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Cross-section behaviour for cold-formed high strength steel (HSS) irregular hexagonal hollow section (IHexHS) stub columns under combined compression and bending is studied and presented in this paper. Finite element models were developed and validated using the existing experimental data collated from the previous research. Upon the validated finite element models, extensive parametric studies were subsequently carried out to generate more numerical data covering a wider range of cross-section dimensions, steel grades and load combinations from pure compression to pure bending. The obtained numerical results were utilised to assess the accuracy and the applicability of the current design codes, such as Eurocode of EN 1993-1-12 (EC3) and the North American code of ANSI/AISC 360-16 (AISC) for cold-formed HSS IHexHS stub columns under combined loading. It was demonstrated that the existing design codes can be safely applied and can be extended for cold-formed HSS IHexHS stub columns design under combined loading. In cross-sectional resistance predictions, conservative results were provided from the existing design codes. The over-predictions were primarily due to the neglect of the strain hardening and plate element interaction. The end points used in the interaction curves of EC3 and AISC adopt an idealised elastic-plastic material model to derive the corresponding resistance in cross-sectional level. The employment of Continuous Strength Method (CSM) leads to improved accuracy in cross-sectional resistance prediction with updated end points in the interaction curve. More consistent and reliable predictions were revealed by carrying out reliability analysis in accordance with EN 1990. [ABSTRACT FROM AUTHOR]

In this article, the bending properties of functionally graded material (FGM) sandwich beams are analyzed by using the scaled boundary finite element method (SBFEM) for the first time. The model of FGM sandwhich beams is realized by using high order spectral elements, and only the axial dimension of the beam needs to be discretized. The analytical formula along the thickness direction can better satisfy the properties of the FGM. More importantly, only a small number of the high order spectral element is used to discretize the FGM sandwich beam model, which greatly improves the computational efficiency. [ABSTRACT FROM AUTHOR]

For the stability analysis of functionally graded material (FGM) sandwich plates, a semi-analytical scaled boundary finite element method (SBFEM) is established within the frame work of layerwise theory in this paper. Two different configurations of FGM sandwich plates are studied, one of which consists of ceramic-rich core and FGM face sheets, and another involves metal-rich and ceramic-rich material face sheets as well as a FGM core, and the modulus of elasticity for each FGM layer is assumed to be changed continuously along thickness according to a power-law distribution. The layerwise theory performed in present work is based on the three-dimensional theory of elasticity for each individual layer satisfying the displacement continuity boundary conditions at layer interfaces, and the two-dimensional high order spectral element with three degrees of freedom per node is employed to discrete the reference surface of each individual layer. And then, based on the principle of virtual work, the SBFEM governing equation for each individual layer of FGM sandwich plates is derived, and a dual variable including the displacement and internal nodal force is used to reduce the governing equations to a system of first-order ordinary differential equation, which is solved analytically by a general approach. Finally, the critical buckling load can be obtained by solving the eigenvalue equation once the bending stiffness matrix and geometric stiffness matrix of FGM sandwich plates are determined. Fast rate of convergence of the proposed formulations is confirmed and comparison studies are presented to construct its high accuracy and excellent predictive capability. Furthermore, effects of gradient index, side-to-thickness ratio, layer configuration, and boundary conditions on dimensionless critical buckling loads of FGM sandwich plates are also studied. The proposed semi-analytical approach is simple in program implementation, accurate and computationally efficient. [ABSTRACT FROM AUTHOR]

Natural soil exhibits inherent spatial variability due to complex physical and chemical formation processes, making it necessary to analyze, evaluation and design foundations using probabilistic method. In this study, the bearing capacity of rectangular skirted mudmats in spatially variable soil is investigated by three-dimensional random finite element analysis (3D-RFEA). Given the high computational cost of 3D-RFEA, an active learning probabilistic method based on Kriging surrogate model is proposed to predict the mean and coefficient of variation of bearing capacity factor of mudmats. Then, considering the effects of the skirt depth ratio of mudmats and the variation coefficient and scales of fluctuation of the undrained shear strength of soil, a prediction model of probabilistic failure envelope is proposed by combining the normalized deterministic failure envelope and the cumulative distribution function (CDF) of the uniaxial bearing capacity factor. Based on the prediction model of probabilistic failure envelope, an example of probabilistic design optimization of mudmats is finally given. Compared with the normative method, the design method based on the prediction model can design mudmats directly with the permissible failure probability. [ABSTRACT FROM AUTHOR]

To investigate vibration characteristics and delay crack propagations of an asymmetric cracked rotor, the 3D finite element model of the rotor system with a nonlinear contact method is established. Resonance characteristics of the asymmetrical rotor without a crack and within different locations of a crack are investigated systematically. Numerical results show that a crack affects vibration frequencies and the unstable region of the rotor. Meanwhile, an improved proportional integral differential control method with the electromagnetic actuator is used to accomplish the delay crack propagation and the vibration suppression. Based on the mapping model of opening and closing states of a crack, the effects of rotational speeds, an unbalance, and asymmetries of the rotor are discussed in detail. Experimental results show that vibrations and the breathing behavior of cracks in the rotor with the electromagnetic actuator can be suppressed, and the effectiveness of the proposed mapping model of opening and closing states of a crack is verified. [ABSTRACT FROM AUTHOR]

• An ALTC nonlinear vibration model of drilling string in ultra-HPHT curved wells is developed. • The vibration response characteristics of drill string in ultra-HPHT curved wells are revealed. • The influences of operation and structural parameters on stick slip vibration characteristics were investigated. • The methods of improving ROP and the service life of drilling string in ultra-HPHT curved wells is put forward. In view of the vibration failure of drilling string system in ultra-high temperature and high pressure (ultra-HPHT) curved wells, an axial-lateral-torsion coupling (ALTC) nonlinear vibration model of drilling string system was established using energy method and Hamiltonian principle, in which, the influence of wellbore trajectory change, wellbore constraint, interaction between bit and rock and ultra-HPHT of wellbore on elastic modulus and viscosity of drilling fluid were taken into account. The finite element method (FEM) is used to realize the numerical solution of the nonlinear vibration model. The correctness and validity of the ALTC nonlinear vibration model was verified by comparing the measured data of four ultra-HPHT wells with the theoretical calculation results of the proposed model. Based on this, according to the parameters of M directional well in Ledong ultra-HPHT block, South China Sea, the influences of ground rotation speed, drilling string length, weight on bit (WOB), torsional impact tools and drill collar length on stick slip vibration characteristics were investigated, and the method of increasing drilling speed in ultra-HPHT curved wells was put forward. The results obtained demonstrate that, firstly, when other requirements were met, the rotary speed should be increased as much as possible, which can effectively improve the drilling efficiency. Secondly, with the increase of drilling depth on-site, the drilling efficiency will be reduced, the whirl phenomenon of drill string system will be intensified, and the service life of bottom hole assembly (BHA) will be reduced. Thirdly, the optimized parameters of WOB and the torsional impact tool depended on the well structure, downhole tool size, etc. and can be determined using the proposed analysis method. The research results provide a theoretically sound guidance for designing and practically sound approach for effectively improving rate of penetration (ROP) and the service life of drilling string in ultra-HPHT curved wells. [ABSTRACT FROM AUTHOR]

