• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Influence of Vertical Surroundings on the Dynamic Response of Fixed Square Plate Subjected to Blast Loading

    2021-11-03 14:04:00SchoolofNavalArchitectureOceanandCivilEngineeringShanghaiJiaoTongUniversityShanghai200240China
    船舶力學(xué) 2021年10期

    ,(School of Naval Architecture,Ocean and Civil Engineering,Shanghai Jiao Tong University,Shanghai 200240,China)

    Abstract:The dynamic response of fixed square plates with different heights of vertical surroundings subjected to blast loading was studied by using numerical simulation.The covering angle concept was proposed to express the change of the surroundings height.By using the control variable method,the dynamic response of 264 square plates with vertical surroundings was analyzed,and the influence of the covering angle,explosive mass,plate thickness as well as relative detonation distance on the explosion impulse and midpoint deflection of the square plates was investigated.The results show that the existence of vertical surroundings will increase the explosion impulse acting on the target plate.When the height of the surroundings reaches up to a critical value,the value of the explosion impulse will reach its maximum and keep a constant.An empirical formula was proposed to predict the dimensionless impulse Iˉ,which is only related to the covering angle and the relative detonation distance.Moreover,another empirical formula was proposed to predict the midpoint deflection-thickness ratio of the plate considering the influence of the vertical surroundings,and its applicability was discussed.

    Key words:vertical surroundings;covering angle;deflection-thickness ratio;dynamic response;blast loading

    0 Introduction

    A solid plate structure is a basic engineering component widely applied in aerospace engineering,marine and offshore infrastructures,which is likely to be subjected to air blast loading caused by missiles or dynamites during its service[1].Therefore,it is vital to gain an understanding on the nonlinear dynamic response of the plate under blast loading,which has been a research hotspot over the past years[2-3].

    The study on the dynamic response of the plate under blast loading mainly focuses on two general topics according to the difference of impact environment:free air blast and inner blast.For the free air blast,the shock wave only causes a one-time impact on the plate before it disperses and vanishes,which has a relatively simple loading process and the research results are relatively rich[4-8].In contrast,the inner blast occurs in a closed space.It means that the shock wave will be reflected by the boundaries several times.Therefore,the loading process of an inner blast should be much more complicated.In addition,during the inner blast,a high pressure,which is called quasistatic pressure,would be maintained over a relatively long time in the closed space.Consequently,the investigation of the dynamic response of structures under inner blast is a tough issue.Related researches mainly focus on the inner blast loading[9-10],deformation[11-13]and failure modes[9,14]of classical structures and the prediction of quasi-static pressure[15]by conducting numerical and experimental investigations.However,theoretical studies in these fields are relatively rare[16].

    In engineering practice,there exists a circumstance that the blast loading is generated in semiclosed field.For instance,the target plate or the detonation point is next to some barriers,as illustrated in Fig.1.A container is partially disclosed under the inner blast,as illustrated in Fig.2.A typical example found in engineering practice is shown in Fig.3,where the explosive is detonated at the vicinity of the stiffeners.The existence of the stiffeners impedes the dispersion of the shock wave,thereby increasing the impact load on the plate[17-18].According to the unified facilities criteria design manual(UFC-3-340-02)[19],this scenario is defined as a fully-vented blast.Similar to an inner blast,multiple reflection and interaction of the shock wave may occur due to the existence of obstacles or other boundaries.But the quasi-static pressure will be absent under the fully-vented blast as the space is not fully confined.The dynamic response of plate under fully-vented blast is worth studying due to its practical significance.However,few studies have been published in this field.Geretto[11]studied the influence of the degrees of confinement on the final deformation of square mild steel plates subjected to blast loading.Equations for predicting the final midpoint deflection of the plates in three degrees of confinement(namely free air,fully vented and fully confined)were presented.Curry[20]investigated the influence of charge backing on the impact loading and deformation of plates subjected to blast waves both numerically and experimentally.It was shown that the explosion impulse applied on the plate increased 5 times when the charge was metal-backed.But the increment of the plate deformation was much less than the one of impulse.

    Fig.1 Barriers near detonation point

    Fig.2 Structure with one or more sides open

    Considering the possible impact environment as shown in Figs.1-3,the present work aims to study the dynamic response of fixed square plates with rigid vertical surroundings subjected to fully-vented blast loading.The influence of the surroundings height,plate thickness,explosive mass and detonation distance on the explosion impulse and final plastic deformation of the plate is systematically analyzed.Empirical expressions for the explosion impulse and midpoint deflection are proposed based on the parametric study.

    1 Simulation

    1.1 Model

    1.1.1 Geometry

    Fig.4 shows the structure of an explosion model which consisted of a square plate with a thickness oftand a half-width ofL=100 mm as well as vertical surroundings with a height ofh.A spherical explosive was placed above the center point of the target plate with a vertical heightH.

    Fig.4 Explosion model

    For convenience,the following parameters were defined:

    Relative detonation distance

    Relative height of surroundings

    The covering angleθis the angle between the vertical direction and the line from the detonation point to the upper end of the vertical surroundings as shown in Fig.4.

