Elastic Constraints Research Articles

Effects of spring oscillators on the vibroacoustic properties of porous sandwich plates under elastic constraints

Effects of spring oscillators on the vibroacoustic properties of porous sandwich plates under elastic constraints

USV-Tracker: A novel USV tracking system for surface investigation with limited resources

This paper introduces USV-Tracker, a novel tracking system for Unmanned Surface Vehicles (USVs) tailored for practical applications such as surface investigation and target tracking. The system tackles three pivotal challenges: perception robustness, tracking concealment, and planning efficiency. The contributions of this work are manifold: (1) A multi-sensor fusion framework utilizing an Extended Kalman Filter (EKF) to enhance target detection and positioning accuracy, integrating data from cameras, LiDAR, GPS, and IMU sensors. (2) A two-stage path planning algorithm that generates occlusion avoidance trajectories and employs a virtual elastic force constraint to maintain appropriate relative positioning. In dense obstacle environments, the algorithm tends to get closer to the target and incorporates FOV orientation constraints to ensure stable perception. (3) A visibility-aware control strategy that ensures continuous target observability through EKF-based trajectory prediction. Simulations in Gazebo and corresponding physical experiments validate the system’s effectiveness and robustness, demonstrating its applicability in real-world scenarios. The computational workload is managed on a constrained on-board computer, underscoring the system’s practicality.

A data-driven dynamic method of downhole rock characterisation for the vibro-impact drilling system

For the real-time characterisation of an inhomogeneous impact inhibiting constraint such as downhole rock layers, an unconventional method using machine learning (ML) and drill-bit vibrations is investigated. An impact oscillator with one-sided elastic constraint is employed in modelling the bit-rock impact actions. Measurable drill-bit dynamics, such as acceleration, were acquired and processed into features and 2D-images that were later used in developing ML models capable of predicting the stiffness of impacted rock constraint. Explored ML networks include Multilayer Perceptron (MLP), Convolutional Neural Network and Long Short-Term Memory Network. Both simulation and experimental studies have been presented to validate the proposed method while using coefficient of determination (R2) and normalised mean absolute error (NMAE) as the performance metrics of the ML models. Results showed that the feature-based models had better performances for both simulation and experiment compared to the raw signal and 2D-image based models. Aside being simple and computationally less expensive, the feature-based MLP models outperformed other models having R2 values > 0.7 and NMAE values < 0.2 for both simulation and experiment, thus presenting them as the preferred ML model for dynamic downhole rock characterisation. In general, this study presents a new modality to achieving logging-while-drilling during deep-hole drilling operations such as carried out in hydrocarbon, mineral and geothermal exploration.

An isogeometric approach for nonlocal bending and free oscillation of magneto-electro-elastic functionally graded nanobeam with elastic constraints

An isogeometric approach for nonlocal bending and free oscillation of magneto-electro-elastic functionally graded nanobeam with elastic constraints

Rational Polynomial Coefficient Estimation via Adaptive Sparse PCA-Based Method

The Rational Function Model (RFM) is composed of numerous highly correlated Rational Polynomial Coefficients (RPCs), establishing a mathematical relationship between two-dimensional images and three-dimensional spatial coordinates. Due to the existence of ill-posedness and overparameterization, the estimated RPCs are sensitive to any slight perturbations in the observation data, particularly when handling a limited number of Ground Control Points (GCPs). Recently, Principal Component Analysis (PCA) has demonstrated significant performance improvements in the RFM optimization problem. In the PCA-based RFM, each Principal Component (PC) is a linear combination of all variables in the design matrix. However, some original variables are noise related and have very small or almost zero contributions to the construction of PCs, which leads to the overparameterization problem and makes the RPC estimation process ill posed. To address this problem, in this paper, we propose an Adaptive Sparse Principal Component Analysis-based RFM method (ASPCA-RFM) for RPC estimation. In this method, the Elastic Net sparsity constraint is introduced to ensure that each PC contains only a small number of original variables, which automatically eliminates unnecessary variables during PC computation. Since the optimal regularization parameters of the Elastic Net vary significantly in different scenarios, an adaptive regularization parameter approach is proposed to dynamically adjust the regularization parameters according to the explained variance of PCs and degrees of freedom. By adopting the proposed method, the noise and error in the design matrix can be reduced, and the ill-posedness and overparameterization of the RPC estimation can be significantly mitigated. Additionally, we conduct extensive experiments to validate the effectiveness of our method. Compared to existing state-of-the-art methods, the proposed method yields markedly improved or competitive performance.

