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In the new era of blockchain-based multi-agent robotic systems, smart contract programs perform an influential role in implementing decentralized applications with required task allocations. Smart contract programs are developed using script-type of programming languages, and they have already deployed several vulnerable patterns without proper testing and audit. We studied Solidity smart contracts running on the Ethereum platform and identified that they had been exploited because of several programming issues, especially using low-level external calls to malicious sources. Since smart contracts are immutable after their deployment to autonomous multi-robot systems, they should be tested to fix possible development phase issues. We implemented a prototype plugin called SolGuard by extending the solhint linter to prevent three critical issues related to Solidity smart contract programs’ usage of external calls. The SolGuard plugin checks state variable order in the smart contracts, participation of delegatecall invocations, address type parameters in the smart contract’s constructor, and denial of service patterns. We empirically evaluate the SolGuard plugin with existing popular static analysis tools. Our results indicate that SolGuard outperformed the baseline tools in terms of efficiency and accuracy.

With the rapid development of E-commerce, more and more people are used to shopping online, in which the reputation scores of sellers play an important role in helping consumers purchase satisfactory products. However, in the existing E-commerce environments, the reputation scores of users (including sellers and buyers) are centrally computed and stored on a centralized cloud server, which might make errors or even engage in fraud and forgery. To address this issue, we propose a blockchain-based decentralized reputation system (BC-DRS) in the E-commerce environment, i.e., online shopping. In this system, the product information including product descriptions and comments is stored in the interplanetary file system (IPFS) and the corresponding address is returned, and the returned address and the reputation scores of users are stored on the blockchain. The reputation evaluation is implemented by designing and deploying a smart contract on the blockchain. Different from the traditional centralized reputation systems (CRSs), the proposed BC-DRS can protect the product information and users reputation scores from intentional and unintentional modifications, since it is very hard to change any data stored in the blockchain and IPFS. Also, as the reputation scores of users are computed and updated by all the ratings of their transactions weighted by the practical transaction factors, it is effective to resist the common attacks, i.e., unfair rating and collusion. In addition, this system also contains a monetary incentive mechanism for the evaluation, which is helpful to form a virtuous circle in online shopping. The proposed BC-DRS is simulated on the popular blockchain platform, i.e., Ethereum with Solidity language. The experimental results and analysis demonstrate that the proposed BC-DRS has desirable usability and reliability.

This study examined the characteristics of internet rumors in the user-generated content (UGC) mode, analysed the advantages of using the blockchain technology to curb internet rumors, and proposed a framework of the internet rumor reporting system based on the blockchain incentive mechanism. With Truffle as a development framework, intelligent contracts such as create, read, update, and delete were created using Solidity. The end users were connected to the blockchain using the MetaMask plugin. Finally, rewards were obtained by the participants, and the decentralizing program Dapp was created. The results showed that the TRUES could support multiuser reporting and execute intelligent contracts automatically and efficiently in a complex internet rumor environment; for the range of 1–2896 participants, virtual currency rewards could be obtained in 0.5–2.5 d. The conclusion showed that the internet rumor reporting system under the blockchain incentive mechanism had the characteristics of multilevel management, and distributed ledger and digital signatures contributed to the retention and traceability of rumors. Intelligent contracts and consensus mechanisms have obvious advantages in dealing with the complex forms of internet rumors.

The subject of research in the article is the processes and technologies of communication management of infrastructural projects. The possibilities of using blockchain technology in the field of project management are considered. The goal of work: improving the information security of infrastructure projects. The risks of stakeholder communications will be reduced by increasing the security of data access and reducing the time for their processing, which in turn will provide more flexible project management. The tasks of the work: to analyze the current state of development of blockchain technology and conduct a comparative analysis of technology and modern generally accepted management methods, give examples of implementation, determine the advantages of blockchain technology in modern conditions; analyze the benefits of using smart contracts in communication management, apply the smart contract life cycle model in an infrastructure project. Research methods : systems analysis, design approach, structural modeling, instrument Geth, programming language Solidity. The following results were obtained. The main directions of development and implementation of blockchain technology are characterized, examples of the use of blockchain technology in various industries are collected and analyzed, the main advantages and disadvantages of the technology are identified, a comparative analysis of blockchain technology and classical project management methods is carried out, the possibilities of using blockchain technology in the field of project management are described, the main the possibility of implementing reasonable contracts, the advantages and disadvantages of reasonable contracts are identified, the advantages and disadvantages of the instrument of reasonable contracts are analyzed in comparison with the traditional approach. The smart contract life cycle model presents the creation stages, installation to the blockchain contract managing, and contract completion. Provided an example of the smart contract used for the complex financial project, which reduced the risk of project failures. Conclusion . The scientific novelty of the obtained results is in the improvement of the project management life cycle model through the further development of the smart contract model. This allows to increase information security, reduce possible risks and guarantee the implementation of an infrastructure project through the use of blockchain technology in comparison with classical project management methods.

Connected electric vehicles (CEVs) can help cities to reduce road congestion and increase road safety. With the technical improvement made to the battery system in terms of capacity and flexibility, CEVs, as mobile power plants can be an important actor for the electricity markets. Especially, they can trade electricity between each other when supply stations are full or temporarily not available. In this article, we propose an advanced decentralized electricity trading framework between CEVs in parking lots based on consortium blockchain, machine learning, and Game theoretic model. We design a distributed smart contract solution based on a stochastic bidding process, which helps CEVs to sell and buy electricity with their maximum profitability. Finally, numerical simulations with MATLAB and Solidity are conducted to prove the effectiveness of our proposed solution. Also, a comparison with another method in terms of CEVs’ profitability improvement and energy trading management is provided.

