• <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 ?

    Structure-borne Sound Attenuation in A Multi-corner Structure with Attached Blocking Masses

    2010-06-07 10:22:18
    船舶力學 2010年9期

    (School of Naval Architecture,Ocean&Civil Eng.,Shanghai Jiao Tong University,Shanghai 200030,China)

    1 Introduction

    The attenuation of structure-borne sound in built-up structures such as those of a ship has been an issue of great interest for years to researchers concerned with mitigation of vibration and noise.Vibration at high level not only affects operation of machinery and even causes structural fatigue destruction but also becomes the source of structure-borne sound,which is the main offender of ship cabin noise.With the increasing demand for better habitability on board,it is of significance to investigate the mechanism of structure-borne sound attenuation in complex structures.

    Elastic waves will be reflected at any discontinuity on traveling in structure and only part of its energy would be transmitted to the downstream section.This process is referred to as‘attenuation of structure-borne sound’by Cremer and Heckl[1],who provided the idea for preventing vibration energy from traveling without decay.Ship structure consists basically of steel plates and beams with very low loss factor and such structure must be not only statically stable but also watertight.It is not feasible to reduce vibration transmission by means of elastic connection for ship structure.Consequently,some rigid methods,e.g.setting discontinuity and attaching blocking masses may be considered as the effective way for structure-borne sound attenuation.

    The concept of blocking mass,which is usually a beam of relatively large mass and stiffness with rectangular cross section,rigidly attached at the corner interface of plates or mounted straight on a flat plate to block transmission of elastic wave,is also introduced early in Cremer and Heckl’s book[1]on structure-borne sound.In this regard,there are several papers published in literature.Liu Honglin and Wang Deyu analyzed the vibration of plate structure with blocking mass by FEM(Finite Element Method)and made computations of corresponding sound radiation from the structure.Liu Jianhua and Jin Xianding studied the attenuation of flexural(bending)wave transmission with single blocking mass or parallel multi-blocking masses mounted on an infinite flat plate by wave approach[2-3]and the experimental results match well with theoretical analysis in their work.But all above works are restricted to situations of blocking mass attached on single plate and no corner is involved in the structure.However,the problem is complicated for two plates joined at angles in that there are both bending and longitudinal waves in two plates coupled at the corner[4].For this reason,the authors of this paper carried out analyses on attenuation of structure-borne sound at corner interface of two semi-infinite plates with attached blocking mass,taking both bending and longitudinal waves into consideration[5-6].Some new non-dimensional numbers are introduced to simplify equations which govern transmission and reflection.Numerical results revealed that blocking mass attached at the corner is effective for attenuation at high frequencies and transmission loss depends mainly on the weight of blocking mass,which was validated by some simplified experiments.

    Considering a common ship structure,structure-borne waves generated by machineries in engine room will encounter several corners along the way of propagating to the superstructure.So wave analysis in multi-corner structure with attached blocking masses is carried out in this paper.

    2 Theoretical analysis

    2.1 Expressions of wave motion in multi-corner structure

    The multi-corner structure in this paper is modeled as a built-up structure with N corner interfaces consisting of N+1 thin plates of different material and thickness(the left part of Fig.1).The plates are numbered from plate 0 to plate N with finite length li(i=0,1,2,…N),which are supposed to be much longer than the wavelength of the waves propagating in these plates to get rid of the effect of near field.Set N+1 local coordinate systems on these plates in turn and make positive xi-direction along the length of plate i,as shown in the right part of Fig.1.Thus the plates are joined end to end at two parallel boundaries xi=0 and xi=li(i=0,1,2,…N-1).The two free boundaries x0=0 and xN=lNare modeled as ‘reflection-free’ boundaries which absorb most of the incident waves.For more attenuation of structure-borne sound,blocking masses(not shown in Fig.1)may be attached to the corner interface.

    Plane incident waves generated at x0=0 by line excitation propagate along the plates of the structure one by one via corner interface.For a given frequency,the incident waves in plate 0 may be expressed in the form of transverse and longitudinal velocity as

    For the plate of finite length joined at its two boundaries with other plates,primary waves transmitted from the ‘neighbor’ plates will be reflected by the two boundaries back and forth repeatedly,and secondary waves propagating in both positive and negative xi-direction are generated time and again.Consequently,the wave field in the plate is composed of an infinite number of components,which are also partly transmitted back to the ‘neighbor’ plates when impinging on the joints.Meanwhile,to ensure dynamic equilibrium at the corner interface of two plates,part of incident bending wave will be converted to transmitted and reflected longitudinal ones and vice versa[7],along with evanescent near-field generated at the interface.For the reason that near-field waves can only affect transverse motion in the vicinity of corner interface and have almost no influence on vibration energy transmission,they are always neglected in the analysis provided that the length of the plate is much longer than the wavelength.Supposing the total(sum of the resultant components in both positive and negative directions)transverse and longitudinal velocities in plate i( i=0,1,2…N)is expressed as where v+y,iand v-y,iare the transverse velocities at xi=0 and xi=lifor resultant(sum of the primary and all secondary components)bending wave propagating in positive and negative xi-direction respectively,v+x,iand v-x,ithe corresponding longitudinal velocities for resultant longitudinal waves,respectively.

