Procedure to Obtain Added Mass in Ships From Natural Frequencies Measured in Hull Vertical Vibration Full Scale Tests

2013 ◽  
Author(s):  
Luiza de Mesquita Ortiz ◽  
Severino Fonseca da Silva Neto ◽  
Sergio Hamilton Sphaier
Keyword(s):  
Natural Frequencies ◽  
Numerical Procedure ◽  
Quadratic Function ◽  
Added Mass ◽  
Vertical Vibration ◽  
Full Scale ◽  
Vibration Measurement ◽  
Independent Variable ◽  
Numerical Finite Element ◽  
Full Scale Tests

This work shows an experimental-numerical procedure used to determine added mass of ships. A numerical Finite Element ship hull model is constructed according to the weight distribution and the drafts over its length during the full scale vibration measurement. The rate breadth/draft for each frame of the hull is considered as the independent variable of a quadratic function representing the added mass distribution, which coefficients are determined in order to minimize the sum of squared differences between the natural frequencies obtained numerically in respect with those obtained in the correspondent full scale measurement. The added mass coefficients obtained from the experimental data of a first ship are then used to predict numerically the natural frequencies of a second ship of the same type.

Numerical Simulation of the Added Mass of the Fluid Adjacent to the Ship Hull in Vibration Measured During Sea-Trials in Tanker Ships to be Converted to Offshore Construction Vessel

2012 ◽  
Author(s):  
Severino Fonseca Silva Neto ◽  
Silvia Ramscheid Figueiredo ◽  
Marta Cecilia Tapia Reyes ◽  
Luiza de Mesquita Ortiz
Keyword(s):  
Numerical Model ◽  
Kinetic Energy ◽  
Natural Frequencies ◽  
Three Dimensional ◽  
Added Mass ◽  
Vertical Vibration ◽  
Full Scale ◽  
Experimental Results ◽  
Vibration Velocity ◽  
Main Engine

This study aims to analyze the influence of the kinetic energy of the fluid adjacent to the hull of a tanker ship in its vertical vibration frequencies, comparing them with experimental measurements obtained during sea-trials. The one-dimensional modeling of ships allows the construction of simple finite element models from the structural elements of its master section, with structural and added masses, and their frequencies are verified by full-scale measurements, during the sea-trials. The numerical results of these models, with the value of the effective shear area as a fraction of the total area of the strength steel are compared to those obtained in full-scale measurements during sea trials of an oil tanker to be converted to Offshore Construction Vessel. Global vibration measurements were carried out in two of the six ships with the same hull. Accelerometers were installed in eleven strategic points of each hull. Vibration data acquisition was performed simultaneously for these locals in thirteen rotations of the main engine. The amplitude spectra of vibration velocity on the frequency range of measurements were obtained and were plotted graphs of the evolution of the main harmonics, depending on the rotation of the main engine, in order to identify four natural frequencies of the overall vibration of the hull, which were compared to the numerical model. The calculation is performed by the added mass formulations from Burrill, Todd, Kumay and Lewis/Landweber [8] curves, including in all three-dimensional effect by Townsin [17] coefficients, which is checked against the experimental results. The comparison between numerical and experimental results allows assessing the influence of the kinetic energy of the fluid surrounding the hull in the natural frequencies of vibration of the numerical model of the tanker ship and simulating their dynamic behavior after conversion in Offshore Construction Vessel.

scholarly journals Vertical Track Irregularity Influence on the Wheel High-Frequency Vibration in Wheel-Rail System

2016 ◽  
Vol 2016 ◽  
pp. 1-13 ◽  
Author(s):  
Yang Lei ◽  
Xinyu Tian ◽  
Falin Qi ◽  
Dongsheng Chen ◽  
Tian Tian
Keyword(s):  
High Frequency ◽  
Natural Frequencies ◽  
Vertical Vibration ◽  
Vibration Measurement ◽  
Central Difference ◽  
Nonlinear Simulation ◽  
Contact Parameter ◽  
High Frequency Vibration ◽  
Rail System ◽  
Track Irregularity

