Hydrodynamic Forces Research Articles

Poiseuille flow of a concentrated suspension of squirmers

Poiseuille flow is a fundamental flow in fluid mechanics and is driven by a pressure gradient in a channel. Although the rheology of active particle suspensions has been investigated extensively, knowledge of the Poiseuille flow of such suspensions is lacking. In this study, dynamic simulations of a suspension of active particles in Poiseuille flow, situated between two parallel walls, were conducted by Stokesian dynamics assuming negligible inertia. Active particles were modelled as spherical squirmers. In the case of inert spheres in Poiseuille flow, the distribution of spheres between the walls was layered. In the case of non-bottom-heavy squirmers, on the other hand, the layers collapsed and the distribution became more uniform. This led to a much larger pressure drop for the squirmers than for the inert spheres. The effects of volume fraction, swimming mode, swimming speed and the wall separation on the pressure drop were investigated. When the squirmers were bottom heavy, they accumulated at the channel centre in downflow, whereas they accumulated near the walls in upflow, as observed in former experiments. The difference in squirmer configuration alters the hydrodynamic force on the wall and hence the pressure drop and effective viscosity. In upflow, pusher squirmers induced a considerably larger pressure drop, while neutral and puller squirmers could even generate negative pressure drops, i.e. spontaneous flow could occur. While previous studies have reported negative viscosity of pusher suspensions, this study shows that the effective viscosity of bottom-heavy puller suspensions can be negative for Poiseuille upflow, which is a new finding. The knowledge obtained is important for understanding channel flow of active suspensions.

Vertical Profile Characteristics of Dissolved Organic Matter Biochemistry in the Tropical Reservoir Shaped by Hydrodynamic Forces

Dissolved organic matter (DOM) exerts a crucial role in biogeochemical processes and ascertaining water quality in reservoirs, where it is vulnerable to the dynamic impacts of surface water inflows. However, understanding how DOM quantity and biochemical features responds to hydrodynamic forces in tropical reservoirs remains limited. To enhance our understanding of the vertical profiles of DOM characteristics under varying hydrodynamic forces (strong, moderate, and weak regions) in the Chitian Reservoir (18°43′–18°42′ N, 109°68′–109°70′ E), in December 2023, we investigated the concentrations and biochemical characteristics of water column DOM samples using multispectral techniques, a parallel factor model, and two-dimensional correlation analysis. Our results indicated that DOM concentrations (4.34 ± 0.36 mg/L) are the highest in the reservoir center, whereas total nitrogen (0.52 ± 0.04 mg/L), total phosphorus (0.02 ± 0.03 mg/L), and nitrate nitrogen (1.01 ± 0.07 mg/L) present their highest values in the inlet region. As hydrodynamic force decreases, microbial activity increases, whereas DOM’s humification degree and molecular weight decline. DOM in the Chitian Reservoir comprises humic-like components, including three terrestrial sources (accounting for 85.38%~87.03%) and one microbial source, with dominant characteristics of allochthonous origin. The relative abundance of microbial components decreased from 14.62% to 12.97% with the increasing hydrodynamic force and increased with depth. DOM functional groups in the strong hydrodynamic force region and the reservoir’s upper layer show high consistency and uniformity. Phenolic O–H is the most reactive functional group concerning changes in water depth across all hydrodynamic areas, followed by polysaccharide C–O, owing to its high photoactivity. In contrast, aromatic C–H demonstrates the weakest reactivity. DOM’s spectral features are closely linked to nutrient form concentrations (N and P).

Numerical investigation on the hydrodynamic wave forces on the three barges in proximity

Two-dimensional nonlinear hydrodynamic wave forces acting on three side-by-side barges are numerically investigated in this work. A finite volume viscous flow model, incorporating the volume of fluid method for free-surface capturing, is implemented based on OpenFOAM® platform to simulate interactions between nonlinear free-surface waves and multiple barges. The study explores the impact of fluid resonances in the gaps between three barges on the hydrodynamic wave forces. The initial transient and final quasi-steady wave forces are first examined to highlight the significance of transient evolution stage. The steady-state wave forces are subsequently concerned with the amplitude-frequency response of wave forces, along with the pressure and viscous force components. Relationship between wave forces and fluid oscillations within the gaps is then clarified to explain the mechanism of wave forces on the barges associated with gap resonance. Significant nonlinear higher-order harmonics are further demonstrated, with their origins closely linked to fluid oscillations within gaps between the barges. Contributions of higher-order harmonics to the overall wave force amplitudes are explored through harmonic analysis utilizing Fourier transformations. Finally, effects of the normalized incident wave amplitudes on the amplitudes of wave forces and higher-order harmonics are found to be highly dependent on frequency bands.

