Fluid Mechanics Research Articles

Stability analysis, model expansion method, and diverse chaos-detecting tools for the DSKP model

This paper talks about the -model expansion method for the Davey–Stewartson– Kadomtsev–Petviashvili (DSKP) model in (4 + 1) dimensions. This is useful for studying shallow-water waves, coastal engineering, fluid mechanics, and plasma physics. We use a variable relation to transform the model’s partial differential form into an ordinary one. Computational software then examines the resultant model using the previously outlined methods. Combining solutions for Jacobi elliptic, hyperbolic, and trigonometric forms yields novel dynamical optical solitons. We also employ a planar dynamical process to examine the governing model qualitatively. We also investigate stability analysis, bifurcation, and chaotic behavior with diverse chaos-identification tools. The study’s findings allow us to conclude that the approach is favorable, helpful, soothing, and suitable for handling a variety of nonlinear models.

Study on coupling model of reservoir seepage dynamic and horizontal wellbore flow

The dynamic seepage behavior of the reservoir near the wellbore directly affects oil well productivity, fluid properties, and pressure distribution in the wellbore. Accurately describing and understanding this area is crucial for making informed decisions on reservoir management and production optimization, making it one of the current research hotspots. To more accurately characterize the coupled flow behavior between the wellbore and the near-well reservoir, this study proposes a transient coupling prediction model for the wellbore-reservoir system in the completion section of a horizontal well, based on fluid mechanics and reservoir seepage theories. This model addresses the deficiencies of traditional models in describing the interaction of wellbore flow, completion dynamics, and reservoir seepage by explicitly depicting the dynamic interactions between the wellbore and the reservoir. The research results indicate: (1) For the annulus and wellbore, flow rate and pressure stabilize at approximately 100 s, during which complex flow direction information in the annulus is captured, revealing the early transient flow characteristics inside the wellbore. (2) For the reservoir seepage near the wellbore, a larger time interval is selected, and variations in pressure and flow rate are still observed within the 1-day to 10-day range. However, the changes in reservoir pressure and axial flow rate are relatively small, highlighting the spatial and temporal scale differences between the reservoir and wellbore simulations. This coupled model facilitates the evaluation of oil well performance parameters and, by incorporating the behavior of the reservoir near the wellbore, provides theoretical guidance and technical support for production optimization and reservoir management.

Two-layer formulation for long-runout turbidity currents: theory and bypass flow case

Turbidity currents, which are stratified, sediment-laden bottom flows in the ocean or lakes, can run out for hundreds or thousands of kilometres in submarine channels without losing their stratified structure. Here, we derive a layer-averaged, two-layer model for turbidity currents, specifically designed to capture long-runout. A number of previous models have captured runout of only tens of kilometres, beyond which thickening of the flows becomes excessive, and the models without a lateral overspill mechanism fail. In our framework, a lower layer containing nearly all the sediment is a faster, gravity-driven flow that propels an upper layer, where sediment concentration is nearly zero. The thickness of the lower layer is controlled by competition between interfacial water entrainment due to turbulent mixing and water detrainment due to sediment settling at the interface. The detrainment mechanism, first identified in experiments, is the key feature that prevents excessive thickening of the lower layer and allows long-runout. Under normal flow conditions, we obtain an exact solution to the two-layer formulation, revealing a constant velocity and a constant thickening rate in each of the two layers. Numerical simulations applied to gradually varied flows on both constant and exponentially declining bed slopes, with boundary conditions mimicking field observations, show that the predicted lower layer thickness after 200 km flow propagation compares with observed submarine channel depths, whereas previous models overestimate this thickness three- to fourfold. This formulation opens new avenues for modelling the fluid mechanics and morphodynamics of long-runout turbidity currents in the submarine setting.

Flow mechanisms of the air-blood barrier.