A high-performance semi-analytical formulation based on the three-dimensional piezoelectricity theory for bending response and free vibration analysis of circular cylindrical piezoelectric panel subjected to the mechanical and electrical loads is presented. To ensure the accuracy and reliability for the proposed method, a normalized formulation is applied for the constitutive equation of the circular cylindrical piezoelectric panel. By using the scaled boundary finite element method (SBFEM), the normalized dynamic equilibrium equation of cylindrical piezoelectric panel structures in the absence of body force and electric charge is derived into a second-order ordinary differential equation with the analytical form through the weighted residual technique. Under the formulation of the SBFEM, meshes only employed to the boundary of computational domain lead to a reduction of the spatial dimensions by one, so that computation costs can be significantly cut down. After then, the dynamic stiffness equation of whole system is obtained by introducing an intermediate variable. For the static responses, in order to accurately describe the bending behaviors involving the generalized strains and stresses through the thickness, a quadratic function is performed to approximate the generalized displacement vector in the radial direction. For the analysis of free vibrations, the governing equation of motion is rewritten in the expanded form and a condensation of the electric potential degree of freedom is conducted in the system. In this way, the free vibration response of the circular cylindrical piezoelectric panel can be determined by solving the associated eigenvalue problem. Studies of validation and convergence are presented by comparing with those of the published work in which both static and free vibration tests are taken into consideration, and the results show good and convergent performances. Finally, effects of geometric parameters as well as loading conditions on the response characteristics of system are discussed in detail. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) slab is an important component in civil construction and protection engineering, and its dynamic response under impact loading is a complex mechanical problem, especially for two or multiple continuous impact loads. In this paper, a series of drop hammer impact tests were carried out to investigate the dynamic response of RC slabs with two successive impacts. The time history of impact force and the failure characteristic of the slab surface were recorded. Moreover, four influence factors, including slab thickness, reinforcement ratio, impact location, and drop hammer height have been discussed. Besides, a 3D numerical model based on the finite element method (FEM) was established to expand the research of constrained force, deflection, and vertical stress of an RC slab. The results show that increasing the slab thickness and reinforcement ratio can improve the impact resistance of an RC slab. The impact point location and drop hammer height have a great influence on the dynamic response of the RC slab. In addition, the RC slab will have more obvious damage under the second impact, but the dynamic response becomes weaker. It may be because of the local damage in the concrete caused by the first impact that would weaken the propagation of vibration. [ABSTRACT FROM AUTHOR]

This paper extends the idea of using nonuniform rational B-splines (NURBS) based shape functions in the scaled boundary finite-element method (SBFEM) to plate bending formulations, which inherits the advantages of the isogeometric analysis (IGA) as well as the scaled boundary finite-element method. The NURBS are introduced to reconstruct an exact boundary for analysis domain with arbitrary complicated geometry, h -, p -, and k - refinement strategies, which can maintain the same exact geometry as the computer-aided design (CAD) model at all levels. The NURBS basis functions are also used for the approximation of physical quantities inspired by the sense of isoparametric concept, and the high-order continuity of the NURBS basis functions contributes to the better accuracy, convergence, and efficiency of the present isogeometric scaled boundary finite-element method (IGSBFEM). The proposed technique is derived based on the exact three-dimensional elastic theory, which contributes to its high-accuracy property, whereas only discretization of the midplane is required for the present model due to the characteristics of dimensionality reduction and analytical property along the radial direction from the conventional SBFEM, and the solutions along the thickness direction are described as analytical expressions. Five numerical examples involving complicated geometries and multiconnected domains are carried out to examine the applicability of the present approach. Available solutions computed by several other methods (such as the analytic method, FEM, conventional SBFEM, and IGA) are used for comparison. Higher accuracy and efficiency compared with the traditional approaches are achieved. [ABSTRACT FROM AUTHOR]

Truncated carbon nanocones (CNCs) can be taken as energy suppliers because of their special structures. In this paper, we demonstrate the stability of truncated CNCs under compression and the escape behavior of a fullerene catapulted from a compressed CNC by molecular dynamics simulations and theoretical models. The strain energy of a CNC and cohesive energy between a fullerene and the CNC (due to their van der Waals interactions) dominate the stability and catapulting capability of the cone, which strongly depend on geometrical parameters (apex angle, top radius and height) of each CNC and axial distances between them. In particular, the additional transverse vibration of buckled CNCs after released plays a significant role in their catapulting abilities and efficiencies. Finally, finite element method and experiments are further performed to validate the escape mechanism. This study should be of great importance to providing a theoretical support for designing novel nanodevices in mico/nanoelectromechanical systems. [ABSTRACT FROM AUTHOR]

The ball screw pair is a precision drive component that converts rotary motion into linear motion. In practical applications, because the feed system usually has rotational torque and geometric errors, it may increase the contact load of the ball screw pair and reduce the fatigue life. In order to study the influence of different loads and geometric errors on the maximum contact load and fatigue life of ball screw pairs, the following research work was carried out. Firstly, based on the composite load and rotational torque, the ball load distribution model is established, and the accuracy of the model is verified by finite element modeling analysis. Then, the influence of different composite loads, rotation times and geometric errors (including ball size error, lead error and raceway tooth profile error) on the ball load distribution is analyzed. Finally, the influence of compound load, rotating torque and geometric error on the fatigue life of ball screw pairs is studied. The results show that the rotational torque and lead error have a great influence on the load distribution and fatigue life of the ball, and the influence of lead error on load distribution is greater than that of dimension error and tooth profile error. The fatigue life of the ball screw pair with non-uniform load distribution is shorter than that of the ball screw pair with uniform load distribution. [ABSTRACT FROM AUTHOR]