Aiming at insufficient situation to express and operate assets in smart contracts, in this article we attempt to add a new asset model into smart contract language (such as SPESC) through combing method of asset's expressions and transactions in real-world contracts. Moreover, a translation mechanism can be set up to accomplish a conversion from the asset model to an executable contract program. On this basis, we propose a new language design toward asset-driven specific smart contracts, called TA-SPESC. This language complies with the structure of real-world contracts and supports a formal definition composed of four modules: Party, asset, term, and contract attribute. This asset model on it can be used to define various types of rights (including the right of ownership, use, possession, usufruct, and disposition of assets), as well as five asset operations (including asset registration, deposit, withdrawal, transfer, and cancellation) to effectively support asset transaction. More important, a series of generation rules are proposed to translate the TA-SPESC contract to an executable contract program. Moreover, taking house rental contract as an example, we provide a TA-SPESC instance and its specific description of translation process according to the generation rules, which supports a semiautomatic generation to executable programs. Finally, the Solidity codes derived from TA-SPESC contracts are run and tested, and the experiment and comparison results indicate that TA-SPESC contracts have high abstraction and low complexity, as well as versatility and convenience of asset transaction, which lead to more reliable software with less errors and fewer misunderstanding.

Nettings are complex flexible structures used in various fisheries. Understanding the hydrodynamic characteristics, deformation, and the flow field around nettings is important to design successful fishing gear. This study investigated the hydrodynamic characteristics and deformation of five nettings made of polyethylene and nylon materials in different attack angles through numerical simulation and physical model experiment. The numerical model was based on the one-way coupling between computational fluid dynamics (CFD) and large deflection nonlinear structural models. Navier-Stokes equations were solved using the finite volume approach, the flow was described using the k-ω shear stress turbulent model, and the large deflection structural dynamic equation was derived using a finite element approach to understand the netting deformation and nodal displacement. The porous media model was chosen to model the nettings in the CFD solver. Numerical data were compared with the experimental results of the physical model to validate the numerical models. Results showed that the numerical data were compatible with the experimental data with an average relative error of 2.34%, 3.40%, 6.50%, and 5.80% in the normal drag coefficients, parallel drag coefficients, inclined drag coefficients, and inclined lift coefficients, respectively. The hydrodynamic forces of the polyethylene and nylon nettings decreased by approximately 52.56% and 66.66%, respectively, with decreasing net solidity. The drag and lift coefficients of the nylon netting were approximately 17.15% and 6.72% lower than those of the polyethylene netting. A spatial development of turbulent flow occurred around the netting because of the netting wake. However, the flow velocity reduction downstream from the netting in the wake region increased with increasing attack angle and net solidity. In addition, the deformation, stress, and strain on each netting increased with increasing solidity ratio.

This study presents experimental and numerical investigation for the effect of number of blade (solidity) on the power and thrust coefficients of a small-scale horizontal-axis wind turbine HAWT. An experimental set- up was installed on wind turbine rotors with different number of blades, i.e. three, five and six, and at different tip speed ratios, in the closed-circuit open-test section wind tunnel. The obtained results from CFD simulations were performed to compare numerical data with experimental measurements. In addition, there is a lack of information presented for the effect of rotor blade number on the flow field for HAWT like vertical axis wind turbine VAWT. Therefore, the current study extends to study the effect of solidity on the flow field using numerical calculation. The numerical simulation was performed using a steady-RANS method. The SST k- ω turbulence model was used to represent turbulence characteristics. It is found that decreasing the number of blades (which makes the turbine less sensitive to the change in tip speed ratio) the wind turbine with 3 blade configuration has the maximum power coefficient in respect to 5 and 6 blade turbines, higher by around 2 and 4 percent respectively.

The current design of vertical axis wind turbines (VAWTs) suffers from inevitable change in tip speed ratio, λ, in variant wind conditions due to fixed rotor speed. At relatively high wind speeds, which are promising due to high wind power potential, VAWTs operate at low λ with poor power coefficient. Morphing airfoils can be a potential solution by modifying the airfoil shape to optimal at each λ. The optimal airfoil shape for VAWTs at low λ, where dynamic stall is present, has not yet been studied in the literature, therefore, the present study addresses this gap by focusing on this regime to serve as a step towards designing morphing airfoils for VAWTs by identifying the optimal airfoil shape at low λ. The present study performs a combined analysis of three shape defining parameters, namely the airfoil maximum thickness and its position as well as the leading-edge radius, to reveal the overall design space. The analysis is based on 252 high-fidelity transient CFD simulations of 126 identical airfoil shapes. The simulations are verified and validated with three experiments. The results show that the three shape defining parameters have a fully coupled impact on the turbine power and thrust coefficients. When λ reduces from 3.0 to 2.5, the optimal airfoil changes from NACA0018–4.5/2.75 to NACA0024–4.5/3.5, that is increasing the maximum thickness from 18%c to 24%c and shifting its position from 27.5%c to 35%c, while the leading-edge radius index, I, remains 4.5. In general, reducing I from the default value of 6.0 to 4.5 is found to increase the turbine CP.

Delegation of cryptographic signing rights has found many application in the literature and the real world. However, despite very advanced functionalities and specific use cases, existing solutions share the natural limitation that the number of usages of these signing rights cannot be efficiently limited, but users can at most be disincentivized to abuse their rights. In this paper, we suggest a solution to this problem based on blockchains. We let a user define a smart contract defining delegated signing rights, which needs to be triggered to successfully sign a message. By leveraging the immutability of the blockchain, our construction can now guarantee that a user-defined threshold of signature invocations cannot be exceeded, thereby circumventing the need for dedicated hardware or similar assistance in existing constructions for one-time programs. We discuss different constructions supporting different features, and provide concrete implementations in the Solidity language of the Ethereum blockchain, proving the real-world efficiency and feasibility of our construction., The 16th International Workshop on Frontiers in Availability, Reliability and Security (FARES 2021)

Purpose The rapid technological growth, changes in consumer demands, products’ built-in obsolescence, presence of more non-repairable parts, shorter lifespan, etc., lead to the generation of e-waste at an unprecedented rate. Although a number of research proposals and business products to manage e-waste exist in the literature, they lack in many aspects such as incomplete coverage of product’s life cycle, access control, payment channels (in few cases), incentive mechanisms, scalability issues, and missing experimental validation. The purpose of this paper is to introduce a novel blockchain-based e-waste management system aiming to mitigate the above-mentioned downsides and limitations of the existing proposals. Design/methodology/approach This paper proposes a robust and reliable e-waste management system by leveraging the power of blockchain technology, which captures the complete life cycle of e-products commencing from their manufacturing as new products to their disposal as e-waste and their recycling back into raw materials. Findings While the use of blockchain technology increases accountability, transparency and trust in the system, the proposal overcomes various challenges and limitations of the existing systems by providing seamless interactions among various agencies. Originality/value This paper presents a prototype implementation of the system as a proof-of-concept using solidity on the Ethereum platform and this paper performs experimental evaluations to demonstrate its feasibility and effective performance in terms of execution gas cost and transaction throughput.

