Hydrodynamic Pressure Research Articles

Monitoring bay-scale ecosystem changes in bivalve aquaculture embayments using flow cytometry.

Bay-scale empirical evaluations of how bivalve aquaculture alters plankton composition, and subsequently ecological functioning and higher trophic levels, are lacking. Temporal, inter- and within-bay variation in hydrodynamic, environmental, and aquaculture pressure complicate plankton monitoring design to detect bay-scale changes and inform aquaculture ecosystem interactions. Here, we used flow cytometry to investigate spatio-temporal variations in bacteria and phytoplankton (< 20 μm) composition in four bivalve aquaculture embayments. We observed higher abundances of bacteria and phytoplankton in shallow embayments that experienced greater freshwater and nutrient inputs. Depleted nutrient conditions may have led to the dominance of picophytoplankton cells, which showed strong within-bay variation as a function of riverine vs marine influence and nutrient availability. Although environmental forcings appeared to be a strong driver of spatio-temporal trends, results showed that bivalve aquaculture may reduce near-lease phytoplankton abundance and favor bacterial growth. We discuss confounding environmental factors that must be accounted for when interpreting aquaculture effects such as grazing, benthic-pelagic coupling processes, and microbial biogeochemical cycling. Conclusions provide guidance on sampling considerations using flow cytometry in aquaculture sites based on embayment geomorphology and hydrodynamics.

Sliding-Induced Rehydration in Hydrogels for Restoring Lubrication and Anticreeping Capability.

Fluid exudation in cartilage under normal loading can be counteracted by a sliding-induced rehydration phenomenon, which has a hydrodynamic origin related to a wedge effect at the contact inlet. Similar to cartilage, hydrogels also exhibit tribological rehydration properties, and we mimic this phenomenon to restore hydration lubrication and overcome creeping. It occurs within a specific velocity range and is mainly dependent on the applied load and hydrogel network structures. Crucially, a certain velocity in the mixed lubrication regime can produce a hydrodynamic pressure peak at the wedge and drive the rehydration inflow to overcome the extrusion. At lower sliding velocities in the boundary lubrication regime, inflows are insufficient to counteract fluid exudation, whereas at higher velocities in the hydrodynamic lubrication regime, the inlet wedge effect would diminish. These results suggest that tribological rehydration offers a novel approach to enhancing load-bearing capacity and maintaining lubrication in the hydrogels.

Seismic Response Characteristics of a Utility Tunnel Crossing a River Considering Hydrodynamic Pressure Effects

As a long lifeline system of buried structures, the utility tunnel (UT) is vulnerable to earthquake invasion. For utility tunnels with inverted siphon arrangements crossing rivers, the seismic response is more complex due to the basin effect of acceleration in the topography and the influence of fluctuating hydrodynamic pressure, but there is currently a gap in targeted seismic response analyses and references. Based on a UT project in Haikou, this paper studied seismic responses of a cast-in-place UT considering the coupled model of water–soil–tunnel structure on ABAQUS software. Herein, the dynamic fluctuation of hydrodynamic pressure is simulated using an acoustic–solid interaction model. A viscoelastic artificial boundary was used to simulate the soil boundary effect, and seismic loads were equivalent to nodal forces. Considering seismic invading direction and varying water elevation, this paper investigates the dynamic response characteristics and damage mechanisms of river-crossing utility tunnels. This study shows that the basin effect causes the soil acceleration around the UT to show variability in different sections, and the amplification factor of the peak acceleration at the central location is almost doubled. The damage and dynamic water pressure of the UT are intensified under bidirectional seismic excitation, and the damage location is concentrated at the junction of the horizontal section and the vertical section. Bending moments and axial forces are the main mechanical behaviors along the axial direction. Changes in river levels have a certain positive effect on the UT peak MISES, DAMAGEC, and SDEG, and it exhibits a certain degree of energy dissipation and seismic damping effect. For the aseismic design of cross-river cast-in-place utility tunnels, bidirectional seismic calculations should be performed, and the influence of river hydrodynamic pressure should not be neglected.

