Dusty spirals triggered by shadows in transition discs

Context. Despite the recent discovery of spiral-shaped features in protoplanetary discs in the near-infrared and millimetric wavelengths, there is still an active discussion to understand how they formed. In fact, the spiral waves observed in discs around young stars can be due to different physical mechanisms: planet/companion torques, gravitational perturbations or illumination effects. Aims. We study the spirals formed in the gaseous phase due to two diametrically opposed shadows cast at fixed disc locations. The shadows are created by an inclined non-precessing disc inside the cavity, which is assumed to be optically thick. In particular, we analyse the effect of these spirals on the dynamics of the dust particles and discuss their detectability in transition discs. Methods. We perform gaseous hydrodynamical simulations with shadows, then we compute the dust evolution on top of the gaseous distribution, and finally we produce synthetic ALMA observations of the dust emission based on radiative transfer calculations. Results. Our main finding is that mm- to cm-sized dust particles are efficiently trapped inside the shadow-triggered spirals. We also observe that particles of various sizes starting at different stellocentric distances are well mixed inside these pressure maxima. This dynamical effect would favour grain growth and affect the resulting composition of planetesimals in the disc. In addition, our radiative transfer calculations show spiral patterns in the disc at 1.6 {\mu}m and 1.3 mm. Due to their faint thermal emission (compared to the bright inner regions of the disc) the spirals cannot be detected with ALMA. Our synthetic observations prove however that shadows are observable as dips in the thermal emission.Comment: 15 pages, 11 figures, accepted for publication in A&

DustPy: A Python Package for Dust Evolution in Protoplanetary Disks

Many processes during the evolution of protoplanetary disks and during planet formation are highly sensitive to the sizes of dust particles that are present in the disk: the efficiency of dust accretion in the disk and volatile transport on dust particles, gravoturbulent instabilities leading to the formation of planetesimals, or the accretion of pebbles onto large planetary embryos to form giant planets are typical examples of processes that depend on the sizes of the dust particles involved. Furthermore, radiative properties like absorption or scattering opacities depend on the particle sizes. To interpret observations of dust in protoplanetary disks, a proper estimate of the dust particle sizes is needed. We present DustPy: a Python package to simulate dust evolution in protoplanetary disks. DustPy solves gas and dust transport including viscous advection and diffusion as well as collisional growth of dust particles. DustPy is written with a modular concept, such that every aspect of the model can be easily modified or extended to allow for a multitude of research opportunities

Wear test programs for roller-type pitch bearings of wind turbines

Pitch bearings are critical for the safe and efficient operation of wind turbines. They connect the rotor blades to the rotor hub and allow for pitching movements that control loads and rotor speeds. While four-point-contact ball bearings have been dominant in the past, three-row roller bearings are increasingly used in current designs due to their higher load capacity at the same diameter. Wear of the raceways is one of the possible damage mechanisms in pitch bearings. As roller bearings differ significantly from previous designs and because the operational conditions of wind turbines differ from other industrial applications, it is a reasonable de-risking exercise to undergo wear tests prior to the commissioning of such bearings. This study outlines a process for developing a wear test program based on aero-elastic simulation data and wind speed measurements. The process is then applied to an example roller bearing. The final program covers both standstill conditions and pitch cycles. The first is the main addition to former approaches. With existing test rigs and a reasonable budget and timeline, the program can be executed.</p

Micrometre‐sized porous polymer beads as heterogeneous molecular catalysts

Porous polymers have great potential as versatile, chemically stable catalyst supports. Yet, shaping of the resulting powders remains a challenge. Here, we demonstrate the use of suspension polymerisation to design micrometre-sized porous polymers beads containing metal binding sites. The good accessibility of the binding sites ensures high catalytic activity, which is demonstrated for two model reactions: photochemical CO2 reduction and transfer hydrogenation of aromatic ketones. Importantly, the shaping of the host material does not affect the catalytic activity of the active site

Rapid Formation of Massive Planetary Cores in a Pressure Bump

Models of planetary core growth by either planetesimal or pebble accretion are traditionally disconnected from the models of dust evolution and formation of the first gravitationally-bound planetesimals. The state-of-the-art models typically start with massive planetary cores already present. We aim to study the formation and growth of planetary cores in a pressure bump, motivated by the annular structures observed in protoplanetary disks, starting with sub-micron-sized dust grains. We connect the models of dust coagulation and drift, planetesimal formation in the streaming instability, gravitational interactions between planetesimals, pebble accretion, and planet migration, into one uniform framework. We find that planetesimals forming early at the massive end of the size distribution grow quickly dominantly by pebble accretion. These few massive bodies grow on the timescales of ~100 000 years and stir the planetesimals formed later preventing the emergence of further planetary cores. Additionally, a migration trap occurs allowing for retention of the growing cores. Pressure bumps are favourable locations for the emergence and rapid growth of planetary cores by pebble accretion as the dust density and grain size are increased and the pebble accretion onset mass is reduced compared to a smooth-disk model.Comment: 15 pages, 11 figures, accepted by A&

The impact of dynamic pressure bumps on the observational properties of protoplanetary disks

Over the last years, large (sub-)millimetre surveys of protoplanetary disks have well constrained the demographics of disks, such as their millimetre luminosities, spectral indices, and disk radii. Additionally, several high-resolution observations have revealed an abundance of substructures in the disks dust continuum. The most prominent are ring like structures, likely due to pressure bumps trapping dust particles. The origins and characteristics of these bumps, nevertheless, need to be further investigated. The purpose of this work is to study how dynamic pressure bumps affect observational properties of protoplanetary disks. We further aim to differentiate between the planetary- versus zonal flow-origin of pressure bumps. We perform one-dimensional gas and dust evolution simulations, setting up models with varying pressure bump features. We subsequently run radiative transfer calculations to obtain synthetic images and the different quantities of observations. We find that the outermost pressure bump determines the disks dust size across different millimetre wavelengths. Our modelled dust traps need to form early (< 0.1 Myr), fast (on viscous timescales), and must be long lived (> Myr) to obtain the observed high millimetre luminosities and low spectral indices of disks. While the planetary bump models can reproduce these observables irrespectively of the opacity prescription, the highest opacities are needed for the zonal flow bump model to be in line with observations. Our findings favour the planetary- over the zonal flow-origin of pressure bumps and support the idea that planet formation already occurs in early class 0-1 stages of circumstellar disks. The determination of the disks effective size through its outermost pressure bump also delivers a possible answer to why disks in recent low-resolution surveys appear to have the same sizes across different millimetre wavelengths.Comment: 22 pages, 15 figures. To be published in Astronomy & Astrophysic

Comparison of Life Calculations for Oscillating Bearings Considering Individual Pitch Control in Wind Turbines

The fatigue life calculation of bearings under rotating conditions has been well researched and standardized. In contrast, for bearings in oscillating applications no international standards exist. As a result, pitch bearings in wind turbines are designed with different, non standardized approaches. Furthermore, the impact of individual pitch control on pitch bearings has not yet been studied. In this paper four approaches for fatigue life calculation will be applied and compared under individual pitch control conditions. For comparison, the loads and the bearing geometry of the reference turbine IWT 7.5 MW, which is individual pitch controlled, are used. This paper will show how the bearing life calculated by different approaches reacts to individual pitch control conditions. Furthermore, the factors for the modified rating life, according to the ABMA and ISO standards, which implement different operation conditions on the bearings in rotating applications, are calculated for the given loads and the given bearing geometry in oscillating applications