Water trucks tank is - Petra Christian Universityfportfolio.petra.ac.id/user_files/98-023/TI-028.doc · Web viewWith finite element method, calculation that can’t be done manually

DECIDING THE OPTIMUM PROFILE OF WATER TRUCK TANK USING PUGH’S CONCEPT SELECTION METHOD AND FINITE ELEMENT METHOD

Willyanto Anggono 1) , Ian Hardianto Siahaan 2) , Fandi Dwi Saputa 3) , Wiraatmadja Lookman 4)

Product Innovation and Development Centre Petra Christian University1,2,34)

Mechanical Engineering Petra Christian University1,2,3,4)

Jalan Siwalankerto 121-131, Surabaya 60236E-mail : [email protected] 1 )

ABSTRACT

Water truck tank is a storage tank that is attached on a truck and designed to carry liquid loads on the highway. The shape of the standard water truck tank profile is elliptical. This elliptical shape is not the optimum shape considering the thinning of the stocks of fossil fuel in the world. Now a day, the price of fossil fuel became more expensive. For that reason, a competitive design of water truck tank that can adapt to this situation is needed. The solution for this problem is making bigger the capacity of the tank it self. This capacity changes require modification of the tanks design. Changing the length, width, and height of the tank is not permit able because it will change the center gravity of the tank. Changing the profile is more recommended because it’s more easy and efficient. Now a day, many different profiles of the water truck tank can be seen on the highway in Indonesia. This new design used manual calculation in the design process. Manual calculation is not efficient and time consuming, the stress concentration that is happened in the water truck tank is also cannot be predicted and visualized. This stress concentration calculation is commonly used in a large-scale and well-known manufacturer. The most small-scale manufacturer is likely not used any stress calculation at all. They used only formula that are given from DLLAJR (The unit of the Government that’s responsible on publics transport) that requires only volume calculation, the dimension and thickness is fixed and recommended not to be change. This formula is invented for elliptical profile only, another design is not given yet. Using this formula for another design profile can be dangerous and highly not recommended. With finite element method, calculation that can’t be done manually can be simulated so the stress that happened within can be analyzed and predicted nicely. Simulation process can safe money and time spent on designing a model. (Anggono, 2004). The final result of this experiment is to acquire the optimum profile of the water truck tank using Pugh’s concept selection and finite element method. This experiment uses ANSYS (computer software based on Finite Element Method) to analyze the stress of which the tanks suffer and acquire its safety factor based on the value of the maximum stress of the tanks. While the decision matrix is used to decide which tank is the most optimum based on the buyer and manufacturer criteria.Based on the result acquired from the analysis of the water tanks profile (8 models available, according to the market requirements) using ANSYS software and Pugh’s concept selection, Trapezoid profile is the most optimum profile within this experiment. According to the design parameter of this experiment with uniform tanks dimension and thickness. Finite Element Method is highly recommended in designing an optimum profile of water truck tank because it can simulate the stress of the water tank like the real condition.

Keywords: Water truck tank, Optimum Profile, Maximum stress, Finite element method.

1. INTRODUCTION

Due to the energy crisis that happened to the world lately, the price of motors fuel became so expensive and people’s ability to buy has decreased. Water suppliers are demanded to accommodate fresh clean water with affordable price. One of the solution is to cut the expenditure that spent on transportation of the water it self. With bigger design water tanks capacity, more water can be transported. This will effect on

the amount needed to transport the water become more less and efficient. To obtained bigger capacity, the design of the tank must be changed. However, changing the dimension is not an option. The other way to do it, is to modify the profile of the tank. But, the change will effect on the maximum stress that happened within the tank, looking at the shape of the profile that’s so complex (non linear geometry structural). Planning the design using analytical solution with manual calculation is so hard to accomplish. Its due to stress distribution that happened within the tank is so complex to be calculated manually and the areas that suffer maximum stress cannot be predicted. With finite element method, calculation on the tank that cannot be done using manual calculation can be accomplished. Finite element is the best solution applied on the calculation of pressure vessel (Heckman, 1998).

Figure 1. Water Truck with Ellipse Tank

Figure 2. Water Trucks with Non-Ellipse tank

2. REVIEW OF THEORITICAL BACKGROUND AND MODELS RESEARCH METHODOLOGY.

2.1. Finite Element Method

The finite element method (FEM), also called FEA (finite element analysis), is actually an approximate mathematical method for solving problems, which can be determined by differential equations. The main idea of FEM is to break a complicated problem with irregular edge conditions into small pieces

(elements) of a finite size. Each piece is considered to be part of the main problem. Thus connected to the others pieces via the global state information (i.e. deformation) of the elements nodes. Which are common nodes with the neighborhood elements. For the small element it self, the internal physical laws (i.e. Hooks law for elastic deformation problems) can be calculated. The global problem can be transformed into a matrix of simple element equations, which are connected by the condition, that common nodes undergo the same change of global state. Forces, which act on the edge of the global thing, can be simplified as acting at discreet nodes. This all together gives a big system of mostly linear equations, which can be easily solved by computer. The result is the change of global state for each node (i.e. the new node coordinates after the deforming of structures. Having this, further information for the small elements it self can be obtained, i.e. the element stress in each direction (Budynas, 1999)

2.2. The models

The design of the water tank can be limitless, because the design parameters according only to the trucks dimension and the GVW (gross vehicle weight) of the truck, the geometry structural design is up to the designer. Its common to see the design calculation of the water trucks tank from every manufacture different from another. So there are to many designs of experiments in respect of the geometrical profile of the tank to be tested. The experiments range should be narrowed. After many studies on tanks design, eight major models are acquired. These models are to be simulated and tested to acquire the maximum stress that happened within each tanks. The profile of the models are: Ellipse, Circle, Rectangular, 1/2 Elliptical, 1/2

Rectangular, Rectangular with Curved Side, Rectangular with Top Bottom Curved, Trapezoid. And can be seen at Figure 3.