Due to the multidisciplinary nature for the solution of magneto-electro-elastic (MEE) shell structures, developing a novel and accurate computational model is both essential and necessary for the practical engineering. The scaled boundary finite element method (SBFEM) is a semi-analytical technique in which only the surfaces or boundaries of the computational domain need to be discretized, while an analytical formulation can be derived in the radial direction of the surrounding area. These advanced features enable the spatial dimension to be reduced by one, while the accuracy of the proposed algorithm is maintained. In this paper, a novel semi-analytical numerical model based on the SBFEM is developed for the bending analysis of the laminated MEE cylindrical shells under the mechanical or electric/magnetic potential loads. According to the three-dimensional (3D) magneto-electro-elasticity theory, the magneto-electro-mechanical coupling equations and the associated boundary conditions in terms of the mechanical displacement as well as the electrical and magnetical potentials are derived in the scaled boundary coordinate system using the weighted-residual method. The analytical expressions for the generalized displacement and internal nodal force fields are determined by applying the state-space method and have been solved by means of the precise integration technique (PIT). Comparisons between the present numerical results for limiting conditions and solutions available in the published work have been carried out to demonstrate the convergence and accuracy of this approach. At the same time, by utilizing the proposed mechanics, the influences of the aspect ratio and stacking configuration on the through-thickness bending behaviors of the laminated MEE cylindrical shells are studied in detail. [ABSTRACT FROM AUTHOR]

• The finite element method and the contact theory are used to establish a bi-nonlinear vibration model of tubing string. • The longitudinal/lateral coupled vibration and the nonlinear contact of tubing-casing were considering in the model. • A similar experiment of tubing vibration is designed and completed to test the validity of bi-nonlinear vibration model. • The analysis shows that the model has good calculation accuracy and the vibration response law is basically consistent. Fluid-induced vibration (FIV) prediction is an important prerequisite work in wear and fatigue analysis of tubing string in oil & gas well. The finite element method, energy method and Hamiltonian principle are comprehensively used to establish a single nonlinear vibration model of pipe conveying fluid, taking into account the longitudinal/lateral coupled vibration. Based on the contact/impact theory of elastic/plastic body, the nonlinear contact-impact model of tubing-casing is established and introduced into the single nonlinear vibration model to form a bi-nonlinear vibration model of tubing string in oil & gas well. The bi-nonlinear model is numerically discretized by the finite element method, solved by Newmark− β method, and verified preliminarily by a classical contact/impact example in literature in which the influence of inflow is not taken into account temporarily. A similar experiment of tubing vibration is designed and completed to further test the validity of the bi-nonlinear vibration model by comparing the frequency-domain and time-domain responses of the experiment with those from the model. The analysis shows that the bi-nonlinear model has good calculation accuracy and the vibration response law is basically consistent with the experimental results, which can provide an effective theoretical analysis tool for FIV behavior of tubing string in oil & gas well. [ABSTRACT FROM AUTHOR]

This article investigates the bending response performances of the magneto–electro–elastic (MEE) laminated plates resting on the Winkler foundation or the elastic half-space subjected to a transverse mechanical loading.By assuming that the foundation is not electrically and magnetically conductive, the scaled boundary finite element method (SBFEM) based on the three-dimensional (3D) theory of elasticity is applied for both the simulation of the MEE laminated plate and the elastic half-space. The SBFEM model considers the generalized displacement involving the elastic displacement, electric potential and magnetic potential as the nodal degree of freedom for the MEE laminated plates, and only the in-plane of the MEE laminated plate or the boundary of the elastic half-space needs to be discretized leading to reduce the spatial dimension by one. Furthermore, in the SBFEM, the governing equations can be solved by using an analytical approach in the radial direction of the scaled coordinate system, so that it is particularly suitable for the simulation of the elastic half-space. For the Winkler foundation–plate system, the global stiffness coupling governing equation that includes the interaction between the MEE laminated plate and the Winkler foundation is derived directly from the 3D elasticity equations of the MEE laminated plate by assuming that the foundation reactions are proportional to the transverse displacements of the plate structure. While for the MEE laminated plate-half-space system, the whole domain is divided into three sub-domains including the MEE laminated plate structure, the near and semi-infinite far foundation systems based on the sub-structure method, and then the stiffness matrix of each sub-domain can be determined by means of the SBFEM. As a result, the global stiffness equation of the plate-half-space system can be assembled according to the principle of the degree of freedom matching at the same nodes. The numerical results obtained for limiting cases by using the proposed method were compared with the published works and showed excellent agreements with the solutions based on the analytical and numerical approaches, so that the accuracy and applicability of the proposed formulations for the analysis of the interaction problems between the MEE laminated plate and the Winkler foundation or elastic half-space can be verified. Moreover, several numerical examples with various material properties, geometries, stacking sequences, aspect ratios, and supported boundary conditions were presented to show the effects of which on the responses of the plate–foundation system. [ABSTRACT FROM AUTHOR]

Abstract The scaled boundary finite element method (SBFEM) coupled with the finite element method (FEM) for the simulation of the interaction problem between the elastic plate structure and the multi-layered unbounded elastic soil is first developed in this paper. First, the whole system is subdivided into three sub-domains, including the semi-infinite far-field system, the near-field sub-domain, and the plate structure. The far field of the soil is modeled by utilizing the modified scaled boundary finite element method with a scaling line instead of the scaling center used in the traditional SBFEM. In the traditional SBFEM, only the boundary is discretized with surface elements, so the spatial dimension is reduced by one, and the final governing equation can be solved analytically in the radial direction of the scaled coordinate system, and it can exactly meet the infinite domain problem. The stiffness matrix of the three-dimensional (3D) near field is obtained using the standard FEM. The SBFEM is also applied in order to simulate the deformation characteristics of the plate structure based on the 3D elastic equation without introducing any assumption of the thin plate theory, and the high-order spectral element is introduced in order to discretize the middle surface of plate so that the complicated curved boundaries can be better represented. Then, according to the principle of the degree of freedom matching at the same node, the global stiffness matrix of the plate-soil system can be obtained by coupling the stiffness matrices of the sub-domains at the far-field/near-field interface, as well as at the plate/near-field interface. Thus, the response of the whole system under the external load can be solved naturally. Four numerical examples, consisting of a square plate resting on an isotropic soil, multi-layered soil with weak and thin interlayer, a plate with a different geometrical shape and a square plate with a hole, are provided in order to validate the accuracy and versatility of the proposed formulations. [ABSTRACT FROM AUTHOR]

