The complete 3D nonlinear dynamic problem of extensible, flexible risers conveying fluid is considered. For describing the dynamics of the system, the Newtonian derivation procedure is followed. The velocity field inside the pipe formulated using hydrostatic and Bernoulli equations. The hydrodynamic effects of external fluids are taken into consideration through the nonlinear drag forces in various time steps and the added inertia due to the hydrodynamic mass. Following the Newtonian derivation, the dynamics of the pipes element with effects of internal fluid are considered separately and the final governing set is derived by combining the equations of inertia equilibrium. The study focuses specifically on the effect of the inner flow to the global dynamics of the riser. This task is accomplished using time domain teachings and the Finite Element method is used as a powerful numerical method. Moreover the Euler-Bernoulli beam theory is used response to model the dynamic behavior of the flexible risers.

In the present paper the behavior of an elastically mounted cylinder in low and high mass-damping ratio is investigated. For high mass-damping ratio, a classical wake oscillator model is used. At the first, by neglecting all damping and nonlinear terms of this model, the possibility of using a linear model for determination of the lock-in range and the dominant mode is investigated. Then, without neglecting any terms, the nonlinear model is analyzed and the results are compared with experimental results. Due to change of the behavior of the system in low mass-damping ratio and disability of classic model in modeling of this change, a modified wake oscillator model is presented and the results of this model, in both low and high mass-damping ratio, are compared with experimental results.

Free-span occurs normally in a pipeline at uneven seabed, dynamic seabed and pipeline crossing. Free spanning in pipeline causes Vortex Induced Vibration (VIV) fatigue, fracture and bursting. In this paper, a pipeline located in South Pars Gas Field is assessed against local buckling and VIV fatigue using probability of failure theory based on the recommended methodology by Det Norske Veritas (DNV) corresponding to different soil classes and different span length to pipeline diameter and also different water depths by applying First-Order Reliability Method (FORM) and Monte-Carlo Sampling (MCS), separately. Furthermore, the simultaneous effect of local buckling and VIV fatigue is assessed in terms of probability of failure. Finally, in order to determine the effect of each parameter on failure probability, sensitivity analysis is carried out using the alpha index.

In this study, uncertainty analysis of the vortex-induced vibration (VIV) tests, using a VIV test rig is presented. The VIV test rig is set up on the circulation channel in Ata Nutku Ship Model Testing Laboratory at Istanbul Technical University (ITU). The tests are performed using an elastically mounted rigid and smooth circular cylinder in low mass-damping and high Reynolds numbers conditions. The cylinder has one-degree-of freedom. It is allowed to move perpendicular to the flow while inline vibrations are constrained. The aim of the study is to demonstrate and establish a repeatable procedure to predict the uncertainty of VIV tests, utilizing some example applications of existing ITTC recommendations. Within this aim, five distinct VIV tests are carried out following ITTC guidelines and procedures measuring the amplitude (A*) and frequency response (f*) data. Uncertainty analysis study is performed for three different flow velocities, chosen from VIV tests and total uncertainty is calculated by root mean square values of precision and bias uncertainties. The precision uncertainty is predicted using response amplitude values obtained from five sets of VIV tests. The bias uncertainty is predicted utilizing the basic measurements and test results of the components of response amplitude for the cylinder. The results have demonstrated that the current test rig has low uncertainty level. Additionally, it has succeeded to reflect the characteristics of VIV phenomenon in the studied Reynolds number range, which is in the Transition Shear Layer 3 (TrSL3) flow regime. Consequently, it is believed that this study would help in spreading the application of the uncertainty analysis for VIV tests in the future.

Many procedures suggest for reduction of responses of riser to Vortex Induced Vibrations (VIV). Natural frequencies of marine risers is an important parameter that can affect the responses of riser to VIV. Change of riser properties such as top tension and bending stiffness can alter natural frequencies. In this study effects of riser specifications on the responses and fatigue damage of marine risers were investigated analytically and numerically. For numerically analysis 2D wake-structure coupled model is used for modeling of VIV of riser in two directions of Cross Flow (CF) and In Line (IL). The wake dynamics, including IL and CF vibrations, is represented using a pair of non-linear Van der Pol equations that solved using modified Euler method. The Palmgren–Miner Rule is used for evaluation of fatigue damage. Riser of Amir-Kabir semisubmersible placed in Caspian sea is used for case study. Because VIV is self-limiting, it is showed that lower modes have lower curvature, that in some cases this is lead to lesser stress and also fatigue damage. The results show that for tension dominant modes of vibration, natural frequencies was increased with top tension and for a certain Strouhal frequency, dominant modes of vibration was reduced which leads to reduction of stress and fatigue damage. The results show that stress and fatigue damage increased with module of elasticity of riser and reduction of this leads to reducing of stress and fatigue damage. Therefore suitable procedure for reduction of VIV responses of riser should be selected based on the current velocity.

Introduction: Transcatheter mitral valve-in-valve (VIV) & valve-in-ring (ViR) are relatively novel therapeutic alternatives for patients with degenerated bioprostheses or failed annuloplasty rings whose reoperative risk is too high. The predominant procedural access for both procedures is transapical or transseptal. However, whether there are differences in outcomes of this procedure using transseptal versus transapical access has not yet been defined. Methods: We conducted a systematic review of all published articles from MEDLINE and EMBASE to explore the outcomes of these two procedural approaches. Results: A total of 55 studies including 183 patients (154 VIV and 29 ViR) were included. Patients that underwent VIV (101 transapical and 53 transseptal) using the transseptal approach required more iatrogenic atrial septal defect (ASD) closure (19% versus 0. 0 %; P < 0. 001) and hence had a lower device success rate (68% versus 89%; P = 0. 001). However, there was no significant difference between the two groups in procedural success and all-cause mortality at 30 days. Overall severe bleeding complications (major or life threatening) were not different the two groups (3. 7% versus 7. 9%; P = 0. 321). In the ViR group (19 transapical and 10 transseptal), no difference in procedural success, device success or 30-day outcomes were identified between transseptal and transapical groups, although sample size was small. Conclusion: In conclusion, mitral VIV and ViR using the two different procedural approaches appear to confer equal and reasonable 30-day outcomes.