This research presents the influence of the low-solidity design on the loss and stability of the cantilevered stator and the evolution of the hub leakage vortex. The highly loaded 4-stage low-speed research compressor (LSRC) with an embedded cantilevered stator (CS) of Stator 3 (S3) was experimentally measured at the blade row outlet and in the S3 passage, respectively, and the URANS simulation method was calibrated accordingly. Then, the prototype CS blade number was reduced, namely low-solidity cantilevered stator (LSCS), to increase the blade loading. The diffusion factor ( DF) of LSCS at the midspan at the design working condition is 5.2% higher than that of CS. The URANS results show that LSCS provides higher efficiency for the 1.5 stage compressor with a consistent stall margin. For S3, the total pressure loss of LSCS is lower than CS at the design point (DP) working condition, but it is the opposite at the near stall (NS) working condition. For LSCS at the NS point, the blockage region becomes large and occupies the lower half of the fore blade passage because the low-solidity stator could not provide the enough flow turning ability, and the core of the hub leakage vortex (HLV) moves forward and the intensity is strengthened. The high loss region of LSCS at the near stall condition is consistent with the size of two hub leakage vortices. The first HLV breakdown is caused by unsteady mixing flow, and then it twists downstream and contacts with the trailing edge of the adjacent blade pressure surface. The study of the hub leakage flow characteristics of the low-solidity cantilevered stator can help designers to control flow better.

In this paper, the influence of blades number on the performance of pico wind turbine was investigated by using a small-motorized axial DC fan with a rated power of 4W. Fixed streaming air blower was used as a source of wind. Varying in wind speed was accomplished by changing the distance from the blower. A resistor equals to the turbine internal resistance was utilized as a load to collect the electrical power across the load at various wind speeds and for fans of different blades (1, 2, and 5). Values of the cut-in and cut-out speeds were extracted from the power plot. Rated power was recorded, as well. The results have shown that the rated power generated by turbine has decreased due to the reduction of blades number (i.e., reduction in solidity) from 2.6W for a 5-bladed turbine to 0.665W for a 2-bladed turbine and to 0.13W for a 1-bladed turbine. Moreover, the cut-in speed (initial electrical generating speed) has increased from 4.9m/s for 5-bladed to 8m/s for 2-bladed, then to 19.15m/s for 1-bladed. These results are explained by the balancing problems during rotation (polar asymmetrical rotor), and it is seen that the reduction of blades has made a sharp reduction in power coefficient.

Ecumenical carbon dioxide (CO2) emission emanates from car, bus, taxi, and motorcycle is around 45%. Electric vehicle could be the major contributor to abbreviate the pollution level in a transportation sector. According to the Forbes report the ecumenical passenger electric vehicle demand expected to reach 15% in 2025, and 23% in 2030. This research provides a blockchain predicated solution for a pre-owned electric vehicle market that could engender a trust, transparency, immutable records, and an efficient way to track the entire life cycle of a futuristic electric vehicle supply chain. At present most of the pre-owned electric conveyance purchase transpires through the third-party accommodations, websites, and mobile applications. This does not provide the authentic information on electric conveyance history, charging capabilities of the battery, history of the charging records, and performance of the driver (wear and tear affect battery life). Our solution implemented utilizing hybrid blockchain technology. Each stakeholder assigned with the Ethereum blockchain address to track the vehicle records as a distributed ledger. This design considered electric vehicle manufacturer, charging station, battery manufacturer, road convey ascendancy as major stakeholders. Astute contract designed with solidity programming. Truffle platform used to deploy keenly intellective contract in private blockchain that ascertain the privacy of electric conveyance owners and other stakeholders. Meta mask a mobile application utilized kovan network for tracking vehicle in a public blockchain. This application tested with 0.1 Ether for each transaction. Blockchain Electric Vehicle Cloud of Things (BEVCoT) concept proposed to integrate the IoT-Blockchain application in a cloud environment.

H-type Darrieus vertical axis wind turbines (VAWT) have omnidirectional movement capability and can get more power compared to other VAWTs at high tip speed ratios ( 𝜆 ). However, its disadvantages are self-starting inability and low generated power at 𝜆 less than 1. The performance of H-type Darrieus wind turbine at 𝜆

The expenses of a wind turbine modeling in particular a wind farm modeling either numerically or experimentally cause to take the advantages of actuator disks (AD). Porous disks (PD) are used to simulate actuator disks in experiments especially for wake studies. A rotor of a wind turbine replaced by a PD can be modeled efficiently with less cost and process time. For a proper PD selection, some semi‐empirical equations are suggested for a range of solidity of 0.2‐0.6. These equations came from a number of tests. The PDs with different dimensions and solidity values were considered for the tests and models. The results of 2D and 3D numerical simulations and the experimental results show that at the solidity of 0.5, the coefficient of performance of a PD reaches approximately 16/27 which is equal to the Betz's limit; the relation between the coefficient of power and the solidity is fitted by a parabolic equation. The average error of the proposed equations for the power coefficient is reported 1.59%. Finally, based on the current results, some semi‐empirical equations are suggested to help the initial PD selection, and then, the cost of further studies may decrease.

The pharmaceutical industry is prone to many risks and the effect of these risks propagating to patients is enormous. Just like other sectors, the pharmaceutical sector can also benefit from new methodologies in the supply chain network. More effective supply chain management can benefit the pharmaceutical industry by reducing the risks from the current challenges being faced by the industry. Difficulties like missing interest data, human asset reliance, request of the board, distribution center administration, absence of coordination, shipment perceivability and lapse must be confronted. An important observation from these challenges is their dependence on human resources to come about these changes in the state and process information. Inevitably, blockchain can construct the profitability and straightforwardness of flexible chains and vehemently influence everything from warehousing to movement to portion. The core benefits of the blockchain technology are Immutability, Corruption & tamper proof, Secure and Zero downtime. These make the blockchain technology a very effective means for revolutionizing the supply chain management

The Internet of Things (IoT) is becoming an indispensable part of the actual Internet and continues to extend deeper into the daily lives of people, offering distributed and critical services. Mobile agents are widely used in the context of IoT and due to the possibility of transmitting their execution status from one device to another in an IoT network, they offer many advantages such as reducing network load, encapsulating protocols, exceeding network latency, etc. Also, Blockchain Technology is growing rapidly allowing for the addition of an approved security layer in many areas. Security issues related to mobile agent migration can be resolved with the use of Blockchain. This paper aims to demonstrate how Blockchain Technology can be used to secure mobile agents in the context of the IoT using Ethereum and a Smart Contract. The transactions within the Blockchain are used to detect the malevolent mobile agents that could infiltrate the IoT systems. The proposed model aims to provide a secure migration of mobile agents to ensure security and protect the IoT applications against malevolent agents. The case of a smart home with multiple applications is applied to verify the proposed solution. The model presented in this paper could be extended to a wider selection of IoT systems outside of the smart home.

