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Rigorous analysis of the interaction problem of sea ice with a rigid body
Get PDFConsider the set of equations modeling the motion of a rigid body enclosed in sea ice. Using Hibler’s viscous-plastic model for describing sea ice, it is shown by a certain decoupling approach that this system admits a unique, local strong solution within the Lp-setting
Optimal design for compliance modeling of industrial robots with bayesian inference of stiffnesses
Get PDFIn this paper a cost and time efficient approach to setup a compliance model for industrial robots is presented. The compliance model is distinctly determined by the gear’s stiffness parameters which are tuned by an optimal design of experiments approach. The experimental setup consists of different poses of the robot’s axes together with the applied force at the tool center point (TCP). These robot poses represent together with defined forces the experimental setup where the deviation of the robot under defined force is measured. Based on measurements of the displacement of the TCP the stiffness parameters for the compliance model are estimated and afterwards validated in new experiments. The efficiency of this approach lies in the reduced amount of experiments that are needed to identify the stiffness parameters that are parameters inherent to the compliance and the less complex experimental setup
Experimental characterization of the turbulent intake jet in an engine flow bench
Get PDFThe turbulent intake flow of an optically accessible internal combustion engine is modeled using an air flow bench to reduce the complexity in the number of variables inherent within engine flows. By removing the piston and introducing a new optically accessible housing and outlet channel, the flow bench design simulates engine flows in the region just downstream of the intake valves and offers the possibility to measure and calculate quantities that would be difficult or impossible to obtain in the unsteady environment of a dynamic engine. Velocity data obtained via high-speed particle image velocimetry of the flow bench in the symmetry and valve planes are compared with data from a base operating condition of the motored engine at an intake pressure of 0.95 bar and a speed of 800 rpm at -270°CA (270 crank-angle-degrees before compression top dead center), beginning with stationary valves at the corresponding valve lift of -270°CA, then with moving valves. Analysis of the intake jet turbulence for increasing mass flow rates reveals a coherent flapping of the jet at a frequency of 752.5 Hz for only the 100% mass flow rate case. The vortex shedding frequency of the valve stem is estimated to being in the range of 634–799 Hz, indicating a possible link between the coherent jet flapping and the vortex shedding surviving the acceleration through the valve gap. Through comprehensive analysis, this study provides valuable validation data and insight into the intake flows of internal combustion engines
Tool management optimisation through traceability and tool wear prediction in the aviation industry
Get PDFThe aviation industry is characterised by high manufacturing requirements of products with difficult-to-machine materials to ensure quality and safety. Standardised and secured processes and transparency in resource and material flows within production are important requirements for meeting these safety and quality standards while staying competitive on the market. Those requirements also apply to a companies’ tool management and are to be met with an optimised tool change strategy considering economic aspects at the same time. The article presents a use case of a company belonging to the aviation industry striving to achieve goals concerning costs, quality, and time in their tool management. To realise potential improvements a retrofitting traceability solution is illustrated enabling data-based maintenance strategies in the use case. The traceability solution aims to provide transparency about tool inventory, the location of tools on the shop floor and functions as data acquisition system to realise the individual tracking of used tools. Using the individual tracking data of tools and matching them with relevant machining data enables the application of data-based maintenance strategies pointing out possibilities to indicate the tools’ wear state. This approach offers benefits such as reducing the scrap rate or machining down times with a direct impact on quality, costs, or lead times of customer orders
Wie verzichtbar sind Kollektivsingulare wirklich? Über den relativen Gebrauchswert von »Geist«
Get PDFGroßbegriffe und, genauer, die seit Koselleck als auch sozialhistorisch wirksam geschilderten »Kollektivsingulare« stehen in der historischen, der literaturwissenschaftlichen wie auch der philosophischen Begriffsgeschichte unter Metaphysikverdacht, Ideologieverdacht oder mindestens Vereinfachungsverdacht. Dass dies berechtigt ist, stellt der Beitrag nicht in Abrede, plädiert mit einer gewissen Melancholie jedoch für eine pflegliche Archivierung und auch Mitführung der fraglichen Begriffswörter mitsamt ihrer facettenreichen historischen Semantologie. Dies gilt sogar für den »Geist«. Ihn zu verabschieden kann nicht heißen, ihn zu ersetzen oder gar zu tilgen
Optical parametric oscillator and amplifier providing tunable, narrowband nanosecond laser pulses in the mid-infrared with mJ pulse energy