Omnidirectional elastic constraint-based embedded 3D printing in non-yield stress fluids for engineering complex tissues

Embedded 3D printing, relying on yield-stress fluid-based supporting baths, has significantly expanded our ability to create complex tissues and organs. However, many extracellular matrix-based hydrogels, despite their excellent biological performance, such as gelatin and hyaluronic acid (HA) hydrogels, lack yield-stress properties, limiting their use in embedded 3D printing and hindering functional maturation of complex tissue constructs. To address this challenge, we present a method for embedded printing in non-yield stress fluids using sequential printing in a reversible ink template (SPIRIT) strategy. By leveraging an omnidirectional elastic constraint provided by conventional supporting baths, we can precisely fabricate GelMA and HAMA hydrogels into functional tissue constructs with both intricate external structures and internal vessel systems, which cannot be achieved with extant embedded printing techniques. As a proof of concept, we successfully printed a complex ventricle model with high cell density and internal channels using GelMA hydrogel, which demonstrated high cell viability and synchronous beating performance. The omnidirectional elastic constraint-based SPIRIT technique holds promise for advancing organ printing with remarkable structural complexities and biomaterials affinity akin to natural tissue constructs by decoupling from yield-stress fluids.

Contribution of hall and ion slip effects with generalized mass and heat fluxes with entropy analysis on three-dimensional Prandtl model

A major challenging proffered study rely on the inquisitive optimization of entropy together with thermal as well as mass transportation towards the chemically reactive 3-D Prandtl liquid under consideration of applied magnetic field, variable thermal conductivity and also diffusivity, hall current together with ion slip features, viscous dissipation and heat generation. Moreover, in present research study, model such as Cattaneo Christov heat flux was implemented in order to explore the thermal relaxation characteristics. By employing correspondence transformations, the system of modeled equations modified into non-linear ODEs system. The Optimal Homotopy Analysis methodology (OHAM) was adopted to solve the proffered problem. The influential arising constraints demeanor within both velocities (horizontal as well as vertical), temperature and concentration profiles were discussed and also shown graphically. Moreover, outcomes of diverse parameters were also examined and presented graphically within the entropy formation rate and also Bejan number. The effects of implanted factors across the drag force, the rate of thermal as well as mass transportation are accessible in current study via tables and validate the obtained results. Both velocity profiles (horizontal as well as vertical) decreased for increment in Hartman number whilst opposite demeanor seen for other considered constraints. Temperature profile drops for Prandtl number and elastic constraints whereas enhanced for other influential considered parameters whilst concentration profile augmented with Prandtl number. Present problem novelty relies on the modeling of comprehensive system of equations which modified into nonlinear ODEs. In order to obtain the solution numerically, technique such as Optimal Homotopy was opted.

Unraveling Urban Retail Realities: Assessing Revenue Shifts and Policy Effects in Seoul, South Korea, Pre- and During the COVID-19 Pandemic

The post-2020 revenue trends in Seoul’s retail areas, influenced by government policies to curb the epidemic, exhibit diverse impacts across regions. Progressing through three stages—imposing gathering restrictions, easing business limits with reinforced movement constraints, and relaxing epidemic control—the measures, while uniformly applied, yield varied effects based on retail area characteristics. Using Dynamic Time Warping Clustering, this study assessed 1637 Seoul retail areas over 45 months, categorizing revenue changes into highly grown, grown, recovered, and stagnated types. Areas with increased pre-pandemic revenue displayed lower F&B sector proportions, higher sales/experiential sector proportions, and increased spending by 30s/corporate entities. These areas were characterized by lower-income residents and reduced accessibility to public facilities. Conversely, areas with high 20s consumption, lower corporate demand, and proximity to crowd-pulling facilities exhibited lower revenue recovery resilience. The study emphasizes the need for effective urban spatial management to facilitate the recovery of elastic retail area amid mobility and interaction constraints, advocating for fine-tuned measures to minimize pandemic-induced economic impacts on urban retail areas.

