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This paper validates three-dimensional (3D) simulation results of electron beam melting (EBM) processes by comparing experimental and numerical data. The physical setup is presented which is discretized by a 3D thermal lattice Boltzmann method (LBM). An experimental process window is used for the validation depending on the line energy injected into the metal powder bed and the scan velocity of the electron beam. In the process window, the EBM products are classified into the categories, porous, good and swelling, depending on the quality of the surface. The same parameter sets are used to generate a numerical process window. A comparison of numerical and experimental process windows shows a good agreement. This validates the EBM model and justifies simulations for future improvements of the EBM processes. In particular, numerical simulations can be used to explain future process window scenarios and find the best parameter set for a good surface quality and dense products.

We studied dip formation phenomena in a draining water tank using the model of sink arrays. As the parameter for the drain size r increases, the effective Froude number F_eff is found to decrease according to F_eff/F=r^-∊ where F is the Froude number defined as F=q₀/[2π(gh³)^1/2] and ∊ is a constant. Here, q₀ is the total sink strength, h is the submerged depth of the sink array, and g is the gravitational acceleration. For F=0.286, ∊ is found to be ∊ ≈ 0.44. The implications of the results are discussed.

In this paper, the lattice Boltzmann method is employed to simulate buoyancy-driven motion of a single bubble. First, an axisymmetric bubble motion under buoyancy force in an enclosed duct is investigated for some range of Eötvös number and a wide range of Archimedes and Morton numbers. Numerical results are compared with experimental data and theoretical predictions, and satisfactory agreement is shown. It is seen that increase of Eötvös or Archimedes number increases the rate of deformation of the bubble. At a high enough Archimedes value and low Morton numbers breakup of the bubble is observed. Then, a bubble rising and finally bursting at a free surface is simulated. It is seen that at higher Archimedes numbers the rise velocity of the bubble is greater and the center of the free interface rises further. On the other hand, at high Eötvös values the bubble deforms more and becomes more stretched in the radial direction, which in turn results in lower rise velocity and, hence, lower elevations for the center of the free surface.

The effect of the surface on edge dislocation glide in the crystal with point defects both on the surface and in the bulk is studied theoretically. It is shown that the drag force of dislocation can be reduced by the image forces to several orders of magnitude in nanoscale region.

The recently emerged data-driven dynamic mode decomposition (DMD) method was employed to investigate the free surface sloshing dynamics of a partially filled rigid tank excited by horizontal harmonic motions. The volume of fluid algorithm was adopted for liquid–gas free surface tracking, and DMD was utilized for decomposition with physical interpretations of the DMD modes and the eigenvalues. Our results demonstrate that DMD works well for both data reconstruction and future-state prediction in terms of either free surface profiles or the sloshing pressure exerted on the rigid wall. DMD presents an efficient and versatile approach for accelerated reduced-order modeling and future-state forecasting. Our efforts provide the first reference on use of DMD for free surface sloshing problems to the best knowledge of the authors. We publicly share our data and codes for all the implementation.

Nonpotential effects in nonlinear evolution of Marangoni convection patterns are investigated analytically and numerically. Three manifestations of nonpotential effects are considered: (i) spatial modulations of hexagonal patterns; (ii) interaction between a short-scale hexagonal pattern and a long-scale slow deformational (Goldstone) mode; (iii) generation of the mean flow by the free-surface deformation in a large-scale Marangoni convection with poorly conducting boundaries. Nonpotential effects are shown to cause various secondary instabilities leading to skewed hexagonal structures, coexisting u- and d-hexagons, oscillating hexagonal patterns, spatially irregular cellular patterns, etc.

The near sound field generated due to a vertically mounted circular cylinder piercing a free surface in shallow water, is studied computationally using the Large Eddy Simulation (LES) approach and the sound wave equation. The flow is simulated in both the air and water phases. The interface surface is allowed to move and is simulated using the Volume of Fluid technique. The pressure distribution over the cylinder is fed back into the sound wave equation to calculate the near field. The interface surface is modeled as a zero pressure surface in the acoustic calculation and the bottom is taken as having infinite impedence modeling the case of a rigid floor. Two of acoustic calculations methods are used. In the first method, the interface surface is assumed to be fixed and the wave equation is solved in the frequency domain in a post-processing stage. In the second method, the evolution of the interface surface is taken into account and the wave equation is simulated simultaneously with the LES. Both solutions are analyzed and compared to show that the interface surface acts as a strong damper to the low frequency sound by damping the vortex Von Karman rollers as well as causing the low frequency component to be nonradiative. The variation of the near sound field with the water depth and Froude number is investigated and the propagation and damping characteristics are analyzed.

