Search

The drainage of granular assembly from a flat-bottomed silo can be in either funnel flow mode or mixed flow mode. The primary motivation of this work is to investigate whether there exist fundamental differences between the rheological behavior of particles under these two discharge modes. The developments and evolutions of flowing zone and also the characteristics of particle velocity fluctuation during funnel and mixed flow discharges were analyzed and compared by performing 3D Discrete Element Method (DEM) simulations. For funnel flow discharge, the characteristic width of flowing zone at the early discharge state presented a clear history-dependent feature. For mixed flow discharge, the flowing zone sharply shrunk when the upper free surface of the material approached a critical height and the discharge mode then shifted to funnel flow mode. Discrete Fourier transform results demonstrate that resonant motion of particles appeared during both funnel and mixed flow discharges. The correlation analyses indicate that for these two flow modes, there both existed an intermediate region in the converging part of the flowing zone. Its upper boundary located at the position where the flowing zone started to converge along the vertical direction and was featured as the maximum particle compressive force. And its bottom boundary corresponded to the location of free-fall arch and acted as the source of the resonant motion of particles. Our simulation results thus suggest that from the perspective of particle velocity fluctuation, there is no essential difference between granular flows under funnel and mixed discharge modes.

When a laser beam induces surface tension gradient at the free surface of a liquid, a weak surface depression is expected and has been observed. Here we report giant depression and rupture in “optothermocapillary fluids” under the illumination of laser and sunlight. Computational fluid dynamics models were developed to understand the surface deformation and provided desirable physical parameters of the fluid for maximum deformation. New optothermocapillary fluids were created by mixing transparent lamp oil with different candle dyes. They can be cut open by sunlight and be patterned to different shapes and sizes using an ordinary laser show projector or a common laser pointer. Laser driving and elevation of optothermocapillary fluids, in addition to the manipulation of different droplets on their surface, were demonstrated as an efficient controlling method and platform for optofluidic operations. The fundamental understanding of light-induced giant depression and creation of new optothermocapillary fluids encourage the fundamental research and applications of optofluidics.

Environmental flows are generally characterized by complex bed morphology and high current speeds. Such configurations favor the formation of vortex structures that strongly affect hydrody-namics and sediment transport. Large-Eddy Simulation (LES) enables investigation of the dynam-ics of the largest turbulence scales and, thanks to enhanced calculation resources, has now become applicable for simulating environmental flows. In this paper, a LES approach is developed in a CFD code (TELEMAC-3D), which was originally developed to simulate free surface flows using RANS methods. The present developments involve implementing subgrid models, boundary con-ditions and numerical schemes suitable for LES. The LES version of TELEMAC-3D was validated by comparing results on the model with experimental data for flow past a cylinder. Then, the model was applied to a test case representing flow over dunes. After validating the hydrodynamics, the model was used to assess the bottom shear stress, using both a RANS and a LES approach. Com-parison highlighted the potential contribution of LES to investigating the hydrodynamic forces acting on the bottom.

Direct contact membrane distillation (DCMD) is the most studied configuration for desalination and waste treatment, due to its ease of operation. Despite this, this technology has not been scaled for industrial use mainly because of its energy requirements. In this work, a mathematical model is presented in which the free surface approach is used to simulate a tube-and-shell module. The model was successfully validated with experimental data from the literature. The operational parameters were evaluated to determine its influence on the permeate flux. The recycling of concentrate as a strategy to increase water recovery was also studied. In addition, high recycling rates allowed to reduce the specific energy consumption (SEC) and achieve a higher water recovery (REC). Finally, aiming at the use of membrane distillation for desalination in a small-scale plant, various arrangements of modules were evaluated in terms of water recovery, final concentration reached and SEC. The Christmas Tree arrangement turned out to be the most efficient one using a smaller area of membranes allowing to achieve a high degree of water recovery (86.5%), a final concentration of 260 $$\mathrm{kg}/{\mathrm{m}}^{3}$$ with a SEC of 1003 $$\mathrm{kWh}/{\mathrm{m}}^{3}$$ .

The performance and flow field of hydropower turbine in shallow water can be affected by the presence of free surface. Therefore, the influence of free surface on the turbine performance was studied through transient computational fluid dynamics (CFD) analysis. The turbine included three blades made of NACA0018 hydrofoil. Submerged depths and different tip speed ratio (TSR) were two main variables in this numerical simulation. A comprehensive simulation of quantities was performed for submerged depths ranging from h / R = 1.2 to 2.0, and tip speed ratio from λ = 1.0 to 30. The results revealed that the presence of the free surface decreased the power coefficient by 19.05% for the closest submerged depth of h / R = 1.2 at optimal tip speed ratio of λ = 2.5. The wave breaking also occurred when the submerged depth was smaller than h / R = 2.0. In the case of variable pitch, the top speeds for free-to-spin cases were investigated by 6DOF method. The top speed had a 4.24% drop by comparing the largest and the smallest submerged depths. Variable pitch also improved the power coefficient by 28.09% when the free surface was far from the hydropower turbine. However, the power coefficient improvement became significantly small when the hydropower turbine was placed close to the free surface.

The analysis of stresses imposed on structures by offshore environments is critical for their safety and smooth operation. Physical model testing for structural responses on offshore platforms is t...

Sludge recirculation mixing in anaerobic digesters is essential for the stable operation of the digestion process. While often neglected, the configuration of the sludge inlet has a substantial influence on the efficiency of the mixing process. The fluid is either injected directly into the enclosed fluid domain or splashes onto the free surface of the slurry flow. In this paper, the aim was to investigate the effect of the inlet configuration by means of computational fluid dynamics—using ANSYS Fluent. Single-phase and multi-phase models are applied for a submerged and splashing inlet, respectively. To reduce the high computational demand, we also develop surrogate single-phase models for the splashing inlet. The digester mixing is analyzed by comparing velocity contours, velocity profiles, mixing time and dead volume. The non-Newtonian characteristics of the sludge is considered, and a $$k-\varepsilon $$ k - ε model is employed for obtaining turbulence closure. Our method is validated by means of a previous study on the same geometry. Applying a submerged inlet configuration, the resulting dead volume in the tank is estimated around 80 times lower than for the case of a splashing inlet. Additionally, by emulating the multi-phase model for splashing inlet configurations with a single-phase one, the simulation clock time reduced to 15%.

