Initial Force Research Articles

A resource-efficient form-finding approach to tensegrity structures

PurposeThe aim of this article is to obtain a stable tensegrity structure by using the minimum knowledge of the structure.Design/methodology/approachThree methods have been formulated based on the eigen value decomposition (EVD) and singular value decomposition theorems. These two theorems are being implemented on the matrices, which are computed from the minimal data of the structure. The required minimum data for the structure is the dimension of the structure, the connectivity matrix of the structure and the initial force density matrix computed from the type of elements. The stability of the structure is analyzed based on the rank deficiency of the force density matrix and equilibrium matrix.FindingsThe main purpose of this article is to use the defined methods to find (1) the nodal coordinates of the structure, (2) the final force density values of the structure, (3) single self-stress from multiple self-stresses and (4) the stable structure.Originality/valueBy using the defined approaches, one can understand the difference of each method, which includes, (1) the selection of eigenvalues, (2) the selection of nodal coordinates from the first decomposition theorem, (3) the selection of mechanism mode and force density values further and (4) the solution of single feasible self-stress from multiple self-stresses.

Numerical study on influence of particle shape and deformation on friction behavior of flexible cylindrical particle flows

AbstractA discrete element method (DEM) model for deformable particles is established and adopted to investigate the Jenike shear process of flexible cylindrical particles with different aspect ratios (4 < < 6). The DEM model is firstly validated against both experimental data and analytic solutions. Then, numerical simulations are carried out and the effects of particles shape and deformation on their friction behavior are investigated through a particle‐scale analysis on particle deformation, coordinate number, contact forces, orientation and internal friction angle. Comparative results between flexible and rigid particles under the same conditions show that the shear stress increases almost linearly with the normal load regardless of particle stiffness or shape. For both rigid and flexible particles, the shear stress and internal friction angle increase with . The shear stress and internal friction angle of the flexible particles are higher than those of the rigid ones especially when = 6. The latter has more inter‐particle contacts but the former has stronger contact forces. When = 4 and 5, the flexible particles without many initial deformations will deform significantly during the shear process with a complex reconfiguration taking place. However, when = 6, the initial deformation and internal forces of the flexible particles only change slightly during the shear process. It is thus believed that the high shear stress and internal friction angle of the flexible particles with = 6 are caused by their solid packing structure which strongly enhances the capability of the particle flow to resist shear. The current knowledge will be helpful for improving the kinetic theories for granular flow for complex irregular particle flows.

Novel CAD–CAM fabrication of a custom-made ball attachment retentive housing: an in-vitro study

PurposeThis study aims to evaluate the digitally designed ball attachment housing in its initial retentive force and after 2 years of simulated clinical use and to compare it with the regular nylon ball attachment housing.Materials and methodsTwenty implants with their corresponding ball abutments (diameter 4.5 × 4.0 mm) were inserted in resin blocks. They were divided into two groups. In Group I, ten ball abutments each received their corresponding conventional attachment with nylon rings. In Group II, ten ball abutments received the novel CAD–CAM polyetheretherketone ball attachment housing. A universal testing machine was used to measure the retention force. The achieved maximum values of retention force were recorded at the beginning of the study (initial retention) and after 2 years of artificial ageing (2000 cycles of insertion and removal). Results were statistically analyzed using an independent sample T test.ResultsThe PEEK attachment housing showed high retention forces (25.12 ± 0.99 N) compared to the conventional attachment with a nylon ring (15.76 ± 0.93 N) in the initial dislodgement test. There was a statistically significant difference in mean retention at the initial retention test and after 2 years of stimulated usage between the two studied groups, p = 0.000.ConclusionsWithin the limitations of this study, the novel CAD–CAM–PEEK attachment showed high retention characteristics compared to the conventional attachment with nylon rings, initially and after simulated long-term use.

