Effect of Wave Loading on the Seismic Behavior of a Typical Fixed Jacket-Type Platform

2008 ◽  
Author(s):  
Z. Omrani ◽  
A. R. M. Gharabaghi ◽  
S. R. Hosseini ◽  
S. Nouri
Keyword(s):  
Seismic Behavior ◽  
Nonlinear Response ◽  
Offshore Platforms ◽  
Wave Loading ◽  
Response Characteristics ◽  
Finite Element Software ◽  
Structure Response ◽  
Wave Characteristics ◽  
Damping Characteristics ◽  
Time Histories

Design of fixed offshore platforms to resist earthquakes involves many of the same problems and issues as other onshore structures. However, there are some important differences that the most important one is the presence of seawater. It influences the mass, stiffness, damping and strength characteristics of the platform, which can have important effects on the structure response characteristics. The entrained water inside the platform elements and the water that is accelerated by the motions of the structure, have very important effects on the mass and damping characteristics of the platform. The presence of other environmental loads, particularly waves can also influence the response of these structures. In this paper, the nonlinear response of a typical jacket type platform, which has been installed in Persian Gulf, under wave and earthquake loadings are studied. The structure is modeled by ANSYS, finite element software. Time histories of different earthquake loadings are applied. Wave characteristics are based on local information. These loadings are applied separately and simultaneously. Moreover, they are applied in the same direction and different directions. The results are compared with each other and the most sever cases are extracted.

Nonlinear Response Characteristics of Discus Data Buoy Hull

2008 ◽  
Author(s):  
R. Balaji ◽  
S. A. Sannasiraj ◽  
V. Sundar
Keyword(s):  
Experimental Investigation ◽  
Response Time ◽  
Nonlinear Wave ◽  
Nonlinear Response ◽  
Phase Portraits ◽  
Testing Conditions ◽  
Response Characteristics ◽  
Wave Elevation ◽  
Time Histories ◽  
Spectral Representations

The response characteristics of the discus hull shaped data buoy under the influence of nonlinear wave conditions was studied in an experimental investigation. The measured wave elevation and the buoy response time histories were analyzed by phase-portraits as well as through the spectral representations. The details of the model, instrumentation, testing conditions and the analysis are presented and discussed in this paper.

Time Histories of Wave-in-Deck Loading on Jacket Decks

2006 ◽  
Author(s):  
Katrine van Raaij ◽  
Ove T. Gudmestad
Keyword(s):  
Time Variation ◽  
Structural Response ◽  
Engineering Practice ◽  
Offshore Platforms ◽  
Wave Loading ◽  
Extreme Wave ◽  
Incoming Wave ◽  
Time Histories ◽  
The Difference

Most researchers agree that wave-in-deck loading is of dynamic nature and that the dynamic effects on the structural response are important. However, there exists no engineering practice for the determination of load time histories for waves hitting the decks of fixed offshore platforms. This applies to both the time variation and the magnitude of the loading. This paper presents the main recommendations for wave-in-deck loading with reference to wave tank experiments of a model of the Statfjord A Condeep platform subjected to extreme wave loading. The recommendations for loading from these tests comprise time variation as well as magnitude. These recommendations are used as a basis to suggest a simplified method to estimate wave-in-deck loading on jacket platform decks, for which, to the difference from Condeep platforms, the wave height amplification due to the interaction between the incoming wave and the structure (Swan et al., 1997) is negligible. The resulting ‘recipe’ for wave-in-deck time histories on North Sea jacket platforms is compared to relevant results previously reported in the literature. The method is categorised as a ‘global’ approach, that is, one uses an effective deck area as opposed to a detailed deck model. The method is suggested to be applicable for analyses where a ‘rough but reasonable’ estimate for wave-in-deck loading is sufficient.

