ABSTRACT
Offshore wind-turbine (OWT) support structures are subjected to cyclic dynamic loads with variations in loadings from wind and waves as well as the rotation of blades throughout their lifetime. The magnitude and extent of the cyclic loading can create a fatigue limit state controlling the design of support structures. In this paper, the remaining fatigue life of the support structure for a GE Haliade 6 MW fixed-bottom jacket offshore wind turbine within the Block Island Wind Farm (BIWF) is assessed. The fatigue damage to the tower and the jacket support structure using stress time histories at instrumented and non-instrumented locations are processed. Two validated finite-element models are utilized for assessing the stress cycles. The modal expansion method and a simplified approach using static calculations of the responses are employed to estimate the stress at the non-instrumented locations-known as virtual sensors. It is found that the hotspots at the base of the tower have longer service lives than the jacket. The fatigue damage to the jacket leg joints is less than 20% and 40% of its fatigue capacity during the 25-year design lifetime of the BIWF OWT, using the modal expansion method and the simplified static approach, respectively.
ABSTRACT
OBJECTIVE: Camera assistance is important for proper visualization of the operative field in laparoscopic surgery. Navigation grid (NG) has been designed to help the camera assistants focus the camera on the target operative field. This is a randomized, controlled trial to study the effect of the NG on performance of camera assistants. DESIGN: Minimally invasive operations were randomized (1:1) to either with or without use of NG for the camera assistant. The operations were recorded and the time spent inside and outside of the target area were reported. SETTING: A tertiary care teaching hospital. RESULTS: Fifty-eight operations (30 with and 28 without NG) were recorded. Sixteen camera assistants participated. Time spent outside the target area was significantly less with the use of NG (64.5 ± 63 seconds vs 396 ± 226.5 seconds; p < 0.0001). This impact of NG on performance of the camera assistants was significant regardless of their level of training. CONCLUSIONS: NG improved performance of the camera assistant during laparoscopic abdominal procedures. This is a feasible tool that can help camera holders better assist the operating surgeons.
