@inproceedings{MuellerAltherrAholaetal.2019, author = {M{\"u}ller, Tim M. and Altherr, Lena and Ahola, Marja and Schabel, Samuel and Pelz, Peter F.}, title = {Multi-Criteria optimization of pressure screen systems in paper recycling - balancing quality, yield, energy consumption and system complexity}, series = {EngOpt 2018 Proceedings of the 6th International Conference on Engineering Optimization}, booktitle = {EngOpt 2018 Proceedings of the 6th International Conference on Engineering Optimization}, editor = {Rodrigues, H. C.}, publisher = {Springer International Publishing}, address = {Basel}, isbn = {978-3-319-97773-7}, doi = {10.1007/978-3-319-97773-7_105}, year = {2019}, abstract = {The paper industry is the industry with the third highest energy consumption in the European Union. Using recycled paper instead of fresh fibers for papermaking is less energy consuming and saves resources. However, adhesive contaminants in recycled paper are particularly problematic since they reduce the quality of the resulting paper-product. To remove as many contaminants and at the same time obtain as many valuable fibres as possible, fine screening systems, consisting of multiple interconnected pressure screens, are used. Choosing the best configuration is a non-trivial task: The screens can be interconnected in several ways, and suitable screen designs as well as operational parameters have to be selected. Additionally, one has to face conflicting objectives. In this paper, we present an approach for the multi-criteria optimization of pressure screen systems based on Mixed-Integer Nonlinear Programming. We specifically focus on a clear representation of the trade-off between different objectives.}, language = {en} } @article{AltherrJoggerstLeiseetal.2018, author = {Altherr, Lena and Joggerst, Laura and Leise, Philipp and Pfetsch, Marc E. and Schmitt, Andreas and Wendt, Janine}, title = {On obligations in the development process of resilient systems with algorithmic design methods}, series = {Applied Mechanics and Materials}, volume = {885}, journal = {Applied Mechanics and Materials}, number = {885}, publisher = {Trans Tech Publications}, address = {B{\"a}ch}, isbn = {1662-7482}, doi = {10.4028/www.scientific.net/AMM.885.240}, pages = {240 -- 252}, year = {2018}, abstract = {Advanced computational methods are needed both for the design of large systems and to compute high accuracy solutions. Such methods are efficient in computation, but the validation of results is very complex, and highly skilled auditors are needed to verify them. We investigate legal questions concerning obligations in the development phase, especially for technical systems developed using advanced methods. In particular, we consider methods of resilient and robust optimization. With these techniques, high performance solutions can be found, despite a high variety of input parameters. However, given the novelty of these methods, it is uncertain whether legal obligations are being met. The aim of this paper is to discuss if and how the choice of a specific computational method affects the developer's product liability. The review of legal obligations in this paper is based on German law and focuses on the requirements that must be met during the design and development process.}, language = {en} } @article{SunAltherrPeietal.2018, author = {Sun, Hui and Altherr, Lena and Pei, Ji and Pelz, Peter F. and Yuan, Shouqi}, title = {Optimal booster station design and operation under uncertain load}, series = {Applied Mechanics and Materials}, volume = {885}, journal = {Applied Mechanics and Materials}, publisher = {Trans Tech Publications}, address = {B{\"a}ch}, issn = {1662-7482}, doi = {10.4028/www.scientific.net/AMM.885.102}, pages = {102 -- 115}, year = {2018}, abstract = {Given industrial applications, the costs for the operation and maintenance of a pump system typically far exceed its purchase price. For finding an optimal pump configuration which minimizes not only investment, but life-cycle costs, methods like Technical Operations Research which is based on Mixed-Integer Programming can be applied. However, during the planning phase, the designer is often faced with uncertain input data, e.g. future load demands can only be estimated. In this work, we deal with this uncertainty by developing a chance-constrained two-stage (CCTS) stochastic program. The design and operation of a booster station working under uncertain load demand are optimized to minimize total cost including purchase price, operation cost incurred by energy consumption and penalty cost resulting from water shortage. We find optimized system layouts using a sample average approximation (SAA) algorithm, and analyze the results for different risk levels of water shortage. By adjusting the risk level, the costs and performance range of the system can be balanced, and thus the system's resilience can be engineered}, language = {en} } @incollection{MuellerAltherrAholaetal.2018, author = {M{\"u}ller, Tim M. and Altherr, Lena and Ahola, Marja and Schabel, Samuel and Pelz, Peter F.