Analysis of Offshore Structures Subjected to Various Types of Sea Wave

2004 ◽  
Author(s):  
K. Kuntiyawichai ◽  
S. Chucheepsakul ◽  
M. M. K. Lee
Keyword(s):  
Finite Element ◽  
Wavelet Analysis ◽  
Dynamic Behaviour ◽  
Time History ◽  
Offshore Structures ◽  
Offshore Platforms ◽  
Wave Loading ◽  
Offshore Structure ◽  
Finite Element Software ◽  
Jacket Structures

The principal aim of this paper is to study the dynamic behaviour of offshore platforms subjected to wave loading. A general review of offshore structure, wave loading and their effects on offshore structures are presented. A brief review on the basics of Wavelet analysis is also mentioned in this study. The techniques for modeling wave loading in finite element analyses are described and discussed in detail. A series of 3D analyses were carried out using the ABAQUS finite element software to study the effects on the dynamic response of the change in support conditions at the seabed. The effects of wave height, wave period and wave velocity on platform behaviour were studied. The results from time history analysis are characterized using Wavelet Analysis in order to obtain the response pattern due to wave loading. These analyses allow the frequency response of the jacket structures to be described in the time domain. These results give a clear view on the response of jacket structure. The important parameters on offshore modeling have also been identified and discussed in this paper. The results presented in this study can be used as a guidance for engineer in order to understand the dynamic behaviour of jacket structures subjected to wave loading.

Dynamic Response Analysis of Docking Chamber Structure Considering Viscoelastic Boundary Condition

2013 ◽  
Vol 405-408 ◽  
pp. 1939-1944
Author(s):  
Gui Lan Tao ◽  
Li Zhang
Keyword(s):  
Boundary Conditions ◽  
Secondary Development ◽  
Response Analysis ◽  
Elastic Model ◽  
Cross Point ◽  
Finite Element Software ◽  
Structure Response ◽  
Structure Dynamic ◽  
Fixed Boundaries ◽  
Incident Waves

Spring-damper units were set on the boundaries to absorb incident waves and reflected scattering waves to realize viscoelastic artificial boundary (VAB). The equivalent node load input method was used to simulate the VAB and viscoelastic boundary element wave input. Programming is based on APDL secondary development language with ANSYS finite element software. Considering the interaction between chamber structure and the surrounding soil, docking chamber structure dynamic model is established based on the VAB. The linear elastic model was used for concrete structure. The D-P nonlinear model was used for the back soil calculation. Docking chamber structure dynamic analysis under conditions of fixed boundaries and viscoelastic boundaries were conducted. The result indicated that under the viscoelastic boundary conditions, dynamic acceleration response is significant on the top of the lock wall, which is approximately 2.5 times of the value on the bottom of the lock wall. The maximum response stress appears near the cross point of the lock wall and the bottom floor with value of approximately 5620 kPa;.The chamber bottom floor is subjected to tension and maximum stress with the value of approximately 6180 kPa. Usually, the structure response under the fixed boundary conditions is higher than the structure response under the viscoelastic boundary conditions.

scholarly journals An experimental decomposition of nonlinear forces on a surface-piercing column: Stokes-type expansions of the force harmonics

2018 ◽  
Vol 848 ◽  
pp. 42-77 ◽  
Author(s):  
L. F. Chen ◽  
J. Zang ◽  
P. H. Taylor ◽  
L. Sun ◽  
G. C. J. Morgan ◽  
...  
Keyword(s):  
High Order ◽  
Quality Data ◽  
Wave Group ◽  
Wave Loading ◽  
Harmonic Force ◽  
Wave Basin ◽  
Wide Range ◽  
Time Histories ◽  
Focused Wave ◽  
Sloping Bed