The power performance of twin vertical axis wind turbines (VAWTs) is believed to surpass that of their individual counterparts. In this study, the power performance of twin VAWTs was investigated via computational fluid dynamics (CFD) simulations by changing their configuration parameters, including the airfoil section (NACA), solidity ratio (σ), pitch angle (β), rotational direction (φ), and turbine spacing (S/D). The CFD model was validated against wind tunnel test data from the literature. An L16 (45) orthogonal table was adopted to optimize the power performance using the Taguchi method. The rated power coefficient (CP) and rated tip speed ratio (TSR) were calculated for the 16 cases in the table. The extent of impact of the five parameters on the rated TSR ranked as σ ˃ β ˃ NACA ˃ φ ˃ S/D. In comparison, the extent of impact of these parameters on CP ranked as β ˃ S/D ˃ σ ˃ NACA ˃ φ. The optimal and worst configurations of the twin VAWTs were determined and their CP values increased by 13% and 8%, respectively, from that of their standalone counterparts. Moreover, the rated TSRs of the twin VAWTs differed from those of their standalone counterparts.

In this paper, a numerical code for predicting the hydrodynamic performance of vertical-axis tidal turbine array is developed. The effect of the tip speed ratio, solidity, and preset angle on the hydrodynamic performance are discussed using a series of calculations. The load principle of the rotor and the variation principle of the turbine power coefficient are studied. All these results can be considered as a reference for the design of vertical-axis tidal turbines.

With the Augmented Reality mirror display method using a half-mirror, there is a difference in the focal length between the mirror image and the AR image. Therefore, the observer perceives a mismatch in depth perception, which impairs usability. In this study, we developed an optical-reflection AR display, ALiSE (Augment Layer interweaved Semi-reflecting Existence), which enhances the depth perception experience of AR images by adding a gap zone with the same depth as the target depth between the display and the half-mirror. We conducted an experiment to view 3D objects and achieve virtual fitting using the existing AR with video synthesis and the proposed ALiSE method. As a result of the questionnaire survey, although the comfort of wearing virtual objects was below existing methods, we confirmed that the presence and solidity were superior with the proposed method to other approaches. This is an attempt to create a sense of the stereoscopic effect despite the 2D projection, as the object to be projected is simultaneously reflected in the mirror along with the observer themselves.

Profound changes driven by decarbonization, decentralization, and digitalization are disrupting the energy industry, bringing new challenges to its key stakeholders. In the attempt to address the climate change issue, increasing penetration of renewables and mobility electrification augment the complexity of the electric grid, thus calling for new management approaches to govern energy exchanges while ensuring reliable and secure operations. The emerging blockchain technology is regarded as one of the most promising solutions to respond to the matter in a decentralized, efficient, fast, and secure way. In this work, we propose an Ethereum-based charging management framework for electric vehicles (EVs), tightly interlinked with physical and software infrastructure and implemented in a real-world demonstration site. With a specifically designed solidity-based smart contract governing the charging process, the proposed framework enables secure and reliable accounting of energy exchanges in a network of trustless peers, thus facilitating the EVs’ deployment and encouraging the adoption of blockchain technology for everyday tasks such as EV charging through private and semi-private charging infrastructure. The results of a multi-actor implementation case study in Switzerland demonstrate the feasibility of the proposed blockchain framework and highlight its potential to reduce costs in a typical EV charging business model. Moreover, the study shows that the suggested framework can speed up the charging and billing processes for EV users, simplify the access to energy markets for charging station owners, and facilitate the interaction between the two through specifically designed mobile and web applications. The implementation presented in this paper can be used as a guideline for future blockchain applications for EV charging and other smart grid projects.

One of the important questions in cardiac electrophysiology is to characterise the arrhythmogenic substrate; for example, from the texture of the cardiac fibrosis, which is considered one of the major arrhythmogenic conditions. In this paper, we perform an extensive in silico study of the relationships between various local geometric characteristics of fibrosis on the onset of cardiac arrhythmias. In order to define which texture characteristics have better predictive value, we induce arrhythmias by external stimulation, selecting 4363 textures in which arrhythmia can be induced and also selecting 4363 non-arrhythmogenic textures. For each texture, we determine such characteristics as cluster area, solidity, mean distance, local density and zig-zag propagation path, and compare them in arrhythmogenic and non-arrhythmogenic cases. Our study shows that geometrical characteristics, such as cluster area or solidity, turn out to be the most important for prediction of the arrhythmogenic textures. Overall, we were able to achieve an accuracy of 67% for the arrhythmogenic texture-classification problem. However, the accuracy of predictions depends on the size of the region chosen for the analysis. The optimal size for the local areas of the tissue was of the order of 0.28 of the wavelength of the arrhythmia. We discuss further developments and possible applications of this method for characterising the substrate of arrhythmias in fibrotic textures. © 2021, The Author(s). Research was funded by the Russian Foundation for Basic Research (№ 18-29-13008) and BOF of Ghent University.