    The covering angle reflects the relationship amongh,HandL,which is more efficient than using the absolute heighthalone in the parametric study.The larger the value ofθis,the more the blast wave will act on the whole model.The covering angle without surroundings(h=0)was defined as the air blast covering angleθ0.

    1.1.2 Material

    A bilinear elasto-plastic model was employed to estimate the relationship between the true stress and the equivalent plastic strain of the material.The yielding stress is dependent on the dynamic strain rate following the Cower-Symonds model[21]:

    whereσdis the dynamic yield stress,σythe static yield stress,ε˙the equivalent plastic strain rate,and the materials constantsD=40/s andP=5.The strain hardening is taken into account as following[21]:

    whereσ0is the initial yield stress,Eis the elastic modulus,Ehis the hardening modulus andεpis the equivalent plastic strain.

    The modelling parameters consist of the densityρ=7.85×103kg/m3,the elastic modulusE=2.1×105MPa,the Poisson’s ratioμ=0.3,the static yield stressσy=235 MPa,the hardening modulusEh=250 MPa and the failure strainδ=0.28.

    The air condition is described by the ideal-gas equation,also known as the Gamma equation[21].

    wheree=2.1×105J/kg is the specific internal energy of air,ρ=1.25 kg/m3is the density of air,andγ=1.4 is the specific heat ratio.The explosive charge is simulated as high energy density air,with a density of 1 600 kg/m3and an energy density of 4.2×106J/kg.

    1.2 Validation of the nonlinear finite element results with experiments

    Geretto[11]presented the experimental results of square mild steel plates subjected to air blast loading.The target plates(200 mm×200 mm×3.1 mm)were clamped and bolted between two clamp frames which were then attached to a ballistic pendulum.The blast loads were generated by detonating different mass(30-70 g)of spherical plastic explosives at a constant distance of 100 mm from the target plate.

    Experiments in Ref.[11]were numerically simulated in order to determine a suitable finite element mesh size and validate the accuracy of the present numerical method.The finite element model of the square plate was established by using MSC.Patran.All the six degrees of freedom of four edges were restricted.The Eulerian element was used to simulate explosive charge and air,and the Lagrangian element was applied to simulate the plate.The duration of the simulation time was 0.003 s.The numerical calculations were conducted on MSC.Dytran.The coupling mode was formulated using General Coupling Algorithm,and the ROE solver was used for the solution due to its high calculation precision.It should be noted that the explosive was PE4 in Ref.[11],while the equivalent mass of TNT is used in present simulations.

    The sensitivity of the mesh size is firstly studied.Five different mesh sizes(10 mm×10 mm,8 mm×8 mm,5 mm×5 mm,4 mm×4 mm and 3 mm×3 mm)are considered here.The explosion impulse acting on the plate with five different mesh sizes are 33.35 N·s,35.16 N·s,37.98 N·s,38.95 N·s and 39.96 N·s respectively.The midpoint deflection values are 13.74 mm,13.68 mm,13.63 mm,13.60 mm and 13.58 mm respectively.In order to ensure the result accuracy while the calculation is not time-consuming,the model with the mesh size of 4 mm×4 mm is chosen.The geometry properties and coordinate system of the ship hull plate are shown in Fig.5.The longitudinal,transverse and vertical directions are denoted asx,yandz.

    Fig.5 FE model of the square plate

    The time histories of the explosion impulse and the midpoint deflection of the plate under each case are illustrated in Figs.6-7.The comparison of the numerical results and the experimental results is summarized in Tab.1 and Figs.8-9.It should be noted that the impulse in Tab.1 is the total impulse acting on the square plate when the midpoint deflection of the square plate reaches the maximum value,and the midpoint deflection in Tab.1 is the average value from 0.002 s to 0.003 s.

    Fig.6 Time history of the explosion impulse

    Fig.7 Time history of the midpoint deflection

    Fig.8 Impulse versus the mass of explosive

    Tab.1 Comparison of simulation and experiment results

    Fig.9 Midpoint deflection versus the mass of explosive

    As shown in Tab.1,the errors between the numerical and experimental results are about 2%,indicating that the present numerical method can be applied due to its high accuracy.Then,the verified numerical model was used to study the influence of vertical surroundings on the response of fixed square plate subjected to blast loading.

    1.3 Simulation case design

    Various combinations of relative surrounding height-h,explosive massm,plate thicknesstand relative detonation distance-Hwere considered.A total of 12 cases and 264 FE models were designed since each case had 22 FE models with different relative surroundings heights(-h=0,0.05,0.1,0.2,0.3,…,1.8,1.9,2.0).The simulation cases are detailed in Tab.2.

