Optimization Design of Arm Frame of Folding Arm Type Tower Crane Based on ANSYS Ge-ning XU, Wen-ju LIU * and Yan-fei TAO

Transcription

1 2016 International Conference on Applied Mechanics, Mechanical and Materials Engineering (AMMME 2016) ISB: Optimization Design of Arm Frame of Folding Arm Type Tower Crane Based on ASYS Ge-ning XU, Wen-ju LIU * and Yan-fei TAO School of Machinery Engineering, Taiyuan University of Science and Technology, Taiyuan , China *Corresponding author Keywords: Arm rack, APDL, Parameterization, Optimal design. Abstract. Aiming at the problem of the light weight of the arm frame structure of some folding arm type tower crane at present. The folding arm type tower crane jib is analyzed based on the APDL language, including parametric modeling module and optimization design module, Finite element analysis is carried out on the condition of the most dangerous position at the end of the arm frame. Under the condition of the strength, rigidity and stability of the boom, the optimization function of ASYS is used to reduce the weight of the boom. Through analysis, the optimization results are compared with the original design scheme and the weight of the arm is reduced by 14.89%. The optimization effect is good, which greatly improves the quality and efficiency of the design. The reference is provided for the design of the metal structure or similar structure of the arm frame of the folding arm type tower crane. Introduction Folding arm type tower crane is a new type of tower crane, which is a combination of luffing jib tower crane and tower crane arm. Internationally, in the construction of cooling towers, television towers, skyscrapers and other projects have been widely used. QT20 folding arm type tower crane designed by Professor Zhang Ming Qin fill a gap in China's light tower crane. The advantage of folding arm type tower crane is as follows: when the big arm is in the horizontal position, its working range is the biggest. When the big arm is lifted, in the case of no increase in the standard section of the tower, we can increase the height of the tower within a few minutes, broaden the functionality of the device greatly. The parametric modeling of arm frame reduces the workload of designers, and improves the work quality and efficiency of designers. Under the condition of satisfying the strength, rigidity and stability, the weight of the arm frame can be reached to the lightest by optimization. Boom is the key part of the folding arm type tower crane, the research on the arm has a very important sense of the practical engineering. Establishment of Boom Structure Model Modeling Assumptions The arm frame of the folding arm type tower crane is composed of a large arm, a small arm and a supporting frame, and three major parts. Accord to the provisions of the state on the design of tower cranes. Each part of the tower crane must work within the elastic range of the material. For the analysis of the structure of the small and medium sized tower crane, the nonlinear factors are not considered generally. Therefore, the article discusses the various properties of the arm frame structure under normal temperature condition. Without affecting the accuracy of the calculation, in order to reduce the workload of a large number of trusses, it is necessary to simplify the calculation. (1) In the process of load, the direction of the axial force of the rod is always unchanged; (2) The section size of the rod after applying the load is always the same; (3) It is considered that the material is an ideal linear elastic model; (4) Each node of the arm frame is a smooth hinge point; (5) The axes of each rod are straight and pass through the center of the hinge.