Design and analysis of buckling-induced honeycombs with tailorable out-of-plane crushing performance

Novel honeycombs with buckling-induced features and tailorable properties have been designed and fabricated using the fused deposition modeling (FDM) method. Quasi-static out-of-plane compression tests were carried out to investigate the topological dependence of the crushing behavior of the buckling-induced honeycombs (BIHs). The results demonstrated that the crushing performance of BIHs can be artificially controlled by altering their shape parameters. In particular, the initial peak force (IPF) and the undulation of the mechanical response of BIH can be effectively reduced by increasing the layer number or arranging the asymmetric layers. A finite element model validated against experimental results was also utilized to reveal the underlying deformation mechanism and study the corresponding displacement-crushing force responses for BIHs with different topological parameters. It was uncovered that the buckling-induced mechanism is beneficial for tuning the stiffness and mitigating local buckling resistance through the pre-determined collapse behavior of cell walls. Further, a multi-objective optimization process of BIH was performed to seek the optimal design solution for energy-absorbing structures in specific scenarios. The findings of this study provide a theoretical basis for the development of new ideas and optimization solutions for the design of lightweight and performance-tailored energy-absorbing structures.

Dynamic response of bionic non-convex tubes with proportional distribution of bulkhead

Non-convex tubes that have superior energy absorption potential may expand and deform unstable during impact, limiting energy absorption. The bamboo node can strengthen bamboo by resisting expansion. Therefore, bulkhead proportional distribution of bionic non-convex (BPDBN) tubes, an integrator of them, may present more efficient energy absorption performance. This research proposed to investigate the effect of geometrical parameters on the crashworthiness characteristics of BPDBN tubes. The position of bulkheads was assumed to vary according to the positive proportional function primarily determined by proportional coefficient k. The dynamic response was evaluated by the initial peak force (IPF), specific energy absorption (SEA), and crush force efficiency (CFE). Multi-objective optimization method was utilized to further improve the energy absorption performance. The optimal design lowered the IPF (34.00%), increased the SEA (37.16%) and the CFE (42.95%). This paper emphasizes that optimizing the geometrical parameters and the bulkhead distance proportion can significantly improve the crashworthiness performance of BPDBN tubes.

Dynamic crushing and energy absorption of bio-inspired shear thickening fluid-filled origami metastructure

In this study, a novel approach is proposed to enhance the crushing efficiency and energy-absorbing performance of origami metastructure by incorporating the shear thickening fluid (STF), which mimics the existence of the viscoelastic material found inside the protective mechanism in nature. The dynamic crushing and energy-absorbing performances of the proposed STF-filled origami metastructure are numerically investigated using the commercial software LS-DYNA. A fluid-structure interaction (FSI) technique is employed to simulate the coupling between the structure parts and the infilled fluid. The crushing performances of the proposed STF-filled origami metastructure (STF-OM) are investigated and compared with the non-filled and viscous fluid-filled counterparts under various crushing velocities. The effects of the filled height of STF, the viscosity of STF, and the origami folding angle on the crushing performances of STF-OM are also investigated. It is found that the proposed STF-OM can generate a higher and more steady crushing force without inducing a significantly high initial peak force. Its crushing resistance and energy-absorbing capability increase with the increase in crushing velocity, demonstrating its adaptive crushing performance for various impact scenarios. The filled height and viscosity of STF, as well as the origami folding angle, significantly affect the energy-absorbing efficiency and crushing performance of the proposed structure.

Energy absorption characteristics of aluminum foam-filled corrugated tube under axial compression loading

