Coastal environments, in particular heavily populated semi-enclosed marginal seas and coasts like the Baltic Sea region, are strongly affected by human activities. A multitude of human impacts, including climate change, affect the different compartments of the environment, and these effects interact with each other. As part of the Baltic Earth Assessment Reports (BEAR), we present an inventory and discussion of different human-induced factors and processes affecting the environment of the Baltic Sea region, and their interrelations. Some are naturally occurring and modified by human activities (i.e. climate change, coastal processes, hypoxia, acidification, submarine groundwater discharges, marine ecosystems, non-indigenous species, land use and land cover), some are completely human-induced (i.e. agriculture, aquaculture, fisheries, river regulations, offshore wind farms, shipping, chemical contamination, dumped warfare agents, marine litter and microplastics, tourism, and coastal management), and they are all interrelated to different degrees. We present a general description and analysis of the state of knowledge on these interrelations. Our main insight is that climate change has an overarching, integrating impact on all of the other factors and can be interpreted as a background effect, which has different implications for the other factors. Impacts on the environment and the human sphere can be roughly allocated to anthropogenic drivers such as food production, energy production, transport, industry and economy. The findings from this inventory of available information and analysis of the different factors and their interactions in the Baltic Sea region can largely be transferred to other comparable marginal and coastal seas in the world.
Future distribution grids are likely to shift away from a passive grid consuming power to an active grid with a high share of weather-dependent renewable generation. Distribution grid operations are greatly interlinked between different voltage levels and depend upon the fluctuating load demand. Thus it is imperative to study and analyze multi-voltage level distribution grids to understand the challenges and opportunities in a distribution grid with a high share of weather-dependent generation. In this research, an open-source multi-voltage level distribution grid model, named the DTU 7k-Bus Active Distribution Grid Model, is presented. The distribution grid model spans across three voltage levels and is modeled on geographical data for network topologies. The generation and load time-series provided with the model are simulated from weather data and derived from measurement data respectively. This work addresses key features of the model and highlights challenges due to the high share of renewables.
In this paper, the challenges for integrating smart substation automation system into traditional substation is presented. The preparation of a long-term field demonstration for coordinated voltage control in distribution grid in western Denmark is used as a case study. The paper also briefly describes the functionality (the methodology for the implemented voltage control), operating principle and the components of the automation system with the required testing for each part of the system. The control system is installed in parallel with existing Automatic Voltage Regulation (AVR), with only few additional components. The objective of the smart control system is to increase the grid hosting capacity for distributed generation, to reduce network losses, to enhance voltage quality, and to postpone network reinforcement needs. The aim of this paper is to share the experiences of the field demonstration implementation, to emphasize the importance to reduce the gap between academic research and reality, and to propose a comprehensive testing methodology for successful field demonstration. The paper also highlights additional questions to be solved when the algorithms and prototype devices are taken into field.
One promising design solution for increasing the efficiency of modern horizontal axis wind turbines is the installation of curved tip extensions. However, introducing such complex geometries may move traditional aerodynamic models based on blade element momentum (BEM) theory out of their range of applicability. This motivated the present work, where a swept tip shape is investigated by means of both experimental and numerical tests. The latter group accounted for a wide variety of aerodynamic models, allowing us to highlight the capabilities and limitations of each of them in a relative manner. The considered swept tip shape is the result of a design optimization, focusing on locally maximizing power performance within load constraints. For the experimental tests, the tip model is instrumented with spanwise bands of pressure sensors and is tested in the Poul la Cour wind tunnel at the Technical University of Denmark (DTU). The methods used for the numerical tests consisted of a blade element model, a near-wake model, lifting-line free-wake models, and a fully resolved NavierâStokes solver. The comparison of the numerical and the experimental test results is performed for a given range of angles of attack and wind speeds, which is representative of the expected conditions in operation. Results show that the blade element model cannot predict the measured normal force coefficients, but the other methods are generally in good agreement with the measurements in attached flow. Flow visualization and pressure distribution compare well with computational fluid dynamics (CFD) simulations. The agreement in the clean case is better than in the tripped case at the inboard sections. Some uncertainties regarding the effect of the boundary layer at the inboard tunnel wall and the post-stall behavior remain.
The k-out-of-n system model is widely applied for the reliability evaluation of many technical systems. Multi-state system modelling is also widely used for representing real systems, whose components can have different levels of performance. For these researches, recently multi-state k-out-of-n systems have been comprehensively studied. In these studies, it is usually assumed that the system has a single task function to complete in a given environment. Moreover, the system or component performance is characterised by one measure, for example “electric power” in generation systems or “flow-rate” in transmission systems. However, this can be a simplification for some real-life engineering systems. For example, an intertwined district heating and electricity system consists of combined heat and power generating units, which can produce both electricity and heat. In this paper, definitions of multi-performance weighted multi-state components are provided and two generalized multi-performance multi-state K¯-out-of-n system models are proposed. Universal generating function approach is developed for the evaluation of such systems, with two numerical examples.
