CHAPTER 1

1.1 Introduction

A ocean simulator is a physical basin or tank used to carry out hydrodynamic tests with ship models, for the purpose of designing and refining a ship's performance at sea.  There are mainly two ways of estimating a vessels performance before it is built: numerical calculations and with model testing. In the former method, the ship´s performance is investigated by using mathematical models. The latter method has a more practical approach. The idea behind model testing is to make a scaled-down copy of the original vessel. The model can then be tested in a basin where the environment can be controlled. Forces, accelerations and other characteristics are measured on the model and then scaled up to represent the real vessel. This method is considered to be the most accurate way of predicting the vessels performance. The accuracy of numerical calculations has become better but is still not competitive with model testing. Numerical calculations are today used to estimate the performance of the ship and to optimize the ships geometry. However, model trials are needed to verify the calculations before the final ship geometry are decided. Due to its importance, model testing is a large part of the syllabus in most maritime educations

As contrary to large scale unitized mass production like motorbikes or cell phones, mega machines such as ships involve rigorous vigil at each and every point of construction, starting from the design phase to the ship launching phase. As ship design and construction are time-consuming and tedious processes, various errors and inaccuracies are assessed right from the very early stages, by taking precautions and tests at each and every step.

It is for this reason that ship model testing plays a pivotal role right from the basic design stages of a pre-constructed ship. The purpose or the need for ship modeling is explanatory in its name itself; wherein a large object such as a floating vessel can be assessed on a miniature scale, allowing visualizing of a ships behavior and other physical characteristics before the commencement of ship construction.

Not only for ship designers, but even in vast research and development field of naval architecture or ocean engineering studies, model tests are crucial for study of waterborne structure such as offshore rigs, oil platforms, oil wells, floating harbors or jetties, etc. In recent times, the emergence of ship design software and other path-breaking simulation systems have eased the complexities of manual model testing operations to a considerable extent. However, the significance of physically testing a model still remains as even the software-based approaches have their limitations and often rely on the empirical relations established through physical tests.

1.2 Background

Experimental facilities for model testing of ships have a long tradition. Improved resistance performance of the ships was early the main driving force behind the development of ship model testing. It is known that Leonardo Da Vinci (about year 1500) carried out tests with 3 models of ships, all with equal length, but with different fore and aft shape. Based on his experiments he was able to give recommendation about which shape gives the highest speed. Later Samuel Fortey (1622‐1651) also did tests with ship models and in 1721 Emanuel Swedenborg gave a detailed proposal for ship model testing introducing the principle with falling weight for towing of the models. In this way he was able to achieve a known and constant towing force.  In 1761 this principle was used in Peerlesspool in London as shown on the picture given in Figure 1.1. At that time no scaling laws were available to predict full scale behavior and one had to assume that the winner was the best also in full scale. William Froude (1810‐1879) is often given the honor for the method of really using model testing for ship design by the development of a method for scaling from model resistance to the actual ship resistance. This may be right, but several other works from the same time also contribute significantly to this development. The establishing of the scaling methods should therefore more be regarded as a result of the increasing interest and activities within this field. Froude’s towing tank was built in South England in ca 1870 and is regarded as the beginning of modern model testing. The main dimension of the tank was L x B x d=85 m x 11 m x 3m. It was equipped with a rail in the roof, which carried the dynamometers. Maximum speed was 5 m/s. Shortly after this tank was established, several other tanks were built in England, Germany and elsewhere. The towing tank in Trondheim was completed in 1939 with dimension L x B x d=170 m x 10.5 m x 5m, which was a normal tank size at that time. Later, the development within ship technology has initiated development and building of specialised facilities as cavitation tunnels, manoeuvring and sea keeping basins. During the last 20‐25 years the needs from the offshore industry have pushed this development even further, and complex laboratories with the possibility of testing structures in realistic conditions including wind, current as well as multidirectional waves, have been built. An example of this type of laboratory is the Ocean Basin at MARINTEK. Different types of facilities are described in more details further into this work.

1.3 Statement of the problem

The inability of ship builders to test ship model perfectly before building so as to know the limitations and correction to be made on the ship when building a new design. The inability to create a test tank that can hold water perfectly at the same time control the flow of water. The high cost of building large size test tank

1.4 Aim& Objectives

To design and construct a ship model design water flow tank

Objectives

1.       To achieve relevant design data to verify performance of actual concepts for ships and other marine structures  

2.       Verification and calibration of theoretical methods and numerical codes

3.       To obtain a better understanding of physical problems.  

3.All the aims can be associated to the often very complicated nature of problems connected to the interaction between fixed and floating structures and the marine environment.  

4.      To select system component

5.      To select system material

1.5 Significance of the work

To create a simulation of river that can aid the testing of water crafts or water vehicle models as in the case of real life Situations so as to discover the challenges short comings that the vehicle might develop when built and correct them before the commencement of the real design. It also aids in revealing the behavior of the intended design in real life situations when the model is tested on the tank. It also shows the rise and fall in tide and shows the normal behavior of water as in the case of a flowing river.

1.6 Scope of research

·         Carry out literature review on the study of marine test tank for ship model design

·         Discuss in details types of test tank

·         Discuss the theories that are applied in the design of this wo

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