Different drag laws and turbulence models were compared to evaluate gas distribution and fluid flow velocities in a Rheinstahl–Heraeus (RH) reactor. The discrete phase model was adopted to track injected gas bubbles, and the volume of fluid model was applied to describe a more actual free surface. The prediction accuracy of the numerical model was evaluated by the measured flow velocity in an air-water model and the measured circulation flow rate of molten steel in a real RH system. Results indicate that Morsi’s drag law predicts more accurate local velocity compared with Schiller’s and Harmathy’s laws. The influence of turbulent dispersion on the injected gas bubbles is non-negligible for predicting the gas–liquid flow in a RH reactor. In addition, although the large eddy simulation (LES) approach predicts more actual free surface fluctuation, the realizable k-e model shows better agreement with the measured local velocity in the furnace.

The “three shells” cooperative support technology was proposed herein according to both the large deformation of the rock surrounding large-section chambers in deep mines and the precarious stability of the support structures therein. The development range of the plastic zone in the surrounding rock was controlled by a stress shell to reduce the difficulty of controlling the surrounding rock. Additionally, the residual strength of the rock mass in the plastic zone and the self-bearing capacity of the surrounding rock were improved by a reinforced load-bearing shell. Furthermore, a passive load-bearing shell could restore the triaxial stress state of the surrounding rock on the free surface, reduce the influence of the external environment on the surrounding rock, and reinforce the surrounding rock with the strength of the shell. Reasonable layouts of large-section chambers were determined by analyzing the control effect of the stress shell on the surrounding rock under three kinds of in situ stress fields. The orthogonal test method was applied to reveal the influences of different support parameters in the reinforced load-bearing shell and passive load-bearing shell on the surrounding rock stability. The surrounding rock control effect of the “three shells” collaborative support technology was analyzed through numerical simulation and field monitoring. The results show that the maximum displacement between the roof and floor of the coal preparation chamber in the Xinjulong coal mine was approximately 48 mm, and the maximum displacement between its two sides was approximately 65 mm, indicating that the technology proposed herein could meet the long-term control requirements of the surrounding rock stability for large-section chambers in deep mines.

Several types of fishways are designed to allow the upstream passage of fish during the reproductive migration. Despite being the subject of many studies, improvements are still necessary to ensure an adequate flow for fish passage. This work aims to study the hydraulic parameters of the free-surface flow in the Igarapava HPP fishway, in Brazil, by comparing numerical results with available experimental data. Recent formulations for smoothed particle hydrodynamics were investigated in the numerical simulation using DualSPHysics. Open boundary conditions with buffer layers were applied to simulate inflow and outflow in the model. Three different model settings compared the effectiveness of the density diffusion term and the viscosity coefficient. Spurious oscillations were significantly reduced in the velocity field by using a combination of diffusion term and artificial viscosity coefficient that resulted in a smoothing effect near the walls and fewer oscillations in water level.

Fluid sloshing usually causes some serious safety issues during the transportation and utilization of liquid fuel in different engineering applications. In this paper, a computational fluid dynamics model is established to investigate the thermal physical process and sloshing hydrodynamics in a cryogenic fuel storage tank. Both the experimental validation and calculation grid sensitive analysis are conducted. The present numerical calculation model was turned out to be acceptable and proper for fluid sloshing prediction. Based on the proposed numerical model, the sloshing force and moment, the tank pressure variation, the fluid temperature distribution and the dynamic response of the free surface are investigated and analyzed respectively. The results show that the sinusoidal excitation has obvious influences on the thermodynamic and hydrodynamics performance in cryogenic fuel storage tanks. With some valuable conclusions obtained, this study is of significance to the depth understanding on the non-isothermal fluid sloshing, and may supply some technique supports for the safety design of cryogenic storage tanks.

To study the hydrodynamic characteristics of a floating horizontal-axis tidal turbine (HATT) with rotation and surging motion under the condition of the free surface, a numerical simulation method based on CFD is established. The axial load coefficient and energy utilization ratio at different blade tip-immersion depths, surge periods and surge amplitudes were analyzed. The results show that the instantaneous values of the axial load coefficient and energy utilization ratio have obvious periodic fluctuations, and the fluctuation amplitude increases with the increase of the frequency and amplitude of surging. On this basis, the hydrodynamic load is divided into the hydrodynamic load in case of rotation only, the damping force and the additional mass force. The damping and additional mass coefficients are obtained based on the least square method. The damping coefficient of axial load coefficient changes little with the increase of surge frequency and amplitude, but increases with the increase of the blade tip-immersion depth. The damping coefficient of energy utilization ratio fluctuates periodically, and the fluctuation period is equal to the surge period. The research findings can provide relevant data for studying the coupling motion of floating tidal current energy device and control design of the output electricity.

A numerical scrutiny was performed to analyze the effect of driving forces on molten pool in gas metal arc welding. In addition to the basic governing equations required for a general heat and mass transfer analysis by computational fluid dynamics, a volume-of-fluid equation for free surface tracking and additional conservation equations for calculating the distribution of alloy elements were used. Driving forces—buoyancy, drag force, arc pressure, electromagnetic force, Marangoni pressure, and droplet impingement—and the arc heat source were mathematically modeled and applied to the simulation. In order to examine the effect of driving forces, a two-dimensional axisymmetric simulation was performed, and the effect of each driving force was analyzed using the velocity components. In the radial velocity component, the effect of droplet impingement and the Marangoni force was large, and in the vertical velocity component, the droplet impingement effect was dominant. A three-dimensional simulation was also performed considering all the driving forces together, and the result was verified by comparison with experimental results. Relatively high alloying element contents were found at the bottom of the fusion zone, which was due to the droplet impingement generating a high vertical velocity.