}, title = {Optimizing pressure screen systems in paper recycling: optimal system layout, component selection and operation}, publisher = {Springer}, address = {Cham}, isbn = {978-3-030-18499-5}, doi = {10.1007/978-3-030-18500-8_44}, pages = {355 -- 361}, year = {2018}, abstract = {Around 60\% of the paper worldwide is made from recovered paper. Especially adhesive contaminants, so called stickies, reduce paper quality. To remove stickies but at the same time keep as many valuable fibers as possible, multi-stage screening systems with several interconnected pressure screens are used. When planning such systems, suitable screens have to be selected and their interconnection as well as operational parameters have to be defined considering multiple conflicting objectives. In this contribution, we present a Mixed-Integer Nonlinear Program to optimize system layout, component selection and operation to find a suitable trade-off between output quality and yield.}, language = {en} } @article{LeiseEsserEichenlaubetal.2021, author = {Leise, Philipp and Eßer, Arved and Eichenlaub, Tobias and Schleiffer, Jean-Eric and Altherr, Lena and Rinderknecht, Stephan and Pelz, Peter F.}, title = {Sustainable system design of electric powertrains - comparison of optimization methods}, series = {Engineering Optimization}, journal = {Engineering Optimization}, publisher = {Taylor \& Francis}, address = {London}, issn = {0305-215X}, doi = {10.1080/0305215X.2021.1928660}, year = {2021}, abstract = {The transition within transportation towards battery electric vehicles can lead to a more sustainable future. To account for the development goal 'climate action' stated by the United Nations, it is mandatory, within the conceptual design phase, to derive energy-efficient system designs. One barrier is the uncertainty of the driving behaviour within the usage phase. This uncertainty is often addressed by using a stochastic synthesis process to derive representative driving cycles and by using cycle-based optimization. To deal with this uncertainty, a new approach based on a stochastic optimization program is presented. This leads to an optimization model that is solved with an exact solver. It is compared to a system design approach based on driving cycles and a genetic algorithm solver. Both approaches are applied to find efficient electric powertrains with fixed-speed and multi-speed transmissions. Hence, the similarities, differences and respective advantages of each optimization procedure are discussed.}, language = {en} } @inproceedings{LeiseBreuerAltherretal.2020, author = {Leise, Philipp and Breuer, Tim and Altherr, Lena and Pelz, Peter F.}, title = {Development, validation and assessment of a resilient pumping system}, series = {Proceedings of the Joint International Resilience Conference, JIRC2020}, booktitle = {Proceedings of the Joint International Resilience Conference, JIRC2020}, isbn = {978-90-365-5095-6}, pages = {97 -- 100}, year = {2020}, abstract = {The development of resilient technical systems is a challenging task, as the system should adapt automatically to unknown disturbances and component failures. To evaluate different approaches for deriving resilient technical system designs, we developed a modular test rig that is based on a pumping system. On the basis of this example system, we present metrics to quantify resilience and an algorithmic approach to improve resilience. This approach enables the pumping system to automatically react on unknown disturbances and to reduce the impact of component failures. In this case, the system is able to automatically adapt its topology by activating additional valves. This enables the system to still reach a minimum performance, even in case of failures. Furthermore, timedependent disturbances are evaluated continuously, deviations from the original state are automatically detected and anticipated in the future. This allows to reduce the impact of future disturbances and leads to a more resilient system behaviour.}, language = {en} } @inproceedings{LorenzAltherrPelz2019, author = {Lorenz, Imke-Sophie B. and Altherr, Lena and Pelz, Peter F.