Hydrodynamic Pressure Distribution Research Articles

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.

Numerical study of liquid sloshing in three-dimensional flexible cylindrical tank under multi-directional seismic excitation

The present study aims to evaluate the effect of the flexibility of three-dimensional (3D) cylindrical tank on liquid sloshing inside the tank as well as the influence of the hydrodynamic forces on the structure's deformation. A ground-supported cylindrical flexible tank filled with water and subjected to seismic excitation is investigated using a numerical coupling methodology to take into account the fluid–structure interactions. The Navier–Stokes equations in the fluid domain are solved using the finite volume method, while the finite element method is used to solve the linear-elastic equations of the structure. The arbitrary Lagrangian–Eulerian formulation is applied for the moving mesh in two-phase flow system. The simulations are conducted using free open-source software: OpenFOAM for fluid dynamics and FEniCS for solid mechanics, both utilize the preCICE library for data exchanging and fluid–structure coupling. The numerical methodology is validated by the experimental and numerical results given in literature. A multi-directional earthquake ground motion is then considered as external loading, and the elasticity of the tank wall is varied to investigate the effect on the fluid sloshing. It has been shown that the more flexible the tank walls are, the greater will be both the sloshing height and the structural deformations during an earthquake event. Several flow field information and structural responses have been provided, such as the sloshing height, hydrodynamic pressure, structure deformations, and structural stress distribution. The potential elephant's foot buckling phenomenon at the lower part of tank can also be predicted.

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.

A comprehensive unsteady RANS numerical investigation to unveil the influence of wave steepness on the motion dynamics and added resistance of a ship in waves

In this study, we investigate the influence of wave steepness on both ship motions and added resistance in regular head waves by conducting simulations at three distinct wave steepness levels using unsteady RANS method. Numerical results show that, when wavelength comparable to the ship length, the interaction of body nonlinearity and wave nonlinearity results in highly nonlinear behavior in the time history of added resistance. The study illustrates, step-by-step, the hydrodynamic pressure distribution on the hull during an encounter period, highlighting the time-varying nature of the added resistance. Examining the visualised results, it is observed that in certain instances, high pressure may be exerted on the flat bottom of the trimmed ship and contribute significantly to the added resistance. It is observed that, when wavelength is comparable to ship length, the added resistance coefficient decreases with increasing wave steepness. Specifically, at λ/LPP = 1.15, |CAW,H/λ=1/30−CAW,H/λ=1/60|CAW,H/λ=1/60 = 27.1%. In relatively short waves the diffraction phenomena dominate and the resulting added resistance exhibits limited nonlinearity. However, obtaining stable results in such cases proves challenging. Finally, the influence of wave steepness on added resistance is quantified. The results are useful for improving the transparent methods for predicting the added resistance in wave.

Numerical Simulations and Experimental Validation of Squeeze Film Dampers for Aircraft Jet Engines

Squeeze film dampers are used to reduce vibration in aircraft jet engines supported by rolling element bearings. The underlying physics of the squeeze film dampers has been studied extensively over the past 50 years. However, the research on the SFDs is still ongoing due to the complexity of modeling of several effects such as fluid inertia and the modeling of the piston rings, which are often used to seal SFDs. In this work, a special experimental setup has been designed to validate the numerical models of SFDs. This experimental setup can be used with various SFD geometries (including piston ring seals) and simulate almost all conditions that may occur in an aircraft jet engine. This work also focuses on the inertia forces of the fluid. The hydrodynamic pressure distribution of a detailed 3D-CFD model is compared with the solution of the Reynolds equation including inertia effects. Finally, the simulation results are compared with experimental data and good agreement is observed.

