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Carl M. Larsen - One of the best experts on this subject based on the ideXlab platform.

  • dominant parameters for vortex induced vibration of a steel catenary riser under vessel motion
    Ocean Engineering, 2017
    Co-Authors: Carl M. Larsen, Jungao Wang, Rolf Baarholm, Halvor Lie
    Abstract:

    Abstract Recent research has confirmed a new type of vortex-induced vibration (VIV) in steel catenary risers (SCRs), purely caused by vessel motion. Vessel motion-induced VIV occurs because the SCR is exposed to the equivalent oscillating current due to its own motions relative to the still water. Preliminary results indicate that vessel motion-induced VIV is quite different from ocean current-induced VIV and is characterized with distinct time-varying features. In the present study, we aim at further summarizing the dominant parameters that govern the general vessel motion-induced VIV responses. Throughout the comparative studies on the instantaneous and statistical VIV responses including strain, displacement, response frequency, fatigue damage and top Tension Variation, the maximum Keulegan-Carpenter number K C max and the maximum equivalent current velocity Vn_max are found to be the two dominant parameters that govern the vessel motion-induced VIV responses. Generally speaking, when K C max is sufficiently large (larger than 39 according to the present study), the general vessel motion-induced VIV response is dominated by V n _ max . However, when K C max is small, the VIV response is less time-varying and shows strong correlation with both K C max and the local K C number distribution along the SCR. Vessel motion-induced VIV response frequency models are also reviewed and discussed considering different K C max and V n _ max ranges. Hopefully, these results can provide some general guidelines for future vessel motion-induced VIV prediction and for industrial references.

  • out of plane vortex induced vibration of a steel catenary riser caused by vessel motions
    Ocean Engineering, 2015
    Co-Authors: Jungao Wang, Shixiao Fu, Rolf Baarholm, Jie Wu, Carl M. Larsen
    Abstract:

    A large-scale model test of a truncated steel catenary riser (SCR) was performed in an ocean basin to investigate the riser responses under top vessel motion. Top end of the model was forced to oscillate at given motion trajectories, corresponded with the motion at the truncation point of a full-length SCR under vessel motion. Out-of-plane vortex-induced vibration (VIV) was confirmed under pure top vessel motions, characterized with distinctive time-varying features. Results further indicate that vessel motion-induced VIV was strongly dependent on the KC number and the instantaneous equivalent flow profile. Meanwhile, Tension Variation was found to be another key factor causing response discrepancy between the ‘lift-up’ and ‘push-down’ phase for the large top vessel motion case. Finally, the relationship between the out-of-plane VIV dominant response frequency, maximum equivalent flow velocity and KC number were unveiled, which provides references for future vessel motion-induced VIV predictions.

  • fatigue damage of a steel catenary riser from vortex induced vibration caused by vessel motions
    Marine Structures, 2014
    Co-Authors: Jungao Wang, Rolf Baarholm, Carl M. Larsen
    Abstract:

    A large-scale model test of a truncated steel catenary riser (SCR) was performed in an ocean basin to investigate the vortex-induced vibration (VIV) and its fatigue damage under pure top vessel motion. The top end of the test model was forced to oscillate at given vessel motion trajectories. Fiber Bragg grating (FBG) strain sensors were used to measure both in-plane and out-of-plane responses. Four different factors have been discussed to understand the VIV responses and fatigue damage results: instantaneous shedding frequency, touch down point (TDP) Variation, Tension Variation and traveling waves. Out-of-plane VIV associated with strong time-varying features was confirmed to have occurred under pure vessel motion. Both KC number and maximum shedding frequency were investigated and indicated that the middle part of the truncated model riser was the ‘power-in’ region for out-of-plane VIV. Meanwhile, fatigue damage caused by out-of-plane VIV was found to be strongly dependent on both top motion amplitude and period. The probability distribution of the maximum damage exhibits 3 critical locations in the test model: TDP, upper sag-bend and top of the SCR. Strong traveling waves, TDP Variation and end wave reflection have been proven to cause the maximum damage locations to shift from the ‘power-in’ region to these three positions. Finally, a maximum fatigue damage diagram with top motion amplitude, period and maximum shedding frequency was constructed.

