Wave and Wind Responses of a Very-Light FOWT with Guy-Wired-Supported Tower: Numerical and Experimental Studies

A floating offshore wind turbine (FOWT) concept with a guy-wire-supported tower was investigated to obtain motion results in waves considering its elastic model characteristics. The FOWT concept studied aims to reduce the construction costs by using a light-weight structure tensioned with guy wires and a downwind type. Wave tank experiments of an elastically similar segmented backbone model in the 1:60 scale were carried out to clarify the dynamic elastic response features of the structure. The experimental results were compared with numerical simulations obtained from NK-UTWind and WAMIT codes. The bending moment measured at the tower and pontoons had two peak values for different wave periods carried out. The short-wave period peak was due to sagging/hogging when the wavelength matched the floater length. The second peak was due to the large tower top acceleration, which caused a large bending moment at the tower base and pontoon to support the inertia force. The wind force was not significant to modify the FOWT response. The sensibility analysis in pontoons and tower rigidities confirmed the importance of the guy wires to support the inertia due to the waves and wind incidence. The new concept of a very-light FOWT with a guy-wire-supported tower may be an option for future FOWT developments.

Performance-Based Assessment of a Guyed Incinerator Stack Using Field Measurements

ASME STS-1 provides guidelines for the design, fabrication, and erection of steel stacks, however there are no specific guidelines for the assessment of guyed steel stacks already in service. For example, drift (i.e., displacement) acceptance criteria are only provided for initial installation. Furthermore, existing literature regarding the proper re-tensioning of guy wires is scarce or nonexistent. This procedure is particularly important for stacks that experience significant thermal growth. This effect is further exacerbated by differential wind cooling effects on both the guy wires and on the stack itself. This paper investigates the effect of guy wire spacing, position, tension pattern, and operating and shutdown tension settings on the structural response of a guyed steel stack. Field thermography readings, ultrasonic testing (UT) thickness data, guy wire tension measurements, and laser scans are used to refine a finite element model of the stack. Using elastic-plastic nonlinear “pushover” analyses based on API 579 – 1 Level 3 fitness-for-service methodology and FEMA 356 rehabilitation guidelines, a performance-based methodology resulting in a “watch circle” approach for lateral displacement is provided to guide fitness-for-service assessments and mitigation implementation. Example application of this methodology and recommendations regarding guy wire tensioning are provided for an incinerator stack with 9 guy wires (3 levels – 3 guy wire configuration).

Numerical and Experimental Comparison of the Wave Response of a Very Light Floating Offshore Wind Turbine With Guy Wires

A floating offshore wind turbine (FOWT) concept with a guy wire-supported tower was investigated to obtain results of motion in waves considering its elastic model characteristics. The FOWT concept aims to reduce construction costs by using a light-weight structure tensioned with guy wires and a downwind turbine concept type. A wave tank experiment of an elastically similar segmented backbone model in the 1/60th scale was conducted to clarify the dynamic elastic response features of the structure. The results were compared with numerical simulations obtained with software NK-UTWind (in house software developed by the University of Tokyo) and WAMIT code. It was clarified that the bending moment for tower and pontoons had two peak values when the response for each wave period was examined. The peak in the short-wave period was due to sagging when the wavelength matched the floater length. The other peak was due to the largest tower top acceleration, which caused a large bending moment at the tower base and pontoon to support the inertia force.

Calculational model for first-mode eigenfrequency of a semi-guy-wired vertical-axis wind turbine tower

A simple model for accounting for tower mass when estimating the first-mode eigenfrequency of a semi-guy-wired tower has been derived. This extends previous work where an analytical model of the semi-guy-wired tower of a 200-kW vertical-axis wind turbine was developed. The model was primarily used to estimate the eigenfrequencies as a result of adding guy wires to a free-standing tower (thus creating a semi-guy-wired setup). However, a weakness with the model was that the tower mass was accounted for in a rough way that essentially ignored the guy wires, which gave a larger-than-necessary error. In this work, an effective top mass, that takes into account the tower mass and the constraints from the guy wires, is derived to achieve a higher accuracy when estimating the first-mode eigenfrequency. This, together with the earlier models, gives a more complete method to estimate the eigenfrequencies for a semi-guy-wired wind turbine.

Finite element method for the static and dynamic analysis of FRP guyed tower

A research study has been carried out to provide design guidelines for glass-fiber reinforced polymer (GFRP) guyed tower. Both material testing and theoretical analysis are involved. The tower examined in this study has 81 m in height with a uniform equilateral triangle cross section having sides of 450 mm. The tower supported by seven sets of guy wires oriented at 120°, each set consisting of three guy wires. The tower was assumed to be supported at the base by means of a pinned connection to provide full moment release. The tower was analyzed using the finite element ANSYS software and was designed to satisfy both the ultimate and the serviceability limit state requirements of the CSA-S37-01 Standard. The guyed tower was analyzed in static to evaluate the tower strength failure using several advanced failure theories. Modal analysis and full dynamic analysis using CSA-37-01 Standard were extensively performed to evaluate the vibration performance and to obtain an accurate dynamic response of the full-scale tower. The paper presents the results obtained from material testing and from a finite element, ANSYS models developed for the static and dynamic analysis of the multi-cells 81 m lightweight-guyed towers. Highlights The research = involved the analysis and the design of FRP guyed tower composed of individual cells fabricated from fiberglass matting bonded together to form an equilateral triangle. The layout, the dimensions of the tower and the thickness of the cell walls were determined from a finite element analysis. Fifteen coupons were fabricated and tested based on ASTM standards to evaluate the mechanical properties of the GFRP material. Several non-linear finite element models were developed to meet both the manufacturing constraints and strength requirements. Several non-linear finite element models were carried out for the static and dynamic analysis of an 81 m tower.