External Load Force Research Articles

Математичне моделювання напруженого стану ґрунтового середовища

A mathematical model has been developed that describes the stress state of the soil environment. The basic calculation model of the soil massif is presented in the form of a dispersed medium. Its stress state is described by a discrete-continuum model under the action of all stress components. This approach made it possible to use the main provisions of the theory of elasticity to construct a system of differential equations for the equilibrium of a disperse medium in a plane formulation of the problem. It also makes it possible to use the probabilistic properties of dispersed media to solve systems of differential equations that describe the distribution of stresses in a spacer dispersive medium with a distributive property. When an external load in the form of a concentrated force is applied to the soil mass, a differential equation for the distribution of the vertical normal stress of a parabolic type was obtained. It is one of the varieties of the heat equation. To solve the differential equations for the distribution of vertical stresses, the approach of applying an exponential function is used. It allows to ensure the symmetry of the distribution of stresses with respect to the line of action of the concentrated vertical force. It also allows characterizing the structure of the soil environment itself. To determine the adequacy of the developed mathematical model of the stress state of the soil mass, an external load in the form of a force was used. This force is given as a normal distribution function over the surface of the soil mass. Based on the developed mathematical model, the distribution function of tangential, normal vertical and horizontal stresses was obtained for a normal external force load on the soil mass. A comparative analysis of the results of theoretical and experimental studies on a prototype fine sand type showed a high degree of adequacy of the developed mathematical model of the stress state of the soil environment.

Characterisation of the chemo-mechanical behaviour of clays polluted by BTEX: a case study of benzene

In chemo-mechanical coupling of clays, chemical phenomena are likely to have a stronger influence on the mechanical behaviour and mechanical actions can modify the chemical behaviour. The understanding of these different phenomena, taking into account the coupled mechanisms, is essential in the context of the problem of the durability of structures and works built on polluted sites. Thus, the laboratory characterisation of the chemo-mechanical behaviour of a clay contaminated by light hydrocarbon pollutant (BTEX: benzene) was carried out. First in the absence of pollutants, i.e., by the presence of water only, then under the influence of the pollutant, all in two stages: with no external stress, then under imposed external stress. This study presents an experimental protocol based on a series of uniaxial consolidation tests, specific oedometric tests and direct shear strength, this tests performed under controlled saturation conditions and in the presence of organic contamination by benzene. All results confirm the influence of pollutants in different concentrations on the mechanical behaviour of the soil. They show a strong increase in compressibility and a significant increase in swelling, the soil becomes more cohesive, low friction and less elastic. Furthermore, the results show that external load forces play a major role in modifying the behaviour of clay.

The Problem of Engines in Statistical Physics.

Engines are open systems that can generate work cyclically at the expense of an external disequilibrium. They are ubiquitous in nature and technology, but the course of mathematical physics over the last 300 years has tended to make their dynamics in time a theoretical blind spot. This has hampered the usefulness of statistical mechanics applied to active systems, including living matter. We argue that recent advances in the theory of open quantum systems, coupled with renewed interest in understanding how active forces result from positive feedback between different macroscopic degrees of freedom in the presence of dissipation, point to a more realistic description of autonomous engines. We propose a general conceptualization of an engine that helps clarify the distinction between its heat and work outputs. Based on this, we show how the external loading force and the thermal noise may be incorporated into the relevant equations of motion. This modifies the usual Fokker–Planck and Langevin equations, offering a thermodynamically complete formulation of the irreversible dynamics of simple oscillating and rotating engines.

Do non-rearfoot runners experience greater second metatarsal stresses than rearfoot runners?

Stress fracture of the second metatarsal is a common and problematic injury for runners. The choice of foot strike pattern is known to affect external kinetics and kinematics but its effect on internal loading of the metatarsals is not well understood. Models of various complexities can be used to investigate the effects of running characteristics on metatarsal stresses. This study aimed to compare second metatarsal stress between habitual rearfoot and non-rearfoot strikers during barefoot running, using a novel participant-specific finite element model, including accurate metatarsal and soft tissue geometry. Synchronised force and kinematic data were collected during barefoot overground running from 20 participants (12 rearfoot strikers). Stresses were calculated using a previously evaluated and published 3D finite element model. Non-rearfoot strikers demonstrated greater external loading and joint contact forces than rearfoot runners, but there were no differences in stresses between groups. Additionally, the study allowed for a qualitative assessment of bone geometries and stresses. No correlation was found between bone volume and stresses, however, there was found to be a large variation in metatarsal shapes, possibly accounting for the lack of difference in stresses. This emphasises the importance of bone geometry when estimating bone stress and supports the suggestion that external forces should not be assumed to be representative of internal loading.