}, title = {Graph-theoretic resilience analysis of a water distribution system's topology}, series = {World Congress on Resilience, Reliability and Asset Management 2019}, booktitle = {World Congress on Resilience, Reliability and Asset Management 2019}, pages = {106 -- 109}, year = {2019}, abstract = {Water suppliers are faced with the great challenge of achieving high-quality and, at the same time, low-cost water supply. In practice, the focus is set on the most beneficial maintenance measures and/or capacity adaptations of existing water distribution systems (WDS). Since climatic and demographic influences will pose further challenges in the future, the resilience enhancement of WDS, i.e. the enhancement of their capability to withstand and recover from disturbances, has been in particular focus recently. To assess the resilience of WDS, metrics based on graph theory have been proposed. In this study, a promising approach is applied to assess the resilience of the WDS for a district in a major German City. The conducted analysis provides insight into the process of actively influencing the resilience of WDS}, language = {en} } @inproceedings{MeckMuellerAltherretal.2020, author = {Meck, Marvin M. and M{\"u}ller, Tim M. and Altherr, Lena and Pelz, Peter F.}, title = {Improving an industrial cooling system using MINLP, considering capital and operating costs}, series = {Operations Research Proceedings 2019}, booktitle = {Operations Research Proceedings 2019}, publisher = {Springer}, address = {Cham}, isbn = {978-3-030-48438-5 (Print)}, doi = {10.1007/978-3-030-48439-2_61}, pages = {505 -- 512}, year = {2020}, abstract = {The chemical industry is one of the most important industrial sectors in Germany in terms of manufacturing revenue. While thermodynamic boundary conditions often restrict the scope for reducing the energy consumption of core processes, secondary processes such as cooling offer scope for energy optimisation. In this contribution, we therefore model and optimise an existing cooling system. The technical boundary conditions of the model are provided by the operators, the German chemical company BASF SE. In order to systematically evaluate different degrees of freedom in topology and operation, we formulate and solve a Mixed-Integer Nonlinear Program (MINLP), and compare our optimisation results with the existing system.}, language = {en} } @article{MuellerLeiseLorenzetal.2020, author = {M{\"u}ller, Tim M. and Leise, Philipp and Lorenz, Imke-Sophie and Altherr, Lena and Pelz, Peter F.}, title = {Optimization and validation of pumping system design and operation for water supply in high-rise buildings}, series = {Optimization and Engineering}, volume = {2021}, journal = {Optimization and Engineering}, number = {22}, publisher = {Springer}, issn = {1573-2924}, doi = {10.1007/s11081-020-09553-4}, pages = {643 -- 686}, year = {2020}, abstract = {The application of mathematical optimization methods for water supply system design and operation provides the capacity to increase the energy efficiency and to lower the investment costs considerably. We present a system approach for the optimal design and operation of pumping systems in real-world high-rise buildings that is based on the usage of mixed-integer nonlinear and mixed-integer linear modeling approaches. In addition, we consider different booster station topologies, i.e. parallel and series-parallel central booster stations as well as decentral booster stations. To confirm the validity of the underlying optimization models with real-world system behavior, we additionally present validation results based on experiments conducted on a modularly constructed pumping test rig. Within the models we consider layout and control decisions for different load scenarios, leading to a Deterministic Equivalent of a two-stage stochastic optimization program. We use a piecewise linearization as well as a piecewise relaxation of the pumps' characteristics to derive mixed-integer linear models. Besides the solution with off-the-shelf solvers, we present a problem specific exact solving algorithm to improve the computation time. Focusing on the efficient exploration of the solution space, we divide the problem into smaller subproblems, which partly can be cut off in the solution process. Furthermore, we discuss the performance and applicability of the solution approaches for real buildings and analyze the technical aspects of the solutions from an engineer's point of view, keeping in mind the economically important trade-off between investment and operation costs.}, language = {en} } @inproceedings{MuellerAltherrLeiseetal.2020, author = {M{\"u}ller, Tim M. and Altherr, Lena and Leise, Philipp and Pelz, Peter F.