M. Schrittwieser, O. Bíró, E. Farnleitner and G. Kastner
The purpose of this paper is to approximate the convective heat transfer using a few non-dimensional parameters in the design process of large synchronous machines. The computed…
Abstract
Purpose
The purpose of this paper is to approximate the convective heat transfer using a few non-dimensional parameters in the design process of large synchronous machines. The computed convective wall heat transfer coefficient can be used in circuit models or can be defined in numerical heat conduction (HC) models to compute the thermal field in the solid domains without the time consuming computation of the fluid domain.
Design/methodology/approach
Computational fluid dynamics (CFD) has been used to include a wide range of different designs, operating conditions and cooling schemes to ensure accurate results for a wide range of possible machines. Neural networks are used to correlate the computed heat transfer coefficients to various design parameters. The data set needed to define the weights and bias layers in the network has been obtained by several CFD simulations. A comparison of the evaluated solid temperatures with those obtained using the conjugate heat transfer (CHT) method has been carried out. The results have also been validated with calorimetric measurements.
Findings
The validation of the HC model has shown that this model is capable of yielding accurate results in a few minutes, in contrast to the several hours needed by the CHT solution. The workflow to determine the convective heat transfer in a specific part of an electrical machine has been also been established. The approximation of the convective wall heat transfer coefficient is shown to be obtainable in sufficient detail by using a neural network.
Research limitations/implications
The paper describes a method to approximate the convective heat transfer accurately in a few seconds, which is very useful in the design process. The heat convection can then be characterized in a HC model including the solid domains only. The losses can be defined as sources in the solid domains, e.g. copper and iron, obtained by electromagnetic calculations and the thermal field can hence be easily computed in these parts. This HC model has the main advantage that the time consuming computation of the fluid domain is avoided.
Originality/value
The novelty in this work is the approximation of the convective heat transfer by using a neural network with an accuracy of less than 5 percent as well as the development of a HC model to compute the temperature in the solid domains. The investigations presented pinpoint relevant issues influencing the thermal behavior of electrical machines.
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Maximilian Schrittwieser, Oszkár Bíró, Ernst Farnleitner and Gebhard Kastner
The purpose of this work is to propose a numerical method based on computational fluid dynamics (CFD) for reconstructing the heat transfer inside electrical machines. The used…
Abstract
Purpose
The purpose of this work is to propose a numerical method based on computational fluid dynamics (CFD) for reconstructing the heat transfer inside electrical machines. The used conjugate heat transfer (CHT) method takes heat convection and heat conduction into account to determine the temperature rise and the thermal losses in stator duct models of large hydro generators. Three different test cases are studied with different slot section components. The numerical models are validated with measurement data for a range of different mass flow rates.
Design/methodology/approach
The work presented is based on the combination of two complementary approaches, namely numerical simulation and measurements. The measured data for the air mass flow and the heat losses are used as boundary conditions for the identification of the temperature distribution in the solid and fluid domains (using a commercial software for CFD). The CHT method is an additional application of CFD and is used to solve the energy equations in the solid domains. Therefore, it is possible to define a thermal source in the solid domains.
Findings
The data obtained by the numerical computation are compared with measurement data for different mass flow rates of the cooling fluid. The quality of the computed values depending on the different mass flow rates shows a good agreement with the measured data. The temperature distribution in the solid domains depending on different material properties is also pointed out in this investigation.
Research limitations/implications
The topic describes a method for solving the heat transfer in the fluid as well as the solid domains. The losses can be defined as sources in the solid domains, e.g. copper and iron, obtained by electromagnetic calculations. This boundary condition defines the situation more accurately than, for example, a constant value of the heat flux or the temperature at the walls like in common used CFD simulations. Another advantage of CFD over other approaches is the consideration of the actual wall heat transfer coefficient.
Originality/value
The presented investigations show relevant issues influencing the thermal behaviour of electrical machines.
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Peter Kieseberg, Sebastian Schrittwieser, Lorcan Morgan, Martin Mulazzani, Markus Huber and Edgar Weippl
Today's database management systems implement sophisticated access control mechanisms to prevent unauthorized access and modifications. For instance, this is an important basic…
Abstract
Purpose
Today's database management systems implement sophisticated access control mechanisms to prevent unauthorized access and modifications. For instance, this is an important basic requirement for SOX (Sarbanes‐Oxley Act) compliance, whereby every past transaction has to be traceable at any time. However, malicious database administrators may still be able to bypass the security mechanisms in order to make hidden modifications to the database. This paper aims to address these issues.
Design/methodology/approach
In this paper the authors define a novel signature of a B+‐tree, a widely‐used storage structure in database management systems, and propose its utilization for supporting the logging in databases. This additional logging mechanism is especially useful in conjunction with forensic techniques that directly target the underlying tree‐structure of an index. Several techniques for applying this signature in the context of digital forensics on B+‐trees are proposed in the course of this paper. Furthermore, the authors' signature can be used to generate exact copies of an index for backup purposes, thereby enabling the owner to completely restore data, even on the structural level.
