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Advances on numerical and experimental investigation of ship roll damping

Journal of Hydrodynamics 2023年第3期35卷 431-448页

作者： Patrick Sumislawski Moustafa Abdel-Maksoud Institute for Fluid Dynamics and Ship Theory Hamburg University of Technology (TUHH) Hamburg Germany

This paper presents recent developments towards efficient and reliable methods for roll damping estimation based on numerical simulations as well as model tests using the harmonic excited roll motion(HERM)technique.A newly designed automatic roll damping estimation procedure shows the advantage of a just-in-time post processing of experimental measurement ***-time analysis of the measured roll damping values permits a considerable shortening of the test ***,a large number of investigations can be carried out with relatively manageable effort in order to determine the roll damping behavior of different keel configurations or at operating conditions,e.g.,different sized keels or Froude *** addition,HERM measurement method is applied to investigate the memory *** this purpose,different excitation schemes are introduced and the results are ***,a study of the scale effect on the roll damping properties is conducted,in which experimental and numerical investigations are performed for two scales of a ship ***,a method is developed that significantly reduces the effort of Reynolds average Navier-Stokes(RANS)-based simulations of roll *** reduction of simulation time is achieved by introducing an artificial *** obtained results show that the developed method is very well applicable for numerical as well as in experimental *** the model tests using HERM technique,the model is free and the rudder is used to keep the straight-ahead *** analysis of the numerical and experimental results shows that the influence of the rudder induced force and moment during HERM tests is not negligible and the contribution of the rudder must be taken into account by estimating the roll ***,a new concept is developed to investigate the parametric roll behavior of ships,which allows neglecting the consideration of the complex modelling of free surface waves in the *** the RAN

关键词： Roll damping harmonic excited roll motion rudder HERM experimental fluid dynamics(EFD) CFD

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Towards maximized utilization of iridium for the acidic oxygen evolution reaction

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Nano Research 2019年第9期12卷 2275-2280页

作者： Marc Ledendecker Simon Geiger Katharina Hengge Joohyun Lim Serhiy Cherevko Andrea M. Mingers Daniel Gohl Guilherme V. Fortunato Daniel Jalalpoor Ferdi Schuth Christina Scheu Karl J. J. Mayrhofer Department of Interface Chemistry and Surface Engineering Nanoanalytics and Interfaces Max-Planck-Institut fur Eisenforschung GmbH40237 DusseldorfGermany Department of Heterogeneous Catalysis Max-Planck-Institut fur KohlenforschungKaiser- Wilhelm-Platz 145470 Mulheim an der RuhrGermany Helmholtz-Institute Erlangen-Nurnbergfar Renewable Energy (IEK-11) Forschungszentrum Jillich91058 ErlangenGermany Department of Chemical and Biological Engineering Friedrich-Alexander- Universitat Erlangen -Nurnberg91058 ErlangenGermany Institute of Chemistry Universidade Federal de Mato Grosso do SulAv. Senador Filin to Muller1555Campo GrandeMS 79074-460Brazil

The reduction in noble metal content for efficient oxygen evolution catalysis is a crucial aspect towards the large scale commercialisation of polymer electrolyte membrane *** catalytic stability and activity are inversely related,long service lifetime still demands large amounts of low-abundant and expensive *** this manuscript we elaborate on the concept of maximizing the utilisation of iridium for the oxygen evolution *** combining different tin oxide based support materials with liquid atomic layer deposition of iridium oxide,new possibilities are opened up to grow thin layers of iridium oxide with tuneable noble metal ***-situ,time-and potential-resolved dissolution experiments reveal how the stability of the substrate and the catalyst layer thickness directly affect the activity and stability of deposited iridium *** on our results,we elaborate on strategies how to obtain stable and active catalysts with maximized iridium utilisation for the oxygen evolution reaction and demonstrate how the activity and durability can be tailored *** results highlight the potential of utilizing thin noble metal films with earth abundant *** for future catalytic applications in the energy sector.