}, title = {Optimization of pumping systems for buildings: Experimental validation of different degrees of model detail on a modular test rig}, series = {Operations Research Proceedings 2019}, booktitle = {Operations Research Proceedings 2019}, publisher = {Springer}, address = {Cham}, isbn = {978-3-030-48438-5}, doi = {10.1007/978-3-030-48439-2_58}, pages = {481 -- 488}, year = {2020}, abstract = {Successful optimization requires an appropriate model of the system under consideration. When selecting a suitable level of detail, one has to consider solution quality as well as the computational and implementation effort. In this paper, we present a MINLP for a pumping system for the drinking water supply of high-rise buildings. We investigate the influence of the granularity of the underlying physical models on the solution quality. Therefore, we model the system with a varying level of detail regarding the friction losses, and conduct an experimental validation of our model on a modular test rig. Furthermore, we investigate the computational effort and show that it can be reduced by the integration of domain-specific knowledge.}, language = {en} } @article{AltherrLeisePfetschetal.2018, author = {Altherr, Lena and Leise, Philipp and Pfetsch, Marc E. and Schmitt, Andreas}, title = {Algorithmic design and resilience assessment of energy efficient high-rise water supply systems}, series = {Applied Mechanics and Materials}, volume = {885}, journal = {Applied Mechanics and Materials}, publisher = {Trans Tech Publications}, address = {B{\"a}ch}, issn = {1662-7482}, doi = {10.4028/www.scientific.net/AMM.885.211}, pages = {211 -- 223}, year = {2018}, abstract = {High-rise water supply systems provide water flow and suitable pressure in all levels of tall buildings. To design such state-of-the-art systems, the consideration of energy efficiency and the anticipation of component failures are mandatory. In this paper, we use Mixed-Integer Nonlinear Programming to compute an optimal placement of pipes and pumps, as well as an optimal control strategy.Moreover, we consider the resilience of the system to pump failures. A resilient system is able to fulfill a predefined minimum functionality even though components fail or are restricted in their normal usage. We present models to measure and optimize the resilience. To demonstrate our approach, we design and analyze an optimal resilient decentralized water supply system inspired by a real-life hotel building.}, language = {en} } @inproceedings{LeiseAltherr2018, author = {Leise, Philipp and Altherr, Lena}, title = {Optimizing the design and control of decentralized water supply systems - a case-study of a hotel building}, series = {EngOpt 2018 Proceedings of the 6th International Conference on Engineering Optimization}, booktitle = {EngOpt 2018 Proceedings of the 6th International Conference on Engineering Optimization}, publisher = {Springer}, address = {Cham}, isbn = {978-3-319-97773-7}, doi = {10.1007/978-3-319-97773-7_107}, pages = {1241 -- 1252}, year = {2018}, abstract = {To increase pressure to supply all floors of high buildings with water, booster stations, normally consisting of several parallel pumps in the basement, are used. In this work, we demonstrate the potential of a decentralized pump topology regarding energy savings in water supply systems of skyscrapers. We present an approach, based on Mixed-Integer Nonlinear Programming, that allows to choose an optimal network topology and optimal pumps from a predefined construction kit comprising different pump types. Using domain-specific scaling laws and Latin Hypercube Sampling, we generate different input sets of pump types and compare their impact on the efficiency and cost of the total system design. As a realistic application example, we consider a hotel building with 325 rooms, 12 floors and up to four pressure zones.}, language = {en} } @incollection{StengerAltherrMuelleretal.2018, author = {Stenger, David and Altherr, Lena and M{\"u}ller, Tankred and Pelz, Peter F.}, title = {Product family design optimization using model-based engineering techniques}, series = {Operations Research Proceedings 2017}, booktitle = {Operations Research Proceedings 2017}, publisher = {Springer}, address = {Cham}, isbn = {978-3-319-89919-0}, doi = {10.1007/978-3-319-89920-6_66}, pages = {495 -- 502}, year = {2018}, abstract = {Highly competitive markets paired with tremendous production volumes demand particularly cost efficient products. The usage of common parts and modules across product families can potentially reduce production costs. Yet, increasing commonality typically results in overdesign of individual products. Multi domain virtual prototyping enables designers to evaluate costs and technical feasibility of different single product designs at reasonable computational effort in early design phases. However, savings by platform commonality are hard to quantify and require detailed knowledge of e.g. the production process and the supply chain. Therefore, we present and evaluate a multi-objective metamodel-based optimization algorithm which enables designers to explore the trade-off between high commonality and cost optimal design of single products.