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Experimental and Numerical Investigation of Centrifugal Pumps with Asymmetric Inflow Conditions

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Journal of Thermal Science 2015年第6期24卷 516-525页

作者： sten Mittag Martin Gabi Institute of Fluid Machinery Karlsruhe Institute of Technology KIT

Most of the times pumps operate off best point *** are changes of operating conditions,modifications,pollution and wearout or *** consequences non-rotational symmetric flows,transient operational conditions,increased risk of cavitation,decrease of efficiency and unpredictable wearout can *** construction components of centrifugal pumps,in particular intake elbows,contribute to this *** elbows causes additional losses and secondary flows,hence non-rotational velocity distributions as intake profile to the centrifugal *** a result the impeller vanes experience permanent changes of the intake flow angle and with it transient flow conditions in the blade *** paper presents the first results of a project,experimentally and numerically investigating the consequences of non-rotational inflow to leading edge flow conditions of a centrifugal *** two pumpintake-elbow systems are compared,by only altering the intake elbow geometry:a common single bended 90°elbow and a numerically optimized elbow(improved regarding rotational symmetric inflow conditions and friction coefficient).The experiments are carried out,using time resolved stereoscopic PIV on a full acrylic pump with refractions index matched(RIM)working *** allows transient investigations of the flow field simultaneously for all blade leading *** CFD results are validated and used to further support the investigation *** comparing an analog pump system with ideal inflow conditions.

关键词： non-rotational symmetric inflow centrifugal pump intake elbow PIV RIM CFD

Experimental Study of An Aquaculture Net Cage in Waves and Current

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China Ocean Engineering 2015年第3期29卷 325-340页

作者： David KRISTIANSEN Pal LADER Фsten JENSEN David FREDRIKSSON SINTEF Fisheries and Aquaculture United States Naval Academy

Model experiments of a floating fish cage subjected to waves and current have been performed. The objective was to study the dynamic behaviour of the fish cage model in waves and current. The fish cage model was composed of a model net, a flexible floating collar of the circular plastic type and a weight system. It was found that there are many wave periods in which cancellation of the wave-induced forces on the model occur. These cancellation wave periods are within the range of dimensioning wave periods commonly used for testing of fish farm structures and hence are important to be aware of. Large deformations of the net under realistic wave and current conditions were observed, where contact between the net and other parts of the structure were identified. This may cause damages to the net due to abrasion.

关键词： aquaculture structure hydrodynamic loads hydroelasticity

Cryogenic nanosecond and picosecond high average and peak power(HAPP) pump lasers for ultrafast applications

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High Power Laser Science and Engineering 2016年第2期4卷 37-67页

作者： David C.Brown sten Tornegrd Joseph Kolis Snake Creek Lasers LLC Clemson University Department of Chemistry

Using cryogenic laser technology, it is now possible to design and demonstrate lasers that have concomitant high average and peak powers, with near-diffraction-limited beam quality. We refer to these new laser systems as HAPP lasers. In this paper, we review important laser crystal materials properties at cryogenic temperature, with an emphasis on Yb lasers, and discuss the important design considerations, including the laser-induced damage threshold, nonlinear effects and thermal effects. A comprehensive model is presented to describe diode pulsed pumping with arbitrary duration and repetition rate, and is used with the Frantz–Nodvik equation to describe, to first order, the performance of HAPP laser systems. A computer code with representative results is also described.

关键词： cryogenic lasers high-average-power lasers high-peak-power lasers ultrafast lasers Yb lasers

Investigations on the Flow Field in an Unshrouded Pump Impeller Geometry

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Journal of Thermal Science 2012年第2期21卷 136-144页

作者： sten Sieber Friedrich Frhlig Saban Caglar Martin Gabi Fchgebiet Strmungsmaschinen Karlsruhe Institute of Technology Germany

Transient CFD simulations are performed to investigate the flow behaviour inside an unshrouded pump using the SAS method. Two blade designs are compared at two different tip clearances and the results are validated by measurements. The detected vortex structure is visualized by the normalized helicity, further discussed regarding its development and behaviour and finally implicated to the efficiency of the two different blade designs.