Extensive models used in debris flow runout simulations are two-dimensional with many limitations. Considering these limitations, a new three-dimensional computational fluid dynamics (CFD) code based on the finite difference method (FDM) was introduced to simulate debris flow runouts. The unique fractional area-volume obstacle representation (FAVOR), true-volume of fluid (Tru-VOF), and the renormalized group (RNG) model in the 3D CFD code were used to tackle mesh processing, free surface tracking, and turbulence, respectively. The RNG model has great performance in describing low-intensity flows and flows with strong shear regions. In addition, the 3D CFD modeling considers the vertical mobility of debris flow, which offers higher simulation accuracy compared to 2D approaches. Through simulating a case and a mesh size study, the accuracy of the model was validated and the optimal mesh size of Xiaojia Gully debris flow model was obtained, respectively. The affected areas, runout distances, deposition depths, and velocities of potential debris flows in Xiaojia Gully were acquired by adopting the present model. The simulation results show that debris flows with return periods of 50 years, 100 years, and 200 years will threaten the lives and safety of residents and their property in Xiaojia Gully. A sensitivity analysis was used to evaluate the influences of rheological parameters on this model, further verifying the rationality of the selected parameters. In general, the present model can scientifically and accurately simulate debris flows on irregular terrain and can be employed for similar risk management and engineering designs.

When waves from two weather systems converge at a certain sea area, cross waves can be produced. It is important to have a better understanding of the motion characteristics of ship in cross sea to ensure its navigation safety. In this paper, the motion responses of a S175 container ship hull in cross sea is first analyzed based on CFD technique using RANS method. VOF method is used to model and capture the free surface and overset grid technique is adopted to simulate ship motions in waves. Verifications on ship motion by the numerical method have been conducted for time step- and grid-independent studies. According to the motion results by numerical simulation, typical conditions are chosen for further investigation of slamming pressure on bow area and green water on deck. It is found that vertical motion responses of ship induced by cross waves can be quite large and the ship experienced obvious roll–pitch-coupled motion. Severe bow slamming and green water under cross sea state are also observed. The bow flare slamming pressure on the baseline can be quite large in symmetric cross wave. Asymmetrical slamming impacts occurred when the ship sails in an asymmetric cross wave field.

Solid object water entry is a common problem in various natural, industrial and military applications, which involves large deformation of free surfaces and violent fluid–structure interactions. In computational fluid dynamics (CFD), this is a type of problem that tests the robustness and capacity of any CFD numerical algorithm. In this work, the newly-developed updated Lagrangian particle hydrodynamics (ULPH) method, which is a fluid version of peridynamics, is enhanced and applied to simulate solid object water entry problems. ULPH method is Lagrangian meshfree particle method that can ensure the specific free surface conditions automatically satisfied. The density filter and artificial viscosity diffusion are adopted in the ULPH scheme to stabilize and smooth the pressure field. In the process of a rigid body entering water, it may induce negative pressure in some areas of impact region, which can cause spurious tensile instability in some meshfree particle simulations, such as SPH and ULPH. A tensile instability control technique based on the ULPH framework has been developed to overcome the numerical instability. To validate the stability and accuracy of the ULPH approach in simulating water entry problems, several 2D and 3D examples of water entry have been carried out in this work. The necking and cavity pinch-off phenomena are visible in the numerical results. The simulation results of the ULPH method are well compared with experimental data and other numerical solutions. The water crown, cavity shapes and stream pattern formed around the rigid body entering the water can be well captured. The computation results show that the ULPH method has the ability to simulate the complex solid object water entry precess accurately.

application/pdf, Acta Astronautica. 2020, 181, P.151-166

Large-scale geometric roughness elements is one of the solutions that is used to protect openchannels from erosion. It is use to change the hydraulic characteristics of the flow. It may be concrete blocksor large stone placed at the bed of the channel to impose more resistance in the bed. The height of theseroughness elements is an important parameter that can affect the hydraulic characteristics of the flow. Usinga series of tests of T-shape roughness elements at three different heights, 3, 4.5, and 6cm, arranged in thefully rough configuration in order to investigate the velocity distributions along the flume. ANSYSParametric Design Language, APDL, and Computational Fluid Dynamics, CFD, were used to simulate theflow in an open channel with roughness elements. This simulation helps to find the best height of roughnesselements that can be used to change the hydraulic characteristics of the flow. The results showed that thevelocity values are decreased near the bed by about 61%, 58%, and 64% in case of 3cm, 4.5cm, and 6cmroughness heights consequently compared with the velocity of the control case. The velocity values areincreased near the free surface by about 32% and 19% in case of roughness elements height 6cm comparedwith 3cm and 4.5cm roughness heights respectively. The case of 6cm roughness height is considered to bethe effective case for decreasing the velocity values near the bed of the flume.

In this work, the effect of hydrostatic initial stress is studied with the exited semiconductor material. Electrons are exited at the free surface of the elastic semiconductor medium using the phot...

In the present research, a numerical modeling approach of the initial stage of consolidation during spark plasma sintering on the microscopic scale is presented. The solution of a fully coupled thermo-electro-mechanical problem also accounting for grain boundary and surface diffusion is found by using a staggered way. The finite-element method is applied for solving the thermo-electro-mechanical problem while the finite-difference method is applied for the diffusion problem. A Lagrange-based non-linear formulation is used to deal with the detailed description of plastic and creep strain accumulation. The numerical model is developed for simulating the structural evolution of the involved particles during sintering of powder compacts taking into account both the free surface diffusion of the particles and the grain boundary diffusion at interparticle contact areas. The numerical results obtained by using the two-particle model—as a representative volume element of the powder—are compared with experimental results for the densification of a copper powder compact. The numerical and experimental results are in excellent agreement.