Particle manipulation under X-force fields.

Particle manipulation is a central technique that enhances numerous scientific and medical applications by exploiting micro- and nanoscale control within fluidic environments. In this review, we systematically explore the multifaceted domain of particle manipulation under the influence of various X-force fields, integral to lab-on-a-chip technologies. We dissect the fundamental mechanisms of hydrodynamic, gravitational, optical, magnetic, electrical, and acoustic forces and detail their individual and synergistic applications. In particular, our discourse extends to advanced multi-modal manipulation strategies that harness the combined power of these forces, revealing their enhanced efficiency and precision in complex assays and diagnostic frameworks. The integration of cutting-edge technologies such as artificial intelligence and autonomous systems further enhances the capabilities of these microfluidic platforms, leading to transformative innovations in personalized medicine and point-of-care diagnostics. This review not only highlights current technological advances, but also forecasts the trajectory of future developments, emphasizing the escalating precision and scalability essential for advancing lab-on-a-chip applications.

Aptamer-based biotherapeutic conjugate for shear responsive release of Von Willebrand factor A1 domain.

Smart polymers that mimic and even surpass the functionality of natural responsive materials have been actively researched. This study explores the design and characterization of a Single-MOlecule-based material REsponsive to Shear (SMORES) for the targeted release of A1, the platelet binding domain of the blood clotting protein von Willebrand factor (VWF). Each SMORES construct employs an aptamer molecule as the flow transducer and a microparticle to sense and amplify the hydrodynamic force. Within the construct, the aptamer, ARC1172, undergoes conformational changes beyond a shear stress threshold, mimicking the shear-responsive behavior of VWF. This conformational alteration modulates the bioavailability of its target, the VWF-A1 domain, ultimately releasing it at elevated shear. Through optical tweezer-based single-molecule force measurement, ARC1172s role as a force transducer was assessed by examining its unfolding under constant pulling force. We also investigated its refolding rate as a function of force under varied relaxation periods. These analyses revealed a narrow range of threshold forces (3-7 pN) governing the transition between folded and unfolded states. We subsequently constructed the SMORES material by conjugating ARC1172 and a microbead, and immobilizing the other end of the aptamer on a substrate. Single-molecule flow experiments on immobilized SMORES constructs revealed a peak A1 domain release within a flow rate range of (40-70 μL min-1). A COMSOL Multiphysics model translated these flow rates to total forces of 3.10 pN-5.63 pN experienced by the aptamers, aligning with single-molecule force microscopy predictions. Evaluation under variable flow conditions showed a peak binding of A1 to the platelet glycoprotein Ib (GPIB) within the same force range, confirming released payload functionality. Building on knowledge of aptamer biomechanics, this study presents a new strategy to create shear-stimulated biomaterials based on single biomolecules.

Modeling the navigating forces behind BSA aggregation in a microfluidic chip.

Microfluidic chips are powerful tools for investigating numerous variables including chemical and physical parameters on protein aggregation. This study investigated the aggregation of bovine serum albumin (BSA) in two different systems: a vial-based static system and a microfluidic chip-based dynamic system in which BSA aggregation was induced successfully. BSA aggregation induced in a microfluidic chip on a timescale of seconds enabled a dynamic investigation of the forces driving the aggregation process. This study employed a combination of experimental approaches, including biophysical and microscopic methods, and computational simulations using MATLAB and COMSOL Multiphysics. Obtained results revealed that Brownian movement, advective mixing, and laminar flow applied in favor of the formation of amyloid-like aggregates through the entire pathway. Furthermore, heating provided the necessary energy for the initial BSA's partial unfolding. In the following, space restriction and the cumulative effects of repulsive electrostatic and attractive van der Waals forces contributed to forming BSA clusters as a partially unfolded intermediate in the first few seconds of the aggregation process. Consequently, the synergistic effects of hydrodynamic forces (including shear force), hydrophobic interaction, and space restriction resulted in the deposition of larger aggregates on the channel sidewalls. Due to the elevated local concentration of BSA clusters alongside the strong shear force toward the channel sidewalls, the deposited structures underwent a structural conversion to form amyloid-like aggregates within a few seconds. In this study, we not only elucidated the molecular mechanisms underlying BSA aggregation but also highlighted the forces driving the aggregation process in microfluidic systems, explaining how it occurs within a timescale of seconds.

