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1、专业好文档基于载荷叠加法的LPG船结构强度分析张荣鑫李德祥摘 要：本文根据LPG船鞍座和液罐间的受力形式，结合IGC规则和CCS散装运输液化气体船舶构造与设备规范，提出了一种载荷叠加的计算方法；在此基础上，运用三维有限元建模技术，解决了该类船舶的舱段/鞍座结构分析问题。实例证明了该方法的有效性和可行性。关键词：LPG船、强度、有限元、载荷叠加法1 前 言液化石油气体（Liquefied Petroleum Gas，LPG）船是一种高技术高附加值船1，具有广阔的市场发展前景。LPG船与常规散货船、油船结构上有所不同，结构更加复杂且安全性能要求更高。现有的IGC规则和CCS散装运输液化气体船舶构造
2、与设备规范2（以下统称规则）在船体结构方面无详细设计标准且载荷计算复杂，使得结构设计方面存在很多不定因素，增加了设计难度，故有必要对舱段结构进行有限元强度分析，提高结构安全性，为结构设计提供指导。本文首先对液化气船的船体结构及应用前景进行了分析，得出了结构有限元分析的必要性；其次根据规则的相关载荷要求，对计算载荷进行叠加，得到与事实相符合的计算载荷，并给出了相应的边界条件；然后建立了船体舱段三维有限元模型，对满载和压载两种工况进行了强度分析并得出了结论。2 LPG船设计载荷船舶在航行中运动状态比较复杂，主要承受以下载荷：内部压力、外部压力、船舶运动引起的动载荷、晃荡载荷、船舶变形引起的载荷、液
3、货舱和货物重量在支持构件部位的相应的反作用力等2。2.1 内部压力船体结构的内部压力主要是压载水压力，计算公式见文献3:2.2 外部压力船体结构的外部压力主要有静水压力和波浪水动压力，计算公式见文献2：2.3船舶运动引起的动载荷 以船舶在北大西洋中相当概率水平10-8的运动而产生的加速度分量为指导公式，加速度计算公式如下1：（1） 垂向加速度：（2） 横向加速度：（3） 纵向加速度：（4）其中：式中：为船长，m；为方形系数；B为最大型宽，m；X为船中到装货的液货舱重心之间的纵向距离，m（船中前，X为正值，船中后，X为负值）；Z为船舶的实际水线到装货的液货舱重心之间的垂向距离，m（水线上，Z为正
4、值，水线下，Z为负值）；V为营运速度；K通常取1。 为相应方向上的最大无因次加速度（相对于重力加速度）。计算时，可以认为它们是分别作用的，不包括静重力分量，包括横摇在横方向上引起的静重力分量，包括纵摇在纵方向上引起的静重力分量。2.4 载荷叠加由于液货舱和船体结构是独立的，因此在考虑货物载荷以及液货舱和货物重量在支持构件部位的相应的反作用力时，要同时考虑到船舶运动引起的动载荷。液货舱通过鞍座与船体相作用，因此，鞍座上的力要包含：）液货舱自身重量；）液货重量；）液货舱和液货由于船舶运动引起的动载荷； 按照规则要求，可以正弦/余弦函数的分布形式模拟液货舱向鞍座的施载方式，具体见下图1，其中和分别为
5、液货舱的垂向和横向力分量。 图1 鞍座载荷施加方式设为最大垂向力，其与垂向间夹角，则Pz可以定义为，为力作用点所在径向力与垂向间夹角，弧度；鞍座宽度为b，个数为n，则垂向合力：（5）同理可得横向合力 （6）则即可求得。实际上鞍座受到径向力作用，如图2所示：图2 鞍座受力形式则可直接定义鞍座的径向力，为径向力与垂向间夹角，为鞍座的包角。则1） 船舶仅垂荡时，仅有垂向加速度，则径向力；2） 船舶仅横摇时，仅有横向加速度，则径向力；3） 船舶横摇和垂荡时，既有垂向加速度，又有横向加速度，则仅鞍座一侧受力，径向力为变力，（7）（8）式（6）可转化为：（9）由于横摇时，仅一侧受力，故式（7）可转化为（1
6、0）式（8）、（9）左右两边平方后相加得： （11）故： （12）也可定义径向力为一正弦/余弦函数，当时有最大值，则定义，则根据式（12）得： （13）4） 船舶纵摇时，纵向加速度与垂向、横向加速度无关，可在鞍座上加纵向力即可。按照上面四条原则，鞍座处的载荷即可确定。3 LPG船边界条件和应力衡准由于计算模型为舱段模型，故在模型两端就需要有一定的边界条件。根据文献3的规定，可采取以下的方式定义边界条件（模型采用全宽模型），见表1。表1模型边界条件线位移X线位移Y线位移Z角位移X角位移Y角位移ZA端Link-Link-LinkLinkB端Link-Link-LinkLinkCL-Cons.-Co
7、ns.-Cons.刚性点ACons.Cons.Cons.Cons.BMCons.刚性点B-Cons.Cons.Cons.BMCons.注：Cons.表示对应的位移约束；Link表示面内相关点位移与独立点连接；BM表示端面所受的总弯矩。A、B端的端面弯矩计算方法见文献3的规定。至此，载荷、边界条件和应力衡准都已确定，则液化气船舱段/鞍座结构就可进行校核。4 案例分析本文选取某LPG船进行舱段/鞍座结构有限元分析，该船有两个LPG液舱，每个液舱有一个液罐，液舱区域为双壳单底结构。4.1船体参数和模型构造4.1.1船体参数垂线间长：型 宽：型 深：设计吃水：方形系数：航 速：4.1.2 结构模型本文
8、采用MSC.Patran计算软件进行有限元分析4,5，模型节点数共34103个，单元53771个。根据实际装载工况和文献2的要求，共需计算9种工况，如表2所示。表2 计算工况工 况GP1P2F1/2F-1/4压载工况纵摇+垂荡1.01.01.01.01.0横摇+垂荡1.01.01.01.01.0纵摇+横摇+垂荡0.80.80.91.01.01.0满载工况纵摇+垂荡1.01.01.01.01.0横摇+垂荡1.01.01.01.01.0纵摇+横摇+垂荡0.80.80.91.01.01.0独立工况（1）1.0独立工况（2）1.0独立工况（3）1.0注：为相应方向上的最大无因次加速度（相对于重力加速度
9、），G为液罐自重，P1为海水压力，P2 为附加调平载荷，F1/2为（舱+货）向前1/2冲力，F-1/4 为（舱+货）向后1/4冲力，为静横倾载荷。4.1.3计算结果分析舱段在弯矩和剪力作用下产生弯曲变形1，图3和图4表达了压载工况和满载工况（纵摇+横摇+垂荡）下的变形，该两工况均为中拱状态，单位为mm。图3压载工况（纵摇+横摇+垂荡）挠度图4满载工况（纵摇+横摇+垂荡）挠度计算模型的板相当应力见图5、6，单位为：图5压载工况（纵摇+横摇+垂荡）板相当应力图6满载工况（纵摇+横摇+垂荡）变形板相当应力从上面的计算结果可以看出，压载工况时挠度及船底板和主甲板应力较大，该工况较危险；而满载工况时，最
