Powering long range wireless nodes with harvested energy

LPWAN systems are important elements in IoT networks. They allow small amount of data to be efficiently transferred over long distances, reducing the number of gateways. Long range (or improved robustness) often comes at the cost of data rate, meaning that frames require more time and thus more energy to be sent or received. This increase in energy affects the ability of using cost-competitive energy harvesting techniques for LPWAN systems, compared to WPAN systems. In this work, we present a design that uses energy harvested from a relatively small indoor solar panel to power a sensor node and enable data transmission with LoRa. Results from first measurements show that using the module near a window will provide enough energy to measure and transmit hundreds of messages per day.  This is more than the amount of messages that can actually be sent per day per node on the public LPWAN network of some telecom operators

Sensitivity analysis of the residual stress state in friction stir welding of high strength aluminum alloy

In this paper, the friction stir welding process was numerically investigated for 6 mm thick aluminum alloy AA2024-T3. The finite element software COMSOL Multiphysics was used to calculate the transient thermal field during welding and the mechanical reaction depending on different mechanical clamping conditions and hardening models subsequently. A thermal pseudo-mechanical (TPM) heat source was implemented. Softening effects of the material due to precipitation hardening dissolution caused by the frictional heat were accounted for. The transient temperature evolution measured by thermocouple elements at various locations was compared to the numerical results. A good agreement was found for the thermal field. A sensitivity study of the mechanical models showed the strong influence of the clamping conditions and the softening model.In diesem Artikel wird der Rührreibschweißprozess für 6 mm dicke Bleche aus AA2024-T3 numerisch untersucht. Die Finite-Elemente-Software COMSOL Multiphysics wurde eingesetzt, um sowohl das transiente Temperaturfeld während des Schweißvorgangs, als auch die entstehenden mechanischen Spannungen für verschiedene Einspannbedingungen und Verfestigungsmodelle zu berechnen. Dabei wurde eine thermo-pseudo-mechanische (TPM) Wärmequelle genutzt. Entfestigungseffekte des Materials, verursacht durch die Reibwärme bedingte Auflösung der Ausscheidungshärtung beim Rührreibschweißen, wurden berücksichtigt. Die transiente Wärmeausbildung wurde mittels Thermoelementen an verschiedenen Positionen gemessen und mit den numerisch ermittelten Werten verglichen. Dabei wurde eine gute Übereinstimmung für das Temperaturfeld erzielt. Eine Sensitivitätsstudie der genutzten mechanischen Modelle zeigt den starken Einfluss der Einspannbedingungen sowie der Entfestigung

Evaluating the performance of smartphones scanning for low energy beacons

Smartphones are now regularly used to scan for the presence of beacons. The information received by the scanner can be displayed or used to start other processes. It happens that smartphones fail to find beacons, although they are advertising. There are several reasons for that failure. A major one is the scanning behaviour of the smartphone. We designed and implemented ways of testing the performance of smartphones while they scan for Bluetooth Smart beacons or for low-power sensors. We used the tests to determine important tuning parameters. We also used the tests to compare a number of popular smartphones and verify the effect of parameter adjustments on their performances

Finite element modeling of an alternating current electromagnetic weld pool support in full penetration laser beam welding of thick duplex stainless steel plates

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in M. Bachmann et al., J. Laser Appl. 28, 022404 (2016) and may be found at https://doi.org/10.2351/1.4943906.An electromagnetic weld pool support system for 20 mm thick duplex stainless steel AISI 2205 was investigated numerically and compared to experiments. In our former publications, it was shown how an alternating current (AC) magnetic field below the process zone directed perpendicular to the welding direction can induce vertically directed Lorentz forces. These can counteract the gravitational forces and allow for a suppression of material drop-out for austenitic stainless steels and aluminum alloys. In this investigation, we additionally adopted a steady-state complex magnetic permeability model for the consideration of the magnetic hysteresis behavior due to the ferritic characteristics of the material. The model was calibrated against the Jiles–Atherton model. The material model was also successfully tested against an experimental configuration before welding with a 30 mm diameter cylinder of austenitic stainless steel surrounded by duplex stainless steel. Thereby, the effects of the Curie temperature on the magnetic characteristics in the vicinity of the later welding zone were simulated. The welding process was modeled with a three-dimensional turbulent steady-state model including heat transfer and fluid dynamics as well as the electromagnetic field equations. Main physical effects, the thermo-capillary (Marangoni) convection at the weld pool boundaries, the natural convection due to gravity as well as latent heat of solid–liquid phase transitions at the phase boundaries were accounted for in the model. The feedback of the electromagnetic forces on the weld pool was described in terms of the electromagnetic-induced pressure. The finite element software COMSOL Multiphysics 4.2 was used in this investigation. It is shown that the gravity drop-out associated with the welding of 20 mm thick duplex stainless steel plates due to the hydrostatic pressure can be prevented by the application of AC magnetic fields between around 70 and 90 mT. The corresponding oscillation frequencies were between 1 and 10 kHz and the electromagnetic AC powers were between 1 and 2.3 kW. In the experiments, values of the electromagnetic AC power between 1.6 and 2.4 kW at oscillation frequencies between 1.2 and 2.5 kHz were found to be optimal to avoid melt sagging or drop-out of melt in single pass full-penetration laser beam welding of 15 and 20 mm thick AISI 2205

