Separating inviscid flows

Summary The separating flow of an inviscid fluid is not only a limit solution of the steady separating, laminar fluid flow at high values of the Reynolds number but it is also part of its structure (Smith [1], [2]). This work aims at reexamining the separating flow of inviscid fluid past a bluff body which is fixed in an otherwise uniform stream of fluid. For the purpose of this paper we will assume that the bluff body is a circular cylinder but the theory is applicable to bodies of any shape. It is further assumed that the fluid is in steady two-dimensional motion and is inviscid and of constant density. The flow structure is assumed to consist of a separated flow region, caviting flows in which there exists a free surface on which the pressure is constant, and a wake. A twin spiral vortex model is used in order to determine the shape of the free streamline. Based on the free streamline theory the problem reduces to solving a mixed boundary value problem and a Hilbert solution for the inverse problem in the auxiliary plane is obtained. When we consider the flow in the physical plane the problem is transformed into a direct problem in which the geometry of the solid body is given in advance. We assume that the separation is smooth and thus the curvature of the free streamline at the point of free detachment be equal to that of the body surface. A numerical method for solving the two-dimensional potential flows past arbitrarily shaped curved bluff bodies is developed.When the cavitation number is zero the angle of separation is approximately 55° and the computed results predict that the position of the separation point will move backward as the cavition number increases. The relationships between the drag coefficient, and the width and length of the cavity is determined and is found to be in very good agreement with the predictions of Smith [1].     

Wind excitation of neighbouring tall buildings

There is a growing concern about the importance of interaction effects between neighbouring tall buildings subjected to wind loading. Available results indicate that both the peak dynamic response as well as the mean wind loads may increase substantially due to building interaction.An extensive wind-tunnel study of the interaction between two square prisms with a height-to-base length equal to six was undertaken at the LAC, UFRGS. Fifteen relative prism positions were studied, for wind orientations at every 15°, under smooth-uniform as well as turbulent-shear wind. Mean force and torsional moment coefficients for uniform flow were reported in previous publications. Herein, complete results for turbulent wind are given. In addition, the most important interaction effects observed under both flow conditions are discussed in detail.     

Subdivision of work on construction projects

In order to control a project, construction management requires project information. This is obtained through accounting, estimating, cost management and scheduling functions which produce project reports. These reports are best obtained by subdividing the project into small parts. The ways in which each of these functions subdivides a project in order to produce its reports is discussed, together with a means of interrelating this information with a technique known as the work breakdown structure.     

Behavior of cylindrical tanks whose axes are horizontal

A cylindrical tank is mounted with its axis horizontal. Supports on either side run lengthwise. If the tank wall is thin, deformations significantly affect the stresses, so that standard stress formulae (which ignore deformations) may over-estimate stresses by a factor of ten or more. In this paper, deformations are accounted for by a nonlinear analysis. Stresses and deformed shapes are reported for various positions of the supports, radius to thickness ratios, and depths of fill.     

Formation of cube texture in nickel-palladium alloys for epitaxial substrates for deposition of high-temperature superconductors

The texture, structure, and magnetic and mechanical properties of thin ribbons of nickel-palladium alloys have been studied. It has been demonstrated that in Ni₉₄Pd₆ and Ni_92.5Pd₅W_2.5 alloys, a sharp cube texture can be formed that is stable up to rather high annealing temperatures. Segregation of palladium atoms to surface layers of ribbons has been found, which gives additional advantages for using these ribbons as substrates for epitaxial deposition of high-temperature superconductors.     

Surface tension isotherms of a free surface and grain boundaries in the Cu-Sn system

Surface tension of pure copper and its alloys with Sn has been measured at 1000°C in a hydrogen atmosphere. Surface tension of a free surface equaled 1.81 N/m for pure copper, and 1.55, 1.38, and 1.28 N/m for the alloys with 0.05, 0.22, and 0.33 at % Sn, respectively; surface tension at grain boundaries equaled 0.5 N/m for pure copper, and 0.36, 0.3, and 0.23 N/m for the alloys, respectively. Based on these data, the concentration dependence of tin absorption at a free surface and grain boundaries has been calculated. Parameters of Sn absorption at grain boundaries and a free surface of copper have been compared with those of Sb and Bi.     

A DSP-Based Remote Control Laboratory

This paper presents a framework for rapid remote experiment implementation in the field of automatic control. The proposed solution is based on in-house developed embedded control hardware and two commercially available software packages. MATLAB/Simulink is used for rapid experiment control algorithm development, while LabVIEW is used for the user front-end and remote control. A combination of presented hardware and software solutions enables the rapid and easy creation of different interactive remote control experiments. Using this solution, a digital-signal-processor-based remote control laboratory for teaching purposes has been realized. This remote laboratory enables the remote users to easily interact with a set of physical control experiments through the Internet. In the friendly user interface, the remote user can change predefined system parameters and observe system response in textual, graphical, or video format. In addition, this remote laboratory includes a booking system, which enables remote users to book experiments in advance.     

Laser scanning path generation considering photopolymer solidification in micro-stereolithography

It is essential to automate the scanning path generation process to effectively implement the micro-stereolithography. However, a scanning path that is generated based only on a 3D CAD model introduces dimensional inaccuracies. In micro-stereolithography, the photopolymer solidification is affected by fabrication conditions, such as the optical properties (laser power, laser scanning speed, laser scanning pitch focusing condition, etc.) and material properties of the photopolymer. Thus, the photopolymer solidification phenomena must be considered when generating a laser scanning path. In this paper, a scanning path generation algorithm that uses 3D CAD data and considers the photopolymer solidification phenomena is proposed to improve the dimensional accuracy in micro-stereolithography. Multi-line photopolymer solidification experiments were performed for various laser scanning conditions to examine the photopolymer solidification phenomena. From these experiments, linear relations between the solidification length (width) and scanning length (width) were acquired and stored in a database. Subsequently, these data were utilized to compensate the scanning path of the laser beam. In addition, experiments for determining the layer thickness in the z-direction were performed and these results were also used in the scanning path generation algorithm.This research was supported by the Highly Advanced National Project (http://www.most.go.kr), which performs some of the National R&D Program, and sponsored by the Korean Ministry of Science and Technology under the contract project code M10214000116-02B1500-02010.