CAESARII培训讲义.ppt

1、2020/8/30,Basic Stress Theory use M/Z,2020/8/30,Basic Stress Theory lets move to a plane element:,2020/8/30,Basic Stress Theory K x = f. In this equation, we know K and f, and we are solving for x, the displacement vector. In CAESAR II, when we setup an expansion case, we define it as DS1 - DS2, whe

2、re the 1 and 2 refer to the displacement vector (x) of load cases 1 and 2 respectively.,2020/8/30,Basic Stress Theory & CAESAR II Implementation,Load Cases for Code Compliance,膨胀工况的解释Expansion Case Explained (Obviously the load case numbers are subject to change on a job by job basis.) What do you g

3、et when you take DS1 - DS2? Well x1 - x2 yields x, a pseudo displacement vector. x is not a real set of displacements that you can go out and measure with a ruler, rather it is the difference between two positions of the pipe. Once we have x, we can use the same routines used in the OPE or SUS cases

4、 to compute element forces, and finally element stresses.,2020/8/30,Basic Stress Theory & CAESAR II Implementation,Load Cases for Code Compliance,膨胀工况的解释Expansion Case Explained However, these element forces are also pseudo forces, i.e the difference in forces between two positions of the pipe.力的大小是

5、两个工况力的差值 Similarly, the stresses computed are not real stresses, but stress differences.应力不是真实应力，是应力的差值 This is exactly what the code wants, the stress difference, which was computed from a displacement range.二次应力是位移变化量导致的 As to whether or not this stress difference is the extreme, well that depends

6、 on the job.,2020/8/30,Basic Stress Theory & CAESAR II Implementation,Load Cases for Code Compliance,膨胀工况的解释Expansion Case Explained DS1-DS2 和 T1“一样吗？. 有可能. 如果是线性系统，答案是一样的。 如果是非线性系统 (如你有 +Ys, or gaps, or friction), 答案是不一样的。 原因是两个工况应用K x = f。 The reason for this can be found by examining the equation

7、 K x = f for the two different methods.,2020/8/30,Basic Stress Theory & CAESAR II Implementation,Load Cases for Code Compliance,Expansion Case Explained For this discussion, rearrange the equation to x = f / K, where we know we dont really divide by K, we multiply by its inverse. OPE: xope = fope /

8、Kope = W + T1 + P1 / Kope SUS: xsus = fsus / Ksus = W + P1 / Ksus EXP: xexp = xope - xsus = W + T1 + P1 / Kope - W + P1 / Ksus Can we simplify the above equation as follows? EXP: xexp = W + T1 + P1 / K - W + P1 / K,2020/8/30,Basic Stress Theory & CAESAR II Implementation,Load Cases for Code Complian

9、ce,膨胀工况解释Expansion Case Explained Can we simplify the above equation as follows? EXP: xexp = W + T1 + P1 / K - W + P1 / K Canceling like terms (the ones in red) yields: xexp = T1 / K 问题在于Kope 和 Ksus是否相等. 线性系统相等. 非线性系统不相等,2020/8/30,Basic Stress Theory & CAESAR II Implementation,Load Cases for Code Co

10、mpliance,膨胀工况解释Expansion Case Explained 如果一个系统有两个操作温度。Another proof that the DS1-DS2 method is the correct way to go is to consider a job with two operating temperatures, one above ambient and one below ambient. 如 T1 = +300, and T2 = -50. CAESAR II 软件自动建立如下工况: (1) W + T1 + P1 (OPE) (2) W + T2 + P1 (

11、OPE) (3) W + P1 (SUS) (4) DS1 - DS3 (EXP) (5) DS2 - DS3 (EXP),2020/8/30,Basic Stress Theory & CAESAR II Implementation,Load Cases for Code Compliance,膨胀工况解释Expansion Case Explained 上述工况正确，但没能说明规范要求的最大应力范围因为CII并不能判断荷载所代表的具体含义 为满足规范的要求，用户必须自己定义: (6) DS1 - DS2 (EXP) 这个工况是最大位移膨胀应力，正是规范所要求的。 您根本不能考虑使用T1来

12、计算膨胀应力.,2020/8/30,Basic Stress Theory & CAESAR II Implementation,Load Cases for Code Compliance,Expansion Case Explained膨胀工况的解释 To summarize:概括如下 We take the difference between two load cases to determine a displacement range.两个工况确定位移范围 From this range we compute a force range and then a stress rang

13、e.由此我们确定力的范围和应力范围 The code requires the extreme displacement stress range.规范要求极端的应力范围 The user only has to worry about whether or not the “extreme” case has been addressed.用户仅考虑最大应力范围即可,2020/8/30,Basic Stress Theory & CAESAR II Implementation,Linear vs Non-Linear线性和非线性,Terminology applies to boundar