Кисневі конвертори часто використовуються у виробництві сталі для видалення вуглецю з чавуну за допомогою продувки киснем та для розплавлення металобрухту. Шлак на поверхні розплаву всередині конвертора уповільнює газові бульбашки, що утворює велику кількість емульсії або піни. Іноді рівень піни може перевищувати ви-соту конверторної ванни. Щоб запобігти цьому, металургам потрібно прогнозувати подібні ситуації та відповідно зменшувати вдування газу в небезпечні періоди. Після багатьох років використання кисневих перетворювачів металурги отримали досвід і знають безпечні режими цього процесу. Однак ці режими можна вдосконалити за до-помогою математичного моделювання, яке користується популярністю в наші дні, оскільки воно має менші витрати, ніж реальні експерименти на заводі чи в лаборато-рії. Гідродинамічні процеси в конверторі складні, тому математична модель повинна уникати надмірного спрощення та враховувати важливі деталі про них. У попередній роботі представлена модель з детальним описом рівнянь (Нав'є-Стокса) та граничних умов. Чисельне рішення простіше отримати, ніж аналітичне для такої складної моде-лі. Для перевірки адекватності моделі використовуються такі припущення: загальна кількість газу повинна бути збережена у випадку закритого об'єму, а також поле ти-ску повинно збільшуватися відповідно до отриманої кількості газу; у разі переміщення вільної поверхні рівень піни повинен змінюватися відповідно до приходу газу і поверта-тися до початкового значення після того, як весь газ піде з рідини.Представлені малюнки ілюструють зміну рівня піни у випадку, коли газ надходить у розплав протягом перших 20 секунд з лінійним зниженням до нуля через 20 секунд. Об-числювальна область має 72x144 комірок. Ефективність обчислень знижується, коли рівень піни зростає, оскільки в розрахунку бере участь більше клітин. На інших рисун-ках показано газове поле (кольором) і поле швидкості (стрілками) для двох випадків: коли об’єм закритий і коли поверхня розплаву рухається. У закритому об’ємі зазначені вище припущення перевірено та подано графік залежності кількості газу. На основі цього зроблено висновок про якісну адекватність моделі. 2D-візуалізація здійснюється у комп’ютерної програми, розробленої на популярній мові.

Numerical simulation of dam-break water flow over a horizontal dry bed has been performed. We have modified and verified computational techniques, including methods for determining the position of the interface and the continuum model for the surface tension force implemented in the PIFI code, as well as the OpenFOAM software with the interFoam solver and various cases of the two-parameter ( $$k{-}\varepsilon$$ ) model with corrections made taking into account the behavior of flows in regions of low Reynolds numbers. Calculated integral characteristics of dam-break flow were analyzed and compared with measured data. It is shown that taking into account surface tension and using an adequate turbulence model leads to deceleration of water flow and hence to a decrease in the velocity of the wave front, resulting in better agreement between the results of calculations and laboratory experiments.

Purpose This paper aims to develop a numerical model of bead spreading architecture of a viscous polymer in fused filament fabrication (FFF) process with different nozzle geometry. This paper also focuses on the manufacturing feasibility of the nozzles and 3D printing of the molten beads using the developed nozzles. Design/methodology/approach The flow of a highly viscous polymer from a nozzle, the melt expansion in free space and the deposition of the melt on a moving platform are captured using the FLUENT volume of fluid (VOF) method based computational fluid dynamics code. The free surface motion of the material is captured in VOF, which is governed by the hydrodynamics of the two-phase flow. The phases involved in the numerical model are liquid polymer and air. A laminar, non-Newtonian and non-isothermal flow is assumed. Under such assumptions, the spreading characteristic of the polymer is simulated with different nozzle-exit geometries. The governing equations are solved on a regular stationary grid following a transient algorithm, where the boundary between the polymer and the air is tracked by piecewise linear interface construction (PLIC) to reconstruct the free surface. The prototype nozzles were also manufactured, and the deposition of the molten beads on a flatbed was performed using a commercial 3D printer. The deposited bead cross-sections were examined through optical microscopic examination, and the cross-sectional profiles were compared with those obtained in the numerical simulations. Findings The numerical model successfully predicted the spreading characteristics and the cross-sectional shape of the extruded bead. The cross-sectional shape of the bead varied from elliptical (with circular nozzle) to trapezoidal (with square and star nozzles) where the top and bottom surfaces are significantly flattened (which is desirable to reduce the void spaces in the cross-section). The numerical model yielded a good approximation of the bead cross-section, capturing most of the geometric features of the bead with a reasonable qualitative agreement compared to the experiment. The quantitative comparison of the cross-sectional profiles against experimental observation also indicated a favorable agreement. The significant improvement observed in the bead cross-section with the square and star nozzles is the flattening of the surfaces. Originality/value The developed numerical algorithm attempts to address the fundamental challenge of voids and bonding in the FFF process. It presents a new approach to increase the inter-bead bonding and reduce the inter-bead voids in 3D printing of polymers by modifying the bead cross-sectional shape through the modification of nozzle exit-geometry. The change in bead cross-sectional shape from elliptical (circular) to trapezoidal (square and star) cross-section is supposed to increase the contact surface area and inter-bead bonding while in contact with adjacent beads.

In this study, the water entry of wedges in regular waves is numerically investigated by a two-dimensional in-house numerical code. The numerical model based on the viscous Navier-Stokes (N-S) equations employs a high-order different method—the constrained interpolation profile (CIP) method to discretize the convection term. A Volume of Fluid (VOF)-type method, the tangent of hyperbola for interface capturing/slope weighting (THINC/SW) is employed to capture the free surface/interface, and an immersed boundary method is adopted to treat the motion of wedges. The momentum source function derived from the Boussinesq equation is applied as an internal wavemaker to generate regular waves. The accuracy of the numerical model is validated in comparison with experimental results in the literature. The results of water entry in waves are provided in terms of the impact force of wedge, velocity and pressure distributions of fluid. Considerable attention is paid to the effects of wave parameters and the position of wedge impacting the water surface. It is found that the existence of waves significantly influences the velocity and pressure field of fluid and impact force on the wedges.

