1,720,971 research outputs found
THE EFFECT OF THUNDERSTORM EXTREME WINDS ON LIGHTWEIGHT STRUCTURES
No full textThis paper describes an extensive research aimed at evaluation of thunderstorm properties and their effect on lightweight structures. Starting from an unprecedented monitoring network including anemometric and structural response signals, the downburst wind field generated by thunderstorm events and the dynamic response of structures are inspected. On these bases, a new generation of wind loading models, namely the response spectrum technique, the time-domain integration and evolutionary spectral density approaches, are described and compared with real structural response, with the aim of producing outcomes physically correct and transferable to design procedure
Structural response and fatigue assessment of a small vertical axis wind turbine under stationary and non-stationary excitation
No full textThe paper discusses the response and fatigue damage of the supporting tower of a small vertical axis wind turbine subject to stationary and non-stationary excitation due to wind, turbine rotation, emergency stop and start. Using in-field measurements and the Hot Spot Stress Approach, the study analyses a number of aspects that are usually disregarded in design verifications. The results highlight the importance of the detail modeling, the fundamental role played by the non-stationary conditions and the errors committed when using conventional models of the load. The emphasis of this paper is put on two main aspects: the use of full scale data and the detection of isolated events of non-stationary vibrations, the effects of which can be disregarded when using stress time-histories of 10 min - 1 h
The annual rate of independent events - A key interpretation for traditional extreme value distributions of wind velocity
No full textThe extreme value theory has been object of engineering studies for more than a century. The analysis of extreme winds plays a key role for complex civil structures and a driving role in different stages of wind turbines lifetime. Most of extremes probability models depend on the annual rate of independent events (ARIE) which has been traditionally considered a constant value. The authors have embraced a recent belief considering the ARIE as a function of the wind velocity. Even though a certain agreement has been achieved across the researches, some issues are still pending. In this regard, the paper shows that the annual, seasonal and daily fluctuations embedded in time series of the mean wind speeds, constrain its probability distribution and time correlation to be physically consistent. Besides, a new physical interpretation of the ARIE is presented, expressing how the independence across wind observations increases with the wind speed, up to the point that all yearly observations are independent if larger than a suitable speed value. Such a tendency is not revealed if the annual, seasonal and daily fluctuations are excluded by the analysis, leading to a deceitful shape of the ARIE. Finally, the paper shows how the velocity-dependent ARIE model is consistent with the conventional asymptotic extreme value theory, if a sufficiently large left-censorship applies to the dataset. The study of the ARIE presented in this paper is based on long-term Monte Carlo simulation of the mean wind speed
Resilience framework for seaport infrastructure under extreme wind
No full textThe efficient transportation of goods is vital for the economic growth of communities, making developing and maintaining seaport infrastructure an essential component of the marine transportation system. Given their geographic locations, ports are consistently at risk from natural hazards, making the resilience of port infrastructure an essential goal. Despite considerable progress in resilience research, there remains a gap in methods tailored explicitly to assessing port resilience, particularly under extreme wind events. Current approaches often do not capture the full complexity of port systems, as they tend to focus on isolated aspects, such as structural resilience. This paper introduces the PORT Resilience Framework, addressing these gaps by evaluating resilience through a comprehensive list of indicators gathered from various legitimate sources. The indicators are then organized under four comprehensive resilience dimensions: Physical Infrastructure, ICT (i.e., Information and Communication Technology) and Equipment; Organization and Business Management; Resources and Economic Development; and Territory, Environment, and Stakeholders. This classification is summarized under the acronym "PORT." This paper also introduces a method for aggregating resilience indicators by considering their performance before and after a specific hazard, transforming the data into a quantifiable Loss of Resilience index. The approach is applied to a case study, assessing the resilience of a real Terminal against wind action using real data sourced from the port management. The case study analysis revealed that human resources and quay operations were the most critical factors affecting recovery, with insufficient staffing leading to prolonged recovery periods. The study further demonstrated that post-disruption activity surges, captured by different serviceability function methodologies, often created operational bottlenecks, challenging the port's overall recovery
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Wind tunnel experimental investigation of the aerodynamic coefficients reduction due to sheltering surroundings on a cruise ship moored in port
No full textThe recent growth of cruise and container ships size, which is involving the shipping industry, determines the greater and greater importance of evaluating properly the wind actions on such big ships, especially during the mooring phase. Accidents and damages may occur in port areas during extreme wind events due to the breakage of mooring clamps, jeopardizing the safety of human beings and vessels as well as producing significant economic losses. Despite extreme winds are one of the main dangers for large ships within ports and standardised procedures to accurately assess wind loads are still missing. To shed light on this topic, a set of wind tunnel tests was carried out to investigate the shielding effect that the surroundings can play in reducing the wind forces acting on a 1:600 model of the large cruise ship in the Port of Monfalcone (Italy). The longitudinal and transversal forces and yaw moment were measured for three main sets of tests: (1) open sea condition; (2) ship and quay; (3) ship, quay, and other shielding ship upwind. The results showed a strong dependence of the wind load on the cruise ship according to different surrounding configurations. In particular, a reduction of the aerodynamic forces up to 60% for the wind directions orthogonal with respect to the ship was measured. On one hand, this demonstrated quantitatively that the shielding effects of complex surrounding buildings may guarantee an increase in port safety with the reduction of the overall forces acting on ships. On the other hand, it highlights the huge uncertainty which currently characterizes the assessment of wind loads in the mooring system design, pointing out that a novel approach should be adopted in which every mooring system is designed on a specific site-analysis base
Fatigue life assessment of a slender lightning rod due to wind excited vibrations
No full textThe wind-excited vibrations of structures induce fluctuating stresses that may result in the accumulation of fatigue damage, ultimately posing a risk of structural failure. This paper presents the findings of a research program assessing the fatigue life of a 30 m high slender and tapered lightning pole under wind induced vibrations. A three-stage study has been conducted to understand the causes of fatigue damage. In the first step, a hybrid numerical and full-scale experimental investigation was carried out to identify the natural frequencies, modal shapes and modal damping ratios. In the second step, results from the dynamic identification test were used to estimate vortex shedding induced vibrations. Critical resonant conditions on the first and second vibration modes have been investigated, adopting standards and calculation techniques from literature. Finally, in the third step, the fatigue damage induced by vortex shedding vibrations was estimated. The findings demonstrate that the fatigue issues of the lightning rod are mainly related to the wind induced stress at the base of the pole, highlighting the contribution of vortex shedding resonant with the second vibration mode. The paper also discusses the large uncertainties affecting the analysis, showing that errors in parameter estimates give rise to very large scatter in the fatigue damage assessment
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