Simple Kinematic Research Articles

Simplified kinematic hardening plasticity framework for constitutive modelling of soils

A simplified kinematic hardening plasticity framework for the constitutive modelling of soils is presented. In contrast to conventional kinematic hardening plasticity, the yield surfaces do not enter explicitly into the governing equations but are used only for the purpose of computing an effective hardening modulus. This leads to models reminiscent of conventional nonlinear elastic/perfectly plastic models, thus facilitating an efficient numerical implementation. The framework is detailed both with respect to total and effective stress analysis. Its capabilities are illustrated by the development of a simple model for undrained total stress analysis of clays.

Fizeau drag in graphene plasmonics.

Dragging of light by moving media was predicted by Fresnel1 and verified by Fizeau's celebrated experiments2 with flowing water. This momentous discovery is among the experimental cornerstones of Einstein's special relativitytheory and is well understood3,4 in the context of relativistic kinematics. By contrast, experiments on dragging photons by an electron flow in solids are riddled with inconsistencies and have so far eluded agreement with the theory5-7. Here we report on the electron flow dragging surface plasmon polaritons8,9 (SPPs): hybrid quasiparticles of infrared photons and electrons in graphene. The drag is visualized directly through infrared nano-imaging of propagating plasmonic waves in the presence of a high-density current. The polaritons in graphene shorten their wavelength when propagating against the drifting carriers. Unlike the Fizeau effect for light, the SPP drag by electrical currents defies explanation by simple kinematics and is linked to the nonlinear electrodynamics of Dirac electrons in graphene. The observed plasmonic Fizeau drag enables breaking of time-reversal symmetry and reciprocity10 at infrared frequencies without resorting to magnetic fields11,12 or chiral optical pumping13,14. The Fizeau drag also provides a tool with which to study interactions and nonequilibrium effects in electron liquids.

Analytical estimation of the key performance points of the tensile force-displacement response of Crescent Shaped Braces

The technical note investigates the tensile force-displacement response of the hysteretic steel yielding brace known as Crescent Shaped Brace and characterized by a boomerang-like geometrical shape. The force-displacement curve is governed by three key performance points which correspond to the transition points separating the initial elastic behaviour, the flexural plastic behaviour, the geometrical hardening behaviour and the final axial plastic behaviour.In particular, the influence of the main geometrical parameter of the device, the so-called “lever arm”, on the strongly non-linear force-displacement behavior is analyzed by means of a simplified kinematic model. Based on this, analytical estimations of the key performance points are derived and compared with numerically simulated force-displacement curves.

Design, modeling and control of a miniature bio-inspired amphibious spherical robot

It is a huge challenge for an amphibious robot with a high locomotory performance to locomote in amphibious environments, including crawling on rough terrains, maneuvering underwater, and launching and landing motion between land and water. To deal with such a challenge, a miniature bio-inspired Amphibious Spherical Robot (ASRobot) with a Legged, Multi-vectored Water-jet Composite Driving Mechanism (LMWCDM) has been designed. In this paper, locomotory performance of the robot in amphibious field environments is studied. First, a simplified kinematic model was built to study crawling gaits, and with an online adjustment mechanism, the gaits were adjusted, enabling the robot to climb up slopes more stably. Then, using a dynamic underwater model, a real-time dynamic thrust vectoring allocation strategy is proposed to generate the water-jet thrust and joint angles using desired forces and torques computed by four parallel PID algorithms. Finally, a set of experiments were carried out to evaluate the performance of on land locomotion and underwater locomotion. Further, outdoor locomotion experiments including crawling on various terrains, launching and landing motion, were conducted in field environments. The results demonstrate that the robot prototype possesses the high locomotory performance which endows its wide application of disaster rescue, reconnaissance and resource exploration in amphibious environments.

