Large Structural Deformations Research Articles

Morphogenesis of a chiral liquid crystalline droplet with topological reconnection and Lehmann rotation

Morphogenesis is a hierarchical phenomenon that produces various macroscopic structures in living organisms, with high reproducibility. This study demonstrates that such structural formation can also be observed in a chiral liquid crystalline droplet under a temperature gradient. Through specific control of the temperature change process, we were able to switch the final structure obtained as a result of the formation via the appearance and reconnection of loop defects in the transient state during structure formation. Simultaneously, the existence of the gradient resulted in a characteristic rotational phenomenon called Lehmann rotation, which was prominently induced in the transient state. By demonstrating three-dimensional measurements of the flow field, we revealed the existence of Marangoni convection in the state. Consequently, it is indicated that the convection results in high-speed Lehmann rotation and large structural deformation with topological changes, thereby playing a significant role in the structure formation.

An efficient partitioned framework to couple Arbitrary Lagrangian-Eulerian and meshless vector form intrinsic finite element methods for fluid-structure interaction problems with deformable structures

The Vector Form Intrinsic Finite Element (VFIFE) is an advanced meshless Lagrangian structural solver. This study introduces a partitioned framework to integrate Arbitrary Lagrangian-Eulerian and VFIFE methods into fluid-structure interaction (FSI) problems featured by large structural displacements and deformations. The VFIFE method enables the FSI simulations with deformable structures due to the nature of Lagrangian particles, which is challenging for traditional computational fluid mechanics techniques. In addition, the VFIFE can be effectively equipped with the partitioned coupling schemes because of the versatility of governing equations. In this algorithm system, several matrix problems in finite element methods and mapping and interpolation in the fluid-structure interface can be avoided. The significant potential of this algorithm in tackling complex FSI problems is demonstrated through various benchmarks, encompassing scenarios like Taylor-Green vortex, flow over a rigid cylinder (Re = 40 ∼ 200), forced vibration of a rigid cylinder, vortex-induced vibration (VIV) of an elastically mounted cylinder, and VIV of a rigid cylinder with an attached flexible cantilever beam. Finally, an experiment on flow past a curtain in a water tank is conducted to further evaluate the precision and stability of the current coupling strategy in three dimensions, demonstrating the feasibility of such methods in flexible structures.

A parallel acceleration GPU algorithm for large deformation of thin shell structures based on peridynamics

A parallel acceleration GPU algorithm for large deformation of thin shell structures based on peridynamics

Investigation on Response of Site of Typical Soil–Rock Composite Strata in Changchun Induced by Shield Construction of Parallel Twin Tunnels

Underground engineering construction will inevitably change the stress state of surrounding strata, which will force a negative impact on the surrounding environment, even leading to the large deformation and damage of some adjacent structures. With a focus on the deformation of a typical soil–rock composite stratum site in the construction of Changchun Metro, relying on the shield construction of a parallel twin tunnel project between Northeast Normal University Station and Gong-Nong Square Station, which belongs to the Changchun Metro Line 1, the site deformation characteristics during the shield driving process of parallel twin tunnels were studied. Based on the data obtained from field monitoring and numerical simulation, ground settlement in shield driving was analyzed, the settlement trough was studied with the Peck formula, and the action of shield driving on the adjacent tunnel was discussed. Moreover, the influence range of shield driving was suggested, and the interaction between the twin tunnels with different axis spacings in shield driving was discussed. Some regular results obtained can provide support through data for similar projects in Changchun, China.

Deformation behavior of rectangular underground structures in liquefiable deposits correlated to ground motion intensity measures

Rectangular underground structures in liquefiable deposits are susceptible to larger deformation during earthquake events. The intensity of earthquake motions, as one of the critical factors that would induce large deformation of underground structures in liquefiable deposits, however, was not received enough recognitions. In this paper, nonlinear dynamic analyses with a probabilistic seismic demand model (PSDM) were conducted for a two-dimensional liquefied soil-structure system, considering a variable thickness of liquefiable layer below the structure. The nonlinear soil behavior was simulated by the nonlinear constitutive model PDMY02. The constitutive parameters of saturated sand were calibrated by a slope model in the centrifuge test from LEAP-2017. Interstory drift ratio (IDR) and uplift ratio (UR) of underground structures were selected as engineering demand parameters (EDP). There were totally 18 recorded earthquake motions and 8 intensity measures (IMs) included for the PSDM. Numerical results show that the uplift behavior of underground structures is more sensitive to the variable thickness of liquefiable deposits compared to the horizontal drift of the structure. According to the performance of correlation, efficiency, practicality and proficiency, the velocity-related IMs are more appropriate than the acceleration-related IMs for the evaluation of seismic deformation behavior of underground structures. The deformation response as well as the adaptability of velocity-related IMs are further discussed and evaluated by considering more general cases including different buried depths and height-width ratios for rectangular underground structures.