    Thus there are altogether 4(N+1)unknown velocities to be solved for the whole structure.The dynamic equilibrium condition at the ith(i=0,1,2…N)corner interface gives:

    The 4N independent equations about the resultant wave components are deduced by applying Eqs.(5)~(8)to all corners from i=1 to i=N.It is noted that the ‘reflection-free’ boundary assumption at x0=0 and xN=lNassociated with Eqs.(1)and(2)gives:

    Then the rest 4N velocities can be solved if incident wave in plate 0 is known.And the total transverse and longitudinal velocities at any position in plate i( i=0,1,2…N)are ready to be obtained through Eqs.(3)and(4).

    For a certain frequency,the spatial averaged vibration energy density is deduced as:

    where ρiis the density of plate i,[]*denotes the complex conjugate.

    Then the energy density in a certain frequency band is calculated as:

    where ω1and ω2are the lower and upper cutoff frequency of the frequency band respectively.

    2.2 Transmission efficiency and transmission loss in double-corner structure

    The approach discussed above is then applied to investigate vibration energy transmission through the simplest multi-corner structure i.e.double-corner structure consisting of three plates with blocking masses attached at the two corner interfaces,as shown in Fig.2.

    Incident waves,either bending or longitudinal,generated at x0=0 propagate throughout the whole structure via each plate and generate secondary waves when encountering corner interfaces.Under conditions of incident waves expressed in Eqs.(1)and(2)and the ‘reflection-free’boundaries at x0=0 and x2=l2,the transverse and longitudinal velocities in plate 2 are written as:

    where TBB,TBLare bending and longitudinal transmission coefficient from plate 0 to plate 2 for bending wave incidence,numerically equal to corresponding bending and longitudinal velocities at x2=0 caused by unit velocity incidence of bending wave in plate 0,and TLB,TLLthe corresponding coefficient for longitudinal wave incidence respectively.By applying Eqs.(5)~(8)to both corners,the above transmission coefficients are solved as:

    representing the resultant bending or longitudinal waves propagating in the positive x1-direction at x1=0 caused by unit primary waves transmitted from plate 0 to plate 1,in which:

    representing secondary bending or longitudinal waves at x1=0 generated by unit primary waves after traveling one ‘round trip’in plate 1,which means the process that wave starting from the first corner is reflected at the second corner and travels back to the first one.

    It is noted that velocity fields in the structure are always complex.It is more meaningful to consider vibration transmission in terms of energy(or power)other than velocity.So transmission efficiencies τBB,τBL,τLBand τLLrepresenting the ratios of vibration energy outputted from x2=l2to those inputted at x0=0 are introduced.They are expressed by using corresponding transmission coefficients from Eqs.(17)~(20)as follows:

    where P represents the power flow(subscript I for input and O for output),density per unit area mi″=ρi·hi,in which hiis the thickness,CB,iand CL,ithe corresponding group velocities of bending or longitudinal wave respectively.

    As mentioned earlier,attenuation of structure-bore sound is the main aim.And transmission loss(TL)is more commonly used to evaluate structure-borne sound attenuation in engineering for the sake of intuition and convenience of measurement.TL is defined by using transmission efficiency as in which τ may be chosen as any one of the transmission efficiencies expressed in Eqs.(29)~(32)to gain the corresponding transmission loss.

    2.3 Notes

    (1)For the reason that the transmission and reflection coefficients for corners consisting of two semi-infinite places used in Eqs.(5)~(8)are deduced under Kirchhoff’s plate theory[8],plates discussed in this paper should be restricted to thin plates.This requires λB>6h which sets an upper frequency limit as[1]

    As for frequencies higher than fmax,shear deformations in the cross section should be taken into consideration so that equations will be deduced with Mindlin’s plate theory for thick plates[9].But for ship structures,fmaxdoes not add much inconvenience for the reason that thin plate assumption can be satisfied in most cases.For example,the common thickness of steel plate used in ship structure is about 20mm for which fmaxwill be 13.5kHz and that is high enough for general purpose of structure-borne sound investigation.

    (2)The wave number kBand kLin discussion are those without consideration of damping.If the internal distributed damping in the structure is included,kBand kLshould only be replaced by[1]:

    where η is the structural loss factor,cBand cLare phase velocities for bending and longitudinal waves without damping respectively.

    3 Numerical investigation

    Fig.3 to Fig.6 show the computational results of transmission losses in double-corner structure.All three plates of the structure are steel plates of 15mm in thickness and 1 000mm in length.Both corners are at the angle of π/4 with two attached steel beams of rectangular cross section 100mm×100mm as the blocking masses.The results are also compared with those of the same structure without blocking masses.