Figure 3. (left-right) Ellipse, Circle, Rectangular, 1/2 Elliptical, 1/2 Rectangular, Polygon Rectangular with Curved Side, Rectangular with Top Bottom Curved, Trapezoid with Curves.

2.3. Element Type

To be familiar with some element types and potential element types to fulfill the needs in this problem that can be used in ANSYS are needed before using the ANSYS program to solve the problem. The possible

element types that can be used to solve the problem are SHELL63 4-Node structural shell, SHELL93 8-Node structural shell, and SOLID95 3-D 20-Node structural solid.The simulation is very important to solve the problem. After knowing the possibilities using element type and the material behavior from the explanation above, we perform a simulation in ANSYS using SHELL63 element type because it’s easier and take less time to produce a model (Lookman,2007).

3. RESEARCH METHODOLOGY

Figure 4. Research Methodology

4. RESULTS AND ANALYSIS

4.1. Simulation and ResultsThe models are simulated with ANSYS using symmetric shell modeling with both free and mapped meshing. After the models are finished, they will be applied with boundary condition and displacements to achieve simulation based on real water tanks and applied with internal hydrostatic water pressure afterwards. The simulation is complete and the results are ready to be analyzed.

Figure 6. Deformation and Von Misses Stress of each tanks(left-right) Ellipse, Circle, Rectangular, 1/2 Elliptical, 1/2 Rectangular,

Polygon Rectangular with Curved Side, Rectangular with Top Bottom Curved, Trapezoid with Curves

4.2. Profile Selection

The goal of this experiment is to achieve optimum profile, where the optimum is not according only to its safety factor but also from the criteria that have been surveyed from both manufacturers and buyers. The main and decisive criteria are:1. Volume/Capacity2. Price, (according only to material point of view)3. Production Process and maintenance.

Below are the data of the capacity and surface area of the tanks, this data is acquired using Mechanical Desktop. As a software that are used to design the models.

Table 1. Maximum Stress and Safety Factor of each Tanks

The safety factor of the tanks that less than 2, is considered not safe and can’t be used. This according to theoretical calculation of thin walled pressure vessel, where safety factor of pressure vessel with information on yield stress can’t be less than 2.

This criteria later, are combined with the safety factor that acquired before. And be made a design comparison according to Pugh’s weighted decision matrix with 5-point scale weighing factor. With the result as follow:

Table 2. Decision Matrix for Optimum Profile

Trapezoid in this table of comparison acquired the highest score of all with total weighing value of 34. Therefore Trapezoid is the most optimum profile within this experiment according to its safety factor and any other criteria from the market.

5. CONCLUSION

Designing Water Trucks tank with manual calculation is very hard and require a lot of time. The stress distribution within also cannot be predicted. Therefore designing with manual calculation is not efficient and inaccurate. Using finite element method technology changing material and shape are very easy to do and many other designs can be made easily. Reducing cost, material and time of the design is the most important aspect.

Stress that happened within the tank is depends on its profile (in condition the material and thickness is uniform). The main concern of designing a water tank is it’s lower half profile, the area beneath equator

line. Because this area suffer the maximum pressure of water. So it’s crucial to have curvature geometry at the bottom of the profile to minimize stress concentration.

In this experiment, Trapezoid is the best profile regarding to the criteria that surveyed trough market. It has a high standard of safety and could store much more water. The cost that needs to build it is not much different from the standard tank (according to it’s material). See Table 1 for the details. It’s recommended to use this profile if the capacity is one of the main concerns. (According to this experiment design parameters).

6. REFERENCES

[1] Anggono, W. (2006) Analisa Pengaruh Radius Heads Terhadap Besar Tegangan Maksimum pada Air Receiver Tank Horisontal dengan menggunakan Metode Elemen Hingga. Proc. National Seminar on Application and Research in Industrial Technology 2006 (Yogyakarta) April 27th, pp 78-86.

[2] Lookman, Wiraatmaja. (2007) Analisa Pengaruh Penampang Tangki Muatan Truk Air Terhadap Tegangan Maksimum Yang Terjadi Akibat Tekanan Hidrostatis Dengan Menggunakan Metode Elemen Hingga Dalam Penentuan Profil Optimum, Tugas Akhir Jurusan Teknik Mesin, Universitas Kristen Petra, Surabaya, (2007)

[2] Harvey, John F. Theory and Design of Modern Pressure Vessel 2nd edition. New York: Van Nonstrand Reinhold Company, 1974.

[3] Farr, James R. Guidebook for The Design of ASME Section VIII Pressure Vessel. New York: ASME, 2001[4] Pugh, S. (1991). Total Design: Integrated Methods for Successful Product Engineering, Addison-Wesley Publishing

Company, Inc., USA pp 8-59.[5] Budynas, Richard, G (1999) Advanced Strength and Applied Stress Analysis, McGraw-Hill Book Company,

Singapore pp 7-69.[6] ANSYS, Inc. (2005) ANSYS 10.0 Documentation, USA.[7] Heckman, David. Finite Element Analysis of Pressure Vessel MBARI 1998.[8] Zero-G neogravity.com Pressure Vessel Requirement.[9] Logan, Daryl L. Mechanics of Material. New York, 1991.[10] Dieter, George E. Engineering Design 3rd Edition. Singapore: McGraw-Hill Book Company, 2000.