Cannabis sativa: Extraction Methods for Phytocannabinoids -An Update

This review paper highlights and updates the recent robust extraction methods for phytocannabinoids, hydrodynamic extraction technology and use of vegetable oil as the solvent system. Hydrodynamic cannabis extraction is a recent development within the cannabis industry that can be used to produce full-spectrum cannabis extracts with high bioavailability. According to the patented hydrodynamic extraction technology by Clean Green Biosystems, Chennai, Tamilnadu, India, the system is the first of its kind to be able to use whole, freshly harvested cannabis materials. Clean Green Biosystems, Chennai, Tamilnadu, India reports that Hydyne is innovative new hydrodynamic extraction system that uses the entire fresh plant materials to preserve all the unique phytochemicals and phytonutrients compounds in a full spectrum/broad spectrum extract. Hydrodynamic system converts the cannabis plant material into a cannabis nano-emulsion by means of hydrodynamic force and ultrasonification by breaking the cell walls of the plant material and releases them into the aqueous phase. PhytoXTM (USA) is another new hydrodynamic extraction system developed by IASO Inc (Incline Village, Nevada, USA) that can process whole, fresh, un-dried cannabis plants, which maximizes plant utilization, reduces processing costs, and increases yields. Many traditional extraction methods can not guarantee the integrity of unstable compounds. Hydrodynamic extraction is designed to use fresh and whole plants, ensuring these volatile molecules are kept intact. Additionally, the distillation prevents the phytocannabinoids from thermal degradation, further protecting molecule integrity. The aroma of the resultant cannabis products is stronger than traditional extracts. Because the plant material is frozen in the preparation stage of the system, it allows the aromatic compounds to remain intact.

Alterations of the Physical and Biochemical Structure in the Izmit Bay Following the Blockage Events at the Istanbul Strait

In December 2021 and March 2022, synoptic-scale weather systems triggered blockages in the Istanbul Strait, resulting in a notable alteration of the water dynamics of the upper layer of the northeastern Marmara Sea. The blockages resulted in the disruption of water mass exchanges between İzmit Bay and the eastern Marmara basin, driven by intensified hydrodynamic forces and severe wind conditions. The blockage of the two-layer flow in the strait led to an intensification of upper layer dynamics, resulting in an elevation of nutrient levels through mixing with nutrient-rich lower waters and/or the redistribution of nutrient fluxes via an enhanced jet current. This study demonstrates the occurrence of rapid changes in the biochemical structure of İzmit Bay, as evidenced by ADCP measurements and near-weekly temperature and salinity profiles. The analyses demonstrate significant shifts in flow dynamics, with salinity serving as an indicator of enhanced mixing. This mixing enabled the transport of nutrient-rich deep waters to the upper productive layer, thereby stimulating increased biological activity. The findings highlight that the altered dynamics resulted in a notable surge in nutrient concentrations and biochemical activity, potentially fostering the expansion of mucilage-forming species in İzmit Bay.