    Tab.2 Simulation cases

    2 Results and discussion

    2.1 Impulse analysis

    Fig.10 shows the variation of the explosion impulseIwith the covering angleθwhencan be observed that the influence of the covering angleθon the explosion impulse with different explosive masses is similar.The results show that the value ofIincreases with the increase ofθwhenθ<2.2 rad and then approaches a constant value whenθ>2.2 rad.In other words,the explosion impulse increases with the height of surroundings.When the height of surroundings reaches up to a critical value,the value of the explosion impulse reaches the maximum and keeps a constant.This is because the blast wave will interact with the vertical surroundings,causing the wave to reflect and converge to the target square plate,which increases the impulse of the plate.With higher surroundings,there is more reflected and converged shock wave,thereby leading to a greater impulse.However,when the height of the surroundings is larger than the charge height,the reflected shock wave no longer propagates to the target plate,and the converging effect reduces gradually.As the height of the surroundings reaches up to a critical value(θ=2.2 rad),the amount of the reflected and converged shock wave acting on the target plate will not further increase,and the value of the explosion impulse of the target plate will eventually be constant.Fig.10 also reveals that the explosion impulse is dependent on the explosive mass but independent of the plate thickness.

    Fig.10 Impulse versus covering angle under different masses of explosive(

    In order to investigate the influence of surroundings height on the explosion impulse,a dimensionless impulse as following is defined:

    whereI0is the explosion impulse without surroundings(air blasth=0),Iθis the explosion impulse with covering angleθ.Therefore,the dimensionless impulserepresents the enhancement effect of the vertical surroundings on the explosion impulse.

    The variation of the dimensionless impulsewithθwhenis shown in Fig.11.It is seen that all the values of the curves in Fig.11 are almost the same at the sameθafter non-dimensional-ization,which means the dimensionless impulseis independent of explosive mass.This is because the explosive mass affects the absolute value ofIθandI0,but the dimensionless impulseepresents the enhancement ofIθcompared withI0,which is equivalent to an amplification coefficient.Therefore,the enhancement effect of the vertical surroundings on the explosion impulse with different explosive mass is the same once the covering angleθis fixed.

    Results of the dimensionless impulseversus the covering angleθwitht=3 mm andm=60 g for different relative detonation distanceare presented in Fig.12.It is seen that the value ofincreases with the increase ofwhenθis fixed.But the trend of the dimensionless impulsewith the covering angleθf(wàn)or differentis similar to that shown in Fig.11.This indicates thatcan be expressed as a function ofθand

    Fig.11 Dimensionless impulse versus covering angle with different mass of explosive

    Fig.12 Dimensionless impulse versus covering angle with t=3 mm and m=60 g for different

    The expression for the dimensionless impulsecan be derived based on Fig.12.Whenθ<2.2 rad,is a power function ofθ;whenθ≥2.2 rad,is a constant.

    This gives the following expression:

    whereAare coefficients related to the relative detonation distance

    The coefficients for differentcan be obtained by using data-fitting method based on data points in Fig.12,and the corresponding equations and fitting curves are shown in Fig.13.

    Fig.13 Fitting curves and corresponding equations for different(t=3 mm,m=60 g)

    According to data-fitting results,the coefficients in Eq.(9)can be expressed as:

    The final form of the dimensionless impulse is obtained by substituting Eq.(10)into Eq.(9).

    The obtained empirical formula Eq.(11)was used to predict the dimensionless impulse of the fixed square plate when1.6 with differentThe dimensionless impulseobtained from simulation and empirical formula results are compared in Tab.3.It can be found that the error of the results obtained from the two methods is relatively large whenis equal to 0.05(about 9%)and 0.1(about 10%),but is less than 6%in other data points.This indicates that Eq.(11)can meet the accuracy requirements of engineering application.Therefore,the proposed empirical formula can be used to predict the explosion impulse of the square plate with vertical surroundings subjected to blast loading.Once the explosion impulseI0under air blast(without surroundings)is estimated by simulation,experiment or theoretical method,the proposed empirical formula which is only related to explosion impulseI0can be used to predict the explosion impulse.

    Tab.3 Comparison ofbetween the empirical formula predictions and the simulation results with=1.6

    Tab.3 Comparison ofbetween the empirical formula predictions and the simulation results with=1.6

    ?

    Tab.3(Continued)

    2.2 Midpoint deflection

    Based on experimental results,Nurick and Martin[2-3]proposed a dimensionless damage numberφqto characterize the explosion impulse received by a rectangular plate under air blast.

    whereIis the explosion impulse of the plate,tis the plate thickness,LandBare the plate length and plate width respectively,ρis the density andσyis the static yield stress of the material.The relation between midpoint deflection-thickness ratio(δ/t)and the dimensionless damage numberφqis as follow:

    The midpoint deflection-thickness ratio is linearly proportional toφq,so a more general form is

    Therefore,the coefficientsKcan be expressed as

    Eq.(15)was used to predict the value ofK.The variation of the coefficientKwith the covering angleθf(wàn)or different relative detonation distanceis shown in Fig.14.It can be seen that the value ofKdecreases with the increase ofθandWhenKis independent of the explosive mass,but is just a function ofθ.This indicates thatKcan be expressed as a function ofθand

    According to Fig.14,the coefficientKcan be expressed as

    Eventually,substituting Eq.(17)into Eq.(14),the final form of the empirical formula for midpoint deflection-thickness ratio is as follow:

    sults agreed well with the simulation results,as shown in Fig.15 and Tab.4.It can be seen from Tab.4 that the maximum error ofδ/tby using the empirical formula and simulation is about 7%,implying a satisfactory prediction accuracy can be obtained by use of proposed empirical formula for computing the midpoint deflection of a plate subjected to fully-vented air blast.