The hydraulic behavior of the flow can be changed by using large-scale geometric roughness elements in open channels. This change can help in controlling erosions and sedimentations along the mainstream of the channel. Roughness elements can be large stone or concrete blocks placed at the channel's bed to impose more resistance in the bed. The geometry of the roughness elements, numbers used, and configuration are parameters that can affect the flow's hydraulic characteristics. In this paper, velocity distribution along the flume was theoretically investigated using a series of tests of T-shape roughness elements, fixed height, arranged in three different configurations, differ in the number of lines of roughness element. These elements were used to find the best configuration of roughness elements that can be applied to change the flow's hydraulic characteristics. ANSYS Parametric Design Language, APDL, and Computational Fluid Dynamics, CFD, was used to simulate the flow in an open channel with roughness elements. CFD can be used to study the hydrodynamics of open channels under different conditions with inclusive details rather than relying on the costly field and time-consuming. Runs were implemented with different conditions, the discharge, and water depth in upstream and downstream of the flume. T-shape roughness elements with height equal to 3cm placed in three different configurations, two lines, four lines, and fully rough configurations were tested. The results show that the effect of roughness elements increasing with increasing the number of lines of roughness elements. Cases of four lines and fully rough configurations have almost the same hydraulic performance by having the same results of the velocity decrease percentage, which is decreased by approximately about 66% and 61% of the control case's velocity in the zone near the roughness elements consequently. But the difference is that four lines configuration is affected in a part of the test section. This behavior increases the velocity values by about 11% in the other side and by about 10% near the free surface in the case of four lines configuration and increased by about 32% above the roughness elements in a fully rough configuration.

A key factor that governs the wave interferences of a submerged body is the dimensionless Froude number. Computational Fluid Dynamics (CFD) is used to describe the resistance force coefficients and the generated waves of two SUBOFF submarine models. Grid independence studies are performed on two cases, totally and shallowly submerged cases, with four sets of computing meshes. The highest peaks are marked by red points at given wavelengths, a line is fitted to those points with a least-squares approximation, and the half wake angle at multiple Froude numbers is defined between the fitted line and the centerline of the free surface. The results show that when the depth of the target is 1.1D, constructive interferences occur at Fn = 0.3 and 0.5, while destructive interference occurs at Fn = 0.35 with distortion of the waveform. The half wake angle is less than 19.47° because of the interference between the bow and stern wave systems.

Adjusting the free-surface condition facilely controls the in-plane and out-of-plane orientations in liquid crystalline polymer (LCP) films. Top coating with aromatic molecules onto LC polymethacrylate films with N-benzylideneaniline (NBA) or 4-methoxybiphenyl (MB) side groups (PNBAM or PMBM) and subsequent annealing generate a random planar orientation while simultaneously removing the coated aromatic molecules, whereas annealing noncoated films induces a homeotropic orientation of the mesogenic side groups. Additionally, irradiating a top-coated PNBAM film with linearly polarized (LP) 365 nm light induces an in-plane molecular reorientation of the NBA side groups without changing the orientation in the homeotropically oriented region. Changes in the surface topology of the LCP films due to the reorientation processes are investigated in detail. Inkjet coating with aromatic molecules and LP 365 nm light exposure precisely controls the in-plane and out-of-plane alignment pattern in a PNBAM film.

Phase separation in space is critical for gas-free propellant supply, life support systems, refueling of spacecraft in low earth orbit (LEO), and for deep space exploration missions. In the absence of gravity, the stability of the liquid-gas interface depends on capillary forces. High liquid flow rates, sudden accelerations, and vibrational disturbances can cause the free surface of the liquid to collapse, which results in the ingestion of gas. Propellant tanks may have screen channel liquid acquisition devices (SCLADs) to position and maintain a gas-free propellant supply to the outlet. A saturated porous screen permits liquid to pass through but acts as a barrier to the gas. We investigated phase separation in porous media integrated capillary channels during parabolic flights (33rd DLR parabolic flight campaign in March 2019). An open side of a rectangular channel was covered with a dutch twill weave 200×1400. The liquid was ingested into the channel from its surroundings by establishing a differential pressure across the screen section. The gas-phase was blocked during the liquid withdrawal. We could show that the gas breakthrough occurs when the pressure difference across the screen exceeds the bubble point pressure. The experimental results showed good agreement with correlations from literature.

This work studied the capability of a commercial CFD code in modelling two-phase flow from a header through two branches. The geometry considered in this study consists of a rectangular tank with two horizontal outlet branches of the same diameter d = 6 . 35 mm, separated by a distance L centre to centre L ∕ d = 1 . 5 with their centrelines falling in a plane inclined an angle θ = 30° from the horizontal. A block-structured, hexahedral computational mesh was used. The gas–liquid flow was computed using the inhomogeneous, free surface model of ANSYS CFX. Mesh-independence tests were conducted and the solutions of the discretized equations were progressed in time using a small time step size ( ≈ 0.0001 s). Results were obtained for the critical heights of the interface at the onsets of gas and liquid entrainment at both branches, as well as the outlet mass flow rate and quality during two-phase discharge. Good agreement was found between the numerical results and the available experimental data and correlations.

A numerical analysis and experimental validation of sloshing phenomenon in three-dimensional square tank with varying resonant frequency and amplitude of excitation is carried out in this study. Nu...

