Displacement Control Method Research Articles

Application of bilateral iterative displacement control method to nonlinear free vibration analysis of dual-FG nanocomposite circular plates

This paper studies the geometrically nonlinear free vibration of a novel nanocomposite circular plate. The matrix of the nanocomposite structure is made of functionally graded (FG) polymer, and the distribution of graphene platelets (GPLs) as the reinforcement is assumed based on the five various linear FG models. Therefore, this novel nanocomposite is called dual-FG. The Voigt rule of mixture and Halpin-Tsai method are employed to homogenize FG polymer, and distribution of the GPLs within the matrix, respectively. Moreover, the whole structure is fixed on a nonlinear Kerr elastic foundation. The displacements of the plate are estimated by means of the first-order shear deformation theory (FSDT). Von-Kármán type of geometrically nonlinear relations expresses the plate's strains. The generalized differential quadrature (GDQ) technique, bilateral iterative displacement control method (BIDCM), and the weighted residual Galerkin procedure are implemented to extract the free vibration characteristics of the structure. The developed structure is validated with those reported in the open literature. A comprehensive parametric study is conducted to illustrate the effect of various parameters on the dynamic response of the dual-FG nanocomposite circular plate. It will be observed that the influence of the volume fraction and distribution model of GPL is more pronounced on the vibration frequency in the FG matrix. It was noted that the volume fraction of graphene platelets (GPL) and the power-law index of the matrix exhibit a direct and inverse relationship, respectively, with the natural frequency of the structure. Furthermore, the V-GPL model exhibits the highest percentage growth in nonlinear frequencies, while the Λ-GPL model shows the least growth. This observation is particularly pronounced for plates with hinged boundary conditions.

Using LQR controller for vertical position control on EAST

Vertical position control is essential for stabilizing plasma with elongated configurations. The EAST tokamak is equipped with a set of in-vessel control (IC) coils dedicated to this purpose. Currently, a PD controller with fixed parameters is used for the vertical position control of EAST plasma. However, the response of the plasma in the vertical position changes with changes in plasma configuration, which can result in different control parameter requirements. It is essential to develop a model-based fast-tuning control algorithm for ensuring stability in the vertical position under different configurations. In this study, a model-based vertical position controller tuning method based on a linear quadratic regulator algorithm (LQR) is proposed. Compared with contemporary PD controllers, the proposed model-based LQR controller can enable adjusting controller parameters based on the response of the system, achieving stable control under different vertical position responses. In the EAST experiment, the model-based LQR controller achieved stable control under a shot with a continuously increasing growth rate and reached a maximum controllable vertical displacement growth rate of 968 s−1. The robustness of the system was also demonstrated in a free drift experiment. The new vertical displacement control method can be adapted to different system states and plasma configurations and improve the controllability and safety of future devices.

Initial load factor adjustment through genetic algorithm for the generalized displacement control method: Implementation on non-rigid origami analysis

The nonlinear analysis of structural systems relies on effective nonlinear solution schemes, known as nonlinear solvers or path-following methods. This paper explores the challenge of determining the initial load factor in such analyses, with a particular focus on complex origami structures. This study presents a novel approach that leverages genetic algorithms (GA) to efficiently determine the initial load factor for the generalized displacement method. Building upon the concept of stiffness parameters, our method offers a systematic solution. In this work, GA serves as a tool to discover the appropriate initial load factor based on changes in the stiffness parameter, providing a more rational and user-friendly approach. To demonstrate the practical applicability of our approach, we apply it to a range of complex origami problems, including the folding of Miura-ori, folding of an egg-box origami, bending of an egg-box origami, and folding of an arc Miura-ori. These examples, along with a truss example, encompass highly nonlinear behaviors, including limit points, extreme stiffness fluctuations, snap-through, and snap-back. Our results showcase the effectiveness of our method in accurately tuning the initial load factor to capture and track intricate nonlinear behaviors. Furthermore, it offers the flexibility to fine-tune the distribution of points along the path and manage the resolution of the depicted equilibrium path. This versatility underscores its potential applications in fields such as deployable structures and complex large deformation structural analysis.