Design, static analysis and development of a new three-legged shake table

In this paper, an alternative design is proposed based on a family of three-legged manipulators. Such manipulators have two actuators (one vertical and one horizontal) in each leg, unlike the standard UP̅S Stewart platform, which has one actuator in each leg. The arrangement of the two actuators is such a way that, to have vertical motion of the shake table only the Vertical Motion Actuators (VMA) are actuated and for longitudinal or lateral motion, the Horizontal Motion Actuators (HMA) alone are moved. Due to its inherent features such as simplified kinematics, control and distributed loading, a study is carried out to determine the performance of such three-legged manipulators as a shake table. Sinusoidal motion and white noise motions are given to the actuators and shown that the VMA forces have linear relationship with the platform forces. The translational stiffness and the torsional stiffness are studied separately for the manipulators. In the dynamic analysis, it is highlighted that the gravity load of the legs is borne by the Vertical actuators, irrespective of the motion being spatial or planar. Hence, this topology provides scope for lighter electromechanical actuation. The performance analysis of the 3 legged configuration is accomplished using simulation results, in comparison to a 7-UP̅S configuration of shake table. A prototype of the shake table is fabricated and tested with earthquake data of El Centro.

The COS-legacy survey of C iv absorbers: properties and origins of the intervening systems

ABSTRACT We present here results from a survey of intervening C iv absorbers at z < 0.16 conducted using 223 sightlines from the Hubble Spectroscopic Legacy Archive. Most systems (83%) out of the total sample of 69 have simple kinematics with 1 or 2 C iv components. In the 22 C iv systems with well constrained H i column densities, the temperatures from the b-values imply predominantly photoionized plasma (T ≤ 105 K) and non-thermal dynamics. These systems also have solar or higher metallicities. We obtain a C iv line density of $\mathrm{ d}\mathcal {N}/\mathrm{ d}X = 5.1\pm 1.0$ for $\log [N(\rm {C}\, \rm {{iv}})~(\rm {cm}^{-2})]\ge 12.9$, and $\Omega _{\rm {C}\, \rm {\rm {iv}}}=(8.01\pm 1.62) \times 10^{-8}$ for $12.9 \le \log [N(\rm {C}\, \rm {{iv}})~(\rm {cm}^{-2})] \le 15.0$. The C iv bearing diffuse gas in the z < 0.16 Universe has a metallicity of (2.07 ± 0.43) × 10−3 Z⊙, an order of magnitude more than the metal abundances in the IGM at high redshifts (z ≳ 5), and consistent with the slow build-up of metals in the diffuse circum/intergalactic space with cosmic time. For z < 0.015 (complete above L > 0.01L⋆), the Sloan Digital Sky Survey provides a tentative evidence of declining covering fraction for strong C iv (N > 1013.5 cm−2) with ρ (impact parameter) and ρ/Rvir. However, the increase at high separations suggests that strong systems are not necessarily coincident with such galaxies. We also find that strong C iv absorption at z < 0.051 is not coincident with galaxy overdense regions complete for L > 0.13L⋆.

Seismic responses analysis of suction bucket foundation for offshore wind turbine in clays

Suction buckets are widely used as foundations for offshore wind turbines because of its many advantages such as simple structure, convenient installation, low construction cost and reusable. It is very essential to perform the seismic response analysis of suction bucket foundations for the design of offshore wind turbines. However, the related research is still relatively rare. In this research, three-dimensional finite element analysis is performed to predict seismic responses of suction buckets for offshore wind turbines in clays by using a simplified kinematic hardening constitutive model available in the Abaqus library. The seismic bearing mechanism of bucket foundation in clays is investigated, and various factors affecting seismic responses of suction bucket are analyzed, including the soil strength, seismic intensity and frequency, and bucket geometry. The research results can provide a reference for the seismic design of suction bucket foundations for offshore wind turbines.

Effective rheology of a two-phase subduction shear zone: Insights from numerical simple shear experiments and implications for subduction zone interfaces

Inspired by exhumed subduction shear zones that commonly exhibit block-in-matrix characteristics (mélanges), we create synthetic models with different proportions of strong clasts within a weak matrix and compare them to natural mélange outcrops. Using 2D Finite Element visco-plastic numerical simulations in simple shear kinematic conditions, we determine the effective rheological parameters of such a two-phase medium, comprising blocks of basalt embedded within a wet quartzitic matrix. We treat our models and their structures as scale-independent and self-similar and upscale published field geometries to km-scale models, compatible with large-scale far-field observations. Like in the laboratory deformation experiments, we vary confining pressures, temperatures and strain rates to evaluate effective rheological estimates for a natural subduction interface. As expected, the block-in-matrix ratio affects deformation and strain localization, with the effective dislocation creep parameters (A, n, and Q) varying between the values of the strong and the weak phase, in cases where both materials deform by viscous creep. At conditions where the blocks are frictional and the matrix viscous, the mélange deforms effectively by dislocation creep but the locally frictional deformation of the blocks leads to higher stresses. This results in an effective value of the stress exponent, n, greater than that of both pure phases, as well as an effective rate-dependent viscosity lower than that of the weak phase. In combination with an appropriate evolution law for the block concentration of a mélange, our effective rheology parameters may be used in large scale geodynamic models as a proxy for a heterogeneous subduction interface.

