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2020

Development of a Flexible Lightweight Hydraulic-Pneumatic Flywheel System for Wind Turbine Rotors

Alhrshy, L., Jauch, C., & Kloft, P. (2020). Development of a Flexible Lightweight Hydraulic-Pneumatic Flywheel System for Wind Turbine Rotors. Fluids, 5. http://doi.org/10.3390/fluids5040162

Abstract

In this paper, the design of a flexible piston accumulator for application in a hydraulic-pneumatic flywheel system in a wind turbine rotor is presented. The flywheel system enables a wind turbine to vary the inertia of its rotor blades to control the power output and, most importantly, to influence the vibratory behaviour of wind turbine components. The method used for designing the flexible accumulator is based on the one hand on test results of a flexible piston accumulator prototype, and on the other hand, on simulation results of a model of a flexible piston accumulator. As a result, a design of flexible piston accumulators for application in the flywheel system is implemented and compared with the design of conventional steel accumulators. Due to the proposed design of the flywheel system, the impact on the mechanical loads of a wind turbine is analysed. The simulation results show that the new design of the piston accumulators causes a lower impact on the mechanical loads of the wind turbine than a previously published design of piston accumulators. It is further shown that the considered wind turbine can take on the flywheel system without the need for reinforcements in the rotor blades.
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Alhrshy, Laurence

Jauch, Clemens

Forschungsprojekt

Schwungrad

Abteilung/Einrichtung

Wind Energy Technology Institute

Fachbereich

Fachbereich 2: Energy and Life Science
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2020

Journal Article

Laurence Alhrshy

Prof. Dr. Clemens Jauch

Peter Kloft
Construction of arithmetic secret sharing schemes by using torsion limits

Tutdere, S., & Uzunkol, O. (2020). Construction of arithmetic secret sharing schemes by using torsion limits. Hacettepe Journal of Mathematics and Statistics, 49, 638–647. http://doi.org/10.15672/hujms.460348
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Uzunkol, Osmanbey

Fachbereich

Fachbereich 3: Information und Kommunikation
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2020

Journal Article

Seher Tutdere

Osmanbey Uzunkol
Motivating Factors for Implementing Apparel Certification Schemes—A Sustainable Supply Chain Management Perspective

Oelze, N., Gruchmann, T., & Brandenburg, M. (2020). Motivating Factors for Implementing Apparel Certification Schemes—A Sustainable Supply Chain Management Perspective. Sustainability, 12. http://doi.org/10.3390/su12124823

Abstract

The motivations for clothing companies to implement dedicated certification schemes as sustainability practices has received limited attention in sustainable supply chain management (SSCM) research so far. Therefore, it is important to understand how different rationales for the implementation of certification schemes have developed in the past because they considerably influence the overall success of sustainability management efforts. This paper picks up on this gap and presents the results of an in-depth comparative case study drawing on interviews conducted with five managers of three companies from the clothing sector in 2018 and abductive content analysis. By applying such a qualitative approach, this study explores motivations and benefits as well as elaborates on the implementation of certification schemes in apparel supply chains. It outlines that certification in the clothing sector is driven by strategic factors, marketing considerations, and information considering sustainability aspects. The study also shows that certification schemes may strengthen the marketing and competitive position of clothing companies as well as sustainability awareness in textile and apparel supply chains in general. Finally, a framework conceptualized from the findings of the interviews presents relevant SSCM practices in the clothing industry. Therefore, the present study contributes to theory building in SSCM by confirming and extending previous research on the implementation of certification schemes for sustainability, as well as to practice by examining reasons to apply certification schemes and potential performance outcomes.
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Brandenburg, Marcus
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2020

Journal Article

Nelly Oelze

Tim Gruchmann

Marcus Brandenburg

2019

Impacts of stakeholder influences and dynamic capabilities on the sustainability performance of supply chains: a system dynamics model