Uncoupled Quasistatic Problem of Thermoelasticity for a Two-Layer Hollow Thermally Sensitive Cylinder Under the Conditions of Convective Heat Exchange

We determine the unsteady temperature field depending on the radial coordinate and the thermoelastic state caused in a two-layer hollow thermally sensitive cylinder both by this field and the action of external force loads. The nonlinear boundary-value problem of heat conduction with discontinuous coefficients is reduced by the integro-interpolation method to the Cauchy problem for a system of ordinary differential equations, which is solved numerically. The stressed state is determined from the integral equations of the second kind and integral conditions obtained as a result of direct integration of the problem of quasistatic thermoelasticity in stresses. We study the influence of the temperature dependence of the thermal and mechanical characteristics of the layers of materials on the values and character of distributions of temperature and stresses caused by this dependence in a two-layer cylinder.

DETERMINATION OF STRESS FIELDS FROM THE ACTION OF A DISTRIBUTED LOAD

The influence of the external deformation effect of the distributed load on the stress state in the region of the wedge-shaped twin has been established. The change in stress fields in the near-surface region containing a twin is shown, depending on the intensity, uniformity and size of the external force loading zone     &nbsp

Upper and lower adjacent segment range of motion after fixation of different lumbar spine segments in the goat: an in vitro experiment.

ObjectivesThe purpose of this study was to examine the biomechanical effects of fixation on range of motion (ROM) in the upper and lower adjacent segments of different lumbar spine segments in a goat spine model.MethodsFifteen goat spine specimens (vertebrae T12–S1) were randomly divided into three groups: A (single-segment fixation), B (double-segment fixation), and C (triple-segment fixation). Motion in different directions was tested using a spinal motion simulation test system with five external loading forces. Transverse, forward–backward, and vertical displacement of the upper and lower adjacent segments were measured.ResultsAs the external load increased, the upper and lower adjacent segment ROM increased. A significantly greater ROM in group C compared with group A was found when the applied external force was greater than 75 N. The upper adjacent segment showed a significantly greater ROM than the lower adjacent segment ROM within each group.ConclusionsAdjacent segment ROM increased with an increasing number of fixed lumbar segments. The upper adjacent segment ROM was greater than that of the lower adjacent segments. Adjacent segment stability after lumbar internal fixation worsened with an increasing number of fixed segments.

Elastoplastic-damage-seepage coupling model and numerical algorithm for rock slope stability evaluation

The stability of slope under complex geological conditions is one of the essential issues in geotechnical engineering. The mechanical damage caused by external force load and the hydraulic property of rock have both significant influences on slope stability. However, the two factors and the coupling process between them are not considered in the traditional slope safety calculation method. Firstly, in this paper, an elastoplastic-damage-seepage coupling model is established based on the modified Mohr-Coulomb (M-C) criterion. This model takes into account the weakening effect of damage on the strength of rock mass. Further, according to the Biot's theory and the evolution equation of permeability coefficient, a complete hydraulic-mechanics (HM) coupling model is established. Secondly, the fully implicit backward Euler algorithm and "strict-cornered" algorithm are used to integrate the stress precisely. The complete coupling analysis of HM is implemented by the step-by-step iterative method. By combining the centrifugal loading method (CLM) with the FEM program, the factor of slope safety (FOS) under the coupling influence of damage-seepage can be solved. The calculation results showed that, compared with the traditional rounded M-C model, the results obtained by the "strict-cornered" algorithm method in this paper are closer to the theoretical solution. The solution process is robust with a global second-order convergence rate. After considering the effects of damage and seepage, the FOS is obviously reduced. Finally, the model is applied to the stability evaluation of an actual engineering. The variation rules of pore water pressure, displacement field, damage zone and FOS are calculated under different head heights. The model built in this paper considers the coupling characteristics of rock seepage-stress-damage well. The proposed numerical algorithm ensures the accuracy and rationality of the calculation results which provides a theoretical foundation for engineering application.

