Hydrodynamic Analysis Research Articles

Pathogenesis of Pachyvein Formation in Central Serous Chorioretinopathy: A Hydrodynamic Analysis.

Objectives: To attain an understanding of pachyvein formation seen with central serous chorioretinopathy (CSC) by measuring the choroidal blood flow (CBF) velocity and to apply the findings to existing hydrodynamic theorems. Methods: Nineteen subjects with monocular CSC (mean age 51.8 ± 12.7 years) were included. Laser speckle flowgraphy measured the mean blur rate (MBR) in the foveal and perifoveal regions, and the findings were applied to the Equation of Continuity (Q = AV) and Bernoulli's theorem (1/2V2 + P/ρ = constant). Results: The mean foveal/perifoveal MBRs in the CSC eyes were 6.4 ± 3.2/9.6 ± 3.2 (p < 0.001). The mean MBRs in the non-CSC eyes were 8.3 ± 3.2/7.9 ± 2.4 (p = 0.37). The significant foveal CBF velocity decrease in CSC eyes occurs because of exudation from the hyperpermeable choriocapillaris. The subsequent decrease in blood volume due to the exudation elicits a decrease in the blood flow velocity in the inferior venules in accordance with the Equation of Continuity. The decrease in the blood flow velocity may result in an elevated blood flow pressure in the inferior venules and veins at the exudation site, in accordance with Bernoulli's theorem. Conclusion: A significant decrease in the foveal MBR may result from exudation from the hyperpermeable macular choriocapillaris. This decreased velocity may elicit a blood pressure elevation that can expand the inferior venules and veins at the exudation site, so-called pachyvein and pachychoroid formation. The application of hydrodynamic theorems to the measurement of ocular blood flow can provide new insights into the understanding of the pathogenesis of chorioretinal disease.

Global Stability and Forced Response Analysis of Swirling Flows In Aviation Combustors

Abstract Swirling jets are canonical flow fields used to stabilize flames in many gas turbine combustion systems. These flows amplify background acoustic disturbances and perturb the flame, producing combustion noise and potentially combustion instabilities. Hydrodynamic flow response to acoustic excitations in reacting flows is an important modeling task for understanding combustion noise and combustion instabilities. This study utilizes a global hydrodynamic stability analysis in a Bi-Global and Tri-Global framework to model the vortical hydrodynamic modes of a reacting, swirling LES mean flow based on a commercial nozzle. After conducting an unforced, natural Bi-Global stability analysis to study the unstable eigenmodes of the flow, linearized equations of motion are used to study flow response of the flow to forcing. An empirical velocity transfer function is constructed by determining the flow response to a harmonically varying 150-1500 Hz u' velocity disturbance at the inflow boundary. These disturbances are strongly amplified, with amplification factors ranging from about 20 to 50 and peaking at about 1050 Hz, or st = 0.375. A comparison study with a cartesian, three-dimensional reacting base flow is also performed where the base-flow varies spatially in three-dimensions. The study utilizes a stable, high accuracy, but computationally effective centered finite difference scheme based on a three-dimensional structured mesh. Illustrative results present the qualitative modes and quantitative transfer functions for Bi-Global and Tri-Global stability analyses.

Hydrodynamic Analysis and Drag-Reduction Design of an Unmanned Underwater Vehicle Based on Computational Fluid Dynamics

Hydrodynamic Analysis and Drag-Reduction Design of an Unmanned Underwater Vehicle Based on Computational Fluid Dynamics

Exploring an Electrochemical Batch Reactor for Nutrient Recovery from Wastewater: Continuum Modeling Analysis of Hydrodynamics and Tertiary Current Distribution

