Impact Of Long-period Wave On The Channel Wave Response Allowance

With the development of China’s the economy,the construction of domestic ports has been continuing to develop offshore,and the number of port projects abroad has increased.These open ports directly facing the ocean are suffering from long-term swells and wind waves from the ocean all year round.At present,the parameters of domestic waterway design specifications are mostly based on the calculation results in short-period wave environment,while the research on the relevant design parameters in long-period wave environment needs to be further discussed.The complex and changeable wave environment in the ocean leads to the relatively complex fluid-solid coupling motion of the ship in the wave,and the wave amplitude(wave height),wave frequency(wave period),wavelength,wave velocity and angle of wave attack all have different degrees of influence on the amplitude change of the dynamic motion response of the ship.Therefore,the calculation of the ship’s motion response caused by dynamic wave factors is the key and difficult point in determining the channel design depth.In order to ensure the safety of ships entering and leaving the port,reduce(or avoid)marine accidents such as bottom dragging,bottom hitting,stranding and out of control,reduce the waste of channel resources,and give consideration to navigation safety and efficiency,it is necessary to study and calculate the channel wave response allowancce more accurately.The main methods and conclusions of this study are as follows:(1)I adopts the approaches of theoretical analysis and potential flow theory and numerical simulation to predict the dynamic motion response of ships on the foundation of potential flow theory,thus study the combined effect of wave and swell on the channel wave response allowancce.5-common bulk carrier as the main research object,the hull system as a whole as a nonlinear spring,set up the critical matrix to solve the divergence problem of motion of ships in the ideal fluid considering the vertical movement of heaving and rolling and pitching subsidence caused by the change,establish the mass distribution model on the basis of division of hull wet surface and free surface finite element mesh,and builds finite element model of the ship,with the help of numerical simulation method to obtain the ship RAO,meanwhile,by using spectrum analysis method to estimate maximum of motion response in the short run,so as to solve the channel wave response allowancce.(2)In order to study the influence of grid density and the grid quantity on the test results,and to verify the accuracy of the research method.Taking the ship WigleyⅠas an auxiliary research object,a finite element analysis model was established based on the model value data,and the motion response of the ship WigleyⅠunder unit amplitude conditions was calculated using the three-dimensional frequency domain method.Comparison with ship pool test results shows that the method used in this paper to calculate the ship motion response is feasible,and after the grid density is changed,the ship motion response calculation result is basically unchanged,that is,the result accuracy is improved little by changing the grid density and increasing the grid quantity,but as the grid density increases,the computational efficiency will be greatly reduced.(3)By constructing a numerical analysis model to calculate the wave force of hull of traditional bulk carrier,motion response of ship and wave response allowancce by combining the methods of three-dimensional zero speed linear frequency domain with the three-dimensional nonlinear time-domain,so that the time history and spectral characteristics of the hull motion are obtained.The wave height,wave period,wave direction angle and the heave,pitch and roll wave forces of speed and channel depth are analyzed,and the motion response law and amplitude of each degree of freedom of the ship hull are studied,based on the above the wave response allowancce of each key factor is calculated.The results show that: with the change of wave height,the wave force and wave moment subjected to the pitching and heave of the ship change significantly.The overall response of the ship motion presents a linear change trend,and the change of wave height has the greatest impact on the pitching of the ship.When the wave height is less than 2m,2.97m(0.24 draft)can be taken as the wave response allowancce.With the increase of wave period,the wave forces on ships that showed a trend of increase,and moment of force of waves around the X,Y,Z axis presented the change trend of strong at first and then subdued,the peaks of rolling motion response show the increasing big of wave direction angle;with the wave cycle into consideration,when necessary,should keep at least 2.4 m 0.19 times(draft)wave response allowancce;motion response of ships are discord under the influence of different directional angle of waves of the inherent oscillation period of the approaching ships,generally speaking,with the change of wave direction Angle,the motion response of the ship hull presents the change trend of "single peak" or "single valley".Considering the influence of wave direction angle,the wave response allowancce of 3.7m(0.3 times of draft)should be retained at least.Compared with wave factors,speed of ships and fairway depth have relatively little influence on motion response of ship.(4)Taking into account the extreme sea conditions,JONSWAP spectrum and Torsethaugen spectrum were used to simulate the actual sea conditions in which pure wind waves and wind waves and swells coexist.The amplitude of the vertical motion response of the hull was calculated using the spectrum analysis method.The numerical simulation test results show that under the action of the two spectrums,the hull motion response is significant at low frequency components,and the effect of the swell component is significantly stronger than the wind wave,and as the sea state increases,the sinking amplitude of the hull becomes more significant;based on The actual sea-state wave data of once-in-a-year and once-in-a-year-on-sea areas have calculated the short-term forecast values of the motion response of traditional bulk carriers,thereby determining the numerical calculation methods and results of the wave response allowancce under long-term wind waves and swells;The sensitivity analysis of the wave parameters shows that the change of the swell parameters has a greater impact on the roll motion than the heave motion,but has a smaller impact on the pitch motion and sinking motion.The general law of vertical movement in wind and swells provides recommendations for subsequent engineering practice.