scholarly journals Discussion: “Time Series Simulations of Wide-Band Spectra for Fatigue Tests of Offshore Structures” (Lin, N. K., and Hartt, W. H., 1984, ASME J. Energy Resour. Technol., 106, pp. 466–470)

1984 ◽  
Vol 106 (4) ◽  
pp. 471-471
Author(s):  
P. D. Spanos
Keyword(s):  
Time Series ◽  
Wide Band ◽  
Offshore Structures ◽  
Fatigue Tests ◽  
Band Spectra

Time Series Simulations of Wide-Band Spectra for Fatigue Tests of Offshore Structures

1984 ◽  
Vol 106 (4) ◽  
pp. 466-470 ◽  
Author(s):  
N. K. Lin ◽  
W. H. Hartt
Keyword(s):  
Time Series ◽  
Fatigue Testing ◽  
Wide Band ◽  
Simulation Method ◽  
Offshore Structures ◽  
Fatigue Tests ◽  
Time Series Model ◽  
Long Time ◽  
Band Spectra ◽  
Time Series Simulation

A time-series simulation method, based on the principle of time series modeling for dynamic systems, is used to reproduce a wide-band stress history from a prescribed stress spectral model for fatigue testing of offshore structures. The optimization procedures and stability of the time series model for the prescribed spectrum are presented and discussed. The optimization procedures are developed on the basis of the Levison-Durbin algorithm, which usually produces a stable time series model if the order of the time series model is even. An example is presented to demonstrate the applicability of the proposed method to long-time, high-cycle fatigue testing.

Time series

1950 ◽  
Vol 10 (01) ◽  
pp. 13-23
Author(s):  
N. L. Johnson
Keyword(s):  
Blood Pressure ◽  
Time Series ◽  
Time Series Analysis ◽  
Fatigue Tests ◽  
Annual Production ◽  
Index Numbers ◽  
Standard Task ◽  
Technical Details ◽  
The Subject ◽  
Routine Inspection

The object of this note is to provide an introduction to methods used in time-series analysis, together with a general appraisal of their usefulness. The treatment is purely expository and, of necessity, rather condensed. Nothing more than a broad survey of the subject is attempted; those interested in the technical details of theory and application should consult the references given at the end.The termtime seriesis applied to any series of observed values of some character when theorderof the items in the series, as well as their actual magnitudes, is of importance. Examples of such series are common in statistical practice, and the following may be cited in illustration: economic series such as weekly, monthly or annual production figures, prices or index numbers; series of results of routine inspection and testing of successive batches of manufactured product; continuous blood-pressure records; results of psychological fatigue tests expressed as the rate of working on some standard task in successive 5 sec. intervals. In all these examples the factor which determines the order of the observations istime. The study of ordered series of observations is entitled ‘Time Series’ because in a large proportion of applications time is the ordering factor. Nevertheless, it is not necessary that the series be ordered according to time.

Mechanic, Metalurgic and Factografic Characterization of a Composite of Microalloyed Steel (API X65) Cladded With Austenitic Stainless Steel (AISI 308L)

2006 ◽  
Author(s):  
Carlos R. da Cunha ◽  
Telmo R. Strohaecker
Keyword(s):  
Stainless Steel ◽  
Hardness Test ◽  
Offshore Structures ◽  
Fatigue Tests ◽  
Mechanical Resistance ◽  
Bending Tests ◽  
Internal Surfaces ◽  
Steel Aisi

In some offshore structures, pipes with good mechanical resistance and internal surfaces that have also good corrosion resistance are necessary. To associate these properties, one possibility is to make a cladding process in the pipe. To evaluate this kind of composite, a pipe (API X65) was clad with stainless steel (ASTM 308L) by GMAW process and sectioned in several specimens for different analyses. The work starts qualifying the quality of the composite with bending tests. The load that was recorded in this test was the guide to three-point-fatigue tests that gave us the possibility to plot an S-N curve. The tension was the most tensioned point in the specimen. To verify the metallographic conditions of both materials and the interface, metallographic analyses with a transversal cut in the specimens and hardness test across the composite were accomplished. The fatigue tested specimens were submitted to fracture analyses to know how the failure occurs. These analyses contain photos of the specimen’s fracture - showing the origin of the failure, a metallographic of the specimen’s interface to check undesired microstructures that could cause a failure and micrographs of the most tensioned point of the specimen to check the initial failure mechanism. The results in the following work show a good way of cladding process.