关键词： oxygen evolution reaction liquid atomic layer depositi on catalysis iridium core-shell nano particles

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Turbulence model performance for ventilation components pressure losses

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Building Simulation 2022年第3期15卷 389-399页

作者： Karsten Tawackolian Martin Kriegel Hermann-Rietschel-Institut EnergyComfort&Health in BuildingsTU BerlinGermany

This study looks to find a suitable turbulence model for calculating pressure losses of ventilation *** building ventilation,the most relevant Reynolds number range is between 3×10^(4) and 6×10^(5),depending on the duct dimensions and airflow *** loss coefficients can increase considerably for some components at Reynolds numbers below 2×10^(5).An initial survey of popular turbulence models was conducted for a selected test case of a bend with such a strong Reynolds number *** of the turbulence models failed in reproducing this dependence and predicted curve progressions that were too flat and only applicable for higher Reynolds *** effects near walls played an important role in the present *** turbulence modelling,near-wall damping functions are used to account for this influence.A model that implements near-wall modelling is the lag elliptic blending k-ε*** model gave reasonable predictions for pressure loss coefficients at lower Reynolds *** example is the low Reynolds number k-εturbulence model of Wilcox(LRN).The modification uses damping functions and was initially developed for simulating profiles such as aircraft *** has not been widely used for internal flows such as air duct *** on selected reference cases,the three closure coefficients of the LRN model were adapted in this work to simulate ventilation *** predictions were obtained with new coefficients(LRNM model).This underlined that low Reynolds number effects are relevant in ventilation ductworks and give first insights for suitable turbulence models for this *** the lag elliptic blending model and the modified LRNM model predicted the pressure losses relatively well for the test case where the other tested models failed.

关键词： HVAC ductwork CFD simulation turbulence model model calibration

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Deformation and water/gas flow properties of claystone/bentonite mixtures

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Journal of Rock Mechanics and Geotechnical Engineering 2021年第4期13卷 864-874页

作者： Chun-Liang Zhang Gesellschaft fur Anlagen-und Reaktorsicherheit(GRS) Braunschweig38122Germany

As a potential engineered barrier material for disposal of radioactive waste in clay formations,claystone aggregate excavated from the Opalinus clay(OPA),its mixture with bentonite MX80 in a mass ratio of 7/3,and pure bentonite were extensively investigated with respect to the hydro-mechanical properties and *** these materials,a series of parallel experiments was performed under sequentially applied conditions of hydration with synthetic porewater of the clay formation,consolidation and water flow under increased stresses,and gas injection into the water-saturated and compacted materials under *** responses of the clay mixtures were *** findings include:(1)the hydration and induced swelling of the mixtures are mainly dominated by bentonite content and dry density;(2)the consolidation decreases the porosity and water permeability exponentially by 2-3 orders of magnitude to low values of 10^(-18)-10^(-20) m^(2) at stresses of 2-5 MPa,depending upon bentonite content;and(3)the gas penetration in the water-saturated and compacted bentonite is characterised by a cyclic pressure rising/dropping process limited in between the upper breakthrough and lower shut-off boundaries,whereas the compacted claystone and claystone/bentonite mixture allow for gas release at low and moderate *** results are helpful for design of the engineered barriers for safe isolation of radioactive waste in repositories.

关键词： Crushed claystone Claystone/bentonite mixture Hydration Swelling Consolidation Water permeability Gas penetration

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Thermo-hydro-mechanical behavior of clay rock for deep geological disposal of high-level radioactive waste

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Journal of Rock Mechanics and Geotechnical Engineering 2018年第5期10卷 992-1008页

作者： Chun-Liang Zhang Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) Repository Safety Research Division Theodor-Heuss-Str 4 Braunschweig 38122 Germany

