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in creator/contributor: "Lobitz, D."

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Creep fatigue damage under multiaxial conditions

When structural components are subjected to severe cyclic loading conditions with intermittent periods of sustained loading at elevated temperature, the designer must guard against a failure mode caused by the interaction of time-dependent and time-independent deformation. This phenomena is referred to as creep-fatigue interaction. The most elementary form of interaction theory (called linear damage summation) is now embodied in the ASME Boiler and Pressure Vessel Code. In recent years, a compe… more

Date: January 1, 1977

Creator: Lobitz, D. W. & Nickell, R. E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Elastic dynamics of a complete wind turbine structure: Theoretical development

This paper develops a pseodo-linear formulation of the equations of motion for analyzing elastic bodies which undergo large rotations relative to one another with an emphasis on its application to HAWTs. This procedure greatly simplifies the computational aspects of the solution algorithm over the nonlinear alternatives and should yield a significant improvement in computer speed. Additional speed can be achieved by ordering the nodes such that a minimum bandwidth can be realized (leading to ap… more

Date: January 1, 1992

Creator: Lobitz, D. W.; Arguello, J. G. & Veers, P. S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Performance of twist-coupled blades on variable speed rotors

The load mitigation and energy capture characteristics of twist-coupled HAWT blades that are mounted on a variable speed rotor are investigated in this paper. These blades are designed to twist toward feather as they bend with pretwist set to achieve a desirable twist distribution at rated power. For this investigation, the ADAMS-WT software has been modified to include blade models with bending-twist coupling. Using twist-coupled and uncoupled models, the ADAMS software is exercised for steady… more

Date: December 7, 1999

Creator: Lobitz, D. W.; Veers, P. S. & Laino, D. J.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Shape control of solar collectors using torsional shape memory alloy actuators

Solar collectors that are focused on a central receiver are designed with a mechanism for defocusing the collector or disabling it by turning it out of the path of the sun`s rays. This is required to avoid damaging the receiver during periods of inoperability. In either of these two cases a fail-safe operation is very desirable where during power outages the collector passively goes to its defocused or deactivated state. This paper will be principally concerned with focusing and defocusing the … more

Date: March 1, 1996

Creator: Lobitz, D. W.; Rice, T. M. & Grossman, J. W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Aeroelastic behavior of twist-coupled HAWT blades

As the technology for horizontal axis wind turbines (HAWT) development matures, more novel techniques are required for the capture of additional amounts of energy, alleviation of loads and control of the rotor. One such technique employs the use of an adaptive blade that could sense the wind velocity or rotational speed in some fashion and accordingly modify its aerodynamic configuration to meet a desired objective. This could be achieved in either an active or passive manner, although the pass… more

Date: December 31, 1998

Creator: Lobitz, D. W. & Veers, P. S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Aeroelastic tailoring in wind-turbine blade applications

This paper reviews issues related to the use of aeroelastic tailoring as a cost-effective, passive means to shape the power curve and reduce loads. Wind turbine blades bend and twist during operation, effectively altering the angle of attack, which in turn affects loads and energy production. There are blades now in use that have significant aeroelastic couplings, either on purpose or because of flexible and light-weight designs. Since aeroelastic effects are almost unavoidable in flexible blad… more

Date: April 1, 1998

Creator: Veers, P.; Lobitz, D. & Bir, G.

Item Type: Article

Partner: UNT Libraries Government Documents Department