    Tab.4 Comparison of δ/t between the empirical formula predictions andthe simulation results with=1.6

    Tab.4 Comparison of δ/t between the empirical formula predictions andthe simulation results with=1.6

    -h 0 δ/t Error/%1.195-2.602-7.177-4.598 1.560 5.210 6.024 5.190 3.293 1.179-0.770-2.247-2.885-2.530-1.353-0.010 0.480 0.215-0.023-0.215-0.377-0.532 0.05 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 θ/rad 0.559 0.582 0.607 0.663 0.729 0.806 0.896 1.002 1.123 1.261 1.412 1.571 1.730 1.881 2.018 2.140 2.246 2.336 2.413 2.478 2.535 2.583 FE method 2.635 3.032 3.410 4.089 4.794 5.597 6.551 7.618 8.765 9.904 10.955 11.838 12.477 12.844 12.982 13.009 13.011 13.010 13.010 13.009 13.008 13.009 Empirical formula 2.666 2.953 3.165 3.901 4.868 5.888 6.946 8.013 9.053 10.021 10.871 11.572 12.117 12.519 12.806 13.007 13.073 13.038 13.007 12.981 12.959 12.940

    Fig.15 Comparison of K between the empirical formula predictions and the simulation results with

    2.3 Scope of applicability

    The coefficientKobtained from simulation results and that from Eq.(17)with different explosive masses whenare compared in Fig.16.It is shown that Eq.(17)predicts the coefficientK

    Fig.16 Comparison of K between the empirical formula and the simulation results for different explosive masses

    with a good accuracy over a certain range of explosive mass,e.g.m=50 g,60 g,and 70 g.When the mass of explosive is small,the error becomes significant.For instance,the relative large error can be seen at a low covering angle(θ<0.9 rad)whenm=40 g.Whenm=30 g,the prediction result is significantly unreliable withθ<1 rad,but is accurate when the covering angleθis larger than 1 rad.

    Fig.17 shows the relationship between the midpoint deflection-thickness ratio and the dimen-sionless damage number of the fixed square plate without surroundings under air blast withIt can be found that the deformation of the square plate can be divided into two stages with the increase of impact load:bending deformation and tensile deformation.An exponential relationship between bending deformation and dimensionless damage number can be drawn,while the relationship between the tensile deformation and dimensionless damage number is linear as shown in Eq.(14).This explains why the empirical formula underestimates the value of the coefficientKwhen the explosive mass is small.This is because the plate deformation is in the bending deformation state when the impact load is small.The linear relationship in Eq.(14)can not predict the exponential relationship accurately.Therefore,the proposed formula Eq.(18),which is based on Eq.(14),is only suitable for the tensile deformation stage when the impact load is relatively large.For the bending deformation stage,the problem needs to be treated separately and another formula should be derived.

    Fig.17 Ratio of deflectionand thicknessversus dimensionlessdamage number(1.0,h=0)

    3 Conclusions

    A series of simulations were carried out to investigate the effect of vertical surroundings on the dynamic response of a fixed square plate subjected to fully-vented blast.The influence of the parameters including covering angleθ,explosive massm,plate thicknesstand relative detonation distanceon the explosion impulse and midpoint deflection were evaluated.Based on the investigations,the following conclusions are drawn:

    (1)The existence of vertical surroundings leads to an increase of the explosion impulse acting on the target plate.The explosion impulseIincreases with the height of the surroundings.Once the height reaches up to a critical value(θ=2.2 rad),the value ofIreaches its maximum value and keeps a constant.It should be noted that the effect of plate thickness on the impulseIcan be ignored.

    (2)The dimensionless explosion impulseis a function of the covering angleθand the relative detonation distancebut is independent of the explosive mass and plate thickness.An empirical formula was proposed to predict dimensionless explosion impulse.

    (3)An improved empirical formula considering the influence of covering angleθand the relative detonation distanceis proposed to predict the midpoint deflection-thickness ratio of the fixed square plate with vertical surroundings under fully-vented blast load.

    (4)The applicability of the proposed deflection-thickness ratio empirical formula is discussed.The deformation of the plate can be divided into two stages with the increase of impact load:bending deformation and tensile deformation.The present empirical formula is only applicable in the tensile deformation stage.

