Distributed Wake-Body Resonance of a Long Flexible Cylinder in Shear Flow

The fluid-structure interaction mechanisms involved in the development of narrowband and broadband vortex-induced vibrations of long flexible structures placed in non-uniform currents are investigated by means of direct numerical simulation. We consider a tensioned beam of aspect ratio 200, free to move in both the in-line and cross-flow directions, and immersed in a sheared flow at Reynolds number 330. Both narrowband and broadband multi-frequency vibrations may develop, depending on the velocity profile of the sheared oncoming current. Narrowband vibrations occur when lock-in, i.e. the synchronization between vortex shedding and structure oscillations, is limited to a single location along the span, within the high current velocity region; thus, well-defined lock-in versus non-lock-in regions are noted along the span. In contrast, we show that broadband responses, where both high and low structural wavelengths are excited, are characterized by several isolated regions of lock-in, distributed along the length. The phenomenon of distributed lock-in impacts the synchronization of the in-line and cross-flow vibrations, and the properties of the fluid-structure energy transfer, as function of time and space. Topics: Resonance, Shear flow, Wakes, Cylinders, Locks (Waterways), Vibration, Synchronization, Cross-flow, Oscillations, Vortex-induced vibrationBP-MIT Major Projects Progra

Fluid-Structure Energy Transfer of a Tensioned Beam Subject to Vortex-Induced Vibrations in Shear Flow

The fluid-structure energy transfer of a tensioned beam of length to diameter ratio 200, subject to vortex-induced vibrations in linear shear flow, is investigated by means of direct numerical simulation at three Reynolds numbers, from 110 to 1,100. In both the in-line and cross-flow directions, the high-wavenumber structural responses are characterized by mixed standing-traveling wave patterns. The spanwise zones where the flow provides energy to excite the structural vibrations are located mainly within the region of high current where the lock-in condition is established, i.e. where vortex shedding and cross-flow vibration frequencies coincide. However, the energy input is not uniform across the entire lockin region. This can be related to observed changes from counterclockwise to clockwise structural orbits. The energy transfer is also impacted by the possible occurrence of multi-frequency vibrations. Topics: Energy transformation, Fluids, Shear flow, Vortex-induced vibrationBP America Production CompanyBP-MIT Major Projects Progra

Validation of Computational Fluid-Structure Interaction Analysis Methods to Determine Hydrodynamic Coefficients of a BOP Stack

Drilling riser systems are subjected to hydrodynamic loads from vessel motions, waves, steady currents and vortex-induced motions. This necessitates a proper structural analysis during the design phase using techniques such as finite element analysis (FEA). Common approaches within the FEA packages approximate the individual components including BOP/LMRP (Blow-Out Preventer/Lower Marine Riser Package), subsea tree and wellhead using 2D or 3D beam/pipe elements with approximated effective mass and damping coefficients. Predicted system response can be very sensitive to the mass, hydrodynamic added mass and drag of the large LMRP/BOP/Tree components above the wellhead. In the past, gross conservative estimates on the hydrodynamic coefficients were made and despite this, design criteria were generally met. With the advent of large sixth-generation BOP stacks with the possibility of additional capping stacks, such approximations are no longer acceptable. Therefore, the possibility of relying on the more detailed capability of computational fluid-structure interaction (FSI) analysis for a better calculation of these coefficients is investigated. In this paper, we describe a detailed model developed for a 38:1 scaled down BOP and discuss the subsequent predictions of the hydrodynamic coefficients. The model output is compared against the data from the concurrent tests conducted in an experimental tow tank. The comparison demonstrates that computational FSI can be an effective and accurate tool for calculating the hydrodynamic coefficients of complex structures like BOPs

Re-Evaluation of VIV Riser Fatigue Damage

The paper describes a new characterization of the properties of the vortex-induced vibrations (VIV) of marine risers, which emerges from processing field and experimental data. We show that two currently employed assumptions: (a) that VIV is a statistically steady-state response containing one or several frequencies, and (b) that VIV consists of alternating dominant modes (mode-sharing), are inadequate. Instead, we find that the response either contains strong traveling wave components accompanied by high force harmonics; or consists of a chaotic wandering among several traveling and standing waves, associated with a wide-band spectrum; both types of response require careful consideration for correct fatigue evaluation. Topics: Fatigue damage, Pipeline risers, Vortex-induced vibrationBP-MIT Major Projects Progra

The airplane: A simulated commercial air transportation study

The 'Airplane' is a moderate-range, 70 passenger aircraft. It is designed to serve demands for flights up to 10,000 feet and it cruises at 32 ft/s. The major drivers for the design of the Airplane are economic competitiveness, takeoff performance, and weight minimization. The Airplane is propelled by a single Astro 15 electric motor and a Zinger 12-8 propeller. The wing section is a Spica airfoil which, because of its flat bottom, provides simplicity in manufacturing and thus helps to cut costs. The wing is constructed of a single load bearing mainspar and shape-holding ribs coated with Monokote skin, lending to a light weight structural makeup. The fuselage houses the motor, flight deck and passenger compartments as well as the fuel and control actuating systems. The wing will be attached to the top of the fuselage as will the fuel and control actuator systems for easy disassembly and maintenance. The aircraft is maneuvered about its pitch axis by means of an aft elevator on the flat plate horizontal tail. The twin vertical tail surfaces are also flat plates and each features a rudder for both directional and roll control. Along with wing dihedral, the rudders will be used to roll the aircraft. The Airplane is less costly to operate at its own maximum range and capacity as well as at its maximum range and the HB-40's maximum capacity than the HB-40

