Spring Constraints Research Articles

Spring-reinforced pneumatic actuator and soft robotic applications

Abstract Compared to rigid-structure robots, soft robots possess higher degrees of freedom and stronger environmental adaptability, which has aroused increasing attention in the robotic field. Among them, soft pneumatic robots have excellent performances in various practical applications. However, the nonlinearity and instability of pressure response of soft actuators caused by lateral expansion come to a great challenge. To address this problem, we proposed to embed a spring constraint layer around each single air chamber. Following the design concept, we obtained single-cavity and multi-DoF pneumatic actuators and evaluated their elongation and bending characteristics. Experimental results demonstrated that our proposed actuators have more linear pressure response as well as higher consistency. Eventually, through robotic applications, including soft robotic hand and gripper our proposed actuators could facilitate flexible manipulation and elaborate performance.

Stiffness optimization method of locking unit for space manipulator based on plant root adaptive growth theory

Based on plant root adaptive growth theory of monocotyledons, a stiffness optimization method of locking unit for multi-rigid body space manipulator is proposed. The optimization process of locking unit stiffness is transformed into the increase and elimination of spring constraints. The kinematic model of the locking unit is established, and the equivalent method of the locking stiffness of the locking unit is proposed to make the three-dimensional support model of the locking unit correspond to the three-dimensional stiffness of the locking space. According to the proposed optimization method of locking unit and equivalent method of locking stiffness, a parallel optimization method is used to optimize the stiffness of space manipulator locking unit. The stiffness optimized locking system is compared with the conventional locking system, and the higher fundamental frequency of the system is verified by simulation analysis, which proves the effectiveness of the stiffness optimization method of the locking unit.

Physics-Infused Reduced-Order Modeling of Aerothermal Loads for Hypersonic Aerothermoelastic Analysis

This paper presents a novel physics-infused reduced-order modeling (PIROM) methodology for efficient and accurate modeling of nonlinear dynamical systems. The PIROM consists of a physics-based analytical component that represents the known physical processes and a data-driven dynamical component that represents the unknown physical processes. The PIROM is applied to the aerothermal load modeling for hypersonic aerothermoelastic (ATE) analysis and is found to accelerate the ATE simulations by two to three orders of magnitude while maintaining an accuracy comparable to high-fidelity solutions based on computational fluid dynamics. Moreover, the PIROM-based solver is benchmarked against the conventional proper-orthogonal decomposition/kriging surrogate model and is found to significantly outperform the accuracy, generalizability, and sampling efficiency of the latter in a wide range of operating conditions and in the presence of complex structural boundary conditions. Finally, the PIROM-based ATE solver is demonstrated by a parametric study on the effects of boundary conditions and rib supports on the ATE response of a compliant and heat-conducting panel structure. The results not only reveal the dramatic snapthrough behavior with respect to spring constraints of boundary conditions but also demonstrate the potential of the PIROM to facilitate the rapid and accurate design and optimization of multidisciplinary systems such as hypersonic structures.

Resonance frequencies of functionally graded nanocantilevers subjected to nonlinear spring constraint and attached nanoparticle

Resonance frequencies of functionally graded nanocantilevers subjected to nonlinear spring constraint and attached nanoparticle

Rigidity transitions in zero-temperature polygons.

We study geometrical clues of a rigidity transition due to the emergence of a system-spanning state of self-stress in underconstrained systems of individual polygons and spring networks constructed from such polygons. When a polygon with harmonic bond edges and an area spring constraint is subject to an expansive strain, we observe that convexity of the polygon is a necessary condition for such a self-stress. We prove that the cyclic configuration of the polygon is a sufficient condition for the self-stress. This correspondence of geometry and rigidity is akin to the straightening of a one dimensional chain of springs to rigidify it. We predict the onset of the rigidity transition and estimate the transition strain using purely geometrical methods. These findings help determine the rigidity of an area-preserving polygon just by knowing its geometry. Since two-dimensional spring networks can be considered as a network of polygons, we look for similar geometric features in underconstrained spring networks under isotropic expansive strain. We observe that all polygons attain convexity at the rigidity transition such that the fraction of convex, but not cyclic, polygons predicts the onset of the rigidity transition. Acyclic polygons in the network correlate with larger tensions, forming effective force chains.