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

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

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

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

Hydrodynamic Thrust Bearing Test Rig with Novel Bearing Alignment System

Abstract This study presents the design and development of a new hydrodynamic thrust bearing test rig with a novel (patent pending) hydrodynamic pressure feedback bearing alignment control system. The bearing alignment system maintains even distribution of thrust load across the bearing thrust pads using active hydrodynamic pressure as input to manipulate bearing orientation with stepper motors. The test rig is used to conduct performance evaluation of fixed geometry hydrodynamic thrust bearings with variable taper depths. The influence of helical taper angle, rotational speed, and applied load on key performance characteristics including minimum oil film thickness (MOFT), hydrodynamic pressure distribution, and bearing temperature is presented and analyzed. A numerical model based on the Reynolds equation is used to support the experimental results obtained. Trends in performance established by the numerical analysis show mutually agreeable results compared to experimental data. The average percent deviation of the experimentally gathered change in MOFT as load is increased with respect to the numerically predicted values is 24%. Comparison of experimental to numerical pressure distribution data shows an overall average percent deviation of 32%.

Experimental investigation of liquid-tank interaction effects on full containment LNG storage tanks through shaking table tests

Liquefied natural gas (LNG) storage tanks play a crucial role as primary storage facilities in modern gas supply systems. This study investigates the seismic response of full containment LNG storage tanks through shaking table tests. A 1/14 scale model structure is meticulously constructed and subjected to testing. The test comprises two distinct phases: an empty tank phase and a water-filled tank phase. The primary emphasis of this paper is the exploration of the effects of liquid–tank interaction. A novel no-contact binocular video synchronization measurement system is developed by utilizing high-speed cameras to accurately measure the liquid sloshing height. The seismic responses of both the liquid and the tank, including acceleration and hydrodynamic pressure, are meticulously measured and analyzed. Findings reveal that the filling fluid has a significant effect on the tank, particularly the steel inner tank. The liquid sloshing phenomenon influences the hydrodynamic pressures, with the magnitude of influence decreasing as the liquid depth increases. In addition, a comparison is conducted between the experimental liquid sloshing height and hydrodynamic pressure results and those obtained from liquid linear forced sloshing theory. Liquid linear forced sloshing theory fails to accurately predict liquid sloshing height for large-amplitude sloshing but provides a rough estimate of hydrodynamic pressure distribution on the tank wall. Two simplified mechanical models for liquid sloshing are proposed and compared with the experimental results. The outcomes demonstrate that the Housner method exhibits relatively large errors, while the simplified mechanical models based on liquid linear forced sloshing theory accurately describe cases with small-amplitude liquid sloshing.

Experimental and numerical investigation of focused wave interactions with a vertical truncated dumbbell-shaped cylinder

A new type of vertical truncated dumbbell-shaped cylinder is commonly adopted as the cap or cofferdam in sea-crossing bridges and may be subject to large typhoon waves. Focused waves can be employed to simulate typhoon-induced waves, which produce longer periods and larger wave heights. In this study, a series of wave flume tests of focused wave interactions with a vertical truncated dumbbell-shaped cylinder are conducted. The influences of the maximum wave amplitude, peak frequency and frequency range of focused waves are considered experimentally and numerically. Based on the verified numerical model, the influence of the focusing position is analyzed. Furthermore, the flow patterns, including the free surface, velocity and hydrodynamic pressure distribution around the structure, are given numerically to better explore the interactions between the focused waves and the cylinder. The results show that the maximum wave amplitude, peak frequency, and focusing locations have significant impacts on the flow field characteristics and focused wave forces. However, the influence of the frequency range on the flow patterns and wave forces seems very slight. This study will enhance the understanding of the interaction mechanics between focused waves and a vertical truncated dumbbell-shaped cylinder under various working conditions.

