Vortex-induced Force Model: Radial Basis Function Neural Network for Two-edge Box Girders

The cross-flow vortex-induced vibration (VIV) response of an elastically mounted idealized undulatory seal whisker (USW) shape is investigated in a wide range of reduced velocity at angles of attack (AOAs) from 0° to 90° and a low Reynolds number of 300. The mass ratio is set to 1.0 to represent the real seal whisker. Dynamic mode decomposition is used to investigate the vortex shedding mode in various cases. In agreement with past studies, the VIV response of the USW is highly AOA-dependent because of the change in the underlying vortex dynamics. At zero AOA, the undulatory shape leads to a hairpin vortex mode that results in extremely low lift force oscillation with a lowered frequency. The frequency remains unaffected by VIV throughout the tested range of reduced velocity. As the AOA deviates from zero, alternating shedding of spanwise vortices becomes dominant. A mixed vortex shedding mode is observed at AOA = 15° in the transition. As the AOA deviated from zero, the VIV amplitude increases rapidly by two orders, reaching the maximum of about 3 times diameter at 90°. An infinite lock-in branch is present for AOA from 60° to 90°, where the VIV amplitude remains high regardless of the increase in reduced velocity.

Effects of end condition and aspect ratio on vortex-induced vibration of a 5:1 rectangular cylinder

A methodology is developed to analyze the vortex-induced vibration of moored or towed cable systems. The fluctuating forces are considered as sources of energy which generate waves propagating through the cable-body system with dissipation and scattering in the process. Because of its emphasis on energy flow, this method facilitates the incorporation of various vortex models into dynamic cable analysis. INTRODUCTION Cables exposed to current in deep-ocean moors or used for towing bodies or arrays for ocean survey are subject to transverse oscillations from vortex-induced forces. This phenomenon, called strumming, has been under investigation for many years because it affects the fatigue life of the structure and the noise of any attached sensors. Experiments conducted in water channels indicate that the vortex-induced vibration can be substantially reduced by introducing hydrodynamic disturbances to the flow near the structure. For example, mechanical devices, such as splitter vanes, trailing ribbons and fairings, have been used to disturb the formation of the vortex flow, while spiral wrappings have been used to disturb their spanwise coherence. Other investigations have been made concerning the nature of the vortex flow and to model the vortex-induced cable vibrations. Wind tunnel and water channel experiments were carried out to measure the characteristics of vortex formation and cable responses. However, due to limitations of the experimental equipment, the motion of a full-scale system cannot easily be modeled experimentally. Thus, numerical modeling is probably the best way to analyze the dynamic motion of a cable system under strumming excitation. To this end, empirical models have been developed recently in which the fluid oscillation near the cable is represented by a non-linear, self-excited oscillator that is dynamically coupled to the structural member. These models can reproduce the synchronization effect as the shedding frequency approaches the natural frequencies of the structure. The models have been used to simulate the motion of an elastically mounted circular cylinder. The results are in good agreement with experimental data of the maximum amplitude in the resonant or entrained state when the vortex shedding frequency is equal to the natural frequencies of the vibrating cylinder. Studies are underway to couple the models to the equations of motion of a flexible cable to simulate the motion of a cable under vortex excitation. The purpose of this paper is to present the bond graph method as a modeling technique that can incorporate a dynamic model of vortex-induced forces in models of cable systems. Using this method, the response of a complete cable system under various environmental conditions is simulated. In the next section this modeling technique is compared with other cable dynamic modeling techniques. A review of oscillator models then is presented with some examples given to demonstrate the feasibility of the bond graph method as a modeling technique for vortex-induced cable system vibrations. DYNAMIC ANALYSIS OF CABLE-BODY SYSTEMS Since cable-body systems are being used in more and more ocean facilities, there is a strong interest in valid analytical tools which require development of analytical approaches supported by experimental validation. Mathematical modeling and numerical techniques have been used by l 2 3 many investigations.

A rigid jumper is an important part of the subsea production system, it may experience significant vortex induced vibrations (VIV) if subjected to current. It has normally non-straight geometry shape in three-dimensional space. Consequently, the response of a rigid jumper under VIV is much more complicated compared to straight pipeline structures. Currently, there are very limited studies and design guidelines including methods on how to assess the fatigue damage of rigid jumpers under VIV. The methodology used for straight pipelines is often applied by ignoring the non-straight geometry characteristics and the multi-axial stress states (coexisting of flexural and torsional stress). However, both experimental and numerical results show that the torsional stress does exist besides the flexural stress for rigid jumpers under VIV. On the other side, the response of the rigid jumper under VIV is also challenging. The objective of this study is to do a fatigue assessment practice based on state-of-the-art calculation methods to a rigid jumper on model scale. The VIV response is inherited from experimental tests and numerical calculations by either force or response model methods. The influence of torsional stress on fatigue assessment is demonstrated. Two approaches have been investigated. In the first method, the flexural and torsional stresses are evaluated separately. The second method uses the 1st principle stress to calculate the fatigue damage, thus the flexural and torsional stresses are evaluated together. It is shown that the use of the 1st principle stress gives higher fatigue damage if the torsional stress contribution is significant. Further, the principle stress method is also less time-consuming on processing the results. Detailed discussions based on results have been performed, which could be also applied to general real scale rigid jumpers.