Acoustic characteristics of a cylindrical shell coupled to an acoustic cavity under complex excitations

In this research, we analyze the acoustic–vibration coupling of liquid-filled cylindrical shells under complex excitations. A calculation model to determine the acoustic characteristics and steady-state response of a cylindrical shell coupled to an acoustic cavity is proposed. The displacement and sound pressure of the cylindrical shell are described by a Chebyshev–Fourier series in three dimensions. The uncertain expansion coefficient is determined with a Rayleigh–Ritz model. The accuracy and convergence of this method are compared with those of the finite element method. The spring constraint is applied to simulate arbitrary boundary parameters. The impact of these parameters on the coupled natural frequency is analyzed. Finally, the steady-state response of a coupled system for various excitation parameters is analyzed.

Size-dependent free vibration of functionally graded beams with a tip nanoparticle and a nonlinear spring constraint via strain gradient theory

In this article, the free vibration of a functionally graded Euler–Bernoulli beam with a tip nanoparticle and a nonlinear/linear spring constraint is presented for the first time using strain gradient theory. It is assumed that there is a nonlinear/linear spring and a nanoparticle at one end of the beam while the other is clamped. The influence of different parameters, such as the material length scale parameter, the mass of the nanoparticle, and the nonlinear/linear spring constant on the natural frequencies, is discussed in detail. The presented benchmark tables can be used as an excellent database to verify approximate or analytical solutions in future works. The presented results can be useful for those designing micro/nano electromechanical devices.

Analysis of Equivalent Flexural Stiffness of Steel–Concrete Composite Beams in Frame Structures

Vertical deflection of a frame beam is an important indicator in the limit-state analysis of frame structures, particularly for steel–concrete composite beams, which are usually designed with large spans and heavy loads. In this study, the equivalent flexural stiffness of composite frame beams is analysed to evaluate their vertical deflection. A theoretical beam model with a spring constraint boundary and varied stiffness segments is established to consider the influence of both the rotation restraint stiffness at the beam ends and the cracked section in the negative moment region, such that the inelastic bending deformation of the composite beams can be elaborately described. By an extensive parametric analysis, a fitting formula for evaluating the equivalent flexural stiffness of the composite beams, including the effects of the rotational constraint and the concrete cracking, is obtained. The validity of the proposed formula is demonstrated by comparing its calculation accuracy with those of existing design formulas for analysing the equivalent flexural stiffness of the composite beam members. Moreover, its utility is further verified by conducting non-linear finite element simulations of structural systems to examine the serviceability limit state and the entire process evolution of beam deflections under vertical loading. Finally, to facilitate the practical application of the proposed formula in engineering design, a simplified method to calculate the deflection of composite beams, which utilises the internal force distribution of elastic analysis, is presented based on the concept of equivalent flexural stiffness.

Static characteristics analysis of three-tower suspension bridges with central buckle using a simplified model

Compared with traditional two-tower suspension bridges, three-tower suspension bridges have to face challenges caused by the mid-tower effect, which requires the stiffness of the mid-tower satisfying two contradictory parameters, the deflection-to-span and the saddle sliding resistance coefficient, simultaneously. Meanwhile, the central buckles are often utilized to reduce the live load deflection and the torsional vibration caused by wind in two-tower suspension bridges. This study proposes an analytical model for predicting the structural responses of three-tower suspension bridges with central buckle under vehicle loads and examines the effect of the central buckle on suppressing the mid-tower effect. The analytical model simplifies the bridge as a series of cables with horizontal spring constraints. The validation analysis based on the structural parameters of the Yingwuzhou Yangtze River Bridge using the nonlinear finite element method demonstrates that the error of the proposed model does not exceed 5%. The parametric investigations show that the central buckle can significantly improve the performance of three-tower suspension bridges by enhancing their stiffness and reducing the unbalanced tension of the main cable on both sides of the mid-tower. Three-tower suspension bridge with central buckle has a much wider feasible mid-tower stiffness range than that of the traditional three-tower suspension bridges, and the critical dead-to-live load ratio for the feasible dimensionless stiffness range has decreased from 6.7 to 4.4.