АНАЛИЗ ПРОЧНОСТИ КОНТЕЙНЕРОВ-ЦИСТЕРН ПРИ УДАРНЫХ ВОЗДЕЙСТВИЯХ НА ОСНОВЕ КОМПЬЮТЕРНОГО МОДЕЛИРОВАНИЯ

The paper presents the strength analysis results for a tank-container designed for liquid cargo transportation by rail, automobile and water transport based on computer modeling. The most severe in terms of loads and extreme operation mode of tank-containers is chosen as the conditions for the computer experiment, implying an impact in the longitudinal direction when railway cars collide during their dismantling from the hill at marshalling stations. Calculations are performed using the static analysis module Static Structural of the ANSYS Workbench engineering software package for two loading options for a transport tank: a standard one, corresponding to GOST 33211-2014, and a refined loading option for the tank-container shell. Based on the numerical solution of the differential equations system for the liquid cargo movement, the analysis of which is performed using the finite volume method in the CFX module of the ANSYS Workbench engineering software package, the obtained values of hydrodynamic pressures in the tank are accepted as the initial data for the refined computer simulation. Conclusions are drawn on the influence of taking into account the distribution of hydrodynamic pressure inside the transport tank on the stress-strain state of the tank-container. The distributions of normal, equivalent von Mises stresses, as well as deformations for two loading schemes are obtained. Using the Fatigue Tool of the Static Structural static analysis module, the number of cycles that the structure can withstand is determined, taking into account the equivalent stresses concentration areas. The conclusions are formulated based on the computational results, and the recommendations are offered to improve transportation safety and ensure the safety of cargo using tank-containers.

Flood-induced forces and collapse mechanism of historical multi-span masonry arch bridges: The Putang bridge case

In order to obtain an adequate understanding of the vulnerability of historical multi-span masonry bridges during flood hazards for the better conservation, a typical multi-span stone arch bridge, Putang Bridge, is chosen to carry out the study on the collapse mechanism of the bridge under flood-induced forces based on numerical simulations. This study has a twofold objective: to simulate numerically the forces exerted by floods on the bridge, and to figure out the collapse mechanism under the obtained flood loads. The hydrodynamic pressure distribution and drag and lift forces on the bridge are predicted with CFD simulation considering eight different flooding levels. The simulation method is validated in advance with existing experiments. A bridge with higher cutwaters is modeled to assess the effects of the height of cutwaters on mitigating the flood loads. A finite element model of the bridge is developed and the obtained flood loads are applied to investigate the vulnerability of arch bridges in floods. The findings of this research could contribute to a clear comprehension of the flood-induced forces on arch bridges and the structural vulnerability, and also could provide some insights on preparing the early warning strategy and preventive measures for historical masonry arch bridges.

Experimental simulation of seepage field distribution for small interval tunnel under varying-head infiltration

In complex hydrogeological environments, it is difficult to achieve a dynamic equilibrium state for the recharge, seepage, and discharge of tunnel groundwater. Especially in case of reservoir flood discharge, local heavy rainfall, extreme dry climate or other emergency situations, the groundwater level will rapidly change, and the tunnel will be under the action of hydrodynamic head height within a certain period of time. Therefore, as urban tunnels in water-rich areas develop towards large cross-section, small spacing and complex sensitive stratum, studying the spatial distribution characteristics of seepage and stress fields in small interval tunnels under variable water head infiltration conditions is an urgent problem to be solved. In this paper, using the self-developed seepage model testing equipment, tunnel seepage tests under different hydrodynamic head heights and heavy rainfall conditions are carried out on the Kexuecheng Tunnel, which is a typical small interval tunnel in complex hydrogeological environment of Chongqing, China. According to the test results, as the burial depth and water level increase, the water pressure at each monitoring point gradually increases. Benefiting from the superimposed drainage effect of adjacent hole, the average water pressure at the inner side is 8 ∼ 12% lower than that on the outer side. The grouting circle and high groundwater level will further aggravate the asymmetric distribution of hydrodynamic pressure on the lining structure. However, as the hydrodynamic head height increases, the effective stress of the stratum decreases, and the earth pressure on the tunnel decreases by 24 ∼ 40%. Under heavy rainfall conditions, the evolution of lining structure pressure can be divided into initial infiltration stage, rapid growth stage, gradually stable stage and slowly decreasing stage. Suffered by the influence of rainstorm on seepage field and stress field, the overall pressure acting on the vault, left haunch, right haunch and bottom of lining structure increase by 45.4%, 132.3%, 117.4% and 147.4%, respectively.