Advancing electrochemical reactors for nutrient recovery from wastewater requires an integration of continuum modeling alongside experimental investigations to appropriately capture transport effects on electrode performance. This continuum modeling approach facilitates the comprehensive evaluation and optimization of electrochemical reactor performance, especially with respect to intricate phenomena that may be challenging to observe solely through experimentation. The optimization process not only enhances the efficacy of existing batch reactors but also lays the foundation for designing and scaling up continuous electrochemical reactors for nutrient recovery [1].A key transport phenomenon in electrochemistry is hydrodynamics because flow dynamics around electrodes dictate mass transport magnitude and uniformity, thereby impacting current distribution, efficiency, and electrolytic energy consumption during electrolysis. Achieving homogeneous velocity fields while avoiding undesirable flow features is essential to prevent non-uniform potential and current density distributions along the electrodes, mitigating side reactions and ensuring the overall efficacy of the electrochemical processes [2].In this study, a two-dimensional model of an electrochemical batch reactor was developed using COMSOL Multiphysics software to investigate reactor hydrodynamics, electrochemical reactions, and mass transfer of species. Employing the finite element method, the model incorporated the k-epsilon turbulence model for hydrodynamics simulation, widely used in literature for simulating fluid flow and mixing behavior [3]. Electrochemical reactions at the cathode (oxygen reduction) were modeled using the Butler-Volmer equation, while the Tafel equation was applied at the anode (hydrogen evolution). Boundary conditions were a grounded counter electrode (anode) and a potential of -1.1 vs Ag/AgCl(sat.) applied to the working electrode (cathode). Fick's second law diffusion-convective equation was employed to model the mass transfer of species, including hydroxide and oxygen.Preliminary findings indicate that while impellers contribute to turbulence and affect local conditions around electrodes, the impact on the backside of the modeled electrodes is relatively weak (Figure 1). This observation may adversely influence mass transfer rates and electrochemical reactions, underscoring the significance of integrating these results with electrochemical reactions for a comprehensive understanding of reactor behavior. Additional results will be presented at the meeting.

Analysis of thermo-hydraulic flow and optimisation heat augmentation in 3D dimpled pipe based on design of experiment method and Taguchi technique evaluation

In this work, the numerical analysis concentrates on investigating thermal flow patterns, pressure drops, varying velocity components and heat transfer behaviour. Impacts of four parameters on the enhancement of thermohydraulic performance are carried out using three-dimensional calculations employing CFD techniques: different spacing, diameter, number and distance for dimples were investigated. Additionally, utilising a design of experiments (DoE) strategy together with the Taguchi technique (TT) and response surface methodology (RSM), the impacts of the factors listed below are optimised. The results indicated that the different flow fields and heat transfer patterns were because of the use of depressions on the tube's inner surface. A comprehensive flow investigation with the dimple and tube wall was established to explain the mechanism of pressure drop and heat transfer change. The results of orthogonal experiments show that the optimal design of the spiral tube in this investigation using computational fluid dynamics using DoE, RSM and TT has a temperature difference and heat transfer coefficient of about 35.75% and 36.1% higher improved pipes. The results show a high PEF value greater than 1. According to the above results, various design applications require flow hydrodynamic analysis and heat performance enhancement.

Hydrodynamic performance analysis of dual vertical axis turbine

Abstract This article adopts a biomimetic approach and uses the profile of the fastest sailfish in the ocean as the airfoil profile of a water turbine. Integrating centrifugal and axial flow turbines on one drive shaft can effectively integrate wave and current energy (wave current integration). The wake of a centrifugal turbine flows into the flow field of an axial flow turbine, and based on the Kantar effect, the energy harvesting coefficient of the axial flow turbine is improved. The five blades of the axial flow turbine and centrifugal turbine are subjected to uneven forces, resulting in torsional and radial forces on the drive shaft, causing periodic series motion of the turbine and reducing the overall lifespan of the machine.

Hydrodynamic lubrication analysis of curved conductive liquid conducting film at rail-armature interface

Hydrodynamic lubrication analysis of curved conductive liquid conducting film at rail-armature interface

Investigation of thermal performance at forced convection in plate-fin heat sink

Interest in studies on more effective and faster heat dissipation in microelectronic equipment has increased in recent years due to the cooling area and equipment size limitations. This study attempts to focus on the effect of different fin geometry parameters on pure forced convection heat transfer. Total surface areas of plate-fin heat sinks were kept constant and were carried out for ten different heat sinks in these analyses. The Ansys-Fluent 2023 R1 commercial package program was used to perform the thermal and hydrodynamic performance analyses. Three-dimensional turbulent forced convection heat transfer analyses at heat sinks were subjected to fluid flow (500≤Re≤3000). The effects of gap between fins, fin thickness, fin height, fin number, and air velocity on the heat transfer and the friction factor were obtained and discussed for heat sinks. It was observed that there was a maximum difference of 0.27 % between the maximum temperatures obtained as a result of this analysis and the experimental study results in the literature. Among the ten cases examined (from Case 1 to Case 10), the highest heat transfer coefficient was obtained in Case 2 (number of fins 6, gap between fins 4 mm, fin height 17 mm and fin thickness 2 mm) at Re = 3000. The heat transfer coefficient of Case 2 was 41.29 % higher than the heat transfer coefficient of Case 4 at Re = 3000; though, the friction factor of Case 2 is 55.93 % higher than Case 4. Also, a useful correlation for the heat transfer coefficient was generated for the fin geometric parameters and Reynolds number.

