rectangular configuration
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CivilEng ◽  
2021 ◽  
Vol 2 (3) ◽  
pp. 692-711
Author(s):  
Boglárka Bokor ◽  
Akanshu Sharma

Anchorages of non-rectangular configuration, though not covered by current design codes, are often used in practice due to functional or architectural needs. Frequently, such anchor groups are placed close to a concrete edge and are subjected to shear loads. The design of such anchorages requires engineering judgement and no clear rules are given in the codes and standards. In this work, numerical investigations using a nonlinear 3D FE analysis code are carried out on anchor groups with triangular and hexagonal anchor patterns to understand their behavior under shear loads. A microplane model with relaxed kinematic constraint is utilized as the constitutive law for concrete. Two different orientations are considered for both triangular and hexagonal anchor groups while no hole clearance is considered in the analysis. Two loading scenarios are investigated: (i) shear loading applied perpendicular and towards the edge; and (ii) shear loading applied parallel to the edge. The results of the analyses are evaluated in terms of the load-displacement behavior and failure modes. A comparison is made between the results of the numerical simulations and the analytical calculations according to the current approaches. It is found that, similar to the rectangular anchorages, and also for such non-rectangular anchorages without hole clearance, it may be reasonable to calculate the concrete edge breakout capacity by assuming a failure crack from the back anchor row. Furthermore, the failure load of the investigated groups loaded in shear parallel to the edge may be considered as twice the failure load of the corresponding groups loaded in shear perpendicular to the edge.


2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Shuai Jiang ◽  
Yiping Shen ◽  
Songlai Wang ◽  
Yanfeng Peng ◽  
Yi Liu

Piezoelectric fiber rosettes respond to the directivity characteristics of Lamb waves, and therefore, are useful in detecting the Lamb wave propagation direction. Considering material damage as a secondary wave source, two piezoelectric fiber rosettes are arranged to measure the scattered wave propagation directions for damage localization. The influences of various rosette configurations, i.e., 45°-rectangular, 135°-rectangular, 60°-delta, and 120°-delta, on the estimation accuracy of the propagation direction are investigated in this paper. The response of the piezoelectric fiber to the A 0 mode Lamb wave under narrowband tone-burst excitation is theoretically derived. Experimental tests and piezoelectric coupling simulations are performed to obtain the Lamb wave signal of each fiber. The matching pursuit (MP) algorithm is applied to extract the weak damage-related wave packet by using Hann-windowed narrowband excitation as an atom. The Lamb wave propagation directions are estimated based on the error function. The accuracies of the directions with 4 types of rosette configurations are compared, and their error sources are discussed. The results show that the accuracy of the 135°-rectangular configuration is relatively satisfactory, and the errors depend on the size and location of each fiber in the rosette. The proposed damage localization method is validated by experimental tests. The predicted locations are close to the actual damage location. The research results are significant for piezoelectric fiber rosette design and optimization and damage location without wave speed or time-of-flight information in complex or irregular structures.


Author(s):  
Maria Betania Evangelista da Silva ◽  
Gilda Guimarães ◽  
Izabella Oliveira

