Response Characteristics of Serially Connected Semisubmersibles

1999 ◽  
Vol 43 (04) ◽  
pp. 229-240
Author(s):  
H. R. Riggs ◽  
R. C. Ertekin
Keyword(s):  
Energy Loss ◽  
Natural Frequencies ◽  
Normal Modes ◽  
Induced Response ◽  
Linear Wave ◽  
Response Characteristics ◽  
Response Modes ◽  
Wave Induced ◽  
The Impact ◽  
Large Aircraft

One design for a mobile offshore base is to link serially as many as five large semisubmersibles to form a platform long enough to support large aircraft. This paper investigates the linear, wave-induced response characteristics of serially-connected semisubmersibles. A major motivation of this study is to understand more completely the forces required to link semisubmersible modules. The impact of connector strategy and damping on the response, especially the connector forces, is investigated, and the response "modes" which contribute to the connector forces are evaluated in detail. It is shown that the response characteristics can be impacted significantly by the connection strategy, and that connector damping can be a significant source of energy loss when compared to radiation damping. The wet natural frequencies and normal modes are also determined and used to explain the response characteristics of different connection strategies. Although the analyses are based on a specific semisubmersible design, the results provide insight on how other systems of connected semisubmersibles would likely behave.

Structural Dynamics with Parameter Uncertainties

1987 ◽  
Vol 40 (3) ◽  
pp. 309-328 ◽  
Author(s):  
R. A. Ibrahim
Keyword(s):  
Structural Dynamics ◽  
Structural Parameters ◽  
Normal Modes ◽  
Forced Response ◽  
Experimental Investigations ◽  
Continuous Systems ◽  
Parameter Uncertainties ◽  
Response Characteristics ◽  
Random Eigenvalues ◽  
The Impact

The treatment of structural parameters as random variables has been the subject of structural dynamicists and designers for many years. Several problems have been involved during the last few decades and resulted in new theorems and interesting phenomena. This paper reviews a number of topics pertaining to structural dynamics with parameter uncertainties. These include direct problems such as random eigenvalues and random responses of discrete and continuous systems. The impact of these problems on related areas of interest such as sensitivity of structural performance to parameter variations, design optimization, and reliability analysis is also addressed. The paper includes the results of experimental investigations, the phenomenon of normal modes localization, and the effect of mistuning of turbomachinery blades on their flutter and forced response characteristics.

Influence of Flexible Connections on Response Characteristics of a Beam

1980 ◽  
Vol 102 (4) ◽  
pp. 829-834 ◽  
Author(s):  
R. Fossman ◽  
A. Sorensen
Keyword(s):  
Dynamic Load ◽  
Natural Frequencies ◽  
Normal Modes ◽  
Response Characteristics ◽  
Uniform Beam ◽  
Load Factors ◽  
Subsequent Application ◽  
Flexible Connections ◽  
Support Conditions

The natural frequencies and normal modes of a uniform beam depend upon support conditions. The effect of translation and rotation springs at the base is examined in this presentation. This is done in terms of non-dimensional variables and parameters to enhance the utility of the results. The paper also develops the mode participation and dynamic load factors for subsequent application.

scholarly journals Two-dimensional model of wave-induced response of seabed around permeable submerged breakwater

2019 ◽  
Vol 11 (3) ◽  
pp. 168781401983080 ◽  
Author(s):  
Richard Asumadu ◽  
Ji-Sheng Zhang ◽  
Osei-Wusuansa Hubert ◽  
Alex Baffour Akoto
Keyword(s):  
Dynamic Response ◽  
Navier Stokes ◽  
Induced Response ◽  
Two Dimensional ◽  
Navier Stokes Equation ◽  
Structure Variation ◽  
Submerged Breakwater ◽  
Response Status ◽  
Wave Induced ◽  
The Impact

