Wake Effects on A Hybrid Semi-Submersible Floating Wind Farm with Multiple Hub Heights

Wind farms generally consist of a single turbine installed with the same hub height. As the scale of turbines increases,wake interference between turbines becomes increasingly significant, especially for floating wind turbines(FWT).Some researchers find that wind farms with multiple hub heights could increase the annual energy production(AEP),while previous studies also indicate that wake meandering could increase fatigue loading. This study investigates the wake interaction within a hybrid floating wind farm with multiple hub heights. In this study, FAST.Farm is employed to simulate a hybrid wind farm which consists of four semi-submersible FWTs(5MW and 15MW) with two different hub heights. Three typical wind speeds(below-rated, rated, and over-rated) are considered in this paper to investigate the wake meandering effects on the dynamics of two FWTs. Damage equivalent loads(DEL) of the turbine critical components are computed and analyzed for several arrangements determined by the different spacing of the four turbines. The result shows that the dynamic wake meandering significantly affects downstream turbines’ global loadings and load effects. Differences in DEL show that blade-root flapwise bending moments and mooring fairlead tensions are sensitive to the spacing of the turbines.

Study on Vortex-Induced Motions of A New Type of Deep Draft Multi-Columns FDPSO

A numerical simulation and an experimental study on vortex-induced motion(VIM) of a new type of deep draft multi-columns floating drilling production, storage and offloading(FDPSO) are presented in this paper. The main dimension, the special variable cross-section column and the cabin arrangement of the octagonal pontoon are introduced based on the result. The numerical simulation is adapted to study the effects of current incidence angles and reduced velocities on this platform's sway motion response. The 300 m water depth equivalent truncated mooring system is adopted for the model tests. The model tests are carried out to check the reliability of numerical simulation. The results consist of surge, sway and yaw motions, as well as motion trajectories. The maximum sway amplitudes for different types of offshore platform is also studied. The main results show that the peak frequencies of sway motion under different current incidence angles and reduced velocities vary around the natural frequency. The analysis result of flow field indicates that the change of distribution of vortex in vertical presents significant influences on the VIM of platform. The trend of sway amplitude ratio curve of this new type FDPSO differs from the other types of platform. Under 45° current incidence angle, the sway amplitude of this new type of FDPSO is much smaller than those of other types of offshore platform at 4.4 ≤ V_r ≤ 8.9. The typical ‘8' shape trajectory does not appear in the platform's motion trajectories.

Composite Electrodeposited PbO2/Co3O4 on a Ti Substrate as Positive Electrode Materials for a Hybrid Supercapacitor

PbO2/Co3O4 composites were prepared on a Ti substrate by means of a composite electrodeposition method in Pb2 plating solution containing dissolved nano-Co3O4 particles.X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive spectrometry(EDS)and transmission electron microscopy(TEM)were used to characterize the chemical composition and morphology of the PbCh/CogC^composites.The electrochemical and capacitanee performance of the composites were investigated by cyclic voltammetry(CV),charge-discharge tests and electrochemical impedance(EIS).The results indicate that the composites comprise rutile phase CO3O4 and 0?PbC)2?In addition,the surface of the composite electrode is rough and porous.The PbO2/Co3O4 composites exhibit a high specific capacitance up to 215 F/g,which is ten times higher than that of the pure-PbO?and two times higher than that of the pure-Co3O4 in 1 mol/L NaOH electrolytes.

Superhigh selective capture of volatile organic compounds exploiting cigarette butts-derived engineering carbonaceous adsorbent

Herein,we develop cost-efficient superhigh-performance of engineering carbonaceous adsorbent from cigarette butts using combined wet-impregnated and re-dispersed method of KOH,which optimizes the implant approach of activator,breaking the restriction of selective capture of toluene using traditional activated carbon.The Brunauer-Emmett-Teller(BET)surface area and pore volume of targeted adsorbent can attain 3088 m^(2)·g^(-1) and 1.61 cm^(3)·g^(-1),respectively,by optimizing the temperaturedependent synthetic factor effect of the adsorbent.The adsorption capacity of resultant adsorbent for presenting volatile benzene and toluene shows a positive correlation with increasing carbonization temperature of carbon precursor.Besides,we demonstrated the unsmoked and smoked butts derived adsorbents afford feeble difference in saturated adsorbed capacity of volatile organic compounds(VOCs).The highest adsorption capacity of sample CF-800 for benzene and toluene in CF group is as high as 1268.1 and 1181.6 mg·g^(-1) respectively,slightly higher than that of sample UF-800,but far outperforming reported other adsorbents.The predicted adsorption selectivity of CF-800 and UF-800 for C_(7)H_(8)/H_(2)O(g)using the DIH(difference of isosteric heats)equation reach up to ca.3800 and 7500 respectively,indicating the weak adsorbability of water vapor on the developed adsorbent and greater superiority of the smoked butts derived adsorbents in selective capture of VOCs at low relative humidity in the competitive adsorption process for practical mixed VOCs.

