Large Displacement Problems Research Articles

Unsupervised Non-rigid Histological Image Registration Guided by Keypoint Correspondences Based on Learnable Deep Features with Iterative Training.

Histological image registration is a fundamental task in histological image analysis. It is challenging because of substantial appearance differences due to multiple staining. Keypoint correspondences, i.e., matched keypoint pairs, have been introduced to guide unsupervised deep learning (DL) based registration methods to handle such a registration task. This paper proposes an iterative keypoint correspondence-guided (IKCG) unsupervised network for non-rigid histological image registration. Fixed deep features and learnable deep features are introduced as keypoint descriptors to automatically establish keypoint correspondences, the distance between which is used as a loss function to train the registration network. Fixed deep features extracted from DL networks that are pre-trained on natural image datasets are more discriminative than handcrafted ones, benefiting from the deep and hierarchical nature of DL networks. The intermediate layer outputs of the registration networks trained on histological image datasets are extracted as learnable deep features, which reveal unique information for histological images. An iterative training strategy is adopted to train the registration network and optimize learnable deep features jointly. Benefiting from the excellent matching ability of learnable deep features optimized with the iterative training strategy, the proposed method can solve the local non-rigid large displacement problem, an inevitable problem usually caused by misoperation, such as tears in producing tissue slices. The proposed method is evaluated on the Automatic Non-rigid Histology Image Registration (ANHIR) website and AutomatiC Registration Of Breast cAncer Tissue (ACROBAT) website. It ranked 1st on both websites as of August 6th, 2024.

Numerical steady-state and transient responses of a SDOF system constrained by two optimally designed bumpers

Seismically isolated structures can be subjected to large horizontal displacements relative to the ground, especially in Near-Fault earthquakes, which are characterized by one or more intense pulses of velocity and displacement of long period. One strategy to mitigate the problem of large displacements, which occurs in linearly isolated structures, is the use of deformable and dissipative devices (bumpers). The impact between the structure and the bumpers, if the bumpers are appropriately designed, can produce beneficial effects on the dynamic response of the system, both on displacements and accelerations. In this paper the response obtained from a numerical model of isolated single-degree-of-freedom (SDOF) systems constrained by two bumpers, arranged symmetrically on both sides of the mass of the system with an initial gap, subjected to base harmonic excitation, is studied. This model is called Vibro-Impact Isolation System (V-IIS). The objective of this work is to define a methodology for choosing the design parameter defining the V-IIS (mechanical characteristics of the bumpers, gap and isolation frequency of the system) by observing both steady-state and transient responses of both the system and the bumpers. The study of the transient response is compared with that obtained in the steady-state to assess how representative the latter is of the V-IIS transient response. From the definition of the methodology for choosing the parameters of the V-IIS, through optimal design, the only design parameters are the gap and the isolation frequency of the system. Therefore, an appropriate choice of the gap makes it possible to bring frequency-selective viscous damping in V-IISs, introducing two advantages over linear systems: the reduction of the peak intensity of the responses in the resonance range (both displacement and acceleration) and the reduction of the static displacement of the system, but keeping the dynamic response with which the system is designed unchanged.

Simulation of large-deformed discontinuity system with translation and rotation by discretized virtual internal bond

Discretized virtual internal bond (DVIB) is an effective mechanical modeling approach of solid material. It introduces no small deformation hypothesis in the constitutive model intrinsically, which leads to more convenience for the simulation of large deformation and large displacement problem, such as the multi deformable bodies system. However, DVIB is still underdeveloped for the simulation of multi discontinuities involved collision and interaction. To model the contact interaction happened among the discontinuous bodies, a key problem is to establish an effective contact characterization scheme in DVIB method. In this paper, the Munjiza’s penalty-based model with no binary search algorithm is introduced into DVIB to simulate the contact of discontinuities with large deformation and large displacement. Using this method, the large rotation and translation of deformable and contactable multi-body system can be straightly modeled without any mesh reconstruction or deformation decomposition. The results of numerical cases suggest the proposed method provides a simple and feasible alternative for the discontinuous deformation analysis of multi-body system.

A Post-Processing Method Based on Radial Basis Functions for the Fast Retrieval of the Strain Field in Digital Image Correlation Methods.