    It is seen from the comparison of TL curves that:

    (1)All TL curves fluctuate with frequency,which indicates transmission loss in doublecorner structure depends greatly on whether the intermediate plate(plate 1)responds at resonance.As has been discussed before,secondary wave will be generated at x1=0 after any wave finishing a ‘round trip’ in plate 1.If the primary and secondary waves are in phase with each other,then the resultant velocity in the positive x1-direction will be the largest and more vibration energy will be transmitted to plate 2,corresponding to the vales in figures.And if the pri-mary and secondary waves at the first corner are out of phase or,in other words,counteract with each other,less vibration energy will be transmitted to plate 2,corresponding to the peaks in the figures.

    (2)Though fluctuating acutely,values of TL in double-corner structure with attached blocking masses are larger than those without blocking mass at high frequencies,especially for TLBB,which indicates blocking masses attached to double-corner structure are effective for structure-borne sound attenuation at high frequencies.

    (3)TL curves with and without attached blocking masses have little difference at low fre-quencies except in the vicinity of certain special frequency.

    (4)Each TL curve without attached blocking masses has a vale with negative value of TL in the vicinity of 50Hz,which is more evident for TLBBand TLBL.This vale corresponds to the first resonant frequency for bending of plate 1,at which all primary and secondary bending waves at x1=0 are in phase with each other.In this case,the first corner acts as a kind of amplifier,which is bad for structure-borne sound attenuation.But value of TL at the vale is significantly increased in case of attached blocking masses.This indicates that blocking masses improve attenuation of vibration energy at resonant frequency of plate 1.

    (5)Difference between values of TL with and without attached blocking masses for TLBBand TLLBis larger than that for TLBLand TLLLat high frequencies,which indicates blocking masses are more effective for bending wave attenuation comparing with longitudinal one.

    4 Experiment

    An experiment on a simplified test sample analogous to the hull of a ship was carried out to validate the results from numerical computation.The test sample is a symmetrical structure consisting of six steel plates(2mm in thickness)numbered from①to⑥as shown in Fig.7.A rigid beam is attached to the joint of plate①and②at the centre line to ensure plane wave produced in plates of the sample by point excitation[6].The beam also divides the test sample into two double-corner subsystems on both sides i.e.plates①-③-⑤ without blocking masses on the left and plates②-④-⑥ with blocking masses on the right.The blocking masses attached on the right side subsystem are two steel beams of rectangular cross section 20mm×20mm.The sample was placed upside down with the free ends of plates⑤and⑥embedded in two sand boxes by 300mm to guarantee ‘reflection-free’ boundaries as shown in Fig.8.

    For the reason that machinery excitation on its foundation produces predominantly bending waves into the ship structure[10],only bending wave incidence is considered here.On testing,a broad band point excitation force exerted on the rigid beam generates incident bending waves of the same magnitude into both sides.And both transverse and longitudinal vibration re-sponse at four measurement points on plates①,②,⑤ and⑥ respectively were recorded and processed.This procedure was repeated for 9 times with locations of the measurement points changed for each time.The measurement points on the right side subsystem are shown in Fig.7(right)and those on the left side are allocated symmetrically.

    The measurement results from 9 measurement points on each plate are averaged and converted into transmission loss in 1/1 octave band with central frequency from 31.5Hz to 4kHz.Comparisons are shown in Fig.9 and Fig.10 and it is seen that:

    (1)TLBBand TLBLmeasured in double-corner subsystem with blocking masses show almost the same trends as predicted.

    (2)The values of measured TLBBand TLBLwith blocking masses are higher than those without blocking masses above 1kHz,which validate that blocking masses are effective for attenuation of structure-borne sound especially at high frequencies.

    (3)Certain discrepancy is observed in Fig.9,which may be caused by the following factors:

    (a)Plane wave assumption is no longer valid by point excitation on the rigid beam at frequencies much higher than the first mode(or resonant)frequency of the beam[5-6].

    (b)The blocking masses attached to the test sample are not ideally rigid.And the elastic deformations of them can not be neglected at high frequencies where the wave length is very short.

    (c)Under conditions of the free ends of the sample embedded in sand boxes,there are still some reflections remained,especially at low frequencies,which lower the transmission loss measured.

    (d)Near field effect at the joint of two plates is neglected in numerical computation,which causes discrepancy especially at low frequencies.

    (4)The discrepancy for TLBLis smaller than that for TLBBat high frequencies,which indicates violation of normal incidence of plane wave assumption and deformations of steel beam have less effect on longitudinal wave than bending one.This phenomenon is also observed in the simplified experiment on single corner structure[5].