2 Basic Parameters Folding arm type tower crane boom structure is welded by different types of steel. Rated lifting moment 3200k m; maximum range 32000mm; yaw angle of article 5 ; lifting speed 20m/min; Rotary speed 1.6r/min; Working wind pressure 150Pa; Material Q235B; Work level A4; Elastic modulus of material E= /m 2 ; Poisson ratio µ=0.3;density ρ = 7860 kg/m 3 ; Yield strength σ = 235 MPa. s Define Unit Type, Material Properties, and Real Constants Select Unit Type. The BEAM188 unit is adopted in the parametric modeling of the boom. The chord and the web of the arm frame are mainly welded by seamless steel tubes. After the load is applied, each member can generate tension and compression deformation. The BEAM188 element is based on Timoshenko beam theory, and considering the shear deformation effect, it is very suitable for linear, large angle rotation and nonlinear large strain problems. BEAM188 is a three-dimensional linear beam, each node generally has 6 or 7 degrees of freedom, including the movement of the x, y, z direction and the rotation of the x, y, z direction along the coordinate system. This unit provides the ability to analyze the bending, lateral displacement and torsion. Define Material Properties. The choice of the type of the arm is not only related to the safety of the tower crane, but also related to the economic performance of the material. Therefore, the selection of materials should consider the importance of structure, load characteristics, working level, stress state, connection mode and other factors. Most of the material used in the arm of folding arm type tower crane is Q235B, All the analysis parameters are set per the material analysis. Set Real Constant. BEAM188 beam element does not need to set the real constant, but it needs to carry on the section definition. Big arms and small arms are the cross sections of the normal triangle. The truss structure of the large arm is made up of seamless circular steel tubes. The small arm string is made of steel, and the shape of the cross section is rectangular. The supporting frame structure is composed of a seamless circular steel pipe. The Establishment of the Parametric Model Per the section size of the arm frame, parametric modeling was carried out under the three conditions. In this paper, the finite element model is established by the bottom-up approach. First define the lowest primitive, that is, the node, and then from the point of connection into the line, from the bottom to form a more advanced entity. The method of establishing the model is completed in the current active coordinate system. ASYS parametric model of boom system is shown in figure 1~ figure 3. Figure 1. Big arm level. Figure 2. Big arm up 45. Figure 3. Big arm up 90. Constraints, Coupling and Loading Impose Constraints. The roots of the large arm of the tower crane relate to the rotary part through a pin shaft. Boundary conditions can be set as follows: D,1,,,,,,UX,UY,UZ,ROTX,ROTY D,2,,,,,,UX,UY,UZ,ROTX,ROTY The boundary condition of the tie rod connected with the boom can be set as follows: D,1006,,,,,,UX,UY,UZ

3 Coupling. The arm frame of the folding arm type tower crane is composed of three parts, which are the big arms, the small arms and the support frame. In this paper, the coupling method is used to simulate the connection between multiple arms. In addition to the rotation degrees of freedom, all the degrees of freedom need to be coupled pin. cp,1,rotx,a11,10000+a11 cp,2,roty,a11,10000+a11 cp,3,ux,a11,10000+a11 cp,4,uy,a11,10000+a11 cp,5,uz,a11,10000+a11 Loading. The force acting on the arm is usually the lifting load, the dead load, the wind load, the inertia load and so on. Because the folding arm type tower crane is a small and medium-sized lifting equipment, it can be considered that the wind load is the uniform distribution of the load on the wind surface.!!!!wind load SEL,S,LOC,Z,0 SEL,A,LOC,Z,B/2 *GET,UMB,ODE,0,COUT F,ALL,FZ,-Ff/UMB!!!!Offset horizontal force F,number,FZ,-Pt!!!!Vertical force F,number,FY,-FCC F,number,FY,-FCC!!!!Self-weight and horizontal inertia force ACEL,0,9.81,gxjs Solution After the load is applied, the finite element method can be solved. The essence of finite element is using the finite element method to solve the simultaneous equations. Usually the solution of ASYS includes the basic solution and the derived solution. The basic solution is the value of the node's degree of freedom. The derived value of the original solution is the unit solution, that is, the unit stress, deformation and so on. Users can choose per the needs of different. Arm Frame Optimization The mathematical model based on the actual structure size is the first step in the structural optimization design. Both the static and dynamic problems of the structure can be expressed in the form of nonlinear programming, as follows: min f ( x) s. t. g ( x) = 0 ~ j( j = 1 ~ p) j g ( x) < 0 ~ j( j = p+1 ~ m) j l u x < x < x Design Variables T Based on the above expressions, x = ( x1, x2 x n )is the design variable in the mathematical model. X u is the upper limit of X, X l is the lower limit of X. In the actual structure, the design variables are as follows: the radius of big arm chord member R1, wall thickness D1; the radius of big arm web member R3, wall thickness D3; the height of small arm chord member R5, width R6, wall thickness HD; the radius of small arm web member R7, wall thickness D7; the radius of bow R9, wall thickness D9. (1)

