Noise and vibration on maritime vessels

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Noise and vibration on maritime vessels are not the same but they have the same origin and come in many forms. The methods to handle the related problems are similar, to a certain level, where most shipboard noise problems are reduced by controlling vibration.

Contents

Sources

The main producers of mechanically created noise and vibration are the engines, but there are also other sources, like the air conditioning, shaft-line, cargo handling and control equipment and mooring machinery.

Diesel engines

When looking at diesel driven vessels, the engines induce large accelerations that travel from the foundation of the engine throughout the ship. In most compartments, this type of vibration normally manifests itself as audible noise. The problem with diesels is that, for a given size, there is a fixed amount of power generated per cylinder. To increase power it is necessary to add cylinders but, when cylinders are added, the crankshaft has to be lengthened and after a very limited number of additions, the lengthened crankshaft begins to flex and vibrate all on its own. This results in an increase of vibrations spread all over the ships structure. Crankshaft vibration can be reduced by a harmonic balancer.

Electrical engines

Large vessels sometimes use electrical propulsion motors, the electrical power being provided by a diesel generator. Noise and vibration of electric motors include, besides mechanical and aerodynamic sources, an electromagnetic source due to electromagnetic forces which is responsible for the "whining noise" of the motor.

Turbines

Steam turbines and gas turbines, on the other hand, when new and/or in good repair, do not, by themselves generate excessive vibration as long as the turbine blades are in a perfect condition and rotate in a smooth gas flow. But after some time microscopic defects appear and cause small pits to appear in the surface of the intake and the blades which set up eddies in the gas flow, resulting in loss of performance and vibrations. Vibration levels may change with different loading conditions or when doing a manoeuvre.

Other sources

Besides mechanical produced vibrations, other sources are caused by the motion of the sea, slamming of the vessel on the waves and water depth to mention just a few. The main problem here is that they are less controllable.

The engine-gearbox interaction is usually a source for noise and vibrations. Here, it can be installed highly flexible couplings between the engine and the gearbox. These type of couplings are used because of their low torsional stiffness. [1]

Exposure limits

Exposure to noise and vibrations is regulated and limits for maritime vessels are given in the ISO standard 6954: Guidelines for permissible mechanical vibrations on board seagoing vessels to protect personnel and crew.

Because there are different noise regulations from country to country, the International Maritime Organization (gago) sets some standards for vessels. The table below gives some comparisons of preferred maximum noise levels on board of vessels and onshore levels.

AreaNoise limit land (dB)IMO noise limit (dB)
workshop7085
kitchen6075
control rooms5575
offices5565
dining rooms5565
sleeping area4560

Noise and vibration control

Noise generated on board ships and submarines can have far-reaching effects on the ability of the vessel to operate safely and efficiently. Military vessels in particular need to be quiet to avoid detection by sonar, so many methods have been used to limit a vessel's noise signature. Controlling noise is therefore a defense measure, most acutely for submarines.

Prevention

At the design table, the naval architect makes the necessary choices concerning the ship's structure to achieve an optimized design towards noise and vibration control. Decisions are made about the engine and shaft, what kind of instruments and material can be used to reduce noise and vibrations throughout the vessel and what is the best way to implement these. Advanced computer technology tries to simulate these vibrations under different ship conditions to provide an overview of weak spots. The generated vibrations are also compared with the natural frequencies of the different parts/sections and adaptions can be done to the structure. On board, noise travels through the structure (mainly low frequencies), more than through the air, so insulating the engine room is not enough as a way to avoid the noise travelling through the boat. [2]

Control at source

To control the mechanical vibrations at the origin, isolating fittings, elastic mounting of engines, elastic holding of pipes or dampers can be installed. These will absorb a part of the vibrations (and the noise) produced by the machines. To control the electromagnetic vibrations at the origin, skewing the electric motor or choosing a better slot/pole combination [3] will reduce electromagnetic force harmonics or avoid resonances between magnetic forces and structural modes of the electric motor.