10、大应力发生在约束处（应力集中处），可以忽略。在满载工况下，由于液罐内装满液货，其重量通过鞍座传递到船底，这就使得船底部结构产生不均匀性，在此状态下，鞍座处应力较高。5 结论通过对该LPG船两种工况的舱段有限元结构分析，可得出以下结论：l 液罐与船体结构不是一个整体，故需考虑惯性力载荷等影响，载荷形式复杂，是计算的难点和重点；l LPG船局部载荷较大，容易造成应力集中、板格屈曲强度不足，故鞍座处需加强。l 压载工况受中拱波浪弯矩作用，船体受弯矩作用最大，变形和应力均达到最大。 本文通过有限元方法，较为真实地模拟了船舶受力、变形和应力情况，能够有效地指导该类型船舶的结构设计，具有一定的实用工程价值
11、。参考文献：1 陈庆强、朱胜昌等，2万2千方液化气船整船和舱段三维有限元强度分析。船舶力学，1999（10）。2 中国船级社，散装运输液化气体船舶构造与设备规范。人民交通出版社，2007（1）。3 中国船级社，油船结构强度直接计算指南。4 MSC PATRAN&MSC NASTRAN 使用指南。5 刘兵山、黄聪等，Patran从入门到精通。中国水利水电出版社，2003（3）。Cargo Tank Structural Strength Analysis of LPG Ship Based on the Loads Superposed MethodZhang R.X, Li D.X(China
12、 Classification Society Dalian Branch)Abstract: The paper provides a loads superposed method(LSM) based on the force modality between bicycle saddle and liquid tank of LPG ship and LGC Rule. It resolves the structural analysis question of the tank and bicycle saddle with the LSM and 3D FEM Method. T
13、he example proves that this method is effective and rational in engineering.Key Words: LPG Ship, Structural Strength, FEM, LSMEditors note: Judson Jones is a meteorologist, journalist and photographer. He has freelanced with CNN for four years, covering severe weather from tornadoes to typhoons. Fol
14、low him on Twitter: jnjonesjr (CNN) - I will always wonder what it was like to huddle around a shortwave radio and through the crackling static from space hear the faint beeps of the worlds first satellite - Sputnik. I also missed watching Neil Armstrong step foot on the moon and the first space shu
15、ttle take off for the stars. Those events were way before my time.As a kid, I was fascinated with what goes on in the sky, and when NASA pulled the plug on the shuttle program I was heartbroken. Yet the privatized space race has renewed my childhood dreams to reach for the stars.As a meteorologist,
16、Ive still seen many important weather and space events, but right now, if you were sitting next to me, youd hear my foot tapping rapidly under my desk. Im anxious for the next one: a space capsule hanging from a crane in the New Mexico desert.Its like the set for a George Lucas movie floating to the
17、 edge of space.You and I will have the chance to watch a man take a leap into an unimaginable free fall from the edge of space - live.The (lack of) air up there Watch man jump from 96,000 feet Tuesday, I sat at work glued to the live stream of the Red Bull Stratos Mission. I watched the balloons pos
18、itioned at different altitudes in the sky to test the winds, knowing that if they would just line up in a vertical straight line we would be go for launch.I feel this mission was created for me because I am also a journalist and a photographer, but above all I live for taking a leap of faith - the f
19、eeling of pushing the envelope into uncharted territory.The guy who is going to do this, Felix Baumgartner, must have that same feeling, at a level I will never reach. However, it did not stop me from feeling his pain when a gust of swirling wind kicked up and twisted the partially filled balloon th