Effect of oblique incidence angle and frequency content of P and SV waves on the dynamic behavior of liquid tanks

The dynamic behavior of liquid tanks is very different from those of other structures. Great effort has been put into the study of water tanks under vertical incident ground motion, but studies are still lacking regarding how different incidence angles influence the dynamic characteristics. This paper developed a model for the tank-soil-fluid system to study the variation and distribution of impulsive, convective, and total hydrodynamic pressures on the tank wall duel to water when subjective to earthquakes from different angles of incidence. The role of earthquake type (P or SV waves) and frequency contents are also considered. The tank-fluid interaction is modelled by the coupled acoustic-structural approaches. With the viscous-spring artificial boundary, the ground motions of oblique incidence can be transformed into the forces acting on the nodes of the truncated boundary of the finite-element model. It is concluded that the response of the tank-soil-fluid system is highly sensitive to incidence angles, earthquake type (P or SV waves), and earthquake record frequency contents. Therefore, in the design of tanks, not only the characteristics of the tank should be considered, but also the seismic characteristics should be considered.

Effect of boundary slip on elastohydrodynamic lubrication with arbitrary entrainment angle in elliptical contacts

PurposeThe purpose of this study is to describe and observe the influence of boundary slip associated with an arbitrary entrainment angle on the contact lubrication properties of ellipses.Design/methodology/approachBased on the modified Reynolds equation, the boundary slip of any angle is considered in the elliptic contact, and numerical simulation is carried out. In the above calculation, the progressive mesh densification method is used, which greatly reduces the computation time.FindingsThe results indicate that the variation of film thickness corresponding to different entrainment angles is distinct from those without considering boundary slip. In addition, boundary slip reduces the central film thickness and minimum film thickness, which makes the hydrodynamic pressure distribution smoother.Originality/valueThe present study focuses on the specific condition with the arbitrary direction of rolling and sliding velocity found in hypoid gears and worm, and some other components. The influence of boundary slip associated with arbitrary entrainment angle on the lubrication film thickness in elliptical contacts is first revealed, which improves a good understanding of elastohydrodynamic lubrication characteristics.

Efficient time-domain approach for hydroelastic-structural analysis including hydrodynamic pressure distribution on a moored SFT

This study investigates the hydroelastic analysis of a moored SFT (submerged floating tunnel) and the corresponding hydrodynamic pressure distribution under wave excitations. Time-domain discrete-module-beam (DMB) method, in which an elastic structure is modeled by multiple sub-bodies with beam elements, is employed to express the deformable tunnel with multiple mooring lines. Moreover, the top-down scheme is also adopted for detailed structure analyses with less computational cost, which applies the calculated hydrodynamic pressure distribution over SFT's surface to the three-dimensional finite element model. The hydrodynamic pressure includes both wave-induced diffraction pressure and motion-induced radiation pressure. For the validation of the developed numerical approach, comparisons are made with computationally intensive hydroelastic-structural direct-coupled method, two-dimensional wave flume experiment, and independently developed inhouse moored-SFT-simulation program. Furthermore, the influences of flexural motions with buoyancy-weight ratio (BWR) (or bending stiffness) and regular/irregular wave conditions on the dynamic pressure distribution and the resulting local stresses are investigated.

Probability Distribution Analysis of Hydrodynamic Wave Pressure on Large-Scale Thin-Walled Structure for Sea-Crossing Bridge

Evaluation of hydrodynamic wave pressure on large-scale structure is an important task in the wave load design of thin-walled components used in sea-crossing bridge. This study focuses on the probability distribution of hydrodynamic wave pressure on a large-scale thin-walled structure using on-site measurement data. An in-situ observation project is conducted to collect the wave elevation and the wave pressure on a rectangle cofferdam during a tropical cyclone event. With the measured data, the wave conditions and the fluctuating wave pressure are extracted, and the corresponding statistical characteristics such as the cumulative density function (CDF) are derived. In addition, a time domain boundary element model (TDBEM) is introduced to provide the statistical comparison. Several wave conditions derived by the statistical wave indicators during the cyclone event are fed to the numerical model for pressure investigation. Based on the statistical indicators and the modeling results, the comparison of wave pressure spatial distribution between TDBEM and the on-site measurement is presented. The pressure probability distribution is presented to further reveal the differences on the statistical characteristics. The resultant bias mainly occurs in the low-exceeding-probability range on the up-wave side and the high-exceeding-probability range on the down-wave side.

