Shell Plate Research Articles

Double-layered timber plate shell

This article presents a new lightweight construction system for doubly curved shells made from timber plates, inspired by the masonry vaults of Eladio Dieste. The system was developed for a specific case-study project, and general applications to other freeform surfaces are being discussed. The shells are built from two interconnected layers of structural wood veneer plates, using integral through-tenon joints for a fast, precise, and simple assembly. This allows for the construction of a series of differently shaped vaults without a costly mold or support structure. Instead, inclined joints cut with a 5-axis computer numerical controlled milling machine embed the correct location and angle between plates into the shape of the parts. This constrains the relative motions between joined parts to one assembly path. To take advantage of the benefits of such connectors, the constrained assembly paths must be considered in the fundamental design of the system, allowing for the insertion of each plate. This imposes additional constraints in the segmentation process of doubly curved shells. In order to meet the requirements and resolve the multi-constraint system, we use a global, nonlinear optimization approach. Developed as a close collaboration between architects, computer scientists and structural engineers, this article includes an experimental analysis of the influence of parametric modifications in the shape of connectors on their load-bearing performance.

On the approximations in formulation of the Vening Meinesz–Moritz theory of isostasy

Different approximations are used in Moho modelling based on isostatic theories. The well-known approximation is considering a plate shell model for isostatic equilibrium, which is an oversimplifie ...

Modelling vibro-acoustic coupling in flexible micro-perforated plates by a patch-impedance approach

This study proposes a Finite Element (FE)-based efficient numerical model of the vibro-acoustic coupling in flexible micro-perforated plates (f-MPPs) where each perforation is described as an imposed impedance boundary condition (uniform impedance patch) on the plate. This approach opens the possibility of predicting the influence of perforation distribution on the acoustic performance of f-MPP. Micro perforated plates have been a topic of interest as a promising sound absorber in a wide range of applications, from room acoustics to combustion systems. One great advantage of these plates is that it gives the designer the freedom of choice on material in production. Depending on the material and the dimensions, the acoustical modes of the medium can couple with the structural modes of the plate. This coupling changes the number of absorption peaks, frequency and amplitude of the Helmholtz resonance of the system, therefore the coupling becomes an extra parameter in the design process. Current analytical models superpose the mechanical impedance of the plate with the acoustic impedance of the perforations to compute this coupling. This approach works fairly well for plates with uniform perforation distribution. This study proposes a numerical method which assumes perforations as discrete impedance patches on the flexible plate so that they can be considered separately. The method couples the solution of the Helmholtz equation in air with shell plate theory to model the vibro-acoustic effects and the impedance patches are represented as imposed transfer impedance boundary conditions. The assessment of the method is performed in terms of comparing the calculated absorption coefficient values from the simulations of several test cases, fundamental theories and measurement results from the literature. The simulation results agree both with these theoretical limits and measurement results. The use of the method is illustrated by considering an example of the influence of modification of the spatial distribution of perforations on the sound absorption of a membrane.

Beak from the body chamber of an Early Carboniferous shelled longiconic coleoid cephalopod from Arkansas, USA

Here we report the discovery of an Early Carboniferous (Late Visean) 3D cephalopod beak displaying significant similarity to the lower beak of Recent coleoids. It was uncovered in a fragmentarily preserved, longiconic shell from the Moorefield Formation in Arkansas, USA. This shell comprises a fractured 29-mm-long body chamber having a maximum diameter of ~14 mm and showing an indistinct pro-ostracum-like structure. The beak-bearing shell could easily have been mistaken for a bactritid or orthocerid if it were not for a coleoid-type, weakly mineralized, evidently organic-rich shell wall which shows a lamello-columnar ultrastructure of a bulk of shell wall thickness and plate ultrastructure of thin outer layer. The specimen is assigned to an as-yet unnamed shelled coleoid of a so far unknown high-level taxonomic group. A partially exposed, 4.0-mm-long portion of the beak is the lower beak in oblique view from its left side. It exhibits fractured anthracite-like black, apparently originally chitin material, helmet-like general shape, broad hood with narrow shallow median groove and small notch posteriorly, pronounced pointed, non-biomineralized upside belt rostrum, high shoulder and about a 90–100 degrees jaw angle. A broad hood and massive rostrum emphasize its similarity to the lower mandible of Recent Vampyroteuthis and signify that its unique, among living coleoids, structure has been existed for at least since Late Visean time (~333 my).

Error cascade in taxonomy: The case of Cardiomya perrostrata (Mollusca: Bivalvia: Cuspidariidae) in Brazilian waters.

