Stresses and Forces on Ships - Example

Student Name: xxxxxx Tutor: xxxxxxx Title: Stress and Forces on Ships. Institution: xxxxxxx @2016 Table of Contents Abstract 3 Introduction 3 Types of ships 4 Sea based commercial vessels 4 Special purpose ships 4 Naval Vessels 5 Parts of a ship 5 Forces in a ship 9 Types of forces in ships 9 Static forces 9 Dynamic forces 9 Stresses in a ship 10 Types of stresses in a ship 10 Causes of stresses 10 Effects of stresses in a ship structure 10 Stress Detection Technologies 11 Failure modes in ships 12 Sinking 12 Overturning 12 Conclusion 12 References 13 Abstract This paper contains detailed information on the structural components of a ship as well as their respective functions. The types of ships as well as their uses is also covered in detail. The various types of forces experienced by a ship under loading is discussed in detail. Information of the effect of such forces on the ship are also covered. The various technologies used in ship industry to detect such forces are also discussed in detail. The report utilizes visual aids including diagrams and real pictures to enhance understanding of the reader. Introduction Ship as a means of transport was developed in the late 3000BC and was majorly used by Egyptians as well as Greeks. However, its use saw rapid developments during the first and the Second World War. A ship can therefore be defined as a large water based vehicle whose locomotion majorly depends on its buoyancy (Sofronas, 2006). The ships vary in sizes as well as their use as therefore, various types can be defined. Of importance is the difference between a ship and a boat whose difference is majorly attributed to its size. Ships are majorly used in large water bodies such as lakes and seas as well as large rivers. They are majorly used in transporting purposes such as transportation of cargo, people and in some special cases used for other secondary purposes such as entertainment or warfare. Despite of the various types of ships in existence, their structure both in design and mode of operation are similar. The development is ships from its early designs have seen great advancements. The major enhancements are majorly on their locomotion techniques. The early ships majorly depended on wind energy to sail and experienced a lot of difficulties in navigation. However, in the recent past, engine based locomotion ships have been developed coupled with very advanced navigation as well as cruise control systems. Safety in the sea travel has been on the spotlight and manufactures have put this consideration into their latest design. The ships can be categorized in to various types depending on their use. Types of ships Sea based commercial vessels Commercial vessels are commonly referred to as merchant vessels and can be divided into various other sub-categories based on their functionality. Fishing, cargo ships, passenger ships as well as special purpose ships fall into this category. The locomotion of sea based commercial vessels depends on engine driven propeller or less often gas turbine driven shaft. The end of the shat is fitted with a propulsion mechanism through which ships are propelled (Corp OTC, 1991). Fishing ships – Fishing ships are not normally large in size as compared to commercial ships and are commonly between 30 meters and 100 meters long. They are designed and equipped with tools and equipment that facilitates effective fishing activities. Cargo ship – cargos ships are usually large in size and are used to transport cargo over long overseas locations. They are normally used to transport either solid cargo or liquid cargo and in some cases both. The cargo are normally transported in bulk in containers that are stacked carefully in the container. Passenger ships – passenger ships vary in size from the small river ships to huge ships that house and transport people over long oversea distances. Such ship are equipped with life support facilities such as housing, entertainment as well as environment control. Their design is majorly based on safety. Special purpose ships These are ships designed specially to accomplish dedicated purposes within the ocean or the seas. A good example of a special purpose ship is the weather ship that is normally stationed at specific locations within the sea. Such a ship is used to accomplish marine weather forecasting operations. The ship houses weather forecasting crew as well as weather forecasting equipment. Information transmission equipment are also housed that facilitates relay of weather forecast information to the required destination (Derrett & Barrass, 2006). Naval Vessels These are ships designed for navy military services the advancements in naval vessels have seen a greater development as compared to other types of shipping vessels. Modern warships have been designed to have advanced and enhanced capabilities such as navigation as well as safety and protection against attacks. Parts of a ship Despite of the various types of ships, they all have great similarity in their designs. Thus, the common parts of a ship include; a) The hull This is the part of a ship that facilitates its floating abilities. Therefore, during the design of a ship, it should be put into consideration that the weight of the ship must be less than the weight of water displaced by the hull. The hull is composed of various other components that makes up the entire hull structure (Derrett & Barrass, 2006). These includes; The bow – this is the foremost part of the hull. The keel – this is the bottom most part of the hull and extends through the entire length of the ship. Stern – this is the rear part of the hull. Propellers – these are propulsion equipment. Rudders – are used for steering of the ship and thus help achieve navigation purposes. Sonar domes - these are sensory devices used to detect unprecedented objects within the line of travel of the vessel. Figure 1: The hull of a commercial ship b) Propulsion systems Propulsion systems in ships can either be human propulsion, sailing or mechanical propulsion. Human and sailing methods of propulsion are uncommon and mechanical propulsion is dominant. Mechanical propulsion systems consist of the propellers, engines that can either be steam or diesel engines as well as crank shaft to transfer the rotary motion from the engine to the propeller. Figure 2: Propulsion unit of a commercial ship c) Steering systems Ships have independent steering systems and consists of rudders. The steering systems are developed and designed to allow for efficient navigation of the vessel. The rudders in most large ships are located in the rear of the hull. The rotation of rudders generate a lateral force which helps turn the ship in the desired direction. Figure 3: The rudder and propeller of a ferry d) Holds and compartments These are parts of the structure with multiple decks and compartments and are used to house containers for cargo