Seismic analysis of a tall metal wind turbine support tower with realistic geometric imperfections

The global growth in wind energy suggests that wind farms will increasingly be deployed in seismically active regions, with large arrays of similarly designed structures potentially at risk of simultaneous failure under a major earthquake. Wind turbine support towers are often constructed as thin-walled metal shell structures, well known for their imperfection sensitivity, and are susceptible to sudden buckling failure under compressive axial loading. This study presents a comprehensive analysis of the seismic response of a 1.5-MW wind turbine steel support tower modelled as a near-cylindrical shell structure with realistic axisymmetric weld depression imperfections. A selection of 20 representative earthquake ground motion records, 10 ‘near-fault’ and 10 ‘far-field’, was applied and the aggregate seismic response explored using lateral drifts and total plastic energy dissipation during the earthquake as structural demand parameters. The tower was found to exhibit high stiffness, although global collapse may occur soon after the elastic limit is exceeded through the development of a highly unstable plastic hinge under seismic excitations. Realistic imperfections were found to have a significant effect on the intensities of ground accelerations at which damage initiates and on the failure location, but only a small effect on the vibration properties and the response prior to damage. Including vertical accelerations similarly had a limited effect on the elastic response, but potentially shifts the location of the plastic hinge to a more slender and, therefore, weaker part of the tower. The aggregate response was found to be significantly more damaging under near-fault earthquakes with pulse-like effects and large vertical accelerations than far-field earthquakes without these aspects

Current pre-clinical and clinical advances in the BCR-ABL1-positive and -negative chronic myeloproliferative neoplasms

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Dimensional response analysis of multistorey regular steel MRF subjected to pulselike earthquake ground motions

An alternative and efficient procedure to estimate the maximum inelastic roof displacement and the maximum inelastic interstorey drift ratio along the height of regular multi-storey steel MRF subjected to pulse-like ground motions is proposed. The method and the normalized response quantities emerge from formal dimensional analysis which makes use of the distinct time scale and length scale that characterize the most energetic component of the ground shaking. Such time and length scales emerge naturally from the distinguishable pulses which dominate a wide class of strong earthquake records and can be formally extracted with validated mathematical models published in literature. The proposed method is liberated from the maximum displacement of the elastic single-degree-of-freedom structure since the self similar master curve which results from dimensional analysis involves solely the shear strength and yield roof displacement of the inelastic multi-degree-of-freedom system in association with the duration and acceleration amplitude of the dominant pulse. The estimated inelastic response quantities are in superior agreement with the results from nonlinear time history analysis than any inelastic response estimation published previously

Genome-wide DNA methylation in chronic myeloid leukaemia

Epigenetic alterations occur frequently in leukaemia and might account for differences in clinical phenotype and response to treatment. Despite the consistent presence of the BCR-ABL1 fusion gene in Philadelphia-positive chronic myeloid leukaemia (CML), the clinical course of patients treated with tyrosine kinase inhibitors (TKI) is heterogeneous. This might be due to differing DNA methylation profiles between patients. Therefore, a validated, epigenome-wide survey in CML CD34+ progenitor cells was performed in newly diagnosed chronic phase patients using array-based DNA methylation and gene expression profiling. In practice, the CML DNA methylation signature was remarkably homogeneous; it differed from CD34+ cells of normal persons and did not correlate with an individual patient’s response to TKI therapy. Using a meta-analysis tool it was possible to demonstrate that this signature was highly enriched for developmentally dynamic regions of the human methylome and represents a combination of CML-unique, myeloid leukemia-specific and pan-cancer sub-signatures. The CML profile involved aberrantly methylated genes in signaling pathways already implicated in CML leukaemogenesis, including TGF-beta, Wnt, Jak-STAT and MAPK. Furthermore, a core set of differentially methylated promoters were identified that likely have a role in modulating gene expression levels. In conclusion, the findings are consistent with the notion that CML starts with the acquisition of a BCR-ABL1 fusion gene by a haematopoietic stem cell, which then either causes or cooperates with a series of DNA methylation changes that are specific for CML.Open Acces