20、at would take him to the upper end of our atmosphere. As soon as the 40-acre balloon, with skin no thicker than a dry cleaning bag, scraped the ground I knew it was over.How claustrophobia almost grounded supersonic skydiverWith each twist, you could see the wrinkles of disappointment on the face of
21、 the current record holder and capcom (capsule communications), Col. Joe Kittinger. He hung his head low in mission control as he told Baumgartner the disappointing news: Mission aborted.The supersonic descent could happen as early as Sunday.The weather plays an important role in this mission. Start
22、ing at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. The balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. It will climb higher th
23、an the tip of Mount Everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. As he crosses the boundary layer (called the tropopause), he can expect a lot of turbulence.The balloon will slowly
24、drift to the edge of space at 120,000 feet (22.7 miles/36.53 kilometers). Here, Fearless Felix will unclip. He will roll back the door.Then, I would assume, he will slowly step out onto something resembling an Olympic diving platform.Below, the Earth becomes the concrete bottom of a swimming pool th
25、at he wants to land on, but not too hard. Still, hell be traveling fast, so despite the distance, it will not be like diving into the deep end of a pool. It will be like he is diving into the shallow end.Skydiver preps for the big jumpWhen he jumps, he is expected to reach the speed of sound - 690 m
26、ph (1,110 kph) - in less than 40 seconds. Like hitting the top of the water, he will begin to slow as he approaches the more dense air closer to Earth. But this will not be enough to stop him completely.If he goes too fast or spins out of control, he has a stabilization parachute that can be deploye
27、d to slow him down. His team hopes its not needed. Instead, he plans to deploy his 270-square-foot (25-square-meter) main chute at an altitude of around 5,000 feet (1,524 meters).In order to deploy this chute successfully, he will have to slow to 172 mph (277 kph). He will have a reserve parachute t
28、hat will open automatically if he loses consciousness at mach speeds.Even if everything goes as planned, it wont. Baumgartner still will free fall at a speed that would cause you and me to pass out, and no parachute is guaranteed to work higher than 25,000 feet (7,620 meters).It might not be the moo
29、n, but Kittinger free fell from 102,800 feet in 1960 - at the dawn of an infamous space race that captured the hearts of many. Baumgartner will attempt to break that record, a feat that boggles the mind. This is one of those monumental moments I will always remember, because there is no way Id miss this.10