Naval Architecture - Coursework Example

Naval Architect By Professor Class University City Date of submission Abstract With the modern technology, the construction of the ships is taking a different dimension with major focus on the designs and methods of reducing the forces and stress which are likely to cause sinking and overturning of the ship. The paper analyzed the various types of ships especially the commercial vessels, special purpose vessel ships, and naval ships. The report defined their specific features, forces resulting from the operations of the ship, and associated stresses caused by the stress. A the report also undertook a deep analysis of the various parts of the ship and their functions. Introduction With the rising technology, construction of the ships is becoming more efficient and effective with the naval architects ensuring reduction in the stresses and quality of the materials during construction. Ships are susceptible to different forms of stress, which could result in fatalities or failure in some of the ship operations (Molland, 2008, 99). There are different types of ships depending on the purpose and construction. For example, the naval ships are used by the army and differ from the civilian ships by construction and purpose. Therefore, there is need for such sheep to be resilient to damages and armed with the weapon systems. Types of ships There are several types of ships with their differences based on the type of cargo that the ship transports. However, most ships have some basic things in common. The ship design determines the type and purpose. There are ships meant to carry containers, people, and oil and petroleum products with each experiencing defined stress and force types. Sea based commercial vessels The commercial vessels are also merchant ships majorly divided into four different categories: the special-purpose ships, fishing ships, cargo ships, and passenger ships. In the modern society, the commercial vessels are typically powered using a single propeller that uses the diesel or the gas turbine engines. However, in the mid-19th century, the propellers were predominantly square sail rigged. Among the commercial vessels, the pump jet engines are the fastest. To maximize the capacity of their cargo, most commercial vessels use the full hull-forms, which are made from the steel. In some cases, the commercial vessels use hulls made from aluminium in making the faster craft and vessels that provide smaller services. On the larger commercial vessels, there is usually the crew headed by the captain, marine engineers, and deck officers. However, the case differs in the special-purpose vessels that in most cases have specialized crew with scientists abroad. Fishing boats is also an example of commercial vessel. Within the fish-processing vessel, the catch could be made ready for the market and immediately sold upon reaching the market. The passengers ship often range in the sizes from the small rivers to the large ships meant for cruising. These vessel types include the ferries, which move both the passengers and vehicles on the short trips. The ocean liners also carry passengers from one place to another. Another commercial ship is also the cruise ships carrying the passengers on the voyages majorly for pleasure purposes, those visiting different places associated with leisure activities in board. Special purpose ships From the name, these types of vessels are at the sea for special reasons. In most cases, their primary role is drilling for oil, creation of the artificial islands, installation of the wind cables, and laying the cables. Therefore, it is critical for the ships to sail the sea in a more efficient and safe as possible. Moreover, these ships use the typical full hull, thrusters, and propellers with nozzles. As a result, the special purpose ships require dynamic positioning and workability, which special approaches are concerning the design, calculations, and the test of different models used. The common issues addressed in these ships include flow separation, moon-pool oscillation, and sea keeping behaviour during transit, the dynamic positioning capability, thrusters-hull interaction, dynamic tracking, and zero speed (Varyani & Krishnankutty, 2006, 1093). Weather ship is a special vessel usually stationed at the ocean to conduct both the surface and meteorological observations on the upper air for application in the marine weather forecasting. The ships often take surface weather conditions on hourly basis. Initially, the weather ship was used in supporting and conducting the rescue operations and supporting various transatlantic flights. To some extent, special ships in wind and wave studies for safety reasons for the ships and air flights. The weather ships assisted in monitoring the storms at the sea. Generally, the special vessels have special designs to accommodate important specific features to ensure the achievement of the desired results. Naval vessels The naval vessels are special ships used by the navy for military activities. Although there are many types of naval ships, their objectives remain similar, war vessels. In the modern naval ships, there are of two different types vessels: the surface warship, support and auxiliary vessels, and submarines. Moreover, there are different types of surface warships including amphibious assault ships, aircraft carriers, frigates, submarines, cruisers, destroyers, and corvettes. Most naval ships have no major differences since similar vessels might have different descriptions in distinct navies. There are two types of military submarines: attack submarines and ballistic missile submarine. During the World War II, the role of the