Flow Incidence Angle Research Articles

Wind tunnel measurements of cross-ventilation flow in a realistic building geometry: Influence of building partitions and wind direction

Wind tunnel measurements have widely been used for validation of computational fluid dynamics simulations of natural ventilation airflows. However, the majority of such measurements employed simple generic single-zone buildings, while there is a lack of studies on realistic buildings including flow-critical geometrical features (e.g. internal partitions). To assess the effect of internal partitions at different incident flow angles (α = 0° and α = 30°), wind tunnel measurements of velocities in and around a cross-ventilated realistic residential building (with and without internal partition) were performed. Measurements were conducted at a geometric scale 1:40, using laser Doppler anemometry. Results indicate a large impact of the internal partition on indoor airflow distribution and resulting ventilation flow rates. For instance, for α = 0°, on the partitioned building side, regions of velocity increase (from ∼0 m/s to ∼80% of the outdoor reference velocity, Uref), but also regions of velocity decrease (from ∼50% of Uref to ∼0 m/s) were observed. The ventilation flow rate through the windows at the partitioned side decreased by 23% and 32%, respectively. For the partitioned building, a change from α = 0° to α = 30° resulted in regions of velocity increase from 0 m/s to ∼60% of Uref.

Obstacle arrangement can control flows through porous obstructions

Previous work suggests that the arrangement of elements in an obstruction may influence the bulk flow velocity through the obstruction, but the physical mechanisms for this influence are not yet clear. This is the motivation for this study, where direct numerical simulation is used to investigate flow through an array of cylinders at a resolution sufficient to observe interactions between wakes of individual elements. The arrangement is altered by varying the gap ratio $G/d$ (1.2 – 18, G is the distance between two adjacent cylinders, d is the cylinder diameter), array-to-element diameter ratio $D/d$ (3.6 – 200, D is the array diameter), and incident flow angle ( $0^{\circ} - 30^{\circ}$ ). Depending on the element arrangement, it is found that the average root-mean-square lift and drag coefficients can vary by an order of magnitude, whilst the average time-mean drag coefficient of individual cylinders ( $\overline{C_{d}}$ ), and the bulk velocity are found to vary by up to $50\,\%$ and a factor of 2, respectively. These arrangement effects are a consequence of the variation in flow and drag characteristics of individual cylinders within the array. The arrangement effects become most critical in the intermediate range of flow blockage parameter $\mathit{\Gamma_{D}^{\prime}} = 0.5-1.5$ ( $\mathit{\Gamma_{D}^{\prime}}=\overline{C_{d}}aD/(1-\phi)$ , where a is frontal element area per unit volume, and $\phi$ is solid volume fraction), due to the high variability in element-scale flow characteristics. Across the full range of arrangements modelled, it is confirmed that the bulk velocity is governed by flow blockage parameter but only if the drag coefficient incorporates arrangement effects. Using these results, this paper proposes a framework for describing and predicting flow through an array across a variety of arrangements.

Numerical Simulation Method for the Aeroelasticity of Flexible Wind Turbine Blades under Standstill Conditions

With the trend towards larger and lighter designs of wind turbines, blades are progressively being developed to have longer and more flexible configurations. Under standstill conditions, the separated flow induced by a wide range of incident flow angles can cause complex aerodynamic elastic phenomena on blades. However, classical momentum blade element theory methods show limited applicability at high angles of attack, leading to significant inaccuracies in wind turbine performance prediction. In this paper, the geometrically accurate beam theory and high-fidelity CFD method are combined to establish a bidirectional fluid–structure coupling model, which can be used for the prediction of the aeroelastic response of wind turbine blades and the analysis of fluid–structure coupling. Aeroelastic calculations are carried out for a single blade under different working conditions to analyze the influence of turbulence, gravity and other parameters on the aeroelastic response of the blade. The results show that the dominant frequency of the vibration deformation response in the edgewise direction is always the same as the first-order edgewise frequency of the blade when the incoming flow condition is changed. The loading of gravity will make the aeroelastic destabilization of the blade more significant, which indicates that the influence of gravity should be taken into account in the design of the aeroelasticity of the wind turbine. Increasing the turbulence intensity will change the dominant frequency of the vibration response in the edgewise direction, and at the same time, it will be beneficial to the stabilization of the aeroelasticity response.