A numerical framework for modelling settlements of railway ballast layers

Permanent deformation in ballast layers is a major contributing factor to the railway track geometry deterioration. In spite of a considerable amount of research on understanding and predicting performance of ballast layers, accurately capturing their settlements remains a challenge. In order to contribute to solving this important issue, a new numerical method for predicting ballast settlements is presented in this paper. This method is based on the finite element (FE) method combined with a constitutive model that captures permanent deformation accumulation in unbound materials under cyclic loading. This allows predicting permanent deformations of large structures and at large number of load cycles in a computationally efficient manner.The developed constitutive model is validated based on triaxial test measurements over wide range of loading conditions. Stress state in ballast layers has been examined with a 3D FE model, for several embankment structures and traffic load magnitudes. The determined stress distributions and loading frequencies were used as an input of the constitutive model to evaluate permanent strains and settlements of ballast layer. The influence of embankment structural designs and traffic loading magnitudes on the ballast layers settlements is examined and the results obtained are compared with the existing empirical performance models.

Importance of geometric parameters in modeling of porous materials – a finite element study

AbstractPorous materials consist of interconnected skeletal structure around a porous space. The skeletal structure is usually formed of a solid phase and the pores are typically filled with a fluid (liquid or gas). Porous materials are characterized by two essential geometric properties: porosity and pore size distribution (PSD), which influence their bulk mechanical properties. Porosity, which is defined in terms of the ratio between the envelope and the skeletal densities, is sufficient to describe the elastic bulk properties of porous materials. Gibson and Ashby developed a power scaling law expressing the linear relation between the elastic modulus and the relative density. The PSD describes the spatial variation of the pore sizes and has recently been shown to influence the mechanical properties of porous materials. In addition to porosity and PSD, the pore characteristics, namely pore size and shape, and pore‐wall size and shape, also determine the geometric properties that influence the bulk response of these materials. In this study, the importance of the above‐mentioned geometric parameters in the modeling of the porous materials is studied using a computational framework. The bulk mechanical response under large deformation of various porous structures with PSD based on different probability density functions (PDF) and different combinations of other geometric properties under uniaxial compression is investigated. The sensitivity of mechanical response to these geometric parameters is studied. Interdependent parameters which are significantly influential are identified. By controlling these parameters, the synthesis of porous materials can be guided and optimized.

An efficient solid shell material point method for large deformation of thin structures

AbstractThe standard material point method (MPM) encounters severe numerical difficulties in simulating shell structures. In order to overcome the shortcomings of locking effects, the discretization size of background grid should be small enough, usually smaller than 1/5 of the shell thickness, which however will lead to prohibitive computational cost. A novel solid shell material point method (SSMPM) is proposed to efficiently model the large deformation of thin structures. The SSMPM describes the material domain of shell structures by shell particles with hexahedral particle domains. The locking treatments of solid shell element are then introduced in SSMPM, which results in the correction of strain field throughout the shell thickness. Namely, the assumed natural strain (ANS) method is adopted to eliminate the shear locking and trapezoidal locking, while the enhanced assumed strain (EAS) method is employed to eliminate the thickness locking. With the precise description of bending modes, a single layer of particles and a coarse background grid could be used in shell structure simulations with the SSMPM, which dramatically increases the computational efficiency. A local multi‐mesh contact method is presented to naturally couple SSMPM and MPM for the contact situations of shells with other objects. Several numerical examples, including beam vibration, pinched cylinder with free edges and full hemispherical shell, are performed to verify and validate the SSMPM, which shows that the SSMPM considerably outperforms the standard MPM in these situations. A fluid–structure interaction problem and the penetration of a thin plate are investigated based on the contact method and the results are in good agreement with those in the literature.