electrically or diesel driven submarine was the anti-ship warfare, insertion, and removal of the covert agents and military forces (Biran, 2003, 122). With the current development, there has been emergence of the nuclear propulsion, homing torpedo, efficient sonar system that also makes the submarines become effective in hunting one another. In addition, the emergence of the cruise missiles and submarine-launched nuclear contributed to the substantial ability and long-ranged capacity of the submarines to attack both the sea targets and land with different weapons. Most naval vessels include different types of support and auxiliary vessels such medical treatment facilities and offshore patrol vessels. More importantly, the fast combat ships including the destroyers and cruisers normally have fine hulls, which aim at maximizing the speed and the manner in which the ships manoeuvre. Parts of a Ship Hull The ship majorly has two main parts, which include the hull and the machinery. Hull is the major structure or body with exclusion of the fittings. The hull’s backbone is keel that runs from the front to the rear on the vessel’s bottom. Hull has three areas: fore end, which is the bow, after end, which is the stem, and amidships. The ships right and left hands are starboard and port respectively. The draught is the bottom or keel below the waterline while ship’s beam is the distance between the two sides (Daley, 2006). The complete skeleton of the hull include the frames, floors, beams, and bulkheads. The frames form the ship’s rib covered using plates; bulkhead are vertical partitions that separate the compartments. Deck The upper deck covers the holds or the tanks. The equipment’s of the deck are cargo handling, steering, anchoring, and the mooring arrangements. The cargo is usually loaded or unloaded on the hatches using the cranes or derricks fitted to the masts on the deck operated using the winches. The hatches are openings found on the deck that gives access to the holds and spaces below. The mast carries antennas; whistle; flags; navigational lights, and holding the sails up on the sailing vessels. The crane is a machine used in hosting and lowering the heavy objects. The anchor is used in securing the ship in a stationary position to the seabed with the anchor chain connecting the anchor and the ship. The anchoring arrangement is the windlass majorly used to lower and raise the anchor. The mooring arrangement consists of the winch, capstans, bitts, and fairleads, which secure the vessel in a position at a quay to the buoy. The vertical posts used in securing the hawser and mooring ropes are bollards or bitts. The capstan is a vertical revolving cylinder on the forecastle used to heave the cables and the mooring ropes (Varyani & Krishnankutty, 2006, 1097). Lifeboats are arranged on the ports and the sides of the starboards and carried in the davits used in life saving reasons. The lifebuoy is specifically designed to float used to throw overboard and keeping person afloat in the water until rescued. Stern A rudder is flat plate at the stem of the ship used for steering. Stern is the rear part of the ship. The steering engine located within the steering gear compartment, which turns the rudder. The propellers are responsible for moving the ship through the water. The shafts transmit the rotary motion of the engine of the ship to the propellers. The engine is usually in the engine room. The bridge is the place from which the captain and the navigating officers control the area from the ship. Funnel is near the bridge and is a casing used in exhaust pipes from the engines. The place used in preparing the meals and doing the laundry are galleys and laundry room respectively. Compartment meant for private use by the crew or passengers is the cabin. Forces in a ship The size and features of the ship are determined by the ship’s mission, cost, and intended services. Moreover, besides the basic functional processes, it is critical to consider different requirements including the stability, different navigational restrictions on the beam, low resistance, good sea-keeping, and high propulsive efficiency all which tend to affect the dimensional and form choices. The structure of the ship needs to be designed with consideration of basic constraints with the aim ensuring sustainability of all the loads expected to emerge within the seagoing environments (Molland, 2008, 108). Contrary to the land structures, the ships do not rest on the fixed foundations. However, the ships derive their whole support from the buoyant pressures exerted through the dynamic and ever-changing ocean environment, which play vital roles of the friend and foe to the ship. From such background, it is critical to divide the loads acting on the ship into two major categories: static and dynamic forces. Static force The static loads are those which change when the weight of the ship changes or distribution in ship’s weight. The factors contributing to the static force of the ship are weight of the ship and its contents, the static buoyancy of the ship while resting or moving, the thermal loads that result from the temperature gradient within the hull, and concentrated loads caused by the dry-docking or grounding. The forces are due to the internal forces resulting from structural, machinery, and cargo weight. The external forces are the hydrostatic pressure of the water on the hull. A ship that floats on calm water often experience two different forces that act along its length: the ship’s weight and content acting vertically downloads. However, the buoyancy of the vertical component associated with the hydrostatic pressure would act upwards. Generally, two forces act