The air-blood barrier protects the lung from blood/serum entering the air spaces, i.e., from "drowning in your own fluids". Failure leads to pulmonary edema, a regularly fatal complication during the Covid-19 pandemic which claimed 7 million lives worldwide. Finding no mathematical models for the underlying fluid mechanics, we created the first. Governing flow equations for alveolar capillary, interstitium, and alveolus are coupled by crossflows at the capillary and epithelial membranes and end-exit flows to the lymphatics. Case examples include normal/recovery, cardiogenic pulmonary edema, acute respiratory distress syndrome, effects of positive end expiratory pressure, and a wide range of parameter values for permeability of the membranes and interstitial matrix. Previously unknown membrane fluid shear stresses calculate to values that affect cell function in many systems. We add active epithelial reabsorption which has two effects: shifting streamlines to favor alveolar-lymphatic clearance and adding to the direct alveolar-capillary clearance. Simple algebraic equations are derived for the interstitial fluid pressure, pi, membrane crossflow velocities and the critical capillary pressure, pcrit, above which edema occurs. For validation, the pcrit predictions fit clinical definitions and flow calculations of lymphatic vs capillary clearance match animal experimental data. For decades the value of pi has been imposed as an input, whereas we calculate the value as an output. They don't agree. Since the space is too small for measurements, the ability to calculate pi and pcrit offers new insights, questions long-held beliefs, and opens applications from physiological studies to personalized clinical care.

Stiffness and damping characteristics of highly accurate rock simulation system based on gas–liquid coupling mechanism under nonharmonic impact

To address the issue of the performance testing of hydraulic rock drills under specific working conditions, a stiffness–damping multi-stage adjustable rock simulation system has been proposed. Firstly, based on Kelvin rock theory, a rock vibration model under nonharmonic excitation is established. An integer-order model of the simulation system is created based on fluid mechanics theory. The stiffness–damping characteristics of granite and the system are studied, discussing the influencing factors of the stiffness–damping characteristics. Next, a drop hammer calibration experiment and an impact drilling experiment for the simulation system are designed. Finally, the stiffness–damping characteristics of the system in actual drilling are investigated, validating the effectiveness of the numerical model. Model simulations show that the smaller the stiffness of granite and the simulation system, the larger the drilling displacement. The larger the damping coefficient, the smaller the drilling displacement. Lower initial gas pressure and volume of the accumulator can provide greater stiffness. The greater the preload of the overflow valve and the cylinder diameter, the greater the damping produced. The experimental results show that the stiffness–damping error between the system and the granite does not exceed 10% with exceptionally high accuracy.

A new look at the controllability cost of linear evolution systems with a long gaze at localized data

We revisit the classical issue of the controllability/observability cost of linear first order evolution systems, starting with ODEs, before turning to some linear first order evolution PDEs in several space dimensions, including hyperbolic systems and pseudo-differential systems obtained by linearization in fluid mechanics. In particular we investigate the cost for localized initial data and, in the dispersive case, for initial data which are semiclassically microlocalized.

Investigation on the Chaotic Mixing Mechanism of High-Viscosity Fluids with Laminar Flow in an Irregular Impeller Stirred Tank

Investigation on the Chaotic Mixing Mechanism of High-Viscosity Fluids with Laminar Flow in an Irregular Impeller Stirred Tank

Analysis of Velocity for Different Density Using Different Height

This study investigates the relationship between velocity, density, and height in various fluid systems, providing a comprehensive analysis of how these factors interact under different conditions. The experiment involved measuring the velocity of fluids with varying densities as they flowed through channels of differing heights. Key principles such as fluid mechanics, Bernoulli's equation, and the continuity equation were applied to water bottles with three different height holes and interpreted the results. It was observed that greater water heights resulted in higher velocities due to increased gravitational potential energy, while variations in density, simulated by adding solutes, provided additional insights into flow characteristics. This analysis highlights the relevance of height and density in fluid flow applications, offering a clear understanding of fundamental fluid mechanics concepts through an accessible experimental setup. The experimental setup consisted of water bottles with different heights which are 0.055 m, 0.150 m and 0.225 m. Variations in fluid density were introduced by dissolving different solutes such as water, salted water and wasted oil to simulate changes in the physical properties of the fluid. Results indicated that the initialheight of the fluid significantly influenced its velocity, with taller columns of water producing higher exit velocities due to increased gravitational potential energy. Hole C have higher velocity compared to hole A and B meanwhile hole A have lower velocity compared to hole B and C for each liquid. Additionally, fluids with higher densities exhibited slower velocities under similar conditions, demonstrating the inverse relationship between density and flow rate when other factors remain constant. The study demonstrates the importance of easily accessible experimental instruments, such as water bottles with holes, in the teaching and analysis of fluid mechanics by highlighting the significance of height and density as crucial variables in regulating flow behavior. Based on the result, if position of the hole from the surface of the liquid is higher, the velocity of the flow will increase for each liquid.