Abstract The impact pressure field in oil&gas wellbore during perforating shaped charge (PSC) explosion has strong impact on the perforation tubing string vibration as well as perforation operation safety. Based on PSC jet theory, π theorem and similarity law, a pressure field model of oil&gas wellbore during PSC explosion is presented and its important parameters are discussed by numerically simulating the evolution process of perforation overpressure using the nonlinear finite element software LS-DYNA combined with the ALE and AMR techniques. Firstly, the evolution process of underwater explosion overpressure is simulated numerically, based on which the key parameters of the peak pressure formula in the pressure field model are fitted out. Secondly, using the analysis method, the simulation model of the shaped charge jet is established, and the energy conversion rate of the PSC to the detonation shock wave is analyzed. The influence of the explosive type, the charge density, the PSC diameter and the charge height on the conversion rate are investigated. Thirdly, On the basis of the above work, a simulation model for the actual wellbore overpressure analysis is established and the mechanism of the overpressure evolution are analyzed. Highlights • A perforating pressure model considering the perforating energy conversion in actual wellbore has been presented. • The process of energy concentrating jet in the actual wellbore has been discussed. • The overpressure evolution process in the actual wellbore has been investigated. • PSC with intensity explosives can shorten the jet completion time and reduce the energy conversion rate. • The explosion peak pressure mainly depends on the equivalent charge quantity of a single PSC. [ABSTRACT FROM AUTHOR]

Highlights • SBFEM are used to laterally-excited sloshing in cylindrical tank with dual porous structures. • Only the circumferential boundary of the domain needs to be discretized with very little nodes. • The governing equation of this proposed method can be solved analytically in the radical direction. • Solution by the proposed method has higher convergence, accuracy and efficiency. • Effects of several key parameters upon sloshing features are investigated. Abstract This study presents a semi-analytical solution with the scaled boundary finite element method (SBFEM) for the sloshing of liquid in vertical cylinders with the coaxial dual circular or arc-shaped porous structures in the context of the linear potential theory. Firstly, the whole flow domain can be divided into three sub-domains with the porous structures and the wall of tank, in which the arc-shaped porous structure should be extended to the whole circle and the perforated coefficient of the extension section is set to infinite. Then the velocity potential of flow in each sub-domain is determined by utilizing the SBFEM for solving the Helmholtz equation or the modified Helmholtz equations, and the fundamental equations and the solution process of the SBFEM for this sloshing problem have been derived in detail. In the SBFEM, one of the superior features is that only the circumferential boundary of the computational domain needs to be discretized with the same form of the finite element. As a result, the spatial dimension of the problem can be reduced by one. As a key point, although there are the dual circular or arc-shaped porous structures, only the wall of tank should be discretized. Meanwhile, the governing equations can be solved analytically in the radial direction by using the Bessel functions or the modified Bessel functions. Numerical examples show that only a small quantity of the discretized elements over the cylindrical boundary can achieve an excellent agreement between the numerical results obtained by the proposed method and the analytical solutions, which demonstrate the accuracy and efficiency of this formulation. Finally, several numerical examples are further studied to investigate the effects of the radius of the porous structures, the porous-effect parameter, the nondimensional wave number, and the opening degree together with the distribution of the centre of the arc-shaped porous structures on the sloshing characteristics of liquid in the cylindrical container with the porous structures. [ABSTRACT FROM AUTHOR]

This paper extends the modified scaled boundary finite element method (SBFEM) to analyse the static behaviors of the complex model with rigid bedrock. In this method, the original scaling center is replaced by scaling line, which makes the proposed method be very suitable for analyzing the horizontal multilayered soil model. The displacement governing equation is obtained by introducing the dual variables in the Hamilton system. This new derivation approach for the modified SBFEM is firstly investigated. Meanwhile, the derivation process is greatly concise and straightforward by introducing the dual vectors. The displacement equation is transformed into an equivalent system of nonlinear first order differential equation. The static stiffness equation is a standard algebraic Riccati equation which can be solved directly. By coupling with the nearfield, the global static governing equation of the horizontal layered unbounded domain is obtained. By that, the accurate global displacement of the modified SBFEM can be solved. In order to model the inclined model, the sub-structure method is presented. Numerical examples demonstrate the accuracy and wide applicability of the proposed method for the complex multilayered model. [ABSTRACT FROM AUTHOR]

The landing string is an important component of deepwater riserless drilling systems. Determination of the dynamic characteristics of the landing string plays an essential role in its design for ensuring its safe operation. In this paper, a dynamic model is developed to investigate the dynamic response characteristics of a landing string, where a landing string in a marine environment is modeled as a flexible slender tube undergoing coupled transverse and axial motions. The heaving motion of the drilling platform is taken as the upper boundary condition and the motion of the drilling bit caused by the interaction between the rock and the bit as the lower boundary condition. A semiempirical Morison equation is used to simulate the effect of the load imposed by the marine environment. The dynamic model, which is nonlinearly coupled and multibody, is discretized by a finite element method and solved by the Newmark technique. Using the proposed model, the dynamic responses of the displacement, axial force, and moment in the landing string are investigated in detail to find out the influences of driving depth of surface catheter, platform motion, bit movement, and marine environment on the dynamical characteristics of the landing string. [ABSTRACT FROM AUTHOR]

A novel simulation approach based on the isogeometric analysis (IGA) and scaled boundary finite element method (SBFEM) is proposed in this paper for bending and buckling analyses of cylindrical shells resting on elastic foundation. The proposed formulation is derived from the 3D theory of elasticity. By using the cylinder axis as the scaling center, the cylindrical shell is reduced into 2D plane. The Non-uniform rational B-splines (NURBS) used in the Computer-aided Design (CAD) model are employed as the basis functions to describe the geometry and approximate the unknown fields in an isoparametric fashion. The present technique offers several major advantages over many other numerical methods, namely: only the in-plane dimension of the degenerative 2D plane required to be discretized into IGA elements, this effectively reduces the number of degrees of freedom (DOFs) and cuts down the computational costs; The physical fields along the thickness direction are described analytically, consequently the shear locking phenomena can be eliminated naturally without any special treatment; Due to the higher-order continuity and the locally supported properties of the NURBS, the present model can exactly represent arbitrary complex geometries at any level, which leads to superior accuracy and robustness; The intrinsic flexibility of the NURBS elements dramatically contributes to the excellent adaptability of the present approach on irregular meshes. Several numerical examples are carried out to evaluate the high performance of the present IGSBFEM on accuracy, efficiency and applicability. • First comprehensive investigation of cylindrical shells resting on elastic foundation using IGSBFEM. • Excellent adaptability on arbitrary complex geometries. • High accuracy and robustness for cylindrical shells with or without elastic foundation. • Computational cost is significantly reduced by using 2D IGA elements. • Shear locking phenomena can be eliminated naturally without any special treatment. [ABSTRACT FROM AUTHOR]