Wind Farm Support Vessel Extreme Roll Assessment While Docking in the Bohai Sea

Robust prediction of extreme motions during wind farm support vessel(WFSV)operation is an important safety concern that requires further extensive research as offshore wind energy industry sector widens.In particular,it is important to study the safety of operation in random sea conditions during WFSV docking against the wind tower,while workers are able to get on the tower.Docking is performed by thrusting vessel fender against wind tower(an alternative docking way by hinging is not studied here).In this paper,the finite element software AQWA has been used to analyze vessel response due to hydrodynamic wave loads,acting on a specific maintenance ship under actual sea conditions.Excessive roll may occur during certain sea conditions,especially in the beam sea,posing a risk to the crew transfer operation.The Bohai Sea is the area of diverse industrial activities such as offshore oil production,wave and wind power generation,etc.This paper advocates a novel method for estimating extreme roll statistics,based on Monte Carlo simulations(or measurements).The ACER(averaged conditional exceedance rate)method and its modification are presented in brief detail in Appendix.The proposed methodology provides an accurate extreme value prediction,utilizing available data efficiently.In this study the estimated return level values,obtained by ACER method,are compared with the corresponding return level values obtained by Gumbel method.Based on the overall performance of the proposed method,it is concluded that the ACER method can provide more robust and accurate prediction of the extreme vessel roll.The described approach may be well used at the vessel design stage,while defining optimal boat parameters would minimize potential roll.

Formation and Structural Evolution of Fe72.5B15.6Si7.8Nb1.7Zr1.7Cu0.7 Nanocrystalline Alloy

A 2.5-mm Fe72.5B15.6Si7.8Nb1.7Zr1.7Cu0.7 glassy rod was successfully fabricated using copper mold casting.The introduction of Cu resulted in the formation of large quantities of a-Fe nanoparticles embedded in the glassy matrix after isothermal annealing.The Fe72.5B15.6Si7.8Nb1.7Zr1.7Cu0.7 nanocrystalline alloy exhibited high saturation magnetization(~1.26 T) and a low coercive force(~0.8 A/m) after annealing at 833 K for 15 min due to the precipitation of ~15-nm-sized a-Fe nanoparticles in the glassy matrix.The structural evolution of the FeBSiNbZrCu amorphous alloy during the annealing process was discussed using a dual-cluster model.

Preparation and lithium storage performances of g-C_(3)N_(4)/Si nanocomposites as anode materials for lithium-ion battery

As the anode material of lithium-ion battery,silicon-based materials have a high theoretical capacity,but their volume changes greatly in the charging and discharging process.To ameliorate the volume expansion issue of silicobased anode materials,g-C_(3)N_(4)/Si nanocomposites are prepared by using the magnesium thermal reduction technique.It is well known that g-C_(3)N_(4)/Si nanocomposites can not only improve the electronic transmission ability,but also ameliorate the physical properties of the material for adapting the stress and strain caused by the volume expansion of silicon in the lithiation and delithiation process.When g-C_(3)N_(4)/Si electrode is evaluated,the initial discharge capacity of g-C_(3)N_(4)/Si nanocomposites is as high as 1033.3 mAh/g at 0.1 A/g,and its reversible capacity is maintained at 548 mAh/g after 400 cycles.Meanwhile,the improved rate capability is achieved with a relatively high reversible specific capacity of 218 mAh/g at 2.0 A/g.The superior lithium storage performances benefit from the unique g-C_(3)N_(4)/Si nanostructure,which improves electroconductivity,reduces volume expansion,and accelerates lithiumion transmission compared to pure silicon.

Facile Synthesis of Layered Sodium Manganese Oxide for Application in Asymmetric Supercapacitor

Layered sodium manganese oxides(LSMOs),with two-dimensional channels for ion diffusion,have been regarded as the promising electrode materials in the application of asymmetric supercapacitors(ASCs).In this work,the layered Na0.5Mn2O4·1.5H2O was synthesized through a facile hydrothermal method by controlling the molar ratio of sodium and manganese.When the molar ratio of sodium to manganese is 3:1,Na0.5Mn2O4·1.5H2O has shown the best capacitance of 369 F/g with current density of 0.5 A/g,and maintained a capacitance of 265 F/g after 2000 cycles.The asymmetric supercapacitor consists of the sodium manages oxides as the positive electrode and active carbon(AC)as the negative electrode in 1 mol/L Na2SO4 solution.The voltage of the asymmetric supercapacitor has been expanded to 0~2 V with an energy density of 10.13 Wh/kg at a power density of 500 W/kg based on the total weight of both active electrode materials when the mass ratio of AC to Na0.5Mn2O4·1.5H2O was 3:1.