Civil aviation is aiming at fuel efficient aircraft concepts. Propulsion systems using boundary layer ingestion (BLI) are promising to reach this goal. The focus of this study is on the DLR UHBR fan stage of a tube and wing aircraft with rear-integrated engines. In this integration scenario the propulsion system and especially the fan stage receives distorted inflow in steady-state flight conditions. The distortion pattern and distortion intensity are dependent on the operating conditions. Consequently, the interaction of the fan and the distortion changes over the flight envelope. The first part of the paper aims at gaining knowledge of the BLI fan performance in the operating points end of field, approach, cruise (CR) and top of climb (TOC) using high-fidelity, unsteady RANS approaches. The analysis includes fan map performance metrics and a deeper insight into the flow field at CR and TOC. The preliminary design of a fan stage requires fast turn-around times, which are not fulfilled by high-fidelity approaches. Therefore, a fast, throughflow-based methodology is developed, which enables aerodynamicists to design distortion-tolerant fans. The main characteristics of the methodology is outlined in the second part. Consequently, the methodology is taken advantage of to investigate parameter sensitivities in terms of tip speed, blade thickness, solidity, the annulus geometry and a non-axisymmetric stator. This study suggests that distortion-tolerant fans should be designed at higher tip speeds than conventional design experience recommends to limit the local operating point excursion.

With the advancement of blockchain technology at a breakneck pace, numerous organizations are now experimenting with blockchain solutions for their operations. In this nascent stage, due to the scarcity of blockchain domain experts, there is a growing trend towards an automated conversion of legacy systems to blockchain-based systems. To this aim, this paper presents an automated framework that facilitates the migration of centralized Java-based applications to decentralized Solidity-based Ethereum applications. The experimental results are encouraging, demonstrating its ability to handle large-scale Java codebase. To the best of our knowledge, this is the first proposal of its kind that enables the translation of Java source codes to Solidity source codes.

This paper focus on the problem that advanced smart contract language (ASCL) are hard to put into practice due to the lack of an effective conversion method from ASCL contract to executable smart contract programs. Aiming at this problem, we take SPESC as example to explore how to design conversion rules from the contract in it to the target programming language in Solidity. These rules provide an approach to convert the definition of SPESC contracting parties into party-contracts on target language, as well as to produce SPESC contract terms into main-contract on target language. Moreover, the proposed framework specifies not only program architecture and storage structure on general smart-contract layer, but also important mechanisms, including personnel management, timing control, exception handling, etc., which can assist programmers to write smart contract programs. Furthermore, taking four SPESC contracts as testing objects, we provide the whole process of converting from SPESC contracts to Solidity programs by SPESC-Translator, and verify the efficiency and security of the conversion process, including coding, deploying, running, and testing through Ethereum. The instance results show that the proposed rules can simplify the writing of smart contracts, standardize program structure, and help programmers to verify the correctness of contract programs.

Spatial crowdsourcing is an effective and novel method. In crowdsourcing systems, a centralized platform is traditionally used to allocate tasks and select workers. Centralized platforms always face following challenges: 1) How to ensure the rationality of tasks allocating; 2) How to ensure the payments of workers in the system when dishonest requesters exist; 3) How to ensure the maximum number of tasks are assigned. 4) How to ensure the integrity and reliability of the centralized platform. To solve these problems, this article proposed a distributed blockchain-based crowdsourcing framework - TSWCrowd (Task Select Worker Crowd). In this framework, tasks are sorted according to specific rules, thus tasks with higher priority are assigned to workers earlier. Workers who are available for a task will be selected and return a result. Then the deployed smart contracts will pay the basic payment automatically. At the same time, relevant contracts also calculate and pay the quality payment according to the proposed quality reward formulation. The proposed TSWCrowd framework on-chain involves a public dataset and uses solidity to compile the smart contracts. The framework was deployed on a local private blockchain. The decentralization property of the blockchain ensures the reliable assignment of tasks. Task-select-worker (TSW) algorithm sorts tasks to ensure reliability. In this paper, the proposed framework was compared with the ABCrowd auction mechanism on-chain and the VCG mechanism off-chain. The results show that the average distance is shorter and the payment is higher, thus reaches the reasonability, reliability and availability.

In this paper, a fully distributed auction-blockchain-based crowdsourcing framework is proposed- ABCrowd . In a typical crowdsourcing framework, independent workers compete to be allocated requesters’ tasks. These workers advertise their costs to the centralized platform, which then decides the final allocation of tasks. While performing the allocation, centralized platforms face two main challenges: 1) how to ensure trusted execution for the allocation of tasks, and 2) how to motivate workers to declare their truthful costs. To address these challenges, ABCrowd proposes to run the crowdsourcing platform entirely on Ethereum Blockchain while incorporating auctions. Blockchain and smart contracts guarantee trusted execution for the allocation through autonomous and transparent on-Chain execution. ABCrowd uses the Repeated-Single-Minded Bidder (R-SMB) auction mechanism, which motivates workers to bid truthfully before allocating them and calculating their payments. R-SMB is an approximation of the optimized off-Chain Vickrey-Clarke-Groves (VCG) mechanism in terms of maximized profit. It entails repeating the Single-Minded Bidder (SMB) auction mechanism to meet the allocation requirement of crowdsourcing applications. ABCrowd is implemented and evaluated using Solidity on a private Ethereum Blockchain, where a real publicly available dataset is used. The proposed on-Chain R-SMB auction mechanism is compared to the off-Chain VCG mechanism, where the results show that R-SMB provides similar performance to VCG in terms of the average number of allocated tasks. Furthermore, R-SMB outperforms VCG in workers’ travelled distance and requesters’ costs, at a low execution cost.

With the growing popularity of smart contracts, the problem of validation of their correctness becomes more and more relevant, but at the moment there are no universally recognized tools for their testing. In this paper, we propose to apply the mutational analysis to improve reliability of Solidity smart contracts. We identified wide spread errors in the source code of existing contracts and developed a RegularMutator tool for mutation analysis. It has shown its effectiveness in testing a large smart contracts project. As a result of our analysis, we managed to improve the test suites of the project to find the discovered defects and, increase the quality of the test suite.