Algorithmic Improvements to EVO for Optimizing BPNN in Solving Dynamic Inverse Problems

This research develops evolutionary optimization (EVO) algorithm to resolve the dynamic inverse problem and make back propagation neural networks (BPNN) work better. Standard BPNN faces difficulties such as getting stuck in local minima and taking too long to converge while adjusting poorly to changing conditions. To overcome these challenges, this study introduces three key improvements: Our approach features mechanisms to preserve population diversity, updates that adjust to changing conditions, and an optimization system that handles multiple objectives. Our innovations strengthen the algorithm's global search power plus its fast reaction time while making it work better. The effectiveness of the improved algorithm is demonstrated through three experimental scenarios: Our research uses tools like dynamic system control, signal reconstruction, and fluid mechanics inverse models. Our experimental findings demonstrate that EVO-optimized BPNN achieves better optimization results than standard EVO and competing methods across all performance indicators. The new algorithm reduces reconstruction errors to 0.012 and cuts optimization time by about 35%. This study presents a new way to enhance BPNN performance and flexibility in changing environments.

Study on the two-phase coupling migration mechanism of deceleration aggregate and water in coal mine water inrush channel

Currently, perfusing deceleration aggregate is the most effective way to create water-blocking sections for controlling coal mine water inrush disasters. Clarifying the two-phase coupling migration mechanism of deceleration aggregate and water in coal mine water inrush channels is the key to quantitatively determining the deposition and migration distance of aggregate after entering the water inrush channel from the perfusion hole. Based on fluid mechanics, slurry pipeline transportation theory and sediment dynamics, this paper categories the entire migration process of aggregate entering the water inrush channel from the perfusion hole into three motion stages: free fall, curved-throwing, and sliding. The motion and force characteristics of each stage are analyzed, and a theoretical model for single-aggregate sedimentary migration is established. The CFD-DEM method is used to establish a transient bidirectional coupling numerical calculation model of aggregate-water to verify the theoretical model (overall error not exceeding 10%). Finally, based on this research, reasonable suggestions are proposed for the actual engineering of plugging by perfusing deceleration aggregate.

Institutional distance between academia and industry in relation to the pedagogy in a fluid mechanics course

This study investigates the pedagogical approaches in fluid mechanics within aerospace engineering education, exploring the institutional distance between academic teachings and industry demands. Utilizing the Anthropological Theory of the Didactic (ATD) as a theoretical framework, the research examines the relationship between educational practices in fluid mechanics and the societal, institutional, and professional contexts. Through semi-structured interviews with experts from both academia and industry, including professors and professional engineers, the study gathers diverse perspectives on effective teaching methodologies. The responses reveal a clear dichotomy: while academic experts favor a traditional, theory-focused approach involving progressively complex problem-solving, industry professionals advocate for real-world, project-based learning that fosters practical skills and collaborative problem-solving. This divergence highlights an institutional gap where academic programs may not fully align with industry expectations, suggesting a need for curricular adjustments to better prepare graduates for professional challenges. Future research should focus on longitudinal studies to track the effectiveness of various teaching methods and cross-institutional collaborations that integrate practical industry experiences into academic curricula. The goal is to enhance the educational outcomes in fluid mechanics and reduce the gap between theoretical knowledge and practical application, ensuring that graduates possess the necessary skills to thrive in a dynamic professional environment.

Integration of Energy Conservation Principles Across Mechanical Engineering Curriculum: Updates on A Work-in-Progress Project

This ongoing project, now in its fourth year, strengthens the integration of energy conservation principles within the undergraduate mechanical engineering curriculum, with a specific focus on heat exchangers. Building upon previous efforts, this phase emphasizes both theoretical understanding and practical application of energy transfer and efficiency. Students’ progress through Thermodynamics, Fluid Mechanics, and Heat Transfer courses, reinforcing the First Law of Thermodynamics and its application to energy balance equations governing heat exchangers. This year, the project introduced a dedicated heat exchanger lab component, where students conduct experiments to validate theoretical calculations and observe real-world energy transfer phenomena. Additionally, computational work using simulation software allows students to model and analyze complex heat exchanger designs, exploring the impact of various parameters on performance. Direct and indirect evaluations, including problem-solving exercises, lab reports, computational analyses, and surveys, assess conceptual mastery and practical application skills. Preliminary results indicate that the combined approach of theoretical instruction, hands-on experimentation, and computational modeling significantly enhances student comprehension and retention of energy conservation principles as applied to heat exchangers. This presentation details the progress and findings of this phase, building upon presentations at previous WVAS meetings, and demonstrates how this project refines engineering education by equipping students with the tools to address complex thermal system challenges.