Findings
For database systems in enterprise environments, compliance to regulatory standards such as SOX (Sarbanes‐Oxley Act), whereby every past transaction has to be traceable at any time, is a fundamental requirement. Today's database management systems usually implement sophisticated access control mechanisms to prevent unauthorized access and modifications. Nonetheless malicious database administrators would be able to bypass the security mechanisms in order to make modifications to the database, while covering their tracks.
Originality/value
In this paper, the authors demonstrate how the tree structure of the underlying store engine can be used to enhance forensic logging mechanisms of the database. They define a novel signature for B+‐trees, which are used by the InnoDB storage engine. This signature stores the structure of database storage files and can help in reconstructing previous versions of the file for forensic purposes. Furthermore, the authors' signature can be used to generate exact copies of an index for backup purposes, thus enabling the owner to completely restore data, even on the structural level. The authors applied their concept to four real‐life scenarios in order to evaluate its effectiveness.
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The purpose of this paper is to extend PriS (privacy safeguard), a privacy requirements engineering method for eliciting and modelling privacy requirements during system design…
Abstract
Purpose
The purpose of this paper is to extend PriS (privacy safeguard), a privacy requirements engineering method for eliciting and modelling privacy requirements during system design, with the addition of privacy-aware cloud-based concepts to assist analysts to reason and model about privacy in cloud environments.
Design/methodology/approach
An analysis of previous findings on the file of cloud privacy based on previous work has been conducted and a set of privacy-related concepts that need to be considered during privacy analysis for cloud-based systems have been revealed. These concepts were used for extending the conceptual model of PriS.
Findings
The main finding of the paper is the design of a new, novel conceptual model that assists analysts and designers in reasoning about privacy in cloud environments. A new template using the JSON (Javascript notation object) format has been introduced for better expressing the privacy requirements along with the related concepts presented through the conceptual model, thus letting the developers to better understand the findings during the design stage and better guide them to the implementation of the respective solution.
Research limitations/implications
The design of a cloud-based process that will guide analysts in detail for eliciting and modelling the identified privacy-related requirements is the limitation and in parallel the next step of the specific work presented here.
Practical implications
The conceptual model has been applied on a real case scenario regarding its efficiency on capturing and mapping all necessary concepts for assisting analysts proceed with the design of the privacy-aware system. The results were positive, all concepts were easy to use and totally understandable from the design team and the stakeholders and the use of the JSON template received very positive comments, especially from the developer’s team.
Originality/value
The paper presents a novel conceptual model for reasoning about privacy requirements in the cloud. The applicability of the proposed model has also been tested on a real case study.
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Joakim Kävrestad, Fredrik Eriksson and Marcus Nohlberg
Using authentication to secure data and accounts has grown to be a natural part of computing. Even if several authentication methods are in existence, using passwords remains the…
Abstract
Purpose
Using authentication to secure data and accounts has grown to be a natural part of computing. Even if several authentication methods are in existence, using passwords remains the most common type of authentication. As long and complex passwords are encouraged by research studies and practitioners alike, computer users design passwords using strategies that enable them to remember their passwords. This paper aims to present a taxonomy of those password creation strategies in the form of a model describing various strategies used to create passwords.
Design/methodology/approach
The study was conducted in a three-step process beginning with a short survey among forensic experts within the Swedish police. The model was then developed by a series of iterative semi-structured interviews with forensic experts. In the third and final step, the model was validated on 5,000 passwords gathered from 50 different password databases that have leaked to the internet.
Findings
The result of this study is a taxonomy of password creation strategies presented as a model that describes the strategies as properties that a password can hold. Any given password can be classified as holding one or more of the properties outlined in the model.
Originality/value
On an abstract level, this study provides insight into password creation strategies. As such, the model can be used as a tool for research and education. It can also be used by practitioners in, for instance, penetration testing to map the most used password creation strategies in a domain or by forensic experts when designing dictionary attacks.
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Hongbo Qiu, Xutian Zou and Xiaobin Fan
Owing to the salient pole structure and stator slots of hydro-generator, the air gap magnetic field in the generator is unevenly distributed. High-frequency harmonic components…
Abstract
Purpose
Owing to the salient pole structure and stator slots of hydro-generator, the air gap magnetic field in the generator is unevenly distributed. High-frequency harmonic components contained in the inhomogeneous air gap magnetic field will have a negative impact on the generator performance. The purpose of this paper, therefore, is to improve the distribution of air gap magnetic field by using appropriate magnetic slot wedge, thereby improving the generator performance.
Design/methodology/approach
Taking a 24 MW, 10.5 kV bulb tubular turbine generator as an example, the 2 D electromagnetic field model of the generator is established by finite element method. The correctness of the model is verified by comparing the finite element calculation data with the experimental data. The influences of the permeability and thickness of the magnetic slot wedge on the generator performance are studied.
