Modelling dan Pembuatan Algoritma Aliran Fluida pada External Ballistics dengan Model G1-Standard-Bullet Menggunalan Metode Lattice Boltzmann

INTISARIKomputasi dan eksperimental dalam dunia teknik permesinan (mechanical engineer) merupakan bidang yang saling melengkapi. Komputasi dilakukan untuk memberikan gambaran dan penjelasan rasional dari fenomena yang dihasilkan pada eksperimen. Komputasi juga memberikan prediksi sebelum dilakukan eksperimen untuk lebih mematangkan kondisi-kondisi dari sebuah eksperimen. Komputasi dengan metode Lattice Boltzmann adalah metode yang relatif baru dan menjanjikan di dunia komputasi aliran fluida atau CFD (Computational Fluid Dynamics), sebagai alternative metode yang sudah lama dikembangkan dari persamaan kontunum Navier-Stokes. Metode Lattice Boltzmann berangkat dari logika interaksi sekumpulan partikel dan ditelusuri pola interaksinya melalui bantuan pola jaringan (lattice). Pada riset ini akan digunakan metode Lattice Boltzmann untuk membuat model matematis dan algoritmanya pad aliran fluida yang mengalir di sekitar External Ballistics model G1-Standard-Bullet. Tahap riset selanjutnya adalah pengembangan pembuatan coding pemrograman dan simulasi visual untuk mengetahui pola aliran dan analisis-analisis aerodinamisnya. ABSTRACTComputational and experimental in the world of mechanical engineering is a complementary field and providing a picture and a rational explanation of the phenomena generated from the experiment. Computation with the Lattice Boltzmann method is a relatively new and promising method in the world of fluid flow computation or CFD (Computational Fluid Dynamics), as an alternative to the long-established method of the Navier-Stokes continuum equation. The Lattice Boltzmann method departs from the logic of the interaction of a set of particles and traces its interaction pattern through the aid of a network pattern (lattice). In this research we will use the Lattice Boltzmann method to create a mathematical model and algorithm for the flow of fluid flowing around External Ballistics model G1-Standard-Bullet. The next stage of research is developing the development of coding programming and visual simulation to know the flow pattern and aerodynamic analysis.

Modeling of the Critical Deposition Velocity of Cuttings in an Inclined-Slimhole Annulus

Summary A coupled computational-fluid-dynamics/discrete-element-method (CFD/DEM) theory is developed to simulate the transportation of cuttings in an inclined-slimhole annulus. In this theory, the liquid phase is governed by the Eulerian continuum equation and the Navier-Stokes momentum-conservation equation. The collisions between particle and wall, between particle and drillstring, and among particles are treated as the spring-damping system, and the particle-contact model is then established. The particle-governing equation based on Newton's second law is established by analyzing the forces on the particles. The CFD/DEM theory is developed by analyzing the forces on the dispersed particles per unit volume, which is the source term in the coupling. Using this CFD/DEM coupling algorithm, cuttings transportation in slimhole drilling is investigated, and the particle velocity and distributions are calculated. The calculated annular cuttings concentration is in good agreement with experimental data from the literature (Kim et al. 2014). The effects of the annular-fluid velocity, angle of inclination, cuttings concentration in feeding, and rotation speed of the drillstring on the annular cuttings concentration are also investigated. A correlation of critical deposition velocity has been proposed by use of dimensional analysis and nonlinear regression analysis. The correlation of annular cuttings concentration is also concluded. The new method proposed in this work is of great significance to hole-cleaning calculation and hydraulic-parameter design in slimhole drilling.

Fuzzy Solutions for Two-Dimensional Navier-Stokes Equations

A new methodology via using an adaptive fuzzy algorithm to obtain solutions of “Two-dimensional Navier-Stokes equations” (2-D NSE) is presented in this investigation. The design objective is to find two fuzzy solutions to satisfy precisely the 2-D NSE frequently encountered in practical applications. In this study, a rough fuzzy solution is formulated with adjustable parameters firstly, and then, a set of adaptive laws for optimally tuning the free parameters in the consequent parts of the proposed fuzzy solutions are derived from minimizing an error cost function which is the square summation of approximation errors of boundary conditions, continuum equation and Navier-Stokes equations. In addition, elegant approximated error bounds between the exact solution and the proposed fuzzy solution with respect to the number of fuzzy rules and solution errors have also been proven. Furthermore, the error equations in mesh points can be proven to converge to zero for the 2-D NSE with two sufficient conditions.

A comparison of various basis functions based on meshless local Petrov-Galerkin method for linear stability of circular jet

Various basis functions based on Fourier-Chebyshev Petrov-Galerkin spectral method are described for computation of temporal linear stability of a circular jet. Basis functions presented here are exponentially mapped Chebyshev functions. There is a linear dependence between the components of the perturbation vector field, and there are only two degrees of freedom for the perturbation continuum equation. According to the principle of permutation and combination, the basis function has three basic forms, i. e., the radial, azimuthal or axial component, respectively. The results show that three eigenvalues for various cases are consistent, but there is a preferable basis function for numerical computation.

Theory of Passive Permeability through Lipid Bilayers

Recently measured water permeability through bilayers of different lipids is most strongly correlated with the area per lipid A rather than with other structural quantities such as the thickness. This paper presents a simple three-layer theory that incorporates the area dependence in a physically realistic way and also includes the thickness as a secondary modulating parameter. The theory also includes the well-known strong correlation of permeability upon the partition coefficients of general solutes in hydrocarbon environments (Overton's rule). Two mathematical treatments of the theory are given; one model uses discrete chemical kinetics and one model uses the Nernst-Planck continuum equation. The theory is fit to the recent experiments on water permeability in the accompanying paper.

Direct Measurement of Ion Beam Induced, Nanoscale Roughening of GaN

AbatractThe formation of ion induced nanoscale patterns such as ripple, dots or pores can be described by a linear continuum equation consisting of a surface roughening term due to curvature-dependent sputtering or asymmetric attachment of vacancies, and a surface smoothing term due to thermal or ion-induced diffusion. By studying ion-induced dimple volume change using atomic force microscopy, we show a method to measure the ion-roughening coefficient. Using this method, we found the roughening coefficient í was 45 nm2/sec at 730K for initial ion etchings with 300 eV Argon ions. Cathodoluminescence measurements indicated Ga-vacancy formation during ion bombardment. The activation energy for surface relaxation after ion etching was about 0.12 eV as measured by reflection high energy electron diffraction.

Unstable Etching Of Si(110)with Potassium Hydroxide

ABSTRACTWe present the experimental data for the morphological evolution of Si(110) etched with Potassium Hydroxide. The observed results are interpreted using a continuum equation. The results reveal the presence of unstable etching, which leads to the formation of a columnar structure on the surface. The early stage of the formation of this columnar structure can be explained by a linear theory. This instability is caused by anisotropic surface tension.

A Model for Ion-Sputtering: from Pattern Formation to Rough Surfaces

ABSTRACTMany surfaces eroded by ion-sputtering have been observed to develop morphologies which are either periodic, or rough and non-periodic. We have introduced a discrete stochastic model that allows to interpret these experimental observations within a unified framework. A simple periodic pattern characterizes the initial stages of the surface evolution, whereas the later time regime is consistent with self-affine scaling. The continuum equation describing the surface height is a noisy version of the Kuramoto-Sivashinsky equation.