Power engineering of the tangential supply device of the microturbine of the thermal control system of a promising spacecraft

This paper presents an overview of the current technical problem related to two-phase spacecraft thermal control systems and possible technical applications of thermal energy recovery in the organic Rankine cycle as an integral part of thermal management systems. The design solution involves the integration of a steam microturbine behind an evaporator radiator. The microturbine is a tangential supply device and a radially centripetal impeller of low speed nst40. In this area, there is no reliable data on the design and energy of both the supply device and the impeller. The energy (loss of enthalpy) of the supply device mainly determines the transport of the swirling flow to the impeller and, as a result, the circumferential operation on the turbine. A prototype of a radial microturbine has been developed and presented in order to evaluate the design of the flow part of both the supply device and the impeller. As a result of the analysis, the main determining hydrodynamic areas necessary for hydrodynamic analysis and mathematical elaboration of the flow calculation algorithm with an assessment of energy losses are identified: the flow of a swirling flow of a radial-annular slit; axial-annular slit and tangential supply device. The first two algorithms assume computational modeling, the model of energy losses in a tangential supply device is not amenable to analytical modeling because it includes a sequence (or compatibility) of flows under boundary conditions defined as “local resistances”: the sudden expansion, reversal of the flow, together with a section of radially circumferential flow, the mutual influence of these boundary conditions assumes only an expe rimental assessment of energy losses in a tangential supply device through the loss coefficient of local resistance in the range of changes in geometric and operating parameters. As a result of experimental studies, a database has been proposed on the loss coefficient of tangential microturbine supply devices in the field of the practical range of the existence of operating and design parameters.

TensorFlow Hydrodynamics Analysis for Ly-[formula omitted] Simulations

We introduce the Python program THALAS (TensorFlow Hydrodynamics Analysis for Lyman-Alpha Simulations), which maps baryon fields (baryon density, temperature, and velocity) to Lyα optical depth fields in both real space and redshift space. Unlike previous Lyα codes, THALAS is fully differentiable, enabling a wide variety of potential applications for general analysis of hydrodynamical simulations and cosmological inference. To demonstrate THALAS’s capabilities, we apply it to the Lyα forest inversion problem: given a Lyα optical depth field, we reconstruct the corresponding real-space dark matter density field. Such applications are relevant to both cosmological and three-dimensional tomographic analyses of Lyman Alpha forest data.

Verification and validation of a coupled CFD–FEM approach with overset structured grid through free decay and regular wave tests

This paper presents a comprehensive verification and validation study applied to the hydrodynamic analysis of a semi-submersible Floating Offshore Wind Turbine (FOWT) platform. The numerical simulation is conducted using a coupled Computational Fluid Dynamics-Finite Element Method (CFD–FEM) approach. The CFD program incorporates an overset grid interpolation method, facilitating a more systematic grid refinement in the estimation of discretization uncertainties. A mooring analysis program, based on the FEM scheme, is integrated with the CFD program to simulate the dynamic responses of mooring system. The necessity of the nonlinear mooring model is demonstrated by comparing solutions with a comparative test using a linear mooring model. The verification study, based on a least-squares-based extrapolation method, quantifies the spatial and temporal discretization errors of the numerical model. The numerical solutions based on the baseline model are further validated against the model test measurements. A pitch free decay model test and a regular wave model test conducted within the OC5 project are utilized for the verification and validation study. Results from both tests demonstrate the reliability and accuracy of the coupled method.

Hydrodynamic performance analysis and diving trajectory prediction of a novel deep-sea lander with flapping hydrofoils

Traditional deep-sea landers lack maneuverability during the diving process, making it difficult to effectively regulate the diving trajectory and velocity. In this paper, a novel deep-sea lander with flapping hydrofoils is proposed, and the simplified geometric model and typical flapping modes are introduced. Through computational fluid dynamics (CFD) simulation, the effectiveness of the flapping hydrofoils in regulating the diving trajectory and velocity of the lander is verified, and the influence of the amplitude of flapping angle and flapping frequency of the hydrofoils on the maneuverability of the lander and the propulsion efficiency and deceleration ratio of the flapping hydrofoil is explored. The relationship between the thrust generated by flapping hydrofoils and the maneuverability of the lander, as well as the relationship between the vortex topology and the propulsion efficiency and deceleration ratio of the hydrofoil are explained, respectively. And the diving trajectory of the lander is predicted based on Gaussian process (GP). The results show that the lander can have a certain degree of maneuverability through flapping hydrofoils, and the prediction error of the diving trajectory is within 4%. This paper provides reference for the design and application of the novel deep-sea lander with flapping hydrofoils.