To improve the energy absorption characteristics of thin-walled structures and reduce the initial peak compression force and load fluctuation, a novel aluminum foam-filled corrugated tube was proposed in this study. Finite element model validated by quasi-static compression experiments was adopted to investigate the crashworthiness performances of aluminum foam-filled corrugated tubes and their combined energy-absorbing structures. The effects of structure parameters including corrugation radius, wall thickness, corrugation length and corrugation radius increments on axial compression characteristics were investigated through finite element analysis. The results showed that compared with aluminum foam-filled straight tubes, the initial peak compression force of aluminum foam filled corrugated tube was reduced by 22.87 %, the compression force efficiency was increased by 6.69 % and the load fluctuation was reduced by 17.94 %. The smaller the values of corrugation radius, wall thickness and corrugation length, the smaller the initial peak compression force; Because the corrugation radius had a great effect on the peak compression force, the order that the corrugations were compressed into folds can be controlled by designing the corrugation radius; In view of the peak and valley values of compression force, an innovative combination of single tubes with different △H was obtained, which had better energy absorption performance. Compared with a single aluminum foam-filled corrugated tube, the compression force efficiency of the combined structure (△H: 0–5–10) was increased by 18.15 % and the load fluctuation was reduced by 33.60 %. The research results can provide a reference for the design and optimization of energy-absorbing devices.

Seismic behavior of earthquake-damaged hybrid connections reinforced with replaceable energy-dissipating elements

In recent years, self-centering post-tensioned concrete structures have received extensive research attention owing to their excellent seismic performance and post-earthquake functional recoverability. This study entailed the development of a novel repair method for earthquake-damaged unbonded post-tensioned hybrid connections (PTHCs) by using a novel energy-dissipating device to improve seismic resilience. To investigate the effectiveness of the repair method, four connections with different degrees of seismic damage were repaired using different repair methods, and quasi-static experiments were then conducted. The test variables included the position of the glass fiber-reinforced polymer (GFRP) arrangement, connection method of energy-dissipating devices, number of replaceable energy-dissipating elements (REDEs) of the damper, and initial prestressing force of post-tensioned (PT) strands. The experimental results indicate that the proposed repair methods can recover the lost capacities of PTHCs, and the mechanical properties of the reinforced self-centering precast connections (RSCPCs) can even be restored by replacing the REDEs under a second rare earthquake. The proposed energy-dissipating device facilitates increase or decrease of the REDEs to meet the energy dissipation and stiffness targets of the component for different levels of earthquake damage. The calculation results based on the recovery force model were in good agreement with the test results, showing that the proposed model could reasonably predict the hysteresis behavior of the RSCPCs.

Finite element analysis of zonular forces

To determine the effect of zonular forces on lens capsule topography, a finite element (FE) analyses of lens capsules with no lens stroma and constant and variable thickness with anterior capsulotomies of 1.5 mm–6.5 mm were evaluated when subjected to equatorial (Ez), anterior (Az) and posterior (Pz) zonular forces. The lens capsule was considered in the unaccommodated state when the total initial zonular force was 0.00075 N or 0.3 N. From the total 0.00075 N zonular force, the Ez force was increased in 0.000125 N steps for a maximum force of 0.03 N and simultaneously the Az plus Pz force was reduced in 0.000125 N steps to zero. In addition, the force of all the zonules was reduced from 0.00075 N and separately from 0.3 N in 0.000125 N steps to zero. Only when Ez force was increased as Az and Pz force was reduced did the capsule topography simulate in vivo observations with the posterior capsule pole bowing posteriorly. The posterior bowing was directly related to Ez force and capsulotomy size. Whether the total force of all the zonules in the unaccommodated state was 0.00075 N or 0.3 N and reduced in steps to zero, the lens capsule topography did not emulate the in vivo observations. The FE analysis demonstrated that Ez tension increases while the Az and Pz tension decreases and that all the zonules do not relax during ciliary muscle contraction.

Research on Initial Force Determination and Mechanical Behaviors of Crossed Spoke Cable-Truss Structure

Research on Initial Force Determination and Mechanical Behaviors of Crossed Spoke Cable-Truss Structure

Stability of aerostatic equilibria in porous medium flows

This paper is concentrated upon the qualitative analysis of two specific cases of the compressible Euler equations with linear damping: self-balanced non-isentropic system and externally driven isentropic system. We consider initial-boundary value problems of the models on bounded domains in Rd. Both systems are supplemented with the no-normal-flow boundary condition. Under smallness assumptions on the initial perturbation and/or external force, it is shown that non-trivial steady states associated with the initial-boundary value problems are asymptotically stable in the long run.