• The effect of spatial variability of soil on the size and shape of failure envelopes for caisson foundations was analyzed. • Random finite element method combined with Kriging method and Monte Carlo simulation was applied to evaluate the stochastic bearing capacity. • Parametric studies examining coefficient of variation and scale of fluctuation of soil's undrained shear strength were performed. • The differences and limitations of the design methods recommended by the existing codes are compared and analyzed, which should be helpful to the design of the foundations in practical engineering. Caisson foundations are increasingly used in offshore engineering and are usually subjected to combined vertical-horizontal-moment (VHM) loading caused by self-weight, wind, waves, and currents. The bearing capacities of foundations under combined loading are represented by the VHM failure envelopes. In the literatures, failure envelopes for caisson foundations were usually established using a deterministic model of soil properties, ignoring the actual uncertainty and spatial variability of marine soil. The present study focuses on the investigation of the bearing capacities for caissons in spatially variable undrained soil under both uniaxial loading and VHM combined loading. Random finite element method combined with Kriging metamodeling technique and Monte Carlo simulation was applied to evaluate the uniaxial bearing capacities and to define the probabilistic VHM failure envelopes. The soil's undrained shear strength was considered to be increasing with depth, while its coefficient of variation was depth-independent. The effects of the coefficient of variation and scale of fluctuation of undrained shear strength on the uniaxial bearing capacity, on both size and shape of VHM failure envelopes for caisson foundations were discussed. It is shown that spatial variability of soil not only causes a change in the size of the failure envelope but also affects its shape when compared with the deterministic case. Therefore, it is necessary to consider the spatial variability of soil when designing caisson foundations and the present results provide some guidance for the design. [ABSTRACT FROM AUTHOR]

Plate anchors are of vital importance for both onshore and offshore facilities. The current study has been focused on the pullout capacity factors of rectangular anchors with wide range of aspect ratios under coupling effects of embedment ratios, anchor inclinations, overburden pressure and non-homogeneity of the clay. Three-dimensional small strain finite element (FE) analyses based on ABAQUS are carried out. After verifying the current model with the existing numerical solutions, the FE results are obtained, and relative comprehensive formulas have been proposed to evaluate the pullout capacity factor with the given parameters. The anchor with aspect ratio less than one has outlier performance in normally consolidated (NC) clay, which has also been discussed based on the soil flow mechanism. [ABSTRACT FROM AUTHOR]

A novel hot stamping technique known as ‘Solution Heat treatment, Forming and in-die Quenching (HFQ ® )’ was employed to manufacture lightweight structural components from AA6082 tailor-welded blanks (TWBs) of different thickness combinations: 1.5–1.5 and 2.0–1.0 mm. A finite element (FE) model was built to study the deformation characteristics during the hot stamping process. The FE model was successfully validated by comparing simulation results with experimental ones. Subsequently, the verified simulation results were analysed through a novel multi-objective FE platform known as ‘Knowledge-Based Cloud – Finite Element (KBC-FE)’. KBC-FE operates in a cloud environment and offers various advanced unique functions via functional modules. The ‘formability’ module was implemented in the current study to predict the limiting dome height and failure mode during the hot stamping process. Good agreements were achieved between the predicted and experimental results, from which studies were extended to predict the forming features of 2.0–1.5 mm TWBs. The ‘formability’ module has successfully captured the complex nature of a hot stamping process, featuring a non-isothermal and non-linear loading path. The formability of TWBs was found to be dependent on forming speed and blank thickness, out of which the latter has a dominant effect. [ABSTRACT FROM AUTHOR]

The scaled boundary finite element method (SBFEM) combined with isogeometric analysis (IGA) is proposed to solve the two-dimensional steady-state heat conduction problems in complex geometries. The main benefit of SBFEM is that the spatial dimension of analyzed domain is reduced by one and the solution is analytical in the radial direction. In this method, only the boundary of the computational domain requires discretization with finite elements leading to the reduction of computational efforts. However, SBFEM suffers from the finite element method related drawbacks. In the case of the complex geometric shapes, a large number of elements are necessary to obtain the exact representation of geometry in finite element method. Isogeometric analysis is a novel numerical technique based on the non-uniform rational B-splines (NURBS), where the geometry can be exactly represented. Moreover, this technique yields superior numerical accuracy, efficiency and convergence property in comparison to finite element method. In the proposed method, the segments of domain boundary with complex geometries are described with NURBS basis functions in IGA, while the straight segments of boundary are represented with polynomial basis functions as in the conventional SBFEM. Thus, the present approach combines the advantages of both SBFEM and IGA. The heat conduction problems of complex geometry can be more effectively handled with the proposed method considering the prescribed heat fluxes and temperatures on side-faces. The accuracy and efficiency of the proposed formulation are demonstrated by modeling five numerical examples involving the complicated geometry. [ABSTRACT FROM AUTHOR]

The patch-plug configuration has been widely used to repair composite structures and restore the structural integrity of damaged composites. In the present research, single-sided CFRP patch-repaired panels, with different patch-plug configurations, are prepared. This is where a circular-shaped damaged area has been removed and a CFRP patch has been adhesively-bonded onto the panel. In some cases, a CFRP plug is inserted into the hole, caused by removal of the damaged area, before the patch is applied. Such patch-repaired panels, and the pristine CFRP panel, are subjected to a low-velocity impact at an energy of 7.5 J. These impacted pristine and repaired panels are then examined using ultrasonic C-scan and optical microscopy to inspect the impact-associated permanent indentation, interlaminar and intralaminar damage. A finite element analysis (FEA) model, which significantly extends a previously validated elastic-plastic (E-P) numerical damage model, has been developed to predict the impact behaviour of the pristine CFRP panel and the various designs of patch-repaired CFRP panels. The comparison between the experimental and numerical results for all the studied cases shows the maximum deviations for the loading response and the damage area are 12% and 15%, respectively. The good agreement between the experimentally-measured impact properties and those predicted using the numerical model demonstrates that the model is a useful design tool. [Display omitted] • Pristine CFRP panels and Single-sided CFRP patch-repaired panels with and without plugs are prepared and impacted at an energy of 7.5 J; • Effects of the diameter and thickness of the patch as well as the presence of plug on the impacted behaviour of repaired composites are investigated; • Good correlation, between the experiment and simulation demonstrates that the developed numerical model is a useful design tool; • The results revealed that the patch thickness has larger effects on the impact behaviour of repaired composites compared to the patch diameter; • A plug can provide added structural integrity to a composite repair and reduce damage in the adhesive bond. [ABSTRACT FROM AUTHOR]

