Wave Exciting Forces of a Free Floating Semi Submersible in Regular Waves

2015 ◽  
Vol 74 (5) ◽  
Author(s):  
Hassan Abyn ◽  
Mohammad Rafiqul Islam ◽  
Jaswar Jaswar ◽  
Amin Mahmoudi ◽  
C. L. Siow ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Domain Analysis ◽  
Offshore Structures ◽  
Source Distribution ◽  
Linear Wave ◽  
Distribution Method ◽  
Exciting Forces ◽  
Domain Models ◽  
Wave Exciting Forces

Drilling and production of oil by semi submersible take place in many locations throughout the world. Generally, floating structures play an important role in exploring the oil and gas from the sea. The force and motion prediction of offshore structures may be carried out using time domain or frequency domain models or model tests. In this paper the frequency domain analysis used because it is the simplified and linearized form of the equations of motion. The time domain analysis, unlike frequency domain models, is adequate to deal with non-linearities such as viscous damping and mooring forces, but it requires sophisticated solution techniques and it is expensive to employ. In this paper, the wave exciting forces of a free floating semi-submersible were carried out using 3D source distribution method within the scope of the linear wave theory. The results obtained from computations were also compared with the results obtained using commercial software MOSES and WAMIT.  

Advances in Frequency and Time Domain Coupled Analysis for Floating Production and Offloading Systems

2005 ◽  
Author(s):  
Donogh W. Lang ◽  
Aengus Connolly ◽  
Michael Lane ◽  
Adrian D. Connaire
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Domain Analysis ◽  
Offshore Structures ◽  
Viscous Drag ◽  
Coupled Analysis ◽  
Diffraction Radiation ◽  
Analysis Tool ◽  
Floating Structure ◽  
The Individual

With the move to the development of remote, deepwater fields, increasing use is being made of floating production, storage and offloading (FPSO) facilities from which oil is intermittently offloaded to a shuttle tanker via offloading lines and an anchor leg mooring buoy. The response of the individual components of these systems is significantly influenced by hydrodynamic and mechanical coupling between adjacent components, precluding the use of traditional analysis techniques such as displacement RAOs derived from tank model tests or diffraction/radiation analyses of the independent components. Consequently, the reliable and accurate design of these complex systems requires an analysis tool capable of determining the fully coupled response of each of the individual components of the system. A recently-developed time domain coupled analysis tool has been extended to incorporate a frequency domain coupled analysis capability. This tool combines radiation/diffraction theory with a non-linear finite element (FE) structural analysis technique used for the analysis of slender offshore structures. This paper describes the application of frequency domain analysis to the coupled FE/floating structure problem, with particular consideration given to the linearisation of viscous drag loads on floating structures and the treatment of low-frequency second-order loads in the frequency domain. Results from frequency domain and time domain coupled analyses of a typical West of Africa type offloading system are compared, highlighting areas of application where frequency domain coupled analysis can offer significant benefits when used in conjunction with time domain analysis. Based on this, recommendations are made for the appropriate use of frequency and time domain coupled analysis for this type of system.

scholarly journals Analysis of Three-Phase Wye-Delta Connected LLC

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3606
Author(s):  
Jing-Yuan Lin ◽  
Chuan-Ting Chen ◽  
Kuan-Hung Chen ◽  
Yi-Feng Lin
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Operation Time ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Complete Analysis ◽  
Plane Analysis ◽  
Analysis Methods ◽  
Three Phase

Three-phase wye–delta LLC topology is suitable for voltage step down and high output current, and has been used in the industry for some time, e.g., for server power and EV charger. However, no comprehensive circuit analysis has been performed for three-phase wye–delta LLC. This paper provides complete analysis methods for three-phase wye–delta LLC. The analysis methods include circuit operation, time domain analysis, frequency domain analysis, and state–plane analysis. Circuit operation helps determine the circuit composition and operation sequence. Time domain analysis helps understand the detail operation, equivalent circuit model, and circuit equation. Frequency domain analysis helps obtain the curve of the transfer function and assists in circuit design. State–plane analysis is used for optimal trajectory control (OTC). These analyses not only can calculate the voltage/current stress, but can also help design three-phase wye-delta connected LLC and provide the OTC control reference. In addition, this paper uses PSIM simulation to verify the correctness of analysis. At the end, a 5-kW three-phase wye–delta LLC prototype is realized. The specification of the prototype is a DC input voltage of 380 V and output voltage/current of 48 V/105 A. The peak efficiency is 96.57%.

Drilling Riser VIV Analysis Using Time Domain Code SimVIV

2013 ◽  
Author(s):  
Djoni E. Sidarta
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Ocean Currents

Drilling risers are often subjected to VIV from ocean currents, which may vary in directions over depth. VIV of drilling riser has commonly been analyzed using frequency domain code. This paper presents an alternative tool of analyzing VIV of drilling riser using time domain code SimVIV. With this tool it is possible to apply currents in varying directions over depth. Measured currents and VIV responses of a drilling riser available in the literature are used in this study. The results of time domain analysis using SimVIV are compared against measured responses. The effect of current directionality over depth on drilling riser VIV response is also analyzed.

scholarly journals Optimal implementation of frequency domain impedances in time domain simulations of building structures on embedded foundations

2020 ◽  
Author(s):  
Danilo S. Kusanovic ◽  
Elnaz E. Seylabi ◽  
Domniki Asimaki
Keyword(s):  
Finite Element ◽  
Frequency Domain ◽  
Time Domain ◽  
Response Spectrum ◽  
Free Field ◽  
Domain Analysis ◽  
Shallow Foundation ◽  
Rigid Base ◽  
Dimensionless Frequency ◽  
Building Structures

Soil-Structure Interaction (SSI) have been studied the last decades, and proper analysis for the linear elastic case in frequency domain has been established successfully. However, SSI is rarely considered in the seismic design of building structures. Regardless of its importance as a significant source of flexibility and energy dissipation, buildings are analyzed using a rigid base assumption, and the design is based on a response spectrum analysis, for which not only the soil, but also time are totally ignored. In a first attempt to improve and to incentivize time domain analyzes compatible with standard finite element packages for the engineering community, the state-of-practice introduces two major simplifications to transform the frequency domain analysis into a time domain analysis: (a) it assumes the frequency at which the impedance value should be read is the flexible-base frequency, and (b) it also assumes that the foundation input motion preserves the phase of the free field motion. Upon these simplifications, the following questions may arise: How does NIST recommendations perform in overall against a full finite element model? Are the embedment effects for shallow foundation not important so that the phase angle can be neglected? What is the best dimensionless frequency to estimate the soil impedance? Is it possible to make a better estimation of the dimensionless frequency to increase the NIST accuracy? In this study, we attempt to address these questions by using an inverse problem formulation.

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