Extreme Response Analysis of Floating Structures Using Coupled Frequency Domain Analysis

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Ying Min Low ◽  
Andrew J. Grime
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Low Frequency ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Coupled Analysis ◽  
Statistical Techniques ◽  
Frequency Domain Methods ◽  
Extreme Response ◽  
The Mean

In the dynamic analysis of a floating structure, coupled analysis refers to a procedure in which the vessel, moorings, and risers are modeled as a whole system, thus allowing for interactions between various system components. Because coupled analysis in the time domain is impractical owing to prohibitive computational costs, a highly efficient frequency domain approach was developed in a previous work, wherein the drag forces are linearized. The study showed that provided the geometric nonlinearity of the moorings/risers is insignificant, which often holds for ultradeepwater systems, the mean-squared responses yielded by the time and frequency domain methods are in close agreement. Practical design is concerned with the extreme response, for which the mean upcrossing rate is a key parameter. Crossing rate analysis based on statistical techniques is complicated as the total response occurs at two timescales, with the low frequency contribution being notably non-Gaussian. Many studies have been devoted to this problem, mainly relying on a technique originating from Kac and Siegert; however, these studies have mostly been confined to a single-degree-of-freedom system. The aim of this work is to apply statistical techniques in conjunction with frequency domain analysis to predict the extreme responses of the coupled system, in particular the modes with a prominent low frequency component. It is found that the crossing rates for surge, sway and yaw thus obtained agree well with those extracted from time domain simulation, whereas the result for roll is less favorable, and the reasons are discussed.

Extreme Response Analysis of Floating Structures Using Coupled Frequency Domain Analysis

2010 ◽  
Author(s):  
Ying Min Low ◽  
Andrew J. Grime
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Low Frequency ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Coupled Analysis ◽  
Statistical Techniques ◽  
Frequency Domain Methods ◽  
Extreme Response ◽  
The Mean

In the dynamic analysis of a floating structure, coupled analysis refers to a procedure in which the vessel, moorings and risers are modeled as a whole system, thus allowing for the interactions between the various system components. Because coupled analysis in the time domain is impractical owing to prohibitive computational costs, a highly efficient frequency domain approach was developed in a previous work, wherein the drag forces are linearized. The study showed that provided the geometric nonlinearity of the moorings/risers is insignificant, which often holds for ultra-deepwater systems, the mean-squared responses yielded by the time and frequency domain methods are in close agreement. Practical design is concerned with the extreme response, for which the mean upcrossing rate is a key parameter. Crossing rate analysis based on statistical techniques is complicated as the total response occurs at two timescales, with the low frequency contribution being notably non-Gaussian. Many studies have been devoted to this problem, mainly relying on a technique originating from Kac and Siegert; however, these studies have mostly been confined to a single-degree-of-freedom system. The aim of this work is to apply statistical techniques in conjunction with frequency domain analysis to predict the extreme responses of the coupled system, in particular the modes with a prominent low frequency component. It is found that the crossing rates for surge, sway and yaw thus obtained agree well with those extracted from time domain simulation, whereas the result for roll is less favorable, and the reasons are discussed.

Hydrodynamic Interactions and Relative Motions Analysis for Installation of an Extendable Draft Platform

2009 ◽  
Author(s):  
Bonjun Koo ◽  
Jang Whan Kim
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Hydrodynamic Interactions ◽  
Coupled Analysis ◽  
Heave Plate ◽  
The Time Domain ◽  
Stabilized Platform ◽  
Relative Motions