As the global warming, the Arctic Shipping Routes are gradually opened. The icebreakers are still in need to ensure the safe navigation of ships. During the voyage from East Asia to North-western Europe, the icebreaker will experience a long-distance voyage where over 60% of the distance is open water. As the bow of the icebreaker is full and the length-beam ratio is relatively high, it is quite important to study added resistance of the icebreaker. The results of added resistance, heave and pitch motion in regular waves are consistent with the variation trend using two methods. For computational efficiency, the nonlinear potential method was used to predict added resistance and vertical movement of the icebreaker at five wind directions. The added resistance in head waves is higher than in other wave directions. The maximum value was obtained at the wave length-ship length ratio of 1.2. The relationship between the phase of motion and resistance can be easily obtained. Meanwhile, the free surface around the hull can also be easily obtained. Moreover, compared to the CFD method, the nonlinear potential method can save more computing resources and time. It has important application value in the early design of the icebreaker.

In the recent years, numerical modeling of free surface flows has experienced a rapid and important development. Several programs and software have been used to simulate free surface flows. Transition from supercritical to subcritical flow regime leads to formation of hydraulic jumps. Numerical modeling of hydraulic jumps has taken an important part in this domain. This work aims to assess the efficiency of Iber software in the simulation of hydraulic jump in a rectangular channel. The location and displacement of the hydraulic jump were simulated by 2D Iber software. The data of these simulations were obtained from the experimental tests carried out at the laboratory. The results of the simulated hydraulic jump surface profiles showed a good agreement with those measured experimentally. The velocity distribution is presented in this study. Numerical simulation results satisfactorily predicted the hydraulic jump location, which gives confidence using of Iber software in the simulation of hydraulic jump.

The pumping station became widely used in many fields. Free surface vortices at intakes of pumps are not favorable. It may cause noise, excessive vibration, damage to the pumping structure, reduction in efficiency and flow for hydro-turbines, etc. One of the important problems encountered during the pump intake design is the depth of submergence and other design parameters to avoid strong free-surface vortices formation. This study aims to compute the critical submergence depth with some geometrical and hydraulic limitations by using Computational Fluid Dynamic (CFD) package. The mathematical model was validated with a laboratory model that had been conducted. The model of three intake pipes was investigated under five different submergence depth (S), three different spaces between intake pipes (b), and five different suction velocities (v). The results showed the best operation cases when the space between intake pipes (b) equal to 4D, the submergence depth of water is equal or greater than 1.25 from the bell mouth diameter of intake pipe (D), and the suction velocity less than 2 m/s. The worst case was when the space between the suction pipe (b) was (2D), in this case, the vortex appeared at submergence depth (S/D = 2) with suction velocity 3 m/s.

In geotechnical engineering, the stability of rigid footings under eccentrically inclined loads is an important issue. This is because the number of superstructures has increased and the situation of structures being subjected to eccentrically inclined loading is occurring more and more frequently. The objective of this paper was to evaluate the bearing capacity of a rigid footing on the free surface of uniform sandy and clayey soils under the action of eccentric and inclined loading using a finite element analysis by assuming that the soils follow the Drucker-Prager yield function. In the two-dimensional analysis of the footing-soil system, the rigid plastic finite element method (RPFEM) was applied to calculate the ultimate bearing capacity of the eccentric-inclined loaded footing. In the numerical analysis, an interface element was introduced to simulate the footing-soil system with the rigid plastic constitutive equation developed by the authors. The footing was considered to be rigid and rough, as it most often is in reality. This study thoroughly considered the effect of the soil properties on load inclination factors iγ and ic in order to investigate the validity of the current design methods. In particular, the effects of the horizontal load in two directions on the ultimate bearing capacity of the footing and the failure envelopes in the V-H-M space were clarified, namely, positive and negative horizontal loads. The results showed that the positive horizontal load had a negative effect on the bearing capacity, while the negative horizontal load had the opposite effect in the presence of eccentrically inclined loading. The failure mode of the footing-soil system was clearly seen in the difference between the two directions of horizontal load. Through a series of numerical analyses, new equations were proposed for load inclination factors iγ and ic, and for the failure envelopes in the V-H-M space, taking into account the direction of the horizontal load. The obtained limit load space was proved to be rational in comparison to those given in the literature. Furthermore, the applicability of the limit load space to different loading paths, and moreover, to the independently prescribed loads of V, H, and M, was examined. Consequently, the failure envelope for each type of soil in the V-H-M space was clearly seen to be unique.

The scour and deposition pattern around an abutment under constant discharge condition is calculated using a three dimensional (3D) Computational Fluid Dynamics (CFD) model. The Reynolds-Averaged Navier Stokes (RANS) equations are solved in three dimensions using a CFD model. The Level Set Method (LSM) is used for calculation of both free surface and bed topography. The two-equation turbulence model (k-e and k-ω) is used to calculate the eddy viscosity in the RANS equations. The pressure term in the RANS equations on a staggered grid is modeled using the Chorin's projection method. The 5th order Weighted Essentially Non-Oscillatory (WENO) scheme discretizes the convective term of the RANS equations. The Kovacs and Parker and Dey formulations are used for the reduction in bed shear stress on the sloping bed. The model also used the sandslide algorithm which limits bed shear stress reduction during the erosion process. The numerical model solution is validated against experimental results collected at the Politecnico di Milano, Milan, Italy. Further, the numerical model is tested for performance by varying the grid sizes and key parameters like the space and time discretization schemes. The effect of varying bed porosity has been evaluated. Overall, the free surface is well represented in a realistic manner and bed topography is well predicted using the Level Set Method (LSM).

In vertical seismic profiling (VSP) exploration, it is difficult to produce an accurate image for large-offset reflections only using reflection waves and the image resolution is low in traditional VSP-CDP stacking as is the number of folds of reflection points. To mitigate these problems, we present an inverse Gaussian beam stacking method for imaging both primary reflections and free-surface multiples. We first compute the stacking weighted functions at each trace location by Gaussian beam forward modeling, and then apply an inverse projection for VSP data to produce common shot gathers (CRP). Since inverse Gaussian beam stacking maps the common-shot data along finite-frequency wave-paths instead of single rays as the traditional ray-based stacking method does, it enlarges the reflection-point coverage, increases stacking fold and reduces the requirement for large bin sizes. We incorporate free-surface multiples into the proposed inverse Gaussian beam stacking, which enables us to expand the horizontal imaging aperture and mitigate the low-fold problem of primary reflections in the shallow large-offset regions for VSP surveys. Numerical examples for synthetic and field data demonstrate the feasibility and adaptability of the proposed inverse Gaussian beam stacking method for VSP data.