Integrated hydrodynamic-structural analysis of flexible floating structures

This paper presents a comprehensive approach for the linearized frequency-domain analysis of hydrodynamic loading and structural responses on a deformable body. The structural and hydrodynamic analyses are integrated by employing the mode superposition method. Commencing with an eigenvalue analysis on the structural model, the shapes of selected modes, mass, and structural stiffness matrices are extracted as input to the subsequent hydrodynamic analysis, where the global response is solved in the modal space. The resulting hydrodynamic and inertial loads are then transferred to the same finite element model for stress assessment. To exemplify the proposed methodology, a bottom-fixed flexible cylindrical monopile and a long box-shaped barge model are investigated. For the barge model, the sectional loads are obtained from the integral of stresses in the cuts along the structure model, which are found to be consistent with those from the hydrodynamic analysis, demonstrating the consistency of the entire workflow. In particular, this paper introduces a straightforward formulation for evaluating the generalized restoring matrices, eliminating the need for spatial derivatives of the mode shape function and thereby significantly reducing numerical uncertainties in using the flexible modes derived from finite element model for hydrodynamic analysis.

Hydrodynamic analysis of three-module semi-submersible platform and its mooring design

The floating platform consisting of three interconnected semi-submersible modules deployed in shallow water with severe environmental conditions will be subject to very high environmental loads during storms and its position keeping will become a huge challenge. Therefore, it is important to investigate the hydrodynamic characteristics of the platform and design a robust mooring system to meet different demands during the service period of the platform. In this study, the hydrodynamic and motion analyses of the three-module semi-submersible platform were conducted by using both numerical simulation and experimental tests. In addition, a distinctive X-shaped mooring system was designed, which is characterized by relatively low stiffness in the direction of beam sea in which the environmental loads are the highest, and better load sharing among different mooring lines so that the extreme tension is curbed. Model tests were performed in a wave basin to acquire the platform motions and mooring tensions, and comparisons were made between the measurements and numerical predictions. The results of the study verify the feasibility of the three-module connected platform and its mooring system.

Efficient modelling of thermo-hydrodynamic properties in lubricated technical systems using NURBS-based isogeometric analysis

Wet grinding is a process that involves many different subprocesses. In order to model this highly complex process, efficient models of the individual subprocesses are required that are robust enough to be used in multiphysics analyses. To approach the modelling of the macroscopic hydrodynamic effects of the grinding wheel as one component of the analysis, this paper is dedicated to the thermo-hydrodynamic problem and its modelling by expanding the isogeometric analysis (IGA) from hydrodynamic analysis to the thermal consideration. Extended by a consideration of flow effects in areas with high surface gradients and particular attention paid to the necessary stabilization of the governing equations, thermo-hydrodynamic systems with temperature- and pressure-dependent fluid properties are considered. Selected benchmarks feasible for computational fluid dynamics (CFD) simulations are used to demonstrate the good suitability of this modelling strategy. The presented modelling strategies can also be applied to lubricated technical systems in general, beyond wet grinding systems.

The hydrodynamic pressure analysis and simplified calculation method of added mass of oscillating horizontal cylinder in finite water depth

Based on the potential flow theory, the hydrodynamic pressure governing equation of an incompressible and ideal fluid acting on a single oscillating horizontal cylinder in finite water depth is derived, solved using the variable separation method. Analytical solutions for the hydrodynamic pressure of the oscillating horizontal cylinder in both sway and heave directions are established via the multipole expansion method and verified against numerical solutions. Using these analytical solutions, the hydrodynamic pressure distributions of the horizontal cylinder under sway and heave motions, varying with dimensionless parameters immersion ratio H (H=h0/h) and diameter-depth ratio L (L=2a/h), are studied. It is found that at the distance of the cylinder from the free surface and seabed is the key factor influencing hydrodynamic pressure distribution. Additionally, the added mass was calculated through integration of hydrodynamic pressure, and the variation of added mass coefficients with L‾ (L‾=2a/h0) and H‾(H‾=2a/(h−h0)) is analyzed. It is observed that, in both sway and heave motions, added mass coefficients increase with decreasing L‾ and increasing H‾. Simplified calculation formulas for added mass coefficients of the horizontal cylinder under sway and heave motions are developed using a two-step fitting method. Finally, errors in calculating the added mass coefficients are compared between the simplified calculation formulas and the analytical solution, showing errors of less than 5%, indicating high accuracy of the proposed simplified calculation formulas for added mass coefficients.