equally and balance to ensure the ship float at a particular draft. Dynamic force The dynamic loads are those, which vary with time and periods that range from few seconds to minutes. Moreover, the dynamic forces might as well be time varying loads of sufficiently high frequency, which have the ability of inducing vibratory response of the ship structure. The pressures contributing to the dynamic force include the wave induced hull pressure variations, the hull pressure variations resulting from the transient ship motions, and the inertial relations coming from the acceleration of the mass of the ship and the contents. Other factors leading to dynamic force are hydrodynamic loads from the propulsive devices, load imparted to the hull through reciprocation or unbalanced machinery; the hydro elastic loads that result from the interaction of the appendages with the flow past the ship, and the wave induced loads that result from the short waves. The major causes of these pressures are the motion of the ship in the sea, the winds, and waves’ action, and effects of operating the machinery. Stress in ship The modern ships are made from the steel plates, section, and build up girders connected to ensure provision of adequate strength in all the parts to withstand all the forces that act on the ship under different conditions. The major forces acting on the ship are static and dynamic which are due to the differences in the weight and buoyancy occurring throughout the ship. The motion of the ship at the sea cause dynamic forces, which in turn leads to various types of stress: longitudinal, transverse, and local stress. The greatest stress within the ship occurs due to the distribution of the load along the ship that cause longitudinal bending. Longitudinal Stress The longitudinal stress occurs in two different types: the weight of the ship and the associated contents that act downloads and hydrostatic pressure from the vertical components. Depending on the direction in which the bending moment acts, the ship would experience either hog or sag. The hogging longitudinal stress occurs if the buoyancy amidships exceeds the weight due to the loading and when the wave crest is amidships even as the beam supported at the middle and loaded towards the end. However, if the weight of the amidships exceeds the buoyancy or the wave trough, then sagging longitudinal stress would occur. Transverse Stress The transverse section of the amidships usually experience static pressure associated with the surrounding water and internal loading caused by the weight of the ship and cargo. However, the are parts of the ship which are resistant to the transverse stress: the transverse bulkhead, floor in the double bottom, the pillars within the hole and tween deck, and the bracket existing between the deck beam and side frame and bracket between the side frame and the tank top plating. Local Stress The local stress operating within the ship are created by the heavy concentrated loads such as the engines and boilers, the dead cargo like timber, vibrations of the hull, and ship resting on the dry dock which also cause the static stress. The local stress affects a given part of the ship while global stress affects the whole ship. Causes of stress in ships The major cause of stress in ships is the localized loading. The localized heavy loads might give rise to a localized distortion of the ship’s transverse section. The local loads could be the machinery especially from the main engine within the engine room and loading of the concentrated ore within the holds. The stress might as well be due to weight distribution. With the ship in a constant draft force, there could be an alteration of both bending and shear through the movement of the loads within the vessel. In place with the weight, such loads might result in deflection downwards of the end leading to hogging (Shkolnikov, 2014, 202). If the weights are centrally located, then middle section of the ship could deflect downwards causing the stresses within the ship’s hull structure. Moreover, even the uneven point loading caused by the cargo and distribution of stores could result in stress within the hull structure. Stress could be due to hydrostatic pressure. The buoyancy coming from the water pressure might result from the weight contained within the vessel. The effect of such pressures often distorts the structure inwards considering the resistance caused by the hull plating and the stiffening arrangements. The stress could as well be due to racking. The uneven water pressure associated with action of the waves often contributes the distortion of the ship due to the resistance caused by the shear stress operating within the ship. The racking stress are the greatest concern within the transverse bulkheads and framing and majorly occur within the corners of the box section. Therefore, there is usual inspection of the brackets. Effects of stress in ships The main effect of the stresses operating in the ship is distortion of the structures due to the dynamic and static forces. Hogging is a form of stress that affects the hull of the ship, which makes the centre of the ship’s keel to bend upwards. Sagging on the hand causes stress on the hull of the ship. In such cases, the keel is placed under when the wave is similar in length as the ship and the ship is within the trough of the two waves. As a result, the stresses make the middle of the ship to bend down slightly, which to some extent could result in a snap, or crack within the hull depending on the level of the bend. The stresses also have effects on the cargo loading. The maximum amount of cargo that the vessels carry often depends on whether the plimsoll mark