Feszített kötél- és ponyvaszerkezetek optimalizálása = Optimization of prestressed cable-net and membrane structures

Az ívtartókra feszített kötél- és ponyvaszerkezetek gazdaságos megoldást kínálnak nagy területű létesítmények belső alátámasztás nélküli lefedésére. Egy szabadalom, a csigasoros függesztőrendszer ezeket a szerkezeteket még hatékonyabbá teszi és megnöveli a statikailag lehetséges fesztávot az ívtartókban fellépő hajlítónyomaték minimalizálásával. A kutatás során ki kellett dolgozni egy numerikust eljárást a csigasorok számítására és az új csigasor elemet be kellett illeszteni a teljes szerkezet számítását végző, dinamikus ellazításon alapuló nemlineáris eljárásba. A kidolgozott program segítségével különböző ívtartókra feszített függőtetőket vizsgáltunk. A csigáknál fellépő súrlódás, az ívtartók számának, fesztávjának, görbületének hatását elemeztük a szerkezetek statikai viselkedésére. Az ívtartókban fellépő igénybevételek, a függőtetőben fellépő erők és a függőtető elmozdulásai kerültek összehasonlításra a különböző geometriájú és topológiájú szerkezetek esetén. A legfontosabb eredmény az, hogy a numerikus vizsgálatok igazolták, hogy csigasoros függesztés segítségével jelentősen csökkenthető az ívtartókban fellépő nyomaték. | Arch-supported tensile structures provide a very efficient way to cover large areas without inner support. An invention, the block and tackle suspension system can make this type of structures even more efficient and increase the possible span of the supporting arches as well by minimizing the bending moment of the supporting arches. A numerical procedure has been developed for the numerical analysis of the block and tackle and it has been integrated into the large displacement analysis of the whole tensile structure. The procedure is based on the dynamic relaxation method. By the help of the developed numerical procedure arch supported tensile roofs have been analysed. The effect of the coefficient of friction between the pulley and its shaft, the number, the free span and the curvature of the supporting arches on the static behaviour of the structure have been analysed. The internal forces of the supporting arches, the forces in the tensile roof and the displacements of the roof have been compared in the case of structures with different geometry and different topology. The results show that the block and tackle suspension system can reduce the bending moments in the supporting arches significantly

Stress analysis of inflated polyhedra for the 32-panel soccer ball

This paper presents a stress analysis of a membrane modelling the 32-panel soccer ball. The most popular soccer ball type and three variations are considered. The discretized mesh of the stress-free polyhedron-shaped membrane is subjected to internal pressure and the sphericity and the stress distribution of the models are compared

STRESS ANALYSIS OF INFLATED POLYHEDRA FOR THE 32-PANEL SOCCER BALL

This paper presents a stress analysis of a membrane modelling the 32-panel soccer ball. The most popular soccer ball type and three variations are considered. The discretized mesh of the stress-free polyhedron-shaped membrane is subjected to internal pressure and the sphericity and the stress distribution of the models are compared

PARTIAL COVERING OF A CIRCLE BY EQUAL CIRCLES. PART I: THE MECHANICAL MODELS

How must n equal circles of given radius be placed so that they cover as great a part of the area of the unit circle as possible? To analyse this mathematical problem, mechanical models are introduced. A generalized tensegrity structure is associated with a maximum area configuration of the n circles, whose equilibrium configuration is determined numerically with the method of dynamic relaxation, and the stability of equilibrium is investigated by means of the stiffness matrix of the tensegrity structure. In this Part I, the principles of the models are presented, while an application will be shown in the forthcoming Part II

Computational Wind Engineering of a Mast-supported Tensile Structure

The Computational Fluid Dynamics (CFD) analysis of wind actions on a cube and on the hyperbolic surface of a mast-supported tensile structure is presented. As standard in Computational Wind Engineering (CWE) the models were analyzed in incompressible fluid flow. For the CWE study, the Reynolds-Averaged Navier-Stokes (RANS) equations were solved with two of the most widely used turbulence models, Realizable k−ε and SST k−ω. The validation of the CWE models included the comparison of the numerically determined pressure coefficient fields with existing Wind Tunnel test (WT) results. The membrane forces and the displacements of the membrane roof were calculated by the Dynamic Relaxation Method (DRM), corresponding to the different (CWE and WT) pressure coefficient fields of the tensile roof. In addition to the pressure coefficients, the membrane force and the displacement fields and their significant values were also compared. It is presented that both turbulence models provide a suitable solution; the pressure coefficients and the membrane forces are also acceptable approaches to the experimental results

