Nye tider – DSB’s køreplan 2016

Søndag den 13. december 2015 træder DSB’s nye køreplan for 2016 i kraft. For første gang i mange år er der med køreplanen for 2016 ikke taget udgangspunkt i sidste års køreplan, men i stedet startet helt fra bunden, hvilket giver ændringer over hele landet. Den nye køreplan betyder dog ikke kun nye minuttal. Køreplanen indeholder både generelle forbedringer og en række nyskabelser. Af de generelle forbedringer kan nævnes reducerede rejsetider, fast systemtime, faste minuttal, jævne frekvenser, symmetrisk køreplan, bedre korrespondancer og bedre muligheder for at genoprette driften efter driftsuorden. Blandt nyskabelserne er 15-minutters drift i Østjylland i myldretiderne, direkte forbindelse mellem Aalborg og Flensborg/Hamborg, Sønderborg kobles på lyntogssystemet i Fredericia samt at IC-toget mellem København og Esbjerg overhales af lyntoget i Odense. Totalt betyder køreplansændringerne, at rejsetiden på årsbasis reduceres med 800.000 timer, og at der er et teoretisk vækstpotentiale på 540.000 DSB-rejser svarende til ca. 100 mio personkm

Transient Studies in Large Offshore Wind Farms, Employing Detailed Circuit Breaker Representation

Switching overvoltages (SOV) are considered a possible source of component failures experienced in existing offshore wind farms (OWFs). The inclusion of sufficiently accurate and validated models of the main electrical components in the OWF in the simulation tool is therefore an important issue in order to ensure reliable switching operations. Transient measurement results in an OWF are compared with simulation results in PSCAD EMTDC and DigSILENT Power Factory. A user-defined model of the vacuum circuit breaker (VCB) is included in both tools, capable of simulating multiple prestrikes during the closing operation. An analysis of the switching transients that might occur in OWFs will be made on the basis of the validated model, and the importance of the inclusion of a sufficiently accurate representation of the VCB in the simulation tool will be described. The inclusion of the VCB model in PSCAD greatly improves the simulation results, whereas little improvement is found in DigSILENT. Based on the transient study it is found that the simulated SOV can be up to 60% higher at the sending end when using the detailed VCB representation compared to the built-in switch, which emphasises the need for accurate representation of the VCB for energisation studies

Nearly ETH-Tight Algorithms for Planar Steiner Tree with Terminals on Few Faces

The Planar Steiner Tree problem is one of the most fundamental NP-complete problems as it models many network design problems. Recall that an instance of this problem consists of a graph with edge weights, and a subset of vertices (often called terminals); the goal is to find a subtree of the graph of minimum total weight that connects all terminals. A seminal paper by Erickson et al. [Math. Oper. Res., 1987] considers instances where the underlying graph is planar and all terminals can be covered by the boundary of $k$ faces. Erickson et al. show that the problem can be solved by an algorithm using $n^{O(k)}$ time and $n^{O(k)}$ space, where $n$ denotes the number of vertices of the input graph. In the past 30 years there has been no significant improvement of this algorithm, despite several efforts. In this work, we give an algorithm for Planar Steiner Tree with running time $2^{O(k)} n^{O(\sqrt{k})}$ using only polynomial space. Furthermore, we show that the running time of our algorithm is almost tight: we prove that there is no $f(k)n^{o(\sqrt{k})}$ algorithm for Planar Steiner Tree for any computable function $f$, unless the Exponential Time Hypothesis fails.Comment: 32 pages, 8 figures, accepted at SODA 201