Application of improved numerical schemes

Two approaches which accelerate the solution of the steady state Navier-Stokes equations are discussed. The SIMPLER algorithm, a revised version of SIMPLE, provides a more accurate pressure field for each iteration through the momentum equations, thereby speeding convergence. PISO (Pressure Implicit Split Operator), performs a secondary correction of the velocity and pressure fields (after the typical pressure correction) which enhances convergence. Both schemes account for terms neglected in the SIMPLE approach, but do so in slightly different ways. Two dimensional driven cavity flow and flow over a step were calculated to examine the effect of geometry on the performance of these schemes. Computations were carried out on a series of progressively finer grids. The effect of relaxation number on convergence rate was analyzed, using results from SIMPLE as criteria for performance correlation. Results show: (1) the improved schemes promoted convergence by up to 60% for the driven cavity and 40% for flow over a step; (2) for the driven cavity problem, the efficiency of PISO and SIMPLER increased as the number of nodes increased; and (3) to ensure faster convergence, higher relaxation numbers must be applied

Implications of Being a Highly Rated Organization: Evidence from Four-Star Rated Nonprofits

This study examines a group of nonprofits rated four stars by Charity Navigator. The purpose is to determine whether this select group of charities exhibits characteristics associated with top charitable organizations, or whether the four-star rating achieved is limited to the more narrow financial metrics employed in the methodology utilized by Charity Navigator. This study finds that organizations rated four stars by Charity Navigator show a lower level of excess cash holdings, report a lower level of compensation expenses and exhibit lower sensitivity of compensation to performance. Financially, these organizations are less vulnerable than their lower rated peers. The results from this study shed light on the continuing debate of the effectiveness of rating agencies to accurately identify top performing charitable organizations

Accelerated convergence for incompressible flow calculations

Two improved algorithms which solve the steady-state Navier-Stokes equations, PISO and SIMPLER, are studied. Computations were carried out on progressively finer grids for the driven cavity and flow over a backward-facing step. The effects of relaxation factor, number of grid nodes and number of sweeps through the pressure equations are studied to evaluate the performance of the PISO and SIMPLER schemes. Results show that these improved schemes accelerate the convergence rate of the solution generally by a factor of two as compared to the SIMPLE method

Self-Directed Death, Euthanasia, and the Termination of Life-Support: Reasonable Decisions to Die

The purpose of this paper is to challenge the common legal and psychiatric presumption that all decisions to die result from a clouded mind. Indeed, a realistic and common sense view of the issue asserts quite the contrary: namely, that self-directed death may prove to be an optimally rational course of action in light of an individual\u27s circumstances and ends. While the state has a legitimate concern in the welfare of its citizens and should seek to prevent unwarranted loss of life, it should be loathe to force a mentally competent adult to remain alive against his will and best interests

Self-Directed Death, Euthanasia, and the Termination of Life-Support: Reasonable Decisions to Die

The purpose of this paper is to challenge the common legal and psychiatric presumption that all decisions to die result from a clouded mind. Indeed, a realistic and common sense view of the issue asserts quite the contrary: namely, that self-directed death may prove to be an optimally rational course of action in light of an individual\u27s circumstances and ends. While the state has a legitimate concern in the welfare of its citizens and should seek to prevent unwarranted loss of life, it should be loathe to force a mentally competent adult to remain alive against his will and best interests

Reducing numerical diffusion for incompressible flow calculations

A number of approaches for improving the accuracy of incompressible, steady-state flow calculations are examined. Two improved differencing schemes, Quadratic Upstream Interpolation for Convective Kinematics (QUICK) and Skew-Upwind Differencing (SUD), are applied to the convective terms in the Navier-Stokes equations and compared with results obtained using hybrid differencing. In a number of test calculations, it is illustrated that no single scheme exhibits superior performance for all flow situations. However, both SUD and QUICK are shown to be generally more accurate than hybrid differencing

Flame radiation and liner heat transfer in a tubular-can combustor

Heat transfer within a combuster were examined. Total and spectral flame radiation in a tubular can combustor at a series of parametric operating conditions was measured. Radiation measurements were taken for a range of inlet air pressures from 0.34 to 2.0 MPa, inlet air temperatures from 533 to 700 K, with two different fuels, Jet-A and ERBS. Measurements of liner temperatures combined with the parametric radiation results allowed a calculation of the combustor liner heat loads. Flame emissivity was determined from the spectral measurements

Playing the Ratings Game: The Significance of the Four Star Rating

This study examines a group of exemplary rated nonprofits, organizations rated four stars by Charity Navigator, to determine if this select group of charities exhibits characteristics associated with top charitable organizations, or if the four-star rating achieved is limited to the more narrow financial metrics employed in the methodology utilized by Charity Navigator. Organizations rated four stars by Charity Navigator report a lower level of excess cash holdings, report lower levels of executive compensation and executive compensation that is less sensitive to performance, and are less financially vulnerable than their lower rated peers. The results shed light on the continuing debate of the effectiveness of the rating agencies to accurately identify top performing charitable organizations

Impaired glucose tolerance: qualitative and quantitative study of general practitioners' knowledge and perceptions

Objective: To investigate general practitioners' knowledge of and attitudes to impaired glucose tolerance. Design: Mixed methodology qualitative and quantitative study with semistructured interviews, focus groups, and questionnaires. Setting: 34 general practitioners in five primary care groups in the north east of England. Results: All the general practitioners had knowledge of impaired glucose tolerance as a clinical entity, but they had little awareness of the clinical significance of impaired glucose tolerance and were uncertain about managing and following up these patients. Attitudes to screening were mixed and were associated with reservations about increased workload, concern about lack of resources, and pessimism about the effectiveness of lifestyle interventions. Some general practitioners felt strongly that screening patients for impaired glucose tolerance and subsequent lifestyle intervention medicalised an essentially social problem and that a health educational approach, involving schools and the media, should be adopted instead. A minority expressed a positive attitude towards a pharmacological approach. Conclusion: Awareness of impaired glucose tolerance needs to be raised, and guidelines for management are needed. General practitioners remain to be convinced that they have a role in attempting to reduce the incidence of type 2 diabetes by targeting interventions at patients with impaired glucose tolerance

The Onset for Compressibility Effects for Aerofoils in Ground Effect

The influence of flow compressibility on a highly-cambered inverted aerofoil in ground effect is presented, based on two-dimensional computational studies. This type of problem has relevance to open-wheel racing cars, where local regions of high-speed subsonic flow form under favourable pressure gradients, even though the maximum freestream Mach number is typically considerably less than Mach 0.3. An important consideration for CFD users in the field is addressed in this paper, the freestream Mach number at which flow compressibility significantly affects aerodynamic performance. More broadly, for aerodynamicists, the consequences of this are also considered. Comparisons between incompressible and compressible CFD siulations are used to identify important changes to the flow characteristics caused by density changes, highlighting the inappropriateness of incompressible simulations of ground effect flows for freestream Mach numbers as low as 0.15