Elasto-hydrodynamic lubrication analysis of a porous misaligned crankshaft bearing operating with nanolubricants

In this paper, the combined effects of the characteristic size and concentration of inorganic fullerene-like tungsten disulphide nanoparticles (IF-WS2 NPs) or molybdenum disulphide nanoparticles (IF-MoS2 NPs) on the nonlinear dynamic behaviour of a gasoline engine crankshaft bearing subject to an arbitrary force torsor (effective applied force and moment vector) are theoretically and numerically investigated using the V. K. Stokes micro-continuum theory. These NPs are the most common additives for lubrication purposes due to their excellent tribological characteristics along with their effect on reducing friction and wear. It is assumed that the journal (crankshaft) currently made of a forged steel is rigid and the main bearing consists of a thin poroelastic liner made of low elastic modulus materials like Babbitt metals fixed in a stiff housing as defined by ASTM B23-00. The Krieger-Dougherty law is included in the proposed EHD model to account for the viscosity variation with respect to the volume fraction of nanoparticles dispersed in the base lubricant. On the other hand, the characteristic size of nanomaterials is introduced by a new material entity, denoted l, which is responsible for a couple-stress property. The Reynolds equation is derived in transient conditions and modified to account for the size of nanoparticles and the bearing-liner permeability property. For an arbitrary force torsor, the hydrodynamic pressure distribution, the squeeze film velocities, and the misalignment angular velocities are determined simultaneously by solving the discretized Reynolds equation and the equilibrium equations with the damped Newton-Raphson iterative method at each crank angle step. The crankshaft center trajectories in three sections of the main journal axis as well as the misalignment angles are deduced from the squeeze film velocities and the misalignment angular velocities by means of a Runge-Kutta scheme. According to the obtained results, the combined effects of the size and concentration of fullerene-like nanoparticles on the dynamic behavior of a compliant dynamically loaded crankshaft bearing operating with dynamic misalignment are significant and cannot be overlooked.

Study on issues of hydrodynamics of the roll squeezing process

The laws of distribution of hydrodynamic pressure and changes in extracted fluid in the pressing area are developed; they take into account the phenomena of contact interaction in the roll pair of the pressing machine. Hydraulic pressure in the compression zone increases from zero at the initial point of contact to a maximum value at a point lying on the line of centers. The distribution of hydraulic pressure in the recovery zone depends on the position of the water division point. It was revealed that the pattern of change of the removed fluid in the recovery zone depends on the position of the water division point. At the beginning of the recovery zone and up to the point of water division, the fluid flows from the coating into the material, and beyond this point, fluid is reabsorbed from the roll coating, and the amount of fluid removed from the material in the recovery zone is greater than the amount of absorbed fluid.

Numerical Simulations on the Flooding into a Damaged Cabin with a Flexible Bulkhead Based on the Mixed-Mode Function-Modified MPS Method

Floodwater entering the damaged cabin and impacting the bulkhead can cause damage to the watertight compartment and affect the survival of the ship. The elastic deformation of the bulkhead can slow down the impact and affect the flow field, which affects the hydrodynamic distribution inside the cabin. In this work, numerical simulations on the flooding phenomena into the damaged cabin with various stiffness, watertight bulkheads are carried out by using the mixed-mode function-modified moving particle semi-implicit (MPS) method, with the objective of investigating the influence of the stiffness of the watertight bulkheads on the structural impact load. Firstly, the numerical model based on the MPS method is set up to predict the dam-break wave impact load on an elastic plate and compared with the experimental measurements to verify the feasibility of the method. Then, the evolution of the flooding process of the damaged cabin with four different stiffnesses are simulated and the impact pressure on the bulkhead is predicted and compared. It is found that the flexible watertight bulkheads not only can reduce the peak pressure acting on it, but also have an effect on the hydrodynamic pressure distribution of the entire cabin. This implies that properly selected stiffness and material properties of watertight bulkheads can mitigate the impact of flooding on the damaged cabin’s bulkheads.