A full-field structural displacement reconstruction method for large-scale floating rafts in marine propulsion systems

Large-scale floating rafts have been widely applied to marine propulsion. Due to the presence of elastic supports, it belongs to the elastic constraints rather than the fixed constraints found in aerospace and bridge structures. This leads to displacement is no longer just elastic deformation, but also includes some rigid-body displacement. However, the existing displacement reconstruction methods are all based on fixed constraints. To address this issue, an improved modal method (IMM) is proposed. The boundary conditions are extended from fixed constraints to elastic constraints and the displacement field is uniformly described. Firstly, by analyzing the modal characteristics of three types of constraints, the reasons for the failure of the current modal method under elastic constraints are presented. Secondly, the IMM is established based on a dimensionless error function between the discrete strain, finite displacement measurements, and their theoretical values. Finally, the feasibility of the IMM is verified by numerical analysis and experiment tests on an elastic support plate structure with high precision and excellent suitability. This method can be applied to the full-filled displacement reconstruction in large-scale floating rafts of marine propulsion systems, which provides significant engineering value for improving the shafting alignment and the raft attitude balance.

Towing an Object With a Rover

Abstract The present study investigates the problem of towing an object that is lying on a surface in a given workspace and the applicability to a planetary rover with four steering wheels. A quasi-static method has been introduced and used for path planning and for the synthesis of both object and rover trajectories. The rover uses a tether as the towing medium which is modeled as an elastic unilateral constraint. Moreover, a kinematic model of the rover which includes steering asymmetrical joint limits is taken into account. The dynamics model of the overall system is then derived and a sensitivity analysis is performed over a finite number of different trajectories, in order to evaluate the quasi-static assumption, the effects of the model, and the influence of the elastic constraint. Finally, experiments have been performed using the novel Archimede rover prototype and compared with dynamics simulations; the remarkable adherence shown with the model validates the overall approach.

Vibration Response of Metal Plate and Shell Structure under Multi-Source Excitation with Welding and Bolt Connection

There are many excitation sources and complex vibration environments in combine harvesters. The coupling and superposition of different vibration signals on the plate and shell seriously affect the working parts of the body. This also reduces the reliability of the whole machine. At present, domestic and foreign research on existing harvesters mainly focuses on harvesting performance, with less research on vibration characteristics. Therefore, in this paper, the vibration response of the metal plate–shell under the two connection modes of bolt connection and welding is studied, in order to optimize the design and structure of the plate–shell structure of the combine harvester and improve the overall performance. First, the welded and bolted plates are numerically modeled using Hypermesh pre-processing functions. Then, the boundary conditions are simulated by continuous variable stiffness elastic constraint experiments. Finally, the intrinsic vibration dynamic model of the four-sided simply supported plate and four-sided solidly supported plate is established using the modal superposition method. By analyzing the modal frequencies and vibration patterns, the following results are obtained. The connection method between the plate and the frame has a significant impact on the inherent vibration characteristics of the plate. The bolt connection will make the plate’s intrinsic vibration frequency higher than that of the welding method, but the effect on the plate’s intrinsic vibration pattern is more minor. At the same time, in order to verify the accuracy of the model, the actual modal vibration patterns and frequencies of the same proportion of plates in the modal test are compared with the results of modal vibration patterns and frequencies obtained by Ansys. The errors of the two dynamic model analytical methods are within 1% and 3%, respectively. This result verifies the accuracy of the dynamic model of the metal plate and shell structure under different connection methods.

Linear and nonlinear vibrations of nonlinearly elastically constrained functionally graded porous microbeams with rough surface

Linear and nonlinear free vibrations of nonlinearly elastically constrained functionally graded porous (FGP) microbeams with rough surface are analytically studied in this paper via the modified couple stress theory. A surface roughness model of the FGP microbeams is developed. The material properties including porous property are supposed to continuously vary along the thickness direction. The higher-order nonlinear governing equation and elastic boundary conditions are derived through the Hamilton principle. A closed-form solution for linear frequency and mode shape is presented. Subsequently, an analytical solution for nonlinear frequency is achieved by employing the Galerkin procedure. Finally, the effects of surface roughness, size parameter, power-law index, porosity volume fraction, and nonlinearly elastic constraints on the linear and nonlinear vibrations of functionally graded porous microbeams are examined.