A three-dimensional deformable finite element model of wheel-rail system is established. The vertical vibration natural frequencies are calculated by modal analysis. The improved central difference method by ABAQUS explicit nonlinear dynamics module is chosen to calculate the vertical vibration of wheel axle. Through the vibration measurement experiment ofLMAwheel by China Academy of Railway Sciences, the contact parameter is optimized and the model is modified. According to the nonlinear simulation results, the important influence of vertical track irregularity on the wheel set high-frequency vibration is discovered. The advantage frequencies through spectrum are close to the vertical vibration natural frequencies of seventh, eighth, ninth, and tenth mode. When the velocity is 350 km/h, system’s nonlinear dynamic characteristic is higher than the results at 200 km/h. The critical wavelength of vertical track irregularity on the wheel vertical vibration is about 0.8 m. In addition, a particular attention should be paid to one situation that the main dominant frequency amplitude is more than 50% of the acceleration amplitude even if the peak acceleration is low.

COMPARISON OF MODELING THE NATURAL FREQUENCIES AND VIBRATION MODES OF A SOUND ISOLATION PANEL FRAGMENT WITH FULL-SCALE TESTS

2021 ◽  
Author(s):  
G. S. Russkikh ◽  
◽  
Z. N. Sokolovskiy ◽  
E. A. Romanenko ◽  
◽  
...  
Keyword(s):  
Natural Frequencies ◽  
Full Scale ◽  
Vibration Modes ◽  
Full Scale Tests ◽  
Ansys Workbench

В статье рассмотрены результаты моделирования собственных частот и форм колебаний, выполненного в программном комплексе Ansys Workbench в сравнении с натурным экспериментом. Целью исследования является верификация модели, построенной в Ansys Workbench. Результаты позволяют сделать заключение об адекватности модели и возможности ее применения для решения задачи определения собственных частот и форм колебаний

Investigation of planing craft maneuverability using full-scale tests

2021 ◽  
pp. 147509022110303
Author(s):  
Kazem Sadati ◽  
Hamid Zeraatgar ◽  
Aliasghar Moghaddas
Keyword(s):  
Full Scale ◽  
Performance Characteristics ◽  
Forward Speed ◽  
Speed Reduction ◽  
Planing Craft ◽  
Full Scale Tests ◽  
Turning Maneuver

Maneuverability of planing craft is a complicated hydrodynamic subject that needs more studies to comprehend its characteristics. Planing craft drivers follow a common practice for maneuver of the craft that is fundamentally different from ship’s standards. In situ full-scale tests are normally necessary to understand the maneuverability characteristics of planing craft. In this paper, a study has been conducted to illustrate maneuverability characteristics of planing craft by full-scale tests. Accelerating and turning maneuver tests are conducted on two cases at different forward speeds and rudder angles. In each test, dynamic trim, trajectory, speed, roll of the craft are recorded. The tests are performed in planing mode, semi-planing mode, and transition between planing mode to semi-planing mode to study the effects of the craft forward speed and consequently running attitude on the maneuverability. Analysis of the data reveals that the Steady Turning Diameter (STD) of the planing craft may be as large as 40 L, while it rarely goes beyond 5 L for ships. Results also show that a turning maneuver starting at planing mode might end in semi-planing mode. This transition can remarkably improve the performance characteristics of the planing craft’s maneuverability. Therefore, an alternative practice is proposed instead of the classic turning maneuver. In this practice, the craft traveling in the planing mode is transitioned to the semi-planing mode by forward speed reduction first, and then the turning maneuver is executed.

Full-scale tests of the trash racks of the Kapchagai hydroelectric station

1984 ◽  
Vol 18 (4) ◽  
pp. 166-170
Author(s):  
A. L. Rakhmanova ◽  
I. O. Rybak
Keyword(s):  
Hydroelectric Station ◽  
Full Scale ◽  
Full Scale Tests
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