Conditional-not Displacement: Fast Multioscillator Control with a Single Qubit

Bosonic encoding is an approach for quantum information processing, promising lower hardware overhead by encoding in the many levels of a harmonic-oscillator mode. Scaling to multiple modes requires weak interaction for independent control, yet strong interaction for fast control. Applying fast and efficient universal control on multiple modes remains an open problem. Surprisingly, we find that displacements conditioned on the state of a single-qubit ancilla coupled to multiple harmonic oscillators are sufficient for universal control. We present the conditional- operation concept, which can be used to reduce the duration of entangling gates. Within this guiding concept, we develop the conditional- displacement control method which enables fast generation and control of bosonic states in multimode systems weakly coupled to a single-ancilla qubit. Our method is fast despite the weak ancilla coupling. The weak coupling in turn allows for excellent separability and thus independent control. We demonstrate our control on a superconducting transmon qubit weakly coupled to a multimode superconducting cavity. We create both entangled and separable cat states in different modes of the multimode cavity, showing entangling operations at low crosstalk while maintaining independent control of the different modes. We show that the operation time is not limited by the inverse of the coupling rate, which is the typical timescale, and we exceed it by almost 2 orders of magnitude. We verify our results with an efficient method for measurement of the multimode characteristic function which employs our conditional- displacement. Our results inspire a new approach toward general entangling operations and allow for fast and efficient multimode bosonic encoding and measurement. Published by the American Physical Society 2024

Geometric Nonlinear Analysis of Angle Section Elements Based on Updated Lagrangian Formulation and Rigid Body Rule

Angle cross-section members are widely used in various transmission towers owing to their convenient connections, easy availability, simple production processes, and high efficiency. Such members are very susceptible to nonlinear behavior when subjected to abnormal or extreme loads. In this work, a new geometric stiffness matrix for thin-walled steel members with an angle cross-section is derived based on the principle of virtual displacement, rigid body rule and updated Lagrangian equations. The generalized displacement control (GDC) method is employed to deal with the issues of non-convergence at the extreme value point and rebound point in the geometric nonlinear analysis, which offers clear physical meaning and can adjust the loading direction. The geometric and the traditional elastic stiffness matrices derived in this work are applied during the prediction phase, while only the traditional elastic stiffness matrix is used in the correction phase. The comparisons of the results obtained by the proposed method with those in the previous literature and ANSYS numerical solutions show that the proposed method is sufficient to ensure the accuracy and applicability for addressing the structural geometrically nonlinear issues.

Fatigue crack growth characterization of composite-to-steel bonded interface using ENF and 4ENF tests

In this paper, mode II fatigue crack growth properties of the composite-to-steel interface are characterised through different test configurations, namely ENF and 4ENF tests. Different loading types including force control and displacement control methods are compared. An innovative shear strain based method is proposed for monitoring the mode II crack growth at the bi-material interface through Digital Image Correlation (DIC). A 3D finite element model with Virtual Crack Closure Technique (VCCT) is built and used for obtaining the strain energy release rate (SERR) to investigate the effect of geometrical nonlinearity, friction at the interface and steel yielding, as well as to verify the mode mixity. The results show that the standard 3-point bending ENF specimen can be unstable under force control and sweeps narrow SERR range by a single test under displacement control. The 4-point bending 4ENF test shows stable crack propagation and clear SERR developing trend. More pronounced geometrical nonlinearity and friction effect exist for 4ENF test which can be considered when interpreting the Paris curves by a nonlinear finite element model.

Axial compressive behavior of recycled aggregate concrete steel composite columns

In this Study the axial load-carrying capacity and behavior of a “Axial Compressive behavior of Recycled Aggregate Concrete Steel Composite Columns” (RACSCC) is investigated experimentally and simulated numerically. The study emphasizes the utilization of materials contributing to the circular economy in construction, specifically integrating steel and recycled aggregate into concrete. The environmentally sustainable concrete columns are formed by filling square steel tube sections with recycled aggregate concrete (RAC). The study includes six SRACC specimens and one bare conventional steel column. The specimens are subjected to axial compressive loading using the displacement control method. The investigation explores the impact of different coarse aggregate sizes of 12 mm, 16 mm, 22.4 mm, 25 mm, and 30 mm, obtained through sieving of demolished buildings materials. The study aims to address the impact of varying aggregate sizes on parameters such as maximum load-carrying capacity, strain, stress, lateral displacement, and failure patterns. The experimental results are validated and compared with the maximum load-carrying capacity, Strain, Stress, Lateral displacement, and failure patterns using numerical simulations conducted with the Ansys Workbench tool. The SRACC column comprises a hollow tube with 20 mm to 22.4 mm and 22.4 mm to 25 mm recycled aggregate and has a maximum load carrying capacity of 610.28 kN at 10 mm displacement. The local buckling failure occurred near the area load applied. The numerical simulations result for the composite columns agreed well with the experimental results. The results show the recycled aggregate concrete (RAC) have a massive potential for construction support in circular economy. To create composite columns using the RAC as an alternative building material that will help to create an environmentally Sustainable construction