The free surface motion in moving containers is an important physical phenomenon for many engineering applications. One way to model the free surface motion is by employing shallow water equations (SWEs). The port-Hamiltonian systems formulation is a powerful tool that can be used for modeling complex systems in a modular way. In this work, we extend previous work on SWEs using the port-Hamiltonian formulation, by considering the two-dimensional equations under rigid body motions. The resulting equations consist of a mixed-port-Hamiltonian system, with finite and infinite-dimensional energy variables and ports. 2000 Math Subject Classification: 34K30, 35K57, 35Q80, 92D25

The aim of this work is to simulate the complex 3D hydrodynamics inside free-surface anti-roll tanks with obstacles and side sub-compartments. The case studies comprise a rectangular tank, a tank w...

This paper aims at finding a proper way to estimate sloshing severity. First, the concept of sloshing severity RAO (SSR) is introduced, and the wave elevation on the liquid free surface is chosen as an initial index for the rough prediction of sloshing severity. Then, compared with experimental data from a 3D regular model test, this index is adjusted and a new index is generated. One step further, sloshing severity under irregular sea states can be achieved by nonlinear combinations of the new index. For validation, the same model tank is tested under a set of irregular sea conditions, and peak pressures and impulse areas are taken as comparison standards. It is found that both numerical and experimental results show a similar tendency of sloshing severity. As a real ship application on the new index, the sloshing severity of a liquefied natural gas floating production storage and offloading (LNG-FPSO) is predicted under a low filling condition. Besides, the ship motion responses with and without sloshing effects are considered for the calculation of severity. From the present observation, this proposed methodology and generated new index is expected to be applicable to the selection of severe sea states for sloshing loads analysis.

A numerical method for solving 3D unsteady potential flow problem of ship advancing in waves was put forward. The flow field was divided into an inner and an outer domain by introducing an artificial matching surface. The inner domain was surrounded by a ship-wetted surface and a matching surface as well as part of the free surface. The free-surface condition for the inner domain was formulated by perturbation about the double-body (DB) flow assumption. The outer domain was surrounded by a matching surface and the rest had a free surface as well as an infinite far-field radiation boundary. The free-surface condition for the outer domain was formulated by perturbation of the uniform incoming flow. The simple Green function and transient free-surface Green function were used to form the boundary integral equation (BIE) for the inner and outer domains, respectively. The Taylor expansion boundary element method (TEBEM) was adopted to solve the DB flow and inner-domain and outer-domain unsteady flow BIE. Matching conditions for the inner-domain flow and outer-domain flow were enforced by the continuity of velocity potential and normal velocity on the matching surface. Direct pressure integration on the ship-wetted surface was applied to obtain the first- and second-order wave forces. The numerical prediction on the displacement, acceleration and added resistance of the 14000-TEU container ship at different forward speeds were investigated by the proposed TEBEM method. Reynolds-Averaged Navier–Stokes (RANS) equations based on Computational Fluid Dynamics (CFD) method were adopted to compare with TEBEM method. The physical tank experiment results also validated the accuracy of the numerical tank results. Compared with the experimental solutions, TEBEM obtained good agreement with the RANS CFD method. TEBEM, however, was much more efficient and robust.

In this article, the variable thermal conductivity which it depending on temperature gradient in context of the photothermal excitation process of a semiconductor elastic material is studied. In the presence of Hall current effect the governing equations is introduced in one dimension subjected to thermal ramp type. The interaction between thermal-elastic-mechanical-plasma waves are used during the models of dual-phase-lag (DPL) and Lord-Shulman (LS) according to thermoelasticity theory. Laplace transform method in one dimension (1D) is used to get the solutions of physical fields quantities under investigation. The mechanical (which describe the case when the traction is free) and thermal ramp type at the free surface are applied through the photo-generated (recombination) transport processes due to the light energy absorption. The inversion of Laplace transform is used to observe the complete solution of physical quantities. The influence of Hall current, thermal memories with variable thermal conductivity are illustrated graphically and discussed on the resulting quantities.

A new microdroplet generation technique based on the bubble oscillation in a funnel-like chamber is developed and investigated numerically using combined BEM-finite difference method. In this technique, the droplet is generated and ejected from the top opening of the chamber due to the oscillation of a transient bubble inside. The water in the chamber is exposed to the atmospheric air from the top side and is connected to a liquid reservoir from the bottom side. The bubble may be generated by an electrical spark, a laser beam or a high-intensity focused ultrasound (HIFU). The effects of the bubble-free surface distance (standoff distance) on the bubble and the ensuing droplet characteristics are evaluated. It was found that the when the bubble is initiated at the narrow part of the chamber it will be affected by the chamber's lateral wall so that parts of its surface that are closer to the wall takes the wall shape. As the bubble gets closer to the free surface, the wall effects are attenuated. In addition, the droplet size and pinch off time depend on the standoff distance so that as the standoff distance increases the droplet size decreases but its pinch off time increases.

This study compared numerical characteristics of volume-of-fluid (VOF) and two-fluid models for the two-phase flow simulation by using open-source computational fluid dynamics software (OpenFOAM). In both models, the pressure-implicit method for pressure-linked equations was solved to obtain transient pressure and velocity fields. For the simulation of subgrid-scale bubbles, the VOF model was coupled with a Lagrangian discrete bubble model (DBM). In the single bubble rising case, kinematic and dynamic parameters predicted by the two-fluid model were poor. However, in the bubbly flow case, this model predicted the gas and liquid velocities well and, similarly, the liquid front position in the free surface flow case. On the other hand, the VOF model was less accurate in describing bubbly flow, despite the inclusion of the DBM. While the two-fluid model is recommended for the simultaneous simulation of separated and dispersed flows, the VOF model is more effective for separated flows.