The Extendable Draft Platform (EDP) is a deep draft, column stabilized platform with a deck box support for topsides and a single, deep draft heave plate that provides suitable motion characteristics to enable the use of dry tree top tensioned risers. The EDP can be fabricated with topsides installed on the deck box and commissioned quayside in a typical construction yard. With the columns in the retracted position, the EDP floats on its deck box and can be towed, in this configuration, to the location of interest. Once the EDP is transported to its final site, the columns and heave plate are lowered to their final operating draft. During the lowering sequence, the deck box and the lower hull become two relatively independent bodies, mechanically connected by chains that control the lowering of the columns and heave plate, and the guides between the deck box and the columns. This multi-body system is hydrodynamically coupled because of radiated and diffracted waves. The global performance analyses of the installation process (lowering of the lower hull) are carried out by three different methods. The first method is frequency-domain analysis by WAMIT and a frequency domain motion solver. In the frequency domain analysis, all the mechanical connections are modeled as linear springs. The second method is time-domain, partially coupled analysis using HARP/WINPOST. In this analysis, the off diagonal 6×6 hydrodynamic interactions are ignored. The last method is a time domain, fully coupled analysis using HARP/WINPOST. In this analysis, full 12×12 hydrodynamic interactions are considered. In the time domain analyses, the mechanical couplings between each column and deck box are modeled with linear springs and the chain connections are modeled with slender rods by using the nonlinear finite element method. This paper presents and compares analysis results based on the three methods for relative motions and loads between the deck box and the lower hull during the lowering of the columns and heave plate.

Significant and Morbid Changes in Heart Rate Variability Precedes and Complicates Symptomatic Hypotension in Peripheral Blood Stem Cell Apheresis.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 4996-4996
Author(s):  
Hirohisa Nakamae ◽  
Yoshiki Terada ◽  
Mika Akahori ◽  
Takahiko Nakane ◽  
Kiyoyuki Hagihara ◽  
...  
Keyword(s):  
Stem Cell ◽  
Frequency Domain ◽  
Time Domain ◽  
Peripheral Blood Stem Cell ◽  
Low Frequency ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Hrv Analysis ◽  
Low Frequency Power ◽  
Frequency Power

Abstract Peripheral blood stem cell harvest (PBSCH) has been widely performed for rescue following high-dose chemotherapy or as an alternative to BMT for allogeneic stem cell transplantation. However, severe complications, which caused sudden death, were reported in PBSCH from healthy donors. Recent cumulative evidence shows that decrease in cardiovascular signal variability of the R-R period (heart rate variability, HRV) is strongly associated with sudden death and/or cardiac event after a myocardial infarction. Furthermore, usefulness of HRV as a clinical tool has been explored in numerous conditions such as hypertrophic cardiomyopathy, obstructive sleep apnea, diabetic neuropathy, and various neurological alterations. Two types, time domain and frequency domain, are included in HRV analysis. In this study, we investigated HRV during and after apheresis for PBSCH in 23 cases [8 autologous transplant patients, 15 allogeneic transplant donors; 8 men, 15 women; median age 47 years (27–55)]. Date from 24-hour ambulatory ECG recordings were analyzed with R-R data analysis software (MemCalc/CHIRAM version 1, Suwatrust, Tokyo, Japan). Acknowledged simple markers in time domain analysis are the standard deviation of all normal beats (SDNN) and the square root of the mean of the sum of squared differences between adjacent normal-to-normal intervals (r-MSSD). On the other hand, markers in frequency domain analysis include LH, low frequency power (0.04–0.15Hz); HF, high frequency power (0.15–0.4 Hz); LH/HF ratio; VLF, very low frequency power (0.003–0.04 Hz); and ULF, ultra low frequency power (<0.0033 Hz). These power spectrum analyses of HRV are used to investigate sympathovagal balance, autonomic cardiovascular control and/or target function impairment. Among frequency domain analysis markers, VLF or ULF reportedly have particular prognostic value in all causes of mortality after myocardial infarction. In our study, SDNN, r-MSSD, HF, VLF, and ULF significantly and markedly decreased to morbid levels during apheresis (all P<0.001). Of 23 harvest cases, symptomatic hypotension occurred during apheresis in 2 cases and after apheresis in one case. Notably, in these 3 cases, SDNN and VLF had already begun to decrease about 5–10 minutes before significant symptomatic hypotension occurred (P=0.03, P=0.04, respectively). Our results suggested that morbidly decreased HRV indicates serious cardiovascular load and suppression of the parasympathetic nervous system in apheresis for PBCSH. HRV analysis might be a useful tool to prevent donors from severe autonomic cardiovascular complications in PBCSH.