Retraction Note to: Integral Backstepping Control of LPMSM Drive System Using Revised Recurrent Fuzzy NN and Mended Particle Swarm Optimization

A linear permanent magnet synchronous motor (LPMSM) drive system is keeping in many nonlinear effects such as the external load force, the flux saturation, the cogging force, the column friction and Stribeck force, and the parameters variations. Due to the uncertainty effects the existing linear controllers can not achieve better control performances for the LPMSM drive system. To raise robustness under occurrence of uncertainty, the integral backstepping control system with hitting function is proposed for controlling the LPMSM drive system in accordance with the Lyapunov function. To improve larger chattering phenomenon under uncertainties effects, the integral backstepping control system with revised recurrent fuzzy neural network (RRFNN) and mended particle swarm optimization (MPSO) is proposed to operate the LPMSM drive system to raise robustness of system. The RRFNN is used to estimate the value of the external lumped force uncertainty. Moreover, the error compensation control with the error compensation mechanism is proposed to compensate the minimum reconstructed error of the error estimation law. Besides, four variable learning rates in the weights of the RRFNN are regulated by virtue of MPSO with segment regulation to speed-up parameter’s convergence. Finally, comparative performances through some tentative upshots are verified that the integral backstepping control system by virtue of RRFNN with MPSO has better control performances than those of the proposed methods for the LPMSM drive system.

Energy-saving and accurate motion control of a hydraulic actuator with uncertain negative loads

Pump controlled hydraulic actuators are wildly used in the aerospace industry owing to the advantages of energy-saving and integrated configurations. Negative loads may occur to actuators due to external force loads or the inertial force when the actuator decelerates significantly. Uncertain negative load working conditions may cause cavitation, actuator vibration, and even instability to the motion control if the actuator is without sufficient meter-out damping. Various types of hydraulic configuration schemes have been proposed to deal with negative loads of hydraulic actuators. However, few of them can simultaneously achieve energy saving and high control accuracy. This study proposes an energy-saving and accurate motion tracking strategy for a hydraulic actuator with uncertain negative loads. The actuator’s motion is driven by a servomotor pump, which gives full play to the advantage of energy-saving. The meter-out pressure is controlled by proportional valves to provide the optimized meter-out damping. The nonlinear adaptive robust control law is designed, which guarantees the control stability and achieve high tracking accuracy. An integrated direct/indirect adaptation law obtains satisfactory parameter estimations and model compensation for asymptotic motion tracking. Comparative experiments under different working conditions were performed to validate the advantages of the proposed control strategy.

Increasing fretting resistance of flexible element pack for rotary machine flexible coupling Part 3. The influence of dynamic loads on flexible coupling flexible element stress-strain state

It has been carried out the analysis of stress-strain state of flexible element pack for flexible coupling as a result of the combined action of the forces from the torque transmitted by the coupling and the forces caused by misalignment of the coupled shafts. Plots of bending moments from external load and reactive forces arising in the flexible elements of the pack have been constructed. There have been obtained the analytical dependences of the deflections and rotations of the sections on the complex load. The effects of various force factors on the stress-strain state of a flexible element have been compared. Directions of increasing the fretting resistance of the flexible elements are proposed.

Fault Estimation and Fault-Tolerant Control for the Pump-Controlled Electrohydraulic System

This paper proposes a fault estimation and fault-tolerant control strategy with two observers for a pump-controlled electro-hydraulic system (PCEHS) under the presence of internal leakage faults and an external loading force. The mathematical model of the PCEHS is dedicatedly derived in the state-space form for developing control methodology. Two different observers are developed in which an extended state observer is applied to estimate the internal leakage flow rate, and a disturbance observer is used to deal with the external loading force. Then, the proposed control is designed based on the backstepping sliding mode technique in which estimated information from the observers is taken into consideration to guarantee the working performance of the system. With the proposed methodology, the robustness and stability of the controlled system are theoretically analyzed and proven by the Lyapunov theorem. Comparative simulation results are given to demonstrate the effectiveness of the proposed methodology through different testing conditions.

Fast simulation of the simplest electric motor with back and forth mechanical motion

The concept of the simplest electrical motor with back and forth mechanical motion as an extended version of a well-known elementary one-conductor DC motor is introduced in the paper. The basic mathematical expressions describing the motor principles of operation were presented. The fast and simple direct approach for the creation of a Simulink model was introduced. The Matlab/Simulink model of the motor consists of the subsystems including an EMF equation, a voltage equation and a movement equation with external load force. The simulation results allow understanding of transient and steady-state processes in the motor. The studying of the simplest electrical motor gives the fast and deep understanding of the main properties of the motors with oscillatory, back and forth motion.