Crown Ether-Metal ‘Sandwiches’ As Linking Mechanisms in Assembled Nanoparticle Films

Crown ether ligands attached to monolayer-protected clusters (MPCs) were assembled as films and the linking mechanism between the crown ether–metal ion–crown ether bridges between nanoparticles was examined. Thicker films exhibited a red shift in the absorbance maximum for the surface plasmon band which was attributed to the increasing aggregation and cross linking within the film. Quantized double layer charging peaks suggest that film growth is selective toward a specific core size or exchange rate, either of which affect the number of potential linking ligands in the periphery of the MPCs. Multi-layer growth of films was only achieved with metal ions capable of coordinating within the cavity of the 15-crown-5 ether. Our exchange reaction parameters are in stark contrast to other types of MPC film assemblies

Reliability Based Factors of Safety for VIV Fatigue Using NDP Riser High Mode VIV Tests

Understanding the level of conservatism in a riser system design for vortex-induced vibration (VIV) fatigue is an important issue for operators. This study represents a demonstration of the calibration methodology to derive consistent values for the Factor of Safety (FoS). The exercise is performed here based on medium scale VIV data and utilizing the most commonly used VIV prediction software by industry. The results emphasize the need for (i) a coherent approach to estimate the FoS to be used and (ii) monitoring/measurement of software improvements as this may increase risk of failure if the influence of such improvements on the FoS is not quantified.DeepStar (Consortium) (DeepStar Phase IX

Using Model Test Data to Assess VIV Factor of Safety for SCR and TTR in GOM

This paper presents results obtained as part of the DeepStar Phase 10 program on VIV Factors of Safety. The objective was to develop a general methodology to calibrate Factors of Safety for VIV-induced fatigue and to apply it to partially straked risers. This was achieved using reliability methods, accepted industry VIV prediction software and state-of-the-art model test experiments. Most oil companies use a Factor of Safety of 20 when predicting VIV damage using VIV software tools. There are numerous software tools currently in use in industry to predict VIV damage to straked risers and each of them will have different accuracy, and therefore an intrinsic level of conservatism. Understanding the level of conservatism in different VIV prediction software is therefore critical to determining what Factor of Safety to use. This study benchmarks the latest generation of industry accepted VIV design tools at the time of the study (2011): SHEAR7v4.6, VIVAv6.5 and VIVANAv3.7.24 against high quality VIV data from three separate straked riser experiments. A bias distribution (predicted to measured VIV damage results) is obtained for each software tool as a function of the strake coverage. A novel reliability framework approach is then developed to incorporate all uncertainties associated with VIV fatigue prediction into a limit state function, including variability in met-ocean conditions and variability in the fatigue resistance of the material characterized by a design S-N curve. The limit state function is analyzed using First Order Reliability Methods to develop Factors of Safety for target probabilities of failure. The general method is then applied on two case studies involving an SCR and TTR in Gulf of Mexico loop currents, but it can be easily extended to different locations and riser configurations. The resulting FoS range from about 1 to 15 for most software, and are lower than industry standards for VIV prediction. The FoS do not vary markedly for different riser configurations, indicating the possibility of reducing excess conservatism when predicting VIV damage on straked risers.DeepStar (Consortium)SHEAR7 JI

Associations between depressive symptoms and disease progression in older patients with chronic kidney disease: results of the EQUAL study

Background Depressive symptoms are associated with adverse clinical outcomes in patients with end-stage kidney disease; however, few small studies have examined this association in patients with earlier phases of chronic kidney disease (CKD). We studied associations between baseline depressive symptoms and clinical outcomes in older patients with advanced CKD and examined whether these associations differed depending on sex. Methods CKD patients (>= 65 years; estimated glomerular filtration rate <= 20 mL/min/1.73 m(2)) were included from a European multicentre prospective cohort between 2012 and 2019. Depressive symptoms were measured by the five-item Mental Health Inventory (cut-off <= 70; 0-100 scale). Cox proportional hazard analysis was used to study associations between depressive symptoms and time to dialysis initiation, all-cause mortality and these outcomes combined. A joint model was used to study the association between depressive symptoms and kidney function over time. Analyses were adjusted for potential baseline confounders. Results Overall kidney function decline in 1326 patients was -0.12 mL/min/1.73 m(2)/month. A total of 515 patients showed depressive symptoms. No significant association was found between depressive symptoms and kidney function over time (P = 0.08). Unlike women, men with depressive symptoms had an increased mortality rate compared with those without symptoms [adjusted hazard ratio 1.41 (95% confidence interval 1.03-1.93)]. Depressive symptoms were not significantly associated with a higher hazard of dialysis initiation, or with the combined outcome (i.e. dialysis initiation and all-cause mortality). Conclusions There was no significant association between depressive symptoms at baseline and decline in kidney function over time in older patients with advanced CKD. Depressive symptoms at baseline were associated with a higher mortality rate in men