Comparative Analysis of Hydrodynamic Loads on Bridge Piers: Assessing Standards through Numerical Modeling

Currently, there is an alarming difference in the estimated actions on piers resulting from flash-floods and tsunamis as prescribed by international Structural Design Codes. Previous studies have explored the interaction between surge waves and piers from a fluid-dynamics perspective, but there is no assessment about the relevance of the methods used in Structural Design to determine the hydrodynamic pressure resultants. To determine the degree of conservatism embedded in design, results from the different approaches are compared against validated numerical simulations. Three-dimensional numerical analyses were conducted using the OpenFOAM platform, employing the Large Eddy Simulation turbulence modeling approach to simulate the dam-break wave impacting the pier. The findings revealed that the maximum force was not necessarily caused by the stream’s first strike and could be sustained over time. The hydrodynamic pressure center consistently occurred at two-thirds of the stream depth, significantly impacting the overturning moments experienced by the pier. Identified inconsistencies between Codes underscore the need for revision of non-conservative approaches in predicting the design forces.

Seismic nonlinear interaction and uplifting effects between the nuclear island building and soil

Since the Fukushima nuclear accident, seismic design requirements have increased, necessitating a more refined evaluation of base uplift for weakly anchored nuclear island buildings. The elevated cooling water over 3000 t is a distinguishing feature of third-generation reactor buildings (RBs). To assess potential safety-adverse coupling effects, seismic wave propagation process through viscoelastic soils, discontinuous interfaces, and sloshing water was analysed. To facilitate nonlinear systematic simulation and parametric study, the traditional soil-structure interaction direct methods are improved and programmed on: thickness-independent viscous-spring elements for stable static-dynamic boundary transitions; seismic forces separated from the artificial boundary for flexible mesh planning; elevated water simulated with gravity stacking and hydrodynamic action. A nuclear island region encompassing water-cooled RBs and underlying soil cushion layer was investigated as a typical scenario to reveal rules using the proposed high-precision simulation platform. Non-negligible structural risks and correlations between multiple factors were quantitatively elucidated according to simulation findings. A time-lagged increase in the base overturning moment may occur because of water oscillations. As the water level increases to 85 %, the uplift height increases, adversely affecting the in-structure response spectra. Earthquake-induced intense uplift may lead to an increase in hydrodynamic pressure along the inner wall. The research results support the practical assessment of buildings with water cooling facilities located in soft composite sites with high seismic intensities.

Dynamic performance of ground supported circular water tank using shaking table

One of the most important lifelines for the human population is the water tank, which needs to be able to continue operating as usual both during and after earthquakes. Due to inadequate design techniques, structures are mainly intended to support static loads. The impact of dynamic loading is not taken into account. When resonance occurs, the effect is even more severe. The main objective of this work is to perform shaking table tests and study the dynamic performance of circular water tanks resting on the ground during shaking. For this investigation, three tanks with different height-to-diameter ratios have been taken into consideration. For various combinations of frequency, amplitude and water height in the tank, the hydrodynamic pressure at various places and the height of the sloshing wave during shaking have been measured experimentally. In comparison to the static water pressure on the container, it is discovered that dynamic pressure increases by 20%–50% during shaking. Resonant frequency drops with increasing tank diameter for a given water head at constant amplitudes.

Optimization of Water Distribution Network Demand Patterns Using Real-Coded Genetic Algorithms

The penetration rate of water supply via water supply facilities in the Republic of Korea has reached 99%, with 94% of the energy for operation consumed by pumps transporting water. Consequently, developing efficient pump operation techniques is crucial for reducing energy costs in water supply systems. This study employs real-coded genetic algorithm techniques to compute optimized demand patterns, considering the utilization of water tanks within networks. Hydraulic appropriateness is verified by evaluating pressure within nodes determined by derived patterns through numerical analysis simulations. Furthermore, after calculating flows supplied to the networks, pump power is determined, and resultant energy costs are estimated to evaluate economic feasibility. Results indicate that pressure distribution in networks with optimal patterns is hydraulically appropriate, meeting hydrodynamic pressure conditions suggested in water supply design standards. Additionally, this study demonstrates a 9% reduction in network energy costs compared to existing patterns. The model presented herein offers a means to efficiently operate water supply systems through water tanks, thereby reducing energy costs.

