BUCKLING OF THIN CYLINDRICAL SHELLS: IMPERFECTION SENSITIVITY, NON-DESTRUCTIVE TECHNIQUE FOR CAPACITY PREDICTION AND APPLICATION FOR WIND TURBINE TOWERS

The presence of imperfections significantly reduces the load-carrying capacity of thin cylindrical shells and the reduction depends on the shape and the size of the imperfections. As a result, the prediction of the shells\u27 buckling capacity requires a priori knowledge about the imperfections---a difficult, expansive, and time-consuming adventure, if not impossible. Consequently, thin cylindrical shells are designed conservatively using the knockdown factor approach that accommodates the uncertainties associated with the imperfections present in the cylinders; almost all the design codes follow this approach explicitly or implicitly. However, cylindrical shells can be designed more efficiently by making them insensitive to imperfections, or by knowing their exact capacity without the difficult task of measuring the imperfections. This dissertation examines these two approaches for the efficient designing of thin cylindrical shells. In addition, we investigate buckling behavior and imperfection sensitivity of thin cylindrical shells under pure bending along with their applications in tall wind turbine towers. For making thin cylindrical shells insensitive to imperfection, wavy cross-sections are proposed instead of circular cross-sections. Past studies have demonstrated the effectiveness of wavy cylinders to reduce imperfection sensitivity under axial compression assuming linear elastic material behavior and using eigenmode imperfections. In this dissertation, using a realistic dimple-like imperfection, new insights are presented into the response of wavy cylinders under uniform axial compression and bending. We found that thin cylindrical shells can be made imperfection insensitive by manipulating their cross-section geometry. For high-fidelity estimates of the capacity of thin cylindrical shells without measuring the imperfections, a novel procedure is proposed based on the probing of the axially loaded cylinders. Computational implementation of the proposed procedure yields accurate results when the probing is near the imperfection; however, the procedure over-predicts the capacity when the probing is away from the imperfection. It demonstrates the crucial role played by the probing location and shows that the prediction of imperfect cylinders is indeed possible if the probing is at the proper location. The behavior of cylindrical shells under bending and their imperfection sensitivity have not been fully understood for all the range of dimensions. In this dissertation, we investigate the buckling behavior and imperfection sensitivity of thin steel cylindrical shells under pure bending, focusing on a specific range of slenderness, which is found in energy structures such as tall wind turbine towers (60 \u3c R/t \u3c 120). We found that strain-hardening models play an impactful role on the bending behavior; moreover, the presence of imperfections reduces the collapse curvature more than the reduction in peak moment. Further, we propose wavy wind turbine towers to make wind turbine towers efficient. The imperfection sensitivity of the wavy towers is evaluated, and we found that the sensitivity of the wavy towers is small compared to that of the circular towers

8-MW wind turbine tower computational shell buckling benchmark. Part 1:an international ‘round-robin’ exercise

An assessment of the elastic-plastic buckling limit state for multi-strake wind turbine support towers poses a particular challenge for the modern finite element analyst, who must competently navigate numerous modelling choices related to the tug-of-war between meshing and computational cost, the use of solvers that are robust to highly nonlinear behaviour, the potential for multiple near-simultaneously critical failure locations, the complex issue of imperfection sensitivity and finally the interpretation of the data into a safe and economic design.This paper reports on an international ‘round-robin’ exercise conducted in 2022 aiming to take stock of the computational shell buckling expertise around the world which attracted 29 submissions. Participants were asked to perform analyses of increasing complexity on a standardised benchmark of an 8-MW multi-strake steel wind turbine support tower segment, from a linear elastic stress analysis to a linear bifurcation analysis to a geometrically and materially nonlinear buckling analysis with imperfections. The results are a showcase of the significant shell buckling expertise now available in both industry and academia.This paper is the first of a pair. The second paper presents a detailed reference solution to the benchmark, including an illustration of the Eurocode-compliant calibration of two important imperfection forms

An unusual case of duplicated left brachiocephalic vein with right sided aortic arch and aberrant origin of LSCA in a patient undergoing implantable cardioverter defibrillator (ICD) implantation

Background: Anomalous left brachiocephalic vein (ALBCV) is a rare venous anomaly. Double Left brachiocephalic vein is the rarest type of ALBCV anomaly. Case report: Here we report a case of gentleman with post myocardial infarction ventricular tachycardia who underwent ICD implantation, where we could not place the lead initially through left side. CT angiography revealed presence of a duplicated circumaortic left BCV. It's cranial limb coursing normally anterior to arch and compressed at its confluence with RBCV and the caudal limb with a subaortic course draining into the RSVC. We report this first case of double LBCV along with right sided aortic arch and aberrant origin of LSCA arising from Kommerel's diverticulum. Conclusion: This case highlights that interventional cardiologists should be aware of these venous anomalies for proper planning and implantation of CIED successfully via transvenous approach

Combined endoscopic-microscopic trans-nasal trans-sphenoidal approach for pituitary adenomas: An institutional experience

Objective. To obtain evidence that the use of endoscopy along with a microscope in the surgical management of pituitary tumours improves intraoperative visualization and significantly impacts operative outcomes in the trans-nasal approach. Material and methods. Each patient underwent endonasal transsphenoidal microscopic tumour resection. The procedure was modified by the use of intrasellar endoscopy as an adjunctive imaging modality. Following complete microscopic resection of tumour, rigid 0° and 30° 4.0-mm endoscopes were used to conduct a final survey of the sellar and parasellar spaces. Residual tumour fragments identified during this endoscopic examination were removed. Results. In 50 patients with pituitary macroadenomas, the rigid 30 ° angled rigid endoscope was found to be highly beneficial. Hidden areas could be visualized and tumour residues were detected. In the majority of the patients with detected tumour residues, adenomatous remnants were safely removed by meticulous endoscopic dissection under optimum visual control after the main part of the tumour had been removed with the operating microscope. Conclusions. Endoscopy provides distinct advantages over microscopy in imaging intrasellar and parasellar structures during pituitary tumour resection which are often missed by microscopy alone

Combined endoscopic-microscopic trans-nasal trans-sphenoidal approach for pituitary adenomas

Objective. To obtain evidence that the use of endoscopy along with a microscope in the surgical management of pituitary tumours improves intraoperative visualization and significantly impacts operative outcomes in the trans-nasal approach. Material and methods. Each patient underwent endonasal transsphenoidal microscopic tumour resection. The procedure was modified by the use of intrasellar endoscopy as an adjunctive imaging modality. Following complete microscopic resection of tumour, rigid 0° and 30° 4.0-mm endoscopes were used to conduct a final survey of the sellar and parasellar spaces. Residual tumour fragments identified during this endoscopic examination were removed. Results. In 50 patients with pituitary macroadenomas, the rigid 30 ° angled rigid endoscope was found to be highly beneficial. Hidden areas could be visualized and tumour residues were detected. In the majority of the patients with detected tumour residues, adenomatous remnants were safely removed by meticulous endoscopic dissection under optimum visual control after the main part of the tumour had been removed with the operating microscope. Conclusions. Endoscopy provides distinct advantages over microscopy in imaging intrasellar and parasellar structures during pituitary tumour resection which are often missed by microscopy alone