Identification of Young’s modulus and equivalent spring constraint boundary conditions of the soft tissue with locally observed displacements for endoscopic liver surgery

In endoscopic surgery, the surgical navigation system needs to calculate the deformation of soft tissue by biomechanical model which requires elastic properties and boundary conditions. However, patient-specific elastic parameters and boundary conditions of soft tissue are hard to measure accurately from the preoperative images, especially the boundary conditions will change during the operation due to the ligament cutting. In addition, simple boundary conditions such as fixed constraints and free-force constraints are not physically adequate to simulate the elastic effect of ligaments attached to the liver. In this paper, we present a novel method to identify the Young’s modulus and equivalent spring constraint boundary conditions of a locally observed soft tissue. Based on the spring constraint boundary condition, a two-step inverse algorithm is developed based on the finite element method (FEM) with integration of energy regularized Gauss-Newton (GN) method and -regularized method, which takes external forces and displacements of observable nodes as inputs. A series of numerical simulations and physical hydrogel phantom experiments were conducted. The results of simulation and physical experiments show that the Young’s modulus and equivalent spring constraint boundary conditions identified by the proposed method agree well with their setup true values.

Mechanical Behavior of Buried Pipelines Subjected to Faults

The length of buried pipelines usually extends thousands of meters or more in engineering, and it is difficult to carry out full-scale tests in the laboratory. Therefore, considering the seriousness of pipeline damage and the difficulty of operating tests and other test limitations, it is necessary to develop a reasonable method to simplify the length of the model for a practical lab test. In this research, an equivalent spring model was established to simulate the small deformation section of the pipeline far away from the fault and the effect of fault displacements, pipeline diameters, wall thicknesses, buried depths, soil materials, and spring constraints on the mechanical properties of pipelines was analyzed. Based on the finite element model using ABAQUS software, the results of the shell model with fixed boundary at both ends were compared; in addition, the dynamic effect of pipelines was investigated. The results show that the two-end spring device can better control the size of the test model and enhance the reliability of the test results. The vibration response of the pipeline mainly depends on the inconsistent movement of soil at both ends of the fault. The analysis results show that choosing a larger pipeline diameter, smaller buried depth, noncohesive backfill soil, and spring with a smaller elastic coefficient is beneficial to reduce pipeline strain and resist pipeline deformation. A simplified formula of the axial compressive strain of buried pipelines across oblique-slip fault is obtained.

Influence mechanism of lumped masses on the flutter behavior of structures

It is well known that lumped masses can change the frequency characteristics of the structural system, and aeroelastic flutter happens due to the coalescence of two modes. Therefore, it can be expected to improve the aeroelastic stability by the lumped mass. This paper studies the influence mechanism of the lumped mass on the aeroelastic behaviors of two-dimensional (2D) panels in supersonic airflow, and proposes an axially functionally graded design method using the lumped mass. In this investigation, the finite element method (FEM) is used to formulate the aeroelastic equation of motion for the panels with the lumped mass and spring constraint. For 2D panels with the lumped mass, the local mode coalescence is observed, and the influences of the weight and location of the lumped mass on the flutter stability and their mechanism are analyzed. The optimal ranges for the weight and location of the lumped mass are given out. For 2D panels with the spring constraint, the sudden decrease of the flutter bound due to the mode veering are analyzed, and an effective method to eliminate it by using the lumped mass is proposed. Finally, a structural optimization method based on the axially functionally graded design is proposed.

