Response Spectrum Estimation for Fixed Offshore Structures With Inundation Effect Included: A Price’s Theorem Approach

2004 ◽  
Vol 126 (4) ◽  
pp. 337-345 ◽  
Author(s):  
Xiang Yuan Zheng ◽  
Chih Young Liaw
Keyword(s):  
Fourier Transforms ◽  
Volterra Series ◽  
Response Spectrum ◽  
Power Spectra ◽  
Memory Systems ◽  
Offshore Structures ◽  
Spectrum Estimation ◽  
Nonlinear Frequency ◽  
Finite Memory ◽  
Jack Up

Instead of a Volterra-series based method, a method based on Price’s theorem and Fourier Transforms is proposed for evaluating the nonlinear response power spectra of fixed offshore structures modeled as finite-memory systems. The numerical computation effort required for spectral estimations using the proposed method is significantly less than that of the Volterra-series method that requires multi-dimensional integrations. Nonlinear frequency-domain analyses of two jack-up platform structures are carried out to study the effects of inundation, cubic and quartic drag terms and polynomialization methods.

scholarly journals DAYENU: a simple filter of smooth foregrounds for intensity mapping power spectra

2020 ◽  
Vol 500 (4) ◽  
pp. 5195-5213
Author(s):  
Aaron Ewall-Wice ◽  
Nicholas Kern ◽  
Joshua S Dillon ◽  
Adrian Liu ◽  
Aaron Parsons ◽  
...  
Keyword(s):  
Large Scale ◽  
Dynamic Range ◽  
Fourier Transforms ◽  
Power Spectra ◽  
High Dynamic Range ◽  
Spectrum Estimation ◽  
Sampled Data ◽  
Optimal Basis ◽  
Intensity Mapping ◽  
Band Limited

ABSTRACT We introduce DPSS Approximate lazY filtEriNg of foregroUnds (dayenu), a linear, spectral filter for H i intensity mapping that achieves the desirable foreground mitigation and error minimization properties of inverse co-variance weighting with minimal modelling of the underlying data. Beyond 21-cm power-spectrum estimation, our filter is suitable for any analysis where high dynamic-range removal of spectrally smooth foregrounds in irregularly (or regularly) sampled data is required, something required by many other intensity mapping techniques. Our filtering matrix is diagonalized by Discrete Prolate Spheroidal Sequences which are an optimal basis to model band-limited foregrounds in 21-cm intensity mapping experiments in the sense that they maximally concentrate power within a finite region of Fourier space. We show that dayenu enables the access of large-scale line-of-sight modes that are inaccessible to tapered discrete Fourier transform estimators. Since these modes have the largest SNRs,dayenu significantly increases the sensitivity of 21-cm analyses over tapered Fourier transforms. Slight modifications allow us to use dayenu as a linear replacement for iterative delay clean ing (dayenurest). We refer readers to the Code section at the end of this paper for links to examples and code.

scholarly journals Simulation of response spectrum-compatible ground motions using wavelet-based multi-resolution analysis

2021 ◽  
pp. 002029402110130
Author(s):  
Guan Chen ◽  
Zhiren Zhu ◽  
Jun Hu
Keyword(s):  
Ground Motion ◽  
Response Spectrum ◽  
Ground Motions ◽  
Power Spectra ◽  
Simulation Method ◽  
Eurocode 8 ◽  
Effective Response ◽  
Multi Resolution Analysis ◽  
Resolution Analysis ◽  
Simulated Ground Motions

This study proposed a simple and effective response spectrum-compatible ground motions simulation method to mitigate the scarcity of ground motions on seismic hazard analysis base on wavelet-based multi-resolution analysis. The feasibility of the proposed method is illustrated with two recorded ground motions in El Mayor-Cucapah earthquake. The results show that the proposed method enriches the ground motions exponentially. The simulated ground motions agree well with the attenuation characteristics of seismic ground motion without modulating process. Moreover, the pseudo-acceleration response spectrum error between the recorded ground motion and the average of the simulated ground motions is 5.2%, which fulfills the requirement prescribed in Eurocode 8 for artificially simulated ground motions. Besides, the cumulative power spectra between the simulated and recorded ground motions agree well on both high- and low-frequency regions. Therefore, the proposed method offers a feasible alternative in enriching response spectrum-compatible ground motions, especially on the regions with insufficient ground motions.