关键词： unshrouded pump tip clearance helicity

Performance evaluation of high/ultra-high-degree global geopotential models over Vietnam using GNSS/leveling data

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Geodesy and Geodynamics 2023年第5期14卷 500-512页

作者： Hoa Thi Pham sten Claessens Michael Kuhn Joseph Awange School of Earth and Planetary Sciences Spatial Sciences DisciplineCurtin UniversityPerthAustralia Faculty of Surveying Mapping and Geographic InformationHanoi University of Natural Resources and EnvironmentHanoiViet Nam

The availability of many high-degree Global Geopotential Models(GGMs), namely EGM2008, EIGEN-6C4,GECO, SGG-UGM-1, SGG-UGM-2, XGM2019e_2159, and GGMPlus, challenges users regarding which model is best for Vietnam. This study, therefore, evaluates their performance by comparing them with GNSS/leveling data over Vietnam. Results show that their absolute and relative performances are largely independent of topographic conditions and geographical location and can be ranked into three classes:(1)XGM2019e_2159 has the highest accuracy,(2) the models EIGEN-6C4, GECO, SGG-UGM-1, SGG-UGM-2, and GGMPlus, have a very similar level of medium accuracy, while(3) EGM2008 is found to be the least accurate. In an absolute sense, the differences between GNSS/leveling and EGM2008-based height anomalies have a standard deviation(STD) of 0.290 ± 0.010 m, whereas, for XGM2019e_2159, this is 0.156 ± 0.006 *** other models have STDs of(0.18-0.19) ± 0.007 m. Regarding relative performance without fitting, all GGMs have comparable accuracies for baseline length of 5-20 km, while for baselines longer than 20 km,the STD of XGM2019e_2159 is 1.5 ppm-0.5 ppm(approximately 19%-40%) lower compared with EGM2008, and 0.5 ppm-0.25 ppm(approximately 7%-36%) lower compared with EIGEN6C4, GECO,SGG-UGM-1, SGG-UGM-2, and GGMPlus. In addition, the STDs decrease significantly from 20 to 12 ppm in the range of 5-10 km, slightly from 12 to 6 ppm for 10-35 km, very slightly from 6 to 2.5 ppm for35-200 km, and then remain almost unchanged for longer baselines. After fitting, the relative accuracies of all GGMs are at the same level with negligible STD/RMSE values. Furthermore, only EGM2008 experiences significant regional differences, while other GGMs show more homogeneous spatial variation of absolute accuracy over Vietnam. These findings can contribute to the development of local quasigeoid models in Vietnam and may be helpful with the improvement of GGMs in the future.

关键词： GGM Evaluation GNSS/Leveling EGM2008 EIGEN-6C4 GECO SGG-UGM-1 SGG-UGM-2 XGM2019e_2159 GGMPlus

A high aspect ratio surface micromachined accelerometer based on a SiC-CNT composite material

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Microsystems & Nanoengineering 2024年第2期10卷 219-230页

作者： Jiarui Mo Shreyas Shankar Roberto Pezone Guoqi Zhang sten Vollebregt Laboratory of Electronic Components Technology and Materials(ECTM)Department of MicroelectronicsDelft University of TechnologyDelftThe Netherlands

Silicon carbide(SiC)is recognized as an excellent material for microelectromechanical systems(MEMS),especially those operating in challenging environments,such as high temperature,high radiation,and corrosive ***,SiC bulk micromachining is still a challenge,which hinders the development of complex SiC *** address this problem,we present the use of a carbon nanotube(CNT)array coated with amorphous SiC(a-SiC)as an alternative composite material to enable high aspect ratio(HAR)surface *** using a prepatterned catalyst layer,a HAR CNT array can be grown as a structural template and then densified by uniformly filling the CNT bundle with LPCVD *** electrical properties of the resulting SiC-CNT composite were characterized,and the results indicated that the electrical resistivity was dominated by the *** demonstrate the use of this composite in MEMS applications,a capacitive accelerometer was designed,fabricated,and *** fabrication results showed that the composite is fully compatible with the manufacturing of surface micromachining *** Young’s modulus of the composite was extracted from the measured spring constant,and the results show a great improvement in the mechanical properties of the CNTs after coating with *** accelerometer was electrically characterized,and its functionality was confirmed using a mechanical shaker.

关键词： composite surface electrical

Supporting integrative maritime spatial planning by operationalising SEANERGY – a tool to study cross-sectoral synergies and conflicts

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International Journal of Digital Earth 2021年第6期14卷 678-695页

作者： Ida Maria Bonnevie Henning sten Hansen Lise Schrøder Department of Planning Aalborg UniversityCopenhagenDenmark

With growing pressures on marine ecosystems and on marine space,an increasingly needed strategy to optimise the use of marine space is to co-locate synergic marine human uses in close spatial–temporal proximity while separating conflicting marine human *** ArcMap toolbox SEANERGY is a new,cross-sectoral spatial decision support tool(DST)that enables maritime spatial planners to consider synergies and conflicts between marine uses to support assessments of co-location ***-sectoral approaches are important to reach more integrative maritime spatial planning(MSP)*** this article demonstrates through a Baltic Sea analysis,SEANERGY presents a crosssectoral use catalogue for MSP through enabling the tool users to answer important specific questions to spatially and/or numerically weight potential synergies/conflicts between marine *** article discusses to what degree such a cross-sectoral perspective can support integrative MSP *** MSP integrative challenges still exist,SEANERGY enables MSP processes to move towards developing shared goals and initiate discussions built on best available knowledge regarding potential use-use synergies and use-use conflicts for whole sea basins at once.