Evaluating the Seismic Resilience of Above-Ground Liquid Storage Tanks

Historical seismic events have repeatedly highlighted the susceptibility of above-ground liquid storage steel tanks, underscoring the critical need for their proper design to minimize potential damage due to seismic forces. A significant failure mechanism in these structures, which play essential roles in the extraction and distribution of various raw or refined materials—many of which are flammable or environmentally hazardous—is the dynamic buckling of the tank walls. This study introduces a numerical framework designed to assess the earthquake-induced hydrodynamic pressures exerted on the walls of cylindrical steel tanks. These pressures result from the inertial forces generated during seismic activity. The computational framework incorporates material and geometric nonlinearities and models the tanks using four-node shell elements with two-point integration, specifically Belytschko shell elements. The Arbitrary Lagrangian–Eulerian (ALE) method is employed to accommodate substantial structural and fluid deformations, enabling a full simulation of fluid–structure interaction through highly nonlinear algorithms. Experimental test data are utilized to validate the proposed modeling approach, particularly in replicating sloshing phenomena and identifying stress concentrations that may lead to wall buckling. The study further presents results from a parametric analysis that varies the height-to-radius and radius-to-thickness ratios of a typical anchored flat-bottomed tank, examining the seismic performance of this common storage system. These results provide insights into the relationship between tank properties and mechanical behavior under dynamic loading conditions.

Experimental Performance Evaluation of a Lightweight Additively Manufactured Hydrodynamic Thrust Bearing

In this paper, a lightweight additively manufactured (AM) fixed geometry hydrodynamic thrust bearing fabricated via laser powder bed fusion (LPBF) is experimentally compared to a traditionally manufactured cast aluminum alloy thrust bearing of similar design. The purpose of this study is to evaluate how weight-saving design features in the AM bearing affect active critical hydrodynamic performance parameters to better understand in-service viability. Under various static operating conditions, performance parameters such as hydrodynamic pressure distribution, minimum oil film thickness (MOFT), bearing temperature and increase in oil temperature are measured. Compared to the traditionally manufactured bearing, the AM bearing showed an average increase in minimum oil film thickness of 53%, an average increase in trailing edge hydrodynamic pressure of 116%, while exhibiting an average decrease in bearing temperature of 1%. Experimental results are compared to numerical simulation showing reasonably good agreement.

Improving the wettability and lubrication properties of gallium-based liquid metal through the reaction adsorption of copper and gallium

Gallium-based liquid metal (GLM) is a promising lubricant used in extreme working conditions. In this paper, a copper-containing friction pair (316L-10Cu) is prepared, and the wettability and lubrication properties of GLM are improved by the reaction adsorption of copper and gallium. Compared with 316L, the contact angle of GLM on 316L-10Cu surface decreases from 153° to 124°. At sliding speeds of 0.01m/s (boundary lubrication) and 0.05m/s (mixed lubrication), the friction coefficients of Si3N4/316L-10Cu decreases by 48.5% and 24.6% compared to Si3N4/316L, and the wear rates decreases by 86.5% and 80.7%. The improved lubrication performance is attributed to copper doping promoting the adsorption of gallium on the frictional interfaces, and better wetting enhancing the hydrodynamic pressure effect of GLM.