Study of flow resistance coefficients acting on regular non-spherical particles in simple shear flow at moderate Reynolds numbers

This contribution is devoted to the study of the aerodynamic characteristics of non-spherical particles of definite regular shape, such as prolate and oblate ellipsoids as well as cylinders, immersed in a locally linear shear flow. The flow resistance coefficients of drag, lift and pitching torque are computed by means of the Particle Resolved Direct Numerical Simulation (PR-DNS) technique for such shapes as function of the Reynolds number Re. The parameter space comprises particle aspect ratio, AR, fluid spin ratio, ζ, and particle orientation angle, α. The Reynolds numbers of interest are in the intermediate range 1≤Re≤100, common in industrial and environmental processes. To properly understand and explain the obtained results, the role of the friction and pressure contributions to total flow coefficients is analyzed in detail for the different cases, allowing the differences between the considered shapes to be pointed out. On the other hand, the behavior of the pressure and skin friction coefficients in the particle plane of symmetry parallel to the flow is investigated as a function of the previous parameters (shape, AR, ζ, α), which provides further insights into the features of the shear flow around the non-spherical particles at finite Re. Finally, the influence of the shear flow magnitude and incidence angle on the location of the center of aerodynamic force is devised for the three shapes considered as function of Reynolds number and particle aspect ratio. It is expected that the information generated in this work will be useful for researchers to enhance the modeling of non-spherical particles immersed in non-uniform flows.

A non-parametric high-resolution prediction method for turbine blade profile loss based on deep learning

Obtaining the aerodynamic performance of the turbine blade by Computational Fluid Dynamics (CFD) methods is accurate. However, it consumes time and computational resources. This paper proposes an evaluation method based on Convolutional Neural Network (CNN) and Artificial Neural Network (ANN) to obtain the aerodynamic performance of the turbine blade accurately and quickly. Compared with the existing data-driven modeling methods, this method innovatively introduces the Residual Network (ResNet), employs a transfer learning strategy for network design, and realizes the automatic extraction of blade profile features and non-parametric input. In processing boundary conditions, the ANN is utilized to fuse the blade profile features with the boundary conditions to realize the mapping between blade profile and aerodynamic performance under different conditions. In addition, to minimize the prediction deviation caused by the severely uneven distribution of the data set, we combined ensemble learning with transfer learning and proposed a two-step prediction strategy. The numerical simulations results show that the ResNet-ANN model established in this paper has a prediction relative error of 5 % on turbine blade aerodynamic parameters under various working conditions. The error is reduced by more than 90 % under −40°-10° incidence angle of incoming flow compared with the empirical model.

Effect of permeable spacer structure on energy loss and mass transfer in reverse osmosis membrane modules

This study used numerical simulation to investigate the effects of a novel permeable cylindrical-flow distributor on energy loss and mass transfer in reverse osmosis (RO) membrane modules. The analysis focused on variables, such as Reynolds number, inlet concentration and flow incidence angle, influencing the improvement of water production efficiency in RO membranes and the reduction of concentration polarisation on the membrane surface. The membrane surface shear stress, vorticity, permeate flux and concentration polarisation factor were used to describe these effects. To better explain the performance of the permeable flow distributor, the viscous resistance coefficient (Du) in the porous media model was used to measure the permeability of the flow distributor. Furthermore, a produced water energy consumption factor (JCP) was defined to represent the energy required for unit water production. The results indicate that the permeable flow distributor significantly reduces pressure loss in the membrane channels, avoiding the high energy consumption associated with traditional flow distributors in RO processes. The Du exhibits an optimal value in the range of 1e8 to 1e10, which maximises the JCP, leading to a 32.9 % improvement compared to traditional impermeable flow distributors. This achievement enables energy-efficient and effective desalination of seawater.

Passive Flow Control for Centrifugal Compressors with Bents Intake Manifold

Centrifugal compressors installations often require bents conduits at the intake due to space constraints. The intake bent manifold creates flow distortion affecting unfavorably the global performance of the compressor. The degradation caused by the inadequate inlet conditions due to turbulence and inlet flow disturbance, which negatively affects the flowing fluid through the curved intake manifold. Hence, significant distortions, within presence of single or twin core vortices whirling off center of the impeller intake alter flow incidence angle and consequently the impeller circumferential energy. Furthermore, inadequate bends configurations generate higher incidence angles, which lead to boundary layer separation and stalling. This paper deals with a 3D numerical investigations of dual bends located upstream of the centrifugal compressor. Several bend setting positions at the compressor intake describing various sequences of intake piping are considered. As first results, specific positions of dual bends are identified for fewer flow disturbance at the impeller eye and stable outflow controlling the incidence angel in a passive mode. it is less cumbersome and cost effective compared to additional devices. For practical industrial prediction, this investigation contribute also toward a mathematical correlation to check the adequacy of intermediate manifold configuration in order to predict the corresponding incidence angle at the impeller intake of the centrifugal compressor for enhanced performance and instantaneous control.

