Parametric Optimization of Hydraulic Modular Trailer Frame using ANSYS (APDL)

Transcription

1 INSTITUTE OF TECHNOLOGY, NIRMA UNIVERSITY, AHMEDABAD Parametric Optimization of Hydraulic Modular Trailer Frame using ANSYS (APDL) A. D. M. Chauhan, B. Prof. S. B. Soni and C. Prof. A. M. Gohil 3 A. M.Tech Student, Mechanical Engg. Department, Institute of Technology, Nirma University, Ahmedabad B. Visiting Professor, Mechanical Engg. Department, Institute of Technology, Nirma University, Ahmedabad C. Professor, Mechanical Engg. Department, Institute of Technology, Nirma University, Ahmedabad Abstract-- Hydraulic Modular Trailer (HMT) is one of the safest way to transport heavy and over dimensional objects on road. Gross laden weight of HMT is fixed based on permitted load per axle as per standards. To have higher pay load capacity, unladen weight of the HMT should be optimum. Major load (unladen) of the HMT is shared by the frame hence weight optimization can be done to increase the payload capacity of the trailer. In this paper, parametric model of the benchmarked frame is prepared using SHELL63 4node elastic element in ANSYS APDL language. Frame is optimized using design optimization module available in ANSYS using first order optimization method. Index Terms Hydraulic Modular Trailer, First order optimization method, Gross laden weight, ANSYS APDL I I. INTRODUCTION n India, the over dimensional cargos (ODC) market is poised to have a good market potential with renewed interest on the infrastructure and industrial development projects. Although there is huge growth potential, there is still need to have suitable transportation methodology and technology compared to developed countries. Further, there is a growing need for providing efficient and safe transportation and for that one of the vehicle types is Hydraulic modular trailer (HMT). Many researchers carried out study on truck frame. C. Karaoglu and N. S. Kuralay investigated stress analysis of truck chassis with riveted joints using FEM. Numerical results showed that stresses on the side member can be reduced by increasing the side member thickness locally. If the thickness change is not possible, increasing the connection plate length may be a good alternative [1]. S. Prabhu has also worked on a stress analysis of a truck chassis through FEA []. T.H.Fui, R.Abd.Rahman presented the study of the vibration characteristics of the truck chassis that include the natural frequencies and mode shapes. The results shows that the road excitation is the main disturbance to the truck chassis as the chassis natural frequencies lie within the road excitation frequency range [3]. A. Dubey and V. Dwivedi have worked on different load cases and boundary conditions for the stress analysis of chassis using FEA in ANSYS. Shell element has been used for the longitudinal members and cross members of the chassis [4]. S. Tiwari has carried out his dissertation work to obtain relationship between high level design variables having dominating effect and performance criteria of a ladder type chassis frame. Lumped Parameter Model (Mathematical Model) was used to perform weight optimization of chassis frame within design envelope. Where time, cost and accuracy based comparison of FE analysis using shell and beam element is given. FE analysis using shell element gives highly accurate result, however time taken and cost are also high [5]. A.M. Harte, J.F. McNamara, I.D. Roddy have studied the optimization of design parameters associated with composite sandwich body shell walls of light rail vehicles (LRV) [6]. Zbigniew Sekulski has applied genetic algorithm (GA) to solve the problem of weight minimization of a high speed vehicle-passenger catamaran structure with several design variables such as dimensions of the plate thickness, spacing between longitudinal and transversal members [7]. The integration of computer aided design and engineering software codes (Pro/Engineering, ADAMS, and ANSYS) to simulate the effect of design changes to the truck frame has been studied by C. Cosme et al. In this paper, shell element is used for analysis in ANSYS [5]. V. Bhasker, R. Babu and V. Shekhar have presented an integration and automation process solution for design and development of automotive frame structures, driven by CAE. Traditionally shell element is used for design and development of automotive frame, here attempt is made to use simplified 1-D FE model using Hypermesh at early design stage to reduce development process time [8]. However authors have not optimized the frame using -D FE model. Here an attempt is made to optimize hydraulic modular trailer frame using ANSYS APDL language. II. HYDRAULIC MODULAR TRAILER 1) General HMT is essentially a robust platform carrying series of wheels with hydraulic suspensions and capable of being steered hydro-mechanically as shown in Figure 1. It is mostly used to transport and handle oversize and overweight structure. Main features of the trailer are steerable wheels (all) by hydro-mechanical steering system, adjustable