Nonlinear inelastic analysis of space semi-rigid steel frames subjected to static load using plastic-zone method

A new hybrid element based on plastic-zone method is proposed for static nonlinear analysis of space semi-rigid steel frames. Four zero-length nonlinear rotational springs are added to the beam ends to model both in- and out-of-plane connection rotational behavior with appropriate semi-rigid connection models. The von Mises yield criteria are applied to govern material plasticity along the member length and throughout the cross-section using Newton–Cotes integration points. The modified generalized displacement control method is used to solve the system of nonlinear equilibrium equations. Some numerical examples are investigated to show the reliability and visual illustration of the proposed hybrid element.

Frictional resistance calculation and jacking force prediction of rectangular pipe jacking

In practical engineering, whilst estimating the jacking force of rectangular pipe jacking using an empirical formula, the results obtained from said formula deviate from reality and manifest inadequate engineering guidance. The equations governing the applied force during the installation of rectangular pipe jacking have been derived for various contact states involving the interaction between the pipe, slurry, and soil. The distinct stress conditions in the pipe jacking process as well as the shear-friction mechanism between the pipe and the surrounding soil have been taken into account. The displacement control method is introduced to simulate the pipe–slurry–soil contact friction during the pipe jacking process in FLAC3D. Additionally, the pipe jacking behavior, pipe–slurry–soil contact frictional force, and variation law of the jacking force are also simulated. Mutual verification was carried out using the results obtained from field monitoring, numerical and theoretical. The findings are as follows: the established equations for calculating pipe jacking force are highly applicable across various conditions of pipe–slurry–soil contact, and the outcomes derived from theoretical formulas align remarkably well with those obtained through field monitoring and numerical simulation. During the jacking process, the sidewalls exhibit initial partial sliding followed by a complete movement as the jacking force intensifies and subsequently diminishes, eventually attaining stability during the behavior adjustment phase. Moreover, the bottom pipe–soil contact is the most common situation in actual construction.

Generalized displacement control technique for mode I/II fracture problems using cohesive zone model within a modified element‐free Galerkin framework

AbstractA modified element‐free Galerkin (EFG) method that combines the Heaviside enrichment and diffraction method is used to study crack propagation problems by employing a cohesive zone model (CZM) with an exponential traction separation law (TSL). The generalized displacement control method (GDCM) is adopted to solve the nonlinearity arising during the damage evolution. The proposed methodology is applied to (1) uncracked three‐point bending (TPB) and (2) adhesively bonded: (a) cracked double cantilever beam (DCB), and (b) end‐notched flexure (ENF) problems. In the passing, a simple 1D study is considered to demonstrate the advantage of level‐set enrichment coupled with CZM. Several parametric studies have been carried out on the EFG method and GDCM (reference and incremental load parameter). The results obtained by the proposed methodology agree well with the experimental/reference results. Specific advantages of GDCM on computational time, number of iterations, and ability to capture snapback vis‐à‐vis the popular Newton–Raphson technique are presented.

Postbuckling of Laminated Composite Circular Conical Shells Under Combined Thermo-Mechanical Loads

In this paper, the postbuckling characteristics of cross- and angle-ply laminated composite conical shells subjected to combined thermo-mechanical loading are studied using shear deformable semi-analytical finite element. The nonlinear governing equations, considering geometric nonlinearity based on Sanders type of kinematic approximations, are solved using Newton-Raphson iteration procedure coupled with adaptive displacement control method to trace the postbuckling equilibrium path. It is brought out from the study that the inward displacement in the postbuckling region is significantly higher as compared to the outward one. The ratio of the lowest load in the postbuckling path and the bifurcation load increases with the increase in the pressure loading proportion and decreases with the increase in the axial loading proportions. The relative load carrying capacity of shells under different set of loading combinations changes with the increase in the maximum postbuckling displacement. It is also observed that the nonlinearity in the load interaction relation corresponding to lowest load in the postbuckling path is less compared to that for bifurcation load.