Wpływ znieczulenia zewnątrzoponowego na przebieg i rodzaj porodu oraz stan urodzeniowy noworodków – badanie retrospektywne

Objectives: to evaluate the impact of epidural analgesia (EA) on labor, delivery and neonatal status. Material and methods: retrospective, observational, cohort study comprising 5593 pregnant women who met the inclusion criteria (singleton pregnancy, cephalic presentation, 37-42 weeks of gestation). Out of them, 2496 had EA and 3097 constituted the control group. Main outcome measures: incidence of labor complications and operative deliveries in women who received EA, neonatal status assessed by Apgar score in 1- and 5-minute, and cord pH values. Results: Labor complications were more frequently observed in the epidural group, with an almost 1.5-fold higher incidence in nulliparous (16.32% vs. 11.29%) and 1.4-fold in multiparous women (9.86% vs. 7.08%). Stepwise logistic regression confirmed that EA is a significant risk factor for labor complications in nulliparous women (OR 1.27, 95% CI 1.03-1.58) and for forceps delivery in multiparous women (5.20, 95% CI 3.31-8.17). Also, EA is an important risk factor for both, low cord arterial pHCel: Ocena wpływu znieczulenia zewnątrzoponowego (ZO) na przebieg porodu oraz stan urodzeniowy noworodków. Materiał i metody: Retrospektywnej analizie poddano 5593 pacjentek spełniających kryteria włączenia do grupy badanej: ciąża pojedyncza, położenie płodu podłużne główkowe, wiek ciążowy ≥37tyg oraz brak stwierdzanych prenatalnie i postnatalnie anomalii rozwojowych. W tej grupie u 2496 ciężarnych zastosowano znieczulenie zewnątrzoponowe porodu, natomiast 3097 stanowiło grupę kontrolną. Oceniane parametry: Częstość występowania powikłań porodowych oraz porodów operacyjnych w grupie pacjentek rodzących w ZO, stan urodzeniowy noworodków oceniony na podstawie skali Apgar (w 1 i 5 minucie) oraz pH krwi pępowinowej. Wyniki: W analizie regresji wieloczynnikowej wykazano, że znieczulenie zewnątrzoponowe jest niezależnym czynnikiem ryzyka powikłań porodowych tylko w grupie pierworódek (IS 1,27, 95% CI 1,03-1,58), natomiast w grupie wieloródek wpływa na zwiększenie odsetka porodów kleszczowych (5,20, 95% CI 3,31-8,17). ZO jest również istotnym czynnikiem ryzyka wystąpienia niskiego pH

Feszített ponyvaszerkezetek szabásmintáinak összehasonlító elemzése

Cutting patterns of a simple form of a tent, so called 'Chinese hat', were analyzed in the paper. Stress distributions in prestressed membrane structures, according to cutting patterns prepared by the help of various numerical methods, were compared. A recently developed computer program, based on the dynamic relaxation method was used for the numerical analysis. The close connection between the shrinking of the cutting pattern and the stressing process of the tent was shown. Shrinking of the cutting pattern means that the stress free size of the tent is smaller than the boundaries of the theoretical shape, the tent structure achieves its shape and prestress during stressing on the original edges. The shrinking can be uniform or proportional to the stresses in the theoretical shape. The cutting pattern prepared without shrinking, produces tent surface that fits to the original boundaries without any strain and stress. To get prestress in the structure, the boundary conditions have to be changed.  Cutting patterns prepared by the help of different methods and based on various models, without shrinking and with different shrinking, were analyzed. After the short demonstration of the different methods, the stresses in warp and weft directions were compared in the different construction shapes

Nasilone wymioty jako nowy objaw rozwijającej się choroby Addisona we wczesnej ciąży