Rebs, T., Thiel, D., Brandenburg, M., & Seuring, S. (2019). Impacts of stakeholder influences and dynamic capabilities on the sustainability performance of supply chains: a system dynamics model. Journal of Business Economics, 89, 893–926. http://doi.org/10.1007/s11573-019-00940- (Original work published 2026)

Abstract

Dynamic capabilities (DCs) are crucial for companies to attain competitive advantage in dynamic business environments and supply chains, where environmental and social aspects are considered by sustainable supply chain management (SSCM). However, the effects of stakeholder influences on SSCM performance, which results from the interplay of DCs and SSCM practices, need to be analyzed. Therefore, a system dynamics (SD) model is proposed to include the influences of governmental, shareholder, and other external stakeholder pressure. The system behavior, i.e., the company’s SSCM performance, can thus be analyzed in face of varying time delays of stakeholder influences. Findings indicate that different intensities of stakeholder influences affect the development of SSCM practices and DCs of a focal company, and thus, overall SSCM performance. Consequently, intensities of stakeholder influences should be managed accordingly, while the impact of time delays has to be understood to control SSCM performance. The insights gained from the model support the decision- and policy-making, which can be considered from the perspective of the focal company, the regulatory authorities, the shareholders, and other external stakeholders that ultimately translate into customer pressure.
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Brandenburg, Marcus
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2019

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Tobias Rebs

Daniel Thiel

Marcus Brandenburg

Stefan Seuring

Sustainable supply chain management

Stakeholder influences

Dynamic capabilities

Practices

System
Wind turbine controller to mitigate structural loads on a floating wind turbine platform

Fleming, P. A., Peiffer, A., & Schlipf, D. (2019). Wind turbine controller to mitigate structural loads on a floating wind turbine platform. Journal of Offshore Mechanics and Arctic Engineering, 141. http://doi.org/10.1115/1.4042938 (Original work published 2026)
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Schlipf, David
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2019

Journal Article

Paul Fleming

Antoine Peiffer

David Schlipf
Integration of Flow Temperatures in Unit Commitment Models of Future District Heating Systems

Boysen, C., Kaldemeyer, C., Hilpert, S., & Tuschy, I. (2019). Integration of Flow Temperatures in Unit Commitment Models of Future District Heating Systems. Energies, 12, 1061. http://doi.org/10.3390/en12061061 (Original work published 2026)
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Tuschy, Ilja

Fachbereich

Fachbereich 2: Energy and Life Science
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2019

Journal Article

Cynthia Boysen

Cord Kaldemeyer

Simon Hilpert

Ilja Tuschy
Minute-scale forecasting of wind power results from the collaborative workshop of IEA wind task 32 and 36

Würth, I., Valldecabres, L., Simon, E., Möhrlen, C., Uzunoğlu, B., Gilbert, C., … Kaifel, A. (2019). Minute-scale forecasting of wind power results from the collaborative workshop of IEA wind task 32 and 36. Energies, 12, 712. http://doi.org/10.3390/en12040712 (Original work published 2026)
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Schlipf, David
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2019

Journal Article

Ines Würth

Laura Valldecabres

Elliot Simon

Corinna Möhrlen

Bahri Uzunoğlu

Ciaran Gilbert

Gregor Giebel

David Schlipf

Anton Kaifel
Comments on “verifiable outsourced attribute-based signature scheme”

Uzunkol, O. (2019). Comments on “verifiable outsourced attribute-based signature scheme”. Multimedia Tools and Applications , 78(9), 11735–11742,. http://doi.org/10.1007/s11042-018-6725-7

Abstract

Ren and Jiang recently published a “verifiable outsourced attribute-based signature scheme” in Multimedia Tools and Applications. In this note, we first provide two attacks on the verifiability of the semi-signatures of this scheme by showing that a malicious signing-cloud service provider (S-CSP) can always cheat the signer unlike the authors’ claim. Moreover, one of these attacks also implies that an untrusted S-CSP can always forge signatures contrary to the claimed unforgeability against chosen message attacks. Therefore, this scheme unfortunately does not satisfy the main security properties for a delegated signature scheme.
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Uzunkol, Osmanbey