    国产淫片久久久久久久久| 精品久久久久久久久久久久久| 国产高清三级在线| 黄色日韩在线| 男人舔女人下体高潮全视频| 欧美激情在线99| 久久精品夜色国产| 天堂网av新在线| 中文亚洲av片在线观看爽| 91aial.com中文字幕在线观看| 99久久精品热视频| 亚洲av熟女| 欧美色欧美亚洲另类二区| 欧美最黄视频在线播放免费| 国产乱人视频| 国产国拍精品亚洲av在线观看| 黄色视频,在线免费观看| 中文欧美无线码| 91午夜精品亚洲一区二区三区| 寂寞人妻少妇视频99o| 久久人妻av系列| 日韩一区二区三区影片| 美女 人体艺术 gogo| 欧美一级a爱片免费观看看| 白带黄色成豆腐渣| 日韩精品有码人妻一区| 好男人视频免费观看在线| 成人二区视频| 99精品在免费线老司机午夜| 久久热精品热| 亚洲av成人av| 亚洲国产精品成人久久小说 | 亚洲精品乱码久久久久久按摩| 深夜精品福利| 午夜老司机福利剧场| 亚洲av电影不卡..在线观看| 大香蕉久久网| 久久这里只有精品中国| 春色校园在线视频观看| 成人综合一区亚洲| 中文字幕av成人在线电影| 长腿黑丝高跟| 热99re8久久精品国产| 午夜精品一区二区三区免费看| 亚洲最大成人中文| 深夜a级毛片| 美女xxoo啪啪120秒动态图| a级毛色黄片| 久久久欧美国产精品| 在线观看av片永久免费下载| 最近视频中文字幕2019在线8| 麻豆成人午夜福利视频| 午夜激情福利司机影院| 91狼人影院| 神马国产精品三级电影在线观看| 中国国产av一级| 一级黄片播放器| 18+在线观看网站| 日韩人妻高清精品专区| 国国产精品蜜臀av免费| 桃色一区二区三区在线观看| 日韩国内少妇激情av| 超碰av人人做人人爽久久| 18禁在线播放成人免费| 国产黄色视频一区二区在线观看 | 欧美最黄视频在线播放免费| 亚洲真实伦在线观看| 欧美性猛交黑人性爽| 能在线免费观看的黄片| 精品久久久久久久人妻蜜臀av| 国产三级中文精品| 日本av手机在线免费观看| a级毛色黄片| 亚洲av电影不卡..在线观看| 人妻久久中文字幕网| 亚洲精品日韩在线中文字幕 | 搡女人真爽免费视频火全软件| 亚洲激情五月婷婷啪啪| 亚洲精华国产精华液的使用体验 | 五月玫瑰六月丁香| 爱豆传媒免费全集在线观看| 97超视频在线观看视频| 久久久精品94久久精品| 97在线视频观看| 麻豆国产97在线/欧美| 两个人视频免费观看高清| 在线观看午夜福利视频| 熟女人妻精品中文字幕| 亚洲一区高清亚洲精品| 亚洲国产精品国产精品| 欧美潮喷喷水| 久久久久久久久久久免费av| 女同久久另类99精品国产91| 免费看a级黄色片| 欧美性猛交╳xxx乱大交人| 婷婷色av中文字幕| 少妇高潮的动态图| 免费不卡的大黄色大毛片视频在线观看 | 蜜臀久久99精品久久宅男| 狂野欧美激情性xxxx在线观看| 久久精品夜色国产| 欧美激情久久久久久爽电影| 我的女老师完整版在线观看| 国产亚洲av嫩草精品影院| 亚洲在线自拍视频| 国产高潮美女av| 国国产精品蜜臀av免费| 夜夜夜夜夜久久久久| 伦精品一区二区三区| 哪个播放器可以免费观看大片| 免费人成视频x8x8入口观看| 内地一区二区视频在线| 国内少妇人妻偷人精品xxx网站| 国产高清视频在线观看网站| 国产视频内射| 婷婷精品国产亚洲av| 亚洲av.av天堂| 免费观看的影片在线观看| 中文字幕久久专区| 国产av在哪里看| 观看美女的网站| 高清毛片免费看| 亚洲人成网站在线播放欧美日韩| 亚洲欧洲日产国产| 亚洲久久久久久中文字幕| av福利片在线观看| 97在线视频观看| 女人被狂操c到高潮| 看免费成人av毛片| 国产蜜桃级精品一区二区三区| 黄色视频,在线免费观看| 女人十人毛片免费观看3o分钟| 日韩国内少妇激情av| 神马国产精品三级电影在线观看| 久久人人爽人人爽人人片va| 男人的好看免费观看在线视频| 久久人妻av系列| 99久久九九国产精品国产免费| 亚洲乱码一区二区免费版| 变态另类丝袜制服| 能在线免费观看的黄片| 国产精品人妻久久久久久| 最好的美女福利视频网| 国产精品国产三级国产av玫瑰| 国模一区二区三区四区视频| 中文字幕制服av| 91精品一卡2卡3卡4卡| 亚洲一区二区三区色噜噜| 村上凉子中文字幕在线| 五月玫瑰六月丁香| 国产精品女同一区二区软件| 国产精品久久视频播放| 99久国产av精品国产电影| 午夜精品国产一区二区电影 | 亚洲一区高清亚洲精品| 国产色爽女视频免费观看| av福利片在线观看| 日本与韩国留学比较| 亚洲精品国产成人久久av| 性色avwww在线观看| 干丝袜人妻中文字幕| 精品国内亚洲2022精品成人| 国产精品乱码一区二三区的特点| 一区二区三区高清视频在线| 日本五十路高清| 久久精品久久久久久噜噜老黄 | 岛国在线免费视频观看| 精品欧美国产一区二区三| 亚洲久久久久久中文字幕| 国产av麻豆久久久久久久| 亚洲国产精品合色在线| 国产三级在线视频| 亚洲av免费在线观看| 国产成人a∨麻豆精品| 国产中年淑女户外野战色| 日本一本二区三区精品| 国产伦一二天堂av在线观看| 在线观看66精品国产| 国产不卡一卡二| 午夜免费激情av| a级一级毛片免费在线观看| 精品人妻视频免费看| 亚洲高清免费不卡视频| 啦啦啦观看免费观看视频高清| 只有这里有精品99| 久久国内精品自在自线图片| 18+在线观看网站| 热99在线观看视频| 午夜激情福利司机影院| 国产白丝娇喘喷水9色精品| 深夜a级毛片| 国产毛片a区久久久久| 中文在线观看免费www的网站| 日韩,欧美,国产一区二区三区 | a级毛片免费高清观看在线播放| 嘟嘟电影网在线观看| 夫妻性生交免费视频一级片| 欧美性猛交╳xxx乱大交人| 又爽又黄a免费视频| 国产爱豆传媒在线观看| 一级毛片电影观看 | 久久久久久伊人网av| 麻豆成人午夜福利视频| 国产白丝娇喘喷水9色精品| 国产成人精品婷婷| 蜜桃久久精品国产亚洲av| 欧美一区二区精品小视频在线| 国产黄色小视频在线观看| 一本精品99久久精品77| 日韩精品青青久久久久久| 99久久无色码亚洲精品果冻| 成人欧美大片| 亚洲综合色惰| 99热这里只有是精品在线观看| 波野结衣二区三区在线| 免费看美女性在线毛片视频| 99热精品在线国产| 久久久成人免费电影| 免费在线观看成人毛片| 两个人的视频大全免费| 性插视频无遮挡在线免费观看| 亚洲在线自拍视频| 色噜噜av男人的天堂激情| 好男人在线观看高清免费视频| 特级一级黄色大片| 波多野结衣高清作品| 久久草成人影院| 国产一级毛片七仙女欲春2| 青青草视频在线视频观看| 又爽又黄a免费视频| 2021天堂中文幕一二区在线观| 能在线免费看毛片的网站| 国产成人午夜福利电影在线观看| 深夜精品福利| 国产乱人偷精品视频| 神马国产精品三级电影在线观看| 国产片特级美女逼逼视频| 亚洲最大成人中文| 亚洲无线在线观看| 精品久久久噜噜| 成人三级黄色视频| 久99久视频精品免费| 午夜免费男女啪啪视频观看| 只有这里有精品99| 最近视频中文字幕2019在线8| 亚洲va在线va天堂va国产| 欧美3d第一页| 少妇的逼水好多| 边亲边吃奶的免费视频| 欧美精品国产亚洲| 日韩亚洲欧美综合| 精品久久久久久久久久久久久| 九九在线视频观看精品| 欧美bdsm另类| 一区二区三区免费毛片| 欧美另类亚洲清纯唯美| h日本视频在线播放| 国产高清激情床上av| 久久午夜福利片| 亚洲在线自拍视频| 国产一区二区三区av在线 | 三级国产精品欧美在线观看| 好男人视频免费观看在线| 中国美白少妇内射xxxbb| 亚洲18禁久久av| 麻豆av噜噜一区二区三区| 日本黄色视频三级网站网址| 卡戴珊不雅视频在线播放| 麻豆一二三区av精品| 日韩欧美一区二区三区在线观看| 特大巨黑吊av在线直播| 国产av在哪里看| 99在线视频只有这里精品首页| 伦理电影大哥的女人| 91久久精品国产一区二区三区| 又黄又爽又刺激的免费视频.| 亚洲乱码一区二区免费版| 亚洲国产精品成人久久小说 | 一进一出抽搐动态| 成年女人看的毛片在线观看| 国模一区二区三区四区视频| 婷婷精品国产亚洲av| 日本免费a在线| 一级毛片aaaaaa免费看小| 久久久久久久久大av| 人妻久久中文字幕网| 国产av在哪里看| 国产精品久久久久久精品电影小说 | av天堂中文字幕网| 日日摸夜夜添夜夜爱| 免费av观看视频| 哪里可以看免费的av片| 国产大屁股一区二区在线视频| 久久精品国产自在天天线| a级毛色黄片| 欧美精品一区二区大全| 麻豆国产av国片精品| 美女脱内裤让男人舔精品视频 | 久久久久久久久中文| 亚洲国产欧美在线一区| 99久久成人亚洲精品观看| 3wmmmm亚洲av在线观看| 精品日产1卡2卡| 午夜福利在线在线| 热99re8久久精品国产| 亚洲欧美精品自产自拍| 插阴视频在线观看视频| 