This article focuses on a two-dimensional numerical model established to determine the seabed dynamic response in the region of a permeable submerged breakwater. The wave motion in this article is governed by the volume-averaged Reynolds-averaged Navier–Stokes equation, whereas Biot’s poro-elastic equation determines the seabed foundation. The water surface is recorded using the volume of fluid technique. In this study, the results for the two-dimensional seabed dynamic response for both the consolidation status and the dynamic wave-induced response status for the seabed foundation coupled with submerged breakwater are illustrated. The numerical results examined from the dynamic pore pressure, the effective stresses, the shear stress, and the seabed soil displacements revealed that the impact of dynamic response at the offshore zone/seaward on the seabed foundation is more developed than at the onshore zone/harbor side. Parametric results analysis as regards the effect of the wave, the seabed, and the submerged breakwater structure variation significantly affected the seabed foundation response coupled with the breakwater structure. The numerical outcome on the liquefaction potential shows that the seabed foundation is more seemingly to liquefy and happen approximately at the toe of the submerged breakwater under the wave loading.

Vibration analysis of an aviation engine turbine shaft shield

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Stanisław Noga ◽  
Kaja Maciejowska ◽  
Tomasz Rogalski
Keyword(s):  
Natural Frequencies ◽  
Dynamic Properties ◽  
Normal Modes ◽  
Measuring System ◽  
Mode Shapes ◽  
Modal Assurance Criterion ◽  
Natural Form ◽  
Content Type ◽  
Turbine Shaft ◽  
The Impact

Purpose This paper aims to deal with the problem of vibration in an aircraft engine turbine shaft shield. The physical model of the system under study is inspired by the PZL-10W aviation jet engine shaft shield and is a structure of the profile circular arc. The main goal of the presented research is to develop a modal model of the discussed object. Another task is to determine the impact of the shaft shield damage on the change of dynamic parameters (the values of the natural frequencies and changing of the shape of the corresponding natural forms) of the discussed object. Finally, the task is connected with the calculation of the excitation speeds of the discussed shaft shield’s respective natural frequencies. Design/methodology/approach To realize the main goal finite element method simulation and experimental investigation were conducted. The quality of the achieved models is determined based on the relative error of natural frequencies and the similarity to normal modes established on the basis of the modal assurance criterion (MAC) indicator. The Campbell diagram was used to calculate the excitation speeds of the discussed shaft shield’s respective natural frequencies. Findings The obtained results indicate the changes in the dynamic properties of the shaft shield as a result of its cracking. On the basis of the adopted measurement (MAC indicator), the level of similarity was established between the numerical simulation results and the measurement results for the undamaged shield. Verification of the different mode shapes using the CrossMAC tool is an effective method, which allows comparing of the shape of the natural form and may be helpful in the process of adjusting modal models to the results of experimental tests. Practical implications It is important to note that as a result of using commercial software (ANSYS program) and a commercial measuring system (Bruel and Kjaer), the presented analysis can be attractive for design engineers dealing with the dynamics of aviation systems. Originality/value The paper presents the authors’ original approach to the dynamic analysis of the aviation engine turbine shaft shield, which can be useful for engineers dealing with the issue of vibration in shaft shield systems.

Atomic resolution characterisation of interface structures by Electron Energy Loss Spectroscopy

1993 ◽  
Vol 51 ◽  
pp. 576-577
Author(s):  
N. D. Browning ◽  
M. M. McGibbon ◽  
M. F. Chisholm ◽  
S. J. Pennycook
Keyword(s):  
High Resolution ◽  
Energy Loss ◽  
Electron Energy ◽  
Electron Energy Loss Spectroscopy ◽  
Imaging Technique ◽  
Atomic Scale ◽  
Atomic Resolution ◽  
Reference Image ◽  
The Impact ◽  
Electron Energy Loss

The recent development of the Z-contrast imaging technique for the VG HB501 UX dedicated STEM, has added a high-resolution imaging facility to a microscope used mainly for microanalysis. This imaging technique not only provides a high-resolution reference image, but as it can be performed simultaneously with electron energy loss spectroscopy (EELS), can be used to position the electron probe at the atomic scale. The spatial resolution of both the image and the energy loss spectrum can be identical, and in principle limited only by the 2.2 Å probe size of the microscope. There now exists, therefore, the possibility to perform chemical analysis of materials on the scale of single atomic columns or planes.In order to achieve atomic resolution energy loss spectroscopy, the range over which a fast electron can cause a particular excitation event, must be less than the interatomic spacing. This range is described classically by the impact parameter, b, which ranges from ~10 Å for the low loss region of the spectrum to <1Å for the core losses.

