Bulk terminal simulation: a simulation model as a means of designing
transhipment facilities for bulk-goods.
Report 92.3.LT.3000, Transport Technology, Logistic Engineering.
Designing dry bulk terminals is a complicated task. The often complicated
control rules and product flows are difficult to describe. The performance
indicators of a complicated terminal model, cannot always be worked out with
standard methods. Hence the need to support the design project with a simulation
programme arises. The simulation programme will serve as a dimensioning tool in
the design of facilities for transhipment and temporary storage of dry bulk
goods. The simulation programme also has to be capable to follow the imitated
unshipment process by means of animation. Animation is the first possibility
to check whether the programma is working properly or not and also is an
important presentation tool to the customer.
Before we can discuss the functional demands, purposes and rules of a
simulation programme for dry bulk goods, a clear view of the terminal
process is indispensable. In chapter 1 the terminal is studied in depth.
The main object of terminal design is to render perfect service to the
client at minimal costs. The choice of handling equipment is therefore of
the utmost importance. In terminal design we are mainly interested in the
functionality of the appliances, we distinguish peak, rated and effective
capacity. The appliances can be divided into three major groups:
Simulation is a synthetical method for supporting and checking the
design process. We can distinguish analog and digital simulation. General
rules for simulation are: keep it simple, simulate long and often, check the
results as often as possible and do not expect exact answers.
- (un)loading systems;
- support systems;
- storage equipment.
For the design of a dry bulk terminal a design route has to be followed.
First a function model has to be made (chapter 2). The function models are
made with the Structured Analysis and Design Technique (SADT, appendix A). The
main steps are: determine requirements terminal, make global design,
integrate and parametrise, evaluate terminal design, specify
configurations. Each of these steps will be 'zoomed in'. From
the function model the data model will be made according to the
Identity Relationship Method (IR-method, appendix B). The data model indicates
the connection and relation between the different dataflows and the dry bulk
terminal. Thereafter the menu structure is made which controls the
terminal simulation programme. Finally the process description and
component/attribute relation for the simulation programma is described.
The order of the process is not as set as described above. During the
design process feedback takes place. Hence the models are subject to
When the terminal design is ready and the data for the
simulation package are set, the software for the simulation model has to
be chosen (chapter 3). MUST has been chosen, a simulation unit that is
added to Turbo Pascal. At a later stage of the project the simulation
software was changed to TAYLOR at the client's request. Taylor is a
menu-controlled simulation programma and is based on nine elements of which
the buffer and machines are most important. The elements can be connected
in order to a model. To each element a number of fundamental entities can
be adapted. For example: disturbance pattern, conditions and triggers that
can manipulate the products that pass the element. After that components
(products) can be guided through the system. Each component can contain a
number of attributes. An attribute is a kind of information carrier.
To approach the continuous character of a dry bulk terminal, a programme
has been chosen whereby the cargo of a ship is divided into sizeable
amounts of cargo-units (chapter 4). At a simulated ship's arrival
(generated or from a datafile) cargo-units are put into an imaginary hold.
Each cargo-unit can thus be treated as an individual component. The cargo
can go in three directions: direct transhipment, semi-direct transhipment,
transhipment into one of the reservoirs (indirect).
When storage takes place a value can be generated that indicates the time
the product spends in the reservoir before being transported. When this
time has passed, the transport generator will be activated. A connection of
the supply- and discharge generator has then been realised. Because adaptation
of the layout is difficult to realise using Taylor, a terminal with ten
generators, ten docking places, forty reservoirs and ten varying transport
generators has been chosen. The amount of lay out groups that will be
active during the simulation can programmed beforehand.
After the simulation is made, a validation has to take place to check
whether the simulation model gives the right performance indicators
(chapter 5). The testing of the performance indicators can be done based
on the performance data of an existing terminal. For the validation of the
terminal simulation programma the data of a terminal in Chittagong,
Bangladesh have been used. The arrival data of mother vessels in '87-'88
have been used as input data for the simulation programma. The performance
indicators of the simulation programme are reasonably similar to the real
or calculated information.
The conclusions of the design of a dry bulk terminal simulation programma
- The designing approach as described in chapter 2 is an indispensable step
for getting a well structured and useful simulation model.
- Taylor is usable simulation software living up to the demand for a dry
bulk simulation model.
- The designed dry bulk terminal simulation programma can be put to good use
for simulation of different types of dry bulk terminals.
- Dividing of the cargo into units is a good method to simulate the
continuous character of a bulk terminal.
- No statement can be made about the accuracy of the simulation results or
the period that has to be simulated when working with generators. This
totally depends on the adaptions of the parameters and the character of
the simulated terminal.
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