Enhancing Sustainability in Marine Structures: Nonlinear Energy Sink for Vibration Control of Eccentrically Stiffened Functionally Graded Panels Under Hydrodynamic Loads

The research examines the impact of nonlinear energy sinks (NES) on the reduction in the nonlinear vibratory responses of eccentrically stiffened functionally graded (ESFG) panels exposed to hydrodynamic loads. To simulate real marine environments, hydrodynamic forces, such as lift and drag that change with velocity, have already been determined experimentally using Matveev’s equations for a particular ship. The material composition of both the panel and the stiffeners varies across their thickness. The stiffeners are modeled using Lekhnitskii’s smeared stiffener approach. Additionally, analytical approaches implement the classical shell theory (CST) with considerations for geometric nonlinearity, along with the Galerkin method for calculations. The P-T method is subsequently employed to determine the nonlinear vibratory behavior of ESFG panels. In this method, the piecewise constant argument is used jointly with the Taylor series expansion, which is why it is named the P-T method. The findings reveal that NES can effectively dissipate vibrational energy, contributing to the extended service life of marine structures while reducing the need for frequent maintenance. This study supports sustainability objectives by increasing energy efficiency, lessening structural fatigue, and improving the overall environmental impact of marine vessels and infrastructure.

Semi‐empirically modelling barrier sediment transport in response to hydrodynamic forcing using UAV‐derived topographical data (Holgate, New Jersey)

AbstractWe conducted monthly surveys, from October 2020 to May 2021, of coastal topography in Holgate, New Jersey. Using unmanned aerial vehicle (UAV)‐photogrammetry and RTK‐GNSS equipment, we generated digital elevations models and cross‐section profiles, capturing spatiotemporal variability in volumetric change. We measured a total loss of 27 500 ± 10 500 m3 of subaerial sediment through the study. From October 2020 to February 2021, over 59 600 ± 10 500 m3 of sediment was eroded, followed by 32 100 ± 10 500 m3 of deposition from February to May 2021. We developed a semi‐empirical model correlating the measured geomorphological change to wave energy and water‐level variations. The calibrated model identified storm conditions that caused erosion and that waves from the south to southeast caused more erosion than those from the east to northeast. These results emphasise that alongshore transport represents a critical component of sediment transport dynamics relevant to beach erosion. Using the calibrated model, we quantified the impact of water‐level variations and wave energy on net sediment transport for a stretch of barrier coastline. Specifically, a water‐level increase of 0.14 m (equivalent to a 1σ variation) generated slightly less erosion (1.18 m3/m per 48 h) than the same variance‐based increase in wave energy, which generates 1.44 m3/m of erosion per 48 h. These variables strongly covary. Alongshore transport modulates the relationship, increasing erosion 0.9 m3/m per 48 h with a 1σ shift in wave energy directed alongshore. Forcing from strong storms, hindcast from 8 years of data, can produce 15–20 m3/m of erosion per 48 h. This modelling approach represents a methodology to produce estimates of potential erosion under predicted storm conditions, which is inherently valuable to coastal management and resilience planning. Our study demonstrates cost‐effective data collection and robust analytical methods that can be applied globally to benefit both the understanding of coastal geomorphology and local communities through data‐driven natural resource management.

Phenotypic Plasticity, Multiple Paternity, and Shell Shape Divergence Across Lake‐Stream Habitats in a Freshwater Mussel Brood (Pyganodon grandis)

ABSTRACT Hydrodynamic forces and their absence appear to exert differential selection pressure on aquatic biodiversity in lake and stream habitats, creating a tight fit between organismal phenotypes and their environments. Ecophenotypic variants may be the result of genetic differentiation or phenotypic plasticity, where a genotype can produce multiple phenotypes dependent on the environment. Freshwater mussels possess a wide degree of morphological variation that frequently covaries with the environment, making them a good system to understand the mechanisms of ecophenotypic variation across hydrological conditions. We designed a two‐year experiment where individuals from the same Pyganodon grandis maternal brood (half and full siblings) were reared at a controlled site and four natural sites involving one lake and three streams. At the end of the experiment, shell shape was quantified for recaptured (N = 70), wild (N = 206), and zoo‐reared (N = 305) mussels. The maternal individual and 46 recaptured mussels were sequenced for genomic single nucleotide polymorphisms to test for multiple paternity and its effect on offspring morphology. Analysis of covariance found significant differences in shell shape between rearing sites, particularly between stream and lake habitats, but no shape differences were detected across the three stream sites. At two of the four sites, the shell shape of recaptured individuals was not significantly different than that of wild populations. Genomic sequencing and parentage analysis identified 11–27 different fathers among recaptured individuals. Yet no genetic differences were present between stream and lake habitats, and there was no paternal effect on shell shape. Taken together, phenotypic plasticity, over genetic differentiation, is identified as the primary mechanism of ecophenotypic variation. Plasticity is likely ubiquitous across freshwater mussels and may be a key adaptation given their high variance in habitat use. Multiple paternity may also play a role in the evolution of phenotypic plasticity, allowing more males from greater distances opportunities for fertilization, thus increasing genetic connectivity. Lastly, phenotypic plasticity and multiple paternity are convenient properties for freshwater mussel conservation and propagation. Multiple fathers increase the genetic variation of propagated broods, while plasticity may provide resilience to the release of stocked individuals across environmental heterogeneity.