Design and analysis of an axial turbine for high-temperature organic Rankine cycle

The organic Rankine cycle (ORC) system is of great importance to achieving the effective exploitation of waste energy. As the essential component of the ORC system, the expander is directly related to the performance and structure size of the ORC system, which deserves to be studied in detail. A single-stage axial turbine with a U-shaped volute is presented for the high-temperature ORC system in this paper. Based on preliminary design and modeling, the turbine aerodynamic performance under design and off-design conditions is investigated in numerical simulation. Results show that the turbine efficiency is 77% with a pressure ratio of 4.78 at the design point and the turbine efficiency can still be maintained above 70% as the pressure ratio reaches 6. It can be concluded that low Reynolds number flow and negative incidence angle are the main reasons for low turbine efficiency under the low pressure ratio, while the shock wave becomes the key factor influencing turbine efficiency under the high pressure ratio. In addition, blade profile optimization and shock wave management is the primary way to maintain high turbine efficiency under a high pressure ratio. Results indicate that the turbine proposed in this paper is proven suitable for high-temperature ORC systems and the relevant research has a certain guiding value for the efficient and compact single-stage axial turbine design.

Analysis of the Risk of Basilar Aneurysm Rupture Based on CTA Morphological Parameters

Objective: To investigate morphological risk factors of basilar aneurysm rupture based on computer tomography angiography (CTA) parameters. Materials and methods: The clinical and CTA data of 43 patients with basilar aneurysm admitted to Shaanxi Provincial People’s Hospital from January 2015 to July 2023 were analyzed. The patients were divided into “ruptured group” and “unruptured group,” and the morphological parameters of aneurysms were measured. The general data and morphological parameters between the two groups were statistically analyzed. Logistic regression was used to analyzed statistically significant parameters, and the receiver operating characteristic curve was drawn to evaluate its diagnostic effectiveness. Results: Irregular aneurysms were more likely to rupture than regular aneurysms (x² = 13.971, P < 0.05). The maximum diameter (4.92 [3.37–6.94] mm), length-width ratio (1.31 [1.14–1.55]), height (4.08 [2.71–5.34] mm), aspect ratio (0.99 [0.84–1.45]), and inflow angle (133.63 ± 11.21°) of aneurysms in the ruptured group were larger than the unruptured group, and the differences were statistically significant (P < 0.05). Binary logistic regression showedthat aneurysm shape (OR = 39.347, P = 0.021), length-width ratio (OR = 313.062, P = 0.033), and inflow angle (OR = 1.156, P = 0.004) were independent risk factors for rupture. The area under the curve were 0.809, 0.842. and 0.894, respectively. Conclusion: Aneurysm shape, aspect ratio, and blood flow incidence angle are independent risk factors for basilar aneurysm rupture, which means that they can be used to predict the risk of rupture to a certain extent.

Quantifying the Impacts of the Angle of Attack on the Morphology of Atmospheric von Kármán Vortex Streets

AbstractA mesoscale model is used to systematically investigate how the incoming flow incidence angle affects the development of atmospheric von Kármán vortex streets for non‐axisymmetric islands. The analysis is focused on an event observed on the leeward side of Guadalupe Island. By keeping the synoptic conditions the same, several simulations are performed for rotated orientations of the island topography, which correspond to a change in the angle of attack (AoA) relative to the upstream flow. The asymmetry of the vortex shedding and the role of the leading and trailing edge are in line with what was observed in laboratory von Kármán vortex streets past a flat plate. The eddies become larger with increasing AoA while the shedding frequency decreases, and the asymmetry between cyclonic and anticyclonic eddies weakens. Cyclonic vortices are more developed and stronger under typical conditions when they are shed from the trailing edge. We also demonstrate that the wake asymmetry is fundamentally between trailing‐edge and leading‐edge eddies rather than between cyclonic and anticyclonic eddies.