Review on the Application of Fractal Theory in Mechanical Engineering

Abstract Fractal theory, rooted in the study of complex and self-similar patterns, has found profound applications in mechanical engineering. This review examines the integration of fractal geometry into various domains, including fatigue and fracture mechanics, tribology, vibration analysis, mechanical design, heat transfer, and fluid mechanics. By leveraging the principles of fractal dimensions and scaling laws, engineers can model irregular structures, optimize designs, and enhance system performance with unprecedented accuracy. The paper consolidates recent advancements, highlights specific methods for applying fractal theory, and explores challenges and future directions, including the potential of fractal-inspired designs in emerging technologies such as additive manufacturing and AI-driven optimization. This comprehensive overview underscores fractal theory’s transformative impact on mechanical engineering, advancing both theoretical understanding and practical innovation.

Nascent water waves induced by the impulsive motion of a solid wall

The description of the generation mechanism of impulse surface waves remains an important challenge in environmental fluid mechanics, owing to the need for a better understanding of large-scale phenomena such as landslide-generated tsunamis. In the present study, we investigated the generation phase of laboratory-scale water waves induced by the impulsive motion of a rigid piston, whose maximum velocity $U$ and total stroke $L$ are independently varied, as well as the initial liquid depth $h$ . By doing so, the influence of two dimensionless numbers is studied: the Froude number $\mathrm {Fr}_p$ = $U/(gh)^{1/2}$ , with $g$ the gravitational acceleration, and the relative stroke $\Lambda _p =L/h$ of the piston. During the constant acceleration phase of the vertical wall, a transient water bump forms and remains localised in the vicinity of the piston, for all investigated parameters. Experiments with a small relative acceleration $\gamma /g$ , where $\gamma =U^2/L$ , are well captured by a first-order potential flow theory established by Joo et al. (1990), which provides a fair estimate of the overall free surface elevation and the maximum wave amplitude reached at the contact with the piston. For large Froude numbers, however, wave breaking hinders the use of such an approach. In this case, an unsteady hydraulic jump theory is proposed, which accurately predicts the time evolution of the wave amplitude at the contact with the piston throughout the generation phase. At the end of the formation process, the dimensionless volume of the bump evolves linearly with $\Lambda _p$ and the wave aspect ratio is found to be governed, at first-order, by the relative acceleration $\gamma /g$ . As the piston begins its constant deceleration, the water bump evolves into a propagating wave and several regimes such as dispersive, solitary-like and bore waves, as well as water jets are then reported and mapped in a phase diagram in the ( $\mathrm {Fr}_p$ , $\Lambda _p$ ) plane. While the transition from waves to water jets is observed if the typical acceleration of the piston is close enough to the gravitational acceleration $g$ , the wave regimes are found to be mainly selected by the relative piston stroke $\Lambda _p$ . On the other hand, the Froude number determines whether the generated wave breaks or not.

Soliton Molecules, Multi-Lumps and Hybrid Solutions in Generalized (2 + 1)-Dimensional Date–Jimbo–Kashiwara–Miwa Equation in Fluid Mechanics

The generalized (2 + 1)-dimensional Date–Jimbo–Kashiwara–Miwa (gDJKM) equation, which can be used to describe some phenomena in fluid mechanics, is investigated based on the multi-soliton solution. Soliton molecules of the gDJKM equation are given by the velocity resonance mechanism. A soliton molecule containing three solitons is portrayed at different times. The invariance of the relative positions of three solitons confirms that they form a soliton molecule. Multi-order lumps are obtained by applying the long-wave limit method in the multi-soliton. By analyzing the dynamics of one-order and two-order lumps, the energy concentration and localization property for lump waves are displayed. In the meanwhile, a multi-soliton can transform into multi-order breathers by the complex conjugation relations of parameters. The interaction among lumps, breathers and soliton molecules can be constructed by combining the above comprehensive analysis. The interaction between a one-order lump and a soliton molecule is an elastic collision, which can be observed through investigating evolutionary processes. The results obtained in this paper are useful for explaining certain nonlinear phenomena in fluid dynamics.