In the context of deep geological disposal of radioactive waste in clay formations, the thermo-hydro- mechanical （THM） behavior of the indurated Callovo-Oxfordian and Opalinus clay rocks has been extensively investigated in our laboratory under repository relevant conditions：（1） rock stress covering the range from the lithostatic state to redistributed levels after excavation; （2） variation of the humidity in the openings due to ventilation as well as hydraulic drained and undrained boundary conditions; （3） gas generation from corrosion of metallic components within repositories; and （4） thermal loading from high-level radioactive waste up to the designed maximum temperature of 90 ~C and even beyond to 150 ~C, Various important aspects concerning the long-term barrier functions of the clay host rocks have been studied：（1） fundamental concept for effective stress in the porous clay-water system; （2） stress- driven deformation and damage as well as resulting permeability changes; （3） moisture influences on mechanical properties; （4） self-sealing of fractures under mechanical load and swelling]slaking of clay minerals upon water uptake; （5） gas migration in fractured and resealed claystones; and （6） thermal impact on the hydro-mechanical behavior and properties, Major findings from the investigations are summarized in this paper,

关键词： Repository Clay rock Deformability Swelling Self-sealing Water permeability Gas migration Thermal impact

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Mechanical behavior of sandy facies of Opalinus Clay under different loadconditions

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Journal of Rock Mechanics and Geotechnical Engineering 2020年第2期12卷 223-241页

作者： Chun-Liang Zhang Ben Laurich Gesellschaft für Anlagen-und Reaktorsicherheit(GRS) BraunschweigGermany Federal Institute for Geosciences and Natural Resources(BGR) HannoverGermany

The mechanical behavior of sandy facies of Opalinus Clay at the Mont Terri underground rock laboratory(URL)in Switzerland was investigated with drained and undrained triaxial compression and extension,cyclic compression,and creep *** were taken from boreholes drilled parallel to *** of the samples were reconditioned to minimize sampling effects of desaturation and *** compression was accomplished by increasing axial stress at constant radial *** extension was carried out by increasing radial stress at constant axial ***,extension was also achieved by simultaneously increasing radial stress and decreasing axial stress under constant mean *** test results showed elastoplastic stress-strain behavior with volumetric compaction until onset of dilatancy at high deviatoric stresses above 80%-90%of the peak failure *** strength is dependent upon load path and mean *** strength under triaxial compression is higher than that under *** respective strength increases with increasing mean *** enhances the stiffness and strength of the *** deformation and strength of the elaystone are *** constant deviatoric stress,the claystone crept continuously with time,which can be characterized by a transient phase and a following stationary phase,and even a tertiary phase at high deviatoric stresses to rupture.

关键词： Clay rock Compression Extension Creep Stiffness

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Fracture propagation in sandstone and slateeLaboratory experiments, acoustic emissions and fracture mechanics

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Journal of Rock Mechanics and Geotechnical Engineering 2015年第3期7卷 237-249页

作者： Ferdinand Stoeckhert Michael Molenda Sebastian Brenne Michael Alber Ruhr-Universitt Bochum

Fracturing of highly anisotropic rocks is a problem often encountered in the stimulation of unconventional hydrocarbon or geothermal reservoirs by hydraulic fracturing. Fracture propagation in isotropic material is well understood but strictly isotropic rocks are rarely found in nature. This study aims at the examination of fracture initiation and propagation processes in a highly anisotropic rock, specifically slate. We performed a series of tensile fracturing laboratory experiments under uniaxial as well as triaxial loading. Cubic specimens with edge lengths of 150 mm and a central borehole with a diameter of13 mm were prepared from Fredeburg slate. An experiment using the rather isotropic Bebertal sandstone as a rather isotropic rock was also performed for comparison. Tensile fractures were generated using the sleeve fracturing technique, in which a polymer tube placed inside the borehole is pressurized to generate tensile fractures emanating from the borehole. In the uniaxial test series, the loading was varied in order to observe the transition from strength-dominated fracture propagation at low loading magnitudes to stress-dominated fracture propagation at high loading magnitudes.