Mechanisms of coupled mode I-II fracture initiation in rocks subjected to heat flow-induced fracture gas-steam pressure and heat flow stress

The construction of tunnel projects in the Sichuan-Tibet region has led to the occurrence of rock fractures caused by high temperature and high humidity, which are inevitable challenges. When there is fracture water in rock fractures and it encounters a heat flow, the water vaporizes into fracture steam, which undergoes thermal expansion to generate fracture gas-steam pressure. The heat flow direction is at an angle to the crack, causing heat flow stress in the rock. To understand the mechanism of crack initiation and propagation in rocks under the joint action of uniform heat flow-induced fracture gas-steam pressure and heat flow stress, the control equation for fracture gas-steam pressure is derived and expressions for stress intensity factor, crack temperature field, stress field, and crack initiation strength criterion are established based on the theory of complex variable functions. The key parameters are analyzed and discussed, finding that under low heat flux density, small incidence angles, and large crack inclination angles, KI values are higher, and the crack initiation is mainly in tension. Under high heat flow density, large incidence angles, and crack inclination angles near 45°, KII values are higher, and the crack initiation is mainly in shear. The coupling effect of KI and KII is more sensitive to heat flow density and inclination angle. The critical initiation angle and initiation strength increase with the increase of heat flow density and incidence angle, with heat flow density being the determining factor.

Fluidelastic instability of a fuel rod bundle subjected to combined axial flow and jet cross-flow

Nuclear fuel bundles are subjected to axial coolant flow in addition to jet cross-flow in a specific design of pressurized water reactors (PWRs). The combined axial flow and jet cross-flow was found to induce fretting wear of the fuel rods at the spacer grid position. Investigating a reduced fuel rod bundle under jet in transverse flow (JITF) condition is necessary to determine safe vibration free operation conditions for these reactors.This paper presents an experimental and theoretical framework to understand the fluidelastic behavior of a rod bundle subjected to axial flow and localized jet cross-flow. A 6x5 axisymmetric flexible single-span rod bundle is used to simulate a part of a fuel assembly under combined flow. Two working flow conditions, pure axial flow, and JITF are studied on a mock-up PWR assembly. The experiments show that the arrays are stable under pure axial flow as expected. Then, the responses of the rod bundles under combined flows (i.e. JITF) are measured at three test axial flow velocities, VAxial= 1.0 m/s, 1.5 m/s, and 2.0 m/s. The results show that the critical jet cross-flow velocity increases linearly with the axial flow velocity with a velocity ratio (VR = VJet/VAxial) of 1.6.The second part of the work is the development of a fluidelastic instability model to predict the stability boundary for rod bundles under combined axial flow and jet cross-flow. The effect of axial flow on the jet cross-flow is introduced by implementing an incidence angle (θ) of jet flow with respect to the rods. The fluid-added damping terms in the developed model are shown to be functions of θ. The fluidelastic forces are expressed as functions of the projected rod area derivative to account for rod vibration. The stability analysis shows the capability of the model to predict the trend of critical jet cross-flow velocity with the axial flow velocity. The model validation shows the predicted critical velocities to be within an absolute error range from 7% to 12.5% when compared to experiments. The theoretical analysis highlights the importance of the cross-coupling fluidelastic forces in predicting the instability of the mock-up PWR assembly.

Effect of the flow incidence angle on the VIV-based energy harvesting from triple oscillating cylinders

The current article is a numerical investigation into the energy harvesting characteristics of the turbulent vortex-induced vibration (VIV) of three sprung circular cylinders located at the corners of a triangle with equal height and base. Five different flow incidence angles (θ=0,45,90,135,and180) are considered depends on how the cylinders are oriented. The Reynolds-averaged governing equations for the turbulent VIV around the cylinders are solved using the finite volume method while a two-way coupling exists between the structure and the fluid. In the triangular arrangements where some cylinders are located in the wake of others, wake-induced vibration (WIV) generally occurs with higher amplitude. Moreover, a comparison of different incidence angles shows that θ=45 is the best choice for energy harvesting with a total root mean square (RMS) of 5.82, followed by θ=0,and90 with a total RMS of 4.1. Also, the amount of harvested power in the θ=45 exhibits a significant growth (288%) compared to the total harvested power from the vibrations of three isolated cylinders.