This work deals with the extension of the partition of unity finite element method (PUFEM) "(Comput. Meth. Appl. Mech. Eng.139 (1996) pp. 289–314; Int. J. Numer. Math. Eng.40 (1997) 727–758)" to solve wave problems involving propagation, transmission and reflection in layered elastic media. The proposed method consists of applying the plane wave basis decomposition to the elastic wave equation in each layer of the elastic medium and then enforce necessary continuity conditions at the interfaces through the use of Lagrange multipliers. The accuracy and effectiveness of the proposed technique is determined by comparing results for selected problems with known analytical solutions. Complementary results dealing with the modeling of pure Rayleigh waves are also presented where the PUFEM model incorporates information about the pressure and shear waves rather than the Rayleigh wave itself.

The vibration reduction for a cantilever beam with an interior sloshing absorber is numerically simulated using an implicit coupling approach of segregated solvers. The sloshing liquid damps the vibration by allowing the sloshing force to lag behind the displacement phase of the beam. The sloshing in the absorber is analyzed both theoretically and numerically. The results show that the impact of free sloshing on the forced sloshing causes the phase to be lagged behind when the free frequency is lower than the frequency of forced vibration. A range of values are considered for the parameters of the absorber and system vibration in the simulations to investigate their effects on the suppression capability of the absorber. In order to explain the effects of the parameters, two new parameters γ and κ are defined to represent the phase lag and magnitude of the sloshing force, respectively. Their applicability is confirmed by a series of numerical simulations. The results reveal the main mechanism of vibration suppression, providing a theoretical basis for optimizing the design of the interior absorber.

An analytical solution is proposed for the free flexural vibration of a finite cylindrical shell submerged in half-space bounded by a free surface in the low frequency range. The motion of the shell is described by the Flügge shell theory and the fluid surrounding the shell is assumed to be an acoustic media. The free surface effect is considered by satisfying the pressure release boundary condition. The accuracy of the present method is verified through comparison with the finite element solution. To throw light on the influence mechanism of free surface on the coupled modal frequencies, a modal added mass is introduced and calculated. Numerical results show that when the shell is close to the free surface, the presence of free surface will make a negative contribution to the modal added mass and finally result in the corresponding increase of the coupled modal frequencies. But the free surface effect will decrease when the immersion depth of the cylindrical shell increases. Finally, the free surface effect can be neglected if the immersion depth is higher than four times the shell radius. This conclusion is helpful to select proper test environment for an experiment on the dynamic characteristics of submerged cylindrical shells.

The scaled boundary finite element method (SBFEM) is used to solve the seepage problems with multi-material regions. Two models of dam base with waterproof screen and dam body with the regions of two materials are established. The numerical solutions are obtained and then compared with the analytical results or numerical solutions in the references. The conclusion shows that the SBFEM has more satisfactory accuracy and less data preparation amount.

In this paper, a numerical model is developed based on coupled boundary element–finite element methods (BEM–FEM) to minimize liquid sloshing pressure in trapezoidal tank with different sidewall angles. Different geometric shapes such as rectangular, cylindrical, elliptical, spherical and circular conical have already been studied for ship storage tanks by other researchers. In this paper, a new arrangement, i.e., trapezoidal containers is suggested for liquid storage tanks. The tank shape is optimized based on sloshing pressures and forces for a range of frequencies and amplitudes of sway motion and tank configuration. Fluid is considered to be incompressible and inviscid. Therefore, Laplace equation and nonlinear free surface boundary conditions are used to model the sloshing phenomenon. The results validated using available data showed that a new arrangement of trapezoidal storage panels has a better efficiency against sloshing phenomenon than the conventional rectangular tanks.