久久久久国产网址| 搡老妇女老女人老熟妇| 中文字幕av在线有码专区| 美女国产视频在线观看| 级片在线观看| 高清日韩中文字幕在线| 国产亚洲av片在线观看秒播厂 | 三级经典国产精品| 久久6这里有精品| 日日摸夜夜添夜夜添av毛片| 一级二级三级毛片免费看| 精品久久久久久久人妻蜜臀av| 又粗又硬又长又爽又黄的视频 | 国内揄拍国产精品人妻在线| 精品日产1卡2卡| 日韩欧美精品v在线| 久久久久性生活片| 一边亲一边摸免费视频| 日本三级黄在线观看| 少妇人妻一区二区三区视频| 国产69精品久久久久777片| 国产乱人视频| 精品无人区乱码1区二区| 寂寞人妻少妇视频99o| 久久久久九九精品影院| 美女脱内裤让男人舔精品视频 | 麻豆成人av视频| 中文字幕熟女人妻在线| 亚洲国产日韩欧美精品在线观看| 日韩强制内射视频| 日日摸夜夜添夜夜添av毛片| 我要搜黄色片| 国产精品99久久久久久久久| 免费大片18禁| 欧美日韩国产亚洲二区| 深爱激情五月婷婷| 一个人看视频在线观看www免费| 听说在线观看完整版免费高清| 国产av麻豆久久久久久久| 中文精品一卡2卡3卡4更新| 亚洲天堂国产精品一区在线| 爱豆传媒免费全集在线观看| 日韩大尺度精品在线看网址| 国产亚洲91精品色在线| av专区在线播放| 中文精品一卡2卡3卡4更新| 久久久久久久亚洲中文字幕| 亚洲精品色激情综合| 十八禁国产超污无遮挡网站| 一本—道久久a久久精品蜜桃钙片 精品乱码久久久久久99久播 | 日韩精品青青久久久久久| 熟女人妻精品中文字幕| 欧美又色又爽又黄视频| 欧美3d第一页| 欧美bdsm另类| 国产av一区在线观看免费| 久久精品夜夜夜夜夜久久蜜豆| av女优亚洲男人天堂| 欧美最新免费一区二区三区| 色综合站精品国产| 国产v大片淫在线免费观看| 人体艺术视频欧美日本| 久久久久久国产a免费观看| 日本在线视频免费播放| 99国产极品粉嫩在线观看| 亚洲四区av| 久久久久免费精品人妻一区二区| 看非洲黑人一级黄片| 午夜爱爱视频在线播放| 内射极品少妇av片p| 国产精品久久久久久精品电影| 国产精品一区www在线观看| 亚洲无线观看免费| 美女黄网站色视频| 欧美3d第一页| 成人亚洲欧美一区二区av| 嫩草影院精品99| 欧美成人免费av一区二区三区| 国产精品久久久久久久电影| 久久久久久国产a免费观看| 欧美高清性xxxxhd video| 国产一级毛片七仙女欲春2| 免费看美女性在线毛片视频| 精品国内亚洲2022精品成人| 一区福利在线观看| 国产成人aa在线观看| 我的老师免费观看完整版| 简卡轻食公司| 只有这里有精品99| 精品日产1卡2卡| 精品国产三级普通话版| 国产在视频线在精品| 亚洲一级一片aⅴ在线观看| 国产成人精品一,二区 | kizo精华| 狠狠狠狠99中文字幕| 国产精品.久久久| 卡戴珊不雅视频在线播放| av福利片在线观看| 日本一二三区视频观看| 欧美不卡视频在线免费观看| 久久综合国产亚洲精品| 国产av一区在线观看免费| 国内少妇人妻偷人精品xxx网站| 听说在线观看完整版免费高清| 久久久久久久亚洲中文字幕| 国产一区二区在线观看日韩| 99热6这里只有精品| 国产精品1区2区在线观看.| 少妇裸体淫交视频免费看高清| 国产高清激情床上av| 久99久视频精品免费| 亚洲成人av在线免费| 欧美性感艳星| 成人一区二区视频在线观看| 男人舔女人下体高潮全视频| 久久人人爽人人片av| av天堂中文字幕网| 午夜亚洲福利在线播放| 麻豆一二三区av精品| 国产男人的电影天堂91| 国产精品久久电影中文字幕| 国产高清激情床上av| 一本精品99久久精品77| 欧美精品国产亚洲| 日日摸夜夜添夜夜添av毛片| 国产高清有码在线观看视频| 久久久欧美国产精品| 五月玫瑰六月丁香| 日韩欧美在线乱码| 日韩成人av中文字幕在线观看| 99精品在免费线老司机午夜| 亚洲国产欧美在线一区| 欧美日本视频| 女人十人毛片免费观看3o分钟| 亚洲成人av在线免费| 日韩亚洲欧美综合| 免费看a级黄色片| 校园春色视频在线观看| 看非洲黑人一级黄片| 日韩欧美国产在线观看| 哪里可以看免费的av片| 伦精品一区二区三区| 少妇猛男粗大的猛烈进出视频 | 99热6这里只有精品| 91av网一区二区| 欧美高清性xxxxhd video| 国产精品爽爽va在线观看网站| 可以在线观看毛片的网站| 免费电影在线观看免费观看| 国产精品伦人一区二区| 