Mechanical properties of UN-5100 envelope material for stratospheric airship

ABSTRACTStratospheric airships are promising aircraft, usually designed as a non-rigid airship. As an essential part of the non-rigid airship, the envelope plays a significant role in maintaining its shape and bearing the external force load. Generally, the envelope material of a flexible airship consists of plain-weave fabric, composed of warp and weft fibre yarn. At present, biaxial tensile experiments are the primary method used to study the stress–strain characteristics of such flexible airship materials. In this work, biaxial tensile testing of UN-5100 material was carried out. The strain on the material under unusual stress and the stress ratio were obtained using Digital Image Correlation (DIC) technology. Also, the stress–strain curve was corrected by polynomial fitting. The slope of the stress–strain curve at different points, the Membrane Structures Association of Japan (MSAJ) standard and the Radial Basis Function (RBF) model were compared to identify the stress–strain characteristics of the materials. Some conclusions on the mechanical properties of the flexible airship material can be drawn and will play a significant role in the design of such envelopes.

First-principles molecular dynamics investigation of ceria/silica sliding interface toward functional materials design for chemical mechanical polishing process

We report a form of chemical mechanical polishing (CMP) in which ceria abrasive particles polish a silicon wafer surface in a water environment. The Car-Parrinello molecular dynamics (CPMD) method, which enables chemical reaction dynamics in non-equilibrium systems to be treated non-empirically, was used. The first application of CPMD was to a model including a silica surface rubbed by a ceria cluster to ascertain the fundamental tribochemical phenomena in the CMP process. The model consisted of a hydrogen-terminated silica surface (a representative model of an oxidized wafer surface) and H4Ce6O12 cluster placed in the vicinity of an asperity in the silica surface. H2O molecules were explicitly considered in order to reflect the presence of slurry water. An external load and shear force were applied to the cluster. Under conditions of finite temperature and friction, a Ce-O-Si bridging bond formed at the interface between the silica surface and the ceria cluster. Subsequently, another Ce-O-Si bridging bond formed. These newly formed bridging bonds changed the silicon atom into a five-coordinated one. Because this state was probably unstable, a pyramid structure was rapidly restored by breaking the original Si-O bond in the asperity, meaning that the wafer surface became flattened. By referring to static density functional theory (DFT) calculations, we concluded that this bond dissociation event was due to multiple Ce-O-Si bonds forming. To discuss the effect of slurry water, a similar CPMD simulation, but without H2O molecules (i.e., dry friction), was performed. Here, the Si-O bond dissociation reaction did not take place even if multiple Ce-O-Si bonds formed. This means slurry water is needed for CMP to occur and it probably helps to weaken the Si-O bond. The second application of CPMD was to a model consisting of a thin water layer sandwiched between silica and ceria plates for studying the effect of the surface orientation of the ceria. Two low-index CeO2 surfaces, (100) and (111), were modeled. A chemical event wherein Ce-O-Si bridging bonds formed on the ceria/silica interface could be observed in both models. However, the bond dissociation reaction of the original Si-O bond on the silica surface proceeded only in the model with the (111) surface, and not on the (100) surface. This difference in reactivity could mainly be explained by the arrangement of atoms of each surface. The (111) surface provides hexagonal adsorption sites that inherently form a structure with five-coordinated silicon atoms, which are important intermediates in the CMP process. On the other hand, the (100) surface exhibits square adsorption sites which hardly form the required intermediate. We successfully examined the effect of the surface orientation of the ceria in addition to the fundamental CMP mechanism wherein multiple Ce-O-Si bonds initiate a chemical reaction including Si-O bond scission.

Simulation of hydraulic transplanting robot control system based on fuzzy PID controller

Abstract At present, there is a problem that the output accuracy of the transplanting manipulator is low due to interference from external factors. To solve the problem of low output accuracy of the transplanting manipulator caused by the interference of external factors to the displacement tracking of the hydraulic seedling picking-up system, a control method of the transplanting manipulator based on the fuzzy PID control strategy is proposed. First of all, the hydraulic seedling taking system was modeled and analyzed, and the total output displacement of hydraulic cylinder piston when the valve core input displacement and external load force were acted on simultaneously was given. Then the PID control method of the hydraulic seedling picking-up system was designed, and by combining the fuzzy control theory with PID control theory, a fuzzy PID controller was designed, which was capable of on-line adjusting the PID parameters. MATLAB/Simulink was used to simulate the control system, and the control effects of conventional PID control and fuzzy PID control on the hydraulic seedling picking-up system were compared. The results showed that when k p value took 4, k i value took 10 and k d value took 0.001, the output response curve of the traditional PID control reaches a stable state in 5 s, while the fuzzy PID control only takes 2.2 s under the same conditions, successfully increasing the step response signal time of the system by 56%. The results showed that fuzzy PID control introduced helped the hydraulic seedling picking-up system to overcome its disadvantages of non-linearity and low control accuracy, and improved the stability and dynamic performance of the system.

