Today, a large number of people access internet through their smart phones to login to their bank accounts, social networking accounts and various other blogs. In such a scenario, user authentication has emerged as a major security issue... more
Today, a large number of people access internet through their smart phones to login to their bank accounts, social networking accounts and various other blogs. In such a scenario, user authentication has emerged as a major security issue in mobile internet. To date, password based authentication schemes have been extensively used to provide authentication and security. The password based authentication has always been cumbersome for the users because human memory is transient and remembering a large number of long and complicated passwords is impossible. Also, it is vulnerable to various kinds of attacks like brute force, rainbow table, dictionary, sniffing, shoulder surfing and so on. As the main contribution of this paper, a new passwordless authentication scheme for smart phones is presented which not only resolves all the weaknesses of password based schemes but also provide robust security. The proposed scheme relieves users from memorizing and storing long and complicated passwords. The proposed scheme uses ECDSA which is based on Elliptic Curve Cryptography (ECC). ECC has remarkable strength and efficiency advantages in terms of bandwidth, key sizes and computational overheads over other public key cryptosystems. It is therefore suitable for resource constraint devices like smart phone. Furthermore, the proposed scheme incorporate CAPTCHA which play a very important role in protecting the web resources from spamming and other malicious activities. To the best of our knowledge, until now no passwordless user authentication protocol based on ECC has been proposed for smart phones. Finally, the security and functionality analysis shows that compared with existing password based authentication schemes, the proposed scheme is more secure and efficient.
This paper presents a novel initiative for reliable high-resolution forecasts on prevailing sea states at 50 important ports worldwide (Accu-Waves; http://accuwaves.eu/). Its goal is to support safe navigation, unhampered vessel... more
This paper presents a novel initiative for reliable high-resolution forecasts on prevailing sea states at 50 important ports worldwide (Accu-Waves; http://accuwaves.eu/). Its goal is to support safe navigation, unhampered vessel approaching to busy harbored areas, and secure ship maneuvering in ports. Accu-Waves 1 is based on integrated, high-resolution, ocean and coastal modeling that uses data from global scale, open-sea forecasts as boundary conditions. The models' setup, coupling, nesting, calibration, verification, and application are reported herein, concerning areas near and inside globally significant port basins. Thus, we present the automated operational setup of the Accu-Waves service for three-day forecasts at three-hourly intervals.
Offshore wind farms located in a shallow water environment and in areas prone to hurricanes may experience extreme breaking waves. Although little is known about their characteristics, breaking waves may represent a dominant load that a... more
Offshore wind farms located in a shallow water environment and in areas prone to hurricanes may experience extreme breaking waves. Although little is known about their characteristics, breaking waves may represent a dominant load that a wind turbine structure is subjected to over its design lifetime. Existing analysis approaches may have limited applicability, especially for large diameter monopiles. The main goal of the research program is to improve methodology for determining the wave loading. Reducing the uncertainty associated with the load spectrum a structure can be subjected to will enable a lower design safety factors, and therefore reduce the cost of offshore wind power generation systems.
The contribution focuses on a CFD study to determine the characteristics of slam loads based on anticipated wave behavior from modeling and physical observation. The model will use a numerical representation of a wave tank with a flap-type wave generator to create virtual breaking waves to analyze slam forces on a monopile foundation. Buoy data from of the North Carolina coast will be used to validate the developed CFD model. The results will be used to assess the applicability of and suggest revisions to the wave load equations for large diameter monopiles.
An updated version of a 2-DH post-Boussinesq wave model is introduced. The model is wavenumber free and as far as the linear dispersion relation is concerned, the approach is exact. It is implemented for the wave propagation and... more
An updated version of a 2-DH post-Boussinesq wave model is introduced. The model is wavenumber free and as far as the linear dispersion relation is concerned, the approach is exact. It is implemented for the wave propagation and transformation due to shoaling, refraction, diffraction, bottom friction, wave breaking, wave-structure interaction, reflection, wave-current interaction, etc. in nearshore zones and specifically inside ports and in the vicinity of coastal structures. Thorough validation of the model is attempted by comparisons with output from classic laboratory-scale wave flume experiments as well as analytical solutions. Physical cases of both regular and irregular wave fields are numerically reproduced with acceptable accuracy. Results concerning a case study in a characteristic Greek port setup are also presented and seem encouraging for realistic scale simulations.