  • Force Variations on Heave Compensating System for Ultra-Deepwater Drilling Risers
    29th International Conference on Ocean Offshore and Arctic Engineering: Volume 5 Parts A and B, 2010
    Co-Authors: Ronny Sten, Carl M. Larsen, Michael Rygaard Hansen, Svein Sævik
    Abstract:

    This paper discusses modeling aspects related to dynamic analysis of deep water drilling risers. These risers must have a heave compensator that maintains a near constant Tension in the riser independent on platform motions. Traditional riser analysis will apply constant top Tension or a simple parametric model that may give approximate Tension Variation. The present paper describes an alternative analysis procedure that consists of the following step: • Global riser analysis including calculation of dynamic stroke of the heave compensator from platform motions and riser dynamics. A “pipe-in-pipe” approach is used to represent the hydraulic cylinders. • Calculation of dynamic Tension Variation from an analysis of the hydraulic Tensioner system. The dynamic stroke found from the first analysis is applied as known piston motions in this analysis. • Identification of parameters in a simple model for dynamic Tension Variation from the results from the second analysis. • Use of the simple model in a second global riser analysis. The difference between the two riser analyses can hence be found, which represents the error one must expect from a traditional riser analysis with constant riser Tension. A case study with realistic data is reported. The conclusion is that the constant Tension model is valid for small heave motions only, while the parametric Tensioner model can give almost correct results for Tension Variation. However, the parametric model must be tuned for each case. Hence, an integrated model that accounts for riser dynamics and pressure Variation in the Tensioner system should preferably be developed.Copyright © 2010 by ASME

J S Walker - One of the best experts on this subject based on the ideXlab platform.

  • solutocapillary instabilities in liquid bridges
    Physics of Fluids, 2002
    Co-Authors: Martin L Witkowski, J S Walker
    Abstract:

    The stability of a steady, axisymmetric flow driven by a surface-Tension Variation due to a solute-concentration gradient is studied with a linear analysis. There is a liquid bridge with a cylindrical free surface between two collinear solid cylinders with the same radius. One cylinder injects the solute into the liquid as it melts at a velocity Vg*, and the other cylinder preferentially absorbs the solute from the liquid as it solidifies at the same velocity. The surface Tension of the free surface is assumed to be a linear function of the solute concentration. For given values of the Schmidt number Sc and of Vg*, the first instability is a Hopf bifurcation at a critical value of a solutal Marangoni number. The present problem is related to the thermocapillary convection in the half-zone problem for which the geometry is the same, the two solids are isothermal at different temperatures and the surface Tension is a linear function of temperature. Differences arise because the solute concentration distribu...

Wenyong Tang - One of the best experts on this subject based on the ideXlab platform.

  • a numerical investigation of vortex induced vibration response characteristics for long flexible cylinders with time varying axial Tension
    Journal of Fluids and Structures, 2018
    Co-Authors: Yuchao Yuan, Wenyong Tang
    Abstract:

    Abstract Vortex-Induced Vibration (VIV) for flexible cylinders is a typical fluid–structure interaction problem, and it becomes more complex when the time-varying axial Tension effect is considered. An available force–decomposition model is proposed in this paper to investigate the cross-flow VIV response characteristics with time-varying Tension. VIV hydrodynamic forces are all based on forced vibration experimental data, and structural stiffness will be updated at each time step to take the Tension Variation into account. Firstly, this VIV model is compared against the published experimental results of a small-scale cylinder with constant and time-varying Tensions. Next, 60 cases of a long flexible cylinder are designed to investigate the time-varying Tension effect comprehensively. Several new phenomena such as amplitude modulation, time-lag, frequency transition, mode jump and multi-frequencies response superposition are captured in the response comparison with the constant Tension case. The effects of initial phase, amplitude and frequency of the varying Tension are respectively discussed in detail. The Mathieu-type resonance between VIV and time-varying Tension excitation is proved existent. The response displacement and strain will enlarge significantly at ω T = 2 ω C T , to which enough attention needs to be paid.

