Ribbed Shells Research Articles

Control of resonant oscillations of viscoelastic systems

Structures in the form of cylindrical ribbed shells and panels are widely used in engineering and construction. The problem of the action of moving loads on an infinitely long cylindrical shell, reinforced along the outer surface with longitudinal stiffeners and containing a viscoelastic inertial filler, is considered. The moving load is transferred to the shell only through the ribs, and there is no load outside the ribs. The discreteness of the location of the ribs is taken into account by writing the equations of motion of the beams, followed by the satisfaction of the conjugation conditions. The influence of the number and stiffness of ribs on the nature of the distribution of shell displacements and contact pressure at the boundary of a viscoelastic filler is shown. The movement of the shell is described by classic equations based on the Kirchhoff?Love hypothesis; for the filler, dynamic equations of the theory of visco-elasticity are used. It has been established that the reinforcement of shells with longitudinal ribs (oscillations of a cantilevered cylindrical shell) leads to a decrease in natural frequencies and damping coefficients in some shells, an increase in the density of the spectrum of natural frequencies, and the appearance of intermediate forms and forms with the same wave numbers, but with different frequencies. External forces increase natural frequencies and damping coefficients. It is found that the frequencies for the inner edges are lower than for the outer edges. In the high-frequency zone, any efforts reduce the natural frequencies and the damping coefficient. This means that additional mass plays a more significant role than additional rigidity. Consequently, the longitudinal strengthening of the shell worsens its dynamic properties.

Topology optimization of shell structures in architectural design

Free-form architectural design has gained significant interest in modern architectural practice. Due to their visually appealing nature and inherent structural efficiency, free-form shells have become increasingly popular in architectural applications. Recently, topology optimization has been extended to shell structures, aiming to generate shell designs with ultimate structural efficiency. However, despite the huge potential of topology optimization to facilitate new design for shells, its architectural applications remain limited due to complexity and lack of clear procedures. This paper presents four design strategies for optimizing free-form shells targeting architectural applications. First, we propose a topology-optimized ribbed shell system to generate free-form rib layouts possessing improved structure performance. A reusable and recyclable formwork system is developed for their effective and sustainable fabrication. Second, we demonstrate that topology optimization can be combined with funicular form-finding techniques to generate a rich variety of elegant designs, offering new design possibilities. Third, we offer cost-effective design solutions using modular components for free-form shells by combining surface planarization and periodic constraint. Finally, we integrate topology optimization with user-defined patterns on free-form shells to facilitate aesthetic expression, exemplified by the Voronoi pattern. The presented strategies can facilitate the usage of topology optimization in shell designs to achieve high-performance and innovative solutions for architectural applications.

Analysis and Experimental Research on Vibration Characteristics of Pressure Shell Structure

The vibration and sound radiation characteristics of the submarine pressure hull structure are important performance indicators for the acoustic design of the submarine structure. In this paper, the spectral element method is used to analyze the vibration of the shell structure. Combined with the periodic structure theory, the theoretical calculation method of the periodic ribbed shell structure is deduced, and the analytical method that can be used to calculate the vibration of the pressure shell structure is established. The feasibility of applying the spectral element method to the vibration calculation of the pressure shell structure is verified by comparing the analytical calculation and the finite element simulation. The vibration characteristics test experiment of the actual submarine pressured hull structure is carried out. The results show that the theoretical analysis is correct.HighlightsThe vibration and sound radiation characteristics of the submarine pressure hull structure have an important influence on the radiated noise of the submarine.A theoretical analysis method of vibration characteristics of pressure hulled based on spectral element method and periodic structure theory is proposed.The experimental study on vibration characteristics and active control of line spectrum of the pressure hull is carried out.

Warm-waterTcherskidiumfauna (Brachiopoda) in the Late Ordovician Northern Hemisphere of Laurentia and peri-Laurentia