Get PDFWe report on an all-solid-state light source for nanosecond (ns) laser pulses, with broad tunability in the mid-infrared, spectral bandwidth close to the Fourier transform limit, and pulse energy in the mJ regime. To this end, we extend a tunable, continuous wave (cw) singly resonant optical parametric oscillator by an optical parametric pre-amplifier with a periodically poled lithium niobate crystal and a power amplifier stage with two bulk lithium niobate crystals. We demonstrate pulse energies beyond 1 mJ in a tuning range between 3.3 and 3.8 μm center wavelength, with options for even larger output pulse energy and tuning range. The total conversion efficiency in the power amplifier reaches 20%. From measurements of absorption spectroscopy, we determine a very narrow linewidth of 108 MHz (full width at half maximum, FWHM), which is only a factor of 1.4 above the Fourier limit. We demonstrate the applicability and versatility of the laser system for nonlinear spectroscopy by resonantly enhanced third harmonic generation and sum frequency mixing in a gas sample of HCl molecules
Dynamic propagation of mode III cracks in a Lattice Boltzmann method for solids
Get PDFThis work presents concepts and algorithms for the simulation of dynamic fractures with a Lattice Boltzmann method (LBM) for linear elastic solids. This LBM has been presented previously and solves the wave equation, which is interpreted as the governing equation for antiplane shear deformation. Besides the steady growth of a crack at a prescribed crack velocity, a fracture criterion based on stress intensity factors has been implemented. This is the first time that crack propagation with a mechanically relevant criterion is regarded in the context of LBMs. Numerical results are examined to validate the proposed method. The concepts of crack propagation introduced here are not limited to mode III cracks or the simplified deformation assumption of antiplane shear. By introducing a rather simple processing step into the existing LBM at the level of individual lattice sites, the overall performance of the LBM is maintained. Our findings underline the validity of the LBM as a numerical tool to simulate solids in general as well as dynamic fractures in particular
Towards a Benchmark for Shared Databases [Vision Paper]
Get PDFTraditionally, data has been held in silos and was rarely shared with other organizations. However, recently data sharing across organizations is becoming more and more important as evidenced by governmental and industrial initiatives such as the EU data strategy. As a result, both academia and industry have been proposing new systems for shared databases, that allow multiple organizations to collaboratively insert and manage data in a common database. Yet, each new system seems to come with its own architectural choices and custom guarantees that make it hard for users to navigate the plethora of shared database systems. While standard benchmarks like the TPC‑C database benchmark have been a well-established tool to compare and analyze traditional database systems, they seem to be unsuited to evaluate shared database systems. This is because these systems are built with fundamentally different assumptions in mind, such as a different threat/trust model since multiple (untrusted) parties access and modify the same data. In this paper, we present a vision and initial ideas for a new benchmark to evaluate shared databases and capture their unique characteristics
Topology optimization using difference-based equivalent static loads
Get PDFTopology optimization of crash-related problems usually involves a huge number of design variables as well as nonlinearities in geometry, material, and contact. The Equivalent Static Load (ESL) method provides an approach to solve such problems. This method has recently been extended under the name Difference-based Equivalent Static Load (DiESL) method to employ a set of Finite Element models, each describing the deformed geometry at an individual time step. Only sizing optimization problems were considered so far. In this paper, the DiESL method is extended to topology optimization utilizing a Solid Isotropic Material with Penalization approach (SIMP). The method is tested using an example of a rigid pole colliding with a simple beam, where the intrusion of the pole is minimized. The initial velocity of the pole is varied in order to examine the influence of inertia effects on the optimized structures. It is shown that the results differ significantly depending on the chosen initial velocity and, consequently, that they exhibit inertia effects. This cannot be seen in the results derived by the standard ESL method. Consequently, the results of the DiESL method’s show a considerable improvement compared to those of the standard ESL method
A multilevel, multi-mode framework for standardization in digital B2B platform eco-systems in international cargo transportation — A multiple case study
Get PDFStandardization is gaining importance for digital platform eco-systems as they try to balance both stability and flexibility of their core as well as their boundary resources. Our knowledge on which factors influence standardization processes in business-to-business (B2B) focused digital platform eco-systems remains limited. Using three B2B platform eco-systems from the cargo transportation and seaport eco-system context, we apply a multiple case study to investigate which factors affect the standardization mode and the standard adoption. Based on 19 interviews and a systematic coding procedure, we identified 24 factors and cluster them into four overarching themes. We show the relatedness between standardization and innovation research, identify standard characteristics as the most important theme of factors and show that standardization has to be seen as a dynamic and interconnected process, as some factors are interdependent but the controllability varies between factors. Lastly, implications of these results and future research directions are discussed