Effects of Empirical Orthogonal Functions in Simplification of Structural Response of a Deep-Water Offshore System Under Current Profile Loading

2020 ◽  
Author(s):  
Michael Binsar Lubis ◽  
Mehrdad Kimiaei ◽  
Hongwei An ◽  
Reza Azarhoush
Keyword(s):  
Deep Water ◽  
Structural Response ◽  
Time History ◽  
Empirical Orthogonal Functions ◽  
Response Analysis ◽  
Good Representation ◽  
Current Profile ◽  
Orthogonal Functions ◽  
Recent Developments ◽  
Guidelines And Standards

Abstract Typical recommended current profiles for marine operations can be found in offshore engineering guidelines and standards. However, for some offshore components (e.g. risers, umbilicals, risers) typical simplified current profiles can easily lead to unrealistic and conservative results. Due to recent developments in current measuring technology, current speed for deep water location can be easily acquired. However, the current speeds are usually recorded for long periods and in many measurement points along the water column. Hence, finding the extreme current profile based on the recorded time-history data is not an easy task since it needs excessive computational efforts. To determine the overall response of an offshore system, various methods have been developed to minimize the required computational efforts in working with big number of irregular current profiles. Mode-based analysis using empirical orthogonal functions is one of these methods. Total number of the utilized modes plays an important role in the numerical complexity of the problem as well as the accuracy of the results. In this study, for a given deep water location, the effects of the reduced number of modes are investigated through response analysis of a simple vertical fixed slender structure under thousands of current profiles. It is found that the reduced-mode profile can produce a good representation of the measured current profile, however it tends to underestimate the structural response.

scholarly journals Data-Driven Interpolation of Sea Level Anomalies Using Analog Data Assimilation

2019 ◽  
Vol 11 (7) ◽  
pp. 858 ◽  
Author(s):  
Redouane Lguensat ◽  
Phi Huynh Viet ◽  
Miao Sun ◽  
Ge Chen ◽  
Tian Fenglin ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Sea Level ◽  
Large Scale ◽  
Empirical Orthogonal Functions ◽  
Data Driven ◽  
Optimal Interpolation ◽  
Observation System ◽  
Orthogonal Functions ◽  
Sea Level Anomalies ◽  
Recent Developments

From the recent developments of data-driven methods as a means to better exploit large-scale observation, simulation and reanalysis datasets for solving inverse problems, this study addresses the improvement of the reconstruction of higher-resolution Sea Level Anomaly (SLA) fields using analog strategies. This reconstruction is stated as an analog data assimilation issue, where the analog models rely on patch-based and Empirical Orthogonal Functions (EOF)-based representations to circumvent the curse of dimensionality. We implement an Observation System Simulation Experiment (OSSE) in the South China Sea. The reported results show the relevance of the proposed framework with a significant gain in terms of Root Mean Square Error (RMSE) for scales below 100 km. We further discuss the usefulness of the proposed analog model as a means to exploit high-resolution model simulations for the processing and analysis of current and future satellite-derived altimetric data with regard to conventional interpolation schemes, especially optimal interpolation.

Wind-Induced Response Analysis of Steel Tower Structure

2012 ◽  
Vol 238 ◽  
pp. 585-588 ◽  
Author(s):  
Chun Feng Wan ◽  
Jiang Wang ◽  
Hong Zhu ◽  
Lei Huang ◽  
Hao Wang ◽  
...  
Keyword(s):  
Wind Speed ◽  
Structural Response ◽  
Time History ◽  
Induced Response ◽  
Response Analysis ◽  
Vibration Modes ◽  
Local Vibration ◽  
Section Area ◽  
History Analysis ◽  
Tower Structure

In this paper, autoregressive (AR) method is firstly introduced to simulate wind speed time series. The agreement of the simulated wind speed spectrum to the target spectrum is verified. A 42m-high steel tower subjected to wind load is analyzed using ANSYS. Through modal analysis, it can be found that the first several modes of the structure are all translational vibration modes. Torsional vibration modes and local vibration modes appear from the 3th order mode. Meanwhile, time history analysis is applied to analyze the structural response. Results show that, under wind loads, the steel tower has large stresses in the chords which have abrupt section area change.

The Use of Empirical Orthogonal Functions for Deriving Response Based Extreme Current Profiles

2012 ◽  
Author(s):  
Gus Jeans ◽  
Liam Harrington-Missin ◽  
Andrew Watson ◽  
Jon Upton
Keyword(s):  
Surface Current ◽  
Empirical Orthogonal Functions ◽  
Current Profile ◽  
Orthogonal Functions ◽  
Data Set ◽  
Near Surface ◽  
Orthogonal Function ◽  
Large Current ◽  
Traditional Assumption

Coherent extreme current profiles are derived to reduce the over-conservatism associated with the traditional assumption that extreme currents occur at all depths through the water column simultaneously. Empirical Orthogonal Function (EOF) analysis has proven effective for derivation of coherent extreme current profiles in regions where it effectively captures the dominant characteristics of the flow regime. This is despite the questionable suitability of EOF for Current Profile Characterisation, which reduces a large current profile data set into a much smaller set of profiles for riser fatigue studies. EOF Mode 1 and 2 are used to represent six years of in-situ current profiles accounting for 97.75% of the original variance. With the assumption that depth integrated speed squared is proportional to drag on a simple riser, three sets of extreme current profiles were derived. A) Profiles associated with extreme near surface current speeds, B) Profiles associated with extreme mid-depth current speeds and C) Profiles associated with extreme drag on a riser.

