The need for compatibility between degrees of freedom of various elements is a major problem encountered in practice during the modeling of complex structures; the problem is generally solved by an additional rotational degree of freedom [1-3]. This present paper investigates possible improvements to the performances of strain based cylindrical shell finite element [4] by introducing an additional rotational degree of freedom. The resulting element has 24 degrees of freedom, six essential external degrees of freedom at each of the four nodes and thus, avoiding the difficulties associated with internal degrees of freedom (the three translations and three rotations) and the displacement functions of the developed element satisfy the exact representation of the rigid body motion and constant strains (in so far as this allowed by compatibility equations). Numerical experiments analysis have been conducted to assess accuracy and reliability of the present element, this resulting element with the added degree of freedom is found to be numerically more efficient in practical problems than the corresponding Ashwell element [4].

The main part of finite element analysis via the force method involves the formation of a suitable null basis for the equilibrium matrix. For an optimal analysis, the chosen null basis matrices should exhibit sparsity and banding, aligning with the characteristics of sparse, banded, and well-conditioned flexibility matrices. In this paper, an effective method is developed for the formation of null bases of finite element models (FEMs) consisting of shell elements. This leads to highly sparse and banded flexibility matrices. This is achieved by associating specific graphs to the FEM and choosing suitable subgraphs to generate the self-equilibrating systems (SESs) on these subgraphs. The effectiveness of the present method is showcased through two examples.

Intersecting cylindrical shells are frequently encountered in various types of engineering structures. Despite their common occurrence, reliable and accurate analytical methods have not been generally available, and consequently accurate design information for such configurations has also been generally lacking. To contribute to the understanding of the problem, a finite element analysis is carried out for two normally intersecting cylindrical shells. Two types of loading have been applied to the structure. Results of stresses are provided, of both the outside and the inside, for the two shells. The overall agreement between the finite element predictions and experimental results is a very good one. It has been shown that by using the finite element method together with a "mesh generation" technique, both computational efficiency and minimum user time can be retained.      

One of the common failure modes of thin cylindrical shell subjected external pressure is buckling. The buckling pressure of these shell structures are dominantly affected by the geometrical imperfections present in the cylindrical shell which are very difficult to alleviate during manufacturing process. In this work, only three types of geometrical imperfection patterns are considered namely (a) eigen affine mode imperfection pattern, (b) inward half lobe axisymmetric imperfection pattern extended throughout the height of the cylindrical shell and (c) local geometrical imperfection patterns such as inward dimple with varying wave lengths located at the mid-height of the cylindrical shell. ANSYS FE non-linear buckling analysis including both material and geometrical non-linearities is used to determine the critical buckling pressure. From the analysis it is found that when the maximum amplitude of imperfections is 1t, the eigen affine imperfection pattern gives out the lowest critical buckling pressure when compared to the other imperfection patterns considered When the amplitude of imperfections is above 1t, the inner half lobe axisymmetric imperfection pattern gives out the lowest critical buckling pressure when compared to the other imperfection patterns considered.

In this paper, free vibration of laminated composite cylindrical shells reinforced with circumferential rings, are investigated with experimental, analytical and finite element methods and natural frequencies are obtained. The analysis is carried out for clamp-free and clamp-clamp boundary conditions and the results are compared with each other. To solve the problem, the equilibrium Equations of motions are written according to the classical shells theory and after simplification, the structural stiffness and mass matrices and the frequency Equation are derived using Galerkin method. The results obtained in this paper, are compared with the results available in the literatures, and the results of experimental and finite element methods and good agreement is observed.