Blockchain technology is found to have its applicability in almost every domain because of its advantages such as crypto-security, transparency, immutability, decentralized data network. In present times, a smart healthcare system with a blockchain data network and healthcare 4.0 processes provides transparency, easy and faster accessibility, security, efficiency, etc. Healthcare 4.0 trends include industry 4.0 processes such as the internet of things (IoT), industrial IoT (IIoT), cognitive computing, artificial intelligence, cloud computing, fog computing, edge computing, etc. The goal of this work is to design a smart healthcare system and it is found to be possible through integration and interoperability of Blockchain 3.0 and Healthcare 4.0 in consideration with healthcare ground-realities. Here, healthcare 4.0 processes used for data accessibility are targeted to be validated through statistical simulation-optimization methods and algorithms. The blockchain is implemented in the Ethereum network, and with associated programming languages, tools, and techniques such as solidity, web3.js, Athena, etc. Further, this work prepares a comparative and comprehensive survey of state-of-the-art blockchain-based smart healthcare systems. The comprehensive survey includes methodology, applications, requirements, outcomes, future directions, etc. A list of groups, organizations, and enterprises are prepared that are working in electronic health records (EHR), electronic medical records (EMR) or electronic personal records (EPR) mainly, and a comparative analysis is drawn concerning adopting the blockchain technology in their processes. This work has explored optimization algorithms applicable to Healthcare 4.0 trends and improves the performance of blockchain-based decentralized applications for the smart healthcare system. Further, smart contracts and their designs are prepared for the proposed system to expedite the trust-building and payment systems. This work has considered simulation and implementation to validate the proposed approach. Simulation results show that the Gas value required (indicating block size and expenditure) lies within current Etherum network Gas limits. The proposed system is active because block utilization lies above 80%. Automated smart contract execution is below 20 seconds. A good number (average 3 per simulation time) is generated in the network that indicates a health competition. Although there is error observed in simulation and implementation that lies between 0.55% and 4.24%, these errors are not affecting overall system performance because simulated and actual (taken in state-of-the-art) data variations are negligible.

One of the main features in the development of deposits of natural facing stone is the requirement to maintain the solidity of the blocks being mined and their decorative properties, to ensure the correct geometric shape. These requirements satisfy the mechanical means of separating blocks. These methods include the hydrocline and wedge method of dividing the array (monolith) into blocks, solid drilling of the array, the use of non-explosive destructive compositions or mixtures (LDCs), diamond-rope cutting, as well as the technology of cutting by disc machines, which is gaining popularity recently. Circular cutting to a greater extent satisfies the conditions of preservation of the solidity and geometric parameters of the blocks. Since, the extraction technology does not involve the process of tipping the monolith. As a consequence, it increases the output of commodity blocks. That is why in the publication on the example of Golovinsky field of labradorites the method of choosing the direction of mining operations for disk machines is given which is based on the study of the fracture of a natural stone deposit on the basis of which the main directions of cracks are highlighted. Microstructural analysis was performed on the basis of the samples taken from the quarry. According to the results of microstructural study, the directions of the easiest cutting with circular saws for Golovinsky Labradorite deposit were obtained. The analysis of the correlation field for the optimal cutting direction and azimuth of crack propagation revealed the presence of certain regularities in the grouping of values. The performed correlation analysis of the relationship of the recommended cutting direction with the azimuth of extension of 60 cracks for Golovinsky Labradorite deposit revealed the presence of a correlation connection, which is characterized by a correlation coefficient of 0.58.

Smart contracts are a special type of programs running inside a blockchain. Immutable and transparent, they provide means to implement fault-tolerant and censorship-resistant services. Unfortunately, its immutability causes a serious challenge of ensuring that a business logic and implementation is correct upfront, before publishing in a blockchain. Several big accidents have indeed shown that users of this technology need special tools to verify smart contract correctness. Existing automated checkers are able to detect only well known implementation bugs, leaving the question of business logic correctness far aside. In this work, we present a symbolic model-checking technique along with a formal specification method for a subset of Solidity programming language that is able to express both state properties and trace properties; the latter constitutes a weak analogy of temporal properties. We evaluate the proposed technique on the MiniDAO smart contract, a young brother of notorious TheDAO. Our Proof-of-Concept was able to detect a non-trivial error in the business logic of this smart contract in a few seconds.

For utilizing the high-quality wind energy around the high-rise building, the aerodynamic performance of building augmented straight-bladed vertical axis wind turbine (BASB-VAWT) was investigated b...

A large number of IoT devices are connected via the Internet. However, most of these IoT devices are generally not perfect-by-design even have security weaknesses or vulnerabilities. Thus, it is essential to update these IoT devices securely, patching their vulnerabilities and protecting the safety of the involved users. Existing studies deliver secure and reliable updates based on blockchain network which serves as the transmission network. However, these approaches could compromise users privacy when updating the IoT devices. In this paper, we propose a new blockchain based privacy-preserving software update protocol, which delivers secure and reliable updates with an incentive mechanism while protects the privacy of involved users. A vendor delivers the updates and makes a commitment by using smart contract to provide financial incentive to the transmission nodes who deliver the updates to its IoT devices. A transmission node can get financial incentive by providing a proof-of-delivery. In order to obtain the proof-of-delivery, the transmission node uses double authentication preventing signature (DAPS) to carry out fair exchange. Specifically, the transmission node uses the DAPS to exchange an attribute-based signature (ABS) of one IoT device. Then, it uses the ABS as proof-of-delivery to receive financial incentives. Generally, to generate an ABS, the IoT device has to execute complex computations which is intolerable for resource limited devices. We propose a concrete outsourced attribute-based signature (OABS) scheme to overcome the weakness. Then, we prove the security of the proposed OABS and the protocol. Finally, we implement smart contract in Solidity to demonstrate the validity of the proposed protocol.

Vertical axis wind turbines (VAWTs) are frequently subjected to fluctuating winds in urban environments. In this paper, we studied the effect of airfoil thickness and solidity on the performance of...

The aerodynamic characteristics of Darrieus vertical axis wind turbines (VAWTs) are affected by several geometrical parameters. Airfoil shape is one of the important factors which have not been received enough attention in the past, compared to other parameters such as solidity, number of blades, chord length, rotor diameter, pitch angle and aspect ratio. In this paper, four airfoils with varying maximum thickness (12%, 15%, 18% and 21%) are investigated by calculating the aerodynamic characteristics of Darrieus VAWTs using computational fluid dynamics technology. The power and torque characteristics, as well as their flow field characteristics, are analyzed. The results indicate that the power coefficient follows a trend of CP_NACA 0018 > CP_NACA 0015 > CP_NACA 0021 > CP_NACA 0012 below an optimum TSR, while it increases with the decrease in airfoil maximum thickness beyond the optimum TSR. The optimum TSR and operational zone also increase with the decrease in airfoil maximum thickness. An optimized airfoil thickness is determined to be between 15 and 18% for a relatively high power coefficient and appropriate optimum TSR, as well as a wider operational zone and a high efficiency band. Moreover, the airfoil maximum thickness influences the strength and region of the vorticity, as well as the interactions between blades and shed vortex, being the main reason for the observed differences in instantaneous torque coefficient. The vorticity of NACA 0015 model is weaker and smaller than that of NACA 0021 model when TSR is 2.0.