Successions of erroneous taxonomic identifications in biodiversity studies are an undesirable but not rare phenomenon. Such cascades of errors frequently involve taxa with few, polymorphic diagnostic characters, such as representatives of the cuspidariid genus Cardiomya. Four species of the genus are believed to live in Brazilian waters: C. cleryana (d'Orbigny, 1842), C. ornatissima (d'Orbigny, 1853), C. striata (Jeffreys, 1876) and C. perrostrata (Dall, 1881). Many reported occurrences of these species are based on misidentifications, but the error cascade of incorrect records of C. perrostrata is by far the most extensive. Although the species has been reported to live in Brazilian waters for about half a century, all previous records seem to be based on a succession of mistaken identifications. This paper redescribes C. perrostrata based on an analysis of the type series, several lots of museum vouchers and new material collected in the Campos Basis (Rio de Janeiro, Brazil). Ontogenetic changes in shell outline and ultrastructural details of the hinge plate, periostracal surface and larval shell are described and illustrated for the first time. Based on a critical appraisal of the literature, we present an updated geographic and bathymetric distribution of the species. Cardiomya perrostrata displays a gradual increase in the relative length of the rostrum during its ontogeny and in larger specimens the rostrum is more prominently curved upwards. The larval shell is of type 2D, measuring about 215-235 μm in length. The periostracum is minutely pitted and a lithodesma is present. Its distribution is Western Atlantic, ranging from 42°N to 30°S, in depths of 18 to 1646-1829 m. Cardiomya knudseni (Allen & Morgan, 1981), a possibly related amphi-Atlantic species whose type material has been lost, is regarded herein as a nomen dubium.

Wave based method for vibration analysis of elastically coupled annular plate and cylindrical shell structures

Free and forced vibrations of elastically coupled thin annular plate and cylindrical shell structures under elastic boundary conditions are studied through wave based method. The method is involved in dividing the coupled structure into shell segments and annular plates. Flügge shell theory and thin plate theory are utilized to describe motion equations of segments and plates, respectively. Regardless of boundary and continuity conditions, displacements of individual members are expressed as different forms of wave functions, rather than polynomials or trigonometric functions. With the aid of artificial springs, continuity conditions between segments and plates are readily obtained and corresponding governing equation can be established by assembling these continuity conditions. To test accuracy of present method, vibration results of some coupled structures subjected to different boundary and coupling conditions are firstly examined. As expected, results of present method are in excellent agreement with the ones in literature and calculated by finite element method (FEM). Moreover, effects of annular plates, elastic coupling and boundary conditions, excitation and damping are also studied. Results show that normal displacement of annular plate mainly affects free vibrations of the coupled structures, while tangential displacement has the greatest effect on forced vibrations as meridinoal or normal excitation forced on the annular plate.

Cuticle of Polyplacophora: structure, secretion, and homology with the periostracum of conchiferans

The plesiomorphic state of the molluscan scleritome remains ambiguous. Chitons are significant because they show a mix of characters considered diagnostic in both aplacophorans and conchiferans, with both shell plates and small calcified girdle elements on an elongate body, and there is no consensus on the homology of structures involved in chiton plate calcification with those in conchiferan shells. Using light, scanning, and transmission microscopy, the present study examined the structure and formation of the cuticle and underlying epithelium in five chiton species collected over several years in southeast Spain and in California, USA. The cuticular matrix in chitons is similar to the translucent layer of the bivalve periostracum, although there are differences in the orientation of the densely spaced laminae with respect to the mantle surface. The cuticle arises in the accessory fold of the ventral girdle mantle. There is full continuity between the outermost layer of the cuticle and the thin outer layer of the tegmentum, suggesting that the latter is derived from the cuticular wedge permanently lying on the plate margins. A homology is proposed between the cuticle/associated girdle mantle epithelium of Polyplacophora and the periostracum/inner side of the outer mantle fold of the Bivalvia. Nevertheless, while the bivalve periostracum slides over the mantle epithelium during growth, the polyplacophoran cuticle remains stationary. The configuration of the cuticle, which overlaps the plate margins, allows it to efficiently close the plate biomineralization compartment, in a way comparable to that of the periostracum of conchiferans.