Seismic vulnerability assessment and retrofitting of historic masonry building of Malek Timche in Tabriz Grand Bazaar

Tabriz Bazaar is the first Bazaar in the world that was registered in the world heritage list of the UNESCO in August 2010. Malek Timche is one of the important and beautiful parts of Tabriz Bazaar. The objective of this research is to assess the seismic vulnerability, structural behavior and failure mechanisms of this historic building, and to propose an appropriate method for retrofitting and improving the seismic performance. The subject is studied in four main steps. To determine the mechanical properties of constructional materials, three-point bending test and compression test are carried out initially. Then, a three-dimensional model of the Malek Timche is established using finite element method, and the static, modal, and dynamic analysis are performed. In the third step, 16 possible failure mechanisms are obtained based on the stress contours achieved from dynamic analyses using the simplified kinematic method based on the Italian code, OPCM 3431. Finally, by using the results of the structural analysis, walls and domes of the structure are strengthened by reinforcements and FRP composites, respectively.

A New Algorithm for Unique Representation and Isomorphism Detection of Planar Kinematic Chains with Simple and Multiple Joints

In this work, a new algorithm is proposed for a unique representation for simple and multiple joint planar kinematic chains (KCs) having any degree of freedom (DOF). This unique representation of KCs enhances the isomorphism detection during the structural synthesis process of KCs. First, a new concept of joint degree is generated for all joints of a given KC based on joint configuration. Then, a unified loop array (ULA) is obtained for each independent loop. Finally, a unified chain matrix (UCM) is established as a unique representation for a KC. Three examples are presented to illustrate the proposed algorithm procedures and to test its validity. The algorithm is applied to get a UCM for planar KCs having 7–10 links. As a result, a complete atlas database is introduced for 7–10-link non-isomorphic KCs with simple or/and multiple joints and their corresponding unified chain matrix.

A New Extensible Continuum Manipulator Using Flexible Parallel Mechanism and Rigid Motion Transmission

Abstract An extensible continuum manipulator (ECM) has specific advantages over its nonextensible counterparts. For instance, in certain applications, such as minimally invasive surgery or pipe inspection, the base motion might be limited or disallowed. The additional extensibility provides the robot with more dexterous manipulation and a larger workspace. Existing continuum robot designs achieve extensibility mainly through artificial muscle/pneumatic, extensible backbone, concentric tube, and base extension, etc. This article proposes a new way to achieve this additional motion degree-of-freedom by taking advantage of the rigid coupling hybrid mechanism concept and a flexible parallel mechanism. More specifically, a rack and pinion set is used to transmit the motion of the i-th subsegment to drive the (i+1)-th subsegment. A six-chain flexible parallel mechanism is used to generate the desired spatial bending and one extension mobility for each subsegment. This way, the new manipulator can achieve tail-like spatial bending and worm-like extension at the same time. Simplified kinematic analyses are conducted to estimate the workspace and the motion nonuniformity. A proof-of-concept prototype was integrated to verify the mechanism’s mobility and to evaluate the kinematic model accuracy. The results show that the proposed mechanism achieved the desired mobilities with a maximum extension ratio of 32.2% and a maximum bending angle of 80 deg.

Communication—An Analysis of Shear Forces in Post-CMP PVA Brush Scrubbing for Stationary and Rotating Wafers

After defining certain sign conventions for sliding velocity and shear force for a PVA brush scrubbing process, a simple kinematics model is used to calculate net sliding velocities in the brush-wafer contact region. Next, a series of experiments are performed where brush velocity is gradually increased while the wafer is kept stationery, and repeated again with the wafer rotating at a certain velocity. For a stationary wafer, with increasing brush velocity, partial lubrication takes effect which results in less brush asperity contact (i.e. a reduction in SF). For a rotating wafer, SF decreases significantly. We attribute this to the net negative sliding velocity across the wafer that partially offsets the positive SF values. However, SF rises with brush velocity which is likely due to fluid distribution effects and increased brush asperity-wafer contact.