Digital image correlation methods allow the determination of the displacement (and thus the strain) field of a target by picture comparisons, without the application of strain gauges or other invasive devices. Homologous sites are mapped from the undeformed to the deformed configuration, and displacements retrieved at a cloud of points in a scattered fashion. Radial basis functions (RBF) offer a rapid and reliable tool to post-process on-the-fly data from image correlation, in order to compute deformations directly without the need for generating a numerical grid over the measurement points. Displacements and associated strains can be computed only where desired, tracking automatically only the most reliable features for each image. In this work, a post-processing strain evaluation method for large displacement problems, based on RBF and the Green-Lagrange tensor, is presented and demonstrated for several test cases. At first, the proposed method is adopted on a set of artificially generated pictures, demonstrating a faster convergence with respect to FEM even when few points are used. Finally, the approach is applied to cases for which experimental results are available in the literature, exhibiting a good agreement.

Dynamic modeling of a fish tail actuated by IPMC actuator based on the absolute nodal coordinate formulation

Ionic polymer metal composite (IPMC) is a smart material with low driving voltage, high energy conversion, light weight and simple structure. It is suitable for driving the tail fin of small bionic fish. Actuators made of this material are quite flexible, and they are laborious to accurately describe the complex deformation of structures. Absolute nodal coordinate formulation (ANCF) has great merits in describing large deformation and large displacement problems. In this paper, the feasibility of ANCF in dynamic modeling of a fish tail actuated by IPMC actuator will be explored for the first time. The tail fin is simplified into two forms: a pure flexible IPMC beam and a hybrid beam that consists of an IPMC beam and a fixed rigid beam. The ANCF one-dimensional two-node beam element is adopted. Considering the influence of deformation curvature, the exact expression of generalized elastic force is obtained. The proposed dynamic model can describe the large deformation problem of the flexible beam. The dynamic responses of the pure IPMC beam tail fin and the hybrid tail fin driven by square wave voltage are calculated. The displacement changes of end nodes are compared, and the swing law under different driving voltage amplitude, frequency, and fluid resistance is analyzed. It is found that the driving efficiency of IPMC can be improved by increasing the driving voltage amplitude, reducing the voltage frequency, and reducing the fluid resistance in a certain range. This research would be beneficial to the study of the large swing motion mechanism of bionic robotic fish.

Construction of a Prediction Model for Distance Education Quality Assessment Based on Convolutional Neural Network.

This paper introduces the principles and operation steps of convolution and pooling of convolutional neural networks in detail. In view of the shortcomings of fixed sampling points and single receptive field in traditional convolution and pooling forms, deformable convolution and deformable pooling are introduced to enhance the network's ability to adapt to image details and large displacement problems. The concepts of warp, loop optimization, and network stack are introduced. In order to improve the optimization performance of the algorithm, three subnetwork structures and stack models are designed, and various methods are used to improve the prediction accuracy of distance education quality assessment. In order to improve the accuracy and timeliness of education quality assessment, this paper proposes a distance education quality assessment model based on mining algorithms. The prediction index is selected by the improved BP neural network. It is required to establish the input layer node as the input vector based on the number of data sources since the input layer is used for data input. The neural network is trained with a quarter of the mining data, and the mining algorithm is further trained with network error trials. A fuzzy relationship matrix is created based on the assessment of teaching quality's hierarchical structure. This leads to the conclusion of the fuzzy thorough evaluation of the effectiveness of distant learning. Experiments show that the proposed model has an average accuracy of 96%, the average teaching quality modeling time is 25.44 ms, and the evaluation speed is fast.

Geotechnical particle finite element method for modeling of soil-structure interaction under large deformation conditions

The possibilities of the particle finite element method (PFEM) for modeling geotechnical problems are increasingly evident. PFEM is a numerical approach to solve large displacement and large strain continuum problems that are beyond the capabilities of classical finite element method (FEM). In PFEM, the computational domain is reconfigured for optimal solution by frequent remeshing and boundary updating. PFEM inherits many concepts, such as a Lagrangian description of continuum, from classic geomechanical FEM. This familiarity with more popular numerical methods facilitates learning and application. This work focuses on G-PFEM, a code specifically developed for the use of PFEM in geotechnical problems. The article has two purposes. The first is to give the reader an overview of the capabilities and main features of the current version of the G-PFEM and the second is to illustrate some of the newer developments of the code. G-PFEM can solve coupled hydro-mechanical static and dynamic problems involving the interaction of solid and/or deformable bodies. Realistic constitutive models for geomaterials are available, including features, such as structure and destructuration, which result in brittle response. The solutions are robust, solidly underpinned by numerical technology including mixed-field formulations, robust and mesh-independent integration of elastoplastic constitutive models and a rigorous and flexible treatment of contact interactions. The novel features presented in this work include the contact domain technique, a natural way to capture contact interactions and impose contact constraints between different continuum bodies, as well as a new simplified formulation for dynamic impact problems. The code performance is showcased by the simulation of several soil-structure interaction problems selected to highlight the novel code features: a rigid footing insertion in soft rock, pipeline insertion and subsequent lateral displacement on over-consolidated clay, screw-pile pull-out and the dynamic impact of a free-falling spherical penetrometer into clay.