14、y conditions.边界条件的类型 Recall the equation being solved: Kx = f This is the equation of a spring. The piping system boundary conditions (i.e. the restraints) are represented as stiffnesses, or springs.管道边界条件代表刚度或弹簧 More complex boundary conditions can be defined, invalidating the “linear spring” assum

15、ption.,2020/8/30,Basic Stress Theory & CAESAR II Implementation,Linear vs Non-Linear线性和非线性,线性约束 boundary condition is a double acting restraint, such as a “Y” support.一种是上下约束 Another example of a linear boundary condition is a spring hanger.一种是弹簧 The force versus displacement curve for these restrai

16、nts is a straight line 力和位移是线性关系 Therefore these restraints are linear.约束是线性的 The slope of the line is the stiffness.斜率是刚度,2020/8/30,Basic Stress Theory & CAESAR II Implementation,Linear vs Non-Linear线性和非线性,非线性约束 A “+Y” support is a non-linear support.支架 Its force vs displacement curve is not a stra

17、ight line.力和位移不是直线关系 Stiffness only exists for negative displacements.向下的位移是刚度是存在的 For positive displacements, the stiffness is zero.向上的位移，刚度变为,2020/8/30,Basic Stress Theory & CAESAR II Implementation,Linear vs Non-Linear线性和非线性,A “gap” is also a non-linear support.间隙的引进 The force vs displacement cur

18、ve is not a straight line.力和位移不是线性关系 There is no stiffness in the gap.间隙部分没有刚度,2020/8/30,Basic Stress Theory & CAESAR II Implementation,Linear vs Non-Linear线性和非线性,Friction makes a restraint non-linear摩擦让约束非线性 Large rotation rods are also non-linear restraints大的转动吊杆让约束非线性 Non-linear restraints in a j

19、ob mean that Kope is not equal to Ksus. 非线性后，热态管道刚度和冷态刚度不一致 (EXP) and (OCC) load cases must be constructed using the difference between two other load cases to account for non-linear restraints.,2020/8/30,Basic Stress Theory & CAESAR II Implementation,偶然工况的建立,Occasional loads are considered “primary

20、”, since they are force driven.偶然荷载是主要载荷，力引起的。 Occasional loads occur infrequently.不经常发生 The codes employ an “allowable increase” factor based on the frequency of occurrence in the determination of the allowable, i.e. k * Sh.基于发生的频率，确定值的大小 Examples of occasional loads are wind and earthquake.偶然载荷是风载

21、荷和地震载荷,2020/8/30,Basic Stress Theory & CAESAR II Implementation,偶然工况的建立,The code equation for the OCCasional load case is:MA / Z + MB / Z kSh Here, MA is the moment term from the SUStained loads,冷态荷载引发力矩 and MB is the moment from the OCCasional loads.偶然荷载引发力矩 This equation states that the OCCasional

22、 case is the sum of the SUStained stresses and the OCCasional stresses.偶然工况是冷态和偶然的叠加 So we cant run a load case with just a “WIND” load and satisfy this code requirement. What about “W + P1 + WIND” as a load case?,2020/8/30,Basic Stress Theory & CAESAR II Implementation,Occasional Load Case Setup,Th

23、e “W + P1 + WIND” case will work for “linear” systems only. For “non-linear” systems, this is not sufficient, for the same reason “T1” is not sufficient for the EXPansion load case. The best way to setup OCCasional load cases is: (1) W + P1 + T1 (OPE) (2) W + P1 + T1 + WIND (OPE) (3) W + P1 (SUS) (4

24、) DS1 - DS3 (EXP) (5) DS2 - DS1 (OPE) (6) ST5 + ST3 (OCC),2020/8/30,Basic Stress Theory & CAESAR II Implementation,Occasional Load Case Setup,(1) W + P1 + T1 (OPE) (2) W + P1 + T1 + WIND (OPE) (3) W + P1 (SUS) (4) DS1 - DS3 (EXP) (5) DS2 - DS1 (OPE) (6) ST5 + ST3 (OCC),This is the normal OPErating c

25、ase This is a combined OPErating case which includes the OCC loads This is the standard SUStained case This is the standard EXPansion case This difference yields the effects of the OCCasional load on the system. This is not a code case, only a construction case, therefore (OPE). This handles non-lin

26、earities. This is our OCCasional code compliance case, stresses from Primary plus Occasional loads.,2020/8/30,Basic Stress Theory & CAESAR II Implementation,工况的定义和维护,CAESAR II will recommend load cases for “new” jobs. By “new” jobs, we mean jobs that do not have a “._J” file. For “old” jobs, having

27、a “._J” file, CAESAR II reads in the defined load cases and presents them to the user. The load case editing screen is shown at the right.,2020/8/30,Basic Stress Theory & CAESAR II Implementation,工况的定义和维护,On this dialog, available load types are listed in the upper left list box.载荷类型 Available load