This paper investigates the effects of thermal radiation and variable viscosity flow down along an inclined plane with boundary conditions at free surface. The major problem includes internal heat generation, increase or decrease in temperature, and other thermo physical properties. The thermo physical properties include Grashf number, Nusselt number, Viscosity and Solar radiation parameter. The problems created have not been examined. Thus, this work examined the effect of temperature and velocity profiles on the various values of coefficient of viscosity, also the effects of solar radiation parameter on the major property of the fluid flow down along an inclined plane.The partial differential equations for the problem are continuity, momentum and energy equations. These are non- linear dimensionless equations governing the fluid flow down the inclined plane using integration method. The equations for the fluid flow, temperature and velocity of the problem are reduced to their final forms using perturbation method. Analytical expressions are employed to obtain the value of the velocity and temperature profiles in terms of parameters under the considerations in the flow field. The parameters are the major factors influencing the properties of the fluid flow down along an inclined plane.Hence, the viscosity of the fluid increases as the velocity of the fluid decreases while increase in the solar radiation parameter increases velocity of the fluid. Also the quantities of radiant energy absorbed by the fluid flow bring changes in the temperature of the fluid. Increase in Nusselt decreases the velocity of the fluid. Grashof number increases while the temperature of the fluid also decreases.In conclusion, viscosity of the fluid decreases with an increase in temperature due to cohesion and molecular momentum exchange between fluid layer and the parameters are found to have a significant effect over the velocity and temperature profiles of the fluid flow down an inclined plane at free surface. It will also useful for the industries in the production of the various fluids (liquid or gas) such as vegetable oil, palm oil and steam generation along an inclined plane and so on.

Floating systems offer an opportunity to expand tidal energy resource through an increase in viable sites and greater flow speeds near the free surface. However, the close proximity of the free surface provides uncertainty regarding power delivery and survivability due to the presence of waves, which could be addressed through a numerical model that is capable of considering all components of a floating tidal system simultaneously. This paper presents the first step in the development of such a tool: using the open-source CFD libraries of OpenFOAM as a basis, a computationally efficient HATT model has been developed for generalised incident flow conditions using actuator theory. A thorough evaluation of the model's sensitivity to key considerations in the simulation of entire floating tidal systems, such as flow speed and mesh alignment, showed that the model is robust, ensuring that it is suitable for future extension to wave-driven environments and integration into a framework for such systems.

To improve the current understanding of the reduction of tsunami-like solitary wave runup by the pile breakwater on a sloping beach, we developed a 3D numerical wave tank based on the CFD tool OpenFOAM® in this study. The Navier-Stokes equations were applied to solve the two-phase incompressible flow, combined with an LES model to solve the turbulence and a VOF method to capture the free surface. The adopted model was firstly validated with existing empirical formulas for solitary wave runup on the slope without the pile structure. It is then validated using our new laboratory observations of the free surface elevation, the velocity and the pressure around a row of vertical slotted piles subjected to solitary waves, as well as the wave runup on the slope behind the piles. Subsequently, a set of numerical simulations were implemented to analyze the wave reflection, the wave transmission, and the shoreline runup with various offshore wave heights, offshore water depths, adjacent pile spaces and beach slopes. Finally, an improved empirical equation accounting for the maximum wave runup on the slope was proposed by taking the presence of the pile breakwater into consideration.

The aim of this investigation is to study a refined multi-phase-lags generalized thermoelasticity theory and coupled plasma theory for a semi-infinite semiconductor elastic medium. The model is studied in context of the Photothermal transport process for isoropic homogenous two dimension medium. The governing equations describe the interaction between elastic-plasma-thermal waves. The normal mode technique is used to get the exact solutions analytically of main physical quantities under investigation. The thermal-plasma and mechanical loads are applied at the free surface of semiconductor medium to obtain the complete solution of the temperature, displacement, stresses and carrier density distributions. Some special cases have been obtained. Results will be displayed graphically and discussed. Comparisons are made between the different theories in thermoelasticity. Keywords: Photothermal process, Multi-phase-lags theory, Semiconductor, Thermoelasticity, Normal mode

The effect of Thomson heating of semiconductor medium is studied. Analytical discussions are made in the presence of thermoelectricity theory and magnetic field in context of Photothermal transport process. The interactions between plasma, thermoelectric, electromagnetic and elastic waves are taken into consideration. The governing equations are investigated in two dimensional deformations of homogenous, isotropic medium. The density of charge is taken as a function of time only of the induced electric current. The normal mode technique is used to obtain the physical quantities field under investigation. Some electro-mechanical loads and thermal effect through recombination process are applied on the free surface of semiconductor elastic medium. The distributions of physical fields in this phenomenon are discussed and represented graphically. The results have been discussed under the effect of thermoelectric parameter and Thomson parameter.

Prior to a critical value of uncut chip thickness (UCT) or the so-called minimum uncut chip thickness (MUCT), the micro milling process is affected by ploughing which causes deterioration of surface quality and reduction of tool life. Stringent surface quality is the major concern during micro milling of P-20 die steel as it has wide application in preparation of micro injection mould. Again, this MUCT value depends upon the workpiece, cutting tool material and its geometry. In this article, we tried to determine MUCT and size effects by considering the variations of surface quality parameters and process signals with the ratio of h/re (UCT (h) to edge radius(re)). MUCT value was determined to be 0.75–1 μm or critical h/re value was found to be in the range of 0.25–0.33. Comprehensive analysis of tool wear and chip morphology with size effect have been instituted those were lacking in the earlier literatures. Curled and helical chips were obtained at feed rate higher than MUCT value, whereas the chips with arbitrary shapes were noticed at feed rates below MUCT. Lamellar structures were observed at the free surface of the chip having both inclined and vertical orientation. Edge rounding, coating delamination and built-up edge formation were observed due to size effect at feed value below MUCT.