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Multi-material topology optimization has become a popular design optimization discipline since it allows to go a step further in topology optimization of the design of lightweight components and structures. However, it also presents additional challenges in terms of managing a higher complexity in the optimization problem, reliably estimating the manufacturing cost taking into account the cost of joining dissimilar materials, or assessing the manufacturability of the design. This paper proposes a set of methods that solve generic multi-material topology optimization problems, while including several novel aspects such as a comprehensive cost model, specific design rules for multi-material design, and model order reduction techniques to improve the computational efficiency. Two different examples, consisting of a sitting bench and a car cowling, have been solved in order to support the benefits of the approach.

When designing a product, care must be taken to ensure that the product can be assembled later on at the manufacturing floor. This paper presents a methodology that takes in a CAD design to check its ease of assembly. The proposed methodology can calculate feasibility scores for an assembly step, then use these scores to calculate the optimal sequence of such assembly steps to construct the end product from its loose parts. Two assembly step scoring rules are presented: local and global assembly feasibility. Local assembly feasibility determines the directions in which two subassemblies can move apart an infinitesimally small distance based on contact faces between the subassemblies. Global assembly feasibility considers whether this small distance can be extended to infinity, by checking the overlap of projections of the pair of subassemblies in locally feasible directions. For both of these rules, problems are reduced to previously calculated scores whenever possible, in order to reduce calculation time. These rules are integrated in an algorithm which generates a complete assembly sequence. This assembly sequence is guaranteed to be the global optimum for the given rules. The algorithm successfully generates an assembly sequence for a small example case; the simplification rules reduced the number of local and global assembly feasibility checks by a factor 10 and 6, respectively.

Designing the layout of a work cell remains a challenging problem due to the large search space of possible layouts which is often subjected to a variety of optimization objectives. This paper proposes a model-based methodology to aid the layout design of a collaborative work cell. This model takes into account feasibility, reachability, safety and ergonomics as constraints in the layout optimization formulation. Determining reachability and static placement feasibility is accomplished using 3D Computer Aided Design (CAD) files as inputs combined with inverse kinematics. Geometric characteristics, like bounding boxes, and assembly requirements are determined from the 3D CAD files and used in the layout optimization. Inverse kinematics is used to calculate the reach of the robots and to reliably estimate ergonomic workload of an operator in the work cell. The optimized layout of the work cell is visualized for every start and end point of an assembly task, which allows to provide task instructions to operators and could potentially be used to program the robots and cobots. The methodology is validated on a practical use case.

This paper proposes an iterative approach to construct a passenger robust railway routing plan and timetable from scratch that also takes supplement and buffer time allocation into account on the signaling level. Each iteration is based on four pillars, which are subsequently executed. First a routing plan that optimizes infrastructure usage is constructed. Secondly, a timetable is constructed that optimizes buffer times between trains while taking passenger numbers into account. Thirdly, simulation is used to evaluate the passenger robustness of the routing plan and the timetable. Finally, the simulation outcome is used to make a new supplement assignment for the next iteration. The algorithm is tested on a case study for the complex station area of Brussels (Belgium). The resulting timetable and routing plan are much more passenger robust than the existing combinations of timetables and routing plans for this case, developed during research or implemented in practice. no ISSN ispartof: pages:190-208 ispartof: Proceedings of 7th International Seminar on Railway Operations Modelling and Analysis (IAROR) vol:2017 pages:190-208 ispartof: RailLille2017 location:Lille, France date:4 Apr - 7 Apr 2017 status: published

In nearly saturated station areas the limited capacity is one of the main reasons of delay propagation. Spreading the trains well in time and space in these areas has a big impact on the passenger robustness, i.e. the total travel time in practice of all passengers in the railway network in case of frequently occurring small delays. We focus on improving the performance in the bottleneck of the network in order to improve the performance of the whole railway network. This paper proposes a method that builds from scratch a routing plan and a cyclic timetable that optimizes the infrastructure occupation and the passenger robustness. An integer linear routing model assigns, without considering a timetable, every train to a route such that the maximal node usage is minimized and that the number of times that each node is used, is quadratically penalized. Thereafter, a mixed integer linear timetabling model assigns to each train the blocking times at which the nodes on its route, assigned by the routing model, are reserved and released. Different from other approaches is that we focus on the occupation of the railway infrastructure before constructing the timetable. The approach is validated on the complex railway station area of Brussels (Belgium). Our routing plan and timetable from scratch improve the passenger robustness up to 11% compared to a reference timetable and routing plan composed by the Belgian railway infrastructure manager Infrabel and by up to 2% compared to a reference timetable and routing plan from literature. ispartof: Transportation Research Part B vol:101 pages:228-244 status: published

We propose a heuristic algorithm to build a railway line plan from scratch that minimizes passenger travel time and operator cost and for which a feasible and robust timetable exists. A line planning module and a timetabling module work iteratively and interactively. The line planning module creates an initial line plan. The timetabling module evaluates the line plan and identifies a critical line based on minimum buffer times between train pairs. The line planning module proposes a new line plan in which the time length of the critical line is modified in order to provide more flexibility in the schedule. This flexibility is used during timetabling to improve the robustness of the railway system. The algorithm is validated on the DSB S-tog network of Copenhagen, which is a high frequency railway system, where overtakings are not allowed. This network has a rather simple structure, but is constrained by limited shunt capacity. While the operator and passenger cost remain close to those of the initially and (for these costs) optimally built line plan, the timetable corresponding to the finally developed robust line plan significantly improves the minimum buffer time, and thus the robustness, in eight out of ten studied cases. publisher: Elsevier articletitle: Integrating robust timetabling in line plan optimization for railway systems journaltitle: Transportation Research Part C: Emerging Technologies articlelink: http://dx.doi.org/10.1016/j.trc.2017.01.015 content_type: article copyright: © 2017 Elsevier Ltd. All rights reserved. ispartof: Transportation Research C, Emerging Technologies vol:77 pages:134-160 status: published

In this paper we study the impact of the `turn conditions' in end stations on the performance of a line plan. If trains have to turn on their platform in an end station, the yoccupy the platform for several minutes. A more preferred option, from a timetabling point of view, would be that a train disappears from the platform in its end station after dwelling and only appears again when departing for a subsequent trip. In this case, the train will not interfere with other trains that dwell on the platform during the time between these events. However, this option is only possible if the train can stay in a exible and large enough shunt. Starting from a given line plan, we compare two timetables, one where trains have to turn on their platform and one where trains can turn in a shunt. We evaluate the impact on the performance of the line plan by its feasibility for timetabling,the minimum overall buffer time between trains, the sum of the buffer times and the buffer times in individual stations. A case study on the DSB S-tog in Copenhagen (Denmark) is performed.