Experimental and numerical assessment of weld pool behavior and final microstructure in wire feed laser beam welding with electromagnetic stirring

Advantages such as element homogenization and grain refinement can be realized by introducing electromagnetic stirring into laser beam welding. However, the involved weld pool behavior and its direct role on determining the final microstructure have not been revealed quantitatively. In this paper, a 3D transient heat transfer and fluid flow model coupled with element transport and magnetic induction is developed for wire feed laser beam welding with electromagnetic stirring. The magnetohydrodynamics, temperature profile, velocity field, keyhole evolution and element distribution are calculated and analyzed. The model is well tested against the experimental results. It is suggested that a significant electromagnetic stirring can be produced in the weld pool by the induced Lorentz force under suitable electromagnetic parameters, and it shows important influences on the thermal fluid flow and the solidification parameter. The forward and downward flow along the longitudinal plane of the weld pool is enhanced, which can bring the additional filler wire material to the root of the weld pool. The integrated thermal and mechanical impacts of electromagnetic stirring on grain refinement which is confirmed experimentally by electron backscatter diffraction analysis are decoupled using the calculated solidification parameters and a criterion of dendrite fragmentation.DFG, 416014189, Simulation des Einflusses der elektromagnetisch unterstützten Durchmischung beim Laserstrahlschweißen dickwandiger Stahlbauteile mit Zusatzmateria

Numerical and experimental investigation of thermo-fluid flow and element transport in electromagnetic stirring enhanced wire feed laser beam welding

The introduction of electromagnetic stirring to laser beam welding can bring several beneficial effects e.g. element homogenization and grain refinement. However, the underlying physics has not been fully explored due to the absence of quantitative data of heat and mass transfer in the molten pool. In this paper, the influence of electromagnetic stirring on the thermo-fluid flow and element transport in the wire feed laser beam welding is studied numerically and experimentally. A three-dimensional transient heat transfer and fluid flow model coupled with dynamic keyhole, magnetic induction and element transport is developed for the first time. The results suggest that the Lorentz force produced by an oscillating magnetic field and its induced eddy current shows an important influence on the thermo-fluid flow and the keyhole stability. The melt flow velocity is increased by the electromagnetic stirring at the rear and lower regions of molten pool. The keyhole collapses more frequently at the upper part. The additional elements from the filler wire are significantly homogenized because of the enhanced forward and downward flow. The model is well verified by fusion line shape, high-speed images of molten pool and measured element distribution. This work provides a deeper understanding of the transport phenomena in the laser beam welding with magnetic field.DFG, 416014189, Simulation des Einflusses der elektromagnetisch unterstützten Durchmischung beim Laserstrahlschweißen dickwandiger Stahlbauteile mit Zusatzmateria

Numerical assessment and experimental verification of the influence of the Hartmann effect in laser beam welding processes by steady magnetic fields

Controlling the dynamics in the weld pool is a highly demanding challenge in deep-penetration laser beam welding with modern high power laser systems in the multi kilowatt range. An approach to insert braking forces in the melt which is successfully used in large-scaled industrial applications like casting is the so-called Hartmann effect due to externally applied magnetic fields. Therefore, this study deals with its adaptation to a laser beam welding process of much smaller geometric and time scale. In this paper, the contactless mitigation of fluid dynamic processes in the melt by steady magnetic fields was investigated by numerical simulation for partial penetration welding of aluminium. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential equations were solved based on temperature-dependent material properties up to evaporation temperature for two different penetration depths of the laser beam. The Marangoni convection in the surface region of the weld pool and the natural convection due to the gravitational forces were identified as main driving forces in the weld pool. Furthermore, the latent heat of solid–liquid phase transition was taken into account and the solidification was modelled by the Carman–Kozeny equation for porous medium morphology. The results show that a characteristic change of the flow pattern in the melt can be achieved by the applied steady magnetic fields depending on the ratio of magnetic induced and viscous drag. Consequently, the weld bead geometry was significantly influenced by the developing Lorentz forces. Welding experiments with a 16 kW disc laser with an applied magnetic flux density of around 500 mT support the numerical results by showing a dissipating effect on the weld pool dynamics