ships. This is where loads are placed in the ship. e) Super structure These is the part of a ship that is always above the main deck and are normally placed near the ships stern. f) Equipment Ships equipment such as engines among other varies from ship to ship depending the size as well as design and purpose of the ship. Some of the equipment commonly used in the ships include masts, ground tackle, cranes among others. Figure 4: A general structure of a commercial ship Forces in a ship Any ship in the sea is subjected to loadings due to its weigh as well as the weight of the loads within the ship. The effects of these forces due to loading are majorly common at the hull. The forces subjected to the ship can be categorized depending on the nature of the loads2. Types of forces in ships The ship is subjected to two types of forces. These include the static forces as well as the dynamic forces. Static forces The static forces in the ship are as a result of the structural weigh as well as the internal forces of the sip. The ship loading with regards to the cargo it carries also contributes to the amount of static forces within the ship. Dynamic forces The dynamic forces in the ship are caused by the ships locomotion within the sea. The cause of dynamic forces are as a result of waves and tides within the sea. The vibrations from engines as well as motors used within the ship also contribute to the total effect of dynamic forces. Stresses in a ship Stresses in a ship is as a result of its loading and the hull of the ship is susceptible to ship stresses. Therefore, the stresses in ships can be analyzed and determined based on its loading characteristics. The effect of stresses in ships can be detrimental if they are not checked and corrected within the required standards. Types of stresses in a ship The stresses in the ship can be categorized into; Longitudinal stresses Transverse stresses. Local stresses. Causes of stresses Causes of primary stresses a) Weight distribution The distribution of forces within the available area of the ship affects the amount of stresses within the ship. The movement and distribution of loads within the ships affect both bending and shear stresses within the ship. b) Hydrostatic pressure All the loadings within the ship are supported by buoyancy from the water pressure. The effect of this water pressure if not well balanced results in structural distortion of the ship. Effects of stresses in a ship structure Hogging Hogging results when the loads are distributed in such a way that the buoyancy at the center of the ship exceeds the total loads on the ship. Sagging Sagging is an effect that also occurs when a ship`s total weight exceeds its buoyancy when analyzed at its center. The concept of sagging is similar to that of beam supported from both ends while loaded at its center. Racking Racking is an effect implicated by uneven water pressure as a result of wave actions. Racking is an effect that is common in the corners of the ship. Docking Docking of ships results in sagging especially when docking is done using a limited number of blocks. However increasing the number of blocks used in docking can help to reduce this effect. Grounding Grounding is an effect caused by uneven loading of the hull of a hip. Uneven loading causes uneven distribution of buoyancy and this leads to grounding. Stress Detection Technologies Modern ships have been designed with state of the art technologies that can detect flaws and stress distributions within the structure of the ship. Such technologies enables the ship users to detect any small stress distribution beyond the required amount and thus initiate the resolution strategies. Some of these technologies are discussed below. Strain gauges The critical parts of the ship such as the hull needs to be stress free at all times. Thus recent designs of the ship hulls incorporates layers of strain gauges within its structure. The strain gauges detects any stress changes in terms of its distribution at all times. As a result of this, detection of any undesired stress distributions within the ship structure such as the hull can be detected easily. Ultrasonic technologies Ultrasonic technologies is one of the most used technology in ships as a way of detecting any stresses within its structure. The technology involves the use of a high frequency sound wave preferably 1MHz and is passed through the structure of the ship whose stress distribution detection is required. A three dimensional image of the stress distribution is developed and detection of uneven or undesired stress distribution can be accomplished easily. Radiography Radiography is one of the technologies that is not highly preferred due to its cumbersomeness in use. The technology involves the use of an x-ray radiation that is passed through a ship structure and an image representing the stress distribution. The interpretation of stress distribution from the two dimensional x-ray image requires skill and expertise in radiography. Failure modes in ships Sinking Sinking is the most dangerous and destructive mode of failure in the ship. Sinking is contributed by several factors such as design flaws, water leakages as well as uneven loading. The design of ship should put into consideration but the sinking protection strategies and technologies should be highly considered. Overturning Overturning of ships is an effect attributed to waves as well as waves. Large waves that hit the ship either laterally or transversely can lead to overturning of the ship. Uneven loading of ship coupled with wave effects results in overturning. The design of the ship should consider protection of the ship from overturning effects by checking on the ships width and height2. Conclusion Ship is the most preferred means of transport and its safety should be highly considered especially during the design stage. Navigation of the ship should also be done in such a way that enhances its safety. The effects of waves as well as loading should be done in a careful manner so as to ensure safety. Technologies exist in markets that helps in simulating and automating loading of the ship in a manner that is well balanced and will ensure stability of the ship. References 1. SOFRONAS, A. (2006). Analytical troubleshooting of process machinery and pressure vessels including real-world case studies. Hoboken, N.J., John Wiley & Sons. http://public.eblib.com/choice/publicfullrecord.aspx?p=244305. 2. EYRES, D. J., & BRUCE, G. J. (2012). Ship construction. Burlington, Elsevier Science. http://www.123library.org/book_details/?id=53617. 3. DERRETT, D. R., & BARRASS, C. B. (2006). Ship stability for masters and mates. Burlington, Mass, Butterworth-Heinemann. http://site.ebrary.com/id/10138627. 4. OFFSHORE TECHNOLOGY CONFERENCE. (1991). 1991 Offshore Technology Conference, May 6-9, Houston, Tx [papers] CORP OTC. (23rd (23rd. Richardson, Tex, Offshore Technology Conference. Read More