The effect of the presence of obstacles on the dynamic response of single-degree-of-freedom systems: Study of the scenarios aimed at vibration control

In this paper, the effect of the presence of (existing or newly added) deformable and dissipative obstacles (bumpers) on the nonlinear dynamic response of a single-degree-of-freedom system, is investigated via parametric numerical analyses. Through the study of possible response scenarios which can occur by varying the bumpers’ parameters (i.e., the position, the stiffness, and the damping, respectively) it is observed that the presence of the bumpers is not always unfavorable compared to the free flight condition. By properly selecting the bumpers’ parameters it is possible to exploit the occurrence of impacts with beneficial effects. Furthermore, a relationship between the stiffness and the damping parameters of the bumpers, which allows to minimize the maximum value of the mass acceleration in primary resonance condition, is identified and discussed. Although this study is inspired by the practical problem of large horizontal displacements in base-isolated structures, it has a transversal nature with respect to different disciplinary fields. Consequently, the results obtained in this work can be extended also to further applications related to vibro-impact dynamics.

On Some Errors in Seismic Data in Highly-Cited Literature on Base Isolation

Several errors have been found in information and data of seismic records in academically published work. These inaccuracies involve use of vertical instead of horizontal signals, wrong peak velocities and peak accelerations. The mistakes were encountered in top cited publications regarding near-fault effects and the large base displacement problem in isolated structures. A reason for these errors is suggested.

Inerter-added transmissibility to control base displacement in isolated structures

A solution to the large base displacement problem in isolated structures under seismic loads is proposed; it is based on a displacement transmissibility formulation that includes the inerter device. The solution is also based on a novel spectral characterization of ground displacement; it should be clear that if the problem is displacement, the focus must be on displacements, both, as the excitation: ground displacement (rather than acceleration which is the norm) and as isolator displacement, through a transmissibility that relates both input and output displacements, all of which is a new approach. The proposal can serve as a passive-control design procedure, either under near-field or far-field conditions, when an inerter at the base level is chosen to solve the large isolator displacement problem. An isolated structural model commonly used in the subject literature is employed to show that the base displacement level can be reduced to under the ground displacement level, which implies a positive comparison with previous passive and active control solutions, including inerter solutions; in fact, the design aim is a competitive 0.95 ratio for both displacements.

A new approach to inertial damper design to control base displacement in isolated buildings

A novel design procedure for tuned mass dampers in isolated structures is presented. The proposed optimization method is specifically developed to control base displacements or to solve the large isolator displacement problem in this type of structures under earthquakes. Therefore, it is based on a displacement transmissibility function, T, a particular case of the general transmissibility concept, which comes from Vibration Isolation. Three contributions are: 1) application of new seismic displacement narrowbandness, 2) simpler relative transmissibility function, and 3) compound design of isolation plus tuned mass damper. A standard isolated model is used to show that the base displacement can be controlled at levels in the proximity of the ground motion (T ≈ 1), which results in a positive comparison with previous isolation plus tuned mass damper solutions; this is one of the main conclusions and it is based on novelty 3 above; in fact, other solutions in the literature compare their attained displacements with respect to the structure without tuned mass damper. Comparison with isolated results is not, therefore, possible herein, but it is not desirable either; actually, what is possible is a positive and more demanding comparison, which is with respect to the very seismic ground displacement itself. The large isolator displacement problem can be solved or attenuated by properly designing a tuned mass damper subsystem jointly with the isolation one.