ResumoO livro didático é uma das principais fontes de consulta dos professores no ensino de estatística. Esse artigo analisa atividades envolvendo tabelas apresentadas nos livros didáticos de Matemática, dos anos iniciais do Ensino Fundamental do Brasil e do Quebec/CA. Nossas análises se fundamentaram em seis categorias: tipo de representação (quadro, banco de dados ou tabela); função da tabela; habilidade explorada; tipo de tabela (simples ou dupla entrada); tipo de variável; representação dos elementos fundamentais da tabela. Os resultados revelam que, em todos os anos de escolarização, podemos encontrar os três tipos de representação, sendo a maior frequência de tabelas em ambos os lugares de publicação. Além disso, a maioria delas é utilizada como objeto de estudo, indicando uma mudança recente de foco nos livros brasileiros, que priorizavam atividades na quais as tabelas eram pretexto para outros conceitos serem abordados. Observamos, entretanto, uma ênfase em interpretar e completar tabelas já estruturadas. Infelizmente, muitas tabelas não apresentam a fonte, principalmente nos livros do Quebec. A ausência de contextos reais e significativos não contribui efetivamente para a aprendizagem Estatística pelos alunos. Palavras-chave: Livros Didáticos. Ensino de Estatística. Tabelas. Anos Iniciais AbstractTextbooks are one of the main sources of consultation for teaching statistics. This article analyzes activities involving tables presented in Primary School Mathematics textbooks from Brazil and from Quebec - CA. Our analysis were based on six categories: type of representation (rectangular configuration, database or table); table function; explored skill; table type (single or double entry); type of variable; representation of the fundamental elements of the table. The results show that in all years of schooling we can find the three types of representation, with the highest frequency of tables in both places of publication. Most of them are used as an object of study, indicating a recent change of focus in Brazilian books that prioritized activities in which tables were a pretext for other concepts to be addressed. However, we still observe an emphasis on interpreting and completing tables already structured. Unfortunately, many tables do not present their source, especially in Quebec textbooks. The absence of real data and significant contexts effectively does not contribute to the students' significant learning of Statistics. Keyword: Textbook. Teaching of Statistics. Tables. Primary School


2020 ◽  
Vol 6 (2) ◽  
pp. 49-56
Author(s):  
Misagh Shafizad ◽  
◽  
Kaveh Haddadi ◽  

Background and Aim: Given the conflicting and unreliable evidence for using cross-links in posterior spine surgery, this review was conducted to highlight the different features and usefulness of these augmentation devices in spine surgeries. Methods and Materials/Patients: After searching databases using specific keywords, the relevant articles were ultimately selected and evaluated. Results: Biomechanically investigating the use of cross-links has not resulted in unanimous explanations for their effect. The site and direction of cross-links have been rarely investigated in the literature. Some studies recommended eliminating their application from clinical practice; nevertheless, these studies do not necessarily yield clinical benefits. Posterior spinal fixation with pedicle screws and without cross-links offers stability in all the planes in most clinical conditions. Conclusion: Excluding the cross-links in posterior spine surgery may shorten the operation time and reduce hospital costs. Researchers have reported other problems for cross-links such as late pain, device failure, infections, device prominence, and pseudarthrosis which may be obliterated through the avoidance of their combination in a spinal construct; nevertheless, the results of animal models of the application of special cross-links in a degenerative disorder or deformity suggest that diagonal cross-links provide the highest stability of the construct if they are matched with a rodonly system or with transverse cross-link constructs resulting in a rectangular configuration.


Author(s):  
Sudheesh Ramadasan ◽  
Longbin Tao ◽  
Arun Kr Dev

Abstract A simple mathematical model is developed based on the single-degree-of-freedom analogy and principle of conservation of energy evaluating various modes of Vortex-Induced-Vibration (VIV) of a jack-up with cylindrical legs in regular waves. Similar to uniform current, mass ratio, damping ratio and mode factor are found to be the important parameters controlling the cross-flow VIV and radius of gyration also for the yaw VIV. Criteria for the initiation of the mentioned VIV modes are developed for the cases of a single 2D cylinder experiencing planar oscillatory flow, four rigidly coupled 2D cylinders in rectangular configuration experiencing planar oscillatory flow and jack-up experiencing regular waves. The newly developed VIV model is validated by a set of experiments conducted in a wind, wave and current flume. The importance of mass damping parameter is further demonstrated in suppressing VIV in regular waves. The mathematical method will equip engineers to consider the effect of VIV due to regular waves in jack-up designs.