of the ship submerges or not. Sagging could reduce the effective capacity of the ship especially if the ship already reached the load line prematurely due to the sagging. Therefore, it is critical to consider such factors while calculating the cargo. Stress Detection Technologies Strain gauge is the oldest technology of measuring the stress. The method applies calibrated devices expressing the stress upon the sample in terms of the strain induction. The strain gauges are of electro-resistive types. However, the modern technologies are providing better accuracy. Based on application, the gauges are short baseline, long baseline, and derived as per location. The short baseline are low cost, installed in small places majorly measure shear stress or stress at hotspots. The long baseline gauges measure hull girder stress within the commercial ships. Another technology is the fibre optic strain gauges, which are inexpensive with the coupling expensive being quite high. The acoustic strain gauges operate without the direct contact. Traditionally, the acoustics were used in bridges considering their ability to penetrate the paint and other surface obstructions. The laser or the RADAR ranging is also stress-detecting technology used in measuring stress in the ship’s hull structures. The racking stress associated with the sway motions in ships could be measured using the motion based stress monitoring. The method is important in making voyage decisions. The fatigue damage sensors (FDS) are important in measuring the fatigue life of the ship structures. Failure modes in ships From the loading perspective, the ship is essentially an elastic beam that floats on the surface of the water and subjected to different fluctuating and steady loads, which generate bending moment and shear force that could be acting on the ship. The failures occur when the ship can no longer perform the intended function. Although the structural components of the ship are designed in a manner that if an element fails, it sheds the load on the other element with the ability to withstand the additional load (Shkolnikov, 2014, 115). Therefore, the failure modes often do not lead to immediate catastrophe, but it is critical to prevent further damage. The failure mode of the hull often occurs due to distortion of the hull structure strained beyond the yield point leading to permanent set and structural distortion. Cracking of the hull structure might as well result in the failure especially when the materials can no longer sustain the load applied in different sections. The loading might exceed the ultimate strength of the material and contributing to failure due to material fatigue causing the cracking and fracture. Failures might result from the structural instability. Sinking Shifting the cargo could result in heavy listing, which might increase ship’s rolling making the vessel to sink if the immersion of the deck place. Therefore, there is need properly secure the cargo in the container vessels. Within the bulk carriers, the cargo needs proper arrangement with the assistance of special plates used within the cargo as a means of preventing the shifts. Synchronous rolling is another factor. Each ship has its natural rolling period. Hence, if the ship experiences a series of swell in such manner that the period of the wave matches the rolling period of the ship, then there would be no time for the ship to make itself straight. Overturning Free surface effect often occur when the ships are half full making the liquid inside the tank to move towards to the ship’s motion and tend to exaggerate in similar manner. For such reason, it is important to ensure the tanks are full or divided using the longitudinal bulkheads, which would assist in reduction of the free surface effect and prevent sinking of the vessel. The free surface could as well occur on the deck due to accumulation of water, as there is not arrangement of removing the water. Conclusion The paper focused on the analysis of the designs of the ships, types, and forces originating from the processes of the ship. Depending on the nature and shape of the ship, there are different forms of forces and stresses likely to affect the efficiency and reliability of the ship during operations. It is from such background that the paper analyzed the different types of ships, components, forces, and stresses operating within the ships. However, with the current technology, there have been emergences of detection mechanisms, which ensure reduction of the negative effects associated with stresses and forces acting on the ship. Ships are as well susceptible to various failure modes, which could result in the general failure of the ship; as a result, the failure modes could contribute to sinking and overturning. Ships require frequent maintenance to ensure minimum impacts of the forces and stresses. The failure modes might not only result in sinking and overturning but also serious aquatic imbalances. Hence, proper structural designs are critical in averting these negative effects. References Biran, A. (2003). Ship hydrostatics and stability. Oxford: Butterworth-Heinemann. Daley, C. G. (2006). Ship Terms and Definitions. Retrieved June 7, 2016, from http://www.engr.mun.ca/~cdaley/5003/ship_terms.pdf Molland, A. F. (2008). The maritime engineering reference book: A guide to ship design, construction, and operation. Amsterdam: Butterworth-Heinemann. Shkolnikov, V. M. (2014). Hybrid ship hulls: Engineering design rationales. Oxford: Butterworth-Heinemann. Varyani, K., & Krishnankutty, P. (2006). Modification of ship hydrodynamic interaction forces and moment by underwater ship geometry. Ocean Engineering, 33(8-9), 1090-1104. Read More