Linkage-based three-dimensional kinematic metamaterials with programmable constant Poisson’s ratio

Metamaterials constructed from the tessellation of units have extraordinary physical properties and material functions. Most mechanical metamaterials are based on the large structural deformation of units, while the transmission and synchronization of these motion deformations among units are poor which leads to difficulty in designing and controlling the properties. In this study, a modular mechanism based on the kinematics of Sarrus linkage is constructed, and this mechanism is tessellated to a metamaterial with constant negative Poisson’s ratios and a clearly defined deformation path. By varying the specific parameters of the modular mechanism, Poisson’s ratios of the metamaterial can be programmed and almost constant. Hence, a novel approach to constructing metamaterials based on the kinematics of linkages is proposed in this work.

Shape optimization of non-rigid origami leading to emerging bistability

Origami structures are a type of thin-walled flexible structures that undergo large deformation. Their inherent non-rigid characteristic empowers them with great potential for applications in space structures, metamaterials, and robotics. To understand the large deformation of origami structures, consideration of nonlinear mechanics is necessary. However, most origami structures are still designed by pure geometric approaches without considering their non-rigid behavior. In this work, we propose a computational design framework that incorporates nonlinear mechanics into the design procedure of origami. Guided by minimization of stored energy, under prescribed displacement boundary conditions, we optimize the configuration of origami structures. Difficulties arise due to the complex energy landscape of origami structures that inevitably induces bifurcation. We develop strategies to keep track of a stable deformation branch during the optimization process. A surprising outcome is that our approach naturally leads to self-emerging bistable structures, which is demonstrated by a series of numerical examples. We believe that our new approach would make substantial contribution to computational design of non-rigid origami structures, benefiting applications in origami-inspired solutions for science and engineering.

A nonlinear mechanical scheme to analyze suspension bridges under large deformation scenarios

This paper proposes an enhanced mechanical model for analyzing the vertical deformation of suspension bridges under large structural deformation scenarios. The model can be superior to the traditional deflection theory by incorporating several factors frequently overlooked, including the horizontal displacement of the main cable, the elongation of the hanger, and the bending of the tower, and a two-step analysis strategy is proposed to integrate these factors into a comprehensive analysis approach. On this basis, a numerical solution based on the weighted residual method and a nonlinear adjustment algorithm is developed to solve the nonlinear model. The case study of a suspension bridge is presented to demonstrate the applicability and accuracy of the proposed method, and the results are compared with those obtained from the finite element method and the deflection theory, which confirm that the proposed method can produce more accurate results than the deflection theory, especially when the bridge deformation is large enough. The subsequent comparative analysis reveals that the horizontal deformation of the cable and the bending of the towers are the key points contributing to this improvement.

Inhomogeneous large deformation of magneto-thermal sensitive hydrogel-based composite structures

Magneto-thermal sensitive hydrogels, created by adding magnetic nanoparticles to thermo-sensitive gel matrices, have gained attention due to their remote controlled actuation. In this study, the inhomogeneous large deformation of magneto-thermal sensitive hydrogels-based composite structures under external stimuli has been investigated. First, based on previous theoretical frameworks, we develop a new finite element approach to simulate the swelling process of magneto-thermal sensitive hydrogel by using UMAT subroutine in the commercial finite element software ABAQUS. Our approach provides more versatility in the imposition of initial conditions compared to existing models that use the UHYPER subroutine. Furthermore, the numerical case is presented to verify the model with a qualitative comparison with experiments, demonstrating its capabilities in explaining complex physical phenomena. Our results can provide a deeper insight into the mechanical mechanism of magneto-thermal sensitive hydrogels and have important implications for their potential applications in tissue engineering and other fields.