Fastening solutions on composite structures: Progressive damage analysis of a unique bolted joint design for single-lap CFRP laminate

This study tested a unique assembly method using single and multi-body sleeves with carbon fiber-reinforced plastic (CFRP) to improve load-carrying capacity in single-lap joints. Advanced techniques were implemented into FE code to simulate progressive material degradation behavior. Ti6-4 bolt, insert, and washers with AISI 304L sleeve joint were conceptually designed to keep bolt and nut together with less relative motion. Failure indices were reduced by 16–54%, damage initiation force was improved by 8–40%, and inter-plate clamp loss was reduced by 18% compared to the sleeveless design. Lateral load-carrying capability of joint and inter-plate clamp load significantly improved.

Electromagnetic force investigation of electromagnets with variable pole area in an electromagnetic diaphragm pump.

Electromagnetic diaphragm pump is a kind of widely applied diaphragm pump that has promising sealing performance, simple structure and low power loss. Planar pole electromagnet is a significant component of the electromagnetic diaphragm pump. However, the sharply changing displacement-force characteristics of the planar pole electromagnet do not match the constant load characteristics of the electromagnetic diaphragm pump. Herein, an electromagnet with variable pole area is put forward. A theoretical relationship between structural parameters, the Ampere turns and the electromagnetic force of the electromagnet with variable pole area is determined by analyzing the equivalent magnetic circuit of the electromagnet with variable pole area. The experimental results imply that the initial electromagnetic force of the electromagnet with variable pole area is 32.51% larger than the planar pole electromagnet, the engaging electromagnetic force of the electromagnet with variable pole area is 22.3% smaller than the planar pole electromagnet and the displacement-force characteristics of the electromagnet with variable pole area match the constant load characteristics of the electromagnetic diaphragm pump.

What drives the growth of china's mariculture production? An empirical analysis of its coastal regions from 1983 to 2019.

China's mariculture (i.e., seafood farming in the ocean) production has grown rapidly. It ranks the first in the world and has made a huge contribution to solving human food security and nutrition issues. This study aimed to examine the development process of China's mariculture since 1983, clarify the main driving factors for the growth of mariculture production, and analyze whether China's experience can help other major producers in the world. Using the data on China's 10 coastal regions, this study applied the Logarithmic Mean Divisia Index (LMDI) from both the national and regional perspectives to analyze the main driving factors for the growth of China's mariculture production from 1983 to 2019. The results indicate that China's total mariculture production showed an overall upward trend and the major driving factor for the increase changed from the initial labor force to unit production. The primary factor for the increase in the Circum-Bohai Sea was labor, whereas that in the South China Sea, Yellow Sea and East China Sea was unit production. China's mariculture production has expanded from resource-driven to efficiency-driven. This study has practical significance for policy formulation and the future development direction of mariculture. This study provides a universally applicable methodology, and has reference significance for the world's major mariculture producers to further study the sustainable growth of mariculture production.

Intermittent isolated anterior displacement of QRS complex – Differential diagnosis

BackgroundThe proposed criteria for diagnosis of left septal (middle) fascicular block (LSFB) appear to be conflicting. Moreover, it has been claimed that isolated anterior displacement (AD) of QRS complex could be a manifestation of a conduction delay of the right bundle branch, besides of LSFB. The purpose of the present study was to better define the etiology of AD through an analysis of the case reports dealing with intermittent AD, published up to now. MethodsPubMed search was performed to include all case reports dealing with intermittent AD occurring spontaneously, with an available 12‑lead electrocardiographic recording. Pertinent data were extracted from the papers for further analysis. ResultsEighteen case reports were found in the literature; in all cases intermittent AD was attributed to LSFB. In all cases AD was associated to changes of initial QRS forces, characterized by disappearance of septal q waves (in I and V6) and/or appearance of a small q wave in leads V1-V3. Morphology of terminal QRS forces, analysed for the first time, was unchanged in 90% of cases. Some Isolated ADs observed during induction of premature atrial extra-stimuli and recorded by vectorcardiographic tracing and some electrocardiographic leads were attributed to a conduction delay of the right bundle branch. In this case, initial QRS forces did not change and terminal QRS forces shifted to the right. ConclusionsIn the presence of intermittent isolated AD, a differential diagnosis between LSFB and a conduction delay of the right bundle branch appears to be possible by the analysis of initial and terminal QRS forces. Instead, the diagnosis of permanent LSFB remains a challenge.

