M2, but not (significantly) at S2 and N2, a difference in tidal (and inertial) scales and hence sources is observed. M2-tides contribute mostly to large-scale coherent motions. The dominant incoherent f−D2 shear is highly variable in time (∼2-day periodicity). Furthermore, inertial and tidal shear are more or less completely separated in space and time, each occurring in different layers in the vertical. The thin shear layers reflect the rapidly varying short vertical scale Ns profile, to within the ∼20 m limitation of ADCP data, rather than the large-scale smooth NL. In each of large-Ns layers Ri≈1, probably. The yearlong smoothed shear magnitude follows NL, but only as stable Ri≈5. The shear polarization is more circular than rectilinear, albeit varying with time, and highly symmetric around f. During transitions, e.g., between stratified and homogeneous layers and between waves from varying sources, near-circular motions can generate near-rectilinear shear in the direction of wave propagation (in the direction of the minor axis of the current ellipse). This contrasts with the possibility of near-rectilinear barotropic oscillatory motions generating near-circular shear under viscosity in shallow seas. 相似文献
10.
G. V. Poghosyan 《Izvestiya Atmospheric and Oceanic Physics》2013,49(7):715-731
A statistical analysis of time intervals between the dates of birth of genetic relatives has been carried out on the basis of 33 family trees. Using the Monte Carlo method, a significant departure of the distribution of birthdays from random results is detected relative to two long-period solar harmonics known from the theory of the Earth tides, i.e., a solar elliptical wave (S a ) with a period of an anomalistic year (365.259640 days) and a solar declinational wave (S sa ) with a period of half of the tropical year (182.621095 days). Further research requires larger statistical samples and involves clarifying the effect of long-period lunar harmonics, i.e., an lunar elliptical wave (M m ) with a period of an anomalistic month (27.554551 days) and a lunar declinational wave (M f ) with a period of half of a tropical month (13.660791 day), as well as the impact of important lunar and solar tides of time intervals with periods of half (14.765294 days, the interval between syzygial tides at new and full moon) and a whole (29.530588 days) synodic month. It is known that the periodic compression and stretching of the Earth’s crust at the time of the tides by means of the piezoelectric effect lead to the generation of long-period electric oscillations with periods corresponding to the harmonics of the theory of the Earth tides. The detection of these harmonics in connection with biological processes will make it possible to determine the impact of regular cosmogeophysical fluctuations (tidal waves) on the processes in the biosphere. 相似文献
11.
This study is undertaken to recalibrate eight existing energy dissipation models and find out the suitable models, which can be used to compute Hrms for a wide range of experimental conditions. The examination shows that the coefficients in the existing models are not the optimal values for a wide range of experimental conditions. Using the new calibrated coefficients, all existing models can be used for computing Hrms and the model of Battjes, J.A., Stive, M.J.F. [1985. Calibration and verification of a dissipation model for random breaking waves. Journal of Geophysical Research 90 (C5), 9159–9167] gives the best predictions. The existing models are also modified by changing the breaker height formulas in the dissipation models. The accuracy of most existing models is improved significantly by using the suitable breaker height formula. 相似文献
12.
The wave transmission, reflection, and energy dissipation of the double rows of vertical piles suspending horizontal steel C shaped bars are experimentally and theoretically studied under normal regular waves. Different wave and structural parameters are investigated e.g. the wave length, the C shaped bars draft and spacing, the supporting piles diameter and spacing, and the space between the double rows. Also, the theoretical model based on an eigenfunction expansion method is developed to study the hydrodynamic breakwater performance. In order to examine the validity of the theoretical model, the theoretical results are compared with the experimental and theoretical results obtained by different authors. Comparison between experiments and predictions showed that theoretical model provides a good estimate to the different hydrodynamic coefficients when the friction factors of the upper and the lower parts are fU = 1.5 and fL = 0.75. The present breakwater physical model gives efficiency near other similar systems of different shapes. 相似文献
13.