Levitation Performance of Radial Film Riding Seals for Gas Turbine Engines

Turbomachinery in gas turbines uses seals to control the leakage between regions of high and low pressure, consequently enhancing engine efficiency and performance. A film riding seal hybridizes the advantages of contact and non-contact seals, i.e., low leakage and low friction and wear. The literature focuses on the leakage performance of these seals; however, one of their fundamental characteristics, i.e., the gap between the rotor and seal surface, is scarcely presented. The seal pad levitates due to the deflection of the springs at its back under the influence of hydrodynamic forces. This study develops a test rig to measure the levitation of film riding seals. A high-speed motor rotates the rotor and gap sensors measure the levitation of the seal pads. Measurements are also compared with the predictions from a Reynolds equation-based theoretical model. Tests performed for the increasing rotor speed indicated that, initially, until a certain rotor speed, the pads adjust their position, then rub against the rotor until another rotor speed is reached, before finally starting levitating with further increased rotor speeds. Moreover, both the measured and predicted results show that pads levitated the most when located 90° clockwise from the positive horizontal axis (bottom of seal housing) compared to other circumferential positions.

Two-dimensionally stable self-organisation arises in simple schooling swimmers through hydrodynamic interactions

We present new constrained and free-swimming experiments and simulations in the inertial regime, with Reynolds number $\mbox{Re} = O(10^4)$ , of a pair of two-dimensional and three-dimensional pitching hydrofoils interacting in a minimal school. The hydrofoils have an out-of-phase synchronisation, and they are varied through in-line, staggered and side-by-side formations within the two-dimensional interaction plane. It is discovered that there is a two-dimensionally stable equilibrium point for a side-by-side formation. This formation is super-stable, meaning that hydrodynamic forces will passively maintain this formation even under external perturbations, and the school as a whole has no net forces acting on it that cause it to drift to one side or the other. Previously discovered one-dimensionally stable equilibria driven by wake vortex interactions are shown to be, in fact, two-dimensionally unstable, at least for an out-of-phase synchronisation. Additionally, it is discovered that a trailing-edge vortex mechanism provides the restorative force to stabilise a side-by-side formation. The stable equilibrium is further verified by experiments and simulations for freely swimming foils where dynamic recoil motions are present. When constrained, swimmers in compact side-by-side formations experience collective efficiency and thrust increases up to 40 % and 100 %, respectively, whereas slightly staggered formations output an even higher efficiency improvement of 84 %, with an 87 % increase in thrust. Freely swimming foils in a stable side-by-side formation show efficiency and speed enhancements of up to 9 % and 15 %, respectively. These newfound schooling performance and stability characteristics suggest that fluid-mediated equilibria may play a role in the control strategies of schooling fish and fish-inspired robots.

Assessing the feasibility of suspended BOP transportation and its impact on fatigue life

The sailing of the drilling rig along with its subsea equipment, such as, the drilling riser and the blowout preventer (BOP), from one well to another using traditional methods is a time-consuming operation. Typically, this process involves lowering and retrieving the BOP after drilling, followed by moving the rig to another well to be drilled, and again lowering the BOP and subsequently retrieving it. This method becomes even more time-consuming in ultra-deep waters, where recent oil field discoveries have taken place, as the deeper the water depths, the more time is required for such operations. Considering the high costs associated with renting and operating drilling rigs, operators are looking for ways to make these processes more efficient. One promising alternative is the method of navigation with the BOP suspended at a certain distance from the seabed, eliminating the need to retrieve the entire drilling riser and BOP, resulting in significant optimization of the process of transferring the drilling rig and its subsea equipment between wells.During the navigation of the BOP, hydrodynamic and inertial forces are exerted on the suspended riser column and the subsea BOP. In this present work, analyses of fatigue resulting from the effects of waves and vortex-induced vibration resulting from current speed and navigation, will be conducted for different lengths of the riser column. The results of these analyses will be presented, and the software used to obtain these results will be Orcaflex and Shear7.