Flexural buckling and second-order analysis of pre-stressed steel beams with un-bonded/bonded deviators

In-plane bucking and nonlinear elastic theories of PS (Pre-stressed) beams subject to not only compression induced by a tendon cable but also to external forces are newly formulated. The system consists of a simply supported/cantilever steel beam, a straight cable with constant eccentricity, anchorages, and multiple deviators. In particular, the effects of having either un-bonded or bonded deviators on the elastic buckling and nonlinear behavior of the PS beam are rigorously investigated. To achieve this, buckling and second-order analysis theories of PS systems with no deviator, one deviator, and multiple deviators are derived in non-dimensional form. In addition, stability and large displacement problems of the simple/cantilever beam system are analytically solved while considering the effect of deviators. In order to verify the validity of the proposed theories, numerical examples for PS systems are given and the results compared with FE analysis results from ABAQUS models. The results show that deviators restrain flexural deformation of beams that have buckled under the initial tension very strongly so that the system’s buckling strength is greatly improved. Particularly, it is found that the critical buckling loads of simple and cantilever PS systems due to initial tension are equal when the number of deviators is identical.

Narrowbandness of seismic ground displacement on a broader area of the lithosphere and importance on base motion in isolated structures

Power spectral density of horizontal ground displacement of large and recent events in earthquake-prone Latin America is analyzed. The results confirm -in a larger region of the world- that strong motion horizontal displacement is a narrowband process, which was previously demonstrated solely on a very limited area: the State of California. Nonetheless, those limited and previous results proved to be important in seismic base isolation; particularly, in the solution of the problem of large displacements at the structure base. This is a current problem for which more expensive techniques than passive control are presently being implemented, as active or hybrid control; therefore, it is emphasized that a solution exists within simple base isolation, and it is based on ground displacement narrowbandness.

Developing the composed coefficient technique for analyzing laterally loaded barrettes

Extreme heavy-loaded structures cause massive axial and lateral loads, which need a special system of foundations to transmit these loads into the surrounding soils. Many structural problems, for these structures, arise mainly from large soil displacements. Barrette foundations can be a major solution for avoiding large soil displacement problems. Because it is large dimensions compared to piles, it reduces considerably displacements especially if the underlying layers contain weak soil. Barrette foundations already used in many foundation systems as in Entisar Tower and Creek Tower in Dubai and the Petronas Towers in Kuala Lumpur. In this paper, the composed coefficient technique (CCT) is further developed to be applicable for analyzing laterally loaded single barrettes. The technique accounts for the three-dimensional full interaction between the barrette and the surrounding soil. In the technique, the three-dimensional coefficients of the stiffness matrix of the barrette are decomposed to be one-dimensional. This enables easily adding these coefficients to those of the stiffness matrix of the soil. A series of validations is carried out to verify the application of the developed CCT. It is found that modeling the barrette by CCT gives approximately the same results when compared with three-dimensional finite element results. In addition, comparative studies of laterally loaded single barrettes in a real subsoil are modeled, in which East Port Said soil properties and stratification are considered, which is similar to soil formations around the world such as London, Frankfurt, Rome and Dammam. Different methods for determining the effective barrette height are discussed, and guidelines for engineers when analyzing laterally loaded single barrettes in East Port Said area are present. The proposed technique is implemented in the program ELPLA.

Weak Point Analysis of Deepwater DST String in Service

Considering the deepwater test technology, in this study, temperature and pressure loads of deepwater drill-stem tested (DST) string in string deployment, pressure perforation, flowing test, and shut-in well stages are evaluated. In view of the large displacement and contact problem, a mathematical model is established for the deepwater DST string system to assess the weak point based on nonlinear contact theory. The results show that the temperature and internal pressure of DST string are mainly determined by test production in the flowing test stage. The pressure perforation and shut-in well stages are more risky for DST string in water, whereas the string deployment and shut-in well stages are more risky for DST string in downhole. With increasing test production, the stress level of DST string decreases in water and increases in downhole as a whole. Extra attention should be paid to the string units adjacent to the top, lower flex joint, hanger, and packer, which are the strength weak points of deepwater DST string. The weak point assessment method provides powerful support for operation risk management and decision-making of DST string in offshore test process.