It has been known that thin plate can carry loads considerably more than the buckling loads. This phenomenon is defined as the post-buckling behaviour, which is affected by material properties, geometric dimensions and boundary conditions of the plate. Hybrid I-section is a design concept where flanges are made of high strength steel and web is made of lower steel grade. In order to investigate the effect of slender web on the local buckling and post buckling of hybrid I-section under pure compression, experimental studies of twelve fixed-ended I-section stub columns with slender web were conducted. Tensile coupon tests and initial local geometric imperfection measurement were carried out before stub column tests. Experimental and theoretical methods for determining the critical local buckling load of plate elements were discussed, followed by a post-test finite element analysis to investigate the effects of stub column length and sectional steel combination on the buckling behaviour. Based on the experimental and numerical results, it was observed that for specimens which web plate failed by elastic local buckling, the ultimate test loads are affected by the web strength grade, indicating that the unbuckled portion of slender web plate still provides the post-buckling strength for I-section stub columns even after yielding. By comparing the existing design methods with the numerical ultimate loads, it was found that the Eurocode 3 gives the less scattered predictions than the North American code, Australian code and Chinese code, as well as the existing direct strength method and continuous strength method. • 12 I-section stub column tests with slender web are conducted. • Three steel grades are considered for the web plate of I-section. • Critical local buckling load of plate elements is evaluated. • The current codified design methods are assessed. • The existing direct strength method continuous strength method are assessed. [ABSTRACT FROM AUTHOR]

Monopiles, which have been most extensively used in the offshore wind industries, are usually subject to threats from local scour. The effects of local scour on the bearing capacity of monopiles have been studied based on deterministic soil properties and local scour dimensions. However, the properties of the seabed soil and the dimensions of the local scour both have uncertainty. In this study, a new nonstationary random field model, which can better simulate the nonstationary characteristics of the seabed clayey soil and result in a safer probabilistic design of foundations, is proposed to characterize the spatial variability of the seabed clayey soil. Then, the effects of the spatial variability of the seabed clayey soil and the uncertainty of the local scour depth on the bearing capacity of monopiles are investigated under both uniaxial loading and vertical-horizontal-moment (VHM) combined loading using the random finite-element method combined with kriging metamodeling technique and Monte Carlo simulation. The undrained shear strength of the seabed clayey soil was simulated with a lognormally distributed nonstationary random field, and the local scour depth was treated as a uniform random variable. The negative correlation between them was also considered. The results show that the factor of safety required for the local scoured seabed decreased from 3.3 to 2.6 as the negative correlation was enhanced, greater than or equal to that [factor of safety (FS)=2.6 ] for the intact seabed. The procedure of analyzing the design failure envelop of a monopile in spatially variable clayey soil with a local scour proposed in this study can provide a reference for geotechnical engineers. [ABSTRACT FROM AUTHOR]

This letter is concerned with the undrained bearing capacity of rectangular footings with various aspect ratios and embedment ratios in uniform clay. It covers thin plate foundations with low aspect ratios and high embedment depth with embedment ratio up to 150. The work is based on small strain finite element analysis (FEA). After verification of the FEA model against existing solutions of the bearing capacity factors of rectangular footings, a series of FEA results are obtained. Based on the FEA results, a simple formulation is proposed to calculate the bearing capacity factor for rectangle footing with different aspect ratio in any embedment depth, extending the existing solutions to cover a wider ranges of footing aspect ratios and embedment ratios. [ABSTRACT FROM AUTHOR]

In this study, the modified scaled boundary finite element method (SBFEM) is developed to solve the three-dimensional heat conduction problems. This technique combines the advantages of the finite element method and the boundary element method. Only the computational domain surface needs to be discretized, so the geometric dimension is reduced by one. The modified SBFEM is a semi analytical technique in which no fundamental solution is needed and the anisotropic material can be directly modeled. The definition of a scaling line which replaces the original scaling center makes the modified SBFEM be more suitable for analyzing the horizontal layered heat conduction model. For the first time, the three-dimensional heat conduction formulation of the modified SBFEM is derived by applying the weighted residuals method. By employing the auxiliary variables, the second-order modified SBFEM temperature governing equation is transformed into a first-order ordinary differential equation. Based on the eigenvalue problem, the heat transfer matrix and the boundary temperature can be determined. Four numerical examples are presented to demonstrate the accuracy of the modified SBFEM for the isotropic/anisotropic layered model. The effects of anisotropic parameters and soft layer are investigated to illustrate the wide applicability of the proposed method. [ABSTRACT FROM AUTHOR]

The conventional non-uniform rational B-spline (NURBS)-based isogeometric analysis (IGA) preserves the exact description of geometrical shapes and significantly improves the computational accuracy, but suffers from the topological limitations of a single intact NURBS patch in the parameter space, which renders IGA to be applied in complex topology like the ridged structure inconvenient. In this present work, trimming technique which is the isogeometric approach for handling two-dimensional topologically complicated geometry with a single patch is employed to demonstrate how this issue can be resolved, and further extended to analyze the quadruple arch-cut ridged circular waveguide. The main benefit of the proposed approach is that only one patch is sufficient to represent the complex two-dimensional topology such as circular or any degrees of polygonal shapes. Because the finite element constituents of the trimmed elements are calculated and mapped into underlying global control variables by remodeling the trimmed elements as a single patch, various properties of conventional IGA are maintained. Numerical example illustrates the flexibility for describing complicated two-dimensional domain, and high computational accuracy and efficiency of present method with much less degree of freedom compared to commercial finite-element software package. Effects of arch-cut ridge dimensions on the cut-off wave numbers of modes are investigated in details. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, the constraint effect caused by a side-groove on creep crack growth behavior in P92 steel was studied using finite element analysis. Creep crack growth simulations were conducted on compact tension specimens for side-grooves with different depths and angles. The simulated outcome indicated that the creep crack growth rate increased as the depth and the angles of the side-grooves in the specimen increased. Next, the profile of the crack front for the different specimens was discussed. The distribution of the average stress triaxiality and the average equivalent stress on the crack front were studied to investigate the mechanical mechanism describing the constraint effect on creep crack growth behavior. Finally, the creep crack growth rate determined from numerical simulation results was determined to be consistent with existing experimental data. [ABSTRACT FROM AUTHOR]