Numerical Study of the Combined Loading Envelope of a Skirted Spudcan Foundation

2014 ◽  
Author(s):  
Ning Cheng ◽  
Mark J. Cassidy ◽  
Yinghui Tian
Keyword(s):  
Clay Soil ◽  
Numerical Study ◽  
Failure Mechanisms ◽  
Small Strain ◽  
Offshore Structures ◽  
Combined Loading ◽  
Finite Element Analyses ◽  
Failure Envelope ◽  
Foundation Type ◽  
Jack Up

Foundations for offshore structures, such as mobile jack-up units, are subjected to large horizontal (H) and moment (M) loads in addition to changing vertical (V) loads. The use of a combined vertical, horizontal and moment (V-H-M) loading envelope to define foundation capacities has become increasingly applied in recent years. However, there is no study on the skirted spudcan, a new alternative foundation type to the conventional spudcan footing for jack-ups. In this study, the combined V-H-M yield envelope of a skirted spudcan foundation in clay soil is investigated with small strain finite element analyses using 3D modeling. The footing’s uniaxial bearing capacities and failure mechanisms are described. The failure envelope for the combined V-H-M loadings is presented. A comparison of the bearing capacities between the spudcan and skirted spudcan of various dimensions is also presented.

scholarly journals New Investigations for Offshore and Onshore structures

2019 ◽  
Vol 1 (1) ◽  
Author(s):  
Levent Yilmaz
Keyword(s):  
State Of The Art ◽  
Offshore Structures ◽  
History Of ◽  
Jack Up

In this research the investigated parameters are given as below: History of offshore and onshore construction…Onshore structures…StorageTanks Breakwaters……Estacada…Offshore structures…Stationary fixed platforms (steel, concrete, combined, arctic)…Floating (Jack-up, semi-submersibles, TLP,…)…Pipe lineThis issues are given as State-of-the-art and written new examined innovative researches.

scholarly journals Making maps of cosmic microwave background polarization for B-mode studies: the POLARBEAR example

2017 ◽  
Vol 600 ◽  
pp. A60 ◽  
Author(s):  
Davide Poletti ◽  
Giulio Fabbian ◽  
Maude Le Jeune ◽  
Julien Peloton ◽  
Kam Arnold ◽  
...  
Keyword(s):  
Cosmic Microwave Background ◽  
Time Domain ◽  
Power Spectra ◽  
Low Frequency ◽  
Frequency Noise ◽  
Spectrum Estimation ◽  
Microwave Background ◽  
Polarization Studies ◽  
Ordered Data ◽  
The Impact

Analysis of cosmic microwave background (CMB) datasets typically requires some filtering of the raw time-ordered data. For instance, in the context of ground-based observations, filtering is frequently used to minimize the impact of low frequency noise, atmospheric contributions and/or scan synchronous signals on the resulting maps. In this work we have explicitly constructed a general filtering operator, which can unambiguously remove any set of unwanted modes in the data, and then amend the map-making procedure in order to incorporate and correct for it. We show that such an approach is mathematically equivalent to the solution of a problem in which the sky signal and unwanted modes are estimated simultaneously and the latter are marginalized over. We investigated the conditions under which this amended map-making procedure can render an unbiased estimate of the sky signal in realistic circumstances. We then discuss the potential implications of these observations on the choice of map-making and power spectrum estimation approaches in the context of B-mode polarization studies. Specifically, we have studied the effects of time-domain filtering on the noise correlation structure in the map domain, as well as impact it may haveon the performance of the popular pseudo-spectrum estimators. We conclude that although maps produced by the proposed estimators arguably provide the most faithful representation of the sky possible given the data, they may not straightforwardly lead to the best constraints on the power spectra of the underlying sky signal and special care may need to be taken to ensure this is the case. By contrast, simplified map-makers which do not explicitly correct for time-domain filtering, but leave it to subsequent steps in the data analysis, may perform equally well and be easier and faster to implement. We focused on polarization-sensitive measurements targeting the B-mode component of the CMB signal and apply the proposed methods to realistic simulations based on characteristics of an actual CMB polarization experiment, POLARBEAR. Our analysis and conclusions are however more generally applicable.

Volterra Models

1999 ◽  
Author(s):  
Ronald K. Pearson
Keyword(s):  
Volterra Series ◽  
Finite Impulse Response ◽  
Moving Average ◽  
Memory Systems ◽  
Volterra Models ◽  
Bilinear Models ◽  
Moving Average Models ◽  
Series Representations ◽  
Moving Average Model ◽  
Wiener Models

One of the main points of Chapter 4 is that nonlinear moving-average (NMAX) models are both inherently better-behaved and easier to analyze than more general NARMAX models. For example, it was shown in Sec. 4.2.2 that if ɡ(· · ·) is a continuous map from Rq+1 to R1 and if ys = ɡ (us,..., us), then uk → us implies yk → ys. Although it is not always satisfied, continuity is a relatively weak condition to impose on the map ɡ(· · ·) . For example, Hammerstein or Wiener models based on moving average models and the hard saturation nonlinearity represent discontinuous members of the class of NMAX models. This chapter considers the analytical consequences of requiring ɡ(·) to be analytic, implying the existence of a Taylor series expansion. Although this requirement is much stronger than continuity, it often holds, and when it does, it leads to an explicit representation: Volterra models. The principal objective of this chapter is to define the class of Volterra models and discuss various important special cases and qualitative results. Most of this discussion is concerned with the class V(N,M) of finite Volterra models, which includes the class of linear finite impulse response models as a special case, along with a number of practically important nonlinear moving average model classes. In particular, the finite Volterra model class includes Hammerstein models, Wiener models, and Uryson models, along with other more general model structures. In addition, one of the results established in this chapter is that most of the bilinear models discussed in Chapter 3 may be expressed as infinite-order Volterra models. This result is somewhat analogous to the equivalence between finite-dimensional linear autoregressive models and infinite-dimensional linear moving average models discussed in Chapter 2. The bilinear model result presented here is strictly weaker, however, since there exist classes of bilinear models that do not possess Volterra series representations. Specifically, it is shown in Sec. 5.6 that completely bilinear models do not exhibit Volterra series representations. Conversely, one of the results discussed at the end of this chapter is that the class of discrete-time fading memory systems may be approximated arbitrarily well by finite Volterra models (Boyd and Chua, 1985).