An improved M-SPEM for modeling complex hydroelastic fluid-structure interaction problems

Hydroelastic fluid-structure interaction (FSI) problems usually involve nonlinear free surface flows, large structure deformations and changing interfaces, which present great challenges for numerical modeling. To deal with violent FSIs, the authors proposed a multi-resolution smoothed particle element method (M-SPEM), which adaptively simulates local fluid regions with an improved smoothed particle hydrodynamics (SPH) method and models other solid/fluid regions with a smoothed finite element method (S-FEM). Both computational accuracy in local fluid domain and entire efficiency can be improved by M-SPEM compared with the conventional partitioned FSI solvers based on SPH-FEM coupling schemes. In this work, an improved M-SPEM is developed and extended to simulate the complex hydroelastic FSI problems with structural deformations considered in the numerical model. To solve the accuracy reduction problem in the multi-resolution simulations, we developed a velocity and position correction technique for the generated fluid and virtual particles. The computational results demonstrated that the new correction technique can effectively improve the computational accuracy of M-SPEM while the corrected schemes produce results very close to the reference ones. The positions of the generated particles should also be appropriately optimized during the element-particle conversion process. With both accuracy and efficiency improved, the improved M-SPEM is proven to be suitable to deal with some challenging hydroelastic FSI problems.

Modeling nonlinear deformation of slender auxetic structures under follower loads with complex variable meshfree methods

The auxetic structure with negative Poisson’s ratio has broad application prospects in many engineering fields. Although it is often simplified as a linear elastic problem in theoretical models, the generally used slender structure, such as the reentrant honeycombs, will inevitably undergo large deformation resulting in significant non-conservative load effects in the service conditions. Therefore, a numerical framework for modeling nonlinear deformation of the auxetic structures under follower loads with the complex variable element-free Galerkin method is developed in this paper. The application of the complex variable meshfree method is to deal with the numerical difficulties caused by mesh distortion that may occur in large deformation problems, and at the same time, it can improve the construction efficiency of meshfree shape functions through the complex variable moving least-squares approximation. The Galerkin weak form of the incremental total Lagrangian formula for large deformation problems with the enforced essential boundary conditions using the penalty method is derived and then discretized in the complex variable meshless implementation. Five numerical examples are presented with detailed convergence study to demonstrate the accuracy of the proposed approach in dealing with non-conservative large deformation of the slender auxetic structures.

Selective sorption of oxygen and nitrous oxide by an electron donor-incorporated flexible coordination network

Incorporating strong electron donor functionality into flexible coordination networks is intriguing for sorption applications due to a built-in mechanism for electron-withdrawing guests. Here we report a 2D flexible porous coordination network, [Ni2(4,4′-bipyridine)(VTTF)2]n(1) (where H2VTTF = 2,2′-[1,2-bis(4-benzoic acid)-1,2ethanediylidene]bis-1,3-benzodithiole), which exhibits large structural deformation from the as-synthesized or open phase (1α) into the closed phase (1β) after guest removal, as demonstrated by X-ray and electron diffraction. Interestingly, upon exposure to electron-withdrawing species, 1β reversibly undergoes guest accommodation transitions; 1α⊃O2 (90 K) and 1α⊃N2O (185 K). Moreover, the 1β phase showed exclusive O2 sorption over other gases (N2, Ar, and CO) at 120 K. The phase transformations between the 1α and 1β phases under these gases were carefully investigated by in-situ X-ray diffraction, in-situ spectroscopic studies, and DFT calculations, validating that the unusual sorption was attributed to the combination of flexible frameworks and VTTF (electron-donor) that induces strong interactions with electron-withdrawing species.

Multi-objective Optimization Design of Solar UAV Overall Parameters

Based on the design background of solar UAV, this paper introduces the characteristics of this kind of UAV, such as high flying height, large wingspan, large structural deformation and low wing load. The mathematical model of multi-objective optimization for this type of UAV is established, and the multi-objective genetic algorithm is used to optimize the design. The optimization results of the aircraft design are obtained by computer. Finally, the summary parameters and basic design drawings of this kind of aircraft are given. The results show that multi-objective optimization can be used in the design of solar UAV, and the optimal combination of the overall parameters of this kind of UAV can be obtained to avoid design defects and improve design efficiency. After the optimization design, the overall performance of the aircraft has been improved. This method has a certain reference value for the design of new aircraft.

