Carbon fiber reinforced polymers (CFRP) have shown considerable potential in the repair and rehabilitation of deficient reinforced concrete (RC) structures. To date, several CFRP strengthening schemes have been studied and employed practically. In particular, strengthening of shear damaged RC members with CFRP materials has received much attention as an effective repair and strengthening approach. Most existing studies on strengthening shear-deficient RC members have used unidirectional CFRP strips. Recent studies on strengthened T-beams demonstrated that a bidirectional CFRP layout was more effective than a unidirectional layout. As such studies are limited, in this study, the feasibility of bidirectional CFRP layouts for the shear strengthening of rectangular RC beams was experimentally evaluated. Bidirectional layout details with CFRP anchors as well as rehabilitation timing were considered and investigated. The test results showed that the members with a bidirectional CFRP layout carried less shear strength capacity than those with unidirectional layouts for the same quantity of CFRP material. Nevertheless, the bidirectional CFRP layout allowed for a uniformly distributed stirrup strain compared to the unidirectional CFRP layout at the same load level, which increased the efficiency of the transverse reinforcement. Additionally, the shear contribution of CFRP material according to the CFRP strengthening timing was verified.

In recent years, integration of electric vehicles (EVs) has increased dramatically due to their lower carbon emissions and reduced fossil fuel dependency. However, charging EVs could have significant impacts on the electrical grid. One promising method for mitigating these impacts is the use of renewable energy systems. Renewable energy systems can also be useful for charging EVs where there is no local grid. This paper proposes a new strategy for designing a renewable energy charging station consisting of wind turbines, a photovoltaic system, and an energy storage system to avoid the use of diesel generators in remote communities. The objective function is considered to be the minimization of the total net present cost, including energy production, components setup, and financial viability. The proposed approach, using stochastic modeling, can also guarantee profitable operation of EVs and reasonable effects on renewable energy sizing, narrowing the gap between real-life daily operation patterns and the design stage. The proposed strategy should enhance the efficiency of conventional EV charging stations. The key point of this study is the efficient use of excess electricity. The infrastructure of the charging station is optimized and modeled.

This study proposes the use of an approach based on proper orthogonal decomposition (POD) to explore reduced-order wake turbulence fields. Waked turbulence fields are first extracted using large eddy simulation (LES) downwind of a wind turbine in a single plane orthogonal to the streamwise flow field. Based on this extracted turbulence field, statistical summaries in the form of covariance matrices and cross power spectral density (CPSD) matrices are estimated. Using proper orthogonal decomposition, important “modes” organized by eigenvalues (dominant energy contributions) are evaluated. Based on a subset of these sorted modes, reduced-order turbulence fields can be generated and these are analyzed and compared directly with the original LES-based target wake turbulence field. Statistical descriptions of the turbulence and their effect on wind turbine loads are investigated. To serve as reference, the free-stream turbulence field upwind of the selected wind turbine is also captured using LES. The same decomposition and simulation procedures are performed on the free-stream field. Compared to POD eigenmodes and eigenvalues of the free-stream field, those for the waked wind fields show distinct patterns that describe a systematic increase in turbulence energy around the top of the rotor. CPSD-based POD (spectral proper transformation) is found to be more efficient in capturing dynamic characteristics and spatial patterns in the waked wind fields using a small number of modes. Reduced-order simulation of waked wind fields using varying numbers of POD modes suggests that the top 10% of these most dominant modes—a greater proportion than what is needed for the free-stream field—is required to yield turbine loads comparable to those based directly on the original LES wind fields.

In wind turbine design, external conditions to be considered depend on the intended site for the planned installation. Wind turbine classes, defined in terms of wind speed and turbulence parameters, cover most sites and applications. In the International Electrotechnical Commission's (IEC's) 61400-1 standard, there is a design load case that requires consideration for ultimate loading resulting from extreme turbulence conditions. Since site-specific wind conditions should not compromise the structural integrity of turbine installations, at some sites where class-based design may not apply, there is sometimes a need to establish extreme turbulence (50-year) levels as part of site assessment by making use of measurements. This should be done in a manner consistent with class-based design where the extreme turbulence model (ETM) provides 50-year turbulence standard deviation (σ) value as a function of the ten minute average hub-height wind speed, V. For one site in Germany and three contrasting terrain sites in Japan, wind velocity data are used to establish 50-year ETM levels. The inverse first-order reliability method (IFORM) is applied with 10 min data for this purpose. Sometimes, as in assessing wind farm wake effects, analysis of turbulence levels by direction sector is important because normal and extreme turbulence levels can vary by sector. We compare ETM levels by sector for the Hamburg, Germany site. The influence of terrain complexity on ETM levels is also of interest; the three sites in Japan have contrasting terrain characteristics—referred to as flat, hilly, and mountainous. ETM levels are compared for these three terrain types. An important overall finding of this study is that site-specific ETM levels can greatly exceed levels specified in the standard for class-based design.

Wind turbines within an array do not experience free-stream undisturbed flow fields. Rather, the flow fields on internal turbines are influenced by wakes generated by upwind unit and exhibit different dynamic characteristics relative to the free stream. The International Electrotechnical Commission (IEC) standard 61400-1 for the design of wind turbines only considers a deterministic wake model for the design of a wind plant. This study is focused on the development of a stochastic model for waked wind fields. First, high-fidelity physics-based waked wind velocity fields are generated using Large-Eddy Simulation (LES). Stochastic characteristics of these LES waked wind velocity field, including mean and turbulence components, are analyzed. Wake-related mean and turbulence field-related parameters are then estimated for use with a stochastic model, using Multivariate Multiple Linear Regression (MMLR) with the LES data. To validate the simulated wind fields based on the stochastic model, wind turbine tower and blade loads are generated using aeroelastic simulation for utility-scale wind turbine models and compared with those based directly on the LES inflow. The study’s overall objective is to offer efficient and validated stochastic approaches that are computationally tractable for assessing the performance and loads of turbines operating in wakes.