    (5)The computed first resonant frequency for bending of plate③(intermediate plate)is about 20Hz and resonance of the plate makes negative effect on transmission losses.So TLBB(even be negative from measurement)and TLBLmeasured at 31.5Hz 1/1 octave in the left side double-corner subsystem without blocking masses are much lower than those at 63Hz.And about 6dB increasing of TLBBand TLBLare observed after attached blocking masses,which validate the results from numerical investigation.

    4 Conclusions

    The work in this paper provides a theoretical and experimental basis for applying blocking masses on structure-borne sound attenuation on board of a ship.The expressions of wave motions in multi-corner structure are deduced by wave approach.And the transmission losses in double-corner structure are investigated as well.It is concluded that

    (1)The transmission losses from bending wave incidence measured in the experiment matches well with those from prediction,which validate the effectiveness of wave approach used in prediction of structure-borne sound attenuation.

    (2)Large increasing of TLBBand TLBLin double-corner structure with blocking masses is measured comparing with those without blocking masses especially at high frequencies.This indicates blocking masses attached to double-corner structure act as a kind of low pass filter,which provides more transmission loss at high frequencies.

    (3)Energy transmission through double-corner structure depends mainly on whether the intermediate plate responds at resonance.And it is found that attenuation of vibration energy can be increased at the first resonant frequency of the intermediate plate in double-corner structure with attached blocking masses,which is also validated in the experiment.

    (4)The deformation of the beam used as blocking mass and the violation of plane wave assumption should be taken into consideration if more accurate prediction is demanded at high frequencies.So more refined modeling is needed for further research.

    [1]Cremer L,Heckl M,Ungar E E.Structure-borne sound[M].Second edition.Berlin:Springer-Verlag,1988.

    [2]Liu Jianhua,Jin Xianding,Li Xiaobin.Attenuation of the plate flexural wave transmission through a vibration isolation mass[J].Journal of Ship Mechanics,2006,10(6):131-137.

    [3]Liu Jianhua,Jin Xianding,Li Xiaobin.Impediment to structure-borne sound propagation from several paralleling arranged vibration isolation mass[J].Journal of Shanghai Jiaotong University,2003,37(8):1205-1208.

    [4]Bercin A N.An assessment of the effects of in-plane vibrations on the energy flow between coupled plates[J].Journal of Sound and Vibration,1996,191(5):661-680.

    [5]Che Chidong,Chen Duanshi.Attenuation effect of blocking mass attached at corner interface on transmission from plane longitudinal wave to bending wave[J].Journal of Ship Mechanics.(accepted and will be published)

    [6]Chen Duanshi,Che Chidong.Analysis of vibration transmission at the corner interface of two plates for reduction of structure-borne sound[C].The Thirteenth International Congress on Sound and Vibration(ICSV 13),2006.

    [7]Langley R S,Heron K H.Elastic wave transmission through plate/beam junctions[J].Journal of Sound and Vibration,1990,143(2):241-253.

    [8]Lowe P G.Basic principles of plate theory[M].Glasgow:Surrey University Press,1982.

    [9]Mindlin R D.Influence of rotatory inertia and shear on flexural motions of isotropic elastic plates[J].Journal of Applied Mechanics,1951,18:31-38.

    [10]Grice R M,Pinnington R J.A method for the vibration analysis of built-up structures,Part I:Introduction and analytical analysis of the plate-stiffened beam[J].Journal of Sound and Vibration,2000,230:825-849.