AbstractThe Late Ordovician (late Katian)Tcherskidiumfauna consisted of large- and thick-shelled virgianid pentamerid brachiopods characterized by large and ribbed shells ofTcherskidiumandProconchidiumand usually associated withHolorhynchus,Deloprosopus, andEoconchidium. This unique fauna was widely distributed across several tectonic plates, largely confined to the paleoequatorial and especially the northern paleotropical zones, such as northern Laurentia, accretionary terranes of Alaska, Kolyma, Baltica, Siberia, Kazakh and adjacent terranes, and South China. In Laurentia, the eponymous genusTcherskidiumwas predominant in regions north of the paleoequator and, in sharp contrast, was absent south of the paleoequator. In this study,Tcherskidium lonein. sp. andProconchidium schleyin. sp. are described from Alaska and North Greenland, respectively, adding new data on theTcherskidiumfauna of the Late Ordovician Northern Hemisphere. Shell gigantism, together with the sharp paleobiogeographic division, suggests that the Late Ordovician (late Katian) Northern Hemisphere had a prevailing warm-water mass, probably due to the lack of large landmass beyond the northern tropics. This was in sharp contrast to the Southern Hemisphere, which was frequently influenced by cold-water invasions from the ice-bearing Gondwana supercontinent centered on the South Pole.UUID:http://www.zoobank.org/25d9b772-bd7d-4ad6-bfc6-ba02b1567cf3

Multigene phylogeny reveals the ribbed shell morphotypes in the land snail genus Sarika (Eupulmonata: Ariophantidae), with description of two new species from Thailand and Myanmar

Abstract The speciose land snail genus Sarika is widely distributed throughout mainland Southeast Asia. This genus is generally recognized by a smooth and polished shell. However, we recognize four species with a ribbed shell surface (S. siamensis, S. theodori, S. costabilis sp. nov., and S. costata sp. nov.) exhibiting genital characters similar to those of Sarika s.s. and so a rearrangement in the systematics of the genus is suggested. Here, we analysed these four ribbed shell species together with Sarika s.s. by a combined morphological and molecular approach to species delineation, the latter based on both mitochondrial (coi and 16S) and nuclear (28S) markers. Our molecular phylogeny affirms the monophyly of the genus Sarika including both smooth and ribbed shell morphotypes that is statistically well supported. The ribbed shell morphotype in the land snail genus Sarika is also well defined in terms of diagnostic morpho-anatomical characters that can be divided into two species groups. The S. costata species group consists of only one species, S. costata sp. nov., while the S. siamensis species group comprises S. siamensis, S. theodori and S. costabilis sp. nov. These findings provide a solid basis for the systematics of family Ariophantidae.

Optimization of the design of the cooling duct of thin!walled heat-stressed structures

The results of modeling of the stressed state of a thinwalled profiled ribbed shell of the cooling duct of heatstressed structures with additional hollow bridges made on the shell ribs with an increased surface for soldering are presented. It is shown that the implementation of the bridges makes it possible to reduce the stresses arising in the inner shell, or to increase the pressure of the cooler in the duct. Keywords: cooling duct, rib, milled inner shell, outer jacket tea_86@mail.ru

Natural Vibrations of the Reinforced Tapered Shell with Taking Into Account the Viscoelastic Properties of the Material

In this paper, the integro-differential equations of natural oscillations of a viscoelastic ribbed truncated conical shell are obtained based on the Lagrange variational equation. The general research methodology is based on the variational principles of mechanics and variational methods. Geometrically nonlinear mathematical models of the deformation of ribbed conical shells are obtained, considering such factors as the discrete introduction of edges. Based on the finite element method, a method for solving and an algorithm for the equations of natural oscillations of a viscoelastic ribbed truncated conical shell with articulated and freely supported edges is developed. The problem is reduced to solving homogeneous algebraic equations with complex coefficients of large order. For a solution to exist, the main determinant of a system of algebraic equations must be zero. From this condition, we obtain a frequency equation with complex output parameters. The study of natural vibrations of viscoelastic panels of truncated conical shells is carried out, and some characteristic features are revealed. The complex roots of the frequency equation are determined by the Muller method. At each iteration of the Muller method, the Gauss method is used with the main element selection. As the number of edges increases, the real and imaginary parts of the eigenfrequencies increase, respectively.

The structure of the Grand Theatre de Rabat, Morocco: from digital design to local construction

This paper describes the structural design, from concept to delivery, of the Grand Theatre de Rabat in Morocco. The project includes an 1800-seat theatre, a large open-air amphitheatre, secondary experimental performance and rehearsal spaces, and a panoramic restaurant. It forms part of a national programme of cultural development located on the Bouregreg River between the ancient twin cities of Rabat and Salé. The complex nature of the programme and the form demanded an advanced digital process for the structural design. The most prominent example of the 3D process is the structural envelope wrapping around the entire building. Its concrete skin is stiffened by a regular grid of ribs, rationalised, but following the complexity of the shape and spanning in an efficient way that provides a continuous system, together with the concrete roof deck, to support the facade cladding. A highly automated parametric workflow was set up to create the geometry of the concrete ribs and shell, closely derived from the architectural design. The concrete ribbed shell and roof envelope went through an iterative process of rationalisation, informed by constructability constraints. The fabrication and delivery of the Grand Theatre de Rabat has been both a technical and a cultural challenge, with a London-led, digitally driven design process bridging to a local, traditional, analogue construction process.