Experimental and Theoretical Study for a Displacement-Controlled Design Method of Embedded Cantilever Retaining Walls (Piles)

Displacement control is critical to the design of retaining walls, especially in urban areas, to avoid any potential damage to adjacent structures during excavations. In this study, model tests are first conducted to investigate the stress and deformation mechanisms of an embedded cantilevered retaining (ECR) wall during excavations. The development of the wall top displacement and the active and passive earth pressures acting on the ECR walls during excavations are studied. Upon the experimental observations, a displacement-dependent earth pressure coefficient is proposed to derive an analytical solution to predict both the active and passive earth pressure acting on the ECR wall (pile), where the displacement value and displacement mode of the ECR wall (pile) are taken into account. Comparisons between the model predictions and test results are carried out. A good agreement is observed, which shows the validity of the proposed solution. Based on the proposed solution, a displacement-controlled method for the design of ECR walls (piles) that takes into account the location of the rotation point is proposed. Parametric studies are conducted to demonstrate the impact of deformation control and excavation depth on the design parameters of ECR walls (piles).

Stochastic analysis of semi-rigid steel frames using a refined plastic-hinge model and Latin hypercube sampling

This paper proposes a stochastic analysis model that combines the refined plastic-hinge analysis method with the Monte Carlo simulation to predict the realistic resistance of steel structures. The model treats the uncertainty quantifications of the material properties, geometry, and semi-rigid connections as independent random variables in the discretized stochastic fields using Latin hypercube sampling. The critical resistance of the structures in each simulation is determined using the general displacement control method and advanced analysis algorithms. The statistical approach is employed to compute the mean values and the standard deviation of the load-carrying capacity of the steel frames. The study finds that the uncertainties in material properties are the most sensitive, and the correlation of these parameters with the strength of structures is also significant. To improve the load and resistance factor design criterion, a resistance factor of 0.93 is suggested for the beam-columns in the frames under axial force, torsion, and biaxial bending moments. A stochastic response spectrum is proposed to define the boundary of strength, where a clearly defined plastic mechanism is attained. Furthermore, this study provides valuable insights into the stochastic resistance of steel frames, which are essential for practical engineering applications.

A novel method to accurately recreate in vivo loads and kinematics in computational models of the knee

Despite availability of in vivo knee loads and kinematics data, conventional load- and displacement-controlled configurations still can’t accurately predict tibiofemoral loads from kinematics or vice versa. We propose a combined load- and displacement-control method for joint-level simulations of the knee to reliably reproduce in vivo contact mechanics. Prediction errors of the new approach were compared to those of conventional purely load- or displacement-controlled models using in vivo implant loads and kinematics for multiple subjects and activities (CAMS-Knee dataset). Our method reproduced both loads and kinematics more closely than conventional models and thus demonstrates clear advantages for investigating tibiofemoral contact or wear.

Nonlinear Analysis of Cable Structures with Geometric Constraints

The purpose of this paper is the modelling in large displacement of systems composed of a rigid platform suspended by flexible cables, as can be observed in lifting systems of a construction crane or in cable-driven parallel robots (CDPRs). A recent approach has been proposed in the literature to model the nonlinear behavior of a cable element based on three dimensional catenary elastic modelling and the general displacement control method (GDCM) as solver. In this paper, two modifications of this method are proposed to take into account the geometric constraints coupling the large displacements of the cable extremities. The first approach is to consider these constraints using penalty functions thus modifying the tangent stiffness matrix and the second method by adding external explicit elastic forces. These two methods are tested and compared by using numerical examples. The first method is numerically safer because it is not dependent on the poor numerical conditioning of the cable’stiffness matrix encountered when internal cable’s tension cannot balance the external forces.