    97超级碰碰碰精品色视频在线观看| h日本视频在线播放| 免费无遮挡裸体视频| 日韩人妻高清精品专区| 久久精品综合一区二区三区| 男人和女人高潮做爰伦理| 亚洲av不卡在线观看| 看黄色毛片网站| 国内精品美女久久久久久| 一a级毛片在线观看| 日韩欧美免费精品| 国产单亲对白刺激| 国产免费男女视频| 此物有八面人人有两片| a级毛片a级免费在线| 国产亚洲av嫩草精品影院| 高清在线国产一区| 国语自产精品视频在线第100页| 精品久久久久久,| 天堂动漫精品| 日本欧美国产在线视频| 啦啦啦韩国在线观看视频| 日韩中文字幕欧美一区二区| 深夜精品福利| 别揉我奶头~嗯~啊~动态视频| 精品久久久久久久久久免费视频| 国产精品久久久久久久电影| 国产精品免费一区二区三区在线| 成年人黄色毛片网站| 黄色丝袜av网址大全| 成人国产综合亚洲| 国产真实伦视频高清在线观看 | 欧美+日韩+精品| 日韩精品青青久久久久久| 变态另类丝袜制服| 国产亚洲精品久久久com| 国产真实乱freesex| 国产精品久久视频播放| 日日干狠狠操夜夜爽| 99国产精品一区二区蜜桃av| 女人十人毛片免费观看3o分钟| 免费在线观看成人毛片| 日日摸夜夜添夜夜添av毛片 | 老司机午夜福利在线观看视频| 在线观看舔阴道视频| 久久欧美精品欧美久久欧美| 一级毛片久久久久久久久女| 如何舔出高潮| 国产亚洲精品久久久久久毛片| 婷婷六月久久综合丁香| 欧美成人一区二区免费高清观看| 国产在线精品亚洲第一网站| 成人毛片a级毛片在线播放| 国产亚洲91精品色在线| 中文字幕精品亚洲无线码一区| 日韩一区二区视频免费看| 12—13女人毛片做爰片一| 国产高清视频在线观看网站| 在现免费观看毛片| 国产在线男女| 国产一区二区三区av在线 | 国产男人的电影天堂91| 一进一出抽搐动态| 国产午夜精品论理片| 午夜福利在线在线| 两个人视频免费观看高清| 亚洲欧美精品综合久久99| 日韩国内少妇激情av| 成人三级黄色视频| 嫩草影院入口| 亚洲av成人精品一区久久| 成人特级黄色片久久久久久久| 国产精品,欧美在线| 午夜免费激情av| 老师上课跳d突然被开到最大视频| 亚洲专区国产一区二区| 日韩精品有码人妻一区| 午夜福利视频1000在线观看| 国产精品一区二区免费欧美| 波多野结衣高清无吗| 欧美日韩中文字幕国产精品一区二区三区| 三级毛片av免费| 人人妻人人看人人澡| 久久欧美精品欧美久久欧美| 少妇猛男粗大的猛烈进出视频 | 日韩中文字幕欧美一区二区| 深夜精品福利| 久久九九热精品免费| 国产高清三级在线| 国产精品综合久久久久久久免费| 国产精品女同一区二区软件 | 久久久久久久久大av| 欧美xxxx黑人xx丫x性爽| 中文字幕人妻熟人妻熟丝袜美| 老熟妇乱子伦视频在线观看| 国产精品一及| 别揉我奶头~嗯~啊~动态视频| 国产在线男女| 成人国产麻豆网| 精品久久久久久久末码| av黄色大香蕉| 国内少妇人妻偷人精品xxx网站| 成年女人永久免费观看视频| 男人狂女人下面高潮的视频| 国产高清不卡午夜福利| 少妇的逼好多水| 精品人妻熟女av久视频| 91在线观看av| 午夜福利欧美成人| 毛片女人毛片| 亚洲无线观看免费| 美女免费视频网站| 久久久久九九精品影院| 亚洲在线观看片| 午夜福利高清视频| 嫩草影院新地址| 亚洲人成网站在线播| 免费av不卡在线播放| 国产精品,欧美在线| 精品一区二区三区视频在线| 欧美人与善性xxx| 3wmmmm亚洲av在线观看| 精品久久久久久久末码| 国产在线男女| 草草在线视频免费看| a在线观看视频网站| 国产在线精品亚洲第一网站| 2021天堂中文幕一二区在线观| 国产黄色小视频在线观看| 亚洲男人的天堂狠狠| 在线观看66精品国产| 97超视频在线观看视频| 午夜激情欧美在线| 国产白丝娇喘喷水9色精品| 99热网站在线观看| 99热6这里只有精品| 欧美绝顶高潮抽搐喷水| 五月玫瑰六月丁香| 亚洲一区高清亚洲精品| 一区二区三区激情视频| 日韩欧美免费精品| 天堂网av新在线| 久久热精品热| 免费大片18禁| 国产色爽女视频免费观看| 国产爱豆传媒在线观看| av视频在线观看入口| 亚洲第一电影网av| 亚洲精品亚洲一区二区| 嫩草影院新地址| 中文字幕人妻熟人妻熟丝袜美| 91久久精品电影网| 女人十人毛片免费观看3o分钟| 乱码一卡2卡4卡精品| 