Straight-bladed vertical axis wind turbines (SBVAWTs) with a fixed pitch are subject to continuous variation in wind attack angle, which leads to low power generation. Variable pitch techniques are thus required to tackle the problem, but a proper analytical tool for pitch optimization and performance assessment must first be determined. This study thus aims to find a proper analytical tool for high-solidity SBVAWTs of low operational speeds for real-world applications. The applicability of the double-disk multiple stream-tube (DMST) model, a mainstream tool for analyzing moderate-solidity SBVAWTs and optimal pitch angles, is first examined for high-solidity SBVAWTs using measurement data obtained from wind tunnel tests. The complex flow field around a high-solidity SBVAWT is found to make current DMST models’ predictions unsatisfactory. A hybrid DMST model, using the attack angle-dynamic aerodynamic force coefficient relationship, is then proposed. The proposed hybrid DMST model predicts the aerodynamic forces acting on the blades with greater accuracy than those from current DMST models. Based on the proposed hybrid DMST model, a method of determining optimal pitch angles is developed and applied to the high-solidity SBVAWT. The results show that the novel method has the potential to significantly enhance power generation in high-solidity SBVAWTs.

In this paper, a new perspective on the aerodynamic performance modelling of crosswind kite power systems (CKPSs) is provided, where the effects of the induction factor or flow retardation by the kite are taken into account. For simplicity, only CKPSs in straight downwind configuration are considered, where the kites sweep an area perpendicular to the wind direction. Moreover, the in-plane or tangential induction factor is neglected. It is argued that the concept of the swept-area-normalized power coefficient, which is commonly used for conventional wind turbines, is not practically important for CKPSs. Instead, a kite-area-normalized power coefficient concept is adopted and is shown to be a more appropriate metric of performance of kite systems. The kite-area-normalized useful and wasted power coefficients for both a lift and a drag mode CKPS are plotted at different values of solidity factor and aerodynamic efficiency. Moreover, it is shown that the two modes of power generation, i.e. lift and drag modes, yield the same amount of useful power when the kite system solidity factor is essentially zero – this is in agreement with the underlying assumption in the crosswind kite power principle. For non-zero solidity factors, thus non-zero induction factors, however, our results suggest that the drag mode has higher power generation potential than the lift mode.

Computational Fluid Dynamics (CFD) simulations of low turbulence fluid flow through three dimensional (3D) wire screens have been carried out within this research to gain more insight into the flow phenomenon through woven wire mesh screens. This paper presents a novel attempt at identifying and distinguishing between fluid flow regions upstream, downstream and within woven wire mesh screen apertures, highlighting regions of velocity changes, as well as regions of change in turbulence quantities. Mesh screens of this type have recently been proposed as noise reduction treatments for aircraft landing gear. Industry now requires low cost computational tools to enable early design phase simulations of mesh screen technologies. This research paper advances previous studies on laminar-flow modeled numerical simulations for woven wire screens by accounting for turbulence with the aid of a suitably selected turbulence model, therefore numerically identifying the nature of turbulence to be found within the wake of woven wire screens. The nature of fluid flow speed reductions from woven wire screens is highlighted and recommendations for suitable woven wire screen locations when applied for possible aerodynamic noise reduction treatments are made. CFD predicted flow loss coefficients are compared against NACA documented experiments and classical correlations of wire screen loss coefficients while downstream near-field turbulence decay values are compared to correlated turbulence intensity decay of mesh wire screens. 3D simulations are carried out for wire screens of open area ratios of β = 49 . 38 % , 51 . 84 % , and 67 . 26 % . Results of flow loss coefficients compared to experimental measured values were within error margins of ± 1 % for best cases, and ± 8 % for worst cases. Results of downstream fluid flow speed reductions from mesh wire screens were shown to correlate with screen solidity ( 1 − β ) to within U m i n = ( 1 − β ) U ∞ .

High-solidity straight-bladed vertical axis wind turbines are a promising type of vertical axis wind turbine, but their power efficiency is relatively low because of continuous variation in their wind attack angle. Blade pitch control techniques are therefore suggested to enhance their power generation. This study first develops an optimal blade pitch function based on optimal blade pitch angles obtained by using a hybrid double-disk multiple stream-tube model. A novel blade pitch control device is then designed and manufactured to implement the developed optimal blade pitch function for a high-solidity straight-bladed vertical axis wind turbine. Wind tunnel tests focusing on the power output of the fixed and variable pitch high-solidity straight-bladed vertical axis wind turbines are finally carried out to verify the feasibility and efficiency of the developed optimal blade pitch function and control device. The test results show that the maximum power coefficient could be significantly increased by 78% with the developed optimal blade pitch function, thus demonstrating that the blade pitch control device developed in this study is feasible, functional, and effective.

In the era of big data, the produced and collected data explode due to the emerging technologies and applications that pervade everywhere in our daily lives, including internet of things applications such as smart home, smart city, smart grid, e-commerce applications and social network. Big data market can carry out efficient data trading, which provides a way to share data and further enhances the utility of data. However, to realize effective data trading in big data market, several challenges need to be resolved. The first one is to verify the data availability for a data consumer. The second is privacy of a data provider who is unwilling to reveal his real identity to the data consumer. The third is the payment fairness between a data provider and a data consumer with atomic exchange. In this paper, we address these challenges by proposing a new blockchain-based fair data trading protocol in big data market. The proposed protocol integrates ring signature, double-authentication-preventing signature and similarity learning to guarantee the availability of trading data, privacy of data providers and fairness between data providers and data consumers. We show the proposed protocol achieves the desirable security properties that a secure data trading protocol should have. The implementation results with Solidity smart contract demonstrate the validity of the proposed blockchain-based fair data trading protocol.

