Python-Modelica framework for automated simulation and optimization

Modeling and simulation are essential for the development of complex engineering systems, such as wind turbines. Thus, Fraunhofer IWES (Fraunhofer Institute for Wind Energy Systems) has developed the MoWiT (Modelica for Wind Turbines) library for fully-coupled aero-hydro-servo-elastic simulations of wind turbine systems. To meet the needs for detailed assessment and design development of such sophisticated engineering systems, which imply iterative steps for design optimization, a Python-Modelica framework is set up and presented in this paper. By means of this, the simulation of MoWiT models can easily be managed, including redefinition of model parameters, specification of output sensors and simulation settings, integration of optimization algorithms, post-processing of simulation results, as well as parallel execution of several simulations. The application of this Python-Modelica framework is shown based on the example of a design optimization task of a floating wind turbine support structure

Design optimization of the OC3 phase IV floating spar-buoy, based on global limit states

Floating offshore wind turbine (FOWT) systems are a fast-evolving technology, however, still have to gain economic competitiveness to allow commercial market uptake. Design optimization, focusing on cost reduction while ensuring optimum system performance, plays a key role in achieving these goals. Hence, in this work, an approach for optimizing a floating concept, utilizing global limit states, is developed. The optimization is carried out in Python, linked with Modelica and Dymola for modeling and simulation. For the FOWT design, the over-dimensioned OC3 spar-buoy is utilized. This is modified during the optimization regarding its geometrical dimensions and ballasting. The optimization criteria stability, mean and dynamic displacements, and tower top acceleration are used for formulating the objective functions. The optimization is carried out for one design load case, which is most critical for the considered criteria. Based on an initial study, NSGAII is chosen as optimizer. The convergence of the optimization is examined and the optimum design solution selected. In post-processing analyses, the overall performance of the optimized FOWT system is approved. The presented approach shows one example for the design optimization of a FOWT system and should deal as basis for more advanced design optimization tasks, including local characteristics and reliability aspects

Development and verification of an aero-hydro-servo-elastic coupled model of dynamics for FOWT, based on the MoWiT library

The complexity of floating offshore wind turbine (FOWT) systems, with their coupled motions, aero-hydro-servo-elastic dynamics, as well as non-linear system behavior and components, makes modeling and simulation indispensable. To ensure the correct implementation of the ulti-physics, the engineering models and codes have to be verified and, subsequently, validated for proving the realistic representation of the real system behavior. Within the IEA Wind Task 23 Subtask offshore code-to-code comparisons have been performed. Based on these studies, using the OC3 hase IV spar-buoy FOWT system, the Modelica for Wind Turbines (MoWiT) library, developed at Fraunhofer IWES, is verified. MoWiT is capable of fully-coupled aero-hydro-servo-elastic simulations of wind turbine systems, onshore, offshore bottom-fixed, or even offshore floating. The hierarchical programing and multibody approach in the object-oriented and equation-based modeling language Modelica have the advantage (over some other simulation tools) of component-based modeling and, hence, easily modifying the implemented system model. The code-to-code comparisons with the results from the OC3 studies show, apart from expected differences due to required assumptions in consequence of missing data and incomplete information, good agreement and, consequently, substantiate the capability of MoWiT for fully-coupled aero-hydro-servo-elastic simulations of FOWT systems

Continuous Development and Management of Credible Modelica Models

Modeling and simulation is increasingly used in the design process for a~wide span of applications. Rising demands and the complexity of modern products also increases the need for models and tools capable to cover areas such as virtual testing, design-space exploration or digital twins, and to provide measures of the quality of the models and the achieved results. In this article, we try to summarize the state-of-the-art and best-practice from the viewpoint of a~Modelica language user, based on the experience gained in projects in which Modelica models have been utilized in the design process. Furthermore, missing features and gaps in the used processes are identified

Towards Modelica Models with Credibility Information

Modeling and simulation is increasingly used in the design process for a wide span of applications. Rising demands and the complexity of modern products also increase the need for models and tools capable to cover areas such as virtual testing, design-space exploration or digital twins, and to provide measures of the quality of the models and the achieved results. The latter is also called credible simulation process. In an article at the International Modelica Conference 2021, we summarized the state of the art and best practice from the viewpoint of a Modelica language user, based on the experience gained in projects in which Modelica models were utilized in the design process. Furthermore, missing features and gaps in the used processes were identified. In this article, new proposals are presented to improve the quality of Modelica models, in particular by adding traceability, uncertainty, and calibration information of the parameters in a standardized way to Modelica models. Furthermore, the new open-source Modelica library Credibility is discussed together with examples to support the implementation of credible Modelica models

A fully integrated optimization framework for designing a complex geometry offshore wind turbine spar-type floating support structure

Spar-type platforms for floating offshore wind turbines are considered suitable for commercial wind farm deployment. To reduce the hurdles of such floating systems becoming competitive, in situ aero-hydro-servo-elastic simulations are applied to support conceptual design optimization by including transient and non-linear loads. For reasons of flexibility, the utilized optimization framework and problem are modularly structured so that the setup can be applied to both an initial conceptual design study for bringing innovative floater configurations to light and a subsequent optimization for obtaining detailed designs. In this paper, a spar floater for a 5 MW wind turbine is used as the basis. The approach for generating an initial but very innovative conceptual floater design comprises the segmentation of the floating cylinder into three parts, the specification of a freer optimization formulation with fewer restrictions on the floater geometry, and the allowance for alternative ballast materials. The optimization of the support structure focuses primarily on cost reduction, expressed in terms of the objective to minimize the floater structural material. The optimization results demonstrate significant potential for cost savings when alternative structural and manufacturing strategies are considered