Dynamics and FNTSM Control of Spacecraft with a Film Capture Pocket System

To solve the problem of space debris, a film capture pocket system is designed in this paper. The film capture pocket is more flexible and reliable, compared with the space rope net. The film capture pocket system contains many flexible structures that are prone to large deformation and vibration during movement. The deformation causes large disturbances to the service spacecraft. It is necessary to establish an accurate rigid-flexible coupling dynamic model for quantitative analysis of disturbances. First, a film dynamic model is developed using high-order absolute nodal coordinate formulation. Second, an attitude tracking control law is designed by using the fast nonsingular terminal sliding mode controller and fixed time dilation observer (FxESO). Finally, combining dynamics and control principles, a virtual prototype of spacecraft with film capture pocket system is established. The simulation results show that higher-order absolute nodal coordinate formulation elements have better convergence, compared to ABAQUS finite element analysis. Meanwhile, the dynamic model simulates the deformation and vibration states of large flexible structures, during the spacecraft maneuver. The FxESO can estimate and compensate the complex disturbance. The error under fast nonsingular terminal sliding mode + FxESO control law converge more rapidly than the nonsingular terminal sliding mode + expansion observer control law. The final spacecraft attitude tracking error is about 10 −4 , indicating the effectiveness of the controller.

Linear and Geometrically Nonlinear Structural Shape Sensing from Strain Data

An aircraft’s shape must be measured during flight to implement active shape controls such as active trim shape, divergence, and sonic boom controls. A basis function method for linear as well as geometrically nonlinear structural shape sensing is proposed in this study. Basis functions can be mode shapes, linear static deformation shapes, and/or geometrically nonlinear static deformation shapes. The proposed basis function method is validated using a high-aspect-ratio wing, a swept test plate, and the National Aeronautics and Space Administration X-59 aircraft. A large structural deformation of a high-aspect-ratio wing is successfully captured using the proposed basis function method with less than 0.3% prediction error at the wing-tip section. The basis function method gives excellent deformation prediction, even with stress concentration. Performance of the basis functions is compared using the X-59 stabilator sample case. In most of the sample load cases, static deformations give a better correlation with the target deformation than do mode shapes. Wing shape sensing with sparse strain data are also demonstrated in this study using the X-59 aircraft. Predicted structural deformations match reasonably with the target deformations, even without strain gauges on some structural components. The predicted deformations have a good match with the target deformations.

A novel pre-processing modelling method for the finite element analysis of the thermal deformation of large structures in the erection stage

The manufacturing process of ships and offshore structures comprises several stages, which include plate cutting, sub-assembly, block assembly, pre-erection, and erection. Accuracy and quality control management are crucial issues in the manufacturing process. Welding-induced distortion and deformation complicate the assembly stage in shipyards. Through conventional finite element (FE) analysis, the manufacturing process can be predicted and controlled up to the sub-assembly stage; however, applying the FE method to the stages between block assembly and erection is difficult. In this study, a new FE analysis method for predicting welding-induced thermal deformation of large blocks, which was difficult to predict with traditional methods, was proposed. In addition, based on this result, we developed a novel pre-processing modelling system that can automatically extract the erection weld lines and automatically divide blocks, which are necessary for the thermal deformation analysis of large blocks. Validation experiments confirmed the applicability of the proposed method to the shaft alignment of a container ship and LNG carrier, with industrial accuracy and quality control in the manufacturing process. Compared with existing methods, the proposed method increases the accuracy of the analysis and reduces the total pre-processing time.

Three-dimensional large deformation reconstruction for slender wing-like structures from strain measurements

Shape-sensing technology has significant applications in real-time monitoring and controlling flexible aerospace structures. Aiming at large deformation of flexible wing-like structures, an algorithm that incorporates geometric nonlinearity is developed for three-dimensional shape reconstruction based on strain measurements. The full-field three-dimensional deformation is described in terms of the deflection of the spatial reference line and the motions of the cross-sectional plane. A certain number of strain measurements distributed on the structural surface are used to estimate the generalized strains and the warping deformation, which can further determine the position of an arbitrary material point in the structure by a series of recursion relations. Instead of the experimental research, the desired strains and the deformation as references are simulated by high-fidelity finite element models. A simple tube model and a more realistic composite wing model are investigated separately to demonstrate the present method in reconstructing deformed shapes under various applied loads. Besides, the modal method was also used to calculate the deformation as a comparison. The result has demonstrated the high accuracy and capability of the present method in three-dimensional shape reconstruction, especially for large deformation problems. The warping effect is demonstrated to have a significant impact on predicting the twist angle. More attention should be paid to accurately describing the warping deformation of complicated wing models, especially when the bending deformation is large.