Incorporating subject-specific geometry to compare metatarsal stress during running with different foot strike patterns

Stress fracture of the second metatarsal is a common and problematic injury for runners. The choice of foot strike pattern is known to affect external kinetics and kinematics but its effect on internal loading of the metatarsals is not well understood. Subject-specific models of the second metatarsal can be used to investigate internal loading in a non-invasive manner. This study aimed to compare second metatarsal stress between habitual rearfoot and non-rearfoot strikers during barefoot running, using a novel subject-specific mathematical model, including accurate metatarsal geometry. Synchronised force and kinematic data were collected during barefoot overground running from 20 participants (12 rearfoot strikers). Stresses were calculated at the plantar and dorsal periphery of the midshaft of the metatarsal using a subject-specific beam theory model. Non-rearfoot strikers demonstrated greater external loading, bending moments and compressive forces than rearfoot strikers, but there were no differences in peak stresses between groups. Statistical parametric analysis revealed that non-rearfoot strikers had greater second metatarsal stresses during early stance but that there was no difference in peak stresses. This emphasises the importance of bone geometry when estimating bone stress and supports the suggestion that external forces should not be assumed to be representative of internal loading.

RETRACTED: Integral backstepping control with RRFNN and MPSO of LPMSM drive system

A linear permanent magnet synchronous motor drive system is existed in many nonlinear effects such as the external load force, the flux saturation, the cogging force, the column friction and Stribeck force, and the parameters variations. Due to the uncertainty effects, the linear permanent magnet synchronous motor drive system is hard to achieve the good control performance by using linear controller. To raise robustness under occurrence of uncertainty, the integral backstepping control system with hitting function is first proposed for controlling the linear permanent magnet synchronous motor drive system. The used integrator can ameliorate the system’s robustness under the parameters uncertainties and external force disturbances. To reduce vibration of control strength, the integral backstepping control system by means of the revised recurrent fuzzy neural network with mended particle swarm optimization is next proposed to operate the linear permanent magnet synchronous motor drive system to raise robustness of system. Furthermore, four variable learning rates in the weights of the revised recurrent fuzzy neural network are adopted by using mended particle swarm optimization to speed up parameter’s convergence. Finally, comparative performances through some experimental upshots are verified that the integral backstepping control system by means of revised recurrent fuzzy neural network with mended particle swarm optimization has better control performances than those of the proposed methods for the linear permanent magnet synchronous motor drive system.

Microinjection Molding of Out-of-Plane Bistable Mechanisms.

We present a novel fabrication technique of a miniaturized out-of-plane compliant bistable mechanism (OBM) by microinjection molding (MM) and assembling. OBMs are mostly in-plane monolithic devices containing delicate elastic elements fabricated in metal, plastic, or by a microelectromechanical system (MEMS) process. The proposed technique is based on stacking two out-of-plane V-beam structures obtained by mold fabrication and MM of thermoplastic polyacetal resin (POM) and joining their centers and outer frames to construct a double V-beam structure. A copper alloy mold insert was machined with the sectional dimensions of the V-beam cavities. Next, the insert was re-machined to reduce dimensional errors caused by part shrinkage. The V-beam structure was injection-molded at a high temperature. Gradually elongated short-shots were obtained by increasing pressure, showing the symmetrical melt filling through the V-beam cavities. The as-molded structure was buckled elastically by an external-force load but showed a monostable behavior because of a higher unconstrained buckling mode. The double V-beam device assembled with two single-molded structures shows clear bistability. The experimental force-displacement curve of the molded structure is presented for examination. This work can potentially contribute to the fabrication of architected materials with periodic assembly of the plastic bistable mechanism for diverse functionalities, such as energy absorption and shape morphing.

Modeling and Experimental Study of a Novel Multi-DOF Parallel Soft Robot

In view of the demand for flexible drive and large load of the soft robot in the practical application, a novel type of flexible-actuated multi-degree-of-freedom (multi-DOF) parallel soft robot is designed. The proposed robot in parallel combination of three groups of flexible-actuated elements (FAEs) realizes large load by increasing the bearing area at the connection between flexible-actuated units (FAUs). In order to improve the driving flexibility, the multi-layer FAU is used to drive independently in parallel so as to realize omnidirectional bending movement by pneumatic drive. With the coupled analysis in terms of motion and force, the mapping model of kinematic attitude parameters and the external load force with output air pressure value is established. Finally, an experimental prototype is developed and an experimental test platform is built. Then, the comparison among the experimental data, simulation results and theoretical results verifies the capability of multi-DOF omnidirectional movement and flexible-actuated large load.