Fachbereich

Fachbereich 3: Information und Kommunikation
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2019

Journal Article

Osmanbey Uzunkol
Secure delegation of group exponentiations: Efficient and fully verifiable schemes with two servers

Moritz, S., & Uzunkol, O. (2019). Secure delegation of group exponentiations: Efficient and fully verifiable schemes with two servers. Security and Privacy, n/a, e70. http://doi.org/https://doi.org/10.1002/spy2.70 (Original work published 2019)

Abstract

Abstract Recent interactions between cloud service providers and mobile resource-constrained devices have increased the interest on the delegation of expensive computations to powerful external server providers. At the same time, security and verifiability of the delegated computation are challenging though highly demanded requirements for various application scenarios. Many security solutions using advanced cryptographic technologies require a large number of highly expensive group exponentiations (GEs). In this paper, we address the problems regarding secure and verifiable delegation of GEs. We first analyze two delegation schemes for GEs both introduced recently in Cluster Computing by Fu et al with the claim that they both provide full verifiability. Particularly, we show that the first scheme is only verifiable with a probability at most 2/3, and the second scheme is totally unverifiable. Then, we propose a secure, efficient and fully verifiable delegation scheme InvDel for a GE using two servers, where one of which is malicious. With InvDel the delegator does not require computations of any group inversions (GIs) while providing full verifiability. Then, we extend InvDel to SimInvDel which is the first, efficient and secure delegation scheme for n-simultaneous GEs achieving full verifiability for n > 1. Secondly, we give implementation results of InvDel and SimInvDel using an Android application together with a comprehensive efficiency analysis of computation and communication with the previous schemes. For instance, when the required CPU costs for a single GE are compared with a 4092-bit modulus, InvDel is more than 220-times (resp. more than two times) more efficient than the local computation (resp. using a previous fully verifiable scheme proposed in the literature). Finally, we also utilize InvDel and SimInvDel to speed-up the verification of Schnorr s signature and Cramer-Shoup encryption schemes.
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Uzunkol, Osmanbey

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Fachbereich 3: Information und Kommunikation
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2019

Journal Article

Stephan Moritz

Osmanbey Uzunkol

cloud security

lightweight cryptography for mobile security

secure delegation

verifiable computation
Vergleich aktueller Patientendatenmanagementsysteme in der Intensivmedizin aus Sicht der klinischen Nutzer

Suchodolski, K., von Dincklage, F., Lichtner, G., Friesdorf, W., Podtschaske, B., & Ragaller, M. (2019). Vergleich aktueller Patientendatenmanagementsysteme in der Intensivmedizin aus Sicht der klinischen Nutzer. Der Anaesthesist, 68(7), 436–443,. http://doi.org/10.1007/s00101-019-0615-x (Original work published Juli 2019)

Abstract

Patientendatenmangementsysteme (PDMS) sind computerbasierte Systeme zur Verarbeitung von medizinischen Daten, die auf Intensivstationen sowohl positive als auch negative Einflüsse auf die Patientenversorgung haben können. Die Faktoren, die darüber entscheiden, ob ein PDMS eher Vor- oder Nachteile bringt und wie deutlich diese ausfallen, werden unter dem Begriff „Gebrauchstauglichkeit“ zusammengefasst. Diese Arbeit fasst die Ergebnisse aus 3 bereits publizierten Arbeiten zu diesem Thema zusammen.
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Podtschaske, Beatrice

Profilbereich

Gesundheit und Life Sciences

Fachbereich

Fachbereich 4: Wirtschaft
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2019

Journal Article

Klaudiusz Suchodolski

Falk von Dincklage

Gregor Lichtner

Wolfgang Friesdorf

Beatrice Podtschaske

Maximilian Ragaller

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2020

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