A conceptual model for unifying variability in space and time: Rationale, validation, and illustrative applications

With the increasing demand for customized systems and rapidly evolving technology, software engineering faces many challenges. A particular challenge is the development and maintenance of systems that are highly variable both in space (concurrent variations of the system at one point in time) and time (sequential variations of the system, due to its evolution). Recent research aims to address this challenge by managing variability in space and time simultaneously. However, this research originates from two different areas, software product line engineering and software configuration management, resulting in non-uniform terminologies and a varying understanding of concepts. These problems hamper the communication and understanding of involved concepts, as well as the development of techniques that unify variability in space and time. To tackle these problems, we performed an iterative, expert-driven analysis of existing tools from both research areas to derive a conceptual model that integrates and unifies concepts of both dimensions of variability. In this article, we first explain the construction process and present the resulting conceptual model. We validate the model and discuss its coverage and granularity with respect to established concepts of variability in space and time. Furthermore, we perform a formal concept analysis to discuss the commonalities and differences among the tools we considered. Finally, we show illustrative applications to explain how the conceptual model can be used in practice to derive conforming tools. The conceptual model unifies concepts and relations used in software product line engineering and software configuration management, provides a unified terminology and common ground for researchers and developers for comparing their works, clarifies communication, and prevents redundant developments

Risk thresholds for alcohol consumption : combined analysis of individual-participant data for 599 912 current drinkers in 83 prospective studies

Background Low-risk limits recommended for alcohol consumption vary substantially across different national guidelines. To define thresholds associated with lowest risk for all-cause mortality and cardiovascular disease, we studied individual-participant data from 599 912 current drinkers without previous cardiovascular disease. Methods We did a combined analysis of individual-participant data from three large-scale data sources in 19 high-income countries (the Emerging Risk Factors Collaboration, EPIC-CVD, and the UK Biobank). We characterised dose-response associations and calculated hazard ratios (HRs) per 100 g per week of alcohol (12.5 units per week) across 83 prospective studies, adjusting at least for study or centre, age, sex, smoking, and diabetes. To be eligible for the analysis, participants had to have information recorded about their alcohol consumption amount and status (ie, non-drinker vs current drinker), plus age, sex, history of diabetes and smoking status, at least 1 year of follow-up after baseline, and no baseline history of cardiovascular disease. The main analyses focused on current drinkers, whose baseline alcohol consumption was categorised into eight predefined groups according to the amount in grams consumed per week. We assessed alcohol consumption in relation to all-cause mortality, total cardiovascular disease, and several cardiovascular disease subtypes. We corrected HRs for estimated long-term variability in alcohol consumption using 152 640 serial alcohol assessments obtained some years apart (median interval 5.6 years [5th-95th percentile 1.04-13.5]) from 71 011 participants from 37 studies. Findings In the 599 912 current drinkers included in the analysis, we recorded 40 310 deaths and 39 018 incident cardiovascular disease events during 5.4 million person-years of follow-up. For all-cause mortality, we recorded a positive and curvilinear association with the level of alcohol consumption, with the minimum mortality risk around or below 100 g per week. Alcohol consumption was roughly linearly associated with a higher risk of stroke (HR per 100 g per week higher consumption 1.14, 95% CI, 1.10-1.17), coronary disease excluding myocardial infarction (1.06, 1.00-1.11), heart failure (1.09, 1.03-1.15), fatal hypertensive disease (1.24, 1.15-1.33); and fatal aortic aneurysm (1.15, 1.03-1.28). By contrast, increased alcohol consumption was loglinearly associated with a lower risk of myocardial infarction (HR 0.94, 0.91-0.97). In comparison to those who reported drinking >0-100-200-350 g per week had lower life expectancy at age 40 years of approximately 6 months, 1-2 years, or 4-5 years, respectively. Interpretation In current drinkers of alcohol in high-income countries, the threshold for lowest risk of all-cause mortality was about 100 g/week. For cardiovascular disease subtypes other than myocardial infarction, there were no clear risk thresholds below which lower alcohol consumption stopped being associated with lower disease risk. These data support limits for alcohol consumption that are lower than those recommended in most current guidelines. Copyright (C) The Author(s). Published by Elsevier Ltd.Peer reviewe

Active Flow Separation Control on a High-Lift Wing-Body Configuration. Part 2: The Pulsed Blowing Application.

