Fluid-Structural interaction study of the structural arrangement of a riverine low-draft combat boat for coastal transit conditions

Control of wave-induced vibrations on floating production systems

The rotordynamic (RD) fluid force generated in fluid elements such as seals in turbomachinery affects the stability of turbomachinery and causes shaft vibrations. Various studies have been conducted to clarify the effects of seals on the stability of rotor systems. Many studies have been conducted on the rotor dynamics of horizontal shaft systems, considering the RD fluid force generated in the seals, and in these studies the stability of horizontal shaft systems has been assessed by eigenvalue analysis using RD coefficients. However, few studies have been conducted on vertical shaft systems. The dynamic behavior of vertical shafts differs significantly from that of horizontal shafts owing to their different structural arrangements. Vertical shaft systems are generally prone to instability because of the fluid film whirl, and the amplitude of shaft whirl tends to be large. When the amplitude is large, the RD fluid force cannot be linearized around the equilibrium point using RD coefficients. Therefore, destabilization and stabilization phenomena that appear in vertical shaft systems cannot be predicted by eigenvalue analysis. To predict such phenomena, Fluid-Structure Interaction (FSI) analysis is required, which considers the interaction between the shaft vibration and the RD fluid force generated in seals. This study used FSI analysis to investigate the effects of unbalance and differential pressure on the stability of a vertical shaft system subjected to RD fluid force generated in the seal.

Deep-sea fishing vessel No. 501 Oryong was fully flooded through its openings and sunk to the bottom of the sea due to the very rough sea weather on the way of evasion after a fishing operation in the Bearing Sea. As a result, many crew members died and/or were missing. In this study, a full-scale ship flooding⋅sinking simulation was conducted, and the sinking process was analyzed for the precise and scientific investigation of the sinking accident using highly advanced Modeling & Simulation (M&S) system of Fluid-Structure Interaction (FSI) analysis technique. To objectively secure the weather and sea states during the sinking accident in the Bering Sea, time-based wind and wave simulation at the region of the sinking accident was carried out and analyzed, and the weather and sea states were realized by simulating the irregular strong wave and wind spectrums. Simulation scenarios were developed and full-scale ship and fluid (air & seawater) modeling was performed for the flooding⋅sinking simulation, by investigating the hull form, structural arrangement & weight distribution, and exterior inflow openings and interior flooding paths through its drawings, and by estimating the main tank capacities and their loading status. It was confirmed that the flooding and sinking accident was slightly different from a general capsize and sinking accident according to the simple loss of stability.

The coastal transition zone and adjacent continental shelf of the Iberian upwelling system was studied in September 1986, during the seasonal transition from upwelling-favored to downwellingfavored winds. The most striking features in the coastal transition zone were: (1) a poleward flow of high salinity Eastern North Atlantic Central Water (subtropical) off the Rias Baixas (Galician western coast); and (2) an anticyclonic eddy off Cape Ortega1 (Galician northern coast). Chemical and biological similarities between both structures, clearly different from the surrounding oceanic waters, suggest that the eddy was an isolated and aged parcel of water originating from the poleward flow. The continental shelf was characterized by: (1) outwelling of chlorophyll-rich waters from the four large coastal embayments (the “Rias Baixas”) in the western coast and; (2) an upwelling front off the northern coast. The coexistence of opposite hydrographic structures, as the poleward flow and the upwelling front, was the consequence of transitional wind conditions in September-October, and we hypothesized transitional conditions to be crucial for the development of the eddy. Both the poleward flow and the eddy precluded the shelf-edge exchange of microplankton populations developed over the shelf, leading to massive in situ sedimentation and subsequent nutrient mineralization over the shelf.

Existing research on interference effects predominantly focuses on rigid structures. However, studies based on rigid models tend to overlook the feedback of structural motions on the flow field, thus failing to capture the intrinsic dynamics of the interference effect induced by wind-induced structural vibrations. This paper provides a comprehensive analysis of the fluid–structure interaction mechanisms considering interference effects involving two parallel square prisms, employing large-eddy simulation (LES). Various factors, including wind speed, arrangement, and vibration amplitude, are meticulously considered in the analysis. The study utilized three-dimensional LES simulations, incorporating the narrowband synthesis random flow generator method for inlet turbulence generation and adjusted through the “feedback” approach to ensure accuracy and efficiency. The research highlighted different structural arrangements exhibited distinct interference effects, and the end effect of the structure could substantially modify the flow pattern at various heights. In the tandem arrangements, the study observed several flow phenomena, including early reattachment, attenuation of the end effect, premature formation of roll structures, increased turbulence in the flow field due to vibration, resulting in wider second leading-edge separation, and a fragmented wake flow on the downstream structure. For side-by-side arrangements, the “acceleration effect” was identified and found to be further intensified by structural vibrations. The vibration of the interfering structure was noted to cause changes in vortex shedding frequencies and alterations in the wake flow pattern. In addition, vibration would enhance the interference effect but increasing amplitude and wind speed might diminish the interference effect. Overall, this study offers valuable insight into the intricate interplay of factors influencing the aerodynamics of parallel structures across diverse arrangements and under varying conditions.