Comprehensive study of the process of cutting screw grooves on the inner surface of a cylindrical steel sleeve with rotary cutting mandrels

The paper presents the results of a comprehensive study of the process of cutting helical internal grooves on the basis of computer simulation in order to establish the influence of technological parameters of cutting on the forming force. Researches of cutting of screw grooves on thinwalled steel sleeves by a cutting mandrel with various cutting speeds have been carried out. The method of processing internal screw grooves on machines with simple kinematics is presented. The dependences of the influence of cutting rates on implementation of the hidden kinematical connection are established. Graphs reflecting the dependence of the cutting rate on the angle of inclination of the cut helical groove are constructed, and a regression equation is obtained describing the dependence of the studied factors on the axial force. Ranges of cutting rates are established, allowing to provide the maximum productivity at various angles of the spiral inclination. The results of processing the experimental data of the study of the influence of tool geometrical parameters on the forming force when cutting helical grooves on the inner surface of the cylindrical shell are shown. Levels of change of factors, variance of experiment results on each of experiments are defined. The regression coefficients are calculated, the regression equation is compiled, the variance of model adequacy is estimated and adequacy of the regression equation is checked, the nature of infl uence of interaction of cutting rate parameters, front angle and the allowable allowance on the forming force is determined. Based on the results of modeling using the Maple program, a regression equation was obtained that reflects dependence of influence of factors on the axial force per tool tooth, dependence of the influence of the studied factors on the change in temperature in a cutting zone, and also constructed a temperature field reflecting the heat distribution in the processing zone on the example of one experiment. The study was performed with the financial support of the Russian Foundation for Basic Research within the research project No. 19-38-90057.

Reconfigurable laminates enable multifunctional robotic building blocks

Folding and assembling of two-dimensional laminated materials have greatly facilitated robot fabrication by creating robots with lightweight body frames, articulated joints, and embedded actuators and sensors. The combinations of rigid laminates bridged by thin-film flexures, often called rigid-flex linkages, have been extensively used in micro- and macro-scale robots to achieve complex joint motions with simplified kinematic and dynamic properties. Much like traditional robots these rigid-flex laminate robots are designed with a fixed body-plan, and thus may face challenges when environments require mechanical reconfiguration such as stiffening joints for load support or changing appendage morphologies for navigating confined spaces. Recent advances in adaptive materials and smart actuators have highlighted the features that robots with morphable geometries and tunable mechanical properties can provide, such as self-folding joints and variable stiffness and damping mechanisms. However, incorporation of these reconfigurable elements into laminate robots has been limited. In this paper, we present a new method for creating quasi two-dimensional structures for robotics, called reconfigurable laminates, that use geometric reconfiguration of laminate layers to alter passive mechanical properties and actuate joints. Unlike traditional rigid-flex linkages with single-layered flexures, here we create laminate joints with dual-layered soft hinges and rigid channels allowing a multitude of reconfiguration opportunities including: sliding-layer laminates for passive stiffness control, snapping-hinge locks for reconfigurable joints, and buckle-bend joints for bending actuation. Through experimental characterization we demonstrate the capabilities of these multifunctional robotic building blocks.

Mathematical model of changing the combined cutting tool durability

The article provides information on the development and study of a mathematical model for changing the durability of a new progressive combined tool. Currently, one effective way to increase productivity in automated manufacturing is to concentrate operations or transitions. With a high degree of operations concentration, the complexity of the kinematics of the equipment increases, its reliability decreases, therefore, downtime and the production cost are rising. The transitions concentration leads to the tool design complexity increasing, while the equipment can have simple kinematics of movements. The compatibility of operations or transitions depends on the required machining accuracy and surface roughness. The accepted procedure for performing operations and transitions determines necessary tool type. The most efficient concentration of operations or transitions can be achieved by using combined tools. Combined tools can be used in the treatment of both stepped and smooth cylindrical holes, which make up 35% of all surfaces used in mechanical engineering. Therefore, this study is devoted to solving the problem of increasing productivity and reducing the cost of threaded holes processing through the use of a new combined tool called the drill-tap.

