A Comparison of Ship-Mounted and Cage-Mounted Passive Heave Compensation Systems

2000 ◽  
Vol 122 (3) ◽  
pp. 214-221 ◽  
Author(s):  
Frederick R. Driscoll ◽  
Meyer Nahon ◽  
Rolf G. Lueck
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Numerical Simulations ◽  
Deep Sea ◽  
Natural Frequencies ◽  
Element Model ◽  
Sea State ◽  
Marine Systems ◽  
Compensation Systems ◽  
Safe Operating

Tethered marine systems experience large tensile loads in their tether when operating in rough seas. Heave compensation systems can be used to reduce these loads and increase the safe operating sea states. In this work, a discrete representation of a passive heave compensator is developed and added to a finite-element model of a deep-sea ROV system to investigate the performance of ship-mounted and cage-mounted compensation systems. Numerical simulations are performed for operating depths ranging from 3280–16,400 ft (1000–5000 m) and a range of compensator stiffnesses. Both ship and cage-mounted systems reduced the natural frequencies, rms cage motion and rms tension, and extended the operating sea state of the ROV. During extreme seas, the cage-mounted compensator effectively eliminated all snap loads. However, the compensator’s characteristics must be carefully chosen because a poorly designed compensator can exacerbate operational problems. [S0892-7219(00)00903-1]

Physical and Numerical Simulations of the Seismic Response of a 1,100 kV Power Transformer Bushing

2018 ◽  
Vol 34 (3) ◽  
pp. 1515-1541 ◽  
Author(s):  
Guo-Liang Ma ◽  
Qiang Xie ◽  
Andrew S. Whittaker
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Numerical Simulations ◽  
Seismic Vulnerability ◽  
Power Transformer ◽  
Element Model ◽  
Ground Shaking ◽  
Earthquake Simulator ◽  
Physical Experiments ◽  
Seismic Tests

Power transformers and bushings are key pieces of substation equipment and are vulnerable to the effects of earthquake shaking. The seismic performance of a 1,100 kV bushing, used in an ultra-high voltage (UHV) power transformer, is studied using a combination of physical and numerical experiments. The physical experiments utilized an earthquake simulator and included system identification and seismic tests. Modal frequencies and shapes are derived from white noise tests. Acceleration, strain, and displacement responses are obtained from the uniaxial horizontal seismic tests. A finite element model of the 1,100 kV bushing is developed and analyzed, and predicted and measured results are compared. There is reasonably good agreement between predicted and measured responses, enabling the finite element model to be used with confidence for seismic vulnerability studies of transformer-bushing systems. A coupling of the experimental and numerical simulations enabled the vertically installed UHV bushing to be seismically qualified for three-component ground shaking with a horizontal zero-period acceleration of 0.53 g.

Support-Condition Analyses of Rotating Beams Under Distributed Imbalance Loading

2011 ◽  
Author(s):  
Kai Jokinen ◽  
Erno Keskinen ◽  
Marko Jorkama ◽  
Wolfgang Seemann
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Cross Section ◽  
Cross Sections ◽  
Natural Frequencies ◽  
Element Model ◽  
Mode Shapes ◽  
Constant Cross Section ◽  
Support Condition ◽  
Beam Elements

In roll balancing the behaviour of the roll can be studied either experimentally with trial weights or, if the roll dimensions are known, analytically by forming a model of the roll to solve response to imbalance. Essential focus in roll balancing is to find the correct amount and placing for the balancing mass or masses. If this selection is done analytically the roll model used in calculations has significant effect to the balancing result. In this paper three different analytic methods are compared. In first method the mode shapes of the roll are defined piece wisely. The roll is divided in to five parts having different cross sections, two shafts, two roll ends and a shell tube of the roll. Two boundary conditions are found for both supports of the roll and four combining equations are written to the interfaces of different roll parts. Totally 20 equations are established to solve the natural frequencies and to form the mode shapes of the non-uniform roll. In second model the flexibility of shafts and the stiffness of the roll ends are added to the support stiffness as serial springs and the roll is modelled as a one flexibly supported beam having constant cross section. Finally the responses to imbalance of previous models are compared to finite element model using beam elements. Benefits and limitations of each three model are then discussed.