MFIX–DEM simulation of gas-solid flow dynamics in a dual fluidized bed system

Abstract To overcome the operational difficulties associated with bubbling and circulating fluidized bed gasifiers, a new gasification technology termed dual fluidized bed gasification (DFBG) has evolved. To strengthen the understanding of the gasification and combustion processes in the DFBG system, a thorough analysis of bed hydrodynamics is of paramount importance. Furthermore, the complexity of the hydrodynamics escalates while incorporating diverse fuels like biomass and coal, along with bed materials fluidized in a single reactor due to its nonlinearity and transience. As a result, the study of hydrodynamics in such a system is indispensable. The present study focuses on the discrete element model (DEM) simulation of the bed hydrodynamic behaviour within the gasifier of a DFBG system. The simulation was conducted using Multiphase Flow with Interphase eXchanges (MFiX) software. The influence of superficial velocity on the number of particles in a gasifier was analyzed using the 2-D discrete element model (DEM). In this numerical investigation, transient variation of pressure drop, axial and radial solid volume fraction, and particle velocity was evaluated, and the data were analyzed using the ParaView software. The simulation results of the gasifier indicated an increase in the bed pressure drop with the rise in inlet air velocity. The effective height of solid volume fraction also increased with the surge in superficial velocity. The solid velocity profile and streamlines were also investigated to understand its variation pertaining to the location within the fluidized bed.

Hydrodynamic performance analysis of swimming processes in self-propelled manta rays

To fill the research gap regarding the whole process (steady-state and nonsteady-state phases) of median and/or paired fin (MPF) mode swimming in underwater organisms, a two-degree-of-freedom self-propelled coupling method of motion and hydrodynamics based on user-defined functions of Fluent software was established, and numerical simulations were carried out for the startup, acceleration, and steady-state phases of manta rays. The interaction mechanism among the hydrodynamic characteristics, vortex evolution, and pressure distribution was investigated in the mentioned phases. We concluded that the negative pressure zone generated by the leading edge vortex and the shear layer contributes to thrust generation and changes in swimming velocity dominate the hydrodynamic characteristics by affecting the evolution of the shear layer and the leading edge vortex, with a 17.54% increase in forward average velocity in the fourth cycle compared to the third cycle and a consequent 9.5% increase in average thrust. In the end, the relationship between the formation of trailing edge vortex rings and changes in thrust was revealed. The vortex ring contributes to the increase in thrust, but the formation of the vortex ring comes at the cost of the loss of the leading edge vortex negative pressure zone, which greatly affects thrust, decreasing to 38.3% of its peak. The swimming mechanism revealed in this study provides a reference for the study of MPF-driven biodynamics and a new simulation strategy for the prediction of bionic navigator motions.

Hydrodynamic Analysis of Payload Bay Berthing for Underwater Vehicles

Hydrodynamic Analysis of Payload Bay Berthing for Underwater Vehicles

Hydrodynamic Analysis of Pipelines Transporting Capsule for Onshore Applications

Abstract— Rapid depletion of energy resources hasimmensely affected the cargo transportation industry.Efforts have been made to develop newer economic andenvironmental friendly modes for this purpose. Bulk solidscan be transported for long distances effectively in pipelines.Raw materials can be stored in spherical containers(commonly known as capsules) transported through thepipeline. For economical and efficient design of anytransportation mode, both the local flow characteristics andthe global performance parameters need to be investigated.Published literature is severely limited in establishing theeffects of local flow features on system characteristics ofHydraulic Capsule Pipelines (HCPs). The present study focuses on using a well-validatedComputational Fluid Dynamics (CFD) based solver tosimulate the unsteady turbulent flow of a sphericalcapsule as a simplified case in HCPs for onshoreapplications. A novel numerical model has beenemployed in the present study with the aid of thedynamic mesh technique for calculating the pressureand the velocity variations within such pipelines. Thenumerical model comprises a straight test section. Thenumerical model for capsule flow yields realisticresults for the global flow parameters as compared tothe experimental data from the test rig developed inthe present study. The influence of the carrying fluid(water) on the capsule has been verified by estimatingthe shear forces and the friction coefficient. Inaddition, novel models have been developed forpredicting the wet friction coefficient considering thestart-up effect in such systems.