Parametric static analysis of a new type of fabricated plate grillard thin shell roof structure

The new fabricated slab ribbed shell roof structure is a new structure based on a large-span steel-concrete composite thin shell roof. An assembly unit composed of a thin-walled steel ribbed plate, a base plate, and concrete provided with bolt holes, and a plate-grid thin shell roof structure formed by the assembling and connecting assembly units. Considering the influence of the structure’s rise span ratio, five groups of rise span ratios were used for finite element analysis and compared with single-layer cylindrical reticulated shells. The analysis shows that the mean value of the ultimate load of the new prefabricated panel latticed thin shell roof structure is increased by 5.3% on average compared with the single-layer cylindrical reticulated shell structure. When the rise span ratio is 1/5, the structure has the largest stiffness and the smallest deformation; when the rise span ratio exceeds 1/5, the growth trend in the ultimate load that the structure can withstand will become smoother, and the average maximum displacement will decrease by 4.3% compared with the single-layer cylindrical reticulated shell, which shows that the grid lattice structure has better stiffness.

HISTORICAL DESIGN OF CANTILEVER SHELLS OF MODERNIST ARCHITECTURE

Introduction : Studying the historical design system of the pioneer concrete shells helps to reveal a relevant part of the History of Construction, which is also fundamental in acquiring the knowledge necessary to conserve and restore this iconic heritage. Cantilevered shells, like large domes, have been the most difficult to design and dimension when computers did not yet exist. Methods: The research included two phases: firstly, the selection and analysis of some of the most relevant pioneer cantilevered shells, and secondly, the comparative analysis of their design systems. Result and discussion: The analysis pointed out that the pioneer master engineers used different design systems. Pier Luigi Nervi and Eduardo Torroja mainly used scale model tests to check the structural behavior of their new continuous structural forms, Ildefonso Sanchez del Rio always used ribbed shells and chose geometric forms that were easy to calculate manually, and Felix Candela used real size models for the tests. The result reveals the different paths that they used to design and build their relevant legacies, which nowadays belong to the international heritage of Modernist Architecture.

Quasi-static stability of a ribbed shell interacting with moving load

Loss of stability of thin-walled structural elements of aircraft is the most common type of destruction. In this work, the definition of the critical velocity of a pressure wave moving over the surface of an acclivous, ribbed cylindrical shell, which is the most common design element of all aviation and rocket systems, is considered. The article takes into account the discreteness of the location of stiffeners (stringers), in contrast to other works, where ribbing is taken into account only within the framework of a constructive orthotropic model. In the quasi-static formulation, the problem of the stability of a shallow shell with a discrete arrangement of stringers under the action of a moving radial load has been solved. The range of critical speeds of movement of the load is defined. An example is considered.

Research of the specific steel shells progressive collapse prevention

The article deals with coatings in the form of the specific steel shells. After a detailed analysis certain number of accidentsand collapses, these collapses can be classified as “progressive” collapse. The main purpose of the article is the developmentof design algorithms for evaluation of the stress-strain state and preventing the progressive collapse of the specific steelshells. The method of prevention progressive collapse has been developed in the form of a constructive modernization.The comparative finite-element analysis of the strained-strain state of the specific shells original models, models of discretecontinualribbed shells (with constructive upgrading) and models of solid ribbed shells has been carried out. From the analysisresults it can be concluded that the proposed modernization method can be considered as one of the possible options forpreventing progressive collapses and increasing the bearing capacity of specific steel shells.

