Cruciform Element Research Articles

A late-Ediacaran crown-group sponge animal.

Sponges are the most basal metazoan phylum1 and may have played important roles in modulating the redox architecture of Neoproterozoic oceans2. Although molecular clocks predict that sponges diverged in the Neoproterozoic era3,4, their fossils have not been unequivocally demonstrated before the Cambrian period5-8, possibly because Precambrian sponges were aspiculate and non-biomineralized9. Here we describe a late-Ediacaran fossil, Helicolocellus cantori gen. et sp. nov., from the Dengying Formation (around 551-539 million years ago) of South China. This fossil is reconstructed as a large, stemmed benthic organism with a goblet-shaped body more than 0.4 m in height, with a body wall consisting of at least three orders of nested grids defined by quadrate fields, resembling a Cantor dust fractal pattern. The resulting lattice is interpreted as an organic skeleton comprising orthogonally arranged cruciform elements, architecturally similar to some hexactinellid sponges, although the latter are built with biomineralized spicules. A Bayesian phylogenetic analysis resolves H. cantori as a crown-group sponge related to the Hexactinellida. H. cantori confirms that sponges diverged and existed in the Precambrian as non-biomineralizing animals with an organic skeleton. Considering that siliceous biomineralization may have evolved independently among sponge classes10-13, we question the validity of biomineralized spicules as a necessary criterion for the identification of Precambrian sponge fossils.

Fluoride-Salt-cooled high-Temperature Advanced Reactor (FuSTAR): An integrated nuclear-based energy production and conversion system

Based on the analysis of energy structure and the development trends of advanced nuclear energy technology, combining the complementary advantages of nuclear energy and other energy sources in China, the Fluoride-Salt-cooled high-Temperature Advanced Reactor (FuSTAR) system has been proposed. FuSTAR system is designed to address production capacity issues in areas with energy shortages or resource concentration and can be combined with high-temperature process heat to achieve high-value-added processes such as hydrogen production. In this paper, the Tri-structural isotropic fuel combined with helical cruciform elements has been studied in detail on the neutron physics and thermal-hydraulic properties, and the flow and heat transfer experiment is carried out for the first time. The multilayer nonlinear programming method has been applied to the design of thermal transport systems. Then the optimal parameters and configuration of the thermoelectric conversion system are obtained by the superstructure optimization method. The inherent safety of FuSTAR is demonstrated through deterministic safety analysis. In addition, the iodine-sulfur cycle technology and the characteristics of tritium production are also analyzed. This study highlights the significant potential of integrating nuclear energy with other energy sources in an optimized energy-production system.

Modelling and calculating the stiffness of a cross-shaped element of a microelectromechanical gyroscope-accelerometer

This article investigates the design of a linear acceleration and angular velocity sensor with three axis of sensitivity. The modelling of the parametrized geometry of the gyroscope-accelerometer and its cruciform stiffener is carried out based on the ANSYS software package. The dependence of the movement of proof mass on the change in the thickness of the elastic beams of the cruciform element of the gyroscope-accelerometer is obtained.

Stiffness metamodelling of 2D bolted extended end-plate steel connections using modal decomposition

The accurate simulation of steel structures requires a precise model of the joint behaviour. The methods proposed by the steel codes are based on either rotating springs or involved models of springs and rigid bars. In this article, a precise method to model the stiffness of 2D bolted steel connections is presented. First, the joint is accurately modelled using finite elements (FE). Then, the FE model is condensed to a cruciform element of 4 nodes (12° of freedom) by constraining each side cross-section to a node located at its centre of gravity. Subsequently, forces are applied to each node to compute the flexibility matrix, which is then used to construct the stiffness matrix that is finally decomposed through singular value factorization. Following this procedure, a parametric study is conducted to build the training and validation sets of the metamodel. Kriging and Radial Basis Functions are chosen to metamodel and predict the stiffness matrices of the cases not included in the parametric study. Finally, steel structures are analysed with both complete finite elements and surrogate models, and the results are used to confirm the accuracy of the proposed method.

Metamodelling of stiffness matrices for 2D welded asymmetric steel joints

Beam-column steel joints usually have a semi-rigid behaviour, and this must be taken into account when carrying out a global analysis of the structure. Rotational springs at each side of the joint are commonly used to simulate this behaviour by means of the component method, but asymmetric welded beam-column steel joints are not included in the formulations of Eurocode 3. This research work proposes a new methodology to obtain the stiffness of welded asymmetrical beam-column steel joints, by means of a cruciform element of 4 nodes and 12 DOF, whose stiffness matrix is directly obtained by means of the meta-modelling of its elements using Kriging's method. The authors have carried out a wide study of 754 different asymmetric welded beam-column steel joints, whose finite element models have been analysed, and then the static condensation method has been used to obtain the equivalent condensed stiffness matrix (Kcond) of the cruciform element for the joints belonging to the training set. These matrices have been used to build the Kriging's model, and the rest of joints have been used for testing the method, which yields very good results. The use of meta-modelling methods to obtain the stiffness matrix of the joint is not only easier in its application than the component method, but it also leads to a formulation that is more accurate, and also takes into account the interactions between the different parts of the joint.