Wave loading on marine structures is the major external force to be considered in the design of such structures. The accurate prediction of the nonlinear high-order components of the wave loading has been an unresolved challenging problem. In this paper, the nonlinear harmonic components of hydrodynamic forces on a bottom-mounted vertical cylinder are investigated experimentally. A large number of experiments were conducted in the Danish Hydraulic Institute shallow water wave basin on the cylinder, both on a flat bed and a sloping bed, as part of a European collaborative research project. High-quality data sets for focused wave groups have been collected for a wide range of wave conditions. The high-order harmonic force components are separated by applying the ‘phase-inversion’ method to the measured force time histories for a crest focused wave group and the same wave group inverted. This separation method is found to work well even for locally violent nearly-breaking waves formed from bidirectional wave pairs. It is also found that the $n$th-harmonic force scales with the $n$th power of the envelope of both the linear undisturbed free-surface elevation and the linear force component in both time variation and amplitude. This allows estimation of the higher-order harmonic shapes and time histories from knowledge of the linear component alone. The experiments also show that the harmonic structure of the wave loading on the cylinder is virtually unaltered by the introduction of a sloping bed, depending only on the local wave properties at the cylinder. Furthermore, our new experimental results reveal that for certain wave cases the linear loading is actually less than 40 % of the total wave loading and the high-order harmonics contribute more than 60 % of the loading. The significance of this striking new result is that it reveals the importance of high-order nonlinear wave loading on offshore structures and means that such loading should be considered in their design.

scholarly journals Numerical Simulation of Transient Electromagnetic Response of Unfavorable Geological Body in Tunnel

2011 ◽  
Vol 90-93 ◽  
pp. 37-40 ◽  
Author(s):  
Lu Bo Meng ◽  
Tian Bin Li ◽  
Zheng Duan
Keyword(s):  
Numerical Simulation ◽  
Finite Element ◽  
Electromagnetic Field ◽  
Electromagnetic Response ◽  
Detection Distance ◽  
Geological Body ◽  
Response Characteristics ◽  
Finite Element Software ◽  
Transient Electromagnetic ◽  
Field Decay

To investigate the transient electromagnetic method of response characteristics in the tunnel geological prediction, the finite element numerical simulation of unfavorable geological body of different location, different resistivity sizes, different shapes, and different volume size were carried out by ANSYS finite element software. The results show that secondary electromagnetic field of different location of unfavorable geological body have same decay rate, when detection distance from 30m to 70m, transient electromagnetic responses are strongest, followed distance from 10m to 30m and from 70m to 90m. The shape, volume and resistivity of unfavorable geological body have strong influence on transient electromagnetic response, unfavorable geological body more sleek, the greater the volume and the smaller the resistivity of unfavorable geological body, the secondary electromagnetic field decay slower.

Shooting With Deflation Algorithm-Based Nonlinear Response and Neimark-Sacker Bifurcation and Chaos in Floating Ring Bearing Systems

2016 ◽  
Vol 12 (3) ◽  
Author(s):  
Sitae Kim ◽  
Alan B. Palazzolo
Keyword(s):  
Nonlinear Response ◽  
Nonlinear Behavior ◽  
Rotor System ◽  
Operating Conditions ◽  
Fluid Film ◽  
Stable Limit ◽  
Bifurcation And Chaos ◽  
Chaotic Motions ◽  
Response Characteristics ◽  
Computation Efficiency

The double-sided fluid film force on the inner and outer ring surfaces of a floating ring bearing (FRB) creates strong nonlinear response characteristics such as coexistence of multiple orbits, Hopf bifurcation, Neimark-Sacker (N-S) bifurcation, and chaos in operations. An improved autonomous shooting with deflation algorithm is applied to a rigid rotor supported by FRBs for numerically analyzing its nonlinear behavior. The method enhances computation efficiency by avoiding previously found solutions in the numerical-based search. The solution manifold for phase state and period is obtained using arc-length continuation. It was determined that the FRB-rotor system has multiple response states near Hopf and N-S bifurcation points, and the bifurcation scenario depends on the ratio of floating ring length and diameter (L/D). Since multiple responses coexist under the same operating conditions, simulation of jumps between two stable limit cycles from potential disturbance such as sudden base excitation is demonstrated. In addition, this paper investigates chaotic motions in the FRB-rotor system, utilizing four different approaches, strange attractor, Lyapunov exponent, frequency spectrum, and bifurcation diagram. A numerical case study for quenching the large amplitude motion by adding unbalance force is provided and the result shows synchronization, i.e., subsynchronous frequency components are suppressed. In this research, the fluid film forces on the FRB are determined by applying the finite element method while prior work has utilized a short bearing approximation. Simulation response comparisons between the short bearing and finite bearing models are discussed.