Seismic performance of new-type box steel bridge piers with embedded energy-dissipating shell plates under tri-directional seismic coupling action

Accurate numerical models are necessary to evaluate the seismic performance and load-bearing mechanism of new-type box steel bridge piers with embedded energy-dissipating shell plates under tri-directional seismic coupling action. Numerical simulations of seismic performance under six types of tri-directional seismic coupling action was conducted. The effects of this stress on the seismic performance of the new-type steel bridge piers was evaluated through analysis of damage mode, hysteresis curve, skeleton curve, stiffness and strength degradation characteristic, and energy-dissipating capacity. This study also compared the numerical analysis with experimental results in order to validate the accuracy of the proposed finite element model. Based on this model, the range of relevant parameters expanded and 88 numerical specimens were analysed for seismic performance, producing further information about the influence of thickness and curvature of the embedded shell plate, spacing of transverse stiffening ribs of the shell, axial compression ratio, and slenderness ratio. Results showed that tri-directional seismic coupling action significantly affects the specimen’s deformation capacity; the embedded shell plate effectively improves the piers’ load-carrying and deformation capacity; and the thickness of the embedded shell plate, width-to-thickness ratio of the wall plate, axial compression ratio, and slenderness ratio significantly affect the seismic performance of the new-type steel bridge piers. To promote the ease of seismic design of new-type box steel bridge piers, this study used theoretical analysis and numerical simulation to calculate equations for the minimum height of the energy-dissipating zone of the bottom embedded shell plate. Finally, formulas were also established to calculate the relevant stability bearing capacity and displacement ductility factor of the new-type steel bridge piers under tri-directional seismic coupling action in order to improve their seismic design.

Ancestral morphology of crown-group molluscs revealed by a new Ordovician stem aculiferan.

Exceptionally preserved fossils provide crucial insights into extinct body plans and organismal evolution. Molluscs, one of the most disparate animal phyla, radiated rapidly during the early Cambrian period (approximately 535-520 million years ago (Ma)). The problematic fossil taxa Halkieria and Orthrozanclus (grouped in Sachitida) have been assigned variously to stem-group annelids, brachiopods, stem-group molluscs or stem-group aculiferans (Polyplacophora and Aplacophora), but their affinities have remained controversial owing to a lack of preserved diagnostic characters. Here we describe a new early sachitid, Calvapilosa kroegeri gen. et sp. nov. from the Fezouata biota of Morocco (Early Ordovician epoch, around 478 Ma). The new taxon is characterized by the presence of a single large anterior shell plate and polystichous radula bearing a median tooth and several lateral and uncinal teeth in more than 125 rows. Its flattened body is covered by hollow spinose sclerites, and a smooth, ventral girdle flanks an extensive mantle cavity. Phylogenetic analyses resolve C. kroegeri as a stem-group aculiferan together with other single-plated forms such as Maikhanella (Siphogonuchites) and Orthrozanclus; Halkieria is recovered closer to the aculiferan crown. These genera document the stepwise evolution of the aculiferan body plan from forms with a single, almost conchiferan-like shell through two-plated taxa such as Halkieria, to the eight-plated crown-group aculiferans. C. kroegeri therefore provides key evidence concerning the long debate about the crown molluscan affinities of sachitids. This new discovery strongly suggests that the possession of only a single calcareous shell plate and the presence of unmineralised sclerites are plesiomorphic (an ancestral trait) for the molluscan crown.

Addenda to the record of machaeridian shell plates in the Wether Law Linn Formation (Late Llandovery), Pentland Hills, Scotland

Additional machaeridian specimens from the Wether Law Linn Formation (Telychian) have increased our knowledge of this poorly recorded but abundant group in the Pentland Hills, located a few kilometres SE of Edinburgh. A new type of anterior outer shell plate is described and is compared with material previously described from the same horizon and locality. Moreover, a new species of Plumulites is established on the basis of a disarticulated but close association of shell plates.

General equations for free vibrations of thick doubly curved sandwich panels with compressible and incompressible core using higher order shear deformation theory

This paper deals with general equations of motion for free vibration analysis response of thick three-layer doubly curved sandwich panels (DCSP) under simply supported boundary conditions (BCs) using higher order shear deformation theory. In this model, the face sheets are orthotropic laminated composite that follow the first order shear deformation theory (FSDT) based on Rissners-Mindlin (RM) kinematics field. The core is made of orthotropic material and its in-plane transverse displacements are modeled using the third order of the Taylor's series extension. It provides the potentiality for considering both compressible and incompressible cores. To find these equations and boundary conditions, Hamilton's principle is used. Also, the effect of trapezoidal shape factor for cross-section of curved panel element (1 ± z/R) is considered. The natural frequency parameters of DCSP are obtained using Galerkin Method. Convergence studies are performed with the appropriate formulas in general form for three-layer sandwich plate, cylindrical and spherical shells (both deep and shallow). The influences of core stiffness, ratio of core to face sheets thickness and radii of curvatures are investigated. Finally, for the first time, an optimum range for the core to face sheet stiffness ratio by considering the existence of in-plane stress which significantly affects the natural frequencies of DCSP are presented.