Experimental analysis of the hydrodynamic coefficients of net panels in current

The hydrodynamic loads on net panels were affected significantly by the net configuration and the Reynolds number. Six groups of net panels with different materials, net solidities and knot patterns were experimentally analyzed in this study. The concept of the cruciform element was proposed to calculate the hydrodynamic loads on net panels. The effect of the net solidity, the net material, the knot pattern and the Reynolds number on the hydrodynamic coefficients of net panels in current was comprehensively discussed. A formula, which was suitable for the net panels with high solidity, was proposed to estimate the hydrodynamic coefficients of net panels in current based on the theoretical and experimental analysis of the measurements. The results indicated that the relationship between the Reynolds number and the drag coefficient of the net panel was similar to that for the circular cylinder when the net solidity was low (0.190); with the increase of the net solidity, the influence of the Reynolds number on the drag coefficient of the net panel decreased. In addition, the net-grouping standard was discussed and a correction factor for modifying the drag-coefficient of the equivalent net model was proposed.

General component based cruciform finite elements to model 2D steel joints with beams of equal and different depths

This paper deals with the formulation of cruciform finite elements that model 2D steel joints for frame analysis. Three different cases are contemplated: single rectangular panels suitable for internal joints with beams of equal depth at both sides; trapezoidal panels for joints with beams of different depths at both sides and inclined stiffeners; and double rectangular panels for the case of joints with beams of different depths at both sides and with or without horizontal stiffeners in the panel zone.The cruciform elements have 4 nodes with 3 degrees of freedom per node, and take into consideration, in a consistent and complete way, the stiffness properties (components in Eurocode), including those of the panel zone. The proposed elements allow modelling simple, rigid and semi-rigid connections. In addition, they take into account all the internal forces that coincide at the joint, and the eccentricities of the internal forces coming from the beams and columns that meet at the joint. Numerical examples are solved that compare the proposed approach with complete finite element models of sample frames. The results validate the approach and demonstrate its advantages.

03.28: Performance of cruciform finite elements that model 2D steel joints with beams of unequal depth in frame analysis

ABSTRACTThis paper deals with the performance evaluation of cruciform finite elements with 4 nodes and 12 degrees of freedom that model 2D steel joints with beams of unequal depth in frame analysis. These elements are capable of modelling joints that have double rectangular panels, with or without horizontal stiffeners in the panel zone, due to beams of different depths at both sides of the joint. In addition, these cruciform elements are suitable for simple, rigid and semi‐rigid connections and therefore can be used for the global analysis of semi‐rigid steel frames. The performance of these elements is assessed by analysing steel frames under different loading conditions, and comparing the results with complete finite element models.The characteristics of these elements (stiffness and resistance) are generated by a previously proposed displacement based modal approach. All the forces and moments coming from the adjacent beams and columns concur at the joint, therefore, the complete force field in the panel zones is known with no need for a transformation parameter β (EC3‐Part 1.8). The proposed element also avoid the use of mechanical models (composed of springs and rigid bars) for frame analyses, which add complexity, numerical overhead —consequence of the larger number of degrees of freedom— and possible round off errors (due to the rigid bars) in the solution process.In addition, since the real dimensions of the joint are included in the proposed elements, the eccentric moments are automatically taken into account. Also, the interaction between the deep and the shallow sides of the column double panels are considered. Numerical simulations and comparison with complete finite element models are carried out that show the validity and computational efficiency of these elements.

Shear behaviour of stiffened double rectangular column panels: Characterization and cruciform element

The behaviour of joints exerts an important influence on the overall performance of steel and composite structures. Modern codes, including Eurocodes 3 (EC3) and 4 (EC4), have included research advances for joint modelling to be used in common practice.The method adopted in EC3 and EC4 to characterize the connections is the so-called component method. One of the most important components is the column web panel in shear, and its behaviour has been investigated thoroughly for the case of single rectangular shear panels arising when the beams have equal depths. However, the case of double column panels, formed by beams of different depths at each side of the column, has not been researched as much.The aim of this paper is the characterization of the shear behaviour of rectangular double column panels attached to beams of unequal depths. In order to isolate the shear behaviour from other components, horizontally stiffened beam to column connections with commercial sections are experimentally tested. Also, finite element modelling and analysis is carried out to compare results. A mechanical model is proposed and a parametric study is performed by means of calibrated finite element models to characterize the different components, and define the analytical expressions for the stiffness and resistance of the proposed mechanical model. In addition, a cruciform finite element that captures the behaviour of the proposed mechanical model has been developed. This general cruciform element is also suitable for semi-rigid connections and can be used for global analysis of semi-rigid steel frames.