Nonlinear Dynamics of Cross‐Flow Tubes Subjected to Initial Axial Load and Distributed Impacting Constraints

The dynamics of cross‐flow tubes were studied in consideration of initial axial load and distributed impacting constraints, modeled as cubic and trilinear spring constraints. The tubes were modeled as Euler–Bernoulli beams and supported at both ends, including the simply supported tube and clamped‐clamped tube. The analytical model involves a time‐delayed displacement term induced by the cross flow based on the quasi‐steady theory. For simplicity, a single flexible supported beam in a rigid square array of cylinders was studied by using the damping‐controlled mechanism. The mean extension of the tube was considered, and thus, it added another nonlinear term in the equation of motion. Results show that the tube loses stability by buckling and fluttering at various initial pressure loads and cross‐flow velocities. An increase was observed for critical velocities and initial pressure loads. Chaotic oscillations were observed for the trilinear spring model. The distribution of the impacting forces was also calculated. Some of the fresh results obtained in the impact system are expected to be helpful in understanding and controlling the dynamic responses of fluid‐conveying pipes.

Development of a specimen-specific in vitro pre-clinical simulation model of the human cadaveric knee with appropriate soft tissue constraints.

A human cadaveric specimen-specific knee model with appropriate soft tissue constraints was developed to appropriately simulate the biomechanical environment in the human knee, in order to pre-clinically evaluate the biomechanical and tribological performance of soft tissue interventions. Four human cadaveric knees were studied in a natural knee simulator under force control conditions in the anterior posterior (AP) and tibial rotation (TR) axes, using virtual springs to replicate the function of soft tissues. The most appropriate spring constraints for each knee were determined by comparing the kinematic outputs in terms of AP displacement and TR angle of the human knee with all the soft tissues intact, to the same knee with all the soft tissues resected and replaced with virtual spring constraints (spring rate and free length/degree). The virtual spring conditions that showed the least difference in the AP displacement and TR angle outputs compared to the intact knee were considered to be the most appropriate spring conditions for each knee. The resulting AP displacement and TR angle profiles under the appropriate virtual spring conditions all showed similar shapes to the individual intact knee for each donor. This indicated that the application of the combination of virtual AP and TR springs with appropriate free lengths/degrees was successful in simulating the natural human knee soft tissue function. Each human knee joint had different kinematics as a result of variations in anatomy and soft tissue laxity. The most appropriate AP spring rate for the four human knees varied from 20 to 55 N/mm and the TR spring rate varied from 0.3 to 1.0 Nm/°. Consequently, the most appropriate spring condition for each knee was unique and required specific combinations of spring rate and free length/degree in each of the two axes.

Welding Deformation of Unequal Thickness Tailor Welded Blanks under Multiple Factors

With the popularity of lightweight requirements, the application of tailor welded blanks with unequal thickness is increasing gradually. The welding deformation of tailor welded blanks with unequal thickness inclined weld is affected by the external constraints and the internal structural parameters of the plates. In this paper, the effect of the external constraints and the internal structural parameters on the multi-layer and multi-pass welding deformation of unequal thickness inclined weld was investigated. The deformation distribution law of butt welding of unequal thickness inclined weld was obtained combined with simulation and experiment results. The results showed that the spring constraint method was similar to the actual welding condition, meanwhile, the control effect of spring constraint on the welding deformation was better. The welding gap had the greatest influence on the welding deformation, followed by the angle of inclined weld, thickness of thick plate and thickness of thin plate. When the thickness difference between two plates was kept at 50%, the control effect of welding deformation was the best.

Numerical Investigation of Vortex Induced Vibration for Submerged Floating Tunnel under Different Reynolds Numbers

A 2D numerical model was established to investigate vortex induced vibration (VIV) for submerged floating tunnel (SFT) by solving incompressible viscous Reynolds average Navier-Stokes equations in the frame of Abitrary Lagrangian Eulerian (ALE). The numerical model was closed by solving SST k-ω turbulence model. The present numerical model was firstly validated by comparing with published experimental data, and the comparison shows that good achievement is obtained. Then, the numerical model is used to investigate VIV for SFT under current. In the simulation, the SFT was allowed to oscillate in cross flow direction only under the constraint of spring and damping. The force coefficients and motion of SFT were obtained under different reduced velocity. Further research showed that Reynolds number has not only a great influence on the vibration amplitude and ‘lock-in’ region, but also on the force coefficients on of the SFT. A large Reynolds number results in a relatively small ‘lock-in’ region and force coefficient.