Type Synthesis of 2T1R Planar Parallel Mechanisms and Their Moduling Development Applications

The two translational degrees-of-freedom (DOF) and one rotational DOF (2T1R) planar parallel mechanisms (PMs) have the characteristics of simple structures, simple kinematic and dynamic models, and ease of control and allow for a variety of application prospects. This paper concentrates on the derivations of the 5-DOF hybrid manipulators based on the synthesized mechanisms. To understand the effect of the constraint on the motion of a rigid body clearly, the method of reciprocal product between the wrench screw (constraint) and the twist screw (motion) is used and the relationships between the constraint and the motion of a rigid body are analyzed as well. The results are extended to the relationships between the limb constraint and the axes of limb joints. Then, limbs are divided into planar motion and spatial motion limbs in view of their motion characteristics, and some common limbs with constraint are listed. After that, based on the type synthesis method, a class of 2T1R planar PMs with common limbs is carried out. Meanwhile, some typical planar closed chains with two same limbs are obtained in the process of type synthesis. Finally, a 2T1R kinematically redundancy planar PM and two 2R1T spatial PMs are derived by making simple changes to the obtained mechanisms, and detailed derivations of three 5-DOF hybrid manipulators with the ability of processing spatial complex surface are given. Proved by the test parts, the accomplishment of deriving novel robot configurations with regard to expectant motion are quite valuable and practical.

Comparison of action recognition from video and IMUs

The aim of the study is to create an intelligent control system for automatic assistance to the operator of a semi-passive exoskeleton. This work solves the problem of recognizing human movements, since it is necessary to build a control system based on human movements in an exoskeleton. An experimental comparative study of two approaches to create human models for action recognition is considered. The first approach is based on the reconstruction of a simplified human kinematic model from IMU data, represented in special format. The second approach is to obtain 2D coordinates of a person’s key points from video from two different views. The sets of human models obtained from these approaches are classified using the XGBoost algorithm. The resulting classifiers are compared in terms of accuracy.

Development of a Cargo Airdrop Modeling Method for a Tactical Blended-Wing-Body UAV

In this paper, the development of a cargo airdrop modeling method is presented for a fixed-wing tactical UAV. The UAV, which is being developed in the framework of the DELAER UAS project, is based on the Blended-Wing-Body layout, and its mission is to deliver cargo and lifesaving supplies via airdrop, to remote and isolated Greek territories as well as over isolated islands in the Aegean Sea. At first, a simplified kinematic model is developed, to describe the trajectory of the cargo. Then, the critical airdrop parameters, such as the aerodynamic drag and the effect of wind gusts, are identified and incorporated to the model. Based on this model, an analysis methodology is proposed, conducted in several simulation loops. In each simulation loop, the cargo mass, release height, drop velocity and wind gust speed are the main variables. The results are given in a form of scatter plots, depicting the simulated cargo airdrop positions on the ground (or sea), around an actual target location, with respect to the drop height, drop velocity and wing magnitude. A solid conclusion is that, by releasing the cargo box with tailwind, the accuracy of the airdrop can be improved as much as 67% compared to any other wind direction.

A novel three-legged 6-DOF parallel robot with simple kinematics

This paper presents a novel three-legged six degrees of freedom (6-DOF) parallel robot with simple kinematics. The main idea behind this novel architecture is that each of the three identical legs is controlled by two prismatic actuators with parallel directions. As a result, it is possible to control simultaneously or separately the position and the orientation of a leg. The reduced number of legs leads to a simple mechanical design with reduced risk for mechanical interferences.

Task Assignment for Deploying Unmanned Aircraft as Decoys

This paper proposes a task assignment based on auction algorithm for a decoy mission using multiple UAVs which can hover against anti-ship missiles. An optimal deployment direction of decoys are also decided based on the cost function that is calculated with the expected signal power of a seeker and decoy, the distance between them, and fuel availability of the decoys. A simple kinematics is considered to generate two-dimensional motions of anti-ship missiles and a target ship. Numerical simulations are conducted under a visualization environment and validate the performance of the proposed algorithm. A parametric study is also conducted for the decoy mission with multiple missiles and decoys. Lastly, non-linear simulations for ducted fan Unmanned Aerial vehicles (UAVs) are performed to evaluate the feasibility of the proposed high-level task assignment comment for the decoy mission.