This article concerns the development of energy‐based variational formulations and their corresponding finite element–boundary element Rayleigh–Ritz approximations for solving the time‐harmonic vibration and scattering problem of an inhomogeneous penetrable fluid or solid object immersed in a compressible, inviscid, homogeneous fluid. The resulting coupled finite element and boundary integral methods (FEM‐BEM) have the following attractive features: (1) Separate direct and complementary variational principles lead naturally to several alternative structure variable and fluid variable methodologies. (2) The solution in the exterior region is represented by a combined single‐ and double‐layer potential which ensures the validity of the methods for all wave numbers; even though this representation introduces hypersingular integrals, for actual computations the hypersingular operator may be rewritten in terms of single‐layer potentials, which can be integrated by standard techniques. (3) Since the discretized equations for the interior region and for the boundary are derived from the first variation of bilinear functionals the resulting algebraic systems of equations are always symmetric. In addition, the transition conditions across the interface are natural. This allows one to approximate the solutions within the interior and exterior regions independently, without imposing any boundary constraints.

To understand the governing mechanisms of bio-inspired swimming has always been challenging due to intense interactions between flexible bodies of natural aquatic species and water around them. Advanced modal decomposition techniques provide us with tools to develop more in-depth understating about these complex dynamical systems. In this paper, we employ proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) techniques to extract energetically strongest spatio-temporal orthonormal components of complex kinematics of a Crevalle jack (Caranx hippos) fish. Then, we present a computational framework for handling fluid–structure interaction related problems in order to investigate their contributions towards the overall dynamics of highly nonlinear systems. We find that the undulating motion of this fish can be described by only two standing-wave like spatially orthonormal modes. Constructing the data set from our numerical simulations for flows over the membranous caudal fin of the jack fish, our modal analyses reveal that only the first few modes receive energy from both the fluid and structure, but the contribution of the structure in the remaining modes is minimal. For the viscous and transitional flow conditions considered here, both spatially and temporally orthonormal modes show strikingly similar coherent flow structures. Our investigations are expected to assist in developing data-driven reduced-order mathematical models to examine the dynamics of bio-inspired swimming robots and develop new and effective control strategies to bring their performance closer to real fish species.

The study investigates the phenomenon of vortex-induced vibration (VIV) using Large Eddy Simulation (LES) at a Reynolds number of 1000, focusing on transitional flow conditions. LES has proven effective in understanding VIV across Reynolds number regimes, aiding in comprehending flow physics and mechanisms behind VIV. The research aims to contribute data for validating numerical models and informing engineering practices. The study employs the Navier-Stokes equation and the continuity equation to analyze fluid flow, treating it as incompressible due to negligible density changes. The three-dimensional incompressible momentum equation is discretized using the finite volume method within the spatial domain. Resolution of the pressure Poisson equation ensures compliance with free divergence conditions, enhancing computational fluid dynamics simulations' reliability. Validation of the fluid flow solver involves comparing computed drag force coefficients with established benchmarks, showing agreement within small discrepancies. The study delves into vibration behavior induced by cross flow at various reduced velocities (), noting distinct patterns ranging from irregularities at low to quasi-periodic behavior at higher values. Analysis of maximum cylinder displacement () across different reduced velocities and mass ratios underscores the complex relationship between system parameters and displacement dynamics. A consistent occurrence of y_max at a specific reduced velocity highlights its significance, while varying mass ratios affect displacement patterns, indicating the importance of understanding these dynamics for optimizing fluid-structure interaction systems.

Wind-assisted ship propulsion systems, such as rigid wingsails, are a promising means to reduce greenhouse gas emissions from shipping. This study uses quasistatic finite element analysis to simulate the structural responses of a crescent-shaped wingsail rig. A few conceptual designs for telescopic rigs are compared, ranging from a rig with a central mast to a mastless rig. The rigs are assessed against three criteria regarding their displacement, strength, and weight. External wind loads are applied to the sails based on the results of aerodynamic simulations in prior studies. The advantages and disadvantages of each concept are discussed, with the aim of providing a strategy for the structural design and arrangement of wind-assisted ship propulsion systems. The results of the study could be used in future work as a basis for structural optimization and fluid–structure interaction analysis.