Aerodynamics and Wake Flow Characteristics of a Four-Cylinder Cluster

The aerodynamic behaviour and wake flow of a cluster of two-dimensional sharp-edged bluff bodies exhibits extremely complex unsteady phenomena in both near and far fields. Due to the high cost of wind-tunnel experiments and numerical simulations, a complete understanding of wake flows and a description of their characteristics are lacking. This paper presents large-eddy simulations (LES) in different flow/wind directions for a cluster of 2 times 2 aligned square cylinders, at a separation distance in streamwise and cross-wind directions equal to cylinder side length, and at Reynolds number {Re}=22,000 based on the single cylinder side length D. The case at 0^circ incidence shows an evident channel-type flow in the along-wind street/gap, and at its exit an irregularly pulsing jet with an intense shedding of large vortices. The wavelet analyses of the side force/lift coefficient and instantaneous velocities in the wake show that the characteristic length and time scales of the large vortical structures in the far-field wake are close to the cluster size 2D; this is the so called ‘cluster effect’. The cluster effect increases monotonically as the flow incidence angle increases. At a large incidence angle in the near-field wake, the cylinder-scale flow structures are much weaker compared to the cluster-scale structures. At the incidence angle of 45^circ, the overall wake flow and the aerodynamic characteristics are well scaled by the scale approximately equal to 2D. Nevertheless, the interaction between cylinders significantly affects the aerodynamics performance of the individual cylinders. The drag and lift coefficients of the individual cylinders differ substantially from each other in the cluster, and are significantly different from observations on a single isolated cylinder too.

A bi-directional flow-energy harvester

Due to a rapid decrease in fossil fuel resources and ever-growing carbon emissions, clean energy is urgently needed as a vital solution. In the past two decades, harvesting clean energy from ambient environment has attracted much attention. Flow induced vibration and energy harvesting performance of a cylinder with fins attached were investigated. Four configurations were studied: a plain cylinder, a cylinder with two windward fins, a cylinder with two leeward fins, and a cylinder with four fins. These four cylinders were tested in a water channel with a reduced velocity ranging between 2 and 25 and a Reynolds number ranging between 1500 and 11 400. It was found that the two-windward-fin cylinder underwent galloping, exhibiting much larger vibration amplitudes and a much broader operational velocity range, whereas the two-leeward-fin cylinder only underwent weak vortex-induced vibrations. By attaching both two windward and two leeward fins to the cylinder, a bi-directional flow-energy harvester was implemented, which outperformed the plain cylinder with much larger vibration amplitudes and a much broader velocity range. More importantly, due to the geometric symmetry, it is able to harvest flow energy from two opposite directions. A tuned-mass-damper system was then attached to the four-fin cylinder for the purpose of demonstration. Within the current flow speed range, the maximal voltage and power outputs are about 7.37 V and 1.81 μW, respectively, about 2.7 and 7.2 times the plain cylinder's peak values. The effects of flow incident angle and fin length were also studied. Numerical simulations were also conducted to provide a detailed information of flow and pressure to uncover the underlying physics. This bi-directional flow-energy harvester is a suitable candidate to operate at sites where the flow periodically switches its directions, such as in tidal flows.

The effect of wind characteristics on tall buildings with porous double-skin façades

Wind loads on tall buildings with porous double-skin façade (PDSF) systems were studied for various wind characteristics. Experiments were performed on a small-scale building model in a boundary layer wind tunnel. A single-skin building model was used as a reference case alongside three PDSF systems of 25%, 50% and 65% porosity. Two atmospheric boundary layer (ABL) simulations were created corresponding to category I (rural) and category III (suburban) ABLs of the EN-1991-1-4:2005 standard. Wind loads on the building model were studied based on high-frequency force balance measurements of integral moments, while pressure distribution on the building model surfaces was analyzed based on pressure measurements. Experiments were performed for ten flow incidence angles 0° < α < 45° with a 5° increment. The obtained results are considered highly relevant both for research purposes and engineering applications, especially considering the lack of similar studies currently available. In particular, the rural ABL simulation yields larger mean pressure coefficients. The effect of the ABL characteristics on the pressure coefficient standard deviation depends substantially on α, while the most notable difference is observed on the windward building model surface at α = 0°, where the suburban ABL causes a substantially higher standard deviation. The mean across-wind moment coefficient of the suburban ABL simulation is lower at all α points, while its standard deviation is lower for α > 0°. The along-wind moment coefficient in the suburban ABL simulation is ∼20% lower than in the rural ABL simulation, a trend which is observed for all α points. In contrast, the along-wind moment standard deviation is ∼25% larger in the suburban ABL simulation. The power spectral density of the along-wind moment is considerably lower in the suburban ABL simulation.