4 State Variables Under different working conditions, the arm frame is different. But the strength, rigidity and stability of each component should be satisfied. The constraint conditions in the actual structure are as follows: (1) Strength condition: σ = / A < [σ] (2) Stiffness condition: 0 / [ ] λ = l r < λ (3) l0 is the calculation length of the component; r is the minimum turning radius of the arm frame cross section, r = I / A ; I is the least moment of inertia of the component section; [ λ] is the maximum length and width ratio of the component, Tower crane boom[ λ ] = 180. (2) Deflection condition: fmax < [ f ] (4) 2 In which [ f ] = 0.7L, L is the total length of the arm. (3) Stability condition M M x y + + < [σ] φa (1 ) Wx (1 ) Wy Ex Ey In which: axial force acting on the member; φ stability coefficient; A gross section area of members; M, M bending moment of cross section on X or Y axes; Objective Function x y W x, W y bending section coefficient of cross section on X or Y axis; E the elastic modulus of steel; [σ] allowable stress of steel; Ex, Ey Euler critical stress of component, in which Ex = π, Ey = π. EA /λ x EA /λ y Because the density of the material is constant, the weight of the boom can be replaced by the net volume. The objective function is the net volume of the whole arm, that is f = min W ( A) = Ai Li, Among them, is the section area of each member of the arm frame, and is the length of the arm frame. Optimization Method Optimization method is a traditional method to achieve the minimum value of a single objective function under the control conditions. ASYS program provides two kinds of optimization methods, zero order optimization method and first order optimization method, under normal circumstances, ASYS can handle most of the optimization problems. The zero-order method uses the dependent variable without its partial derivative, so the calculation time is relatively fast, and the zero-order method can effectively deal with much of engineering problems. The first order method involves the partial derivative of the dependent variable on the design variable, and the computer is treated for a long time, which is more suitable for the accurate optimization analysis. This problem does not n i= 1 (5)

5 exist the partial derivative of the dependent variable to the design variable, so the zero-order optimization method can be used. Optimization Process The order to solve the optimization design is OPEXE. Enter the command OPLIST, ALL,, 1, the system will pop up the results of the optimization of the dialog box. Dialog box can view all the optimization results. Only the optimal design sequence is listed here: *SET 23* (FEASIBLE) R1 (DV) D1 (DV) R3 (DV) D3 (DV) R5 (DV) R6 (DV) R7 (DV) D7 (DV) R9 (DV) D9 (DV) HD (DV) MAXU (SV) SMAX (SV) VTOT (OBJ) E+10 Optimization Results Through the above settings, the ASYS parametric model is generated. The above model was optimized by the optimization method provided by ASYS software. Then, the optimized data are calculated and analyzed. Under the premise of satisfying the strength, rigidity and stability of the design requirements, the net volume of the arm frame of the folding arm type tower crane is reduced by 14.89%. The effect of weight loss is more obvious. Table 1. Optimization results (the units unindicated are mm). ame Original data Optimized data Round data R D R D R R HD R D R D total volume (mm 3 ) E E E+10 max stress ( MPa ) max deformation

6 Figure 4. Equivalent deformation diagram before optimization. Figure 5. Equivalent deformation diagram after round. Conclusions The parametric model is built by ASYS platform folding jib tower crane jib structure. Using the optimization module of ASYS to optimize the parameters of the section parameters of the crane boom, the lightweight design of the arm frame is completed. Under the premise of meeting the strength, rigidity and stability of the boom structure. The maximum equivalent stress of the optimized scheme is increased by 26.95% compared with the original design scheme, the maximum equivalent deformation is increased by 7.03%, the net volume is reduced by 14.89%, and the weight loss effect is remarkable. The results show that the structure optimization design based on ASYS is effective and practical when solving the optimization problem of the large boom structure, especially in the optimization problem of large-scale complex structure with other algorithms cannot be replaced. References [1] Mingqin Zhang. Innovative design of lifting and folding mechanism of light folding arm type tower crane. Engineering Machinery, [2] Gening Xu. Metal structure design of machinery equipment (second edition). China Machine Press, [3] Lingxiao Zhang. Analysis and optimization design of tower crane boom structure based on ASYS. Master Thesis of Yanbian University, [4] Xuehui Zhang. Analysis and design of the structure of the movable arm of the tower crane. Master Thesis of Hebei University of Technology, [5] Lei Li. Study on practical optimization method of steel structure of tower crane. Master Thesis of Shandong Architecture University, [6] Xiuli Zhang, Yingchun Liang,Aihua Yuan. Multi objective fuzzy optimization of mechanical structures [J]. Journal of Harbin Institute of Technology, 2008.