NUMERICAL DETERMINATION OF WIND PRESSURES ON CIVIL ENGINEERING STRUCTURES

AN EFFICIENT NUMERICAL METHODOLOGY FOR THE DETERMINATION OF WIND FORCES ON TWO-DIMENSIONAL, COMPLEX, RIGID STRUCTURES IS DESCRIBED . THIS METHODOLOGY COMBINESTHE DIRECT BOUNDARY ELEMENT METHOD AND THE DISCRETE VORTEX APPROACH FOR THE NUMERICAL TREATMENT OF GENERAL WINDS FLOWS. CASES OF COMPLEX STRUCTURES OR SYSTEMS OF STRUCTURES NOT COVERED BY THE CODES CAN BE EASILY TREATED BY THIS NUMERICAL METHODOLOGY WITHOUT RESORTING TO EXPENSIVE WIND TUNNEL TESTS OR LARGE SUPERCOMPUTERS. NUMERICAL EXAMPLES ARE PRESENTED TO DEMONSTRATE THE ACCURACY AND EFFICIENCY OF THE METHOD AS WELL AS ITS IMPORTANCE DESIGN TOOL BY PRACTICING ENGINEERS.ΣΤΗΝ ΔΙΑΤΡΙΒΗ ΑΥΤΗ ΠΑΡΟΥΣΙΑΖΕΤΑΙ ΜΙΑ ΑΡΙΘΜΗΤΙΚΗ ΜΕΘΟΔΟΣ ΥΠΟΛΟΓΙΣΜΟΥ ΤΩΝ ΑΝΕΜΟΠΙΕΣΕΩΝ ΣΕ ΔΙΔΙΑΣΤΑΤΕΣ, ΣΥΝΘΕΤΕΣ ΚΑΙ ΑΚΑΜΠΤΕΣ ΚΑΤΑΣΚΕΥΕΣ. Η ΠΑΡΟΥΣΑ ΜΕΘΟΔΟΣ ΣΥΝΔΥΑΖΕΙ ΤΗΝ ΑΜΕΣΗ ΜΕΘΟΔΟ ΣΥΝΟΡΙΑΚΩΝ ΣΤΟΙΧΕΙΩΝ ΜΕ ΤΗΝ ΜΕΘΟΔΟ ΤΩΝ ΔΙΑΚΡΙΤΩΝ ΣΤΡΟΒΙΛΩΝ ΓΙΑ ΤΟΝ ΑΡΙΘΜΗΤΙΚΟ ΥΠΟΛΟΓΙΣΜΟ ΤΩΝ ΑΝΕΜΟΠΙΕΣΕΩΝ. ΠΕΡΙΠΤΩΣΕΙΣ ΠΟΛΥΠΛΟΚΩΝ ΓΕΩΜΕΤΡΙΚΑ ΚΑΤΑΣΚΕΥΩΝ 'Η ΚΑΙ ΠΟΛΛΑΠΛΩΝ ΚΑΤΑΣΚΕΥΩΝ, ΠΟΥ ΔΕΝ ΚΑΛΥΠΤΟΝΤΑΙ ΑΠΟ ΚΑΝΟΝΙΣΜΟΥΣ, ΕΠΙΛΥΟΝΤΑΙ ΕΥΚΟΛΑ ΜΕ ΤΗΝ ΠΑΡΟΥΣΑ ΜΕΘΟΔΟΛΟΓΙΑ, ΧΩΡΙΣ ΝΑ ΥΠΑΡΧΕΙ ΑΝΑΓΚΗ ΠΡΟΣΦΥΓΗΣ ΣΕ ΑΚΡΙΒΑ ΠΕΙΡΑΜΑΤΑ. ΠΑΡΟΥΣΙΑΖΟΝΤΑΙ ΕΠΙΣΗΣ ΑΡΙΘΜΗΤΙΚΑ ΠΑΡΑΔΕΙΓΜΑΤΑ ΓΙΑ ΕΞΑΚΡΙΒΩΣΗ ΤΗΣ ΑΞΙΟΠΙΣΤΙΑΣ ΤΗΣ ΜΕΘΟΔΟΥ ΣΥΓΚΡΙΤΙΚΑ ΜΕ ΠΕΙΡΑΜΑΤΙΚΕΣ ΜΕΤΡΗΣΕΙΣ

Maximum displacement profiles for the performance based seismic design of plane steel moment resisting frames

New relations to estimate maximum seismic displacement profiles of plane steel moment resisting frames are proposed. These expressions associate maximum floor displacements with local member deformation seismic demands and are based on statistical analysis of the results of several hundred nonlinear dynamic analyses of steel frames. The influence of specific parameters, such as the number of stories, the number of bays, the joint capacity design factor and the level of inelastic deformation induced by the seismic excitation, is studied in detail. It is concluded that the main structural characteristic that affects the shape of the displacement pattern is the number of stories. Furthermore, the present study reveals that a differentiation between the profile of a frame in the elastic and the inelastic range of response is necessary. A comparison between the proposed displacement patterns and other existing ones is also made to demonstrate the merits of the former

Estimation of seismic drift and ductility demands in plane regular X-braced steel frames

This paper summarizes the results of an extensive study on the inelastic seismic response of X-braced steel buildings. More than 100 regular multi-storey tension-compression X-braced steel frames are subjected to an ensemble of 30 ordinary (i.e. without near fault effects) ground motions. The records are scaled to different intensities in order to drive the structures to different levels of inelastic deformation. The statistical analysis of the created response databank indicates that the number of stories, period of vibration, brace slenderness ratio and column stiffness strongly influence the amplitude and heightwise distribution of inelastic deformation. Nonlinear regression analysis is employed in order to derive simple formulae which reflect the aforementioned influences and offer a direct estimation of drift and ductility demands. The uncertainty of this estimation due to the record-to-record variability is discussed in detail. More specifically, given the strength (or behaviour) reduction factor, the proposed formulae provide reliable estimates of the maximum roof displacement, the maximum interstorey drift ratio and the maximum cyclic ductility of the diagonals along the height of the structure. The strength reduction factor refers to the point of the first buckling of the diagonals in the building and thus, pushover analysis and estimation of the overstrength factor are not required. This design-oriented feature enables both the rapid seismic assessment of existing structures and the direct deformation-controlled seismic design of new ones. A comparison of the proposed method with the procedures adopted in current seismic design codes reveals the accuracy and efficiency of the former