Yichung Tung - One of the best experts on this subject based on the ideXlab platform.

  • study of oxygen Tension Variation within live tumor spheroids using microfluidic devices and multi photon laser scanning microscopy
    RSC Advances, 2018
    Co-Authors: Sreerupa Sarkar, Chienchung Peng, Chiung Wen Kuo, Diyen Chueh, Yuanhsuan Liu, Peilin Chen, Yichung Tung
    Abstract:

    Three-dimensional cell spheroid culture using microfluidic devices provides a convenient in vitro model for studying tumour spheroid structures and internal microenvironments. Recent studies suggest that oxygen deprived zones inside solid tumors are responsible for stimulating local cytokines and endothelial vasculature proliferation during angiogenesis. In this work, we develop an integrated approach combining microfluidic devices and multi-photon laser scanning microscopy (MPLSM) to study Variations in oxygen Tension within live spheroids of human osteosarcoma cells. Uniform shaped, size-controlled spheroids are grown and then harvested using a polydimethylsiloxane (PDMS) based microfluidic device. Fluorescence live imaging of the harvested spheroids is performed using MPLSM and a commercially available oxygen sensitive dye, Image-iT Red, to observe the oxygen Tension Variation within the spheroids and those co-cultured with monolayers of human umbilical vein endothelial cells (HUVECs). Oxygen Tension Variations are observed within the spheroids with diameters ranging from 90 ± 10 μm to 140 ± 10 μm. The fluorescence images show that the low-oxygenated cores diminish when spheroids are co-cultured with HUVEC monolayers for 6 hours to 8 hours. In the experiments, spheroids subjected to HUVEC conditioned medium treatment and with a cell adherent substrate are also measured and analyzed to study their significance on oxygen Tension within the spheroids. The results show that the oxygenation within the spheroids is improved when the spheroids are cultured under those conditions. Our work presents an efficient method to study oxygen Tension Variation within live tumor spheroids under the influence of endothelial cells and conditioned medium. The method can be exploited for further investigation of tumor oxygen microenvironments during angiogenesis.

Svein Sævik - One of the best experts on this subject based on the ideXlab platform.

  • Force Variations on Heave Compensating System for Ultra-Deepwater Drilling Risers
    29th International Conference on Ocean Offshore and Arctic Engineering: Volume 5 Parts A and B, 2010
    Co-Authors: Ronny Sten, Carl M. Larsen, Michael Rygaard Hansen, Svein Sævik
    Abstract:

    This paper discusses modeling aspects related to dynamic analysis of deep water drilling risers. These risers must have a heave compensator that maintains a near constant Tension in the riser independent on platform motions. Traditional riser analysis will apply constant top Tension or a simple parametric model that may give approximate Tension Variation. The present paper describes an alternative analysis procedure that consists of the following step: • Global riser analysis including calculation of dynamic stroke of the heave compensator from platform motions and riser dynamics. A “pipe-in-pipe” approach is used to represent the hydraulic cylinders. • Calculation of dynamic Tension Variation from an analysis of the hydraulic Tensioner system. The dynamic stroke found from the first analysis is applied as known piston motions in this analysis. • Identification of parameters in a simple model for dynamic Tension Variation from the results from the second analysis. • Use of the simple model in a second global riser analysis. The difference between the two riser analyses can hence be found, which represents the error one must expect from a traditional riser analysis with constant riser Tension. A case study with realistic data is reported. The conclusion is that the constant Tension model is valid for small heave motions only, while the parametric Tensioner model can give almost correct results for Tension Variation. However, the parametric model must be tuned for each case. Hence, an integrated model that accounts for riser dynamics and pressure Variation in the Tensioner system should preferably be developed.Copyright © 2010 by ASME