Drilling and production risers experiencing vortex-induced vibrations (VIV) may adversely impact operations in two ways: by increasing deflection due to amplified drag and causing structural fatigue damage due to VIV induced dynamic stresses. Complex hydrodynamic mechanisms controlling correlation length and force dependence on motion and frequency of response are major obstacles in predicting the VIV response, except for a limited number of cases for which extensive experimental calibrations were carried out. A pragmatic VIV analysis methodology has been developed based on correlation length measurements, and riser specific experimental tests to establish basic CD and CL databases for realistic riser configurations with auxiliary lines and buoyancy modules. Correlation length properties are established using flow visualization methods, in particular Digital Particle Image Velocimetry (DPIV), which allows whole-field quantitative information on the velocity and vorticity fields to be obtained. Identification of the role of two basic VIV mechanisms, the formation of braid vortices and the impact of vortex splitting, has provided a robust correlation length model. A VIV analysis program has evolved from these experimental tests in conjunction with extensive research in structural and hydrodynamic riser responses. Introduction The design of drilling risers for mobile offshore drilling units (MODUs) is governed by operational considerations, specifically, the need to keep the riser deflection angle within 1° to 2° during normal drilling operations. This necessitates stringent measures:keep the rig within a tight watch radius of around 0.5% to 2.0% water depth,maintaining high riser top tension, andminimizing riser net in-water weight by the use of buoyancy modules. The occurrence of VIV may adversely impact drilling operability because VIV causes an apparent increase in hydrodynamic drag, resulting in increased riser deflection angles. In addition, fatigue damages appear to be a second concern, however less so since it is feasible to frequently inspect risers. In the event of strong current, the need to keep riser deflection angles at a minimum may dictate the use of faired riser sections. This is, however, a very costly option and must be avoided if at all possible. For example, increased tensioner capability may prove to be just as effective without encountering the same handling difficulties. As for production rigid risers and steel catenary risers for permanently installed platforms, they are much more tolerant of riser deflections and require minimal riser tensions. As a result of low top tension these risers become much more compliant and VIV responsive than rigid drilling risers. Fatigue considerations may dictate that these risers be protected with VIV suppression devices, such as strakes, in ections exposed to strong current. This paper highlights a pragmatic VIV analysis tool (VIVA) based on riser-specific experimental tests and mathematical models. This is followed by a review of VIV analyses for representative rigid drilling and production risers for 3000-foot water depth. VIV response sensitivity is investigated for 1.5-knot slab, linear, and reverse current profiles that are indicative of the 1-year extremes West of Shetland and Brazil. A Pragmatic VIV Analysis Methodology VIVA is a computational tool developed to predict the vortex-induced vibrations and fatigue damage of marine risers in shear flows based on strip theory and an extensive database of hydrodynamic data on sectional force coefficients and correlation length (Reference 1). The program is generically written to allow the input of additional hydrodynam

Numerical simulation of the vortex-induced vibrations of a 4:1 rectangular cylinder subjected to yaw uniform currents

Vortex-induced vibration (VIV) has been occasionally observed on a few long-span steel box-girder suspension bridges. The underlying mechanism of VIV is very complicated and reliable theoretical methods for prediction of VIV have not been established yet. Structural health monitoring (SHM) technology can provide a large amount of data for further understanding of VIV. Automatic identification of VIV events from massive, continuous long-term monitoring data is a non-trivial task. In this study, a method based on the random decrement technique (RDT) is proposed to identify the VIV response automatically from the massive acceleration response without manual intervention. The raw acceleration data is first processed by RDT and it is found that the RDT-processed data show different characteristics for the VIV response and conventional random response. A threshold based on the coefficient of variation (COV) of peak values of processed data is defined to distinguish between the two kinds of responses. Both random vibration and VIV for a three-DOF (degree-of-freedom) mass-spring-damper system are obtained by numerical simulation to verify the proposed method. The method is finally applied to the Xihoumen suspension bridge for identifying VIV response from three-month monitoring data. It is shown that the proposed method performs comparably with the method of novelty detection. A total of 60 VIV events have been successfully identified. Vortex-induced vibrations for the second to ninth vertical modes with modal frequency within 0.1~0.5 Hz occurs at wind velocity 5–18 m/s, with wind direction nearly perpendicular to bridge axis. Amplitude of VIV generally decreases with increase of wind turbulence intensity; however, noticeable VIV amplitude are still observed for turbulence intensity up to 13% in some cases.