Hydroelastic Modal Analysis of the Perforated Cylindrical Shell in SMART

2011 ◽  
Author(s):  
Youngin Choi ◽  
Seungho Lim ◽  
Kyoung-Su Park ◽  
No-Cheol Park ◽  
Young-Pil Park ◽  
...  
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Dynamic Characteristics ◽  
Natural Frequencies ◽  
Element Model ◽  
Mode Shapes ◽  
Steam Generators ◽  
Structure Interaction ◽  
The Finite Element Model ◽  
Reactor Internals

The System-integrated Modular Advanced ReacTor (SMART) developed by KAERI includes components like a core, steam generators, coolant pumps, and a pressurizer inside the reactor vessel. Though the integrated structure improves the safety of the reactor, it can be excited by an earthquake and pump pulsations. It is important to identify dynamic characteristics of the reactor internals considering fluid-structure interaction caused by inner coolant for preventing damage from the excitations. Thus, the finite element model is constructed to identify dynamic characteristics and natural frequencies and mode shapes are extracted from this finite element model.

Thermal Robustness Assessment of a Rigidized Space Inflatable Boom via Experimental Modal Analysis and Finite Element Modeling

2010 ◽  
Author(s):  
Matthew Daly ◽  
Armaghan Salehian ◽  
Alireza Doosthoseini
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Frequency Response Function ◽  
Good Accuracy ◽  
Natural Frequencies ◽  
Beam Theory ◽  
Element Model ◽  
Modal Testing ◽  
Environmental Temperatures ◽  
Robustness Assessment

The following paper presents the results of a thermal robustness assessment of a rigidized space inflatable boom. Modal testing is performed at three different environmental temperatures; spanning a range of 38°C, with the purpose of characterizing dynamic behavior and assessing changes in bending frequencies. Experimental results show that the natural frequencies of the boom shift only marginally within the tested bandwidth. A finite element model is developed in parallel with experiments to determine compatibility with beam theory. The resulting simulation shows that linear beam theory can be used to predict bending frequencies and frequency response function magnitudes with very good accuracy.

Finite Element Model Updating Approach to Damage Identification in Beams Using Particle Swarm Optimization

2008 ◽  
Author(s):  
Mohamed M. Saada ◽  
Mustafa H. Arafa ◽  
Ashraf O. Nassef
Keyword(s):  
Finite Element ◽  
Particle Swarm Optimization ◽  
Finite Element Model ◽  
Natural Frequencies ◽  
Damage Identification ◽  
Model Updating ◽  
Particle Swarm ◽  
Element Model ◽  
Pso Algorithm ◽  
Swarm Optimization

The use of vibration-based techniques in damage identification has recently received considerable attention in many engineering disciplines. While various damage indicators have been proposed in the literature, those relying only on changes in the natural frequencies are quite appealing since these quantities can conveniently be acquired. Nevertheless, the use of natural frequencies in damage identification is faced with many obstacles, including insensitivity and non-uniqueness issues. The aim of this paper is to develop a viable damage identification scheme based only on changes in the natural frequencies and to attempt to overcome the challenges typically encountered. The proposed methodology relies on building a Finite Element Model (FEM) of the structure under investigation. A modified Particle Swarm Optimization (PSO) algorithm is proposed to facilitate updating the FEM in accordance with experimentally-determined natural frequencies in order to predict the damage location and extent. The method is tested on beam structures and was shown to be an effective tool for damage identification.

scholarly journals Application of optimization to change eigenfrequency of a pinion

Mechanik ◽  
2017 ◽  
Vol 90 (7) ◽  
pp. 588-590
Author(s):  
Jacek Stadnicki ◽  
Michał Głąbek
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Final Stage ◽  
Parametric Optimization ◽  
Natural Frequencies ◽  
Element Model ◽  
The Way

During the final stage of designing a pinion which is exploited at different rotational speeds, it is occasionally necessary to offset natural frequencies from frequencies of excitations. The way of solving this problem by means of parametric optimization of the pinion profile, assuming small changes of its shape, is discussed in the paper. The problem is solved using finite element model with regard to monolithic pinion of an aircraft gear.

Modal Analysis and Experimental Research of Marine Gearbox

2014 ◽  
Vol 607 ◽  
pp. 405-408 ◽  
Author(s):  
Wen Liu ◽  
Teng Jiao Lin ◽  
Quan Cheng Peng
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Modal Analysis ◽  
Experimental Research ◽  
Natural Frequencies ◽  
Element Model ◽  
Ansys Software ◽  
Tetrahedral Element ◽  
Spring Element ◽  
Good Agreement

The gear-shaft-bearing-housing coupled finite element model of marine gearbox was established by using the truss element, the spring element and the tetrahedral element. The modal of gearbox was analyzed by using the ANSYS software. Then through the experimental modal analysis, the natural frequencies of gearbox are obtained. Compare the experimental results with the numerical results, it shows good agreement.

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