In recent years, electronically controlled engines have replaced conventional camshaft controlled ones for low speed marine diesel engines in order to meet both IMO NOx regulation and low fuel oil consumption (FOC). Part load or low load optimization methods (such as Exhaust Gas Bypass etc.) and/or longer stroke, high cylinder pressure engines have also been applied to meet the demands for further reduction in FOC. As a result, excitation forces / moments and noise emissions from engines have been increased, which makes it necessary for engine makers and ship builders to investigate vibration and noise in detail than ever before and in some cases, additional countermeasures may be necessary. In this paper, vibration characteristics and countermeasures for MAN B&W’s latest electronically controlled ME engines are introduced.
Recently, the demand for a low noise environment in vessels has increased. Cabin noise consists of several noise sources. In most cases, the primary source of noise is the engine. Generally, the vibration isolator is effective in reducing structure-borne noise. This paper presents three types of vibration isolators for reciprocating engines and application examples for electric propulsion systems.
Recently, the reduction of ship noise and underwater radiated noise has become animportant issue. Engines and Z-pellers (azimuth thrusters) are considered as major sources of noise, and a quantitative evaluation of each sound source is required. In this paper, the contributions of engine and Z-peller were evaluated by noise and vibration measurement results in a hybrid tug ship. In order to predict the structure-borne noise level from the engine, an excitation force measurement was performed for both rigid and rubber-mounted engines. Underwater radiated noise emitted from the Z-peller was evaluated from cavitation noise tests using a water tank. In these tests, two types of Zpeller configurations were proposed, and the noise reduction effect was confirmed. Theresults are presented in this paper.
In this report, we present the outline of anti-vibration design technology of large merchant ship superstructures in recent years. First, the vibration mode characteristics of mega container ship superstructure are shown. Next, effectiveness of the vibration response analysis using whole ship model in order to evaluate the vibration response of superstructures at the early design stage is explained. The modeling technique of whole ship model focusing on superstructure and main engine, and the application technique of main engine exciting forces are introduced. Finally, research and development points to improve the accuracy of analysis regarding the influence of mesh size and the damping modeling technique are shown.
In order to verify the efficacy of antifouling paints, static raft tests were conducted using a series of test paints containing cuprous oxide concentrations of various levels from 0% to 40%. The static raft tests were carried out for 90 days at a site in Nagasaki bay in winter with non-aged test plates, and for 28 days at two sites in the Seto Inland Sea in summer, fall and winter with aged test plates. The aged test plates underwent dynamic immersion pre-treatment for 45 days under a seawater flow of 10 knots at 20°C in a dark room to simulate the actual ships’ conditions. The efficacy of antifouling paints was investigated using the relationship between fouling (animals and algae, slime) and the amount of cuprous oxide. After the end of each test, copper leaching rates for the test plates were measured for the test plates at the laboratory to verify the correlation between the fouling (sea animal species, macro algae, and slime) and the test paints containing various levels of cuprous oxide concentrations. The results showed that the degree of fouling decreased as the cuprous oxide content increased. The threshold of cuprous oxide content for macrofouling prevention was identified to be around 20% for sea animal species and around 5% for algae, while all test plates were subject to microfouling by slime.
In spray combustion, spray flame is formed in a position slightly away from an injection nozzle. In order to simulate spray combustion, it is important to predict precisely the distance called the flame lift-off length (set-off length). In this study, the effect of combustion conditions on the flame lift-off length was investigated using experimental results conducted with light oil and kerosene. A Single fuel spray was injected into a constant volume combustion vessel and self-ignited in high-temperature gas. Pressure, temperature, density of the internal gas, and injection pressure of the fuel were chosen as the combustion conditions considering the operation of the actual combustion equipment and engines. The combustion processes were observed with a high speed video camera. For the purpose of applying calculation models for the simulation of spray combustion, empirical formulas were derived. The formulas showed good correlation between the length and the combustion conditions. The formulas showed that the length of light oil is longer than that of kerosene only in the higher range of pressure and temperature of the ambient gas.