两个人的视频大全免费| 欧美一区二区亚洲| 久久国产精品人妻蜜桃| 日本色播在线视频| 春色校园在线视频观看| 成人精品一区二区免费| 国产免费av片在线观看野外av| 毛片女人毛片| 少妇熟女aⅴ在线视频| 久久99热这里只有精品18| 一本一本综合久久| 亚洲欧美日韩东京热| 日日撸夜夜添| 性欧美人与动物交配| 一个人看的www免费观看视频| 免费不卡的大黄色大毛片视频在线观看 | 乱人视频在线观看| 国产综合懂色| 一进一出抽搐gif免费好疼| 亚洲一级一片aⅴ在线观看| 日本精品一区二区三区蜜桃| 淫秽高清视频在线观看| 免费不卡的大黄色大毛片视频在线观看 | 丝袜美腿在线中文| 久99久视频精品免费| 国产精品久久电影中文字幕| 不卡视频在线观看欧美| 一进一出好大好爽视频| 久久99热6这里只有精品| 免费av不卡在线播放| 色哟哟·www| 亚洲成a人片在线一区二区| 亚洲精品一卡2卡三卡4卡5卡| 国产男人的电影天堂91| 内地一区二区视频在线| 悠悠久久av| 一个人免费在线观看电影| 老师上课跳d突然被开到最大视频| 欧美+亚洲+日韩+国产| 欧美zozozo另类| 日本一本二区三区精品| 男女下面进入的视频免费午夜| 成年人黄色毛片网站| 国产成人一区二区在线| 十八禁网站免费在线| 两人在一起打扑克的视频| 欧美日韩综合久久久久久 | 观看免费一级毛片| 自拍偷自拍亚洲精品老妇| 日韩欧美精品免费久久| 中文字幕av在线有码专区| 欧美bdsm另类| 韩国av在线不卡| 婷婷精品国产亚洲av| 哪里可以看免费的av片| 别揉我奶头 嗯啊视频| 91久久精品电影网| 亚洲aⅴ乱码一区二区在线播放| 亚洲在线自拍视频| 一区福利在线观看| 亚洲人成伊人成综合网2020| 999久久久精品免费观看国产| 俄罗斯特黄特色一大片| 一本精品99久久精品77| 亚洲自拍偷在线| 毛片女人毛片| 国产精品1区2区在线观看.| 男女边吃奶边做爰视频| 精品99又大又爽又粗少妇毛片 | 蜜桃亚洲精品一区二区三区| 亚洲经典国产精华液单| 十八禁网站免费在线| 婷婷丁香在线五月| 国产午夜福利久久久久久| 校园人妻丝袜中文字幕| 成人精品一区二区免费| 天堂动漫精品| 又爽又黄a免费视频| 人人妻人人澡欧美一区二区| 麻豆成人午夜福利视频| 国产视频一区二区在线看| 亚洲性夜色夜夜综合| 中文字幕人妻熟人妻熟丝袜美| 自拍偷自拍亚洲精品老妇| 美女cb高潮喷水在线观看| 欧美绝顶高潮抽搐喷水| 噜噜噜噜噜久久久久久91| 老师上课跳d突然被开到最大视频| 日本与韩国留学比较| 一本久久中文字幕| 欧美日韩国产亚洲二区| 国产精品三级大全| 别揉我奶头 嗯啊视频| av在线观看视频网站免费| 国产亚洲精品久久久com| 91狼人影院| 少妇被粗大猛烈的视频| 亚洲七黄色美女视频| 亚洲av不卡在线观看| 又黄又爽又免费观看的视频| 午夜福利欧美成人| 性色avwww在线观看| av在线老鸭窝| 身体一侧抽搐| 国产精品久久久久久精品电影| 国产高清有码在线观看视频| 成人鲁丝片一二三区免费| 美女被艹到高潮喷水动态| av在线蜜桃| 露出奶头的视频| 国产色爽女视频免费观看| 亚洲精品成人久久久久久| 亚洲成人久久爱视频| 国产老妇女一区| 欧美日韩乱码在线| 91在线观看av| a级毛片a级免费在线| 99热这里只有是精品50| 国产免费av片在线观看野外av| 最新在线观看一区二区三区| 两个人的视频大全免费| 成人无遮挡网站| 特级一级黄色大片| 亚洲狠狠婷婷综合久久图片| 麻豆一二三区av精品| 99热网站在线观看| 久久精品国产亚洲av天美| 国产精品福利在线免费观看| 久久久国产成人免费| av天堂中文字幕网| 久久亚洲真实| 免费无遮挡裸体视频| 深爱激情五月婷婷| 国产精品电影一区二区三区| 深夜精品福利| 男女那种视频在线观看| 美女黄网站色视频| 国产久久久一区二区三区| 波多野结衣高清无吗| 国产欧美日韩一区二区精品| 一区二区三区激情视频| 最后的刺客免费高清国语| 国产探花极品一区二区| 18禁在线播放成人免费| 日本与韩国留学比较| 男人和女人高潮做爰伦理| 三级男女做爰猛烈吃奶摸视频| 少妇裸体淫交视频免费看高清| a级一级毛片免费在线观看| 免费电影在线观看免费观看| 国产av一区在线观看免费| 搡老岳熟女国产| 精品无人区乱码1区二区| 国内精品美女久久久久久| 午夜老司机福利剧场| 成人国产综合亚洲| 99国产精品一区二区蜜桃av| 国产精品国产高清国产av| 免费看美女性在线毛片视频| 午夜免费男女啪啪视频观看 | 天天躁日日操中文字幕| 久久精品国产亚洲av涩爱 | 亚州av有码| 久久精品国产鲁丝片午夜精品 | 观看免费一级毛片| 丰满人妻一区二区三区视频av| 亚洲av电影不卡..