| The safety and economics of buildings with superstructures located in the splash zone,such as offshore platforms,seawalks,open wharves,and offshore highway bridges,often face the threat of wave impact.Strong wave impact can cause partial damage or overall collapse of the structure,affecting the normal operation of the marine structure.In recent years,research on flow field structure and mechanical properties of wave-structures interaction has received increasing attention in coastal and offshore engineering.The waves-structure interaction in-volves complex gas-liquid-solid interactions.In particular,systematically studies on the role of air cushion during impact are still relatively rare,which is not conducive to the complete revealing of the impact mechanism.Therefore,this paper applies the combination of physical model test and numerical model calculation to study the role of the air cushion formed between the liquid and the structural bottom plate during the wave impact process,so as to have a deeper understanding of the wave impact problem mechanism.The main research contents of this paper are as follows:(1)Perform physical model test design and complete basic data processing.According to the synchronization requirements of pressure and image acquisition in the experiment,a con-trol software,based on the UDP protocol(user datagram protocol),was designed and imple-mented.The software accomplished a high synchronization precision between gauge pressures and experimental images,and the automatic data acquisition function is integrated;Through the distortion correction,image re-projection and image stitching of the acquired image,a high precision image digitization of the shooting area is accomplished.Due to the diversity and mass of data,a software for management,analysis and processing is designed and implemented.(2)Based on the air cushion image digitization data obtained in the model tests,the law of formation of the air cushion was statistically analyzed,the effects of air cushion on wave impact pressures are analyzed.The results show that air cushions are very common within our studied situations(0.5?B/H?<2),at the time of maximum total uplift force and the time of maximum local impact pressure,the proportion of conditions with air cushion are up to 90%,based on current 260 experimental conditions.Within multiple wave action cycles,the varia-tion law of air cushions at the bottom of the horizontal plate can be roughly divided into three types:basically unchanged during different action periods,alternating between different ac-tion periods,and no obvious regularity between different action periods.The air cushion-gauge pressure synchronization analysis of a typical wave action process shows that the pressure of the air cushion portion at the time of maximum total uplift force is of the same magnitude as the pressure of wave impact,so the influence of the air cushion cannot be ignored.Wavelet analysis of gauge pressures of different variation laws shows that the wavelet energy is mainly concentrated near the excitation frequency,and when the air cushion is alternately changing,the magnitude of wavelet energy spectrum of the middle and rear gauges is obviously at 0.5 times of incident wave frequency,indicating that the air cushion mainly affects the impact pres-sures of the middle and rear parts of the plate.The wavelet analysis of the total uplift force when the air cushion changes regularly shows that the magnitude of wavelet energy spectrum is also significant at the excitation frequency.When the air cushion changes alternately,the magnitude of wavelet energy spectrum is significant at 0.5fin.Based on 1560 sets of pressure data constituting the maximum total uplift force,the maximum proportion of air phase is up to 96%,and the average value is about 60%.(3)Based on the pressure data of the physical model test,the probability distribution form of the wave impact pressure peak is analyzed.The characteristic parameters of the incident wave wave condition and the horizontal plate position are analyzed.The influences of hor-izontal plate relative clearance and incident wave parameters on the maximum local impact pressure and total uplift force are analyzed in detail.Based on the above analysis results,the empirical formula is obtained.The analysis shows that the measured gauge pressures and the local impact pressure peaks are consistent with the three-parameter Weibull distribution.The parameters of the Weibull distribution are affected by the incident wave conditions.Usually,the Weibull position parameters of pressure gauges at the front and rear ends of the horizontal plate are small,the scale parameters are larger,and the shape parameters are small,indicating that gauge pressures at the front and rear ends of the horizontal plate are generally more ran-dom.The maximum local impact pressure generally increases with the increase of the incident wave height,increases with the increase of the relative incident wavelength,decreases with the increase of the wave steepness,and is more complicated with the change of the clearance.The total uplift force generally increases with the increase of the incident wave height,increases with the increase of the relative incident wavelength,decreases with the increase of the wave steepness,and slightly increases and then decreases with the increase of the relative clearance.(4)A two-phase numerical model of 2D weakly compressible smoothed particle hydrody-namics(WCSPH)is developed to simulate the interaction between waves and thin structures.A new color domain particle(CDP)technique is proposed to overcome difficulties of applying ghost particle method to thin structures in dealing with solid boundaries.The new technique can deal with zero-thickness structures.The two-phase model is also applied here to model air and water phases.The advantages of the two-phase model are verified by a two-phase dam break problem.The basic idea and implementation process of the CDP technology are explained in detail through a hydro-static testing problem and hydrodynamic problems.The versatility and applicability of this technique in dealing with zero-thickness boundaries was verified.(5)The numerical model is used to simulate a typical situation of our physical tests.The results show that the numerical results agree well with the experimental values.The applicabil-ity of the model in dealing with the impact of wave-horizontal plate is verified.The model is applied to study the impact of waves on a horizontal plate with apron.The effects of the height of the apron on the pressure distribution,maximum local pressure and total uplift force on the bottom of the horizontal plate are analyzed in detail through a series of numerical examples.The results show that in the case of small relative clearance,the higher the apron,the smaller the impact load on the bottom of the plate is generally smaller.When the relative clearance is larger,the influence of the apron on the wave transmission is relatively weakened.The partici-pation of air with a skirt will buffer the direct impact of the wave on the plate to a certain extent,but it will not necessarily reduce the total impact. |
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