Structural improvement and weight reduction calcul

Structural improvement and weight reduction calculation and analysis of high-power internal combustion engine locomotive

1 overview

in order to meet the requirements of speed-up and heavy load of railway freight in China, it is planned to develop a heavy-duty locomotive equipped with high-power internal combustion engine. The locomotive body adopts an integral load-bearing structure. Compared with the current general diesel locomotive body (such as Dongfeng 8b locomotive body), the weight of diesel engine, motor and other components borne by the middle of the locomotive body increases a lot, and the center distance of side bearing groups at both ends of the underframe is enlarged. As the main bearing structure of the locomotive, the optimization design of the steel structure of the car body is the main task in the development of the locomotive. The steel structure of the car body must realize the lightweight design under the requirements of the strength and stiffness of the car body, so as to meet the requirements of the axle weight of the locomotive. In order to guide and realize the optimization design of the car body steel structure, we adopted the large-scale finite element analysis software ANSYS of a multi cavity mold. On the basis of many analogy and optimization calculations in the early stage, we calculated, improved, optimized and reduced weight the design scheme of the car body structure of the locomotive again

2 introduction to body structure

the locomotive body is composed of cab, top cover, side wall, underframe, partition wall and other parts, and is the main bearing structure of the locomotive. When the locomotive is in operation, the car body structure should bear not only the vertical load acted by the upper equipment, but also the traction force, transverse force, longitudinal tension, longitudinal compression and other loads that may be encountered with large values. In order to ensure the strength and stiffness requirements of the car body steel structure, the key bearing parts of the car body, such as the diesel engine beam, side bearing beam, main engine beam, side beam, traction beam, cross beam of the underframe, the top chord beam and column of the side wall, and the cab column, The main bearing beams of the top cover adopt the closed composite section structure welded by steel plate, steel plate bending parts, channel steel, etc; The side wall of the car body adopts a truss frame composite structure composed of side wall columns, upper chord beams and cross diagonal braces; A box shaped traction diagonal brace is connected between the traction beam of the underframe of the car body and the side beam of the underframe to ensure that the longitudinal loads such as traction load, tensile load and compression load with large values are effectively transmitted from the plate seat, traction beam and traction diagonal brace to the side bearing beam and the side beam of the underframe through the front and rear, and then to the whole car body; The cab, top cover, side wall, underframe and partition wall of the car body are welded together to make the car body an integral load-bearing car body. When the integral oil tank is used, the oil tank is welded in the middle of the underframe of the car body, so that the car body and the oil tank can be loaded together

3 establishment of calculation model

the structure of the car body is complex and huge, and its structure and load do not have strict symmetry. In order to accurately simulate the structural characteristics of the car body and make the calculation results reflect the working performance of the car body, a whole car model of the car body is established for calculation and analysis, in which the main bearing structure and main bearing parts of the car body are carefully simulated. In order to make the calculation results of the original structure, improved structure and optimized structure of the car body corresponding and comparable, the solid modeling method, lattice division method, lattice size and density control parameters used in the establishment of the model are exactly the same. In order to complete the optimization calculation of the car body, the programming, parameterization, modularization and other technologies of ANSYS software are fully applied when establishing the calculation model

Figure 1 finite element model for calculation of the original structure of the car body (integral oil tank scheme)

Figure 1 is the finite element model for calculation of the original structure of the car body. In order to ensure the calculation accuracy and improve the calculation efficiency, the shell 63 shell element of ANSYS software is used to simulate the steel plate structure of the car body in the model; In the model, according to the installation of the upper equipment of the car body, each upper equipment is simulated with mass21 quality unit acting on its installation position; The secondary spring of the locomotive is simulated by combin14 spring element, and the stiffness of the spring element is considered as 10mm of the static deflection of the locomotive in the servicing state. There are 103098 shell elements, 8832 mass elements, 96 spring elements and 95181 element nodes in the finite element model used for calculation. According to the material of the steel structure of the car body, the material parameters used in the finite element model for calculation are: elastic modulus e=210gpa, Poisson's ratio ν= 0.3, density ρ= 7850kg/mm3, and the mass of the finite element model used for calculation is 20350kg

4 calculation load, calculation working condition, boundary condition and calculation result evaluation of car body

according to different application requirements of locomotive, this analysis refers to tb/t "test method for static strength of car body of internal combustion and electric locomotive", tb/t "code for strength design and test appraisal of railway vehicles", gb3314 "general technical conditions of diesel locomotive", and other specifications and standards, and determines the requirements for calculation working condition and calculation result of car body

4.1 calculation conditions

calculation conditions include: vertical static load condition; Vertical dynamic load condition; Traction condition of forward operation; Traction condition of reverse operation; Forward starting traction condition; 1960kn longitudinal compression condition; 1470kn longitudinal tension condition; Overall lifting condition; One rescue crane working condition; Working condition of two position rescue crane; Protection condition of cab; Modal frequency calculation

4.2 evaluation of calculation results

allowable stress of static strength

material of car body steel structure, the main bearing part is Q345A, and its strength index is yield strength σ S ≥ 345mpa, tensile strength σ b=470~630MPa。

the allowable stress of each working condition is selected as follows:

vertical static load working condition: the safety factor is taken as 2.5, and the allowable stress 〔 σ］= 138MPa；

vertical dynamic load, running traction and other working conditions: the safety factor is taken as 1.5, and the allowable stress is [ σ］= 230MPa；

starting traction, longitudinal tension, longitudinal compression, rescue crane, cab protection and other working conditions: the safety factor is taken as 1.0, and the allowable stress 〔 σ］= 345MPa。