EXPERIMENTAL AND THEORETICAL TESTING OF THE EFFECTIVENESS OF CONSTRUCTIVE MEASURES TO PREVENT THE PROGRESSIVE COLLAPSE OF THE SPECIAL TYPE METAL SHELLS

The article considers frameless structures in the form of special type metal shells. The main structural element of these special shells is arched thin-walled cold-deformed profiles. The construction of structural elements takes place directly at the construction site. The main anomalies of the exploitation of the specified structures are considered. The main of these anomalies of exploitation is a certain number of accidents and collapses, which, after detailed analysis, can be classified as progressive or “avalanche-like” collapse. The computational algorithms for estimating the stress-strain state and preventing measures the onset of a progressive collapse of special type metal shells are considered. As the preventing measure was described constructive modernization of the original junction of arched structural elements. The aim of the research was to assess the impact of the proposed constructive modernization on the deformation properties of special type metal shell during a two-stage full-scale experiment. The block under research was close to a square, in the plan, cylindrical composite coating shell. Block dimensions: span between side elements 22m., Block length 15.6m., Lifting arm 8.37m., Radius of the cylindrical shell 11.585m. The thickness of the steel element was 1.2 mm.A comparative finite-element analysis of the stress-strain state of the original models of special type metal shell, models of the discrete-continuum ribbed shell (with the implementation of constructive modernization of the joint) was also carried out. The results of the analysis are presented in the form of comparative graphs of displacements of tracked points from loading. The results obtained testify to the effectiveness of the proposed constructive modernization of metal shells of a special type, as measures preventing the onset of progressive collapse of these shell systems.

УРАВНЕНИЯ В СМЕШАННОЙ ФОРМЕ ДЛЯ РЕБРИСТЫХ ОБОЛОЧЕК ОБЩЕГО ВИДА И МЕТОДИКА ИХ РЕШЕНИЯ

The paper examines general shells supported from the incurvity side by a cross-sectional ribbing directed parallel to coordinate lines. Ribs’ position on a shell is set using ordinary bar graph functions so that the rib and shell contact is arranged along the strip. A mean shell surface shall be considered as a coordinate surface. Geometrical nonlinearity and transverse shears are considered; and the shell is considered to be shallow. Forces are expressed via stress function in the mid-surface of the shell in such a way that the first two equilibrium equations are fulfilled identically. Shell deformation is expressed via this function. Introduction of ribs by means of ordinary bar graph functions does not cause difficulties for expression of deformations using forces with the consequent insertion to moments, since ordinary bar graph functions may be also used in denominator, this is not applicable for delta-function (when positions of narrow ribs are set using delta-functions). Mixed equations are established starting from the minimum of shell energy deformation functional. At that, except for equilibrium equations, the variational procedure allows obtaining the third equation of strain compatibility in a shell mid-surface for ribbed shells too. Curvature and torsion change functions are registered in the same way as for Kirchhoff-Love model considering transverse shears. Mixed form equations are given for ribbed shells of the general form and for the Kirchhoff-Love model. For ribbed shallow shells, an algorithm for their solution has been developed and the results of calculating their stability for a different number of reinforcing ribs are given.

Effect of Static Loads on the Natural Vibrations of Ribbed Shells

The article is devoted to a further analysis of the natural vibrations of inhomogeneous shells under the action of static loads. The method of investigation is based on a unified methodology that combines the problems of static stability and the vibrations of elastic shells. The problems of natural vibrations take into account the presence of a prestressed state of the shell structure from the action of static loads. The presence of a static load significantly affects the spectrum of the natural frequencies of the shell. This approach allows us to determine the critical load by the dynamic criterion.The method of investigating of inhomogeneous shells is based on the uniform methodological positions of the 3-d geometrically nonlinear theory of thermoelasticity and the finite-element method in the form of the moment finite-element scheme. So, a thin shell is considered by this method as a three-dimensional body which is modeled throughout the thickness by one isoparametric solid finite element with multilinear shape functions.Two nonclassical hypotheses are used to describe the stress–strain state of a thin inhomogeneous shell. The kinematic hypothesis of deformed straight line in the thickness direction: though stretched or shortened during deformation, a straight segment along the thickness remains straight. This segment is not necessarily normal to the mid-surface of the shell. The displacements are assumed distributed linearly along the thickness, which is conventional in the theory of thin shells. The static hypothesis compressive assumes that the stresses in the fibers are constant throughout the thickness of the shell.Modal analysis of a shallow ribbed panel demonstrates the effectiveness of the developed method. The natural frequencies and mode shapes are determined at each increment of static loading.

Connecting pattern to process: Growth of spiral shell sculpture in the gastropod Nucella ostrina (Muricidae: Ocenebrinae).