Accurate Numerical Methods for Calculating the Response Statistics of Compliant Offshore Structures

2005 ◽  
Author(s):  
A. Naess ◽  
H. C. Karlsen ◽  
P. S. Teigen
Keyword(s):  
Numerical Methods ◽  
Volterra Series ◽  
State Of The Art ◽  
Offshore Structures ◽  
Second Order ◽  
Stochastic Response ◽  
Random Seas ◽  
The Mean ◽  
Extreme Responses ◽  
Key Parameter

The state-of-the-art representation of the horizontal motions of e.g. a TLP in random seas is in terms of a second order stochastic Volterra series. Until recently, there has been no method available for accurately calculating the mean level upcrossing rate of such response processes. Since the mean upcrossing rate is a key parameter for estimating the large and extreme responses it is clearly of importance to develop methods for its calculation. The paper describes numerical methods for calculating the mean level upcrossing rate of a stochastic response process represented as a second order stochastic Volterra series. Since no approximations are made, the only source of inaccuracy is in the numerical calculation, which can be controlled.

System Identification of Jack-Up Platform by Spectral Analysis

2010 ◽  
Author(s):  
X. M. Wang ◽  
C. G. Koh ◽  
T. N. Thanh ◽  
J. Zhang
Keyword(s):  
Spectral Analysis ◽  
System Identification ◽  
Time Domain ◽  
Time History ◽  
Offshore Structures ◽  
Wave Load ◽  
History Of ◽  
Structural Responses ◽  
Jack Up ◽  
Numerical Strategy

For the purpose of structural health monitoring (SHM), it is beneficial to develop a robust and accurate numerical strategy so as to identify key parameters of offshore structures. In this regard, it is difficult to use time-domain methods as the time history of wave load is not available unless output-only methods can be developed. Alternatively, spectral analysis widely used in offshore engineering to predict structural responses due to random wave conditions can be used. Thus the power spectral density (PSD) of structural response may be more appropriate than time history of structural responses in defining the objective (fitness) function for system identification of offshore structures. By minimizing PSD differences between measurements and simulations, the proposed numerical strategy is completely carried out in frequency domain, which can avoid inherent problems rising from random phase angles and unknown initial conditions in time domain. A jack-up platform is studied in the numerical study. A search space reduction method (SSRM) incorporating the use of genetic algorithms (GA) as well as a substructure approach are adopted to improve the accuracy and efficiency of identification. As a result, the stiffness parameters of jack-up legs can be well identified even under fairly noisy conditions.

scholarly journals Analysis of Offshore Structures Based on Response Spectrum of Ice Force

2019 ◽  
Vol 7 (11) ◽  
pp. 417 ◽  
Author(s):  
Liu ◽  
Li ◽  
Zhang
Keyword(s):  
Sea Ice ◽  
Large Scale ◽  
Response Spectrum ◽  
Time History ◽  
Offshore Structures ◽  
Potential Threat ◽  
Influence Coefficients ◽  
Design Response Spectrum ◽  
Ice Force ◽  
Bending Failure

With the development of large-scale offshore projects, sea ice is a potential threat to the safety of offshore structures. The main forms of damage to bottom-fixed offshore structures under sea ice are crushing failure and bending failure. Referred to as the concept of seismic response spectrums, the design response spectrum of offshore structures induced by the crushing and bending ice failure is presented. Selecting the Bohai Sea in China as an example, the sea areas were divided into different ice zones due to the different sea ice parameters. Based on the crushing and bending failure power spectral densities of ice force, a large amount of ice force time-history samples are firstly generated for each ice zone. The time-history of the maximum responses of a series of single degree of freedom systems with different natural frequencies under the ice force are calculated and subsequently, a response spectrum curve is obtained. Finally, by fitting all the response spectrum curves from different samples, the design response spectrum is generated for each ice zone. The ice force influence coefficients for crushing and bending failure are obtained, which can be used to estimate the stochastic sea ice force acting on a structure conveniently in a static way. A comparison of the proposed response spectrum method with the Monte Carlo method by a numerical example shows good agreement.

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