5 optimization analysis of weight reduction of car body structure

the purpose of structural weight reduction optimization analysis of car body is to determine the best lightweight design scheme of car body under the condition of meeting the strength, stiffness, modal frequency and other requirements of car body structure. This optimization analysis adopts the design optimization analysis technology to carry out the weight reduction optimization analysis of the improved structure car body. The results of the optimization analysis ensure the weight reduction requirements of the car body structure as much as possible, and reflect the modular characteristics of the car body structure design

5.1 introduction to design optimization method

the design optimization of locomotive body structure aims to determine the body structure design parameters when the body weight is the minimum value under the condition of meeting the requirements of strength, stiffness and modal frequency of the body structure, so as to provide reference and guidance for the weight reduction design of the body structure

in order to ensure the effectiveness and feasibility of the optimization calculation of the car and tilt the metal ruler back slightly, according to the analysis results and design needs of the improved structure scheme of the car body in the early stage, this optimization analysis selects two typical working conditions of vertical static load and 1960kn longitudinal compression. The fatigue limit is expressed as determining the optimization scheme, and then the strength, stiffness and modal frequency of the car body of the optimization scheme are checked

the parameters and constraints used in the design optimization of the car body structure are:

objective function (obj): select the weight of the car body structure as the objective function, and the goal of the design optimization is to minimize the weight of the car body, even if the car body weight is the lightest

state variable (SVS): select the maximum stress value of the car body structure under the calculated working condition as the state variable. The design optimization of the car body is carried out under the condition of vertical static load. The state variables are the maximum stress value svs1 of the bottom surface of the car body structure and the maximum deflection svs2 of the middle part of the underframe side beam relative to the center of the secondary side bearing group at each end of the locomotive; The design optimization of the car body is carried out under the longitudinal compression condition of 1960kn, and the state variable is the maximum stress value svs1 of the bottom surface of the car body structure

constraints: that is, the maximum stress and maximum deflection in the design optimization do not exceed the corresponding allowable value of the calculation standard. The design optimization of vehicle body under vertical static load conditions requires svs1 ＜ 138mpa, svs2 ＜ 6.68mm; For the design optimization of 1960kn longitudinal compression condition, svs1 is required to be less than 345mpa

design variables (DVS): the selection of design variables strives to meet the modular and lightweight design requirements of vehicle body structure. For example, for diesel engine installation beam, diesel engine beam, side bearing beam and traction beam components, the thickness of their upper cover plate, side plate and lower cover plate is represented by a variable respectively; Different variables are used to express the thickness of different underframe beams, side wall bends in different parts, and side wall braces in different parts; For the side wall column, underframe beam, top cover beam, underframe floor, underframe side beam, underframe end, traction diagonal beam, main generator beam and other components, the plate thickness of the components is expressed by a variable. The design variables selected in the design optimization and the corresponding positions represented by their values are shown in Table 1. Table 1 design variables selected for vehicle body structure design optimization

5.2 design optimization results of vehicle body structure and optimization structure

50 iteration results are calculated for each selected working condition in the design optimization analysis. Figure 2-4 shows the relationship between the optimization state variables (maximum stress, maximum deflection) and the mass of the car body model during the optimization calculation. According to the optimization calculation results, the local structure of the car body can be reduced. Table 2 lists the changes of the thickness and weight of the optimized structure car body parts compared with the original structure car body, and the unchanged ones are not listed. The calculated mass of the optimized structure car body model is 19955kg, which is 662kg lighter than the improved structure of the car body and 395kg lighter than the original structure of the car body

Figure 2 the relationship between the maximum stress on the bottom surface of the car body and the mass of the car body model during the optimization calculation of the vertical static load condition

Table 2 the optimized structure and weight reduction of the car body

Figure 3 the relationship between the maximum deflection of the side beam of the car body underframe and the mass of the car body model during the optimization calculation of the vertical static load condition

Figure 4 the relationship between the maximum stress on the bottom surface of the car body and the mass of the car body model during the optimization calculation of the 1960kn compression condition

note: [1] original structure The thickness of each plate at the end of the underframe and the trabecula of the improved structure is different, and the thickness of each plate is unified according to the modular requirements during the optimization calculation. [2] The upper cover plate, side plate and lower cover plate of the car body underframe beam of the original structure and the improved structure are different, so the thickness of the upper cover plate, side plate and lower cover plate shall be unified according to the modular requirements during the optimization calculation. [3] "-" means weight reduction, "+" means weight increase

5.3 check calculation of optimized structure of car body

strength check

Table 3 lists the maximum calculated stress values of optimized structure car body under various working conditions. For comparison, the maximum stress values of original and improved structure of car body are listed in the table. The calculated stress nephogram of the optimized structure car body under various working conditions is omitted here due to space limitations. Table 3 maximum calculated stress value of optimized structure car body under various working conditions MPa

calculation result analysis of optimized structure of car body

the optimized structure of car body not only adopts the results of improved structure analysis of car body, but also strengthens the main bearing parts of car body, such as diesel engine beam and side bearing beam. Therefore, compared with the original structure car body, although the weight of car body is reduced by 395kg, from the calculation situation, The strength of the car body structure is still much better than that of the original structure

only under the two working conditions of vertical static load and 1960kn longitudinal compression, the stress at very few positions of the optimized structure of the car body is 2~3mpa higher than the allowable stress. Considering the simplification of the calculation model and the conservative treatment of boundary conditions compared with the actual situation, it can be determined that the strength of the optimized structure car body still meets the requirements of the calculation standard

compared with the original structure of the car body, the stress of each part of the optimized structure is greatly reduced, and the stress distribution of the optimized structure car body is more uniform. The optimized structure of the car body is relatively