关键词： Sleeve fracturing Acoustic emission(AE) Fracture mechanics Sandstone Slate

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Human Performance in Critical Scenarios as a Benchmark for Highly Automated Vehicles

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Automotive Innovation 2021年第3期4卷 274-283页

作者： Laura Quante Meng Zhang Katharina Preuk Caroline Schießl Institute of Transportation Systems German Aerospace Center(DLR e.V.)Lilienthalplatz 738108 BraunschweigGermany

Before highly automated vehicles(HAVs)become part of everyday traffic,their safety has to be *** use of human performance as a benchmark represents a promising approach,but appropriate methods to quantify and compare human and HAV performance are *** adapting the method of constant stimuli,a scenario-based approach to quantify the limit of(human)performance is *** method is applied to a driving simulator study,in which participants are repeatedly confronted with a cut-in manoeuvre on a *** systematically manipulating the criticality of the manoeuvre in terms of time to collision,humans’collision avoidance performance is *** limit of human performance is then identified by means of logistic *** calculated regression curve and its inflection point can be used for direct comparison of human and HAV ***,the presented approach represents one means by which HAVs’safety performance could be proven.

关键词： Highly automated vehicles Automated driving Proof of safety Human performance Driving performance

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Machine learning based parameter estimation for an adapted finite element model of a blade bearing test bench

Energy and AI

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Energy and AI 2024年第4期18卷 317-326页

作者： Luca Faller Matthis Graßmann Timo Lichtenstein Fraunhofer Institute for Wind Energy Systems IWES Postkamp 1230159HannoverGermany Fraunhofer Institute for Wind Energy Systems IWES Am Schleusengraben 2221029HamburgGermany

Improving the reliability of blade bearings is essential for the safe operation of wind *** challenge can be met with the help of virtual testing and digital-twin driven condition *** such approaches,a precise digital representation of the blade bearing and its test bench is an essential ***,various factors prevent the capture of all parameters of the blade bearing and the associated test *** such as bearing preload,rolling element and raceway dimensions,and bolt preload during assembly vary with each bearing and test bench *** these parameters cannot be measured directly,an alternative solution is *** article presents a methodology to efficiently estimate non-measurable parameters of the test bench using a combination of model-based and data-driven approaches,improving the detailed and accurate virtual testing of blade *** must be ensured to enable the fastest possible,most computationally efficient estimation of parameters during virtual testing or condition *** developed methodology is evaluated using the example of bolt preload on the test *** employing a random forest model and the strain gauge measurements attached to the blade bearing,the bolt preload parameters are *** results demonstrate that the accuracy of the digital model of the blade bearing test bench is improved by up to 11%in three out of four test bench *** great improvement in the accuracy of the digital model highlights the effectiveness of the proposed methodology in enhancing virtual blade bearing testing and digital-twin driven condition monitoring.

关键词： Wind energy Blade bearing Machine learning Virtual testing Digital twin Hybrid models

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Investigation of the heat distribution in dry friction systems during fade and recovery using fiber-optic sensing and infrared technology

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Friction 2022年第3期10卷 422-435页

作者： Albert ALBERS Thomas KLOTZ Chris FINK Sascha OTT IPEK–Institute of Product Engineering Karlsruhe Institute of TechnologyBaden Wurttemberg 76131Germany

The design of dry-running friction pairings and systems determines not only their installation space and costs,but also their reliability under critical load conditions,for example in emergencies,in the case of faults,and in the event of *** knowledge of the contact pattern is highly important for the development of clutches and brakes,the contact-related measurement of the temperature of these systems has not yet been solved in a satisfactory *** its importance,the temperature distribution has only been measured in a few ***,temperature measurements of complete clutches and brakes are carried out using thermocouples *** this study,a new innovative test setup is *** setup is able to measure the heat distribution of the lining and the steel disk of a brake with high spatial resolution by means of fiber optic sensing technology and *** a novelty,it enables measurement of the heat distribution and allows to correlate it with the fade and recovery *** to the expectations,the contact pattern is heterogeneous in circumferential *** causes are discussed using simulation *** with surface analysis,the new setup contributes to the investigation of the causes of fade and recovery.

关键词： dry-running clutch and brake fade and recovery high-resolution spatial temperature distribution measurement

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