}, language = {en} } @article{AltherrBroetzDietrichetal.2018, author = {Altherr, Lena and Br{\"o}tz, Nicolas and Dietrich, Ingo and Gally, Tristan and Geßner, Felix and Kloberdanz, Hermann and Leise, Philipp and Pelz, Peter Franz and Schlemmer, Pia and Schmitt, Andreas}, title = {Resilience in mechanical engineering - a concept for controlling uncertainty during design, production and usage phase of load-carrying structures}, series = {Applied Mechanics and Materials}, volume = {885}, journal = {Applied Mechanics and Materials}, publisher = {Trans Tech Publications}, address = {B{\"a}ch}, isbn = {1662-7482}, doi = {10.4028/www.scientific.net/AMM.885.187}, pages = {187 -- 198}, year = {2018}, abstract = {Resilience as a concept has found its way into different disciplines to describe the ability of an individual or system to withstand and adapt to changes in its environment. In this paper, we provide an overview of the concept in different communities and extend it to the area of mechanical engineering. Furthermore, we present metrics to measure resilience in technical systems and illustrate them by applying them to load-carrying structures. By giving application examples from the Collaborative Research Centre (CRC) 805, we show how the concept of resilience can be used to control uncertainty during different stages of product life.}, language = {en} } @inproceedings{LeiseAltherrPelz2018, author = {Leise, Philipp and Altherr, Lena and Pelz, Peter F.}, title = {Technical Operations Research (TOR) - Algorithms, not Engineers, Design Optimal Energy Efficient and Resilient Cooling Systems}, series = {FAN2018 - Proceedings of the International Conference on Fan Noise, Aerodynamics, Applications and Systems}, booktitle = {FAN2018 - Proceedings of the International Conference on Fan Noise, Aerodynamics, Applications and Systems}, pages = {1 -- 12}, year = {2018}, abstract = {The overall energy efficiency of ventilation systems can be improved by considering not only single components, but by considering as well the interplay between every part of the system. With the help of the method "TOR" ("Technical Operations Research"), which was developed at the Chair of Fluid Systems at TU Darmstadt, it is possible to improve the energy efficiency of the whole system by considering all possible design choices programmatically. We show the ability of this systematic design approach with a ventilation system for buildings as a use case example. Based on a Mixed-Integer Nonlinear Program (MINLP) we model the ventilation system. We use binary variables to model the selection of different pipe diameters. Multiple fans are model with the help of scaling laws. The whole system is represented by a graph, where the edges represent the pipes and fans and the nodes represents the source of air for cooling and the sinks, that have to be cooled. At the beginning, the human designer chooses a construction kit of different suitable fans and pipes of different diameters and different load cases. These boundary conditions define a variety of different possible system topologies. It is not possible to consider all topologies by hand. With the help of state of the art solvers, on the other side, it is possible to solve this MINLP. Next to this, we also consider the effects of malfunctions in different components. Therefore, we show a first approach to measure the resilience of the shown example use case. Further, we compare the conventional approach with designs that are more resilient. These more resilient designs are derived by extending the before mentioned model with further constraints, that consider explicitly the resilience of the overall system. We show that it is possible to design resilient systems with this method already in the early design stage and compare the energy efficiency and resilience of these different system designs.}, language = {en} } @incollection{AltherrDoerigEdereretal.2017, author = {Altherr, Lena and D{\"o}rig, Bastian and Ederer, Thorsten and Pelz, Peter Franz and Pfetsch, Marc and Wolf, Jan}, title = {A mixed-integer nonlinear program for the design of gearboxes}, series = {Operations Research Proceedings 2016}, booktitle = {Operations Research Proceedings 2016}, publisher = {Springer}, address = {Cham}, isbn = {978-3-319-55701-4}, doi = {10.1007/978-3-319-55702-1_31}, pages = {227 -- 233}, year = {2017}, abstract = {Gearboxes are mechanical transmission systems that provide speed and torque conversions from a rotating power source. Being a central element of the drive train, they are relevant for the efficiency and durability of motor vehicles. In this work, we present a new approach for gearbox design: Modeling the design problem as a mixed-integer nonlinear program (MINLP) allows us to create gearbox designs from scratch for arbitrary requirements and—given enough time—to compute provably globally optimal designs for a given objective. We show how different degrees of freedom influence the runtime and present an exemplary solution.