28、case types are listed in the lower left list box.工况类型 Load cases (recommended or previously defined) are shown in the grid at the right.推荐生成的工况 Recommended load cases can always be obtained by clicking on the Recommend button. The analysis commences by clicking on “the running man”.,2020/8/30,Basic

29、Stress Theory & CAESAR II Implementation,Load Case Generation & Maintenance,Say for a “new” job, the load cases at the right are recommended. Say you accept and run these load cases. Upon reviewing the output you discover that pre-defined displacements at node 5 were omitted. You return to input, ad

30、d the displacements, and start the Static Analysis processor again.,2020/8/30,Basic Stress Theory & CAESAR II Implementation,Load Case Generation & Maintenance,CAESAR II reads these existing load cases and presents them. What will your results be if you run these load cases? Exactly the same as befo

31、re, because these load cases dont include the predefined displacements. You must manually add “D1” to the OPE load case, or ask CAESAR II to re-recommend the load cases.,2020/8/30,Basic Stress Theory & CAESAR II Implementation,Load Case Generation & Maintenance,Notice the load type list in the upper

32、 left contains “D1” now. The corrected load cases are shown at the right.,2020/8/30,Basic Stress Theory & CAESAR II Implementation,Load Case Generation & Maintenance,Notice the load type list in the upper left contains “D1” now. The corrected load cases are shown at the right.,2020/8/30,Basic Stress

33、 Theory & CAESAR II Implementation,Load Case Generation & Maintenance,Notice the load type list in the upper left contains “D1” now. The corrected load cases are shown at the right. Any time you add or remove a complete load type, the load cases are insufficient. If you added displacements to node 1

34、10, would the load cases be sufficient?,2020/8/30,Basic Stress Theory & CAESAR II Implementation,确保您分析对象的正确性,Remember CAESAR II is a finite element program.有限元 Remember CAESAR II uses a 3D beam element.3D 梁单元 Remember you must have equilibrium:保持平衡 Resultant loads should equal applied loads作用力等于反作用力

35、 Gravity (weight only) load case should equal the weight of the system重力等于整个系统的总重量 Other basic checks Verify nodal 3D coordinates尺寸输入是否正确 Check for extreme displacements and/or loads最大位移和推力 (see handout),2020/8/30,Basic Stress Theory & CAESAR II Implementation,Problem Solving问题的处理,What do you do whe

36、n you dont like the results? Recall the equation being solved:Kx = fwhere we solve for x, the displacements From these displacements, we compute element forces & moments From these forces & moments, the Code equations are applied and we compute stresses.,2020/8/30,Basic Stress Theory & CAESAR II Imp

37、lementation,Problem Solving,What do you do when you dont like the results? So if you have a stress problem, it can only be caused by two things: A Code related issue (SIFs, code equation, etc.) Extreme forces and/or moments If you have a force/moment problem, they can be caused by only two things: I

38、mproper element characteristics Extreme displacements,2020/8/30,Basic Stress Theory & CAESAR II Implementation,Problem Solving,What do you do when you dont like the results? If you have a displacement problem, it can only be caused by two things: Improper input (density, elastic modulus, applied loa

39、ds) Improper boundary conditions Dont forget to check and recheck the input. Remember that in 3D systems, a load in one location can cause pivoting somewhere else downstream, resulting in excessive forces and moments. Try to isolate the load causing the problem, and trace its origin.,2020/8/30,Basic

40、 Stress Theory & CAESAR II Implementation,Problem Solving,设计和分析过程Design by Analysis - The Design Cycle 收集数据Gather all the data, with assumptions 建立分析模型和工况Generate the model and load sets 分析计算Perform the analysis 检查结果Check the results and assumptions 诊断问题Diagnose any problems 调整、改进和精细模型Make correctio

41、ns and refinements as necessary 再分析Re-run the modified model/load sets 报告和输出Document the analysis,2020/8/30,Basic Stress Theory & CAESAR II Implementation,其他话题Other Important Topics,关联节点Connecting Nodes - CNODEs Important topic - CNODEs will be discussed several times during this seminar. CNODEs 十分灵

42、活，是CII的一大特色。 使用CNODE的关键是切记： 自由度关联Association of Degrees of Freedom 可以将CNODE假设为球头关节Think of a CNODE as a “ball & socket joint”, 有些自由度是关联的 (如移动），而其他不关联 (如转动).,2020/8/30,Basic Stress Theory & CAESAR II Implementation,其他话题Other Important Topics,CNODE 应用案例 管道支撑在结构上面Pipe on structural steel 设备管口和设备的关系Nozzle on a vessel shell,2020/8/30,Basic Stress Theory & CAESAR II Implementation,其他话题Other Important