2 481 INSTITUTE OF TECHNOLOGY, NIRMA UNIVERSITY, AHMEDABAD 38 platform height by hydraulic suspension system and modular in nature so it can connect n number of trailers side by side and end by end as per load type. As per the Automotive Industry Standard, AIS-53[9], HMT is a full trailer [10] and comes under T5 - category (Towed vehicle) Main cross member-mcm Side long member-slm End cross member-ecm Main long member-mlm Fig.1 Schematic view of Hydraulic modular trailer model with transparent frame ) General Specification 1. Permissible axle loadings: As per IRC-3:1983 [11], axle loading should not exceed 18 tones per axle.. Overall width (w) and length (l): As per Central motor vehicles rules, 1989 [1], overall width should not exceed 3 m and length of tractor trailer combination should not exceed 18 m. From survey of different manufacturer, length of six axle trailer is taken as 9 m. So overall dimensions of the frame is 9 m 3 m. 3. Axle spacing (b): As per IRC-3:1983 [11], axle spacing is not less than 1. m but not more than.5 m apart. From survey of different manufacturer, axle spacing is taken as Overall wheelbase (t): From survey of different manufacturer, wheel base is taken as 1.8 m. IV. MODELING AND ANALYSIS PROCEDURE Whole modeling, analysis and optimization are done using ANSYS APDL [13], which stands for ANSYS Parametric Design Language, a scripting language that can use to automate common tasks or even build model in terms of parameters (variables). 1) Modeling All necessary member properties are defined as a parameter. Co-ordinates of key points are defined using parameters and areas are created by connecting those key points. Thus surface model is created of the frame by defining parameter. If we change the value of one parameter, whole model changes accordingly. Then member s flange and web thicknesses are defined as a real constant. Meshing is done using SHELL63 4node elastic element. As per IS 06 [14], the material of frame is E 50(Fe 410 W) C with 50 N/ mm of yield strength and 410 N/ mm of ultimate tensile strength. By considering safety factor.5, permissible yield strength for the frame is 100 N/ mm. Other properties of frame material are as shown in Table II. Table II. Material properties of Tretec frame mm ) Modulus of Elasticity E (N/ 10 3 Density ρ (Kg/ mm ) 7850 Poisson Ratio µ 0.3 Yield Strength (N/ mm ) 50 Tensile Strength (N/ mm ) Fig. General specification of Hydraulic modular trailer III. BENCHMARKING From the survey of different manufacturers, Tretec frame (Six axles) is benchmarked for study. It consists of built up box sections for all the frame members, i.e. main long member, main cross members, end cross members, side long members as shown in Figure 3. Here general members properties (in mm) of Tretec frame are as shown in Table I. Table I. Sectional properties (in mm) of different members of Tretec frame Member Flange width ( B ) Flange thickness ( t f ) Web depth ( D ) Web thickness ( t w ) Fig.3 Surface model of Tratec frame in ANSYS

3 INSTITUTE OF TECHNOLOGY, NIRMA UNIVERSITY, AHMEDABAD ) Analysis First modal analysis is carried out in free-free boundary condition. There is not any rotating part like engine on frame, and road excitation is the main disturbance to the trailer frame. Maximum vehicle speed is 15 km/hr. From modal analysis, natural frequencies are found in the range of 41Hz to 9Hz which is far away from actual working condition. So, only linear static stress analysis is carried out considering dynamic load factor. The load is assumed as a uniform pressure obtained from gross laden weight divided by the total upper flange area of frame [15]. Detail loading of model is shown in Figure 4. The load intensity is determined by: p F A N = = (1) mm = Where, F = (Load /axle) (No. of axle) (Dynamic load factor) g A = Total loading area of frame (mm 3 ) p = Load intensity (N/mm ) Fixed boundary conditions are applied on rectangular area at bottom of side long members, where axle and suspension systems are attached with bearing. The meshed trailer frame has 9800 elements and 9588 nodes. Objective function 3 Volume ( mm ) State Variable Von-Mises stress (N/ mm ) Deflection ( mm ) Design Variable (in mm ) B MCM D B SLM D B ECM D B MLM D Fig.4 loading and boundary condition in Tretec frame V. OPTIMIZATION PROCEDURE Here attempt is made to size optimization of trailer frame. Reduction in volume is taken as objective function. Von- Mises stress and deflection are taken as constrains. Based on functional requirements, members width, height, and plate thickness are taken as design variables and their minimum and maximum limits are given. Optimization is done using first order method available in ANSYS with following inputs: 1. Maximum iterations = 100. Percent step size = Percent forward difference = 0. Optimization variables and their convergence tolerance criteria are as per Table III. VI. RESULTS AND DISCUSSION First linear static stress analysis is carried out of a benchmarked Tretec frame which is to be optimized. After carrying the analysis, Von-Mises stress of the frame is N/ mm which is higher than the permissible yield strength and deflection value is mm as shown in Figures 5 and 6 respectively. In the optimization of the above frame, the solution has converged to the optimum in 81 iterations. Initial parameter and result of optimization is as shown in Table IV. Variation of different parameters against the iteration number are as per the graph as shown in Figures from 7 to14. As the optimized parameter shows non standard value, the parameters are standardized taking the nearest higher value available in IS 1730:1995 [16]. Finally linear static stress analysis of optimized standard frame and the Von-Mises stress and deflection for frame are shown in Figures 15 and 16 respectively. Here, value of Von-Mises stress is less than permissible yield stress. Table III. Optimization variables (in mm) and their convergence tolerance for Tretec frame. Minimum Maximum Tolerance