Rhyolite generation prior to a Yellowstone supereruption: insights from the Island Park-Mount Jackson rhyolite series

The Yellowstone volcanic field is one of the largest and best-studied centres of rhyolitic volcanism on Earth, yet it still contains little-studied periods of activity. Such an example is the Island Park–Mount Jackson series, which erupted between the Mesa Falls and Lava Creek caldera-forming events as a series of rhyolitic domes and lavas. Here we present the first detailed characterisation of these lavas and use our findings to provide a framework for rhyolite generation in Yellowstone between 1·3 and 0·6 Ma, as well as to assess whether magmatic evolution hints at a forthcoming super-eruption. These porphyritic (15–40% crystals) lavas contain mostly sanidine and quartz with lesser amounts of plagioclase (consistent with equilibrium magmatic modelling via rhyolite-MELTS) and a complex assemblage of mafic minerals. Mineral compositions vary significantly between crystals in each unit, with larger ranges than expected from a single homogeneous population in equilibrium with its host melt. Oxygen isotopes in quartz and sanidine indicate slight depletions (δ18Omagma of 5·0–6·1‰), suggesting some contribution by localised remelting of hydrothermally altered material in the area of the previous Mesa Falls Tuff-related caldera collapse. The preservation of variable O isotopic compositions in quartz requires crystal entrainment less than a few thousand years prior to eruption. Late entrainment of rhyolitic material is supported by the occurrence of subtly older sanidines dated by single-grain 40Ar/39Ar geochronology. The eruption ages of the lavas show discrete clusters illustrating that extended quiescence (>100 kyr) in magmatic activity may be a recurring feature in Yellowstone volcanism. Ubiquitous crystal aggregates, dominated by plagioclase, pyroxene and Fe–Ti oxides, are interpreted as cumulates co-erupted with their extracted liquid. Identical crystal aggregates are found in both normal-δ18O and low-δ18O rocks from Yellowstone, indicating that common petrogenetic processes characterise both volcanic suites, including the late-stage extraction of melt from an incrementally built upper crustal mush zone

Full penetration laser beam welding of thick duplex steel plates with electromagnetic weld pool support

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in V. Avilov et al., Journal of Laser Applications 28, 022420 (2016) and may be found at https://doi.org/10.2351/1.4944103.Full penetration high power bead-on-plate laser beam welding tests of up to 20 mm thick 2205 duplex steel plates were performed in PA position. A contactless inductive electromagnetic (EM) weld pool support system was used to prevent gravity drop-out of the melt. Welding experiments with 15 mm thick plates were carried out using IPG fiber laser YLR 20000 and Yb:YAG thin disk laser TruDisk 16002. The laser power needed to achieve a full penetration was found to be 10.9 and 8.56 kW for welding velocity of 1.0 and 0.5 m min−1, respectively. Reference welds without weld pool support demonstrate excessive root sag. The optimal value of the alternating current (AC) power needed to completely compensate the sagging on the root side was found to be ≈1.6 kW for both values of the welding velocity. The same EM weld pool support system was used in welding tests with 20 mm thick plates. The laser beam power (TRUMPF Yb:YAG thin disk laser TruDisk 16002) needed to reach a full penetration for 0.5 m min−1 was found to be 13.9 kW. Full penetration welding without EM weld pool support is not possible—the surface tension cannot stop the gravity drop-out of the melt. The AC power needed to completely compensate the gravity was found to be 2 kW

Assessment of thermal cycles by combining thermo-fluid dynamics and heat conduction in keyhole mode welding processes

A numerical framework for simulation of the steady-state thermal behaviour in keyhole mode welding has been developed. It is based on the equivalent heat source concept and consists of two parts: computational thermo-fluid dynamics and heat conduction. The solution of the thermo-fluid dynamics problem by the finite element method for a bounded domain results in a weld pool interface geometry being the input data for a subsequent heat conduction problem solved for a workpiece by a proposed boundary element method. The main physical phenomena, such as keyhole shape, thermo-capillary and natural convection and temperature-dependent material properties are taken into consideration. The developed technique is applied to complete-penetration keyhole laser beam welding of a 15 mm thick low-alloyed steel plate at a welding speed of 33 mm s-1 and a laser power of 18 kW. The fluid flow of the molten metal has a strong influence on the weld pool geometry. The thermo-capillary convection is responsible for an increase of the weld pool size near the plate surfaces and a bulge formation near the plate middle plane. The numerical and experimental molten pools, cross-sectional weld dimensions and thermal cycles of the heat affected zone are in close agreement.DFG, 411393804, Experimentelle und numerische Untersuchung der Entstehungsmechanismen des Bulgings und dessen Einfluss auf die Bildung von Mittelrippendefekten beim Hochleistungslaserstrahlschweißen niedriglegierter Stähle hoher Blechdick