In megayatchs, the engines and alternators let out unwanted noise and vibrations. To solve this, the solution is a double elastic suspension where the engine and alternator are mounted with vibration dampers on a common frame. Then, this is mounted elastically between the common frame and the hull. While in megayatchs the requirement is the comfort of crew and passengers, in other applications, such as navy ships, the requirements involve that the engines or generators should work under certain shock loads. To achieve this the ships install double elastic suspensions and high deflection mounts are installed between the unit and base frame. Beforehand, the engineers calculate the torsional vibrations or the 6/12 degree of freedom to guarantee the optimum combination of couplings and mounts. [4]

Maintenance

Regular maintenance will have a major influence on the performance of instruments and machines. Lubrication of the joints, tightening of the bolts, good alignment of stern contour of the vessel, adjusting of variables following the weekly and monthly schedule are the most effective routes to noise and vibration control.

Related Research Articles

Engine Machine that converts one form of energy into mechanical energy

An engine or motor is a machine designed to convert one form of energy into mechanical energy. Heat engines convert heat into work via various thermodynamic processes. The internal combustion engine is perhaps the most common example of a heat engine, in which heat from the combustion of a fuel causes rapid pressurisation of the gaseous combustion products in the combustion chamber, causing them to expand and drive a piston, which turns a crankshaft. Electric motors convert electrical energy into mechanical motion, pneumatic motors use compressed air, and clockwork motors in wind-up toys use elastic energy. In biological systems, molecular motors, like myosins in muscles, use chemical energy to create forces and ultimately motion.

Gas turbine Type of internal and continuous combustion engine

A gas turbine, also called a combustion turbine, is a type of continuous and internal combustion engine. The main elements common to all gas turbine engines are:

Electric generator Device that converts other energy to electrical energy

In electricity generation, a generator is a device that converts motive power into electrical power for use in an external circuit. Sources of mechanical energy include steam turbines, gas turbines, water turbines, internal combustion engines, wind turbines and even hand cranks. The first electromagnetic generator, the Faraday disk, was invented in 1831 by British scientist Michael Faraday. Generators provide nearly all of the power for electric power grids.

Starter (engine) device used to start an internal combustion engine

A starter is a device used to rotate (crank) an internal-combustion engine so as to initiate the engine's operation under its own power. Starters can be electric, pneumatic, or hydraulic. The starter can also be another internal-combustion engine in the case, for instance, of very large engines, or diesel engines in agricultural or excavation applications.

Alternator Device converting mechanical to electrical energy

An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature. Occasionally, a linear alternator or a rotating armature with a stationary magnetic field is used. In principle, any AC electrical generator can be called an alternator, but usually the term refers to small rotating machines driven by automotive and other internal combustion engines.

Napier Deltic

The Napier Deltic engine is a British opposed-piston valveless, supercharged uniflow scavenged, two-stroke diesel engine used in marine and locomotive applications, designed and produced by D. Napier & Son. Unusually, the cylinders were disposed in a three-bank triangle, with a crankshaft at each corner of the triangle.

Torsional vibration is angular vibration of an object—commonly a shaft along its axis of rotation. Torsional vibration is often a concern in power transmission systems using rotating shafts or couplings where it can cause failures if not controlled. A second effect of torsional vibrations applies to passenger cars. Torsional vibrations can lead to seat vibrations or noise at certain speeds. Both reduce the comfort.

Combined diesel-electric and gas Modification of the combined diesel and gas propulsion system for ships

Combined diesel-electric and gas (CODLAG) is a modification of the combined diesel and gas propulsion system for ships. A variant, called the combined diesel-electric or gas (CODLOG) system, contains the same basic elements but will not allow simultaneous use of the alternative drive sources.

Marine propulsion Systems for generating thrust for ships and boats on water

Marine propulsion is the mechanism or system used to generate thrust to move a ship or boat across water. While paddles and sails are still used on some smaller boats, most modern ships are propelled by mechanical systems consisting of an electric motor or engine turning a propeller, or less frequently, in pump-jets, an impeller. Marine engineering is the discipline concerned with the engineering design process of marine propulsion systems.

Rotor (electric) Non-stationary part of a rotary electric motor

The rotor is a moving component of an electromagnetic system in the electric motor, electric generator, or alternator. Its rotation is due to the interaction between the windings and magnetic fields which produces a torque around the rotor's axis.

Engine-generator

An engine-generator is the combination of an electrical generator and an engine mounted together to form a single piece of equipment. This combination is also called an engine-generator set or a gen-set. In many contexts, the engine is taken for granted and the combined unit is simply called a generator. An engine-generator may be a fixed installation, part of a vehicle, or made small enough to be portable.