Ductility of Retrofit Column Using Wire Mesh and Self Compacting Concrete Due to Lateral Cyclic Load

Poor construction and ductility are the causes of structural damage and failure in earthquakes. Retrofitting is a way of repairing the damage and increasing the ductility of the column. Selection of wire mesh and self-compacting concrete as retrofit material, as it is easy to process and easy to obtain. The test specimen consisted of 3 columns with a size of 300x300 mm, consisting of a control column (KK), a completely retrofitted column (KR-1) and a retrofitted column in the approximate plastic hinge area (KR-2). The samples were cyclically tested based on the displacement control method. The test results show that the retrofitted with wire mesh and self-compacting concrete has a higher ductility value on the approximate plastic hinge area (KR-2). In addition, the retrofitted column has a higher load-bearing capacity than the column that has not been retrofitted.

Ductility of Precast Beam-Column with Dowel Connection Due to Cyclic Load

Precast concrete elements have advantages in terms of working time efficiency and quality uniformity. But beyond the benefits, there is something else to consider, namely the connection method. In addition, the ductility value is a measure of the success of precast concrete elements in construction, especially when it comes to absorbing earthquake loads in the form of cyclical loads. This study aims to analyze the ductility value of the precast beam-column with dowel connection under cyclic loading. The sample test was performed with cyclic loading based on the displacement control method. The sample consists of 1 monolith beam-column (BN) and 1 beam column with dowel connection (BG). The results of the investigation revealed that the beam-column with dowel connection (BG) had a higher ductility value than the monolith beam-column (BN). Based on the ductility classification according to ASCE 41-17, both samples were categorized as moderate ductility.

Local Instability Analysis for Axial Compressive Steel Columns

This study presents a nonlinear analysis method for steel columns considering local instability under axial compression. The stress-strain relationship of steel is developed while considering the effects of local instability utilizing the energy principles. The second-order effects are considered by stability functions, while the plasticity of steel is captured by a fiber finite element method. Nonlinear equilibrium equations are solved by the generalized displacement control method. As a result, the proposed formulations are effective, accurate, and reliable in predicting the load-carrying capacity and local instability of steel columns.

Isogeometric Level Set-Based Topology Optimization for Geometrically Nonlinear Plane Stress Problems

This paper addresses geometrically nonlinear topology optimization using IsoGeometric Analysis (IGA) and Level Set Method (LSM) under plane stress assumptions. The IGA is employed to solve governing equations and accurately describe geometric modeling. The pointwise gradient-based sensitivity analysis is applied to derive the normal velocity of the Reaction–Diffusion Equation (RDE) to update the control net of the Level Set Function (LSF). The Generalized Displacement Control Method (GDCM) is used to obtain the equilibrium path based on the Total Lagrange (TL) formulation. A pointwise energy interpolation strategy is employed to avoid low-density instabilities. The exact Heaviside function is also applied to obtain a 0/1 manufacturable design. The objective is to maximize the total strain energy of structure, which is defined as the total external work within a specified displacement, while a certain volume of the design domain is considered. To demonstrate the ability and efficiency of the proposed method, several numerical examples are presented. By making comparisons, the results of both optimization algorithm and nonlinear analysis are shown to be in good agreement with the literature. Also, it is shown that obtained layouts are different from those in the linear behavior modeling due to considering buckling effects. In addition, linear and nonlinear final layouts are analyzed under large deformation assumption and the load–displacement curves are compared to illustrate the improvement of the objective function and final load. • Optimized topologies are parameterized using NURBS. • A pointwise energy interpolation strategy is employed to avoid low-density instabilities. • The control net of the design domain is updated by the reaction–diffusion equation. • Pointwise sensitivity analysis of the optimization problem is analytically derived. • 0/1 manufacturable design was performed using an exact (binary) Heaviside step function.

LQG Control of an Open Circuit Axial Piston Pump

In recent years, the development of hydraulic variable displacement axial piston machines has been focused in two main directions: improvement of their construction and improvement of their displacement control methods. The goal of both directions is to increase the efficiency of the machines. Increasing their efficiency is key to improving the efficiency of the entire hydraulic system, whether they are used as pumps or hydraulic motors. This motivates the present work, which essentially contains a developed embedded control system designed for a known type of open circuit axial piston pump. The developed solution is implemented on a laboratory test rig. A detailed description of the hydraulic system in the context of pump displacement control is presented, as well as the developed system architecture for its control. The control system is based on a linear-quadratic Gaussian (LQG) controller. The controller is synthesized on the basis of a model obtained by means of identification based on experimental data. The designed controller is validated through experimental studies, enabling the analysis of its performance.