在线观看| 精品久久久久久久久亚洲 | 黄色女人牲交| 精品99又大又爽又粗少妇毛片 | 老女人水多毛片| 一区福利在线观看| 成熟少妇高潮喷水视频| 国产一区二区在线观看日韩| 如何舔出高潮| 国产一区二区三区av在线 | 久久九九热精品免费| 麻豆成人av在线观看| 日韩av在线大香蕉| 欧美不卡视频在线免费观看| 色播亚洲综合网| 不卡视频在线观看欧美| 深爱激情五月婷婷| 久久精品国产亚洲av涩爱 | 免费高清视频大片| 精品国内亚洲2022精品成人| 精品久久国产蜜桃| 真人做人爱边吃奶动态| 久久久久久大精品| 欧美日本视频| 免费观看人在逋| 尾随美女入室| 欧美一区二区亚洲| 伊人久久精品亚洲午夜| 一区二区三区四区激情视频 | 国产探花在线观看一区二区| 久久久久久久久久黄片| 成人综合一区亚洲| 久久人人爽人人爽人人片va| 国产精品电影一区二区三区| 国产精品日韩av在线免费观看| 国产色爽女视频免费观看| 亚洲av.av天堂| 国产精品永久免费网站| 色综合亚洲欧美另类图片| 欧洲精品卡2卡3卡4卡5卡区| 国产精品久久久久久精品电影| 日韩欧美在线二视频| 国内揄拍国产精品人妻在线| 国产精品久久久久久久久免| 亚洲精品成人久久久久久| 亚洲精品456在线播放app | av黄色大香蕉| 亚洲av免费在线观看| 国产大屁股一区二区在线视频| 99久久精品热视频| 乱码一卡2卡4卡精品| 国产私拍福利视频在线观看| 亚洲av成人精品一区久久| 在线免费观看的www视频| 日韩欧美国产在线观看| 国产精品国产三级国产av玫瑰| 午夜久久久久精精品| 高清日韩中文字幕在线| 国产成人a区在线观看| 日本精品一区二区三区蜜桃| 成人欧美大片| 亚洲精品国产成人久久av| 色综合婷婷激情| 欧美性猛交黑人性爽| 麻豆一二三区av精品| 九九热线精品视视频播放| 色综合婷婷激情| 日韩一区二区视频免费看| 国产高清视频在线观看网站| 国产精品野战在线观看| 综合色av麻豆| 亚洲性久久影院| 美女xxoo啪啪120秒动态图| 在线播放无遮挡| 听说在线观看完整版免费高清| 国产av麻豆久久久久久久| 国国产精品蜜臀av免费| 亚洲国产日韩欧美精品在线观看| 一级毛片久久久久久久久女| 欧美激情久久久久久爽电影| 欧美黑人巨大hd| h日本视频在线播放| 中国美女看黄片| 九九在线视频观看精品| 亚洲av免费高清在线观看| 亚洲电影在线观看av| 亚洲av免费高清在线观看| 免费在线观看影片大全网站| bbb黄色大片| av天堂在线播放| 国产视频内射| av国产免费在线观看| 欧美日韩亚洲国产一区二区在线观看| 日本 av在线| 国产久久久一区二区三区| 久久久久久久久大av| 老师上课跳d突然被开到最大视频| 亚州av有码| 成人一区二区视频在线观看| 淫秽高清视频在线观看| 亚洲va日本ⅴa欧美va伊人久久| 成人午夜高清在线视频| 国产白丝娇喘喷水9色精品| 一边摸一边抽搐一进一小说| 亚洲第一区二区三区不卡| 久久久国产成人免费| 国产乱人视频| 国产69精品久久久久777片| www日本黄色视频网| 亚洲美女搞黄在线观看 | 日韩欧美三级三区| 三级毛片av免费| 午夜福利在线观看免费完整高清在 | 51国产日韩欧美| 精品一区二区三区人妻视频| 日韩av在线大香蕉| 黄色欧美视频在线观看| 美女高潮喷水抽搐中文字幕| av专区在线播放| 欧美性感艳星| 午夜日韩欧美国产| 一区福利在线观看| 午夜影院日韩av| 久久天躁狠狠躁夜夜2o2o| 亚洲午夜理论影院| 久久精品国产亚洲av香蕉五月| 久久99热6这里只有精品| av天堂在线播放| 亚洲四区av| 99久久九九国产精品国产免费| 成人特级av手机在线观看| 欧美一级a爱片免费观看看| 色吧在线观看| 中文字幕人妻熟人妻熟丝袜美| 99久久精品热视频| 欧美中文日本在线观看视频| 一区二区三区激情视频| 校园人妻丝袜中文字幕| 啦啦啦观看免费观看视频高清| 黄片wwwwww| 啦啦啦啦在线视频资源| 成人毛片a级毛片在线播放| 