ISWFoam: a numerical model for internal solitary wave simulation in continuously stratified fluids

A numerical model, ISWFoam, for simulating internal solitary waves (ISWs) in continuously stratified, incompressible, viscous fluids is developed based on a fully three-dimensional (3D) Navier–Stokes equation using the open-source code OpenFOAM®. This model combines the density transport equation with the Reynolds-averaged Navier–Stokes equation with the Coriolis force, and the model discrete equation adopts the finite-volume method. The k–ω SST turbulence model has also been modified according to the variable density field. ISWFoam provides two initial wave generation methods to generate an ISW in continuously stratified fluids, including solving the weakly nonlinear models of the extended Korteweg–de Vries (eKdV) equation and the fully nonlinear models of the Dubreil–Jacotin–Long (DJL) equation. Grid independence tests for ISWFoam are performed, and considering the accuracy and computing efficiency, the appropriate grid size of the ISW simulation is recommended to be 1/150th of the characteristic length and 1/25th of the ISW amplitude. Model verifications are conducted through comparisons between the simulated and experimental data for ISW propagation examples over a flat bottom section, including laboratory scale and actual ocean scale, a submerged triangular ridge, a Gaussian ridge, and slope. The laboratory test results, including the ISW profile, wave breaking location, ISW arrival time, and the spatial and temporal changes in the mixture region, are well reproduced by ISWFoam. The ISWFoam model with unstructured grids and local mesh refinement can effectively simulate the evolution of ISWs, the ISW breaking phenomenon, waveform inversion of ISWs, and the interaction between ISWs and complex topography.

Characteristics of Beaver Ponds and Landforms Induced by Beaver Activity, S Part of the Tuchola Pinewoods, Poland

Currently, there are only two species of beavers described—the North American beaver (Castor canadensis) and Eurasian beaver (Castor fiber). Their natural habitats are confined to the northern hemisphere but instances of beaver introduction to regions of the world they do not normally inhabit have also been recorded. The activity of beavers leads to changes in the natural environment linked to hydrological and geomorphological and plant cover transformations. Beavers live in natural and artificial water reservoirs and rivers. If the water level in the river is too low, they build dams to create a comfortable living environment. This paper aims to present changes in the relief of the valley inhabited by beavers in which sediments accumulate. During the field study, detailed measurements of dams and of the spatial range of beaver ponds were made, and the thickness and spatial distribution of accumulated sediments were determined. In addition, measurements of geomorphological forms in beaver ponds were also made. The samples of sediments were subject to grain-size distribution analysis, the results of which allowed calculating sediment parameters. Beavers appeared in the Gajdówka valley in the southern part of the Tuchola Forest (Poland) in 2008. In 2008–2011 they built 17 beaver dams that impounded ponds. The beaver ponds and beaver dams were of different sizes. They either flooded the whole flat bottom of the valley or only raised the level of water in the riverbed. A characteristic feature of beaver ponds is that they capture sediments. Different landforms were created in the course of the formation and disappearance of beaver ponds. It was established that these include alluvial fans, levees, sand shadow dunes and microterraces formed by deposition and erosion. They do not occur in all ponds. Points at which mineral sediments are supplied to the watercourse, including beaver burrows and erosion hollows, are presented together with the points at which sediments are transferred from ponds upstream to ponds downstream the watercourse. Beaver activity during valley colonization shows changes in the landscape caused by their presence and in particular their impact on the relief and deposition of sediments. Analysis of contemporary changes in the morphology of the Gajdówka Valley leads to the conclusion that beaver activity has had an intense impact on the terrain relief of the valley inhabited by beavers.

Effects of Texture Bottom Profile on Static and Dynamic Characteristics of Journal Bearings

The purpose of this paper is to numerically study the effect of texture bottom profile on static, dynamic, and stability performance parameters of hydrodynamic journal bearings. The different performance parameters of square textured journal bearings with different bottom profiles are numerically investigated and compared with those of smooth journal bearing. There are five bottom profiles of this square texture: flat, curved, isosceles triangle (T1), oblique triangle (T2), and oblique triangle (T3). The static and dynamic coefficients are calculated by solving the steady-state Reynolds equation and the perturbation equations with FDM numerical technique. The performance characteristics under different texture distribution, depth, and bottom profiles are studied, and the current numerical results show that the selection of texture parameters is crucial to improve the static, dynamic, and stability performances of hydrodynamic journal bearing. Meanwhile, it is also found that the square texture with a flat bottom profile has a higher improvement in the values of static performance parameters in comparison to those other bottom profiles. Moreover, the simulation results indicate that the dynamic and stability performances improvement of textured journal bearing is also significant, especially when the eccentricity ratio is smaller.

