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Producing a small series of large complex parts using robotic arc welding is challenging due to the time it takes to program the robot. Currently, offline programming software assists the operator in programming hundreds of welds. This is often still an iterative process because the welding robot or torch may be in collision during part of the weld motion. Adding motion planning software in this workflow could reduce the time required to generate a robot program. However, the capabilities of motion planning algorithms in this context are not clear. We present a generic framework to evaluate and compare motion planning algorithms for robot arc welding. This framework allows integration of existing open source and commercial planners on different levels of abstraction depending on their capabilities. Different planners can be combined and benchmarked as a group if a single planner is not sufficient to solve all aspects of the problem. The framework is applied to two realistic welding cases to show its potential.

The Industry 4.0 concept of a Digital Twin will bring many advantages for wind energy conversion systems, e.g., in condition monitoring, predictive maintenance and the optimisation of control or design parameters. A virtual replica is at the heart of a digital twin. To construct a virtual replica, appropriate modelling techniques must be selected for the turbine components. These models must be chosen with the intended use case of the digital twin in mind, finding a proper balance between the model fidelity and computational load. This review article presents an overview of the recent literature on modelling techniques for turbine aerodynamics, structure and drivetrain mechanics, the permanent magnet synchronous generator, the power electronic converter and the pitch and yaw systems. For each component, a balanced overview is given of models with varying model fidelity and computational load, ranging from simplified lumped parameter models to advanced numerical Finite Element Method (FEM)-based models. The results of the literature review are presented graphically to aid the reader in the model selection process. Based on this review, a high-level structure of a digital twin is proposed together with a virtual replica with a minimum computational load. The concept of a multi-level hierarchical virtual replica is presented.

CUBESPEC is an ESA in-orbit demonstration 6U CubeSat mission, currently in phase A/B. CUBESPEC will deliver months long series of high-resolution spectroscopy to study the structure of massive stars. The payload consists of a Cassegrain telescope with a rectangular primary mirror of 9 x 19 cm2 and a compact high-resolution echelle spectrograph. We aim at a 2023 launch demonstrating the CUBESPEC concept: providing the astronomical community with a generic solution for affordable space-based spectroscopy. The spectrograph design can be configured with minimal hardware changes for low spectral resolution (R = 50) up to high resolution (R ~ 50000) over a over wavelength ranges between 200–1000nm. CUBESPEC will use the KU Leuven ADCS for coarse pointing of the spacecraft, supplemented with a fine-guidance system using a fast steering mirror to center the source on the spectrograph slit. We present the CUBESPEC design and mission analysis, and give an update of the project status.

Wind turbines are one of the most rapid growing and promising technologies for renewable power generation today. However, the share of wind energy in the global energy mix is almost entirely attributed to large turbines. Despite their unique merits, small wind turbines remain a marginal phenomenon, as they lack the technological maturity of their large counterparts. They often have a disappointing energy yield, and consequently, poor economic viability. However, it was observed from test field data that turbines with a higher ratio of rotor size to drivetrain power perform better. This rises the question whether a different design methodology, tailored to the specifics of small turbines, would result in a performance improvement. Therefore, this article presents a techno-economic optimisation method specifically for small wind turbines. Parametrised technical and economic models are integrated within a co-design optimisation process, with maximum economic performance as primary goal. A cost model of the turbine was constructed by collecting price data from wind turbine manufacturers and manufacturers of their main components. The results of the optimisation process confirm that the economic performance can indeed be greatly increased by significantly increasing the ratio of rotor size to drivetrain power.

The fluctuating behavior of wave energy is a challenge to reach high efficiencies of implemented power take-off (PTO) systems due to the bidirectional movement and high variable loads. The described PTO based on a power sharing transmission (PST) tackles this by converting the bidirectional rotation into a unidirectional rotation of a generator equipped with a flywheel to reduce fluctuation in the output. The generator can then be operated at or close to its optimum efficiency. An auxiliary machine is in charge of the controls. The PST is modeled and implemented in an existing hydrodynamic model of a heaving buoy. A basic control is realised in the simulation resulting in the confirmation of the conversion to a unidirectional rotation and facilitating assessment of the machine efficiencies.

The new Coastal and Ocean Basin (COB) located at the Greenbridge Science Park in Ostend, Belgium is under construction since February 2017. The laboratory will provide a versatile facility that will make a wide range of physical modelling studies possible, including the ability to generate waves in combination with currents and wind at a wide range of model scales. The facility is serving the needs in Flanders, Belgium, in the fields of mainly offshore renewable energy and coastal engineering. The COB will allow users to conduct tests for coastal and offshore engineering research and commercial projects. The basin will have state-of-the-art generating and absorbing wavemakers, a current generation system, and a wind generator. It will be possible to generate waves and currents in the same, opposite and oblique directions. The basin is expected to be operational in 2019. This paper presents an overview of the basin’s capabilities, the ongoing work, and selected results from the design of the COB.

Generally, one of the key requirements of modern buildings, besides an appropriate heating and ventilation, is to offer and maintain a suitable lighting. In this contribution, a description of a system capturing and re-directing sunlight into open spaces inside the building without affecting the inside temperature (isotherm) is given. The system mainly consists of three principal components: a mirror capturing the light of the sun and reflecting it inside the building via a prism system, a printed circuit board with two photovoltaic sensors for positioning the mirror, and finally, a motor rotating the printed circuit board and mirror. A closed-loop control system to track the movement of the sun is proposed. The results show good tracking behavior.

This paper introduces a figure of merit for the robustness of continuous-time sigma-delta modulators. It is based on the Nyquist criterion for the equivalent discrete-time (DT) loop filter. It is shown how continuous-time modulators can be designed by optimizing this figure of merit. This way modulators with increased robustness against variations in the noise-transfer function (NTF) parameters are obtained. This is particularly useful for constrained systems, where the system order exceeds the number of design parameters. This situation occurs for example due to the effect of excess loop delay (ELD) or finite gain bandwidth (GBW) of the opamps. Additionally, it is shown that the optimization is equivalent to the minimization of H_infinity, the maximum out-of-band gain of the NTF. This explains why conventional design strategies that are based on H_infinity, such as Schreier’s approach, provide quite robust modulator designs in the case of unconstrained architectures.

Quadrature sigma-delta analog-to-digital converters require a feedback path for both the I and the Q parts of the complex feedback signal. If two separate multibit feedback digital-to-analog converters (DACs) are used, mismatch among the unit DAC elements leads to additional mismatch noise in the output spectrum as well as an I/Q imbalance. This paper proposes new quadrature bandpass (QBP) mismatch shaping techniques. In our approach, the I and Q DACs are merged into one complex DAC, which leads to near-perfect I/Q balance. To select the unit DAC elements of the complex multibit DAC, the well-known butterfly shuffler and tree structure are generalized towards a complex structure, and necessary constraints for their correct functioning are derived. Next, a very efficient first-order QBP shaper implementation is proposed. Finally, the newly presented complex structures are simulated to prove their effectiveness and are compared with each other with respect to performance