DECIDING THE OPTIMUM PROFILE OF WATER TRUCK
TANK USING PUGH’S CONCEPT SELECTION METHOD
AND FINITE ELEMENT METHOD
Willyanto Anggono1), Ian Hardianto Siahaan2), Fandi Dwi Saputa3), Wiraatmadja
Lookman4)
Product Innovation and Development Centre Petra Christian University1,2,34)
Mechanical Engineering Petra Christian University1,2,3,4)
Jalan Siwalankerto 121-131, Surabaya 60236
E-mail : willy@petra.ac.id1)
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 Results
The 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/Capacity
2. 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
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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 2 nd 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.