Buckling mechanism and modified direct strength method of CFS built-up beams with multi-box cross section

A comprehensive study on the buckling mechanism of the Cold-Formed Steel (CFS) box beam composed of C- and U-shaped channels is conducted in order to improve the accuracy of the Direct Strength Method for calculating the bending capacity of CFS beams. Experimental tests involving four-point bending are carried out on six CFS box beams with varying screw spacing and stiffener numbers. In addition, numerical analyses are performed by finite element method. Based on the investigation of experiments and parameter analysis, an elastic constraint model for web buckling is proposed and the buckling coefficient are derived by the application of a generalized variational principle. The experiments reveal an interaction between local buckling in the upper flange under compression and the web. When the upper flange in compression buckles before the web, it leads to a reduction in the lateral constraint stiffness of the flange on the web, consequently, resulting in web buckling. An elastic constraint model for web buckling is proposed, incorporating the constraint effects of the upper flange's elastic support on the web. The critical buckling stress and buckling coefficient of the model are derived using the generalized variational principle. According to the experimental and numerical analysis results, the relative restraint stiffness of the flange on the web shows effects on the buckling coefficient. As the screw spacing and the length of the pure bending area decrease, as well as the number of stiffeners increases, the relative restraint stiffness increases. Subsequently, this leads to an increase in the buckling load and ultimate displacement of the CFS beam. Considering the interaction between the buckling of flange and web, the Direct Strength Method in AISI-2016 is modified for the CFS built-up box beam composed of C- and U-shaped channels. The applicability and correctness of the proposed modified Direct Strength Method is approved through the application of multi-box CFS beams composed of 2C-2 U and 3C–2 U channels. Compared with the Effective Width Method in current Chinese code and Direct Strength Method in AISI-2016, the proposed modified DSM exhibits the highest accuracy in predicting the bending capacity of the CFS box beam. It is shown that the proposed method can be effectively employed to calculate the flexural capacity of CFS beams with multi-box under local buckling control.

Tuning Topology Phases by Controlling Effective Screening and Depolarization in Oxide Superlattices.

Polar topological phases in oxide superlattices attracted significant attention due to their unique properties. Previous work revealed that a polar vortex and polar skyrmions exist in (PTO)/(STO) superlattices under different elastic constraints, i.e., on different substrates. Here, our phase-field simulation demonstrates that manipulating the PTO and STO layers' thickness can control the effective screening provided by STO and the depolarization degree in PTO, thus switching the system among the polar skyrmions, vortex labyrinth, or paraelectric phase without changing elastic constraints. Additionally, reducing the STO thickness creates interlayer coupling among PTO layers, generating the long-range order of topological phases within superlattices. Furthermore, we construct a PTO-STO thickness topological phase diagram. These findings offer insights into the polar topological phases' formation in oxide superlattices, elucidating the roles of ferroelectric and paraelectric layers in their formation.

Effect of spatial setting angle on vibration of elastically restrained rotating beams

For a fully articulated rotor system, there may exist a spatial setting angle and elastically restrained root for each individual blade in rotation procedure due to flapping, drag and pitch hinges. Most of previous studies on rotating blades or beams focused on pitch angle and clamped root. In this paper, a three-dimensional dynamic model is proposed for elastically restrained rotating beams with spatial setting angle. The elastic deformation of the beam is expressed by three scalar variables in three-dimensional space including stretch deformation instead of the conventional axial deformation. The longitudinal shrinkage is considered to capture centrifugal forces. The penalty method is adopted to deal with the elastic constraints, which greatly simplifies the construction of admissible functions. A unified formulation is derived by a variational principle combined with Chebyshev orthogonal polynomials. One of the advantages of the present method is that any linearly independent and complete basis functions can be used as admissible function regardless of boundary conditions, and another advantage is that the present method is capable of handling arbitrary boundary conditions by only adjusting the values of penalty factor. The convergence and accuracy of the present method are validated by comparison, and the effects of boundary conditions, angular velocity and spatial setting angle on vibration characteristics are discussed in detail. The results show that natural frequencies increase as the spring stiffness rises in a certain range and the spatial setting angle plays a more significant role on dynamic characteristics for rotating beams.

Multi-Domain Collaborative Task Allocation and Conflict Resolution in Unmanned Systems under Complex Constraints

Under the background that multi-domain collaborative tasks with complex constraints executed by heterogeneous unmanned systems, based on a consensus-based bundle algorithm, a consensus-based synergy algorithm is proposed to solve the distributed multi-domain collaborative task planning problem. First, a multi-domain collaborative task allocation model and score evaluation system are established by considering task resource requirement constraints, task timing constraints, and path threat constraints. Second, the time sequence constraints of collaborative tasks are transformed into elastic time window constraints. The bidding method based on collaborative constraints is used for task allocation, and the improved consistency conflict resolution principle is adopted to realize distributed multi-domain collaborative task allocation conflict resolution. Finally, the path planning is coupled to the task allocation process by using the Bezier curve path, and the results of multi-domain collaborative task allocation and path planning are obtained synchronously. Simulation results show that the proposed algorithm can effectively solve the problem of multi-domain collaborative task planning for heterogeneous unmanned systems.