Climatic Forecasting of Wind and Waves Using Fuzzy Inference Systems

2017 ◽  
Author(s):  
Christos N. Stefanakos ◽  
Erik Vanem
Keyword(s):  
Time Series ◽  
Fuzzy Inference ◽  
North Atlantic Ocean ◽  
Offshore Structures ◽  
Mean Value ◽  
Initial Time ◽  
The North ◽  
Residual Part ◽  
Time Series Modelling ◽  
Inference Systems

Wind and wave climatic simulations are of great interest in a number of different applications, including the design and operation of ships and offshore structures, marine energy generation, aquaculture and coastal installations. In a climate change perspective, projections of such simulations to a future climate are of great importance for risk management and adaptation purposes. This work investigates the applicability of FIS/ANFIS models for climatic simulations of wind and wave data. The models are coupled with a nonstationary time series modelling, which decomposes the initial time series into a seasonal mean value and a residual part multiplied by a seasonal standard deviation. In this way, the nonstationary character is first removed before starting the fuzzy forecasting procedure. Then, the FIS/ANFIS models are applied to the stationary residual part providing us with more unbiased climatic estimates. Two long-term datasets for an area in the North Atlantic Ocean are used in the present study, namely NORA10 (57 years) and ExWaCli (30 years in the present and 30 years in the future). Two distinct experiments have been performed to simulate future values of the time series in a climatic scale. The assessment of the simulations by means of the actual values kept for comparison purposes gives very good results.

Are the electroencephalograms mainly rhythmic? Assessment of periodicity in wide-band time series

Neuroscience ◽  
2003 ◽  
Vol 121 (1) ◽  
pp. 233-252 ◽  
Author(s):  
T.H Bullock ◽  
M.C Mcclune ◽  
J.T Enright
Keyword(s):  
Time Series ◽  
Wide Band

scholarly journals Neural Networks Applied to the Wave-Induced Fatigue Analysis of Steel Risers

2018 ◽  
Vol 2018 ◽  
pp. 1-16 ◽  
Author(s):  
João P. R. Cortina ◽  
Fernando J. M. de Sousa ◽  
Luis V. S. Sagrilo
Keyword(s):  
Neural Networks ◽  
Time Series ◽  
Cross Sections ◽  
Computational Cost ◽  
Offshore Structures ◽  
Fatigue Analysis ◽  
Element Analysis ◽  
Long Time ◽  
Wave Induced ◽  
Hybrid Methodology

Time domain stochastic wave dynamic analyses of offshore structures are computationally expensive. Considering the wave-induced fatigue assessment for such structures, the combination of many environmental loading cases and the need of long time-series responses make the computational cost even more critical. In order to reduce the computational burden related to the wave-induced fatigue analysis of Steel Catenary Risers (SCRs), this work presents the application of a recently developed hybrid methodology that combines dynamic Finite Element Analysis (FEA) and Artificial Neural Networks (ANN). The methodology is named hybrid once it requires short time series of structure responses (obtained by FEA) and imposed motions (evaluated analytically) to train an ANN. Subsequently, the ANN is employed to predict the remaining response time series using the prescribed motions imposed at the top of the structure by the floater unit. In this particular work, the methodology is applied aiming to predict the tension and bending moments’ time series at structural elements located at the top region and at the touchdown zone (TDZ) of a metallic riser. With the predicted responses (tensions and moments), the stress time series are determined for eight points along the pipe cross sections, and stress cycles are identified using a Rainflow algorithm. Fatigue damage is then evaluated using SN curves and the Miner-Palmgren damage accumulation rule. The methodology is applied to a SCR connected to a semisubmersible platform in a water depth of 910 m. The obtained results are compared to those from a full FEA in order to evaluate the accuracy and computer efficiency of the hybrid methodology.

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