}, language = {en} } @incollection{LeiseAltherrPelz2018, author = {Leise, Philipp and Altherr, Lena and Pelz, Peter F.}, title = {Energy-Efficient design of a water supply system for skyscrapers by mixed-integer nonlinear programming}, series = {Operations Research Proceedings 2017}, booktitle = {Operations Research Proceedings 2017}, publisher = {Springer}, address = {Cham}, isbn = {978-3-319-89919-0}, doi = {10.1007/978-3-319-89920-6_63}, year = {2018}, abstract = {The energy-efficiency of technical systems can be improved by a systematic design approach. Technical Operations Research (TOR) employs methods known from Operations Research to find a global optimal layout and operation strategy of technical systems. We show the practical usage of this approach by the systematic design of a decentralized water supply system for skyscrapers. All possible network options and operation strategies are modeled by a Mixed-Integer Nonlinear Program. We present the optimal system found by our approach and highlight the energy savings compared to a conventional system design.}, language = {en} } @inproceedings{AltherrPelzEdereretal.2017, author = {Altherr, Lena and Pelz, Peter F. and Ederer, Thorsten and Pfetsch, Marc E.}, title = {Optimale Getriebe auf Knopfdruck: Gemischt-ganzzahlige nichtlineare Optimierung zur Entscheidungsunterst{\"u}tzung bei der Auslegung von Getrieben f{\"u}r Kraftfahrzeuge}, series = {Antriebstechnisches Kolloquium ATK 2017}, booktitle = {Antriebstechnisches Kolloquium ATK 2017}, editor = {Jacobs, Georg}, isbn = {9783743148970}, pages = {313 -- 325}, year = {2017}, language = {de} } @inproceedings{RauschFriesenAltherretal.2018, author = {Rausch, Lea and Friesen, John and Altherr, Lena and Pelz, Peter F.}, title = {Using mixed-integer programming for the optimal design of water supply networks for slums}, series = {Operations Research Proceedings 2017}, booktitle = {Operations Research Proceedings 2017}, editor = {Kliewer, Natalia and Ehmke, Jan Fabian and Bornd{\"o}rfer, Ralf}, publisher = {Springer}, address = {Cham}, isbn = {978-3-319-89919-0 (Print)}, doi = {10.1007/978-3-319-89920-6_68}, pages = {509 -- 516}, year = {2018}, abstract = {The UN sets the goal to ensure access to water and sanitation for all people by 2030. To address this goal, we present a multidisciplinary approach for designing water supply networks for slums in large cities by applying mathematical optimization. The problem is modeled as a mixed-integer linear problem (MILP) aiming to find a network describing the optimal supply infrastructure. To illustrate the approach, we apply it on a small slum cluster in Dhaka, Bangladesh.}, language = {en} } @inproceedings{RauschLeiseEdereretal.2016, author = {Rausch, Lea and Leise, Philipp and Ederer, Thorsten and Altherr, Lena and Pelz, Peter F.}, title = {A comparison of MILP and MINLP solver performance on the example of a drinking water supply system design problem}, series = {ECCOMAS Congress 2016 VII European Congress on Computational Methods in Applied Sciences and Engineering}, booktitle = {ECCOMAS Congress 2016 VII European Congress on Computational Methods in Applied Sciences and Engineering}, editor = {Papadrakakis, M. and Ppadopoulos, V. and Stefanou, G. and Plevris, V.}, isbn = {978-618-82844-0-1}, pages = {8509 -- 8527}, year = {2016}, abstract = {Finding a good system topology with more than a handful of components is a highly non-trivial task. The system needs to be able to fulfil all expected load cases, but at the same time the components should interact in an energy-efficient way. An example for a system design problem is the layout of the drinking water supply of a residential building. It may be reasonable to choose a design of spatially distributed pumps which are connected by pipes in at least two dimensions. This leads to a large variety of possible system topologies. To solve such problems in a reasonable time frame, the nonlinear technical characteristics must be modelled as simple as possible, while still achieving a sufficiently good representation of reality. The aim of this paper is to compare the speed and reliability of a selection of leading mathematical programming solvers on a set of varying model formulations. This gives us empirical evidence on what combinations of model formulations and solver packages are the means of choice with the current state of the art.}, language = {en} }