Semi-analytical solutions for forced and free vibration of damped fluid-conveying pipe systems based on complex modal superposition method

In this paper, the response solutions of the damped fluid-conveying pipe system with elastic torsion constraints at both ends are analyzed. The pipe system considering gyroscopic effect induced by internal flow and damping effect is a typical damped gyroscopic system. This system cannot be decoupled in the modal space by the traditional modal analysis, and then the semi-analytical response solutions cannot be obtained by the classical modal superposition method. In order to remedy this problem, this paper proposes a new method based on complex modal superposition method and state-space method to give the semi-analytical response solutions of the damped fluid-conveying pipe system. The adjoint system is introduced through the concept of adjoint operator, and the orthogonality conditions of the damped fluid-conveying pipe system are derived in the state-space by using the eigenvalue relationship between the original system and the adjoint system. The Laplace transformation method is used to solve the eigenvalue problems of the original system and the adjoint system, and the implicit function equations about the eigenvalues and analytical eigenfunctions are obtained. According to the obtained orthogonality conditions, the semi-analytical response solutions of the system under arbitrary initial conditions and excitations are given, and the obtained solutions include transient and steady-state response solutions. In the numerical discussion part, the reliability and accuracy of the present method are verified. This research has positive significance for the dynamic analysis of fluid-conveying pipe systems, and the obtained orthogonality conditions have potential value for the nonlinear dynamics research.

Phase transformation in the palladium hydrogen system: Effects of boundary conditions on phase stabilities

Different elastic constraint conditions affect the phase stabilities of metal-hydrogen systems. This is studied considering the free energy density within a chemo-mechanically coupled approach with linear elastic deformations and homogeneous concentrations. Utilizing the palladium-hydrogen alloy as a model system, the effects of various mechanical constraints in 1D, 2D and 3D are investigated. These constraints change occurring mechanical deformations and strongly influence the systems chemical potential compared to the unconstrained system. With increasing dimensionality of the constraints, large compressive mechanical stresses occur, which destabilize the hydride phase. This yields a reduced critical temperature of hydride formation. Spinodal and equilibrium miscibility gaps of the system are deduced as a function of the boundary conditions. Notably, the critical temperature of the ideal palladium-hydrogen system with 2D constraints is predicted to be ▪, revealing a driving force for hydride formation at room temperature even under these constraints.

Dynamic modeling and vibration characteristics of sandwich cylindrical shell with metal-rubber core

This work aims to identify ways for the equivalent material parameters of metal-rubber (MR), as well as the establishment of theoretical and numerical methods for sandwich cylindrical shells with metal-rubber core (SCS-MR) under thermal conditions. To achieve this goal, the first-order shear deformation theory and Hamiltonian principle are used to derive equations and expressions that consider temperature variations and elastic boundary constraints. This leads to the development of a novel dynamic model for sandwich cylindrical shell structures in a thermal environment. Furthermore, the study analyzes how vibration frequencies are affected by boundary spring stiffness and axial truncation number of displacement-permitted functions using the Jacobi-Ritz method. The impact of aspect ratio, core layer thickness ratio, and temperature on the vibration frequencies of SCS-MR is discussed. The results indicate that temperature slightly affects the frequency of SCS-MR. As the aspect ratio increases, the vibration frequency tends to decrease, irrespective of the circumferential wave number. However, the circumferential wave number plays a considerable role on vibration frequency associated with the core layer thickness ratio.

Modelling cell shape in 3D structured environments: A quantitative comparison with experiments.

Cell shape plays a fundamental role in many biological processes, including adhesion, migration, division and development, but it is not clear which shape model best predicts three-dimensional cell shape in structured environments. Here, we compare different modelling approaches with experimental data. The shapes of single mesenchymal cells cultured in custom-made 3D scaffolds were compared by a Fourier method with surfaces that minimize area under the given adhesion and volume constraints. For the minimized surface model, we found marked differences to the experimentally observed cell shapes, which necessitated the use of more advanced shape models. We used different variants of the cellular Potts model, which effectively includes both surface and bulk contributions. The simulations revealed that the Hamiltonian with linear area energy outperformed the elastic area constraint in accurately modelling the 3D shapes of cells in structured environments. Explicit modelling the nucleus did not improve the accuracy of the simulated cell shapes. Overall, our work identifies effective methods for accurately modelling cellular shapes in complex environments.