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Real-world problems such as computational fluid dynamics simulations and finite element analyses are computationally expensive. A standard approach to mitigating the high computational expense is Surrogate-Based Optimization (SBO). Yet, due to the high-dimensionality of many simulation problems, SBO is not directly applicable or not efficient. Reducing the dimensionality of the search space is one method to overcome this limitation. In addition to the applicability of SBO, dimensionality reduction enables easier data handling and improved data and model interpretability. Regularization is considered as one state-of-the-art technique for dimensionality reduction. We propose a hybridization approach called Regularized-Surrogate-Optimization (RSO) aimed at overcoming difficulties related to high-dimensionality. It couples standard Kriging-based SBO with regularization techniques. The employed regularization methods are based on three adaptations of the least absolute shrinkage and selection operator (LASSO). In addition, tree-based methods are analyzed as an alternative variable selection method. An extensive study is performed on a set of artificial test functions and two real-world applications: the electrostatic precipitator problem and a multilayered composite design problem. Experiments reveal that RSO requires significantly less time than standard SBO to obtain comparable results. The pros and cons of the RSO approach are discussed, and recommendations for practitioners are presented.
This paper introduces UniFIeD, a new data preprocessing method for time series. UniFIeD can cope with large intervals of missing data. A scalable test function generator, which allows the simulation of time series with different gap sizes, is presented additionally. An experimental study demonstrates that (i) UniFIeD shows a significant better performance than simple imputation methods and (ii) UniFIeD is able to handle situations, where advanced imputation methods fail. The results are independent from the underlying error measurements.
Drinking water supply and distribution systems are critical infrastructure that has to be well maintained for the safety of the public. One important tool in the maintenance of water distribution systems (WDS) is flushing. Flushing is a process carried out in a periodic fashion to clean sediments and other contaminants in the water pipes. Given the different topographies, water composition and supply demand between WDS no single flushing strategy is suitable for all of them. In this report a non-exhaustive overview of optimization methods for flushing in WDS is given. Implementation of optimization methods for the flushing procedure and the flushing planing are presented. Suggestions are given as a possible option to optimise existing flushing planing frameworks.
Land-use intensification and urbanisation processes are degrading ecosystem services in the Guapiaçu-Macacu watershed in the state of Rio de Janeiro, Brazil. Paying farmers to forgo agricultural production activities in order to restore natural watershed services might be a viable means of securing water resources over the long term for the approximately 2.5 million urban water users in the region. This study quantified the costs of changing current land-use patterns to enhance watershed services. These costs are compared to estimates of the avoided water treatment costs for the public potable water supply as a proxy of willingness-to-pay for watershed services. Farm-household data was used to estimate the opportunity costs of abandoning current land uses in order to allow natural vegetation succession; a process that is very likely to improve water quality in terms of reducing erosion and subsequently water turbidity. Opportunity cost estimates were extrapolated to the watershed scale based on land-use classifications and a vulnerability analysis for identifying priority areas for watershed management interventions. Water quality and treatment cost data from the primary local water treatment plant (principal water user in the study area) were analysed to assess the potential demand for watershed services. The conversion of agricultural land uses for the benefit of watershed service provision was found to entail high opportunity costs in the study area, which is near the city of Rio de Janeiro. Alternative, relatively low-cost practices that support watershed conservation do exist for the livestock production systems. Other options include: implementing soil conservation techniques, permanent protection of areas that are vulnerable to erosion, protecting and restoring riparian and headwater areas, and applying more sustainable agricultural practices. These measures have the potential to directly reduce the amount of sediment and nutrients reaching water bodies and, in turn, decrease the costs of treatment required for providing the potable water supply. Based on treatment costs, the state water utility company’s willingness-to-pay for watershed services alone will not be sufficient to compensate farmers for forgoing agricultural production activities in order to improve the provision of additional watershed services. The results suggest that the opportunity costs of land-cover changes at the scale needed to improve water quality will likely exceed the cost of additional investments in water treatment. Monetary incentives conditioned on specific adjustments to existing production systems could offer a complementary role for improving watershed services. The willingness-to-pay analysis, however, only focused on chemical treatment costs and one of a potentially wide range of ecosystem services provided by the natural vegetation in the Guapiaçu-Macacu watershed (water quality maintenance for potable water provision). Other ecosystem services provided by forest cover include carbon sequestration and storage, moderation of extreme weather events, regulation of water flows, landscape aesthetics, and biodiversity protection. Factoring these additional ecosystem services into the willingness-to-pay equation is likely to change the conclusions of the assessment in favour of additional conservation action, either through payments for ecosystem services (PES) or other policy instruments. This effort contributes to the growing body of related scientific literature by offering additional knowledge on how to combine spatially explicit economic and environmental information to provide valuable insights into the feasibility of implementing PES schemes at the scale of entire watersheds. This is relevant to helping inform decision-making processes with respect to the economic scope of incentive-based watershed management in the context of the Guapiaçu-Macacu watershed. Furthermore, the findings of this research can serve long-term watershed conservation initiatives and public policy in other watersheds of the Atlantic Forest biome by facilitating the targeting of conservation incentives for a cost-effective watershed management.