Turkstra Models of Current Profiles

2009 ◽  
Author(s):  
Steven R. Winterstein ◽  
Sverre Haver ◽  
Einar Nygaard
Keyword(s):  
Deep Water ◽  
Time Domain ◽  
Current Speed ◽  
Empirical Orthogonal Functions ◽  
Orthogonal Functions ◽  
Direct Function ◽  
Extreme Loads ◽  
Spatial Correlation Structure ◽  
Domain Prediction ◽  
Basis Vectors

Design of deep-water structures requires accurate models of currents versus water depth. Common models are N-year profiles, which conservatively assume the N-year extreme current speed occurs simultaneously at each depth. To address this conservatism, we introduce Turkstra models of current profiles here. These yield a set of current profiles, each of which coincides with the N-year profile at a single depth and is reduced elsewhere. The degree of reduction is a direct function of the spatial correlation structure of the current process. Results are shown for a deep-water North Sea site, and compared with time-domain prediction of extreme loads for linear and drag load mechanisms. Extensions are suggested to combine these methods with procedures such as Empirical Orthogonal Functions, permitting the data to define the most economical set of basis vectors upon which the Turkstra logic is applied.

Structural Response Analysis of Beijing Yin-Tai Center Building under Varying Ground Motions

2011 ◽  
Vol 138-139 ◽  
pp. 217-222
Author(s):  
Fei Wang ◽  
Jie Mei Ma ◽  
Chun Lian Li ◽  
Yun Hui Chen
Keyword(s):  
Seismic Response ◽  
Structural Response ◽  
Time History ◽  
Plastic State ◽  
Response Analysis ◽  
Acceleration Response ◽  
Tangshan Earthquake ◽  
Response Characteristics ◽  
Time Histories ◽  
Contrast Analysis

Deeply studying vibration and seismic response characteristics of Beijing Yin-tai Center provided information reflecting its anti-seismic performance based on which seismic response observation array was to be deployed. Time-historic analytical methods on the basis of modal analysis were applied to carry out structural seismic response. Two load cases were mentioned including the responses under minor earthquakes and moderate earthquakes. El-Centro wave, Northridge wave and synthetized time-histories were adopted with contrast analysis under Beijing Hotel time-history recorded in Tangshan Earthquake. Peak inter-story shift ratios and peak accelerations are obtained and analyzed. The inter-story shift ratio determines elastic state of structure under minor earthquakes and elastic-plastic state under moderate earthquakes. Predominant inter-story displacement and acceleration response provides the floors with more remarkable seismic response, which are vulnerable floors for monitoring in earthquakes.

Empirical Methods in Short-Term Climate Prediction

2006 ◽  
Author(s):  
Huug van den Dool
Keyword(s):  
Climate Prediction ◽  
Empirical Orthogonal Functions ◽  
Data Sets ◽  
Seasonal Forecasts ◽  
Short Term ◽  
Orthogonal Functions ◽  
Ocean Atmosphere Interaction ◽  
Global Coverage ◽  
Atmosphere Interaction ◽  
Global Data

This clear and accessible text describes the methods underlying short-term climate prediction at time scales of 2 weeks to a year. Although a difficult range to forecast accurately, there have been several important advances in the last ten years, most notably in understanding ocean-atmosphere interaction (El Nino for example), the release of global coverage data sets, and in prediction methods themselves. With an emphasis on the empirical approach, the text covers in detail empirical wave propagation, teleconnections, empirical orthogonal functions, and constructed analogue. It also provides a detailed description of nearly all methods used operationally in long-lead seasonal forecasts, with new examples and illustrations. The challenges of making a real time forecast are discussed, including protocol, format, and perceptions about users. Based where possible on global data sets, illustrations are not limited to the Northern Hemisphere, but include several examples from the Southern Hemisphere.

scholarly journals Spatio-Temporal Patterns of Mass Changes in Himalayan Glaciated Region from EOF Analyses of GRACE Data

2021 ◽  
Vol 13 (2) ◽  
pp. 265
Author(s):  
Harika Munagapati ◽  
Virendra M. Tiwari
Keyword(s):  
Temperature Anomaly ◽  
Mass Gain ◽  
Snow Accumulation ◽  
Empirical Orthogonal Functions ◽  
Total Water ◽  
Orthogonal Functions ◽  
Grace Data ◽  
Grace Satellite ◽  
Spatio Temporal ◽  
Gravity Recovery

The nature of hydrological seasonality over the Himalayan Glaciated Region (HGR) is complex due to varied precipitation patterns. The present study attempts to exemplify the spatio-temporal variation of hydrological mass over the HGR using time-variable gravity from the Gravity Recovery and Climate Experiment (GRACE) satellite for the period of 2002–2016 on seasonal and interannual timescales. The mass signal derived from GRACE data is decomposed using empirical orthogonal functions (EOFs), allowing us to identify the three broad divisions of HGR, i.e., western, central, and eastern, based on the seasonal mass gain or loss that corresponds to prevailing climatic changes. Further, causative relationships between climatic variables and the EOF decomposed signals are explored using the Granger causality algorithm. It appears that a causal relationship exists between total precipitation and total water storage from GRACE. EOF modes also indicate certain regional anomalies such as the Karakoram mass gain, which represents ongoing snow accumulation. Our causality result suggests that the excessive snowfall in 2005–2008 has initiated this mass gain. However, as our results indicate, despite the dampening of snowfall rates after 2008, mass has been steadily increasing in the Karakorum, which is attributed to the flattening of the temperature anomaly curve and subsequent lower melting after 2008.

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