Keywords: Renewable energy Marine current turbine Energy yield simulations Cluster/farm optimization Offshore engineering Dynamic interactions a b s t r a c t In this work, several simulations and analyses are carried out to investigate... more
Keywords: Renewable energy Marine current turbine Energy yield simulations Cluster/farm optimization Offshore engineering Dynamic interactions a b s t r a c t In this work, several simulations and analyses are carried out to investigate the feasibility of generating electricity from underwater sea currents at Istanbul Bosphorus Strait. Bosphorus is a natural canal which forms a border between Europe and Asia by connecting Black Sea and Marmara Sea. The differences in elevation and salinity ratios between these two seas cause strong marine currents. Depending on the morphology of the canal the speed of the flow varies and at some specific locations the energy intensity reaches to sufficient levels where electricity generation by marine current turbines becomes economically feasible. In this study, several simulations are performed for a 10 MW marine turbine farm/cluster whose location is selected by taking into account several factors such as the canal morphology, current speed and passage of vessels. 360 different simulations are performed for 15 different virtual sea states. Similarly, 8 different configurations are analyzed in order to find the optimum spacing between the turbines. Considering the spatial variations in the current speed within the selected region, the analyses are performed for three different flow speeds corresponding to ±10% change in the average value. For each simulation the annual energy yield and cluster efficiency are calculated.
—Investigations are conducted to explore the free-surface behavior of small to breaking liquid motions in regular shaped tanks. Computational methods are compared with respect to their ability to capture nonlinear free-surface water... more
—Investigations are conducted to explore the free-surface behavior of small to breaking liquid motions in regular shaped tanks. Computational methods are compared with respect to their ability to capture nonlinear free-surface water waves. Numerical models traditionally treat the moving free surface boundary in one of two ways: either by using Lagrangian tracking of free surface nodes with regridding, or by mappings. The former has the disadvantage that the surface velocities are difficult to predict correctly, and so free surface smoothing is often required. Although mappings inherently overcome this problem, they are less flexible to apply to break-up of free-surface, irregular geometries or to cases where submerged bodies are present in the flow domain. It is shown that nonlinear effects are important to capture as they begin to play a considerable role in wave motion as the wave amplitudes increase generating highly chaotic flows. Test cases for different numerical methods below, at and above critical depth are shown and discussed relative to model scale experiments. Free-surface physics are predicted fairly well by nonlinear potential flow solvers although near and at resonances cases tend to have over-predicted free-surface elevation solutions. In shallow depths, the potential flow solver is invalid. Instead we have tested a single phase lattice Boltzmann approach which showed promising results, especially in bore predictions.
In this paper we present the evolvement of an integrated numerical model (WAVE-L) for the simulation of wave propagation and transformation in areas around and inside ports and harbors. WAVE-L is a high-resolution phase-resolving wave... more
In this paper we present the evolvement of an integrated numerical model (WAVE-L) for the simulation of wave propagation and transformation in areas around and inside ports and harbors. WAVE-L is a high-resolution phase-resolving wave model based on the hyperbolic mild-slope equations, capable of simulating the transformation of complex wave fields over varying bathymetries in harbors and coastal areas in the vicinity of ports. The modeled wave processes include shoaling, refraction, diffraction, total and partial reflection from structures, energy dissipation due to wave breaking and bottom friction in a combined way. The new version of WAVE-L incorporates wave generation simulated on any boundary (longitudinal, lateral or oblique) with corresponding expansion of peripheral sponge layers, providing potential to spatially restrict the computational field in areas adjacent to ports, thus reducing demand of computational time and resources. Moreover, the modified WAVE-L version is able to simulate quasi-irregular, multi-directional waves, whose generation and propagation may furthermore account for various angles and directions simultaneously. WAVE-L is one-way coupled to coarser implementations of an open-sea spectral wave model and a 2-DH hydrodynamic circulation model for storm surges that provide input and boundary conditions. WAVE-L model is thoroughly validated against experimental data on diffraction and multidirectional spectral wave propagation; pilot implementations of it are carried out at the Greek port basin of Thessaloniki. The ultimate goal is to create a tool for high-resolution operational forecasts of wave conditions around and inside significant ports with high traffic load and commercial value (project Accu-Waves).
This article presents an approach based on state observers to identify the parameters of an unknown periodic force exerted on a mechanical system. This approach comprises two stages and can be executed in real time by using only... more
This article presents an approach based on state observers to identify the parameters of an unknown periodic force exerted on a mechanical system. This approach comprises two stages and can be executed in real time by using only displacement measurements. The first stage goal is the estimation of the coefficients of a Fourier series that approximates the periodic force. From the estimated coefficients, the phase and the amplitude of the signal can be simultaneously computed; and from the estimated force, in a second stage, the frequencies of the signal can be estimated. To perform the tasks at each stage, two state observers were designed. To show the applicability of the proposed approach, the reconstruction of a wave force affecting a marine structure as well as the computation of the amplitude and phase of its spectral components was taken as case of study. The performance of the state observer was examined by means of simulations and off-line tests carried out with experimental data. Such data were obtained by executing laboratory tests and measuring waves in the Caribbean sea.