Near-Stall Modelling of a Pitching Airfoil at High Incidence, Mach Number and Reduced Frequency

The prediction accuracy of aeroelastic stability in fans and compressors depends crucially on the accuracy of the underlying aerodynamic predictions. The prevalent approach in the field solves the unsteady Reynolds-averaged Navier—Stokes equations in the presence of blade vibration. Given the unsteady, three-dimensional and often separated nature of the flow in the regimes of aeroelastic interest, the confidence in URANS methods is questionable. This paper uses the simple test case of a pitching symmetric aerofoil with a sharp leading edge to illustrate the challenges of aeroelastic modelling. It compares coupled numerical simulations against time-resolved experimental measurements. The unsteady aerodynamic response of the pitching blade and its dependency on tip-clearance flow and time-averaged incidence angle are analyzed. The results indicate that differences in the unsteady aerodynamics between different numerical approaches close to stall can have a significant impact on local aerodynamic damping. Furthermore, for the chosen test case there is a strong correspondence between the local quasi-steady and unsteady behaviour which weakens, but is still present, towards stall.

Design and optimisation of a passive Atmosphere-Breathing Electric Propulsion (ABEP) intake

In order to extend the orbital lifetime of spacecraft operating in Very-Low Earth Orbit (VLEO), Atmosphere-Breathing Electric Propulsion (ABEP) can be employed for atmospheric drag compensation. The concept is based on the ingestion of rarefied atmospheric particles to be used as propellant for an electric thruster, thereby removing the need for onboard propellant. The present paper aims to design and analyse a passive ABEP intake optimised for the RF Helicon-based Plasma Thruster (IPT), which is selected as the most promising system due to its electrodeless design, as it removes the issue of thruster corrosion, and reduced susceptibility to atmospheric variations. This is achieved by implementing the analytical model, referred to as the Balancing Model (BM), along with its main performance parameters. The Direct Simulation Monte Carlo (DSMC) solver dsmcFoam+ is thus employed to simulate the transmission probability of cylinders and hexagonal prisms with non-zero entrance velocity, yielding a mean percentage error of 2% when compared to independent DSMC results. In addition, a novel DSMC transmittance investigation of square prisms is performed. Various design configurations are optimised for circular and hexagonal intakes based on the functional requirements of the thruster, leading to a maximum collection efficiency of 45% for a cylindrical intake with a hexagonal honeycomb. The optimal intake is hence simulated via DSMC, showing a good accuracy with the BM with or without intermolecular collisions, yielding a percentage error of 0.22% in the former case and 5.53% in the latter one. The variation of incidence flow angle, accommodation coefficient and thruster transmission probability is finally investigated, and the results are validated by the agreement shown with values retrieved from the literature.

A Flexible Flow Sensor for Detecting Airflow Velocity and Incident Angle

A flexible flow sensor is proposed to measure the airflow velocity and incident angle. The sensor consists of a polyimide (PI) substrate, a flat cantilever beam and a graphene piezoresistor. The cantilever beam deforms under the action of fluid-structure interaction (FSI), resulting in changes in the resistance of the graphene piezoresistor. The piezoresistor was prepared by spraying coating of graphene inks using a patterned parylene mask and then encapsulated by coating another polyimide layer to form a sandwiched structure. Experimental results indicate that the flow sensor has a wide detection range of flow velocity (0-30 m/s) and incident angle (0-25°), with a high resolution of 0.94 m/s and 0.23°, respectively. Compared with curved cantilever, the flat cantilever achieves higher sensitivity to the incident angle, and smaller disturbance to the flow field. The arrangement of the flow sensors on an airfoil is discussed for estimation of flight parameters.

Vortex-induced vibration of flexible riser transporting high-speed spiral flow in deep-sea mining

According to Hamilton's principle and a mechanical decomposition model proposed for high-speed spiral flow, vibration governing equations of flexible riser transporting high-speed spiral flow are developed for vortex-induced vibration (VIV) analysis for lifting pipe system in deep-sea mining. The classic van der Pol oscillator is used to simulate the dynamic characteristics of VIV. The governing equations are then discretized and solved by the finite element method and the Runge-Kuta method. Furthermore, dynamic characteristics of VIV of the flexible riser transporting straight flow and spiral flow are investigated and the effects of the spiral flow incidence velocity and angle controlled by the jet device on VIV responses are evaluated. Also, the VIV dynamics considering different damping ratios are examined. The results show that the rotational angular velocity of the spiral flow would amplify the mean deflection of the in-line (IL) direction, and the incidence velocity has a significant nonlinear effect on the dominant frequency of the riser, which would induce the high-order dominant vibration modes when the incidence velocity is large sufficiently. However, the incidence angle has relatively less effects on the VIV responses of flexible riser. Moreover, the locked interval of VIV is less influenced by damping ratio below 0.1.