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%.

scholarly journals Impact of mild orthostatic stress on aortic-cerebral hemodynamic transmission: insight from the frequency domain

2017 ◽  
Vol 312 (5) ◽  
pp. H1076-H1084 ◽  
Author(s):  
Jun Sugawara ◽  
Tsubasa Tomoto ◽  
Tomoko Imai ◽  
Seiji Maeda ◽  
Shigehiko Ogoh
Keyword(s):  
Transfer Function ◽  
Frequency Domain ◽  
Systemic Vascular Resistance ◽  
Vascular Resistance ◽  
Low Frequency ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Slow Oscillations ◽  
Transfer Function Gain ◽  
The Brain

High cerebral pressure and flow fluctuations could be a risk for future cerebrovascular disease. This study aims to determine whether acute systemic vasoconstriction affects the dynamic pulsatile hemodynamic transmission from the aorta to the brain. We applied a stepwise lower body negative pressure (LBNP) (−10, −20, and −30 mmHg) in 15 young men to induce systemic vasoconstriction. To elucidate the dynamic relationship between the changes in aortic pressure (AoP; estimated from the radial arterial pressure waveforms) and the cerebral blood flow velocity (CBFV) at the middle cerebral artery (via a transcranial Doppler), frequency-domain analysis characterized the beat-to-beat slow oscillation (0.02–0.30 Hz) and the intra-beat rapid change (0.78–9.69 Hz). The systemic vascular resistance gradually and significantly increased throughout the LBNP protocol. In the low-frequency range (LF: 0.07–0.20 Hz) of a slow oscillation, the normalized transfer function gain of the steady-state component (between mean AoP and mean CBFV) remained unchanged, whereas that of the pulsatile component (between pulsatile AoP and pulsatile CBFV) was significantly augmented during −20 and −30 mmHg of LBNP (+28.8% and +32.4% vs. baseline). Furthermore, the relative change in the normalized transfer function gain of the pulsatile component at the LF range correlated with the corresponding change in systemic vascular resistance ( r = 0.41, P = 0.005). Regarding the intra-beat analysis, the normalized transfer function gain from AoP to CBFV was not significantly affected by the LBNP stimulation ( P = 0.77). Our findings suggest that systemic vasoconstriction deteriorates the dampening effect on the pulsatile hemodynamics toward the brain, particularly in slow oscillations (e.g., 0.07–0.20 Hz). NEW & NOTEWORTHY We characterized the pulsatile hemodynamic transmission from the heart to the brain by frequency-domain analysis. The low-frequency transmission was augmented with a mild LBNP stimulation partly due to the elevated systemic vascular resistance. A systemic vasoconstriction deteriorates the dampening effect on slow oscillations of pulsatile hemodynamics toward the brain.

A Frequency Domain Analysis of Learning Control

1994 ◽  
Vol 116 (4) ◽  
pp. 781-786 ◽  
Author(s):  
C. J. Goh
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Linear Time ◽  
Planning Horizon ◽  
Time Domain Analysis ◽  
Learning Control ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Convergence Criterion ◽  
The Time Domain

The convergence of learning control is traditionally analyzed in the time domain. This is because a finite planning horizon is often assumed and the analysis in time domain can be extended to time-varying and nonlinear systems. For linear time-invariant (LTI) systems with infinite planning horizon, however, we show that simple frequency domain techniques can be used to quickly derive several interesting results not amenable to time-domain analysis, such as predicting the rate of convergence or the design of optimum learning control law. We explain a paradox arising from applying the finite time convergence criterion to the infinite time learning control problem, and propose the use of current error feedback for controlling possibly unstable systems.

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