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SUMMARYIn this article, we present an improved solid boundary treatment formulation for the smoothed particle hydrodynamics (SPH) method. Benchmark simulations using previously reported boundary treatments can suffer from particle penetration and may produce results that numerically blow up near solid boundaries. As well, current SPH boundary approaches do not properly treat curved boundaries in complicated flow domains. These drawbacks have been remedied in a new boundary treatment method presented in this article, called the multiple boundary tangent (MBT) approach. In this article we present two important benchmark problems to validate the developed algorithm and show that the multiple boundary tangent treatment produces results that agree with known numerical and experimental solutions. The two benchmark problems chosen are the lid-driven cavity problem, and flow over a cylinder. The SPH solutions using the MBT approach and the results from literature are in very good agreement. These solutions involved solid boundaries, but the approach presented herein should be extendable to time-evolving, free-surface boundaries.

PURPOSEThe purposes of this study were to evaluate the staining resistance of CAD/CAM resin-ceramics polished with different techniques and to determine the effectiveness of the polishing techniques on resin-ceramics, comparing it with that of a glazed glass-ceramic.MATERIALS AND METHODSFour different CAD/CAM ceramics (feldspathic ceramic: C-CEREC Blocs, (SIRONA) and three resin-ceramics: L-Lava Ultimate, (3M ESPE), E-Enamic, (VITA) and CS-CeraSmart, (GC)) and one light cure composite resin: ME-Clearfil Majesty Esthetic (Kuraray) were used. Only C samples were glazed (gl). Other restorations were divided into four groups according to the polishing technique: nonpolished control group (c), a group polished with light cure liquid polish (Biscover LV BISCO) (bb), a group polished with ceramic polishing kit (Diapol, EVE) (cd), and a group polished with composite polishing kit (Clearfil Twist Dia, Kuraray) (kc). Glazed C samples and the polished samples were further divided into four subgroups and immersed into different solutions: distilled water, tea, coffee, and fermented black carrot juice. Eight samples (8 × 8 × 1 mm) were prepared for each subgroup. According to CIELab system, four color measurements were made: before immersion, immersion after 1 day, after 1 week, and after 1 month. Data were analyzed with repeated measures of ANOVA (α=.05).RESULTSThe highest staining resistance was found in gl samples. There was no difference among gl, kc and cd (P>.05). Staining resistance of gl was significantly higher than that of bb (P<.05). Staining resistances of E and CS were significantly higher than those of L and ME (P<.05).CONCLUSIONCeramic and composite polishing kits can be used for resin ceramics as a counterpart of glazing procedure used for full ceramic materials. Liquid polish has limited indications for resin ceramics.

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This paper presents a comparative study for the weakly compressible (WCSPH) and incompressible (ISPH) smoothed particle hydrodynamics methods by providing numerical solutions for fluid flows over an airfoil and a square obstacle. Improved WCSPH and ISPH techniques are used to solve these two bluff body flow problems. It is shown that both approaches can handle complex geometries using the multiple boundary tangents (MBT) method, and eliminate particle clustering-induced instabilities with the implementation of a particle fracture repair procedure as well as the corrected SPH discretization scheme. WCSPH and ISPH simulation results are compared and validated with those of a finite element method (FEM). The quantitative comparisons of WCSPH, ISPH and FEM results in terms of Strouhal number for the square obstacle test case, and the pressure envelope, surface traction forces, and velocity gradients on the airfoil boundaries as well as the lift and drag values for the airfoil geometry indicate that the WCSPH method with the suggested implementation produces numerical results as accurate and reliable as those of the ISPH and FEM methods.transfer problems [11], among others. In this method, rather than using an Eulerian fixed mesh, the computational domain is represented by a set of particles that are allowed to move in accordance with the solutions of relevant governing and constitutive equations. In fact, here, the term particle merely refers to a movable point that is bestowed with relevant physical and hydrodynamic transport properties such as temperature, density, viscosity and so forth. The Lagrangian nature of SPH lends itself remarkably to the simulation of a variety of complex fluid flow processes such as flow around bluff-bodies.In the SPH literature, there are two commonly utilized approaches for solving the balance of the linear momentum equations; namely the Incompressible SPH (ISPH), and the Weakly Compressible SPH (WCSPH) methods.The ISPH technique is based on the projection method originally proposed in [12,13] and first implemented to the SPH method in the work of Cummins and Rudman [14], which is referred to as the standard projection method in this work. In this method, the pressure term in the momentum balance equation is computed by solving a pressure Poisson's equation. The standard projection method has been reported to suffer from the density error accumulation during the computation of the intermediate density field [15,16]. To circumvent this and the associated problems, and consequently enhance the accuracy and the performance of the standard ISPH scheme, several modifications have been proposed for it in literature. For example, Shao and Lo [15] enforced the incompressibility in a somewhat similar manner to the one proposed in [14] with two main differences: first, they computed the intermediate velocity and then advected SPH particles; and second, they utilized the density variation as a source term rather than the divergence of the intermediate velocity. Their projection scheme has been re...

This study demonstrates that lithium disilicate porcelain blocks required etching for repairing with composite material. Surface treatments did not increase the bond strength in feldspar ceramic groups and reduced the bond strength in resin nano ceramic groups.

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