In this blog post, we will look at the principle of fatigue, which occurs when repeated forces accumulate, and how it affects ship structures.
On January 16, 1943, an American tanker named “Skinner” anchored in a port in Portland, Oregon, was split in two by fatigue. And until a torpedo was found, fatigue was one of the hypotheses for the cause of the sinking of the Cheonan in 2010. So what is fatigue failure that it can destroy a ship?
Fatigue failure can be easily understood by thinking of bending a piece of wire. A piece of wire will not break unless it is subjected to a strong cutting force at once, but if it is bent repeatedly, it will break easily even with a small force. The same is true for ships. Ships are exposed to repeated forces at sea, and as this process continues, even a force less than that required to destroy the ship will cause it to break at some point.
So, is fatigue the only cause of shipwrecks? Of course not. Like the famous Titanic, a ship may sink after hitting an iceberg, or like the Cheonan, it may be hit by a torpedo or reef, or it may capsize and sink due to strong winds or waves. In addition, ships are subject to various forces while sailing and even when anchored, and if these forces are strong enough, they can destroy the ship and cause it to sink. So what forces do ships encounter at sea?
First, in order for a ship to float, its weight, or the force acting downward, must be equal to the buoyancy of the water, or the force acting upward. In this way, the ship as a whole is in equilibrium between its weight and buoyancy, but in some parts of the ship, the weight may be greater than the buoyancy, and in other parts, the buoyancy may be greater than the weight. Ultimately, the ship is subjected to uneven forces due to the difference in weight and buoyancy in the longitudinal direction, which causes a force that tends to bend the ship in the longitudinal direction.
There is also a force that acts to deform the cross section, or the surface cut perpendicular to the length of the ship. In the part of the ship submerged in water, external water pressure acts, and the weight of the cargo and various machinery on the ship acts to deform the cross section. In addition, when a ship is sailing, it may be tilted to the side by the wind or encounter waves, causing a force that tries to twist the ship. When a ship tilts due to wind or encounters waves, the depth of the ship’s submerged parts on the left and right sides becomes different, which ultimately causes the buoyancy acting on both sides to differ, resulting in a force that twists the ship around its longitudinal axis.
In addition, forces acting locally due to heavy steel and cargo, and forces exerted on the ship by liquid cargo, which moves with the ship, are also forces that can act on the ship. These various forces must be taken into account in the design of ships, and to this end, shipbuilding and marine engineers ensure the structural safety of ships through precise analysis and calculations.
Ensuring the safety of ships is not limited to simply designing them. It is also important to anticipate and prepare for various problems that may arise during the shipbuilding process. For example, optimal welding techniques and inspections are applied to prevent microscopic cracks and deformations that may occur in the welded parts of ships. In addition, when selecting materials for ships, materials that satisfy both corrosion resistance and strength against seawater are used to maintain safety even during long-term operation.
Shipbuilding and marine engineers are deeply involved not only in the design and construction of ships, but also in their maintenance. Ships require continuous inspection and maintenance during operation, which enables the early detection and resolution of problems to prevent major accidents. In particular, it is important to detect early signs of problems such as fatigue failure through regular inspections and take appropriate measures. To this end, non-destructive inspections and structural health monitoring systems utilizing the latest technology are used to monitor the condition of ships in real time.
The ocean covers more than 70% of the earth’s surface, and ships, which are a means of transportation on the ocean, play a variety of roles, including not only cargo transportation but also LNG and LPG transportation, cruise travel, and oil drilling. Even with advances in technology, these roles cannot be easily replaced by automobiles or airplanes, so as long as the ocean exists, shipbuilding and marine engineering and shipbuilding and marine engineers will continue to play an important role.
In the future, marine engineering will play an increasingly important role in a wide range of fields. For example, marine engineering technology is essential in fields such as marine energy development and undersea exploration. Marine energy development requires technology for designing and building structures that can efficiently utilize energy from wave power, tidal power, and offshore wind power. Undersea exploration requires the design and manufacture of special ships and equipment that can operate in the deep sea. As the range of applications for shipbuilding and marine engineering continues to expand, the role of shipbuilding and marine engineers is becoming increasingly important.
Students majoring in shipbuilding and marine engineering can grow into professionals who can play an active role in these various fields. They will be able to develop comprehensive problem-solving skills through not only basic engineering knowledge but also the latest technological trends and practical experience in the industry. These talented individuals will lead the development of the shipbuilding and marine industry and contribute to the protection and sustainable use of the marine environment.
Therefore, shipbuilding and marine engineering students must continuously learn and conduct research in line with ever-changing technologies and environments, and face new challenges. This is not only for personal growth, but also an essential process for the development and safety of the marine industry as a whole. The passion and efforts of shipbuilding and marine engineering students will make the future of the marine industry brighter and safer.