Strength analysis of warship hull’s bottom loaded by the pressure wave from a non-contact explosion of sea mine explosion of sea mine

The study was based on the analysis of stamina of steel flat bottom section of transport warships, burdened by the spherical pressure wave from the non-contact explosion of TNT at a distance of 20 m under the keel. This study aims to determine the TNT mass required to break the hull. The task was solved by finite element method (FEM) explicite using CAE program [1], in which the hull’s bottom was modelled as thin shell space. The hull’s burden with pressure wave was modelled as a pressure impulse specified by the formula introduced by T.L. Geers, K.S. Hunter and R.S. Price [2]. To describe the material properties, considering high-speed strain, the Johnson-Cook model was used [3]. Therefore, the main goal of the hereby paper is to present how to correctly model the impact of large, concentrated masses of the ship’s equipment on its hull. The study presents the results of the calculated stress and strain states of the analysed section of the construction of the hull.

Anti-Biofilm Formation of an Adhesive Containing Calcium Salts of Acidic Monomers against Oral Candida Related to Root Caries

The proportion of older people within the general population is expanding due to the decline of birth rate and the increase of life expectancy. Increasing elderly populations, which is retaining its teeth longer, leads to oral health problems, for example, root caries. The main etiological factor for the initiation and development of root caries is the appearance of cariogenic biofilm. The acid-producing and acid-tolerant bacteria and oral yeast, such as Candida albicans are the major contributors in root caries formation. A new generation of adhesives is developed with several modifications for the prevention of dental caries by incorporating antimicrobial components. The aim of this study was to investigate the antimicrobial effect of adhesive containing calcium salt of acidic monomers on the biofilm formation of oral Candida related to root caries. In the experiments, the flat-bottom surfaces of 96-well plate were painted with an adhesive containing calcium salts of 4-methacryloxyethyl trimellitic acid (CMET) and 10-methacryloyloxydecyl dihydrogen calcium phosphate (MDCP) (Bio-Coat, CA, Sun Medical, Japan). Then they were LED light-cured and coated with sterile saliva at 37 °C for 60 min. The biofilm formation was made by adding of Candida albicans (ATCC 10238 and two clinical strains) suspensions (107 colony forming unit/mL) and incubated at 37°C for 24 h. The amount of vital biofilm was determined by WST-8 Microbial Cell Counting Kit (Dojindo Molecular Technologies, USA). All experiments were done in triplicate and repeated three times. Statistical analysis was performed using Student’s t-test. The results clearly showed that adhesive could significantly inhibit biofilm formation of all tested Candida compared with a control. This suppressive effect was not different among the strains of Candida. The percentages of vital biofilm reduction were 25% to 40%. The ability of this adhesive to suppress biofilm of oral yeast may be its antimicrobial property of acidic monomer or the effect of calcium ion within the adhesive, which can alter Candida cell morphology, and influence their structures or process of biofilm formation. In conclusion, an adhesive containing calcium salts of acidic monomers could significantly inhibit biofilm formation of C. albicans. This adhesive could be effectively applied to exposed root surfaces to prevent or inhibit the progression of root caries. Further studies are necessary to clarify the effect on multispecies biofilm, on long-term activity, and in vivo conditions.

Numerical simulation of wave phenomena using FreeFEM

In this research free surface motion governed by the shallow water equations is considered. A numerical scheme based on the finite element method, which is incorporated in the open source FreeFEM, was used to simulate several wave phenomena. By carefully setting the corresponding initial condition as well as boundary conditions, several numerical computations were conducted. Numerical simulations presented here are standing wave in a closed basin, progressive wave over a flat bottom, as well as wave shoaling over a decreasing depth and wave refraction. In all cases above, the existing analytical formula are used to validate the numerical results. These computations suggest that explicit-implicit scheme is appropriate for varying water wave simulations.

Analyzing the functional structure of pottery jiandiping amphorae

There are numerous, controversial theories on the function of the jiandiping amphorae as Yangshao culture water-drawing vessel, wine vessel, or other. This paper discusses jiandiping amphorae functional form from a typological perspective and presents the view from molding technique. The primary function of the pointed bottom concerned sedimentation, yet the vessel’s small opening was poorly adapted to cereal fermentation. The large jiandiping amphora was less transportable but better suited to long-term storage and sedimentation: wine decanted into medium- or small-sized flat-bottom vessels or jiandiping amphora was easily transferred and used, and decanting served to remove any sediment from turbid wine. Functional differences between the large and small jiandiping amphorae explain varying functions and uses of double-loop handles. The development of sediment separation technique is the key reason for the disappearance of the jiandiping amphorae.