Research on the Calculation Model and Control Method of Initial Supporting Force for Temporary Support in the Underground Excavation Roadway of Coal Mine

This paper proposes a temporary support system for improving the efficiency and safety of underground roadway excavation in coal mines. Firstly, this study establishes a calculation model for the initial supporting force of the excavation of roadway temporary support and a gray system-based automatic prediction model for the initial supporting force level, based on the mechanism of temporary support controlling the roof. These models enable the prediction of the required initial supporting force at different locations along the roadway’s temporary support area, thereby providing a basis for controlling the initial supporting force of the temporary support system. To achieve efficient and adaptive control of the initial supporting force of temporary supports at different locations, this study designs a support force controller based on Simulated Annealing Particle Swarm Optimization Proportional-Integral-Derivative (SAPSO-PID). This study establishes a mathematical model for the hydraulic cylinder pressure system controlled by the temporary support overflow valve and conducts a stability analysis and model verification. The study constructs a simulation control system for the initial supporting force based on SAPSO-PID using the combined simulation platform of AMESim and Matlab. The simulation results demonstrate that the proposed support force control system efficiently achieves adaptive control of the initial supporting force of temporary supports. An experimental system in the underground roadway of a coal mine is constructed to validate the results of the simulation analysis.

Investigation of the performance of the self-centering steel plate shear wall considering stress relaxation in pre-stressed cables

Self-centring systems are one of the novel earthquake-resistant systems that can eliminate permanent earthquake-induced damage in buildings. In these systems, damage can be limited to those members that can be easily replaced after earthquakes. Self-centring steel plate shear walls (SC-SPSW) with pre-stressed cables combine the lateral load-resisting capacity of conventional SPSWs with the self-centring capabilities of PT beam-to-column connections and provide sufficient ductility and stiffness for the system. The stress relaxation phenomenon in pre-stressed cables can lead to stress reduction in cables with the passage of time. This phenomenon should not be neglected. In this study, the self-centering steel plate shear wall is simulated using finite element (FE) modeling and verified based on available experimental results; then, the effect of stress relaxation on stiffness and energy dissipation capability of the system is evaluated at different initial pre-stressing forces and time intervals. According to the results, after five years and for cables with a pre-stressing ratio of 0.7, the stiffness and dissipated energy have reduced by 26 and 5 percent, respectively, in comparison to the time just after pre-stressing. These values was 40 % and 2 % for stiffness reduction and energy dissipation capacity reduction, respectively when the cables were pre-stressed with the pre-stressing ratio of 0.9. Furthermore, A method is also suggested to improve the seismic performance of the self-centering connections which includes employing low yield point steel in energy dissipater devices. Results showed that the energy dissipation capacity of the system doubles by using low-point steel for the web plates. The cumulative dissipated energy was about 1.044 MJ with A1008 steel and it was increased to 2.058 MJ with LYP100 material. This increase was mostly observed after the 10th cycle of the hysteresis curve.