Innovative Coastal Resilience: Design and Application of Hydraulic Geotextile Tubes as Sustainable Breakwater Cores in La Union

The constant assault of waves contributes to the loss of valuable coastal land of La Union, necessitating innovative and sustainable methods to protect the shoreline. In the pursuit of sustainable solutions, innovative technologies such as hydraulic geotextile tubes have emerged as promising contenders for enhancing shoreline protection. This study explores the design and application of hydraulic geotextile tubes as breakwater cores along the La Union shoreline. Due to their permeability and flexibility, hydraulic geotextile tubes offer a viable substitute for conventional breakwater materials. The research aims to provide valuable insights into sustainable coastal management by determining how these tubes can be designed to resist wave forces, ensure stability against hydrodynamic pressures, identify various installation methods, and evaluate their advantages and disadvantages in preventing shoreline erosion and potentially reclaiming sand. The study's findings could inform strategies that balance shoreline protection with environmental preservation. It highlights the interaction between creative engineering solutions and environmental stewardship in addressing evolving coastal challenges.

Experimental and numerical investigation of wave loads on land-based multi-chamber OWC converters

Capturing more wave energy in a cost-effective principle has become a challenging task. Multi-chamber oscillating water column (OWC) devices are gradually gaining favour due to their potentially efficient characteristics. However, there is relatively limited research on dynamic analysis which is crucial for the safety and survival of multi-chamber OWC devices. In the study, model experiments of the hydrodynamic pressures for single-, dual- and three-chamber devices were conducted at a wave flume. A two-dimensional fully nonlinear numerical model for the interaction between waves and the OWC devices was established based on the higher-order boundary element method. The numerical results well cross-validated the experimental data. The wave forces and moments exerted on the devices were numerically calculated. The results indicate that the multi-chamber configurations not only generally reduce the wave loads on front and rear walls in high-frequency waves, but also avoid the sloshing motion of the water column inside the chamber, which induces large wave loads on the converter. However, the additional internal walls impose a redoubled burden on the junction of the top ceiling and the rear wall. The OWC converters sustain the horizontal forces much more than vertical forces. The front lip (i.e., the bottom edge of the front wall), the rear wall and the connection between the seabed and the device are relatively dangerous positions for configurations with any number of chambers.

Effect of elastic deformation on squeezing film lubrication properties of soft tribocontacts with microstructured surface

PurposeInspired by the high-friction performance of the soft toe pads of tree frogs, this study aims to investigate the effect of elastic deformation on the lubrication properties of squeezing films inside soft tribocontacts with microstructured surface under wet conditions.Design/methodology/approachA one-dimensional hydrodynamic extrusion model was used to study the film lubrication characteristics of conformal contact. The lubrication characteristics of the extruded film, including load-carrying capacity, liquid flow and surface elastic deformation, were obtained through the simultaneously iterative solution of the fluid-governing and deformation equations.FindingsThe results show that the hydrodynamic pressure is approximating parabolically and symmetrically distributed in the contact area, and the peak value appears in the center of the extrusion surface. Elastic deformation increases the thickness of the liquid film, weakens the bearing capacity and homogenizes the liquid flow rate of inside soft friction contact. The magnitude of this effect greatly increases as the initial liquid film thickness decreases. Moreover, the elastic deformation directly affects the average film thickness of the extrusion contact. Narrow and shallow microchannels are found to result in a more prominent elastic deformation on the microstructured soft surface.Originality/valueThese results present a design for soft tribocontacts suitable for submerged or wet environments involving high friction, such as wiper blades, in situ flexible electrons and underwater robots.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-02-2024-0049/

A Fully Implicit Coupled Scheme for Mixed Elastohydrodynamic Problems on Co-Allocated Grids

In the modeling of elastohydrodynamic lubrication problems considering mixed friction, strongly coupled dependencies occur due to piezo-viscous effects and asperities, which can make a numerical solution exceptionally difficult. A fully implicit coupled scheme for solving mixed elastohydrodynamic lubrication problems is presented. Our scheme uses finite-volume discretization and co-allocated grids for hydrodynamic pressure and elastic deformation. To provide strong coupling between pressure and deformation even in the highly loaded zone, a correction term that adds numerical diffusion is used. The resulting linear equation system of this scheme can be efficiently solved by Krylov subspace methods. This results in an improved accuracy and computational efficiency compared to the existing methods. This approach was validated and has been shown to be accurate.