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The article presents the results of a study of the theoretical foundations of the Blockchain technology. The analysis of the organization structure of its units and the principles of the system. Algorithms of smart contracts are considered and their advantages and disadvantages are analyzed. The purpose of the study is that based on the analysis of the theoretical foundations of building systems using blockchain technology and introducing them into various areas, to propose a system model using smart contracts on the Etherium platform for use in the workflow system in institutions of higher education. Convenient web interfaces for managing the creation of a contract and a module for the interaction of smart contracts with a Web application have been developed. The management of an institution of higher education, namely, a department, faculty or institute, involves the correct and timely preparation of various documentation, in which the documentation on student learning outcomes holds a special place. On its basis various financial and reporting documents are being prepared. To this end, institutions of higher education are introducing workflow system and office automation systems to manage the processing of documents, as well as to organize control over the implementation of these processes. The paper proposes the introduction of a blockchain system on the Ethereum platform using smart contracts written in the Solidity language. Solidity is a tool that is used to create machine-level code that can be run on an Ethereum Virtual Machine. Solidity allows you to create and execute a smart contract without requiring centralized or trusted parties. The use of such technologies makes it possible to significantly reduce the number of paper-based information carriers and, to a significant extent, further automate the existing the workflow system in institutions of higher education. The proposed system is a part of the workflow system of institutions of higher education, which is designed to automate the process of passing documents related to taking into account and submitting to the dean's office of the faculty or the institute the results of the final controls on academic disciplines or the results of retake of tests and exams. This process requires a large number of documents on paper. The proposed system is deployed in the local computer network of the Educational and Scientific Institute of Information Technologies and Mechatronics of Poltava National Technical Yuri Kondratyuk University and is being tested. The results allow us to draw conclusions about the reduction in the number of paper documents; time to obtain permits. In addition, the level of reliability and protection of information transmitted to the administration of the faculty or institute for further processing has increased. In the future, it is planned to introduce the proposed system for document flow automation for all institutes and faculties of the Poltava National Technical Yuri Kondratyuk University.

Large Eddy Simulations (LES) of three different coupled configurations of Vertical Axis Wind Turbines (VAWT) are reported for two values of Tip Speed Ratio (TSR). A few studies are currently available on the wake features of isolated VAWTs, while detailed understanding of wake interaction between VAWTs is still limited, both from experiments and computations. A better insight would be very useful, since recent field tests suggested that interaction between VAWTs in array configurations is potentially beneficial, improving performance, compared to isolated turbines. It is shown here that mutual vortex interaction between wakes of coupled VAWTs is weak, while blockage effects play an important role in making available an increased momentum flux downstream. Such effects are more obvious at higher TSRs, corresponding to a larger dynamic solidity of the overall system. This result suggests that arranging turbines in staggered wind farms configurations – relative to the typical wind direction at a particular site – is beneficial in increasing the momentum flux available to rows of turbines located downstream.

Straight-bladed vertical-axis wind turbines (SBVAWTs) have unsatisfactory power generation and self-start ability due to continuous variation of attack angle to the blades. This study attempts to propose a proper analytical tool for high-solidity SBVAWTs since high-solidity SBVAWTs could be valuable in application for their comparatively low operational speed and good self-start performance. The applicability of the double-disk multiple stream-tube (DMST) model, which is a mainstream tool for SBVAWTs, is first examined for high-solidity SBVAWTs using the measurement data of aerodynamic forces on the blades obtained from wind tunnel tests. It is found that the complex flow field around the high-solidity SBVAWT introduces difficulties for the current DMST model to make satisfactory predictions. A hybrid DMST model, which uses the attack angle-dynamic aerodynamic force coefficient relationship established based on the measurement data, is then proposed. The aerodynamic forces estimated from the proposed hybrid DMST model manifest that the hybrid DMST model could predict the aerodynamic forces on the blades of the high-solidity SBVAWT with higher accuracy than the existing DMST models.

Straight-bladed vertical axis wind turbines (SBVAWTs) are a promising type of vertical axis wind turbines but their power efficiency is relatively low due to continuous variation of attack angle. Variable-pitch techniques are thus proposed to enhance their power generation. The current pitch control techniques for SBVAWTs are mainly based on some empirical forms and seldom adopted for practical use. This study first proposes an algorithm to search optimal pitch angles by means of the hybrid double-disk multiple stream-tube (hybrid DMST) model proposed by the authors and by taking the maximization of blades’ tangential forces as an objective function. After optimal pitch curves with a wide range of TSRs are computed and obtained, an optimal pitch function is then established and applied to a high-solidity SBVAWT. The results obtained indicate that the power coefficient of the high-solidity SBVAWT could be enhanced prominently with the proposed optimal pitch function.

Cloud computing is one of the leading options to store massive amount of data. The metaphor of the cloud was borrowed from old telecoms network schematics, in which the public telephone network was often represented as a cloud to denote that the just did not a matter it was just a cloud of stuff. However, cost and risk will increase inthe organization which are using cloud platforms. Hence this paper combines Cloud with blockchain technology to produce a secured file storage system. Blockchain is considered by many to be the safest technology. Here, a single file is splited and stored in blocks using the file manipulation and Advanced Encryption Standard (AES) algorithms. A high level, contract oriented language, Solidity is used for writing smart contracts. The system architecture which explains the cloud and blockchain processes is constructed. This system also ensures that it is free from attacks such as Brute force. Finally, the blockchain network in the cloud platform is implemented.

International audience; Smart contracts are the artifact of the blockchain that provides immutable and verifiable specifications of physical transactions. Solidity is a domain-specific programming language with the purpose of defining smart contracts. It aims at reducing the transaction costs occasioned by the execution of contracts on the distributed ledgers such as Ethereum. However, Solidity contracts need to adhere to safety and security requirements that require formal verification and certification. This paper proposes a method to meet such requirements by translating Solidity contracts to Event-B models, supporting certification. To that purpose, we define a restrained Solidity subset and a transfer function that translates Solidity contracts to Event-B models. Besides, we have implemented a translator to improve the conversion efficiency. As a case study, we take advantage of Event-B method capabilities to simulate models at different levels of abstraction and to express the properties of a typical smart contract: Honeypot contract. Lastly, we verify the generated proof obligations of the Event-B model with the help of the Rodin platform.