夜夜爽天天搞| 免费一级毛片在线播放高清视频| 两个人的视频大全免费| 亚洲av熟女| av天堂中文字幕网| 国产精品一区www在线观看 | 国模一区二区三区四区视频| 成人av一区二区三区在线看| 成年免费大片在线观看| 草草在线视频免费看| 天堂网av新在线| 亚洲国产欧美人成| 亚洲欧美日韩东京热| 俺也久久电影网| 日韩一本色道免费dvd| 欧美色欧美亚洲另类二区| 黄片wwwwww| 男女那种视频在线观看| 亚洲性夜色夜夜综合| 国产白丝娇喘喷水9色精品| 亚洲av免费高清在线观看| 99国产极品粉嫩在线观看| 精品久久久久久成人av| 久久人人爽人人爽人人片va| 成人永久免费在线观看视频| 午夜福利在线观看吧| 一进一出抽搐gif免费好疼| xxxwww97欧美| 他把我摸到了高潮在线观看| 波多野结衣巨乳人妻| av视频在线观看入口| 国产午夜福利久久久久久| 无人区码免费观看不卡| www日本黄色视频网| 真实男女啪啪啪动态图| 91久久精品国产一区二区三区| 亚洲欧美日韩东京热| 性色avwww在线观看| 欧美+亚洲+日韩+国产| 亚洲精品456在线播放app | 国产激情偷乱视频一区二区| а√天堂www在线а√下载| 国产老妇女一区| 美女 人体艺术 gogo| 日韩精品有码人妻一区| 日日夜夜操网爽| 最近视频中文字幕2019在线8| 白带黄色成豆腐渣| 久99久视频精品免费| www日本黄色视频网| 欧美一级a爱片免费观看看| 免费大片18禁| 动漫黄色视频在线观看| 干丝袜人妻中文字幕| 精品一区二区免费观看| 国产激情偷乱视频一区二区| 啪啪无遮挡十八禁网站| 日韩人妻高清精品专区| 国产精品久久电影中文字幕| 国产一区二区激情短视频| 免费看光身美女| 男插女下体视频免费在线播放| av天堂在线播放| 黄色丝袜av网址大全| 亚洲精品国产成人久久av| 一个人看的www免费观看视频| 久久久久性生活片| 男人舔奶头视频| 精品人妻1区二区| av在线观看视频网站免费| 最新中文字幕久久久久| 久久天躁狠狠躁夜夜2o2o| 欧美3d第一页| 国产精品野战在线观看| 国产高清视频在线播放一区| 日日撸夜夜添| 美女cb高潮喷水在线观看| 国产色爽女视频免费观看| 小说图片视频综合网站| 丰满人妻一区二区三区视频av| 给我免费播放毛片高清在线观看| 十八禁国产超污无遮挡网站| 一区二区三区激情视频| 长腿黑丝高跟| 国产精品伦人一区二区| 亚洲av五月六月丁香网| 精品午夜福利在线看| 桃色一区二区三区在线观看| 内射极品少妇av片p| 国产一区二区在线观看日韩| 日韩欧美精品免费久久| 国内精品久久久久精免费| 国产高清视频在线播放一区| 乱人视频在线观看| 国内久久婷婷六月综合欲色啪| 久久香蕉精品热| 久久精品影院6| 如何舔出高潮| 午夜福利18| 午夜爱爱视频在线播放| 九九在线视频观看精品| 深爱激情五月婷婷| 亚洲美女搞黄在线观看 | 少妇人妻精品综合一区二区 | 久久人妻av系列| 亚洲一区二区三区色噜噜| 久久久久久久午夜电影| 性欧美人与动物交配| 国产乱人伦免费视频| 哪里可以看免费的av片| 国产精品久久久久久久久免| 成人高潮视频无遮挡免费网站| 精品乱码久久久久久99久播| 国产精品美女特级片免费视频播放器| 桃红色精品国产亚洲av| 国产久久久一区二区三区| 国产一区二区三区视频了| 在线观看美女被高潮喷水网站| 天堂网av新在线| 五月伊人婷婷丁香| 性欧美人与动物交配| 此物有八面人人有两片| 俺也久久电影网| 国产伦在线观看视频一区| 久久精品夜夜夜夜夜久久蜜豆| 国产亚洲精品久久久com| av在线亚洲专区| 国产国拍精品亚洲av在线观看| 亚洲精品456在线播放app | 亚洲内射少妇av| 91精品国产九色| 三级国产精品欧美在线观看| 制服丝袜大香蕉在线| 国产伦精品一区二区三区四那| 18禁黄网站禁片免费观看直播| 亚洲四区av| 少妇熟女aⅴ在线视频| 波多野结衣高清作品| 午夜福利成人在线免费观看| 男女啪啪激烈高潮av片| 国产亚洲精品久久久com| 久久久久国产精品人妻aⅴ院| 琪琪午夜伦伦电影理论片6080| 日本一本二区三区精品| 日本与韩国留学比较| 久久久久九九精品影院| 不卡视频在线观看欧美| 亚洲国产欧美人成| 级片在线观看| 搡老岳熟女国产| 亚洲欧美精品综合久久99| 国产免费一级a男人的天堂| 制服丝袜大香蕉在线|