The fashion industry is one of the most harmful industries in the world. Many garments are produced and dyed on a petroleum base; vast amounts of water are used in the production of textiles and garments; and environmentally harmful chemicals are released into the environment during production. Working towards sustainability in fashion is more relevant than ever. One way of doing this is to design garments with nature. To do so, I am presenting an example of biotechnology in the field of dyeing techniques. The project is innovative and future-driven in that it offers alternatives to industrial, petroleum-based dyeing techniques. A number of bacteria produce different colored pigments. The bacteria strain Janthinobacterium lividum, for example, is considered nontoxic and safe to handle. It is found in nature on the skin of the red-backed salamander. The bacteria produce dark purple pigments called violacein. With the pigment’s antifungal and antibacterial characteristics, it protects itself and its host from intruders. Can the pigment, however, be applied to dye textiles?
Surrogate-assisted optimization has proven to be very successful if applied to industrial problems. The use of a data-driven surrogate model of an objective function during an optimization cycle has many bene ts, such as being cheap to evaluate and further providing both information about the objective landscape and the parameter space. In preliminary work, it was researched how surrogate-assisted optimization can help to optimize the structure of a neural network (NN) controller. In this work, we will focus on how surrogates can help to improve the direct learning process of a transparent feed-forward neural network controller. As an initial case study we will consider a manageable real-world control task: the elevator supervisory group problem (ESGC) using a simplified simulation model. We use this model as a benchmark which should indicate the applicability and performance of surrogate-assisted optimization to this kind of tasks. While the optimization process itself is in this case not onsidered expensive, the results show that surrogate-assisted optimization is capable of outperforming metaheuristic optimization methods for a low number of evaluations. Further the surrogate can be used for signi cance analysis of the inputs and weighted connections to further exploit problem information.
This report presents a practical approach to stacked generalization in surrogate model based optimization. It exemplifies the integration of stacking methods into the surrogate model building process. First, a brief overview of the current state in surrogate model based opti- mization is presented. Stacked generalization is introduced as a promising ensemble surrogate modeling approach. Then two examples (the first is based on a real world application and the second on a set of artificial test functions) are presented. These examples clearly illustrate two properties of stacked generalization: (i) combining information from two poor performing models can result in a good performing model and (ii) even if the ensemble contains a good performing model, combining its information with information from poor performing models results in a relatively small performance decrease only.
When designing or developing optimization algorithms, test functions are crucial to evaluate
performance. Often, test functions are not sufficiently difficult, diverse, flexible or relevant to real-world
applications. Previously,
test functions with real-world relevance were generated by training a machine learning model based on
real-world data. The model estimation is used as a test function.
We propose a more principled approach using simulation instead of estimation.
Thus, relevant and varied test functions
are created which represent the behavior of real-world fitness landscapes.
Importantly, estimation can lead to excessively smooth test functions
while simulation may avoid this pitfall. Moreover, the simulation
can be conditioned by the data, so that the simulation reproduces the training data
but features diverse behavior in unobserved regions of the search space.
The proposed test function generator is illustrated with an intuitive, one-dimensional
example. To demonstrate the utility of this approach it
is applied to a protein sequence optimization problem.
This application demonstrates the advantages as well as practical limits of simulation-based
test functions.
Cyclone Dust Separators are devices often used to filter solid particles from flue gas. Such cyclones are supposed to filter as much solid particles from the carrying gas as possible. At the same time, they should only introduce a minimal pressure loss to the system. Hence, collection efficiency has to be maximized and pressure loss minimized. Both the collection efficiency and pressure loss are heavily influenced by the cyclones geometry. In this paper, we optimize seven geometrical parameters of an analytical cyclone model. Furthermore, noise variables are introduced to the model, representing the non-deterministic structure of the real-world problem. This is used to investigate robustness and sensitivity of solutions. Both the deterministic as well as the stochastic model are optimized with an SMS-EMOA. The SMS-EMOA is compared to a single objective optimization algorithm. For the harder, stochastic optimization problem, a surrogate-model-supported SMS-EMOA is compared against the model-free SMS-EMOA. The model supported approach yields better solutions with the same run-time budget.
Sequential Parameter Optimization is a model-based optimization methodology, which includes several techniques for handling uncertainty. Simple approaches such as sharp- ening and more sophisticated approaches such as optimal computing budget allocation are available. For many real world engineering problems, the objective function can be evaluated at different levels of fidelity. For instance, a CFD simulation might provide a very time consuming but accurate way to estimate the quality of a solution.The same solution could be evaluated based on simplified mathematical equations, leading to a cheaper but less accurate estimate. Combining these different levels of fidelity in a model-based optimization process is referred to as multi-fidelity optimization. This chapter describes uncertainty-handling techniques for meta-model based search heuristics in combination with multi-fidelity optimization. Co-Kriging is one power- ful method to correlate multiple sets of data from different levels of fidelity. For the first time, Sequential Parameter Optimization with co-Kriging is applied to noisy test functions. This study will introduce these techniques and discuss how they can be applied to real-world examples.