This study investigated the vortex-induced vibration (VIV) characteristics of a proposed water-conveying truss pipeline cable-stayed bridge through wind tunnel tests. The experimental results indicated that both vertical bending and torsional VIV responses decreased as the wind attack angle increased. The vertical bending VIV behavior of the bridge was significantly influenced by the lateral spacing and relative height of the pipelines. Adjustments to these geometric parameters markedly affected the structural VIV response. Furthermore, computational fluid dynamics (CFD) was employed to analyze the flow field around the truss pipeline bridge. The results revealed that changes in the lateral spacing and relative height of the pipelines primarily altered the VIV performance by modifying vorticity distribution, separation point position, and other critical flow field parameters around the truss section. These findings underscore the importance of considering the effects of geometric parameters on VIV during the design of the truss section in pipeline bridges.

Numerical investigation on the suppression of vortex-induced vibration system by assembling different rotors based on quasi-active control method

Given the significant influence of wave propagation on the airflow structures and aerodynamic behavior of sea-crossing bridge decks, understanding the effects of the dynamic wave boundary layer (WBL) on vortex-induced vibration (VIV) is crucial. This study proposes a numerical simulation framework to investigate how dynamic WBL impacts VIV characteristics of sea-crossing bridge decks. A wave-following mesh scheme with periodic boundary conditions generates homogeneous dynamic WBL airflows. These validated flow conditions are integrated into a two-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) simulation incorporating fluid–structure interaction to analyze the VIV response of a sea-crossing bridge deck. Simulation results reveal that the oscillatory wind field induced by waves alters vortex shedding and deck surface pressure distribution, thereby disrupting VIV onset conditions and reducing its amplitude. Specifically, as the deck approaches the wave surface, the influence of waves on the aerodynamic performance of the deck becomes more pronounced, leading to a reduction in VIV amplitude with decreasing deck-wave clearance. Notably, under wind speeds outside the VIV range, dynamic WBL induces forced deck vibrations. In such cases, deck vibration frequency and phase synchronize with wave motion, and reduced deck-wave clearance amplifies forced vibration amplitude.

The vortex-induced vibration (VIV) characteristics of twin-box girders are critical in the design of long-span bridges. This study aims to investigate the VIV behavior of a twin-box girder section and to deepen the understanding of the mechanisms underlying VIV. A numerical approach that integrates both free and forced vibration analyses is developed to predict VIV performance. The VIV amplitude is evaluated using the free vibration method within the wind speed range identified by the forced vibration method. Comparisons with wind tunnel test results demonstrate the feasibility of this approach. Meanwhile, flow structure and aerodynamic characteristics of the twin-box girder were analyzed in relation to the VIV mechanism. The results show that flow restrictor plate could effectively suppress vertical VIV at a wind attack angle 0° and reduce the VIV amplitude by 50% at +3°wind attack angle. The central opening slot is identified as a significant factor in inducing VIV, as the upper and lower vortices interact with the airflow passing through the respective sections of the slot. The flow restrictor plates positioned at the upper section of the opening slot cause most upper vortices to shift downstream at wind attack angles of 0° and +3°. This shift results in minimal airflow reflux at the slot, which is crucial for optimizing VIV performance. At a wind attack angle of +3°, the vortices at the lower part of the slot persist, albeit with reduced size. These changes in vortex behavior underscore the sensitivity of vortex formation to variations in wind attack angles.

Review of the excitation mechanism and aerodynamic flow control of vortex-induced vibration of the main girder for long-span bridges: A vortex-dynamics approach

In this paper, the vortex-induced force characteristics of a flexible riser with buoyancy modules and strakes were experimentally investigated. The strain information caused by vortex-induced vibration (VIV) at different cross-sections on the flexible cylinder was measured in the model test. Combined with the modal superposition method and inverse analysis method for vortex-induced force, the vortex-induced forces on the flexible cylinder were inverted, including the excitation force in phase with velocity and added mass force in phase with acceleration. Then, the excitation coefficients and added mass coefficients at each time step were identified via a least-squares method. The results show that the added mass coefficient and excitation coefficient of the flexible riser covering buoyancy modules present a “sawtooth” distribution along the length of the pipe, while the total mass (sum of structural mass and added mass) is consistent along the pipe. The strake has little effect on the added mass coefficient of the buoyancy module and the bare pipe section, but when it covers the bare pipe section, the excitation coefficient of the bare pipe section decreases to a negative value, showing a damping effect. In addition, when the bare pipe section of the flexible riser is completely covered with helical strakes, only the vortex-shedding frequency component of the buoyancy modules remains in the VIV response of the pipe. The reason for this phenomenon is that helical strakes completely suppress the vortex shedding of the bare pipe section, resulting in the reduction in the VIV excitation energy of the original bare pipe section to 0.

Numerical study of vortex-induced vibrations of a circular cylinder at different incidence angles

Experimental exploration of unpowered propellers for vortex-induced vibration suppression of flexible riser