This contribution discusses the implementation of active flow separation control for a 3D high-lift wing-body configuration under atmospheric low-speed wind tunnel conditions. The slot-actuators are applied on the suction side of the trailing edge flap to prevent local flow separation. It is the consequent progression of the work presented in Part 1 of this paper. The active flow control (AFC) method of choice is now the pulsed blowing. The experimental results indicate that this AFC technique is feasible for such applications with a global performance enhancement. Here, the wind tunnel findings are briefly discussed while the emphasis is given on the numerical investigations. The verification of the URANS approach points out that the global enhancement through AFC may easily be overestimated by insufficient numerical convergence. Thus, high computational requirements are needed for a consistent numerical evaluation. The computational results highlight the ability of pulsed blowing at moderate blowing momentum coefficients to suppress the flow separation on the trailing edge flap and support the global aerodynamic enhancement. The numerical results show an acceptable agreement with the experimental results for this AFC application

Active Flow Separation Control on a High-Lift Wing-Body Configuration - Part 1: Baseline Flow and Constant Blowing

This paper describes the influence of grid resolution and turbulence modeling for a 3D transport aircraft in high lift configuration with massive flap separation. The flap is equipped with spanwise slotted active flow control (AFC) devices to allow studies on active separation control. The effects of constant slotted blowing on the high lift performance are highlighted. Oil flow pictures from a mid-scale experiment in the low speed wind tunnel of Airbus in Bremen (B-LSWT) serve as a validation database for the baseline CFD results. RANS calculations are carried out with and without constant blowing boundary conditions. The baseline flow is also investigated with a time-accurate URANS approach. One of the major outcomes of the AFC study is the demonstration of the feasibility to simulate AFC concepts on a 3D configuration. Constant blowing shows the beneficial effect that separation can largely be suppressed because of the energy added to the flow on the suction side of the flap. This study serves as a preceding validation for the subsequent pulsed blowing approach treated in Part 2

Active Separation Control on High-Lift Configurations using a URANS approach

This contribution discusses numerical investigations of active flow separation control for high-lift configurations under atmospheric low-speed wind tunnel conditions. A two dimensional (2D), 2-element airfoil and a three-dimensional (3D), 3-element, wing body setup are the configurations of interest. The slot-actuators are applied on the suction side of the trailing edge flap to prevent the local flow separation. The active flow control (AFC) method of choice is the pulsed blowing. This study explores the resulting effects of the flow control application on the global aerodynamic coefficients and, beyond this, by the analysis of the resulting loads variation by specific actuation parameters. The computational results highlight the ability of pulsed blowing at moderate blowing momentum coefficients to suppress the flow separation on the trailing edge flap and support the global aerodynamic enhancement

Passive Control of the Flow Around the Stratospheric Observatory for Infrared Astronomy

The unsteady flowfield around the Stratospheric Observatory for Infrared Astronomy, a reflecting telescope carried inside an open port of a Boeing 747SP, has been simulated by means of detached eddy simulations and unsteady Reynolds-averaged Navier–Stokes simulations. Vortex generators have been placed upstream of the cavity to control the shear layer spanning the opening. The influence of baffles and displacement bodies placed inside the telescope port on the frequencies of acoustic resonant modes was investigated by acoustic simulations, based on the solution of the homogenous Helmholtz equation. The objective of this study is to improve the telescope’s performance by mitigating the amplitudes and changing the characteristic frequencies of the pressure fluctuations inside the cavity. The present simulations show that the investigated measures have a high potential to increase the telescope’s pointing stability