The violent dynamic behavior of liquid under horizontal excitation is a key factor that needs to be addressed in the seismic-resistant design of liquid tanks. Therefore, this study focuses on the slosh response of the liquid medium in a rectangular tank under Imperial Valley 1979, El Centro 1940 and Kobe 1995 ground motions of different frequency ranges. The ground motions records are selected based on the PGA/PGV ratio. For slosh control, a single vertical perforated baffle plate is used as an anti-slosh element with different configurations of perforations. Considering the free surface elevation as the major response parameter, the effect of percentage of perforation of the baffle plate, clear spacing of perforations and offset distance of the perforated plate are investigated by carrying out the pressure-based transient analysis using computational fluid dynamic (CFD). The optimum perforation varies from 10% to 17%, corresponding to the frequency of ground motion in the range of far-resonant to near-resonant conditions. Additionally, “rapid zone” ($R$-zone) and “moderate zone” ($M$-zone) are identified to pilot the positioning of the perforated baffle plate in liquid tanks. The perforated baffle plate with an optimum range of moderately spaced perforations positioned at the moderate zone of the tank effectively reduces the free surface elevation. Furthermore, the perforated baffle plate is more advantageous during violent sloshing under near-resonant conditions.

The smoothed particle hydrodynamics (SPH) method has been proved as a powerful algorithm for fluid mechanics, especially in the simulation of free surface flows with high speeds or drastic impacts. The solid boundary treatment method is important for the accuracy and stability of the numerical results, as the support domain of fluid particles is truncated near the vicinity of the boundary. This paper presents two commonly used methods for simulating a solid boundary in SPH simulations. Emphasis is placed on the description of the methods, definition of the boundary particles’ parameters, and discussion of their advantages and shortcomings. The classical dam break simulation is conducted using self-developed code and open source models such as DualSPHysics and PySPH in order to investigate the effects of the boundary methods. The results show that methods based on dynamic boundary particles can simulate the free water surface well with a good agreement with experimental results. The conclusions can also be used in research for boundary implementation methods for practical ocean and coastal engineering problems with free surface flows.

Liquid metal first wall is attractive in fusion reactor designs because of its high heat removal and self-refreshment capabilities. In liquid wall study, method of forming stable liquid flows on the front surface of blanket has to be found. In order to do this, free surface magneto-hydrodynamic (MHD) effects and flow velocity distributions of liquid metal under gravity have been studied. In our study, liquid metal flows down along ducts half-opened to face the plasma. Net electromagnetic force forms from induced eddy current interacting with the confinement magnetic field (12T) in the liquid metal flow. For liquid metal lithium (about 4cm thick), distributions of velocity along the flow direction have been obtained by combined calculations of free surface flow and electromagnetic analysis. The results show that MHD baffle might be used to get stable in front of the blanket.

The traditional weakly compressible SPH (WCSPH) method has been reported to suffer from large density variations, resulting in non-physical pressure fluctuations. In this article, a truly incompressible SPH (ISPH) method is developed and extended to free surface flows of shear-thinning fluids, in which the viscosity is modeled by the Cross model. The ISPH method employs a pressure Poisson equation to satisfy the incompressibility constraints, and the Navier-Stokes equations are solved in a Lagrangian form using a two-step fractional method. The method is firstly verified by solving the impact of a Newtonian droplet with a horizontal rigid plate in comparison with the available literature data. Then, ISPH is extended to simulate the phenomena of a Newtonian and a Cross droplet impact and spreading over an inclined rigid plate. In particular, the different flow features between Newtonian and Cross droplets after the impact are discussed. All numerical results show that ISPH method can not only extend to free surface flows of shear-thinning fluids, but also reduce the pressure noise in comparison with WCSPH.

In this paper a new approach is developed to simulate the extrudate swell of viscoelastic fluid. Lattice Boltzmann model is used to solve the complex Navier-Stokes equations and constitutive equations simultaneously at each time iteration. The type of cell is re-initialized by calculating the mass fluxes between neighboring cells after each iteration. The boundary conditions are treated with the non-equilibrium extrapolation method. Finally, by tracking the moving interface, the shape of the extrudate swell is acquired.