Dynamo

A dynamo is an electrical generator that creates direct current using a commutator. Dynamos were the first electrical generators capable of delivering power for industry, and the foundation upon which many other later electric-power conversion devices were based, including the electric motor, the alternating-current alternator, and the rotary converter.

In electrical engineering, electric machine is a general term for machines using electromagnetic forces, such as electric motors, electric generators, and others. They are electromechanical energy converters: an electric motor converts electricity to mechanical power while an electric generator converts mechanical power to electricity. The moving parts in a machine can be rotating or linear. Besides motors and generators, a third category often included is transformers, which although they do not have any moving parts are also energy converters, changing the voltage level of an alternating current.

Free-piston engine

A free-piston engine is a linear, 'crankless' internal combustion engine, in which the piston motion is not controlled by a crankshaft but determined by the interaction of forces from the combustion chamber gases, a rebound device and a load device.

Harmonic damper

A harmonic damper is a device fitted to the free end of the crankshaft of an internal combustion engine to counter torsional and resonance vibrations from the crankshaft. This device must be interference fit to the crankshaft in order to operate in an effective manner. An interference fit ensures the device moves in perfect step with crankshaft. It is essential on engines with long crankshafts and V8 engines with cross plane cranks, or V6 and Straight-three engines with uneven firing order. Harmonics and torsional vibrations can greatly reduce crankshaft life, or cause instantaneous failure if the crankshaft runs at or through an amplified resonance. Dampers are designed with a specific weight (mass) and diameter, which are dependent on the damping material/method used, to reduce mechanical Q factor, or damp, crankshaft resonances. A harmonic balancer is the same thing as a harmonic damper except that the balancer includes a counterweight to externally balance the rotating assembly. The harmonic balancer often serves as a pulley for the accessory drive belts turning the alternator, water pump and other crankshaft driven devices.

Integrated electric propulsion (IEP) or full electric propulsion (FEP) or integrated full electric propulsion (IFEP) is an arrangement of marine propulsion systems such that gas turbines or diesel generators or both generate three-phase electricity which is then used to power electric motors turning either propellers or waterjet impellors. It is a modification of the combined diesel-electric and gas propulsion system for ships which eliminates the need for clutches and reduces or eliminates the need for gearboxes by using electrical transmission rather than mechanical transmission of energy, so it is a series hybrid electric propulsion, instead of parallel.

Magneto Electricity-producing machine

A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. Unlike a dynamo, a magneto does not contain a commutator to produce direct current. It is categorized as a form of alternator, although it is usually considered distinct from most other alternators, which use field coils rather than permanent magnets.

Vulkan Group

The Vulkan Group is a German company with three company divisions: Vulkan Couplings, Vulkan Drive Tech and Vulkan Lokring. Its products comprise couplings, shifting clutches, resilient mounts and connecting elements for refrigerant lines. The owner-managed group of companies has its headquarters in Herne in the Ruhr area. Today the company is active in more than 51 countries and has 19 subsidiaries, 50 agencies and five production facilities worldwide.

Internal combustion engine Engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber

An internal combustion engine (ICE) is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is applied typically to pistons, turbine blades, a rotor, or a nozzle. This force moves the component over a distance, transforming chemical energy into useful work. This replaced the external combustion engine for applications where weight or size of the engine is important.

<i>Futami</i>-class oceanographic research ship Class of oceanographic research ship of JMSDF

The Futami class was a class of oceanographic research ship of Japan Maritime Self-Defense Force (JMSDF) in the late 1970s.

References

Specific
  1. Seiler, Robin. "Diesel & Gas Turbine Worldwide Spring 2020 | Powered by Pocketmags". digimag.dieselgasturbine.com. p. 40. Retrieved 2021-05-30.
  2. "Vulkan: il segreto per creare il silenzio a bordo degli yacht". Barche Magazine ISP. 2018-01-13. Retrieved 2021-06-06.
  3. J. Le Besnerais, V. Lanfranchi, M. Hecquet and P. Brochet, "Optimal Slot Numbers for Magnetic Noise Reduction in Variable-Speed Induction Motors," in IEEE Transactions on Magnetics, vol. 45, no. 8, pp. 3131-3136, Aug. 2009. doi: 10.1109/TMAG.2009.2020736
  4. Solutions for generator sets (PDF). 2020. pp. 19–20.