Flow-induced buckling of a bistable beam in uniform flow

Recent developments in soft materials enable the design and manufacturing of bistable flexible structures. Their fast snap-through buckling mechanisms have been utilized to introduce fast locomotion. In this paper, we aim to understand the impact of fluid–structure interaction (FSI) on the dynamics of bistable structures. We report the numerical analysis of the snap-through buckling phenomena for several bistable flexible structures fixed at both ends. The motion is driven by the fluid loading of different flow speeds. The large deformation of the bistable structure is coupled with the incoming fluid flow via the Arbitrary Lagrangian–Eulerian (ALE) method. During the snap-through buckling process, the corresponding structural deformation patterns, hydrodynamic force distributions, and fluid patterns are discussed. Larger steady-state deformation is found for the bistable structure, compared to its mono-stable counterpart in the same flow condition. The Cauchy number is found to be the critical parameter affecting the buckling dynamics and dimensionless strain energy stored in the system. A prediction model for the dimensionless strain energy as a function of the Cauchy number is proposed. The hydrodynamic lift force generated by the fluid is found to increase the total strain energy of these bistable structures. The research could provide insight in designing morphable marine energy devices and lightweight bioinspired propulsion systems.

Numerical investigation of the fluid-structure interaction of a three-dimensional flexible pitching plate

This research numerically investigates the effect of flexibility on the hydrodynamic efficiency of a pitching flat plate. A sinusoidal pitching motion of frequency 0.6, 1.5, and 2 Hz is imposed on the flexible plate immersed in a hydrodynamic flow, at a laminar Reynolds number of 2000. The fluid-structure interaction (FSI) problem is solved with the computational fluid dynamics code FINE/Marine using a modal approach. A parametric study is carried out on the pitching frequency and the flexibility of the plate, to characterize the combined effects of FSI and pitching motion on the hydrodynamic loads. This work contributes to the understanding of hydrodynamic performances of structures operating with high-dynamic motions combined with a significant level of flexibility. First, the influence of the pitching frequency for a rigid plate is analyzed. It is shown that the amplitude of the hydrodynamic coefficients increases with the pitching frequency and their phase is shifted, due to the plate's angular acceleration. The production of lift is found to be a combination of the vortex dynamics and the acceleration effects due to pitch oscillation. The acceleration effects become prevalent over the vortex dynamics at higher pitching frequencies. In the flexible case, it is highlighted that the synchronization of the acceleration effects due to the vibration of the plate and the pitching motion has a crucial influence on the hydrodynamic forces. In the studied range of pitching frequencies, the lift is increased by a factor of 5.5 due to the pitching motion and up to a factor of 2 due to the flexibility. A ratio between the pitching frequency and the natural frequency of the plate is introduced to characterize the effect of flexibility.

Simulation of a Container Vessel Using Boundary Element Method for the Computation of Hydrodynamic Pressure and Forces

This study presents a comprehensive analysis of the hydrodynamic behavior of a containership under varying wave conditions using the Boundary Element Method (BEM). The hydrodynamic pressure distribution, as derived from BEM simulations, highlights critical pressure zones on the vessel’s hull, with maximum pressures reaching approximately 160 N/mm² near the bow. These high-pressure regions, caused by direct wave impacts, emphasize the structural vulnerability to fatigue, underscoring the need for reinforced designs in areas subjected to repeated loading. Additionally, the pressure mapping reveals patterns that align with expected wave-induced behaviors, validating the effectiveness of the BEM in capturing critical load distributions. The analysis also investigates wave excitation forces and diffraction/Froude-Krylov forces across six motion modes (surge, sway, heave, roll, pitch, and yaw). Translational modes exhibit peak forces of up to 8000 N at low wave frequencies (~0.1 Hz), while rotational modes encounter forces as high as 10^8 N, particularly in roll and pitch. These findings highlight the influence of wave characteristics, such as frequency and angle, on vessel stability and structural stress. The results provide valuable insights for vessel design and operational planning, advocating for enhanced stabilization systems, optimized structural reinforcements, and improved cargo placement strategies to ensure safety, performance, and longevity under various sea conditions.