关键词： Coexistence integrative maritime spatial planning(MSP) SEANERGY spatial decision support tools(DSTs) use-use interactions

A predictive chance constraint rebalancing approach to mobility-on-demand services

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Communications in Transportation Research 2023年第1期3卷 107-117页

作者： sten Elling Tingstad Jacobsen Anders Lindman Balázs Kulcsár Department of Electrical Engineering Chalmers University of TechnologyGothenburg41258Sweden Volvo Cars AB Gothenburg41878Sweden

This paper considers the problem of supply-demand imbalances in Mobility-on-Demand(MoD)*** imbalances occur due to uneven stochastic travel demand and can be mitigated by proactively rebalancing empty vehicles to areas where the demand is *** achieve this,we propose a method that takes into account uncertainties of predicted travel demand while minimizing pick-up time and rebalance mileage for autonomous MoD *** precisely,first travel demand is predicted using Gaussian Process Regression(GPR)which provides uncertainty bounds on the *** then formulate a stochastic model predictive control(MPC)for the autonomous ride-hailing service and integrate the demand predictions with uncertainty *** order to guarantee constraint satisfaction in the optimization under estimated stochastic demand prediction,we employ a probabilistic constraining method with user-defined confidence interval,using Chance Constrained MPC(CCMPC).The benefits of the proposed method are ***,travel demand uncertainty prediction from data can naturally be embedded into the MoD optimization framework,allowing us to keep the imbalance at each station below a certain threshold with a user-defined ***,CCMPC can be relaxed into a Mixed-Integer-Linear-Program(MILP)and the MILP can be solved as a corresponding Linear-Program,which always admits an integral *** transportation simulations show that by tuning the confidence bound on the chance constraint,close to optimal oracle performance can be achieved,with a median customer wait time reduction of 4%compared to using only the mean prediction of the GPR.

关键词： Mobility-on-Demand Travel demand uncertainty Fleet optimization Gaussian process regression Chance constraint optimization Energy efficiency

Identifying the ‘unidentified’ fungi: a global-scale long-read third-generation sequencing approach

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Fungal Diversity 2020年第4期103卷 273-293页

作者： Leho Tedersoo sten Anslan Mohammad Bahram Urmas Kõljalg Kessy Abarenkov Institute of Ecology and Earth Sciences Tartu University14a Ravila50411 TartuEstonia Zoological Institute Braunschweig University of TechnologyMendelssohnstr.438106 BrunswickGermany Department of Ecology Swedish University of Agricultural SciencesUlls väg 1675651 UppsalaSweden Natural History Museum of Tartu University 14a Ravila50411 TartuEstonia

Molecular identification methods,in particular high-throughput sequencing tools,have greatly improved our knowledge about fungal diversity and biogeography,but many of the recovered taxa from natural environments cannot be identified to species or even higher taxonomic *** study addresses the phylogenetic placement of previously unrecognized fungal groups by using two complementary approaches:(i)third-generation amplicon sequencing analysis of DNA from global soil samples,screening out ITS reads of<90%similarity to other available Sanger sequences,and(ii)analysis of common fungal taxa that were previously indicated to be enigmatic in terms of taxonomic placement based on the ITS sequences alone(so-called top50 sequences).For the global soil samples,we chose to amplify the full rRNA gene operon using four partly overlapping amplicons and multiple newly developed primers or primer combinations that cover nearly all fungi and a vast majority of non-fungal *** extracted the rRNA 18S(SSU)and 28S(LSU)genes and performed phylogenetic analyses against carefully selected reference *** SSU and LSU analyses placed most soil sequences and top50 sequences to known orders and classes,but tens of monophyletic groups and single sequences remained outside described ***,the LSU analyses recovered a few small groups of sequences that may potentially represent novel *** conclude that rRNA genes-based phylogenetic analyses are efficient tools for determining phylogenetic relationships of fungal taxa that cannot be placed to any order or class using ITS sequences ***,in many instances,longer rRNA gene sequences and availability of both SSU and LSU reads are needed to improve taxonomic *** leveraging third-generation sequencing from global soil samples,we successfully provided phylogenetic placement for many previously unidentified sequences and broadened our view on the fungal tree of life,with 10-20%new order-level taxa.I

关键词： Soil fungi Top 50 most wanted fungi Phylogenetic diversity PacBio sequencing 18S rRNA gene(small subunit) 28S rRNA gene(large subunit)