Arne Krtzinger Ludger Mintrop Douglas W. R. Wallace Kenneth M. Johnson Craig Neill Bronte Tilbrook Philip Towler Hisayuki Y. Inoue Masao Ishii Gary Shaffer Rodrigo F. Torres Saavedra Eiji Ohtaki Eiji Yamashita Alain Poisson Christian Brunet Bernard Schauer Catherine Goyet Greg Eischeid 《Marine Chemistry》2000,72(2-4)
The ‘International Intercomparison Exercise of fCO2 Systems’ was carried out in 1996 during the R/V Meteor Cruise 36/1 from Bermuda/UK to Gran Canaria/Spain. Nine groups from six countries (Australia, Denmark, France, Germany, Japan, USA) participated in this exercise, bringing together 15 participants with seven underway fugacity of carbon dioxide (fCO2) systems, one discrete fCO2 system, and two underway pH systems, as well as systems for discrete measurement of total alkalinity and total dissolved inorganic carbon. Here, we compare surface seawater fCO2 measured synchronously by all participating instruments. A common infrastructure (seawater and calibration gas supply), different quality checks (performance of calibration procedures for CO2, temperature measurements) and a common procedure for calculation of final fCO2 were provided to reduce the largest possible amount of controllable sources of error. The results show that under such conditions underway measurements of the fCO2 in surface seawater and overlying air can be made to a high degree of agreement (±1 μatm) with a variety of possible equilibrator and system designs. Also, discrete fCO2 measurements can be made in good agreement (±3 μatm) with underway fCO2 data sets. However, even well-designed systems, which are operated without any obvious sign of malfunction, can show significant differences of the order of 10 μatm. Based on our results, no “best choice” for the type of the equilibrator nor specifics on its dimensions and flow rates of seawater and air can be made in regard to the achievable accuracy of the fCO2 system. Measurements of equilibrator temperature do not seem to be made with the required accuracy resulting in significant errors in fCO2 results. Calculation of fCO2 from high-quality total dissolved inorganic carbon (CT) and total alkalinity (AT) measurements does not yield results comparable in accuracy and precision to fCO2 measurements. 相似文献
14.
The skill of modern wave models is such that the quality of their forecasts is, to a large degree, determined by errors in the forcing wind field. This work explores the extent to which large-scale systematic biases in modelled waves from a third generation wave model can be attributed to the forcing winds. Three different sets of winds with known global bias characteristics are used to force the WAVEWATCH III model. These winds are based on the Australian Bureau of Meteorology’s ACCESS model output, with different statistical corrections applied. Wave forecasts are verified using satellite altimeter data. It is found that a negative bias in modelled Significant Wave Height (Hs) has its origins primarily in the forcing, however, the reduction of systematic wind biases does not result in universal improvement in modelled Hs. A positive bias is present in the Southern Hemisphere due primarily to an overestimation of high Hs values in the Southern Ocean storm tracks. A positive bias is also present in the east Pacific and East Indian Ocean. This is due both to the over-prediction of waves in the Southern Ocean and lack of swell attenuation in the wave model source terms used. Smaller scale features are apparent, such as a positive bias off the Cape of Good Hope, and a negative bias off Cape Horn. In some situations, internal wave model error has been compensated for by error in the forcing winds. 相似文献
15.
《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(5):860-868
An analysis of the 234Th method for determining the export flux of particulate organic carbon (PPOC) from the upper ocean using in situ pumps or water bottles shows that the accuracy of the method (the ratio of the experimental value of PPOC divided by the true POC flux, FPOC), defined as the p-ratio, is equal to the mean settling velocity of particulate 234Th divided by that of POC. Therefore, PPOC is equivalent to the true POC flux (FPOC) and the p-ratio is equal to unity if, and only if, POC and particulate 234Th have the same mean sinking velocities. A simple particle settling model is discussed that invokes Stokes’ Law settling velocities, volume:surface area (V:SA) fractionation of C:234Th and two assemblages of particles having different sizes and densities. The model is used to illustrate the ranges of parameter values that conform to values of the p-ratio sufficiently close to unity that the experimentally determined POC flux can be considered to be an accurate representation of the true POC flux.Despite the over-simplification of real systems implicit in the model, the results suggest that p-ratios<1, equivalent to an under-estimate of the POC flux, are representative of single particle settling regimes in which the larger particles dominate the vertical flux. This follows from the assumption that the ratio of C/234Th on particles is governed by the volume to surface area (V:SA) ratio of the particles. This results in a greater proportion of 234Th compared to C being associated with the smaller, more slowly settling particles and, as a result, normalization of the POC flux to the 234Th flux provides an under-estimate of the former quantity. However, when the smaller particle assemblage dominates the vertical flux, as could occur in open ocean regimes having high aeolian inputs of dense, rapidly settling, inorganic particles, then the p-ratio could exceed unity (p-ratio >1) resulting in an over-estimate of the POC flux using the 234Th method. High levels of flocculation associated with phytoplankton blooms in productive regions of the ocean are likely to produce p-ratios approaching unity, because flocs would tend to preserve the V:SA partitioning of the original particle size distribution and thereby minimize differences in the mean settling speeds of POC and particulate 234Th (Waite, A.W., Hill, P.S., 2006. Flocculation, phytoplankton and the accuracy of 234Th-based estimates of the vertical flux of particulate organic carbon in the sea. Marine Chemistry in press). Selective sampling of the large particle fraction using, for example, 53-μm screens can produce a more accurate estimate of the true POC flux, but may not entirely shift the p-ratio to a value of unity. 相似文献
16.