Visualization and characterization of capillary-to-viscous transition in fluid-induced granular deformation

Comprehending pattern transitions during immiscible two-phase flow through granular materials is of paramount scientific and practical importance, as flow conditions are susceptible to variability along transport pathways in natural and engineering systems. The localized fluid displacement frequently mobilizes the hosting grains and triggers diverse morphological deformation. The interplay between such hydrodynamic and mechanical forces renders the deformation transitions inherently complex and hard to predict. Here, we integrate laboratory experiments with numerical simulations to probe the morphodynamics of fluid-driven granular deformation at the fundamental pore scale. Upon systematically varying capillary–viscous flows, we unveil three deformation patterns and propose a new dimensionless number incorporating the overlooked inertial and size effects to capture their transitions from slender channels to circular cavities to ramified fingers. We consistently observe lower residual saturation in the cavity regime attributed to the balanced capillary–viscous forces in this transition zone. Notably, our numerical model accurately mirrors the experimental observations and sheds light on the physics underlying the nucleation of characteristic crossover cavitation based on the microscale quantities of trivial energy leftover and uniform flow resistance.

Predicting the passive control of fluid forces over circular cylinder in a time dependent flow using neuro-computing

The objective of this research is to combine Artificial Neural Networks (ANNs) and Computational Fluid Dynamics (CFD) approaches to leverage the advantages of both methods. To achieve this goal, we introduce a new artificial neural network architecture designed specifically for predicting fluid forces within the CFD framework, aiming to reduce computational costs. Initially, time-dependent simulations around a rigid cylinder and a passive device (attached and detached) were conducted, followed by a thorough analysis of the hydrodynamic drag and lift forces encountered by the cylinder and passive device with various length L=0.1,0.2,0.3 and gap spacing Gi=0.1,0.2,0.3. The inhibition of vortex shedding is noted for gap separations of 0.1 and 0.2. However, a splitter plate of insufficient length or placed at an unsuitable distance from an obstacle yields no significant benefits. The finite element method is employed as a computational technique to address complex nonlinear governing equations. The nonlinear partial differential equations are spatially discretized with the finite element method, while temporal derivatives are addressed using a backward implicit Euler scheme. Velocity and pressure plots are provided to illustrate the physical aspects of the problem. The results indicate that the introduction of a splitter plate has reduced vortex shedding, leading to a steady flow regime, as evidenced by the stable drag and lift coefficients. The data obtained from simulations were utilized to train a neural network architecture based on the feed-forward backpropagation algorithm of Levenberg–Marquardt. Following training and validation stages, predictions for drag and lift coefficients were made without the need for additional CFD simulations. These results show that the mean square error values are very close to zero, indicating a strong correlation between the fluid force coefficients obtained from CFD and those predicted by the ANN. Additionally, a significant reduction in computational time was achieved without sacrificing the accuracy of the drag and lift coefficient predictions.

Research on the flow field and trajectory characteristics of high-speed projectile entry water in waves

The high velocity of supercavitating projectiles in a wave environment alters the flow characteristics and water entry stability, which significantly impacts the development and application of supercavitating weapons. This paper, investigates the effects of waves on the oblique water entry of high-speed supercavitating projectiles using computational fluid dynamics, with Stokes' second-order wave theory as the foundation for wave simulations. The numerical simulation method is validated through high-speed water entry experiments. The analysis explores the impact of wave inclination on cavity formation and the forces acting on the projectile. The results reveal that variations in wave inclination change the actual water-entry angles, affecting the cavitation structure near the free surface, modifying the impact intensity on the tail fins during water contact, and ultimately influencing the hydrodynamic forces acting on the projectile. When the actual water-entry angles are similar, the forces on the projectile during entry remain consistent under different conditions, with the trajectory being determined by the entry angle. Additionally, a reduction in the actual water-entry angle improves the projectile's entry stability but increases the amplitude and frequency of tail slap, ultimately affecting the stability of the projectile's trajectory after water entry.