2017 ◽  
Vol 9 (3) ◽  
Author(s):  
Michael Anson ◽  
Aliakbar Alamdari ◽  
Venkat Krovi

Cable-driven parallel manipulators (CDPM) potentially offer many advantages over serial manipulators, including greater structural rigidity, greater accuracy, and higher payload-to-weight ratios. However, CDPMs possess limited moment resisting/exerting capabilities and relatively small orientation workspaces. Various methods have been contemplated for overcoming these limitations, each with its own advantages and disadvantages. The focus of this paper is on one such method: the addition of base mobility to the system. Such base mobility gives rise to kinematic redundancy, which needs to be resolved carefully in order to control the system. However, this redundancy can also be exploited in order to optimize some secondary criteria, e.g., maximizing the size and quality of the wrench-closure workspace with the addition of base mobility. In this work, the quality of the wrench-closure workspace is examined using a tension-factor index. Two planar mobile base configurations are investigated, and their results are compared with a traditional fixed-base system. In the rectangular configuration, each base is constrained to move along its own linear rail, with each rail forming right angles with the two adjacent rails. In the circular configuration, the bases are constrained to move along one circular rail. While a rectangular configuration enhances the size and quality of the orientation workspace in a particular rotational direction, the circular configuration allows for the platform to obtain any position and orientation within the boundary of the base circle. Furthermore, if the bases are configured in such a way that the cables are fully symmetric with respect to the platform, a maximum possible tension-factor of one is guaranteed. This fully symmetric configuration is shown to offer a variety of additional advantages: it eliminates the need to perform computationally expensive nonlinear optimization by providing a closed-form solution to the inverse kinematics problem, and it results in a convergence between kinematic singularities and wrench-closure singularities of the system. Finally, we discuss a particular limitation of this fully symmetric configuration: the inability of the cables to obtain an even tension distribution in a loaded configuration. For this reason, it may be useful to relax the fully symmetric cable requirement in order to yield reasonable tensions of equal magnitude.


Author(s):  
Jinfu Xiao ◽  
M. Gabr ◽  
M. S. Rahman

A vessel for Offshore Compressed Air Energy Storage (OCAES) is being considered as a part of the emerging technology to store intermittently generated energy from offshore renewable sources. The basic idea is to submerge the storage vessel into the ocean at a large water depth, convert the energy into compressed air, store it with using the hydrostatic water pressure to balance the compressed air pressure without requiring the storage vessels to resist high internal air pressure. An additional advantage is that the interface of air and water acts as a piston to maintain the air pressure level. In this study, a rectangular configuration and a cylindrical configuration are proposed for the OCEAS vessel. Stress controlled analyses are performed for the preliminary design of the OCAES vessel with emphasis on characterization of applied cyclic load induced by the air/water exchange in the inflation/deflation process. The stress distribution and deformation pattern in the OCAES vessel at different loading stages are studied by using the multi-physics FEM program COMSOL. Key parameters including storage volume, geometry of OCAES vessel, and material selection are discussed.


2014 ◽  
Vol 136 (1) ◽  
Author(s):  
Souma Chowdhury ◽  
Jie Zhang ◽  
Weiyang Tong ◽  
Achille Messac

During wind farm planning, the farm layout or turbine arrangement is generally optimized to minimize the wake losses, and thereby maximize the energy production. However, the scope of layout design itself depends on the specified farm land-shape, where the latter is conventionally not considered a part of the wind farm decision-making process. Instead, a presumed land-shape is generally used during the layout design process, likely leading to sub-optimal wind farm planning. In this paper, we develop a novel framework to explore how the farm land-shape influences the output potential of a site, under a given wind resource variation. Farm land-shapes are defined in terms of their aspect ratio and directional orientation, assuming a rectangular configuration. Simultaneous optimizations of the turbine selection and placement are performed to maximize the energy production capacity, for a set of sample land-shapes with fixed land area. The maximum farm capacity factor or farm output potential is then represented as a function of the land aspect ratio and land orientation, using quadratic and Kriging response surfaces. This framework is applied to design a 25 MW wind farm at a North Dakota site that experiences multiple dominant wind directions. An appreciable 5% difference in capacity factor is observed between the best and the worst sample farm land-shapes at this wind site. It is observed that among the 50 sample land-shapes, higher energy production is accomplished by the farm lands that have aspect ratios significantly greater than one, and are oriented lengthwise roughly along the dominant wind direction axis. Subsequent optimization of the land-shape using the Kriging response surface further corroborates this observation.


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