SBFEM with perturbation method for solving the Reynolds equation

AbstractRotordynamic simulations with nonlinear hydrodynamic bearing forces require a solution of the Reynolds equation at every time step. As a computationally efficient alternative to the standard numerical methods, a semi‐analytical solution based on the scaled boundary finite element method (SBFEM) was developed recently. Through a discretization of the hydrodynamic pressure (dependent variable) along the circumferential but not the axial coordinate, the partial differential equation is transformed into a system of ordinary differential equations. This system of differential equations is referred to as SBFEM equation and can be solved exactly if the influence of shaft tilting is neglected. In common numerical models, this influence can be taken into account without difficulties, but as far as this semi‐analytical approach is concerned, shaft tilting complicates the equations substantially. Therefore, previous studies on the SBFEM solution of the Reynolds equation were conducted without consideration of this effect. The formulation presented in the work at hand no longer requires this simplification. The terms representing the influence of shaft tilting in the SBFEM equation are handled by the perturbation method. The pressure field is expressed by a series expansion, where the solution of order correlates to the power of a perturbation parameter chosen proportional to the tilting angle. The differential equation governing the solution contains lower‐order solutions on its right‐hand side, implying a recursive computation of the series from lowest to highest order. A universal expression for the general solution is formulated, where only the coefficients and the maximum power of the axial coordinate differ for every . This allows the implementation of a general algorithm with no inherent limitation regarding the maximum order of perturbation. For verification, the pressure fields computed by the proposed method are compared to a numerical reference solution, showing that the series converges to the correct result for the investigated set of parameters.

Rotational dynamics of a disk in a thin film of weakly nematic fluid subject to linear friction

Dynamics at low Reynolds numbers experiences recent revival in the fields of biophysics and active matter. While in bulk isotropic fluids it is exhaustively studied, this is less so in anisotropic fluids and in confined situations. Here, we combine the latter two by studying the rotation of a disk-like inclusion in a uniaxially anisotropic, globally oriented, incompressible two-dimensional fluid film. In terms of a perturbative expansion in parameters that quantify anisotropies in viscosity and in additional linear friction with a supporting substrate or other type of confinement, we derive analytical expressions for the resulting hydrodynamic flow and pressure fields as well as for the resistance and mobility coefficients of the rotating disk. It turns out that, in contrast to translational motion, the solutions remain well-behaved also in the absence of the additional linear friction. Comparison with results from finite-element simulations shows very good agreement with those from our analytical calculations. Besides applications to describe technological systems, for instance, in the area of microfluidics and thin cells of aligned nematic liquid crystals, our solutions are important for quantitative theoretical approaches to fluid membranes and thin films in general featuring a preferred direction.

Numerical Study of Skipping Motion of Blended-Wing–Body Aircraft Ditching on Calm/Wavy Water

The blended-wing–body (BWB) is hoped to be the main configuration of next-generation transport aircraft. However, its large flat belly may cause a violent skipping motion during the ditching on water. In this paper, the skipping motions of a BWB aircraft ditching on calm and wavy water are numerically investigated. The finite volume method with the volume-of-fluid approach is employed to solve the unsteady Reynolds-averaged Navier–Stokes equations. A coupled method between global moving mesh and overset mesh is proposed to avoid a large background domain and improve the prediction accuracy of the free surface, and its accuracy is well validated by predicting the motions of a skipping stone, the hydrodynamic load and pressure on a flat plate in high-speed ditching, and the fifth-order Stokes wave in a dynamic wave tank. At the beginning of every surfing stage, the flat belly of BWB aircraft impacts heavily on the water surface at a smaller pitch angle and larger speed, resulting in the local vertical overload peak, which is much larger than the peak in the porpoising motion. The wavy water surface intensifies the heave and pitch motions and increases the risk of the cockpit diving into the water.

