A Study on Vibration Characteristics of Liquid Tank with Height Change
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Abstract:
The shipbuilding industry has been in the process of becoming larger and faster. Vessels are made of complex structures and carry a wide variety of cargoes for long periods of time and generally have a long life of more than 30 years. Ships have tanks of various shapes such as fuel, ballast and fresh water tanks, and most of them are in contact with the liquid. The state of the liquid also causes a change in the water level due to the operation of the ship. It has been reported that a resonance, which causes fatigue damage and destruction due to excitation forces of an engine, a propeller, and a wave.BR Therefore, it is considered important to clearly understand the vibration characteristics of these various tanks in contact with the liquid.BR Many vessels currently are equipped with many square shaped tanks and have various conditions of the boundary as well as various ratios of length, width and height of the tanks. Therefore, in this paper, the vibration characteristics of the elastic plate composing the tank through the changes of the boundary condition, the width and the thickness are investigated in a tank structure which is relatively higher than the length and width.Keywords:
Ballast
A Study on Estimation of Propeller Vibration Characteristics for Development of Low-Noise Propellers
Vibration of ship propellers can cause damage to blades and propeller noise, in order to design low-noise propellers the vibration characteristics of propellers must be estimated to a high degree of accuracy and reflected in the design. In this study, in order to estimate the propeller vibration characteristics with high degree of accuracy, a propeller finite element model was created that included the hub and all blades of the propeller and increased the number of finite elements of the blades by about 2.2 times compared to previous studies. The free vibration analysis of the blade finite element model which was a method of previous studies, and the free vibration analysis of the propeller finite element model with fixed or unfixed upper and lower surfaces of the hub were performed. Natural frequencies and mode shapes, which are vibration characteristics of the propeller, were estimated through free vibration analysis, and the effect of the propeller hub on blade vibration was confirmed by analyzing the estimation results. In addition, an impact test was performed, and the accuracy of the estimation of the vibration characteristics was analyzed by comparing the test results with the estimation results of the vibration characteristics. As a result, the propeller have modes with similar natural frequencies and blade mode shapes, this phenomenon occurs because of the coupling effects in which the vibration of a blade affects the vibration of another blade through a hub. The propeller hub affects the blade vibration by the coupling effects and the hub vibration and when the upper and lower surfaces of the hub are fixed, the hub vibration does not affect the blade vibration. In order to estimate the vibration characteristics of the propeller with high degree of accuracy, it was derived that vibration analysis should be performed for the propeller, not just the propeller blade.
Blade element theory
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Model tests have been performed in the deep water towing tank and large cavitation tunnel of the NSMB to study the propeller generated hydrodynamic hull forces of a Great Lakes bulk carrier, which suffered from severe vibrations. The investigation also comprised propulsion, wake, flow and cavitation tests. High speed movies were made to study in detail propeller-hull vortex cavitation and to investigate the correlation between this cavitation phenomenon and the pressure fluctuations on the hull. Further, pressure measurements on full scale were performed and a good agreement with the results from model tests was found. It is shown that a stern tunnel fitted to the hull above the propeller reduced the excitation forces more than a modified propeller design. Application of vertical fins, to avoid propeller-hull vortex cavitation, showed an increase of average excitation level.
Towing
Full scale
Water tunnel
Propulsor
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Ballast is critical in promoting track drainage. This article gives an overview of machines that are used in ballast improvement. These machines are designed to remove and replace, or remove/clean and replace ballast. Vacuum excavators are now being used in the U.S., providing a mechanized method to remove unwanted material from the track structure. Additional ballast is then used to replace the unwanted material that was removed. Another type of machinery available is a ballast undercutter cleaner which removes all material from under the tie, screens the material, moves the waste along to the right-of-way, and then returns the cleaned ballast back into the track. The ballast is unloaded, and this allows the track to be raised and establish a standard ballast section under the ties and along the shoulder. The article includes descriptions of some new products and how they operate.
Ballast
Excavator
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An outstanding problem in naval architecture is the selection of the propeller geometry and the location of the propeller in the aperture in order to reduce the sum of the propeller-induced vibratory bearing forces and moments and the hull surface forces and moments to an acceptable minimum. This paper presents a reliable method for calculating these net excitations for arbitrary stern and propeller configurations. A computer solution for the propeller and hull excitations has been developed and assessed by comparison with two independent sets of model measurments. The paper describes the physical mechanisms involved in visualisation of the velocity field and outlines the mathematical models employed to represent the propeller in the hull wake and the hull surface. Although the method is currently limited to non-cavitating propellers, it can embrace the dominating excitations arising from intermittent blade cavitation. Order from BSRA as No. 54,391.