4 4 481 INSTITUTE OF TECHNOLOGY, NIRMA UNIVERSITY, AHMEDABAD 38 Fig.5 Von-Mises stress in Tretec frame (Before optimization) Fig.7 Top surface area v/s Number of optimization iterations grap Fig.6 Deflection in Tretec frame (Before optimization) Table IV. Section parameter (in mm) of Tretec frame before and after optimization. Member Property Initial Optimized Standardized MCM B t f D t w SLM B t f D t w ECM B t f D t w MLM B t f D t w Fig.8 Pressure acting on frame v/s Number of optimization iterations graph Fig.9 Total volume v/s Number of optimization iterations graph Von-Mises Stress mm ) (N/ Deflection ( mm ) Volume( mm ) Mass ( Kg )

5 INSTITUTE OF TECHNOLOGY, NIRMA UNIVERSITY, AHMEDABAD Fig.10 Von-Mises stress v/s Number of optimization iterations graph Fig.13 Different flange and web thicknesses v/s Number of optimization iterations graph Fig.11 Deflection v/s Number of optimization iterations graph Fig.14 Width and height of different members v/s Number of optimization iterations graph Fig.1 Main long web height v/s Number of optimization iterations graph Fig.15 Von-Mises stress in Tretec frame (After optimization)

6 6 481 INSTITUTE OF TECHNOLOGY, NIRMA UNIVERSITY, AHMEDABAD 38 Fig.16 Deflection in Tretec frame (After optimization) VII. CONCLUSION Tretec frame is optimized and feasible design was obtained with 5 % reduction in mass as shown in Table V. This reduction in mass of the frame increases the payload capacity by tones approximately. Table V. Percentage change in Tretec frame parameter due to optimization Initial standardized % change 3 9 Volume( mm ) Mass ( Kg ) Von-Mises Stress mm ) (N/ Deflection ( mm ) During optimization of Tretec frame, it is found that the value of flange thickness is decreased and value of web thickness is increased in two members namely side long member and main cross member as shown in Table VI. So, web thicknesses value should be kept more than the flange thicknesses value for those respective members. Table VI. Change in flange and web thickness (In mm) of Tretec frame members due to optimization Initial Standardized Main cross flange thickness 0 10 Main cross web thickness 1 16 Side long flange thickness Side long web thickness 10 5 There is a greater reduction in main long member properties of the frame as shown in Table VII. Table VII. Change in main long member properties (In mm) of Tretec frame Initial Standardized Main long flange thickness Main long web thickness 30 8 VIII. REFERENCES [1] C. Karaoglu and N. S. Kuralay, Stress analysis of a truck chassis with riveted joints. Finite element in analysis and design, Elsever, pages , 00. [] S. Prabhu, Stress analysis on truck chassis using finite element analysis. Intenational Journal of mechanical Engineers (India), Volume 1, issue 1, pages 55-61, January- June 008. [3] T. H. Fui and R. Abd. Rahman, Static and dynamics structural analysis of a 4.5 ton truck chassis. Jurnal Mekanikal, No. 4, pages 56-67, 007. [4] A. Dubey and V. Dwivedi, Vehicle chassis analysis: load cases and boundary conditions for stress analysis. In 11th National Conference on Machines and Mechanisms. IIT, Delhi, India, December 003. [5] S. Tiwari, Evolution of empirical relationship between high level design parameters with performance criteria of a ladder type chassis frame. Master's thesis, Institute of Technology, Nirma University, May 007. [6] A.M. Harte, J.F. McNamara, I.D. Roddy, A multilevel approach to the optimisation of a composite light rail vehicle bodyshell., Composite Structures, Elsever, pages , 004. [7] Zbigniew Sekulski, Least-weight topology and size optimization of high speed vehicle-passenger catamaran structure by genetic algorithm., Marine Structures, Elsever, pages , 009. [8] V. Bhasker, R. Babu and V. Shekhar, Process integration and automation solutions for rapid designing of automotive frame structures using altair hyperworks. In Hyperworks Technology Conference. Altair Hyper works, 008. [9] Automotive Industry Standard. AIS-053: Automotive Vehicles-Types - Terminology. [10] Automotive Industry Standard. AIS-93: Code of practice for construction and approval of truck cabs, truck bodies and trailers. [11] The Indian Road Congress, New Delhi. IRC 3: 1083, Dimensions and weights of road design vehicle, first revision edition. [1] The Central Motor Vehicles Rules, [13] ANSYS help. [14] Bureau of Indian Standards, New Delhi. IS 06:1999, Steel for general structural purposes-specification, fifth revision edition. [15] O. Kurdi, R. Abd. Rahman and M. N. Tamin. Stress analysis of heavy duty truck chassis using finite element method. Faculty of Mechanical Engineering, Universiti Teknologi Malaysia. [16] Bureau of Indian Standards, New Delhi. IS 1730:1995, steel plates, sheets, strips and flats for structural and general engineering purposes-dimensions, second revision edition.