Discussion on Structure Design and Optimization of Building Curtain Wall

To discuss the structure design and optimization of building curtain wall, the dynamic characteristics of point supported glass curtain wall system are analyzed by the finite element method. The various technologies are made use of, and according to the characteristics of the structure system, the finite element analysis model with steel structure glass plate beam element and shell element as the basic elements is established. Then, the dynamic characteristics are analyzed, and the modal parameters such as inherent frequency and vibration type are identified. The research results show that the node displacement response power spectrum under the load of wind is obtained, which provides the basis for rationally optimizing the structure. Based on the above findings, it is concluded that the optimization design based on finite element model has a wide significance, which is a useful attempt to reduce the blindness of design and has great engineering significance and application value.

Development of a system for unfolding curved shell plates of ships using iterative geometric algorithm

Development of a system for unfolding curved shell plates of ships using iterative geometric algorithm

Acoustic emission monitoring during hydrotesting of a mounded LPG storage vessel of petrochemical industry

One mounded LPG storage vessel of petrochemical plant got suddenly exposed to cryogenic nitrogenand developed cracks in the shell plate adjacent to the bottom nozzle and was subsequently repair welded.The structural integrity of the repair weld region was assessed by NDT examinations. The integrity of there paired weld region was conrmed by conducting hydrotest. Acoustic emission (AE) monitoring during thehydrotest was also carried out. The acoustic emission signals generated during the hydrotest indicated thatthe signals were due to structural noise and microyielding of the vessel material. During the repressurizingcycle of the hydrotest, negligible AE signals were generated and this conrmed the structural integrity of therepair welded region of the vessel monitored by acoustic emission technique (AET).

A unified formulation for vibration analysis of open cylindrical shells coupled with annular sector plates under general boundary and coupling conditions

A unified formulation for vibration analysis of coupled open cylindrical shell and annular sector plate system with general boundary and coupling conditions is presented in this study by using a modified Fourier-Ritz method. Under the framework, each of the displacements of the open cylindrical shell and the annular sector plate, regardless of boundary and coupling conditions, is expanded as a two-dimensional (2-D) Fourier cosine series supplemented with closed-form auxiliary functions introduced to remove the potential discontinuities at the junction and accelerate the convergence of the series expansion. Since the displacement fields are constructed adequately smooth throughout the entire solution domain, an exact solution is obtained based on the Rayleigh-Ritz procedure by using the energy functions of the coupled system. The arbitrary coupling position and included angle of the open cylindrical shell-annular sector plate structure considered in the theoretical formulation make the present method more general. The convergence and accuracy of the present method are tested and validated by a number of numerical examples for open cylindrical shell-annular sector plate structure with various boundary restraints and general elastic coupling conditions. Some new results are presented to provide useful information for future researchers.

On the material properties of shell plate formed by line heating

This paper is concerned with investigating the plastic material properties of steel plate formed by line heating method, and is aimed at implementing more rational design considering the accidental limit states such as collision or grounding. For the present study, line heating test for marine grade steel plate has been carried out with varying plate thickness and heating speed, and then microscopic examination and tensile test have been carried out. From the microscopic, it is found that the grain refined zones like ferrite and pearlite are formed all around the heat affected zone. From the tensile test results, it is seen that yield strength, tensile strength, fracture strain, hardening exponent and strength coefficient vary with plate thickness and heat input quantity. The formulae relating the material properties and heat input parameter should be, therefore, derived for the design purpose considering the accidental impact loading. This paper ends with describing the extension of the present study.

An analytical method for vibration analysis of cylindrical shells coupled with annular plate under general elastic boundary and coupling conditions

A unified solution for coupled cylindrical shell and annular plate systems with general boundary and coupling conditions is presented in the study by using a modified Fourier-Ritz method. Under the framework, regardless of the boundary and continuity conditions, each displacement for the cylindrical shell and the annular plate is invariantly expressed as the modified Fourier series composed of the standard Fourier series and auxiliary functions. The introduction of the auxiliary functions can not only remove the potential discontinuities at the junction and the extremes of the combination but also accelerate the convergence of the series expansion. All the expansion coefficients are determined by the Rayleigh-Ritz method as the generalized coordinates. The arbitrary axial position of the annular plate coupling with the cylindrical shell considered in the theoretical formulation makes the present method more general. The theoretical model established by present method can be conveniently applied to cylindrical shell-circular plate combinations just by varying the inner radius of the annular plate. The convergence and accuracy of present method are tested and validated by a number of numerical examples for coupled annular plate-cylindrical shell structures with various boundary restraints and general elastic coupling conditions. The effects of the axial position of the annular plate and elastic coupling conditions on the vibration behavior of the coupled system are also investigated. The power of present method compared to conventional finite element method is demonstrated with less computation cost. Some new results are presented to provide useful information for future researchers.