Bursting the Bubble: The Fluids Mechanics That Prove Godzilla Would Survive the Plan

Cinematic and pop culture narratives offer powerful tools for engaging with science by contextualizing complex principles within familiar, imaginative stories. This paper investigates the scientific feasibility of a plan depicted in Godzilla Minus One to neutralize the iconic kaiju through buoyancy reduction, exposure to deep-sea pressure, and rapid decompression. Employing principles from fluid mechanics, thermodynamics, and biomechanics, the study critically examines the use of freon bubbles and additional weight to counteract buoyant forces, the effects of 1500-m oceanic pressure on Godzilla’s physiology, and the potential for barotrauma during rapid ascent. While theoretically plausible, the proposed strategies face insurmountable challenges, including logistical impracticality and Godzilla’s presumed biological adaptations. This interdisciplinary critique highlights the intersection of film and science, encouraging critical analysis of cinematic representations and fostering a deeper appreciation for the scientific principles they attempt to portray.

Complex fluid interface dynamics in water exit by improved diffuse interface-immersed boundary method

Accurate simulation of fluid–structure interaction problems involving multiphase flows remains a significant challenge in fluid mechanics, particularly in simulating water-exit phenomena where the interaction between a solid body and the free surface of water is highly dynamic and nonlinear. This study presents a three-dimensional numerical investigation of the water-exit process using the improved diffuse interface-immersed boundary method, which ensures mass conservation and enforces the no-slip boundary condition at the fluid–structure interface. Three scenarios are investigated: forced water exit of a fully submerged sphere and partially submerged sphere, free water exit under buoyancy forces, and forced water exit of a fully submerged cylinder. The simulation results provide detailed insights into the dynamic evolution of the free surface, including wave generation and air entrainment, and are validated against experimental results. The key phenomena, such as the large deformation of water surface, formation and breakup of water bridges, and splashing during the exit process, are successfully captured. Compared to experimental observations, the numerical model demonstrates high accuracy in predicting the shape and dynamics of the free surface, as well as the internal flow field characteristics.

A temporal super-resolution model for turbulence prediction based on optical flow and artificial neural network

This paper introduces a temporal super-resolution model based on optical flow and artificial neural network to predict the short-term evolution of turbulence in fluid mechanics. The model employs the Farnebäck algorithm to compute optical flow and generate a basic predicted flow field. However, some regions in the flow field do not fully satisfy the usage conditions of the optical flow algorithm, causing significant local errors. Therefore, a multilayer perceptron (MLP) is integrated into the model to learn the relationship between local gradients and prediction errors, providing correction values to improve the prediction accuracy of the optical flow method. To evaluate the model's generalization ability, it is applied to a range of compressible wall turbulence cases with Mach numbers spanning from 2.25 to 10, encompassing typical flow structures such as turbulent boundary layers, shock waves, and separation bubbles. The results demonstrate that the model can accurately reconstruct flow fields between two moments, with the MLP providing significant improvements in the prediction of temperature and density fields using the optical flow method. The computational efficiency of the present model is significantly higher than that of traditional computational fluid dynamics methods.

Formation mechanism and evolution properties of double jets induced by cavitation bubble pair

Interactions between bubbles are prevalent in cavitation flow within fluid mechanics. This study develops a Kelvin impulse model suitable for a bubble pair and conducts extensive high-speed photographic experiments to investigate the dynamic properties of the double jets induced by the bubble pair in a free-flow field. The effects of key parameters, such as the phase difference and radius ratio of the bubble pair, on the variations in jet intensity and direction are quantitatively evaluated, and the parameter ranges corresponding to typical jet cases are classified. In addition, the influence mechanisms of bubble radial oscillation and the bubble boundary effect on the Kelvin impulse and Bjerknes force of another bubble are explored. The results indicated the following: (1) Three typical double-jet scenarios are discovered, including the newly observed co-flowing jets as well as colliding jets and diverging jets; (2) the Kelvin impulse model accurately forecasts changes in jet intensity and direction—with an increase in phase difference, the jet intensities of both bubbles gradually decrease, then increase inversely, and finally tend to zero; (3) compared to the bubble boundary effect, the bubble oscillation effect is consistently the core factor determining the intensity and direction of the Bjerknes force and the Kelvin impulse for another bubble.

Retraction: “Blood flow dynamics and vascular fluid mechanics” [Phys. Fluids 37, 011907 (2025)]

Retraction: “Blood flow dynamics and vascular fluid mechanics” [Phys. Fluids <b>37</b>, 011907 (2025)]