On the transient dynamics of laser-induced cavitation bubbles near the end of a slender cylinder

In this work, we perform high-speed imaging and numerical simulation to investigate the transient dynamics of cavitation bubbles near the end of a slender cylinder. The bubble dynamics can be categorized into four distinct regimes in terms of the types of bubble collapse, corresponding to the regular jet, needle jet, in-phase double jets, and anti-phase double jets, respectively, depending on two dimensionless parameters, the normalized cylinder radius η (=rc/Rmax, where rc is the cylinder radius and Rmax is the spherical bubble radius at maximum expansion), and the dimensionless standoff distance γ (=SD/Rmax, where SD is the standoff distance between the end surface of the cylinder and bubble center). The peak velocity of the liquid jet could easily reach a supersonic state in the regime of the needle jet when the cavitation bubble collapses near a slender cylinder, and the maximum jet velocity can reach up to 635 m/s. Quantitative analysis of the evolution of pressure distribution also indicates that the end surface of the cylinder will have strong hydrodynamic pressure loading, particularly for the case of η=0.3 and γ ranging from 0.5 to 0.83. Additionally, we find that the collapse time of the cavitation bubble near a slender cylinder is close to the Rayleigh collapse time. We believe that our findings can be valuable in mitigating or utilizing cavitation near solid cylinders.

Evaluation of surface texturing on chrome-coated cylinder liners via deterministic mixed lubrication simulation

This study investigates the mixed lubrication performance of various surface texture configurations in the piston ring/cylinder liner conjunction of a two-stroke internal combustion engine using a deterministic mixed lubrication model. The numerical model simultaneously solves the Reynolds equation with mass-conserving cavitation to calculate inter-asperity hydrodynamic pressures and an elastic, perfectly plastic, rough contact model to determine contact pressures at each asperity interaction. Gaussian Mixture Model clustering was employed to enhance surface characterization. The deterministic simulation approach considers the full-scale representation of the cylinder liner topography to accurately capture the influence of surface features on the hydrodynamic support and friction under mixed lubrication conditions. The investigated cylinder liners were initially hard-chrome-coated and honed, resulting in a stochastic arrangement of surface pores, and then deterministic patterns of surface pockets were created by micro electrodischarge machining (EDM). Surface measurements were performed using laser interferometry, providing input for the mixed lubrication simulations. The study also explored the virtual removal of ridges formed around the pockets by the EDM technique. Key findings indicate that the stochastic texture outperformed the hybrid texture (stochastic + deterministic) in the boundary and mixed lubrication regimes, showing higher hydrodynamic support at low separations but increased hydrodynamic shear stresses at higher speeds. Conversely, deterministic textures exhibited a significant decrease in average hydrodynamic shear stress at high velocities. These results highlight the critical role of surface texture in tribological behavior and suggest that localized textures on cylinder liners can potentially optimize engine performance. The study recommends further exploration of a broader range of texture geometries, densities, and distribution patterns to enhance engine design strategies.

Analysis on slope stability by anchorage based on soil creep with flood effect

In order to analyze the adverse effect of flood affection on slope stability, the analytical expressions of buoyancy force and capillary force, hydrodynamic pressure and impact force, and scour erosion were proposed based on the aging characteristics of soil shear strength and limit equilibrium theory. According to the load combination and flood action, shear failure occurs preferentially at the foot of slope. Then, the plastic zone continues to extend upward to produce traction landslide disaster mode. Furthermore, the power function relation between shear strength index and time was established. The nonlinear accelerated creep model was also obtained. At the same time, the safety factor formula for flood loading effect slope aging stability, the time-varying characteristic value of anchor force and the compensation value of anchor force were also obtained and used to research sliding mechanism. In addition, the numerical calculation example shows that the slope safety factor decreases by more than 20 % considering the effect of flood ascending scour and impact, and the compensation value of anchorage force increases obviously with time increasing. Simultaneously, the change rate of compensation value of anchorage force increases nonlinearly with the increase of design safety factor.