This study presents wind wave fields' characteristics over the Baltic Sea obtained with the WAM model and their verification against observations. This is a part of the HIPOCAS research project funded by the European Union with an... more
This study presents wind wave fields' characteristics over the Baltic Sea obtained with the WAM model and their verification against observations. This is a part of the HIPOCAS research project funded by the European Union with an objective to obtain a 44-year hindcast of wind, wave, sea-level, and current climatology for European waters and coastal seas for application in coastal and environmental decision processes. A reasonable agreement between the modelled and observed both in-situ and satellite wave data was obtained. A high-resolution homogeneous wave data set generated with the hindcast system created within HIPOCAS provided a large number of possibilities to examine the long-term statistics and variability of the wind wave fields over the Baltic Sea.
Forecast of wave agitation inside port basins and consequent downtime of berth positions are of utmost importance to make a port "smarter" by efficiently managing its infrastructure. Within Accu-Waves project (http://accuwaves.eu), a... more
Forecast of wave agitation inside port basins and consequent downtime of berth positions are of utmost importance to make a port "smarter" by efficiently managing its infrastructure. Within Accu-Waves project (http://accuwaves.eu), a decision-making tool is being developed to provide forecast data on prevailing sea states in the vicinity of port entrances and inside harbour basins. The said tool will be based on cooperating hydrodynamic models that derive data from global scale, open sea forecasts. The implementation of the project includes development and application of a hydrodynamic circulation model, a spectral wave propagation model and a phase-resolving wave model for port basins. The latter is based on the hyperbolic mild-slope (HMS) equations, capable of simulating wave propagation and reflection. In order to achieve higher levels of simulation accuracy in the vicinity of waterfront structures, we need to robustly model the reflection of incipient waves from such structures (e.g., quay walls). In the present paper, this need is met through the incorporation of an additional, casespecific eddy viscosity coefficient to the governing mildslope equations (of the phase-resolving wave model). This coefficient accounts for the energy dissipation on port structures' fronts and its value is decided based on the corresponding reflection coefficient. A basic set of incident wave scenarios are simulated, required in investigating the numerics of reflection by the corresponding eddy viscosity coefficients in the wave model. Our pilot investigation refers to numerical experiments for several cases of waves approaching an either fully or partially reflective vertical quay wall. The proposed methodology could enhance similar HMS models; its results should be valuable for port operators.
Shipping water (SW) events occur when waves, usually during extreme weather conditions, overtop the deck of vessels or structures. Since SW events take place independently but close enough in time to interact with one another, their... more
Shipping water (SW) events occur when waves, usually during extreme weather conditions, overtop the deck of vessels or structures. Since SW events take place independently but close enough in time to interact with one another, their simulation requires strong nonlinear equations to achieve an appropriate precision. To avoid using equations with high complexity and computational cost, we explore the use of the time fractional diffusion equation (TFDE) for modeling SW events. The idea behind this proposal is to keep the simplicity of the widely used standard diffusion equation, but employing a generalized derivative of order α ∈ [1 , 2]. This order can be used to describe an intermediate behavior between diffusion and wave propagation. For the time derivative, we adopted the Caputo fractional derivative. To demonstrate that the TFDE is a suitable model to describe SW events, we present its results compared against data sets of water free surface elevation recorded during SW experiments carried out in a wave flume. The best agreement was found for a fractional order derivative between 1.69 and 1.75.
In this article, we explore the use of a generalized diffusion equation (GDE) for modeling shipping water (SW) events, which are bodies of water that flood the deck of marine structures during extreme weather conditions. The GDE is... more
In this article, we explore the use of a generalized diffusion equation (GDE) for modeling shipping water (SW) events, which are bodies of water that flood the deck of marine structures during extreme weather conditions. The GDE is obtained by substituting the first-order time derivative of the standard diffusion equation by a generalized derivative of non-integer order. The GDE, which in this contribution is formulated using the Caputo fractional derivative, may permit to approximate the behavior between diffusion and wave propagation observed in SW events. We present numerical results to demonstrate the agreement between the response of the GDE and the standard advection-difussion equation, which has been previously used to describe SW events.
Wave energy converters have been developed and commercialized in past decades; they have now faced numerous challenges of large volume sizes, environmental hazards, and high costs of deployment, components and maintenance. To address... more
Wave energy converters have been developed and commercialized in past decades; they have now faced numerous challenges of large volume sizes, environmental hazards, and high costs of deployment, components and maintenance. To address these challenges and make a wave energy converter practically available for various applications at a reasonable cost, we have developed a soft wave energy harvester that integrated low-cost soft material structures and piezoelectric-based Macro Fiber Composite (MFC). This integrated soft wave energy converter has a straightforward fabrication process and structure that can harvest energy from a broad working frequency of waves. The innovative design combined low-cost and commercially available materials and formed a harvester that addressed the aforementioned problems of commercially available harvesters. Additionally, the low cost and simple design are scalable for large energy conversion in the future. The energy conversion performance of the proposed platform has been investigated in a wave flume with low-frequency incoming waves (<2Hz). The soft energy conversion platform is hung like a curtain and produces a maximum 487nW. Also, the low cost and durable encapsulation can protect the electrical properties of MFCs and circuits, and a single harvester can last through all experiment steps without any degradation, which was more than 170 hours.
