The hydraulic system is the key component in the widely used wave energy converters(WEC).In this paper,we theoretically analyze and describe our investigation of the efficiency of the hydraulic system by simulation an...The hydraulic system is the key component in the widely used wave energy converters(WEC).In this paper,we theoretically analyze and describe our investigation of the efficiency of the hydraulic system by simulation and model testing of the combined heaving-buoy WEC.We derive a new governing equation that includes nonlinear hydraulic resistance in the power take-off(PTO).We conducted a physical model experiment based on a 100-kW prototype and applied a hydraulic system with an energy accumulator.The model test results reveal an important parameter related to efficiency with respect to nonlinear hydraulic resistance.We also studied the relationship between the efficiency and the initial conditions.Finally,based on our numerical simulation results,we discuss the effect on efficiency of the gas content of the hydraulic fluid and ways to reduce its impact.展开更多
Variational problem for irrotational, incompressible inviscid fluid in finite water depth is considered. Based on the variational principle, a special solution of the problem is presented under the assumption that the...Variational problem for irrotational, incompressible inviscid fluid in finite water depth is considered. Based on the variational principle, a special solution of the problem is presented under the assumption that the dispersion μ and the nonlinearity ε satisfied ε = O（μ^2） as the Lagrange thnction is expanded up to O（μ^8） . It is shown that the elevation of the free surface should be expanded to μ^4 order to ensure the Lagrange function is in μ^8 order. Comparison the nonlinear free surface profiles obtained from the solution with the corresponding ones obtained from linear solutions showed that the wave crest of the nonlinear wave is steepened but the trough is flattened compared to the linear wave as expected.展开更多
Studying the relationship between wave steepness and wave age is important for describing wind wave growth with energy balance equation of significant waves. After invoking the dispersion rela- tion of surface gravity...Studying the relationship between wave steepness and wave age is important for describing wind wave growth with energy balance equation of significant waves. After invoking the dispersion rela- tion of surface gravity wave in deep water, a new relationship between wave steepness and wave age is revealed based on the “3/2-power law” (Toba, 1972), in which wave steepness is a function of wave age with a drag coefficient as a parameter. With a given wave age, a larger drag coefficient would lead to larger wave steepness. This could be interpreted as the result of interaction between wind and waves. Comparing with previous relationships, the newly proposed one is more consistent with observational data in field and laboratory.展开更多
This article concerns the calculation of the wave period probability densities in non-Gaussiau mixed sea states. The calculations are carried out by incorporating a second order nonlinear wave model into an asymptotic...This article concerns the calculation of the wave period probability densities in non-Gaussiau mixed sea states. The calculations are carried out by incorporating a second order nonlinear wave model into an asymptotic analysis method which is a novel approach to the calculation of wave period probability densities. Since all of the calculations are performed in the probability domain, the approach avoids long time-domain sinmlations. The accuracy and efficiency of the asymptotic analysis method for calculating the wave period probability densities are validated by comparing the results predicted using the method with those predicted by using the Monte-Carlo simulation （MCS） method.展开更多
基金the support of the Marine Renewable Energy Project(No.GHME2016YY02)the National Natural Science Foundation of China(Nos.41376100 and 41706100)+1 种基金the Shandong Provincial Natural Science Key Basic Program(No.ZR2017ZA0202)the Fundamental Research Funds for the Central Universities(No.201564005)
文摘The hydraulic system is the key component in the widely used wave energy converters(WEC).In this paper,we theoretically analyze and describe our investigation of the efficiency of the hydraulic system by simulation and model testing of the combined heaving-buoy WEC.We derive a new governing equation that includes nonlinear hydraulic resistance in the power take-off(PTO).We conducted a physical model experiment based on a 100-kW prototype and applied a hydraulic system with an energy accumulator.The model test results reveal an important parameter related to efficiency with respect to nonlinear hydraulic resistance.We also studied the relationship between the efficiency and the initial conditions.Finally,based on our numerical simulation results,we discuss the effect on efficiency of the gas content of the hydraulic fluid and ways to reduce its impact.
基金Supported by the High-Tech Research and Development Program of China (863 Program, No. 2001AA633070 2003AA604040) the National Nature Science Foundation of China (No.40376008).
文摘Variational problem for irrotational, incompressible inviscid fluid in finite water depth is considered. Based on the variational principle, a special solution of the problem is presented under the assumption that the dispersion μ and the nonlinearity ε satisfied ε = O（μ^2） as the Lagrange thnction is expanded up to O（μ^8） . It is shown that the elevation of the free surface should be expanded to μ^4 order to ensure the Lagrange function is in μ^8 order. Comparison the nonlinear free surface profiles obtained from the solution with the corresponding ones obtained from linear solutions showed that the wave crest of the nonlinear wave is steepened but the trough is flattened compared to the linear wave as expected.
基金Supported by Specialized Research Fund for Doctoral Program of Higher Education (No.20040423002)by National Natural Science Foundation of China (No.40476008)
文摘Studying the relationship between wave steepness and wave age is important for describing wind wave growth with energy balance equation of significant waves. After invoking the dispersion rela- tion of surface gravity wave in deep water, a new relationship between wave steepness and wave age is revealed based on the “3/2-power law” (Toba, 1972), in which wave steepness is a function of wave age with a drag coefficient as a parameter. With a given wave age, a larger drag coefficient would lead to larger wave steepness. This could be interpreted as the result of interaction between wind and waves. Comparing with previous relationships, the newly proposed one is more consistent with observational data in field and laboratory.
基金the Research Project from the Chinese State Key Laboratory of Ocean Engineering of Shanghai Jiaotong University(No.GKZD010038)
文摘This article concerns the calculation of the wave period probability densities in non-Gaussiau mixed sea states. The calculations are carried out by incorporating a second order nonlinear wave model into an asymptotic analysis method which is a novel approach to the calculation of wave period probability densities. Since all of the calculations are performed in the probability domain, the approach avoids long time-domain sinmlations. The accuracy and efficiency of the asymptotic analysis method for calculating the wave period probability densities are validated by comparing the results predicted using the method with those predicted by using the Monte-Carlo simulation （MCS） method.