Suction embedded plate anchors (SEPLAs) have been applied extensively in deepwater projects due to their high efficiency and low cost. In this paper, a new plasticity model was developed to simulate the keying behavior of SEPLAs. The model was based on three groups of yield envelopes, which considered three different states between the flap and the main plate. Thus, the plasticity model can consider the flap rotation relative to the fluke. The anchor shank was also considered to investigate the three dimensional (3D) effects of the actual SEPLA shape when deriving the yield envelops. A three dimensional large deformation finite element (3D-LDFE) model with flap rotation and shank considered was also set up. Then 3D-LDFE analysis was carried out to verify the plasticity model. The results given by 3D-LDFE analyses agree well with those by plasticity analyses. The effects of the flap on the embedment loss and pullout capacity, and the effects of loading eccentricity and pullout angle on diving behavior are investigated. Optimal padeye offset and pullout angle to drive the anchor diving are proposed. [ABSTRACT FROM AUTHOR]

In the frame of the scaled boundary finite element method (SBFEM), deformations of the magneto-electro-elastic plate with non-uniform materials are solved in this paper. There are no limitations of shapes and kinds of materials of the plate. At the same time, three different types of external loadings are prescribed at the top plane. Starting with the governing equations of equilibrium and the constitutive equations of magneto-electro-elastic materials, and based on the scaled boundary coordinates, the 3D key partial differential equations are converted into the ordinary differential equations without enforcing the kinematics of plate theory. Only the in-plane dimensions of the plate are divided into 2D finite element, which contributes to reducing the space dimension by one. Moreover, making use of the high order spectral element can produce lumped coefficient matrices, which is helpful to acquire high accuracy and efficiency. The elastic displacements, electric potential and magnetic potential in the vertical direction are solved analytically. The analytical solutions are expressed as a matrix exponent in terms of the thickness which is calculated by the Padé expansion. Finally, several numerical examples are provided to demonstrate the accuracy of the proposed solutions and to display the influence of material partition and loading types on the response of the magneto-electro-elastic plate. [ABSTRACT FROM AUTHOR]

The dynamic analysis of two-dimensionalmultilayered anisotropic soilwith rigid bedrock is studied. An efficient numerical approach named the modified scaled boundary finite element method (SBFEM) is proposed in the time domain. Based on introducing the continued fraction method and auxiliary variables, the time domain solution is obtained. This solution can be applied to the transversely isotropic medium without any difficulty. For the modified SBFEM, the original scaling center is replaced by a scaling line. These characteristics enable the modified SBFEM to model the horizontal layered medium. Three significant technologies have been introduced in the formula derivation and solving process. First, the dual system is used to derive the displacement equation of the modified SBFEM, which is built on a Hamilton system. According to the principle of virtual work, the displacement equation is transformed to the dynamic stiffness equation. Second, the new continued fraction method for the unbounded domain resting on rigid bedrock is proposed. By introducing auxiliary variables, the displacement equation of motion of an unbounded domain is built. Third, it is an extremely important point that the accurate precise time-integration method is first employed to solve the global equation of motion of the modified SBFEM. This numerical integral method can achieve the machine precision. By using this method in solving the equation of motion of the modified SBFEM, an extremely accurate solution can be achieved. Finally, numerical examples validate the accuracy of the new proposed method, especially for the complex inclined model with anisotropic soil. [ABSTRACT FROM AUTHOR]

Gravity installed plate anchor (GIPLA) is made mainly of steel plates. It features a swivel mooring arm located close to the anchor tip. Its more complex geometry inevitably complicates the prediction of its keying behavior, hence its capacity. This paper investigated the development of GIPLA׳s movements during its keying and its pullout capacity in NC clay. A plasticity model of yield envelops was constructed and used to predict anchor keying behaviors and its capacities. The plasticity model was validated by 3D large deformation finite element analysis based on remeshing and interpolation technique with small strain model. A parametric study on the keying and capacity development of a deeply embedded GIPLA in NC clay was performed by the plasticity model due to its simplicity and efficiency. The effects of anchor loading angle, anchor padeye eccentricity and soil strength profile were investigated. To encourage anchor “diving” behavior after keying and to keep anchor capacity reasonably high, it was recommended that the anchor loading angle to the horizontal at mudline should be 30° or less and the anchor padeye offset angle be in the range of 15°~25°. The soil non-homogeneity due to the linearly varying strength profile also affect anchor keying trajectory. [ABSTRACT FROM AUTHOR]

The scaled boundary finite method (SBFEM) is developed for analyzing wave propagation problem in the two-dimensional unbounded domain with rigid bedrock. It combines the advantages of the finite element method and boundary element boundary method. Moreover, the original scaling center is replaced by a scaling line which is more suitable for analyzing the multilayered soil model. Therefore, the modified SBFEM develops the original SBFEM. A new derivation of the modified SBFEM equation is built in the frame of Hamilton system. A continued fraction solution of the dynamic stiffness of the soil model with bedrock is obtained for the first time. Then, by introducing the continued fraction solution and auxiliary variables, it leads to the model resting on bedrock can be solved in time domain. The global equation of motion is solved by the efficient precise time-integration method. This integral method is firstly employed in the modified SBFEM. The precision of the proposed method can achieve computer precision. Therefore, an extremely efficient and accurate solution of the modified SBFEM in time domain is obtained. The results of the complex soil model with circular inhomogeneity show that the proposed method yields excellent results, and high accuracy is observed. [ABSTRACT FROM AUTHOR]

A novel semi-analytical plate formulation based on the isogeometric analysis (IGA) and scaled boundary element method (SBFEM) is proposed in this paper, and aims to solving the static bending and free vibration problems of functionally graded material (FGM) plates. The modulus of elasticity and density of the material are assumed to vary continuously along the thickness direction with a power-law distribution. The proposed formulation is derived on the basis of 3D theory of elasticity, while only the 2D in-plane dimension of reference surface needed to be discretized with three degrees of freedom (Dofs) per control points, and the non-uniform rational B-spline (NURBS) basis functions are adopted for both the representation of exact geometry and mechanical analysis. The system equations are obtained by using the principle of virtual work. A set of dual variables involving the displacements and nodal forces are introduced to reduce the system equations into first order ordinary differential equations (ODEs), which can be solved by conventional methods. The proposed approach possesses many advantages, such as the problem dimension is successfully reduced by one due to that the physical fields in the thickness direction are expressed analytically as Padé expansion associated with the material property distributed in gradient form, which are able to predict the stress through the thickness more precisely then traditional formulations. The IGSBFEM meshes can maintain exact geometry at any level without further communication with the computer-aided design (CAD) model, which enables the proposed method a flexible method in simulation of FGM plates with complex geometries. The NURBS basis functions can reach to C ∞ continuous within a knot span, which means that the discontinuity between adjacent elements on the same patch will vanish naturally. Numerous numerical examples are performed to evaluate the superior accuracy, convergence, locking-free, grid adaptability based on the comparison with other references. Effects of gradient index and several aspect ratios on the static and free vibration responses of FGM plates are investigated. [ABSTRACT FROM AUTHOR]

