Blue - A Language for Teaching Object-Oriented Programming

Teaching object-oriented programming has clearly become an important part of computer science education. We agree with many others that the best place to teach it is in the CS1 introductory course. Many problems with this have been reported in the literature. These mainly result from inadequate languages and environments. Blue is a new language and integrated programming environment, currently under development explicitly for object-oriented teaching. We expect clear advantages from the use of Blue for first year teaching compared to using other available languages. This paper describes the design principles on which the language was based and the most important aspects of the language itself

Testing Object-Oriented Programs: Making it Simple

One of the major difficulties facing anyone trying to teach the first programming course is how to encourage students to thoroughly test their programs. We would argue that the main reasons for this are the lack of suitable tools for testing and the need to write extra "debug" code in order to verify correct operation. We further argue that the problem is even worse with object-oriented languages because of multiple classes and encapsulation. In this paper we describe the testing tools within the Blue programming environment which allow object-oriented programs to be thoroughly tested without writing a single line of new code

I/O Considered Harmful (At least for the first few weeks)

One of the major difficulties with teaching the first programming course is input/output. It is desirable to show students how to input data and output results early in the course in order to motivate the students and so that they can see the results of their programs. Output is also a useful tool for testing programs. However, in most programming languages input and output are esoteric and the techniques for performing input and output must be learnt by the students at an early stage, precisely when they are trying to understand the basics of programming. We argue that input/output operations need not be taught in the early stages of a course if the language environment provides appropriate tools for testing programs. This assertion is demonstrated by reference to the Blue objectoriented language and environment

Galaxy Formation: Was There A Big Bang Shell?

The tight correlation of galactic velocity distribution to both luminosity and its black hole mass and the relation of halo parameters to luminous mass distribution, can not be due to collapse dynamics. A big bang shell can solve galaxy formation problems by forming the supermassive black holes necessary to capture the initial blast wave in a coordinated pattern.Comment: 7 pages late

Carbon-13 nuclear magnetic resonance spectra and mechanism of bridge–terminal carbonyl exchange in di-µ-carbonyl-bis[carbonyl(η-cyclopentadienyl)iron](Fe–Fe)[{(η-C5H5)Fe(CO)2}2]; cd-di-µ-carbonyl-f-carbonyl-ae-di(η-cyclopentadienyl)-b-(triethyl -phosphite)di-iron(Fe–Fe)[(η-C5H5)2Fe2(CO)3P(OEt)3], and some related complexes

A mechanism involving carbonyl-bridge breaking, rotation about the Fe–Fe bond, and bridge reformation is shown to account qualitatively for changes in the carbonyl region of the 13C n.m.r spectrum of the complex [(cp)(OC)[graphic omitted]e(cp){P(OEt)3}] and quantitatively for [(cp)(OC)[graphic omitted]e(CO)(cp)](cp =η-cyclopentadienyl).The activation energy for this process, 49.0 ± 4 kJ mol^–1(11.7 ± 1 kcal mol^–1), is close to that reported for cis–trans-isomerization of the cp groups, in accord with this mechanism. Variable-temperature 13C n.m.r. spectra of the complexes [(cp)(OC)[graphic omitted]u(CO)(cp)] and [(cp)(OC)[graphic omitted]i(cp)] are also reported

A Computational Analysis of Wind Turbine and Wind Farm Aerodynamics with a Focus on Dual Rotor Wind Turbines

This dissertation serves to summarize my research into wind farm and wind turbine aerodynamics. Included in this thesis is a summary of the methods I use as well as the four research problems that I investigated. Motivation is provided for my research as well as an overview of the computational methods that I use. These methods include analytical methods such as blade element momentum (BEM) theory and the vortex lattice method as well as computational fluid dynamic methods like the Reynolds averaged Navier-Stokes (RANS) equations and large eddy simulation (LES). These methods are used to investigate wind turbine and wind farm aerodynamics. In particular, I use these methods to confront the various forms of loss that wind turbines and wind farms experience. They include the losses that individual turbines experience due to swirl, induction, and viscosity as well as the loss that wind farms experience due to turbine-wake interaction. Horizontal axis wind turbines (HAWTs) suffer from aerodynamic ineffciencies in the blade root region (near the hub) due to several non-aerodynamic constraints. Aerodynamic interactions between turbines in a wind farm also lead to signifcant loss of wind farm efficiency. A new dual-rotor wind turbine (DRWT) concept is proposed that aims at mitigating these two losses. A DRWT is designed that uses an existing turbine rotor for the main rotor, while the secondary rotor is designed using a high lift-to-drag ratio airfoil. Reynolds Averaged Navier-Stokes computational fluid dynamics simulations are used to optimize the design. Large eddy simulations confirm the increase energy capture potential of the DRWT. Wake comparisons however do not show enhanced entrainment of axial momentum. I extend the prescribed wake vortex lattice method (VLM) to perform aerodynamic analysis and optimization of dual-rotor wind turbines. The additional vortex system introduced by the secondary rotor of a DRWT is modeled while taking into account the singularities that occur when the trailing vortices from the secondary (upstream) rotor interact with the bound vortices of the main (downstream) rotor. Pseduo-steady assumption is invoked and averaging over multiple relative rotor positions is performed to account for the primary and secondary rotors operating at different rotational velocities. This implementation of the VLM is first validated against experiments and blade element momentum theory results for a conventional, single rotor turbine. The solver is then verified against RANS CFD results for two DRWTs. Parametric sweeps are performed using the proposed VLM algorithm to optimize a DRWT design. The problem with the algorithm at high loading conditions is highlighted and a solution is proposed that uses RANS CFD results to calibrate the VLM model. In addition to wake losses, aerodynamic interaction between turbines in wind farms leads to surface flow convergence . This phenomenon has been observed in field tests with surface flux stations. A hypothesis is proposed to explain this surface flow convergence phenomenon - incomplete pressure recovery behind a turbine leading to successive pressure drops in tightly-spaced turbine arrays leads to drop in overall pressure deep inside a wind plant; this low-pressure acts as an attractor leading to flow convergence. Numerical investigations of the phenomenon of surface flow convergence are carried out that support this hypothesis. An actuator disk model to represent wind turbines in an LES CFD solver is used to simulate hypothetical wind plants. The flow convergence phenomenon reflects as change in flow velocity direction and is more prominent near the ground than at turbine hub height. Numerical simulations of wind plant aerodynamics are conducted with various approximations to investigate and explain the flow convergence phenomenon