精品人妻偷拍中文字幕| 嫩草影院入口| 国产精品人妻久久久久久| 色吧在线观看| 国产91av在线免费观看| 久久99蜜桃精品久久| 简卡轻食公司| 国产成人精品久久久久久| 欧美成人一区二区免费高清观看| 亚洲欧美日韩东京热| 欧美一区二区亚洲| 人人妻人人看人人澡| 久久精品综合一区二区三区| 青春草视频在线免费观看| 亚州av有码| 国产精品永久免费网站| www日本黄色视频网| 日本撒尿小便嘘嘘汇集6| 亚洲激情五月婷婷啪啪| 人妻少妇偷人精品九色| av在线蜜桃| 国产精华一区二区三区| 国产精品一区二区在线观看99 | av在线亚洲专区| 国产高清有码在线观看视频| 亚洲中文字幕日韩| 韩国av在线不卡| 久久精品夜夜夜夜夜久久蜜豆| 爱豆传媒免费全集在线观看| 少妇的逼水好多| 欧美zozozo另类| 国产一级毛片七仙女欲春2| 热99re8久久精品国产| 国产不卡一卡二| 精品久久久噜噜| 一级二级三级毛片免费看| 婷婷精品国产亚洲av| 亚洲欧美中文字幕日韩二区| 亚洲成人精品中文字幕电影| 又爽又黄a免费视频| 男女边吃奶边做爰视频| 亚洲最大成人中文| 精品欧美国产一区二区三| 亚洲欧美精品专区久久| 在线播放国产精品三级| 成年女人永久免费观看视频| 少妇高潮的动态图| 成人av在线播放网站| 18禁黄网站禁片免费观看直播| 日韩欧美国产在线观看| 最近视频中文字幕2019在线8| 亚洲经典国产精华液单| 亚洲人与动物交配视频| 热99在线观看视频| 丝袜喷水一区| 精品午夜福利在线看| 久久久a久久爽久久v久久| 久久精品影院6| av在线亚洲专区| 嫩草影院入口| 亚洲精品自拍成人| 午夜精品国产一区二区电影 | 亚洲五月天丁香| 欧美区成人在线视频| 一区二区三区免费毛片| 亚洲一区二区三区色噜噜| 性欧美人与动物交配| 99热网站在线观看| 国产在线男女| 色播亚洲综合网| 国产免费一级a男人的天堂| 色视频www国产| www.色视频.com| a级一级毛片免费在线观看| 69av精品久久久久久| 不卡一级毛片| 性欧美人与动物交配| 黑人高潮一二区| 日日摸夜夜添夜夜添av毛片| 亚洲精品国产av成人精品| 日日啪夜夜撸| 国产精品永久免费网站| 激情 狠狠 欧美| 在线观看免费视频日本深夜| 青春草国产在线视频 | 亚洲av不卡在线观看| 高清日韩中文字幕在线| 国产伦在线观看视频一区| 美女cb高潮喷水在线观看| 黄片无遮挡物在线观看| 亚洲在线观看片| 免费观看人在逋| 亚洲国产高清在线一区二区三| 啦啦啦啦在线视频资源| 亚洲一级一片aⅴ在线观看| 麻豆成人av视频| 日本欧美国产在线视频| 国产 一区精品| 啦啦啦观看免费观看视频高清| 一区二区三区四区激情视频 | 日本黄色片子视频| 国产精品免费一区二区三区在线| 麻豆成人av视频| 精品欧美国产一区二区三| 国产一区二区在线观看日韩| 免费一级毛片在线播放高清视频| 亚洲精品影视一区二区三区av| 神马国产精品三级电影在线观看| 国产大屁股一区二区在线视频| 一级毛片久久久久久久久女| 久久精品91蜜桃| 如何舔出高潮| 精品久久国产蜜桃| 在线观看66精品国产| 夜夜夜夜夜久久久久| 国产高清视频在线观看网站| 大香蕉久久网| 三级毛片av免费| 国产精品一及| 精品少妇黑人巨大在线播放 | 99久久精品一区二区三区| 免费人成视频x8x8入口观看| 久久欧美精品欧美久久欧美| 真实男女啪啪啪动态图| 亚洲av一区综合| 99久久久亚洲精品蜜臀av| 欧美另类亚洲清纯唯美| 日韩强制内射视频| 精品熟女少妇av免费看| 亚洲av电影不卡..在线观看| 91久久精品国产一区二区三区| 高清午夜精品一区二区三区 | 色吧在线观看| 国产探花极品一区二区| av女优亚洲男人天堂| 国产蜜桃级精品一区二区三区| 色5月婷婷丁香| 好男人在线观看高清免费视频| 久久亚洲精品不卡| 中国美白少妇内射xxxbb| 亚洲高清免费不卡视频| 99久久久亚洲精品蜜臀av| 免费看av在线观看网站| 久久99热这里只有精品18| 蜜桃久久精品国产亚洲av| 九九久久精品国产亚洲av麻豆| 久久久a久久爽久久v久久| 亚洲国产欧美人成| 国产精品99久久久久久久久| 欧美xxxx黑人xx丫x性爽| 国产一级毛片七仙女欲春2| 国产精品美女特级片免费视频播放器| 国产精品无大码| 久久精品国产鲁丝片午夜精品| 亚洲内射少妇av| 久久精品国产亚洲av涩爱 | 亚洲av二区三区四区|