Shell morphology is a well-suited and underused system to examine the development of novel forms. The three-dimensional structure produced (the shell) is separate from the largely two-dimensional tissue that secretes it (the mantle), allowing us to disentangle the pattern from the process. Despite knowing a great deal about the mechanics of shell secretion (process), and the variety of shell shapes that exist (pattern), no effort has been made to understand how the mantle changes to produce different shell shapes. We investigated this question in the dimorphic snail Nucella ostrina, which exhibits both smooth and ribbed shells to determine how ribs are formed by the mantle. Rib thickenings are produced only in the outer calcitic shell layer and secreted by the distal Outer Mantle Epithelium (OME) with increased acid phosphatase activity. The evenly thick inner aragonitic layers are secreted by the proximal OME which expresses acid phosphatase. Here we show that locally thicker ribs in N. ostrina are produced by changing the dimensions of the distal OME: elongation in the direction of growth and increased cell height. This should increase the amount of shell material secreted, producing locally thicker shell (ribs). Preliminary evidence suggests this mechanism may be widespread in gastropods.

Transcriptome sequencing and differential gene expression analysis of the schistosome-transmitting snail Oncomelania hupensis inhabiting hilly and marshland regions

The freshwater snail Oncomelania hupensis is the unique intermediate host of the blood fluke Schistosoma japonicum, which is the major cause of schistosomiasis. The snail inhabits two contrasting environments: the hilly and marshland regions. The hilly snails are smaller in size and have the typical smooth shell, whereas the marshland snails are larger and possess the ribbed shell. To reveal the differences in gene expression between the hilly and marshland snails, a total of six snails, three per environment, were individually examined by RNA sequencing technology. All paired-end reads were assembled into contigs from which 34,760 unigenes were predicted. Based on single nucleotide polymorphisms, principal component analysis and neighbor-joining clustering revealed two distinct clusters of hilly and marshland snails. Analysis of expression changes between environments showed that upregulated genes relating to immunity and development were enriched in hilly snails, while those associated with reproduction were over-represented in marshland snails. Eight differentially expressed genes between the two types of snails were validated by qRT-PCR. Our study identified candidate genes that could be targets for future functional studies, and provided a link between expression profiling and ecological adaptation of the snail that may have implications for schistosomiasis control.

Influence of the Parameters of a Non-Constant Disturbing Load on the Transient Process of Vibrations of a Ribbed Cylindrical Shell

A technique for studying the transient process of forced vibrations of a longitudinally and transversely reinforced cylindrical shell under a load with frequency and amplitude varying with time is developed. The discrete arrangement of reinforcing ribs is taken into account. The influence of the damping factor, frequency, and amplitude of loading as well as the duration of the transient process on the shell deflection is studied.

Dynamics of Inhomogeneous Shell Systems Under Non-Stationary Loading (Survey)

Experimental works on the determination of dynamics of smooth and stiffened cylindrical shells contacting with a soil medium under various non-stationary loading are reviewed. The results of studying three-layer shells of revolution whose motion equations are obtained within the framework of the hypotheses of the Timoshenko geometrically nonlinear theory are stated. The numerical results for shells with a piecewise or discrete filler enable the analysis of estimation of the influence of geometrical and physical-mechanical parameters of structures on their dynamics and reveal new mechanical effects. Basing on the classical theory of shells and rods, the effect of the discrete arrangement of ribs and coefficients of the Winkler or Pasternak elastic foundation on the normal frequencies and modes of rectangular planar cylindrical and spherical shells is studied. The number and shape of dispersion curves for longitudinal harmonic waves in a stiffened cylindrical shell are determined. The equations of vibrations of ribbed shells of revolution on Winkler or Pasternak elastic foundation are obtained using the geometrically nonlinear theory and the Timoshenko hypotheses. On applying the integral-interpolational method, numerical algorithms are developed and the corresponding non-stationary problems are solved. The special attention is paid to the statement and solution of coupled problems on the dynamical interaction of cylindrical or spherical shells with the soil water-saturated medium of different structure.

Comparative analysis of the honeycomb and thin-shell space antenna reflectors

Parabolic three-layered reflectors from polymer composite materials with the aluminium honeycomb fillers became widely used in space communication systems in the past decades. There are technological possibilities for creating reflectors in the form of thin-walled ribbed shell with the lower linear density than that of the three-layered structures. The paper presents the results of the temperature and stress-strain analysis for the two types of structures, which could help to select the variant with the best performance characteristics.