Abstract A 32-year old Caucasian was admitted at 14 weeks of gestation with hypotension and weight loss. Family members noted that she appeared “tired” prior to pregnancy. Past medical history included primary hypothyroidism treated with thyroxine (100μg/day). She had a healthy daughter aged 2.5 years who had been born small for gestational age. At about 8 weeks of gestation she started to vomit several times a day. She was treated with antiemetics and intravenous fluids. Following discharge she remained nauseated, weak and lightheaded and lost about 8 kg of weight. After readmission she appeared ill and dehydrated, BMI 16.6 kg/m2, BP 90/60 mmHg supine, 70/50mmHg upright (with faint-like sensation), normal heart sounds, chest clinically clear, abdomen soft and not tender. Investigations revealed severe hyponatraemia (sodium 112mmol/L), normal potassium level 4.3mmol/L, normal renal function, TSH 1.31μIU/mL (reference range (RR): 0.27-4.2), freeT4 1.99ng/dL (RR: 0.93-1.7), freeT3 3.29pg/mL (RR: 2.57-4.43), anti-TPO antibodies 467IU/mL (RR:Streszczenie 32 letnia kobieta rasy kaukaskiej została skierowana do szpitala z powodu hipotensji i utraty masy ciała. Jej członkowie rodziny zwracali uwagę na fakt, że w okresie poprzedzającym ciążę często zgłaszała uczucie zmęczenia i znużenia. W przeszłości rozpoznano u niej pierwotną niedoczynność tarczycy i była leczona tyroksyną (100μg/dobę). Pierwsza ciąża została zakończona urodzeniem noworodka z rozpoznaną hipoptrofią, którego dalszy rozwój przebiegał prawidłowo. W obecnej ciąży od ósmego tygodnia ciąży rozpoczęły się nasilone wymioty. U ciężarnej zastosowano leki przeciwwymiotne oraz dożylną suplementację płynową. Pomimo zastosowanego leczenia nadal obserwowano uporczywe wymioty, osłabienie i znaczną utratę masy ciała (około 8 kilogramów). Po ponownej hospitalizacji stwierdzono nasilenie objawów chorobowych, znaczne osłabienie i odwodnienie, BMI 16,6kg/m2, ciśnienie krwi tętnicze 90/60mmHg w pozycji leżącej, 70/50mmHg w pozycji stojącej z następową hipotonią ortostatyczną. W badaniu fizykalnym tony serca czyste, akcja serca miarowa, szmer pęcherzykowy prawidłowy, brzuch miękki, niebolesny. W badaniach laboratoryjnych stwierdzono hiponatremię (sód 112mmol/L), potas 4,3mmol/L, prawidłowe wykładniki funkcji nerek, TSH 1,31μIU/mL (wartości referencyjne (WR): 0,27-4,2), fT4 1,99ng/dL (WR: 0,93-1,7), fT3 3,29pg/mL (WR: 2,57-4,43), przeciwciała anty-TPO 467IU/mL (WR

Influence of COVID-19 confinement in students’ performance in higher education

Documento procedente de EdArXiv Preprints , se deposita en Biblos-e Archivo versión 2 de 7 Mayo de 2020This study explores the effects of COVID-19 confinement in the students’ performance in higher education. Using a field experiment of 458 students from three different subjects in Universidad Autónoma de Madrid (Spain), we study the differences in assessments by dividing students into two groups. The first group (control) corresponds to academic years 2017/2018 and 2018/2019. The second group (experimental) corresponds to students from 2019/2020, which is the group of students that interrupted their face-to-face activities because of the confinement. The results show that there is a significant positive effect of the COVID-19 confinement on students’ performance. This effect is also significative in activities that did not change their format when performed after the confinement. We find that this effect is significative both in subjects that increased the number of assessment activities and subjects that did not change the workload of students. Additionally, an analysis of students’ learning strategies before confinement shows that students did not study on a continuous basis. Based on these results, we conclude that COVID-19 confinement changed students’ learning strategies to a more continuous habit, improving their efficiency. For these reasons, better scores in students’ assessment are expected due to COVID-19 confinement that can be explained by an improvement in their learning performanceThis work has been financed by the project Erasmus+ 2017-1-ES01-KA203-038266 Project of the European Union: “Advanced Design of e-Learning Applications Personalizing Teaching to Improve Virtual Education