Size-dependent free vibration of axially functionally graded tapered nanorods having nonlinear spring constraint with a tip nanoparticle

According to the present literature review, the axial vibration of the axially functionally graded (FG) tapered nanorod with attached nonlinear spring has not been addressed so far. In this study, the axial vibration of the FG tapered nanorod is studied based on Eringen’s nonlocal theory, in which one end of the nanorod is clamped and the other end is attached to a nonlinear spring and a nanoparticle. The influence of different parameters such as the nonlinear spring constant, mass of the nanoparticle, and the nonlocal parameter on the natural frequencies is presented in detail. The solutions via Tables can be utilized as a reliable reference for evaluating the validity of future researches. The presented nonlocal solutions can be helpful for those who are interested in designing micro/nano electromechanical systems.

Vibration response analytical solutions of cantilever beam with tip mass and spring constraints

Vibration response analytical solutions of cantilever beam with tip mass and spring constraints

Development of a pre-clinical experimental simulation model of the natural porcine knee with appropriate ligamentous constraints.

A robust and stratified pre-clinical natural knee model, which has the capability to more appropriately simulate the biomechanical environment in vivo, will deliver more efficient and reliable assessment of soft tissue interventions before clinical studies. In order to simulate the biomechanical function of the natural knee without the natural ligaments in place, there is a requirement to develop appropriate spring constraints for the natural knee model. Therefore, this study was to investigate the effect of spring constraints on the function and output of the natural porcine knee model, and determine the spring constraint which most closely replicated the function of the natural ligaments. Two linear compression springs with stiffnesses of 9 N/mm (spring-9) and 20 N/mm (spring-20) were set at different free lengths in the anterior-posterior (A/P) axis in a natural knee simulator. The kinematic (A/P displacement) and tribological properties (shear force) output of the simulator were compared at different spring settings. The most appropriate spring setting was determined by comparing the A/P displacement and shear force output at different spring settings with those of the all ligaments model. Spring-9 with a free length of 4 mm showed the minimal difference (-0.03±0.68 mm) in A/P displacement output and spring-20 with a free length of 5 mm showed the minimal difference (-0.10±0.73 mm) in A/P displacement output compared to the all ligament control. There was no statistical difference between the two minimal differences either in A/P displacement or in shear force (paired t-test, p = 0.58, and p = 0.68 respectively) when both spring settings matched most closely to the A/P kinematics of the intact knee. This indicated that both conditions were appropriate spring constraints settings in the A/P direction for the natural porcine knee model.

Deep Deformable Patch Metric Learning for Person Re-Identification

The methodology for finding the same individual in a network of cameras must deal with significant changes in appearance caused by variations in illumination, viewing angle, and a person’s pose. Re-identification requires solving two fundamental problems: 1) determining a distance measure between features extracted from different cameras that cope with illumination changes (metric learning) and 2) ensuring that matched features refer to the same body part (correspondence). Most metric learning approaches focus on finding a robust distance measure between bounding box images, neglecting the alignment aspects. In this paper, we propose to learn appearance measures for patches that are combined using deformable models. Learning metrics for patches avoids strong dimensionality reduction, thus keeping more information. Additionally, we allow patches to change their locations, directly addressing the correspondence problem. As patches from different locations may share the same metric, our method effectively multiplies the amount of training data and allows patch metrics to be learned on the smaller amounts of labeled images. Different metric learning approaches (KISSME, XQDA, and LSSL) together with different deformable models (spring constraints and one-to-one matching constraints) are investigated and compared. For describing patches, we propose to learn a deep feature representation with convolutional neural networks, thus obtaining highly effective features for re-identification. We demonstrate that our approach significantly outperforms state-of-the-art methods on multiple data sets.