Dynamic model for high-speed rotors based on their experimental characterization

2017 ◽  
Vol 2 (4) ◽  
pp. 25
Author(s):  
L. A. Montoya ◽  
E. E. Rodríguez ◽  
H. J. Zúñiga ◽  
I. Mejía
Keyword(s):  
Dynamic Model ◽  
High Speed ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Experimental Characterization ◽  
Rotating Systems ◽  
Computing Performance ◽  
The Impact ◽  
Stiffness Distribution ◽  
Good Agreement

Rotating systems components such as rotors, have dynamic characteristics that are of great importance to understand because they may cause failure of turbomachinery. Therefore, it is required to study a dynamic model to predict some vibration characteristics, in this case, the natural frequencies and mode shapes (both of free vibration) of a centrifugal compressor shaft. The peculiarity of the dynamic model proposed is that using frequency and displacements values obtained experimentally, it is possible to calculate the mass and stiffness distribution of the shaft, and then use these values to estimate the theoretical modal parameters. The natural frequencies and mode shapes of the shaft were obtained with experimental modal analysis by using the impact test. The results predicted by the model are in good agreement with the experimental test. The model is also flexible with other geometries and has a great time and computing performance, which can be evaluated with respect to other commercial software in the future.

scholarly journals Aspects of Strength Testing of Tank Containers in Compliance with the Requirements of the UN Navigation Rules and Regulations

2021 ◽  
Vol 9 (3) ◽  
pp. 349
Author(s):  
Andrii Sulym ◽  
Pavlo Khozia ◽  
Eduard Tretiak ◽  
Václav Píštěk ◽  
Oleksij Fomin ◽  
...  
Keyword(s):  
Natural Frequencies ◽  
Response Spectrum ◽  
Experimental Curve ◽  
Bulk Liquid ◽  
Frequency Range ◽  
Test Configuration ◽  
Shock Response ◽  
Shock Response Spectrum ◽  
Spectrum Curve ◽  
The Impact

This article deals with the method of computer-aided studies of the results of tank container impact tests to confirm the ability of portable tanks and multi-element gas containers to withstand the impact in the longitudinal direction on a specially equipped test rig or using a railway flat car by impacting a flat car with a striking car, in compliance with the requirements of the UN Navigation Rules and Regulations. It is shown that the main assessed characteristic of the UN requirements is the spectrum of the shock response (accelerations) for the interval natural frequencies of the shock pulse. The calculation of the points of the shock response spectrum curve based on the test results is reproduced in four stages. A test configuration of the impact testing of the railway flat car with a tank container is presented, and the impact is performed in such a way that, under a single impact, the shock spectrum curve obtained during the tests for both fittings subjected to impact repeats or exceeds the minimum shock spectrum curve for all frequencies in the range of 2 Hz to 100 Hz. Formulas for determining the relative displacements and accelerations for the interval natural frequencies of the shock wave are given. The research results are presented in graphical form, indicating that the experimental values of the shock response spectrum exceed the minimum permissible values; the equation of the experimental curve of the shock response spectrum in the frequency range 0–100 Hz is described by power-law dependence. The coefficients of the equation were determined by the statistical method of maximum likelihood with the determination factor being 0.897, which is a satisfactory value; a comparative analysis showed that the experimental curve of the impact response spectrum in the frequency range 0–100 Hz exceeds the normalized curve, which confirms compliance with regulatory requirements. A new test configuration is proposed using a tank car with a bulk liquid, the processes in which upon impact differ significantly from other freight wagons under longitudinal impact loads of the tank container. The hydraulic impact resulting from the impact on the tank container and the platform creates an overturning moment that causes the rear fittings to be unloaded.

scholarly journals Energy Loss Due to Adhesion During the Impact of Elastic Spheres

2017 ◽  
Vol 173 ◽  
pp. 238-243 ◽  
Author(s):  
U.B. Jayadeep ◽  
M.S. Bobji
Keyword(s):  
Energy Loss ◽  
The Impact
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