Findings
It is found that the intensity and harmonic content of the air gap magnetic field will change with the permeability of slot wedge and then the performance parameters of the generator will also change nonlinearly. The relationship between the eddy current loss, torque ripple, output voltage and other parameters of the generator and the permeability of slot wedge is confirmed. In addition, the variation of losses and torque with wedge thickness is also obtained.
Originality/value
The influence mechanism of magnetic slot wedge on the performance of hydro-generator is revealed. The presented results give guidelines to selecting suitable magnetic slot wedge to improve generator performance.
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Joakim Kävrestad, Johan Zaxmy and Marcus Nohlberg
Using passwords to keep account and data safe is very common in modern computing. The purpose of this paper is to look into methods for cracking passwords as a means of increasing…
Abstract
Purpose
Using passwords to keep account and data safe is very common in modern computing. The purpose of this paper is to look into methods for cracking passwords as a means of increasing security, a practice commonly used in penetration testing. Further, in the discipline of digital forensics, password cracking is often an essential part of a computer examination as data has to be decrypted to be analyzed. This paper seeks to look into how users that actively encrypt data construct their passwords to benefit the forensics community.
Design/methodology/approach
The study began with an automated analysis of over one billion passwords in 22 different password databases that leaked to the internet. The study validated the result with an experiment were passwords created on a local website was analyzed during account creation. Further a survey was used to gather data that was used to identify differences in password behavior between user that actively encrypt their data and other users.
Findings
The result of this study suggests that American lowercase letters and numbers are present in almost every password and that users seem to avoid using special characters if they can. Further, the study suggests that users that actively encrypt their data are more prone to use keyboard patterns as passwords than other users.
Originality/value
This paper contributes to the existing body of knowledge around password behavior and suggests that password-guessing attacks should focus on American letters and numbers. Further, the paper suggests that forensics experts should consider testing patterns-based passwords when performing password-guessing attacks against encrypted data.
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Robin Mueller, Sebastian Schrittwieser, Peter Fruehwirt, Peter Kieseberg and Edgar Weippl
This paper aims to give an overview on a number of selected applications in comparison to a previous evaluation conducted two years ago, as well as performing an analysis on…
Abstract
Purpose
This paper aims to give an overview on a number of selected applications in comparison to a previous evaluation conducted two years ago, as well as performing an analysis on several new applications. Mobile messaging and VoIP applications for smartphones have seen a massive surge in popularity, which has also sparked the interest in research related to their security and privacy protection, leading to in-depth analyses of specific applications or vulnerabilities.
Design/methodology/approach
The evaluation methods mostly focus on known vulnerabilities in connection with authentication and validation mechanisms but also describe some newly identified attack vectors.
Findings
The results show a positive trend for new applications, which are mostly being developed with security and privacy features, whereas some of the older applications have shown little progress or have even introduced new vulnerabilities. In addition, this paper shows privacy implications of smartphone messaging that are not even solved by today’s most sophisticated “secure” smartphone messaging applications, as well as discusses methods for protecting user privacy during the creation of the user network.
Research limitations/implications
Currently, there is no perfect solution available; thus, further research on this topic needs to be conducted.
Originality/value
In addition to conducting a security evaluation of existing applications together with newly designed messengers that were designed with a security background in mind, several methods for protecting user privacy were discussed. Furthermore, some new attack vectors were discussed.
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Benedict Ifeanyichukwu Okike and Esther W. Oyeniyi
Information resources and services are considered tangible assets which are valuable in decision making. Information can fulfill this function only if it is delivered via…
Abstract
Purpose
Information resources and services are considered tangible assets which are valuable in decision making. Information can fulfill this function only if it is delivered via effective marketing at the end users’ doorsteps. The evolution of ICT, social media in particular, has created changes in all productive sectors and service-oriented organizations such as libraries. As well as discussing the need and use of social media by libraries for marketing efforts, this paper focuses on understanding the myriad of security implications that may exist.
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Konstantina Vemou and Maria Karyda
In the Web 2.0 era, users massively communicate through social networking services (SNS), often under false expectations that their communications and personal data are private…
Abstract
Purpose
In the Web 2.0 era, users massively communicate through social networking services (SNS), often under false expectations that their communications and personal data are private. This paper aims to analyze privacy requirements of personal communications over a public medium.
Design/methodology/approach
This paper systematically analyzes SNS services as communication models and considers privacy as an attribute of users’ communication. A privacy threat analysis for each communication model is performed, based on misuse scenarios, to elicit privacy requirements per communication type.
Findings
This paper identifies all communication attributes and privacy threats and provides a comprehensive list of privacy requirements concerning all stakeholders: platform providers, users and third parties.
Originality/value
Elicitation of privacy requirements focuses on the protection of both the communication’s message and metadata and takes into account the public–private character of the medium (SNS platform). The paper proposes a model of SNS functionality as communication patterns, along with a method to analyze privacy threats. Moreover, a comprehensive set of privacy requirements for SNS designers, third parties and users involved in SNS is identified, including voluntary sharing of personal data, the role of the SNS platforms and the various types of communications instantiating in SNS.