In this paper we conduct study on flow-induced vibration of large-span upwelling radial steel Gate and its hydraulic hoist. Place an emphasis on vibration response characteristics under two working conditions of diversion and drainage, which proves the safety of hydraulic hoist gate vibration caused by gate vibration. Firstly, we study on dynamic characteristics of fluid-structure interaction of association system of gate and start and stop lever, reveals the discipline of the effect fluid having on structural dynamic characteristics. On this basis, flow-induced vibration characteristics under two conditions of with and without start and stop lever action considered. The results indicate that the gate vibration response with hydraulic hoist used decreases, which explains start and stop lever has certain effect of restraining vibration on gate vibration. In addition, under the working condition of drainage the vibration magnitude of start and stop lever is smaller than that of gate body, which explains there is damping action during transference of gate vibration through start and stop lever. The results find out that on the assumption of optimized gate structure and hydraulic arrangement, it is practicable, safe and reliable to adopt hydraulic hoist. The achievement has directive significance on similar projects construction in the future

Existing statistics for use in ship damage stability assessment are based on either accident investigation reports or empirical crew records. This is the reason why the databases used within the context of ship design for safety are either incomplete or miss critical information. This paper introduces a methodology for the probabilistic evaluation of passenger ship damage extents. The model accounts for the influence of crashworthiness in real operational conditions. Based on operational statistical records for ships before grounding, a Monte Carlo simulation is utilized to randomly generate a realistic profile that accounts for variable ship speed, conical rock geometry, rock position, and height in both deep and shallow waters. Subsequently, using the operational parameters as input, a six degrees of freedom fluid–structure interaction (FSI) model is used to combine the influence of ship dynamics, and structural mechanics on the probability distributions of hull breaches. Ship damage stability evaluation is carried out using NAPA software, which measures ship survivability via an attained subdivision index. Probabilistic results are compared against existing distributions of damage extents and demonstrate an increase in the mean distribution of damage length. The findings demonstrate the method's adequacy for improving passenger vessel safety in case of ship grounding. It is concluded that the method allows for low-fidelity optimization of the structural arrangement of the bottom of the ship, probabilistic evaluation of loads associated with ship crashworthiness, and the assessment of operational limitations during an evasive maneuver. It could therefore be used for the future development of ship damage stability standards or ad - hoc forensic investigations.

As a generalization considering small fluid-structural vibrations, the present paper examines the finite amplitude oscillatory motion of an elastically suspended rigid cylinder in an annular volume. The study is rather restricted in the sense that the free transverse planar vibrations of the body immersed in an incompressible and inviscid fluid are considered. The model describing the fluid-structure interaction consists of an equation of motion of the vibrating cylinder (an ordinary differential equation) obtained from the dynamic transition condition, and a dynamic partial differential equation governing the stream function. The second equation is obtained from the two Eulerian equations of momentum describing the motion of the fluid particles using the stream function representation of the planar velocities. A modal expansion in terms of appropriate shape functions is suggested for the stream function to compute an approximation for the associated natural frequency which depends in a characteristic manner on the magnitude of the fluid-structural vibrations. Results of a one-term truncation are presented so that this relationship can be evaluated in an analytical form.

Fluid-structure interaction (FSI) simulations of high-pressure multiphase CO2 flow in 2-inch piping were performed to predict flow-induced piping vibration and stress. Computational fluid dynamics (CFD) was used to predict the unsteady multiphase flow in the piping and the flow-induced forces on the bends. A structural finite element model of the 2-inch piping system was loaded with the CFD-predicted flow-induced loading to predict piping vibration and stress in time domain. A one-way FSI simulation approach was adopted, where the flow interacts with the structure, but it is assumed that the vibration of the structure does not affect the flow field. The 2-inch piping system is a high-pressure flow loop where piping vibration and stress were measured for a range of CO2 multiphase flow conditions in a test campaign aiming to characterize piping vibration responses with CO2 as the working fluid. The numerically predicted piping vibration and stress are compared against physical measurements collected during the test campaign at locations where accelerometers and strain gauges were installed. The selected flow conditions are for CO2 in gas and liquid phases with operation at a phase transition condition of 55 bara and 18°C. Simulations are performed for three flow conditions with increasing gas rate and fixed liquid rate, resulting in flows with decreasing liquid content by volume: 12.5%, 8.85%, and 6.73%. We find good agreement when comparing the predicted vibration levels against those measured by the accelerometers and find that the predicted stress is conservative relative to the stress measured by the strain gauges. The results validate the FSI predictions and instill confidence in the simulation approach, which is recognized as a powerful tool to predict flow-induced vibration of piping in multiphase systems.

An ABAQUS finite element analysis (FEA) of the main strut of a foiling Moth high-performance sailing dinghy has been developed and validated experimentally with full-scale mechanical tests representative of the sailing condition. Agreement between experimental and numerical results was excellent, solely by using engineering-based choices for both the internal structural arrangement and the pertinent experimentally based library material properties, i.e., without the need for ‘calibration’ of the model parameters. This gives a high level of confidence in the validation of the FE model. The FE model is the first stage of the ongoing development of a full fluid-structure interaction (FSI) tool, which will be obtained by combining the FEA with a computational fluid dynamics (CFD) model. This FSI will be a valuable and economic tool in facilitating evaluations of different foil appendage lay-up and fabrication methods designed to optimize the sailing performance.