Propulsor
Stern
Advance ratio
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A practical method for the prediction of cavitation on a propeller operating in a ship wake and hull surface pressure induced by a cavitating propeller is presented.In this method, the following items are applied : i) propeller part : the combination of Hanaoka-Koyama's unsteady lifting surface theory and corresponding 2-D wing theory ii) cavitation part : linearized 2-D cavity theory applying the angle of attack and the local cavitation number derived form i) iii) hull surface pressure part : the application of the method of periodic source in place of cavity volume variation while a propeller blade is turning behind hull, moreover blade loading and blade thickness are includedIn order to stand the practical use, correction factors on the cavitation part are adopted from 2-D cavitation test and actual ship observations. The predicted results on blade cavitation and hull surface pressure are compared with measured one, and the advantages of the method are discussed.
Advance ratio
Propulsor
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High-amplitude fluctuations in hull-surface pressures induced by unsteady propeller cavitation (with consequent hull vibration) are mainly the result of the nature of the wake field, but it must be accepted that the propeller loading distribution associated with maximum propulsive efficiency makes it difficult, if not impossible, to control cavitation under adverse flow conditions. Experience with unusual propeller-loading distributions associated with suppression of noise from warship propellers has led to a consideration of non-optimum, or arbitrary, loading distributions as a more general means of controlling pressure amplitudes, and a research programme has accordingly been carried out in which a design method for an arbitrarily-loaded wake-adapted propeller was developed. The Authors describe this design method, which, because of the uncertainties of such a propeller being successful, was put together from components of existing methods without undue expenditure of effort on the preparation of computer programs. The application of the method to the re-design of a propeller (for a single-screw container-ship) is also described, and an account is given of the associated tests, carried out on models of a 100% tip-unloaded propeller at the National Maritime Institute and consisting of open-water tests, self-propulsion tests with the model hull, and, in the cavitation tunnel, cavitation viewing and pressure measurements behind a partial-hull model. The results of the model tests, and comparisons with results from earlier experiments on models of the as-fitted propeller, are presented and discussed in some detail. It is concluded that, while the design process requires refinement, this research has clearly demonstrated the possibility of controlling hull surface pressure forces by varying the radial distribution of loading on the propeller. The advantages and disadvantages of tip unloading have been clearly defined, and the shipowner is presented with the choice between (i) maximum propulsive efficiency with the risk of severe vibration, and (ii) vibration-free running with reduced efficiency. Reports from the first full-scale application of this research, a retrofit on a large gas-carrier, are good.
Propulsive efficiency
Advance ratio
Naval architecture
Propulsor
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An outstanding problem in regard to the design of ships is the selection of the propeller geometry and the location of the propeller in the aperture in order to reduce the sum of the propeller-induced vibratory bearing forces and moments and the hull surface forces and moments to an acceptable minimum. This paper presents a reliable method to predict these net excitations for quite arbitrary stern and propeller configurations. A computer solution for the propeller and hull excitations has been developed and assessed for its adequacy by comparisons with two sets of model measurements.
Stern
Propulsor
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This paper describes the hydrodynamic performance prediction of ship hull with propeller by using CFD techniques. As an attempt in investigating the flow features around ship hull equipped with a rotating propeller, open water test, resistance test, and self-propulsion test were conducted. The paper discusses also the applicability of different turbulence models which are used to predict the hydrodynamic performance of the propeller, the hull, and the interaction hull-propeller. The hydrodynamic performance prediction method was gotten and was validated. The computational results were validated against the existing experimental data.
Open water
Performance Prediction
Propulsor
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In this paper a new concept in ship design was used to be alternative of ballast water system, to emerge that remedy the introduction of invasive marine species and the disadvantages of ballast water treatment systems.Thus, the hydrodynamic influences due to hull line variation of this kind of ships were studied, using the invariant cross-section area curve under the design draft to change the rise angle at bottom. Then numerical calculation was used to get the resistance and effective power at each angle. Two 3D models were constructed for 59000 DWT oil tankers and 35000 DWT bulk carriers, where the result of the bulk carrier was exposed.
Ballast
Line (geometry)
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