Theoretical and Experimental Analysis of Nonlinear Dynamics in a Linear Compressor

2001 ◽  
Vol 124 (1) ◽  
pp. 152-154 ◽  
Author(s):  
Gyu-Sang Choe ◽  
Kwang-Joon Kim
Keyword(s):  
Steady State ◽  
Nonlinear Response ◽  
Dynamic Models ◽  
Steady State Response ◽  
Describing Function ◽  
Linear Compressor ◽  
Response Characteristics ◽  
State Response ◽  
Jump Phenomena ◽  
Method Effects

Steady-state nonlinear response characteristics of a linear compressor are investigated theoretically and experimentally. In the theoretical approach, motions of not only piston but also cylinder are considered and dynamic models for steady-state response predictions are formulated by applying the describing function method. Effects of piston mass on the jump phenomena are predicted by the derived models as an example of design parameter variation and compared with actual experimental results.

Optimal Vibration Control Strategy for Offshore Platforms Accounting for AMD Constraints

2004 ◽  
Author(s):  
Chunyan Ji ◽  
Qingmin Meng
Keyword(s):  
Control Algorithm ◽  
Feedback Gain ◽  
Offshore Platforms ◽  
Control Force ◽  
Wave Loading ◽  
Offshore Structure ◽  
H2 Control ◽  
Input Control ◽  
The Mathematical Model ◽  
H2 Optimization

In order to control the excessive vibration of offshore platforms under wave excitations, an H2 control algorithm was presented in this paper. In the present study, noise terms for generating filtered wave loading and accounting for model uncertainty are separated. In addition, in H2 optimization problem, AMD’s capacities are considered by setting the limits of AMD stroke and maximum input control force. And the formulations of such algorithm are described. In order to investigate the feasibility and effectiveness of the proposed method, a numerical example applied to an offshore platform is presented in this paper. The numerical results demonstrate that the proposed algorithm is effective in reducing the vibration of offshore structure when there are some uncertainties in building the mathematical model of the structure. In addition, AMD designed by the proposed method can keep its operation by choosing appropriate feedback gain among several gain candidates based on the AMD limits.

scholarly journals Nonlinear response characteristics of neural networks and single neurons undergoing optogenetic excitation

2020 ◽  
Vol 4 (3) ◽  
pp. 852-870
Author(s):  
Jannik Luboeinski ◽  
Tatjana Tchumatchenko
Keyword(s):  
Neural Networks ◽  
Nonlinear Response ◽  
Pulse Frequency ◽  
Simulation Code ◽  
Response Characteristics ◽  
Optogenetic Stimulation ◽  
Spatial Response ◽  
Temporal And Spatial ◽  
Light Beams ◽  
Indirect Stimulation

Optogenetic stimulation has become the method of choice for investigating neural computation in populations of neurons. Optogenetic experiments often aim to elicit a network response by stimulating specific groups of neurons. However, this is complicated by the fact that optogenetic stimulation is nonlinear, more light does not always equal to more spikes, and neurons that are not directly but indirectly stimulated could have a major impact on how networks respond to optogenetic stimulation. To clarify how optogenetic excitation of some neurons alters the network dynamics, we studied the temporal and spatial response of individual neurons and recurrent neural networks. In individual neurons, we find that neurons show a monotonic, saturating rate response to increasing light intensity and a nonmonotonic rate response to increasing pulse frequency. At the network level, we find that Gaussian light beams elicit spatial firing rate responses that are substantially broader than the stimulus profile. In summary, our analysis and our network simulation code allow us to predict the outcome of an optogenetic experiment and to assess whether the observed effects can be attributed to direct or indirect stimulation of neurons.

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