Sea shells are natural-biological objects. They are embedded in geological layers in the form of fossils, but also, to find in archaeological deposits as a result of human activities. Archaeologists can use the provenance of shells in the functional analysis of ancient sites in terms of social archeology and prehistoric trading activities. Aarcheological excavations in several sites of the Iranian Plateau have shown that from the 3rd third millennium B.C. onwards, finds of of sea shells (e.g. Lambis, Dentalium, etc.) rapidely increased. Such shells were for instance discovered from ritual cemetery contexts such as Shahdad, Tepe Hesar, Kale Nisar cemeteries or Bani Surma. These objects are mainly used as natural or polished shells. In some cases, they served as a raw material for making all kinds of beads, buttons, and other ornamental objects.. The main question is to understand the relationship between the use of seashells and archaeological context, and also, their role in Bronze Age ritual life. In this article, the descriptive, analytical method has been used in the biological recognition of all types of shells. This method is also used based on similar studies on this issue in Mesopotamia's archeology of the Sumerian-Akkadian period. The distribution of recognizable species shows that these objects are concentrated in the settlements from south to southeast of Iran in the coastal strip of the Persian Gulf, and from the Oman Sea to the Zagros intermountain valleys, as well as in the northwest and northeast of Iran. The biological origin can be placed in the northern shores of the Oman Sea to the Gulf of Kutch on the northern coast of the Indian Ocean. It seems that with the growth and development of urbanization in Southwest Asia and especially the development of sea trade, oysters have been traded as valuable goods and other prestige goods. The importance of the shell findings is more than the value of the shells themselves because they were used as sacred goods in religious affairs. Analysis of the fields where the shells were discovered is more related to cemeteries and temples as sacred spaces. Also, the significant presence of Lambis shells for the production of specific ritual bowls, placed together with bronze axes in graves, can be seen as the reflection of a patriarchic tradition in the social-political organisiation of the third and second millennia B.C. Despite many excavations and the discovery of many samples of these types of shells, no furthergoing investigation on these specific objects was undertaken so far. This desideratum reveals more valuable findings in the archeology of the Iranian plateau. Therefore, one of this article's final goals is to focus more on analyzing the context of the discovery of seashells in future Excavation

Nowadays, polymer based sandwich panels are widely used in industry because of their excellent physical properties compared to metalic alloys, such as lightness, high strength to weight ratio, and so on. Different mechanisms of damage occur during mechanical loading of the composites. Accumulated defects eventually lead to the composite failure. Matrix cracking, fiber breakage, and delamination are some of the damage mechanisms caused by these types of structures. It is necessary to identify the contribution of each mechanism to the ultimate failure of the composites. Non-destructive monitoring of this type of structures and prediction of damage with simulation by finite element method is very important. In this paper, damage mechanisms under low impact impact for sandwich panel made of glass / polyester shell and polyurethane foam core was investigated. In the present study, the shell and core of the sandwich panel was made manually and the sandwich sample was affected by the impact of 20 Joule, and during the test, acoustic data was stored by the installed sensor and was analyzed. Also, the impact process modeled using Abaqus FE software with explicit dynamic solver and damage mechanisms investigated applying cohesive bonding between layers and the proposed finite element model. The results obtained from the empirical test and simulation were discussed and there is a good agreement observed between them.

In this article, the prominence has been given to study the influence of skew angle on bending response of functionally graded material shell panels under thermo-mechanical environment. Derivation of governing equations is based on the Reddy's higher-order shear deformation theory and Sander's kinematic equations. To circumvent the problem of C1 continuity requirement coupled with the finite element implementation, C0 formulation is developed. A nine noded isoparametric Lagrangian element has been employed to mesh the proposed shell element in the framework of finite element method. Bending response of functionally graded shell under thermal field is accomplished by exploiting temperature dependent properties of the constituents. Arbitrary distribution of the elastic properties follows linear distribution law which is a function of the volume fraction of ingredients. Different combinations of ceramic-metal phases are adopted to perform the numerical part. Different types of shells (cylindrical, spherical, hyperbolic paraboloid and hypar) and shell geometries are concerned to engender new-fangled results. Last of all, the influence of various parameters such as thickness ratio, boundary condition, volume fraction index and skew angle on the bending response of FGM skew shell is spotlighted. Some new results pertain to functionally graded skew shells are reported for the first time, which may locate milestone in future in the vicinity of functionally graded skew shells.

In the current work, the seismic analysis of bent region in buried pipes is performed, and effects of soil properties and modeling methods on pipe’s response are investigated. To do this task, beam, beamshell finite element modeling, and a continuum shell FE model of a 90-degree elbow are employed. In the beam model, the pipe is simulated by beam elements while combined shell-beam elements are used for the continuum shell finite element model. The surrounding soil is simulated by nonlinear springs and solid elements; moreover, soil hardening behavior and soil-pipe slippage are considered in the models. In addition, an equivalent boundary condition has been employed at the end of each elbow leg to simulate far field effects more closely. From these analyses, it can be revealed that axial strain at bends is larger in stiffer soil due to smaller slippage. In addition, a full three dimensional soil-pipe interaction using continuum shell FE model causes a substantial increase of elbow strain.