通过物理模型试验研究海底子母管线分别在规则波加流和不规则波加流作用下的水动力特性。基于Morison方程,采用"等效直径法"分析得到子母管线拖曳力系数CD,惯性力系数CM和升力系数CL(CD+,CL-)。试验分别考察了流速比Uc/Uw,母管与海床间隙比e/D及子母管间的相对缝隙G/D对海底子母管线水动力系数的影响。结果表明水动力系数随Uc/Uw的增大而减小;当e/D<0.5时,海床对子母管线受力的影响比较明显,CD,CM及CL+均随e/D增大而减小,|CL-|随e/D增大而增大;对子母管间的相互影响也不可忽略,CD,CM和|CL-|均随G/D增大而减小,CL+值随G/D增大而增大。 相似文献
17.
The numerical modeling of coastal inundation from severe cyclones is a challenging area for coastal hazard mapping, emergency planning and evacuation measures. There is a need for realistic estimate of onshore coastal inundation by the operational weather centers for precise warnings to minimize loss of life and property. At present, there is no modeling effort to evaluate the extent of coastal inundation for any coastal state in India. The operational center disseminates information only on peak surge and its location just before cyclone landfall, with no prior information about onshore inundation. To bridge this gap, the present study applies the state-of-art ADCIRC hydrodynamic model to evaluate peak surge and onshore inundation along coastal Tamil Nadu for the December 2011 Thane cyclone event. Post-storm analysis and field reconnaissance survey report from IMD and ICMAM were available for the Thane cyclone to skill assess model computation. The model that computed peak surge and onshore inundation is in good concurrence with field measurements. The study signifies that near-shore beach slope has a direct bearing on onshore inundation, and its importance in numerical modeling is highlighted. This study being first of its kind for Indian coast, emphasized that coastal inundation modeling should form an integral part in a storm surge prediction system for operational needs. 相似文献
18.
通过物理模型试验研究海底子母管线分别在规则波加流和不规则波加流作用下的水动力特性。基于Morison方程,采用"等效直径法"分析得到子母管线拖曳力系数CD,惯性力系数CM和升力系数CL(CD+,CL-)。试验分别考察了流速比Uc/Uw,母管与海床间隙比e/D及子母管间的相对缝隙G/D对海底子母管线水动力系数的影响。结果表明水动力系数随Uc/Uw的增大而减小;当e/D<0.5时,海床对子母管线受力的影响比较明显,CD,CM及CL+均随e/D增大而减小,|CL-|随e/D增大而增大;对子母管间的相互影响也不可忽略,CD,CM和|CL-|均随G/D增大而减小,CL+值随G/D增大而增大。 相似文献
19.
Numerical simulation for hydrodynamic characteristics of a bionic flapping hydrofoil 总被引：2，自引：1，他引：1
In order to study the propulsion mechanism of the bionic flapping hydrofoil (BFH), a 2-DoF (heave and pitch) motion model is formulated. The hydrodynamic performance of BFH with a series of kinematical parameters is explored via numerical simulation based on FLUENT. The calculated result is compared with the experimental value of MIT and that by the panel method. Moreover, the effect of inlet velocity, the angle of attack, the heave amplitude, the pitch amplitude , the phase difference, the heave biased angle, the pitch biased angle and the oscillating frequency are investigated. The study is useful for guiding the design of bionic underwater vehicle based on flapping propulsion. It is indicated that the optimal parameters combination is v=0.5m/s, θ0=40°.θ0=30°,Ψ=90°,Фbias=0°,θbias=0°and f=0.5Hz . 相似文献
20.
Xiang Yu Baofu Jiang Binyong Li Xueli Niu Xueyu Zhang 《Marine Georesources & Geotechnology》2013,31(3):312-321
ABSTRACTHaving a reliable ocean carbon flux (f(CO2)) retrieval model is essential to monitoring the global carbon cycle and to evaluating the climate change. Remote sensing techniques provide alternatives for f(CO2) retrieval with its advantages of wide area surveys and real-time monitoring. In the present study, a semianalytical f(CO2) estimation model was developed based on remote sensing data and in situ measurements in the Chinese Bohai Sea. The used model performed well (R2?=?0.84) in deriving f(CO2) based on the collected remotely sensed dataset, including sea surface temperature, estimated sea surface salinity, wind speed, Chl-a concentration. The results showed that the distribution of partial pressure of carbon dioxide (p(CO2)) and f(CO2) varied spatially and temporally during the 12 months in 2009. The spatial fluctuations of p(CO2) and f(CO2) in Bohai Sea in summer and autumn were more obvious than that in Spring and Winter. The highest values of p(CO2) and f(CO2) generally appeared in coastal regions. Moreover, the average f(CO2) value of the 12 months showed that the Bohai Sea performed as a weak carbon source in 2009. The results provided technical and data support for carbon management and climate negotiation in the Bohai Sea. 相似文献