Shear behaviour of trapezoidal column panels. II: Parametric study and cruciform element

In recent years a considerable effort has been dedicated to improve the knowledge on the behaviour of semi-rigid steel connections by techniques such as the component method. One of the most important components of the connections is the column web under shear. This component has a well-known and defined behaviour for the case of rectangular panels, which results in internal beam to column joints with beams of equal depth. However, when the right and left beams have different depths the shear panel becomes trapezoidal, and the application of the formulation corresponding to rectangular panels produces inaccurate results. The results of different laboratory tests and finite element simulations have been shown in the companion Part I paper. Also a mechanical model was proposed to characterize its behaviour.In the present work, the results of a wide parametric study, carried out by means of calibrated finite elements models, are shown. These results form the basis to characterize the different components, and define the analytical expressions for the stiffness of the proposed mechanical model. Additionally, a cruciform finite element has been developed that captures the behaviour of the proposed mechanical model. This general cruciform element is suitable for semi-rigid connections and can be used for the global analysis of semi-rigid steel frames. Finally, this approach is applied to several practical cases and the results are shown.

An efficient cruciform element to model semirigid composite connections for frame analysis

This paper deals with a component-based approach to model internal and external semirigid composite connections for the global analysis of frames. The method is based on a cruciform finite sized elastic-plastic joint element that takes into consideration its deformation characteristics including those of the panel zone as well as the left and right connections. In addition, all the internal forces that concur at the joint coming from the beams and columns and their respective eccentricities are also considered.In the context of advanced global analysis allowed by modern codes, the use of the proposed model could be particularly useful since the joint has its own identity and is modelled independently like any other element of the structure.The accuracy of the modelling process and proposed cruciform element is checked against experimental results. Numerical simulations and comparison to previously proposed models assess the numerical efficiency.

Mechanics of woven fabrics using cruciform elements

This paper presents a cruciform element for finite element modelling of woven fabrics. Unlike shell elements, cruciform elements do not need special forms near curved boundaries. Additionally, cruciform elements represent the discrete nature of textile structures and ensure that the arms of the cruciform are parallel to the warp and weft directions. In this paper, stiffness matrices for three types of loading, biaxial tensile, in-plane shear and in-plane bending, have been derived. FE modelling with cruciform elements has been demonstrated for bias extension of a woven fabric near the fixed clamp region.

Experimental and Numerical Investigation of Crash Behavior of Composite Helicopter Cruciform Elements

Experimental and Numerical Investigation of Crash Behavior of Composite Helicopter Cruciform Elements

Sous les voûtes de Pagan

Some 350 temples at Pagan still have mural paintings on their walls or under their vaults. This is the largest corpus of murals from 11th to 14th centuries AD in South-East Asia. On the walls, the large diversity in decorative and iconographie themes calls for a thorough study and monographs on selected temples. The decoration painted under the vaults is more systematic and can be outlined under two main topics : Emblematic motifs, usually circular, sometimes square, painted under the apex of the vaults : the lotus rosace, at the centre of the cloister vault of shrines ; the Buddha's footprints, under the vault of vestibules and entrance halls in a large number of temples ; the map of universe, with its concentric circles of mountains and rivers around the Mount Meru and the four continents in the peripheral ocean ; the horoscopes of Buddha's life, depicting the zodiacal chart for the major events in the Buddha's life (conception, birth, enlightenment and parinirvana) ; the map of Anotatta Lake, considered by the Buddhist cosmogony to be the source of the five sacred rivers of India. Decorative patterns, generally covering the whole of the vault and composed of simple geometric elements, occasionally with a figure on the centre : the circle pattern, most frequently used, with numerous variations in their detail and in their arrangement ; the polylobe pattern, primarily with quatrefoils or cruciform elements ; the polygon pattern, combining octagons, squares, diamonds or hexagons ; the figure pattern, with rows of Buddha figures generally of very small size ; the floral pattern, which can include figures or animals on a vegetal patterned background.

Hall-effect vector-product generators

Whereas conventional Hall multipliers make no use of the vectorial aspect of the Hall effect, the devices to be discussed here are genuine vector-product generators, able to accept vectorial input signals and to produce an output signal in the direction of, and proportional to, the vector product of the input vectors. In particular, devices will be considered which generate either an output vector of fixed direction from two rotating input vectors, or a rotating output vector from one rotating and one fixed-direction input vector (the rotation occurring at constant angular frequencies). In the first case an output signal containing either the sum or the difference of the input frequencies is obtained. In the second case separate vectorial output components, rotating in the same plane and at the same angular frequency but in different directions, can be extracted; in this way positive frequency differences can be distinguished from negative differences. Possible applications of such devices to telecommunication problems will be indicated. The validity of the new principle was confirmed with a cube-shaped Hall-element (instead of a conventional thin plate), with low efficiency, and with a cruciform element with improved efficiency (a thin-plate version, possessing the efficiency of conventional Hall multipliers will also be discussed). The choice of semiconductor material and the construction of the new devices will be treated in some detail. ∗ ∗ A lecture based on the same material was given by the authors at the Institute of Physics Conference on Recent Applications of Semiconductors, Southampton, England, 27 September 1963.