Phylogenetic reconstruction based on COI reshuffles the taxonomy of hyalosphenid shelled (testate) amoebae and reveals the convoluted evolution of shell plate shapes.

Species diversity in most protistan groups has been underestimated. Many morpho-species are in fact complexes that require detailed morphometric studies to be discriminated. However, which traits can be used for species descriptions remains in many cases unclear. The testate amoeba genus Quadrulella produces self-secreted, siliceous plates with a very characteristic square shape-such plates were assumed to be synapomorphic of the genus. Here we demonstrate that Quadrulella symmetrica (the most common Holarctic species) is not monophyletic. Square plate size and arrangement, test size and general shape are efficient criteria for species discrimination. Based on morphology and sequence data, we describe Quadrulella variabilis sp. nov. from Switzerland, and Quadrulella madibai sp. nov. from South Africa, and confirm the validity of Q.alata. The former species Q.subcarinata does not belong to the genus Quadrulella. We therefore transfer this species to the new genus Mrabella gen. nov. Our results show that hyalosphenids presenting siliceous square shell plates do not form a monophyletic clade. Several possible hypotheses about the origins of square plates are discussed. Additionally, this comprehensive phylogenetic analysis of the family Hyalospheniidae confirms that the genus Nebela is paraphyletic and needs to be divided into genera based on general shell shape: Nebela sensu stricto, Longinebela gen. nov., Planocarina gen. nov., Gibbocarina gen. nov., Cornutheca gen. nov. and Mrabella gen. nov.

Theoretical strength assessment of unstiffened bilge shell plating and some considerations on rule prescriptions

In ship hull structures, bilge part is often composed of unstiffened radiused plating, for which the harmonized CSR stipulates required scantlings, locations of the longitudinals adjacent to the bilge radius, and so on. In recent years, under the increased demand for rational structural design, larger radius than ever is sought, expecting reduction of hull steel weight and welding lengths, thus contributing to the reduction of production cost of structures. However, structural problems arising from the larger bilge radius and associated structural arrangement around the bilge shell are not yet sufficiently identified. In these circumstances, the authors developed theoretical formulae, assuming radiused plating connected to continuous stiffened flat plating with regular stiffener spacing. The results of the theoretical calculations are compared with the results of finite element analysis, and it was found that the derived theoretical formulae well explain the complicated phenomena of the curved shell plating connected to the flat stiffened panels. Utilizing the derived theoretical formulae, parametric studies were carried out with regard to the radius of the bilge shell plating, the distance between the position where the curvature of the bilge plate starts and the adjacent longitudinal, and so on. As a result of the calculations, it was found that large bilge radius exceeding current usual practice is feasible, on the condition that the location of the longitudinals is well controlled to reduce bending stresses on the shell plate, and the buckling strength is satisfied. In such case, the stipulation in the harmonized CSR is not always rational, and the authors propose modified structural design methodologies around the unstiffened bilge shell plating.

Design and simulation of heat exchangers using Aspen HYSYS, and Aspen exchanger design and rating for paddy drying application

Air heating unit is one of the most important parts in paddy drying to ensure the efficiency of a drying process. In addition, an optimized air heating unit does not only promise a good paddy quality, but also save more for the operating cost. This study determined the suitable and best specifications heating unit to heat air for paddy drying in the LAMB dryer. In this study, Aspen HYSYS v7.3 was used to obtain the minimum flow rate of hot water needed. The resulting data obtained from Aspen HYSYS v7.3 were used in Aspen Exchanger Design and Rating (EDR) to generate heat exchanger design and costs. The designs include shell and tubes and plate heat exchanger. The heat exchanger was designed in order to produce various drying temperatures of 40, 50, 60 and 70°C of air with different flow rate, 300, 2500 and 5000 LPM. The optimum condition for the heat exchanger were found to be plate heat exchanger with 0.6 mm plate thickness, 198.75 mm plate width, 554.8 mm plate length and 11 numbers of plates operating at 5000 LPM air flow rate.