A mucoadhesive magnetic millimeter-scale robot with two motion modes for drug delivery to the colon

The small-scale robots for targeted drug delivery are gradually attracting great interest, and increasing the residence time of robots in targeted areas is conducive to increasing bioavailability. A drug-loaded magnetic millimetre-scale robot that can bond to colonic mucosa has been developed. The main body of the robot is composed of two approximately rectangular Poly (lactic acid) (PLA) sheets perpendicular to each other. The magnetic disk and the drug-loaded adhesive film are symmetrically distributed at the tail sheet. The robot has two ways to move: swimming and rolling. A high-frequency-rotating magnetic field can drive it to swim in liquid environments, or a low-frequency-rotating magnetic field can drive it to roll in an air environment. The drug-loaded adhesion patch can attach to both PLA and mucosa, ensuring the bond to the robot during movement and maintaining mucoadhesion to the intestinal mucosa during drug release. The initial contact force applied by a magnet between the robot and the intestinal surface was calculated and measured. The adhesion functionality of the robot to porcine colon was proved in the vitro simulated adhesion experiment.

Seismic behaviors of self-centering steel structural joints with phased energy dissipation

To reduce residual deformation in steel moment-resisting frames under seismic actions and facilitate rapid post-earthquake functionality recovery, a self-centering steel structural joint with phased energy dissipation was proposed. This joint achieves self-centering capability through the restorative force provided by prestressing steel strands. Additionally, it employs two energy dissipation mechanisms, namely frictional sliding between the friction plate and the T-stub web and the plastic deformation of the T-stub itself, at different stages to dissipate seismic energy. This approach enables effective phased energy dissipation. Cyclic loading tests were conducted on four full-scale specimens with varying initial prestressing forces of steel strands and bolt pretension. This study obtained seismic performance parameters of the specimens, including hysteretic curves, skeleton curves, stiffness degradation, and energy dissipation. Furthermore, the phased energy dissipation mechanisms of these specimens at different loading stages were investigated. It was found that the loading process of the specimens could be divided into three stages: elastic stage, sliding stage, and strengthening stage. During the elastic stage, the specimens remained closed, with all components in an elastic state. As the loading progressed to the sliding stage, the specimens dissipated energy through frictional sliding between the friction plate and the T-stub web. In the strengthening stage, the primary energy dissipation mechanism of the specimens was the plastic deformation of the T-stub. Moreover, the initial prestressing force of the steel strands had significant influence on the bending capacity and self-centering capability, while the bolt pretension mainly affected the energy dissipation capacity and bending capacity of the specimens.

Development and investigation of a novel precast beam-column friction hinge joint enhanced with Cu–Al–Mn SMA-plate-based self-centring buckling-restrained devices

To improve seismic capabilities and to reduce post-earthquake residual deformation of precast concrete frames, a novel self-centring hybrid connection (SCHC) composed of a rotational friction hinge device (RFHD) and four self-centring buckling-restrained dampers (SC-BRDs) was proposed and investigated for the dry type precast concrete beam-column joints in this study. The configuration and working principles of the SCHC were first illustrated. The effects of solution heat treatment procedures, strain amplitudes, and cycle numbers on the uniaxial cyclic behaviour of prepared Cu–Al–Mn SMA plates were also tested for the SCHC application. Finite element models of the RFHD, SC-BRD, and novel SCHC were subsequently established and preliminarily verified, followed by parametric analyses on several crucial design parameters of the SCHC to optimize its mechanical performance. Results shown that the self-centring ability and strength degradation resistance of the prepared Cu–Al–Mn SMA plates can be significantly improved by subjecting appropriate solution heat treatment procedures. The SMA core element thickness, initial post-tensioning force of high-strength bolt, and distance between SMA and rotation centre are suggested to be designed within the range of 8 mm–10 mm, 565 kN–705 kN, and 120 mm–130 mm, respectively, to achieve appropriate energy dissipation and self-centring performance of the proposed SCHC. The RFHD and SC-BRD can be conveniently replaced after damage in earthquake, which is conducive for rapid repair of the prefabricated concrete structures. Overall, the proposed SCHC shows excellent seismic mitigation ability, self-centring capability, and repairability. The proposed SCHC can provide a reference for the application of some important prefabricated concrete structures in requirement of uninterruptible or rapidly restorable building functions after high seismic effects.