Shape-controllable ultrafine platinum (Pt) nanodendrites have been synthesized by a facile, one-step pulse electrodeposition method in the absence of any organic additive. The particle morphology went through a transition from hemisphere, nanoflower to nanodendrite by altering anodic potential. The ultrafine tertiary branches on the dendrite exhibited an extremely small diameter of 10-20nm. It was found that the preferential growth direction of the tips differs from the dendrite hierarchy, which is <111>, <110> and <311> of the trunk, secondary and tertiary branch, respectively. Catalytic performance of the platinum towards methanol catalytic combustion turned out to be in the order of dendritic> flower-like>hemispherical Pt particles. Typically, the turnover frequency (TOF) of Pt dendrites reached 0.33 mmol· min−1· mg−1 at 150°C, which is four times that of the spherical one. Moreover, the sharp morphology-induced local electric field intensification, both under external electrostatic field and light irradiation, was demonstrated and visualized by the Electrostatic Force Microscope (EFM) and finite element method. [ABSTRACT FROM AUTHOR]

The alkaline oxygen evolution reaction (OER) is a promising avenue for producing clean fuels and storing intermittent energy. However, challenges such as excessive OH− consumption and strong adsorption of oxygen‐containing intermediates hinder the development of alkaline OER. In this study, we propose a cooperative strategy by leveraging both nano‐scale and atomically local electric fields for alkaline OER, demonstrated through the synthesis of Mn single atom doped CoP nanoneedles (Mn SA‐CoP NNs). Finite element method simulations and density functional theory calculations predict that the nano‐scale local electric field enriches OH− around the catalyst surface, while the atomically local electric field improves *O desorption. Experimental validation using in situ attenuated total reflection infrared and Raman spectroscopy confirms the effectiveness of the nano‐scale and atomically electric fields. Mn SA‐CoP NNs exhibit an ultra‐low overpotential of 189 mV at 10 mA cm−2 and stable operation over 100 hours at ~100 mA cm−2 during alkaline OER. This innovative strategy provides new insights for enhancing catalyst performance in energy conversion reactions. [ABSTRACT FROM AUTHOR]

• A dynamic model for drilling risers under soft suspension evacuation is established. • The nonlinear coupling of longitudinal-CF-IL in three directions is considered. • The correctness and effectiveness of model are verified by experimental results. • The progressiveness of model is verified by comparing with the hard suspension model. • The effect of environmental and operation parameters on response characteristics are investigated. In order to provide theoretical reference for the design and operation of soft suspension riser, firstly, a three-dimensional nonlinear vibration model of risers is established using the Hamilton variation and virtual work principles. In the model, three main nonlinear factors were taken into account: longitudinal-lateral (LG/LT) coupling vibration, vortex induced vibration (VIV) and large deformation. The finite element method (FEM) is used to realize the numerical solution of the nonlinear vibration model. Secondly, the correctness and effectiveness of the nonlinear vibration model is verified by the experimental measured data and ANSYS software. The progressiveness of the model is verified by comparing with the uncoupled model and hard suspension, and it demonstrate that, the proposed model can reflect the high nonlinearity of the riser system and describe the nonlinear vibration of the real riser more accurately. The natural frequency of the nonlinear model was much higher and the modal response more complex. The nonlinear coupling effects increase the vibration amplitude in the cross flow (CF) direction and the in-line (IL) direction. Thirdly, the model was used to analyze the effects of structure parameters, environmental parameters and operation parameters on the response characteristics of soft suspension evacuation riser. Some important phenomena have been found: reasonable allocation rate of buoyancy block can effectively restrain the vibration of riser. The optimal allocation rate of buoyancy block is related to the riser structure and operation conditions, which can be determined using proposed nonlinear model. Meanwhile, it is necessary to evacuate along the flow direction as much as possible, with an evacuation speed of lower than 1 m/s. [ABSTRACT FROM AUTHOR]

To address the problem of flow-induced vibration failure of lifting pipe in deep-ocean hydraulic mining, a multi-field coupling nonlinear vibration model of deep-ocean mining lifting pipe was established by using finite element method, energy method and Hamiltonian variational principle. The longitudinal-lateral coupling effect, external current vortex-induced effect and internal fluid pulsation effect were considered, and the numerical solution of the nonlinear vibration model of lifting pipe was realized with the Newmark-β method, Newton Raphson method and finite volume method. Using the same structural parameters, the correctness and effectiveness of the proposed model were verified by comparing with the simulated experimental measurement data in the literature. On this basis, the influence of the buffer station mass and wave parameter on the vibration response characteristics and nonlinear behavior of the lifting pipe were explored. The results show that the vibration frequency of the lifting pipe near the upper end is higher, and the vibration of the pipe string near the lower end is chaotic. With the increase of the buffer station mass, the in-line flow offset and root mean square stress of the lifting pipe decrease, and the axial force on its top end is greater. Under the higher mass of buffer station, the longitudinal vibration of the lifting pipe tends to quasi-periodic motion of the ring, but the vibration amplitude is larger. Small period and large amplitude waves have obvious influences on the vibration, stress and top axial force of the lifting pipe, and make its longitudinal vibration gradually transition from chaotic motion to quasi-periodic motion. [ABSTRACT FROM AUTHOR]

Conventional inductive contactless power transfer (ICPT) systems have only one energy transmission path, which makes it challenging to meet the power transmission requirements of high-power and reliability. This study proposes a novel multiple-input multiple-output (MIMO) ICPT system. The three-dimensional finite element analysis tool COMSOL is utilised to study various magnetic coupling structures, analyse the influence of cross-coupling between coils on the same side, design the circuit based on this, propose a parameter configuration method for resonance compensation, and, finally, build an experimental platform with small magnetic coupling structures for single-input single-output systems (SISO) and MIMO systems. The results indicate that the co-directional connection of the coils of the E-shaped and UE-shaped magnetic coupling structures has a strengthening effect on the secondary side coupling. The magnetic coupling structure of the E-shaped iron core exhibits the best transmission performance. The transmission power of the MIMO system with the E-shaped magnetic coupling structure as the core device is significantly improved. In addition, the output power is unchanged after a secondary side fault, which verifies the accuracy of the proposed method. [ABSTRACT FROM AUTHOR]