Global motion reconstruction of a steel catenary riser under vessel motion

ABSTRACTUnder vessel motion, dynamic responses of compliant risers, like a steel catenary riser, are no longer small displacement and small deformation problems but characterised with large displacement and small deformation instead. It is therefore difficult to directly obtain the riser global motion based on experimental or field-measured local strain or acceleration data. This paper proposes a generalised global motion reconstruction method for large displacement but small deformation problems, assuming that the global motion can be divided into quasi-static motion and dynamic vibration. The proposed methodology is validated numerically and experimentally with satisfactory accuracy. Parameters like sensor location and mode number to be used in the motion reconstruction are optimised and recommended. Uncertainty analysis considering different noise levels is performed to evaluate the robustness of the proposed method. Most importantly, further comparative hydrodynamic analyses indicate the significance of the drag amplification effect, most probably due to vortex-induced vibrations.

Topology optimization of hyperelastic structure based on a directly coupled finite element and element-free Galerkin method

Meshless methods can solve large classes of problems where grid-based methods are awkward to handle, such as the discretizing of complicated structures, the remeshing in large displacement problems and so on. In this study, a meshless-based topology optimization is proposed for large displacement problems of nonlinear hyperelastic structure. In order to circumvent nonlinear numerical instabilities, the linear and nonlinear analyses are set in the low- and high-stiffness region, respectively. Thus, an interpolation scheme is adopted for hybridizing the linearity and nonlinearity in the structure analysis. A directly coupled finite element and meshless method is introduced to reduce the computational cost of meshless methods and an auto-coupling strategy is proposed for the adaptive arrangement of finite element and meshless regions. Several numerical examples are given to demonstrate the effectiveness of the proposed method.

Fluid–structure interaction of downwind sails: a new computational method

The spreading of high computational resources at very low costs led, over the years, to develop new numerical approaches to simulate the fluid surrounding a sail and to investigate the fluid–structure interaction. Most methods have concentrated on upwind sails, due to the difficulty of implementing downwind sailing configurations that present, usually, the problem of massive flow separation and large displacements of the sail under wind load. For these reasons, the problem of simulating the fluid–structure interaction (FSI) on downwind sails is still subject of intensive investigation. In this paper, a new weak coupled procedure between a RANS solver and a FEM one has been implemented to study the FSI problem in downwind sailing configurations. The proposed approach is based on the progressive increasing of the wind velocity until reaching the design speed. In this way, the structural load is also applied progressively, therefore, overcoming typical convergence difficulties due to the non-linearity of the problem. Simulations have been performed on an all-purpose fractional gennaker. The new proposed method has been also compared with a classic weak FSI approach. Comparable results have been obtained in terms of flying shape of the gennaker and fluid-dynamic loads. The most significant characteristic of the proposed procedure is the easiness to find a solution in a very robust way without convergence problem, and also the capability to reduce the simulation time with regard to the computational cost.

Scene Flow Estimation Based on Adaptive Anisotropic Total Variation Flow-Driven Method

Scene flow estimation based on disparity and optical flow is a challenging task. We present a novel method based on adaptive anisotropic total variation flow-driven method for scene flow estimation from a calibrated stereo image sequence. The basic idea is that diffusion of flow field in different directions has different rates, which can be used to calculate total variation and anisotropic diffusion automatically. Brightness consistency and gradient consistency constraint are employed to establish the data term, and adaptive anisotropic flow-driven penalty constraint is employed to establish the smoothness term. Similar to the optical flow estimation, there are also large displacement problems in the estimation of the scene flow, which is solved by introducing a hierarchical computing optimization. The proposed method is verified by using the synthetic dataset and the real scene image sequences. The experimental results show the effectiveness of the proposed algorithm.

A recursive formulation based on corotational frame for flexible planar beams with large displacement

A forward recursive formulation based on corotational frame is proposed for flexible planar beams with large displacement. The traditional recursive formulation has been successfully used for flexible mutibody dynamics to improve the computational efficiency based on floating frame, in which the assumption of small strain and deflection is adopted. The proposed recursive formulation could be used for large displacement problems based on the corotational frame. It means that the recursive scheme is used not only for adjacent bodies but also for adjacent beam elements. The nodal relative rotation coordinates of the planar beam are used to obtain equations with minimal generalized coordinates in present formulation. The proposed formulation is different from absolute nodal coordinate formulation and the geometrically exact beam formulation in which the absolute coordinates are used. The recursive scheme and minimal set of dynamic equations lead to a high computational efficiency in numerical integration. Numerical examples are carried out to demonstrate the accuracy and validity of this formulation. For all of the examples, the results of the present formulation are in good agreement with results obtained using commercial software and the published results. Moreover, it is shown that the present formulation is more efficient than the formulation in ANSYS based on GEBF.