Effects Of Joint Flexibility Research Articles

Effect of Joint Flexibility on Overall Behavior of Jacket Type Offshore Platforms

Problem Statement: Nonlinear behavior of offshore structure is attracting tremendous amount of attention in recent years. Response of these structures is strictly dependent upon behavior of their joints. Because of the lack of information about this part of a structure, most of the recent analysis and designs do not contain appropriate material in the case of joints. In most cases, joints are assumed to be fully clamped and their deformability is not accounted for in assessment of Jacket Type Offshore Platforms (JTOP) whereas, in reality there is always deformation in joints particularly when members undergo beyond elastic region. Approach: In this study, finite element modeling of tubular connections is carried out in order to assess their nonlinear behavior. As a result in a separate study, two FE models of a platform are made and effect of joint flexibility on these models is investigated analytically. Nonlinear static and dynamic analyses are performed considering joint deformation and compared to platform with clamped connections. Furthermore, some important parametric studies are carried out such as effect of joint flexibility on natural frequency of vibration of the structure and the process of plastic hinge formation in platform. Results: Results prove considerable effect of local joint deformation on nonlinear static and dynamic behavior of offshore structures. Conclusions/Recommendations: Taking into account the calculated results in this paper, it is highly recommended to consider the effect of joints in the design and analysis of offshore structures based on the importance of the project.

Effect of Joint Flexibility on Overall Behavior of Jacket Type Offshore Platforms

Effect of Joint Flexibility on Overall Behavior of Jacket Type Offshore Platforms

Simplified analysis of seismic in-plane stresses in composite and jointed tunnel linings

This paper presents an analytical procedure for evaluating in-plane moments and thrusts in composite and jointed tunnel linings during earthquakes. The analytical procedure treats the tunnel lining as an inner jointed thin-walled shell coupled with an outer thick-walled cylinder embedded in linear elastic soil or rock. The outer thick-walled cylinder can also be used to approximately model a degraded zone around the tunnel lining caused by mechanical disturbance and/or disturbance of the in situ stress field due to tunnel construction. The influence of in-plane shear stress is taken into account by assuming the free-field ground response produced during an earthquake is perpendicular to the longitudinal axis of the tunnel. Solutions for moment and thrust are presented for cases involving slip and no slip at the liner–ground interface. A parametric study is performed to investigate the effects of joint flexibility and a degraded annulus of soil or rock around the lining on the seismically induced moments and thrusts.

Optimal design of frame structures with semi-rigid joints

In this paper, a genetic algorithm is proposed for discrete minimal weight design of steel planar frames with semi-rigid beam-to-column connections. The frame elements are constructed from a predetermined range of section profiles. Conventionally, the analysis of frame structures is based on the assumption that all connections are either frictionless pinned or fully rigid. Recent limit state specifications permit the concept of semi-rigid connection of the individual frame members in the structural design. In a frame with semi-rigid joints the loading will create both a bending moment and a relative rotation between the connected members. The moment and relative rotation are related through a constitutive law which depends on the joint properties. The effect, at the global analysis stage, of having semi-rigid joints instead of rigid or pinned joints will be that not only the displacements but also the distribution of the internal forces in the structure must be modified. In this study, a simplified beam-to-co lumn connection is presented which was specified in EC3 Annex J. In order to capture the changes in the nodal force and moment distribution in terms of joint flexibility, the ANSYS finite element analysis is applied. The structural model is formulated as a combination of 3D quadratic beam elements and linear torsional springs. Present work deals with the effects of joint flexibility to the optimal design problem. The design variables - including joint properties - are discrete. Results are presented for sway frames under different load conditions.

The effect of semi-rigid joints and an elastic bracing system on the buckling load of simple rectangular steel frames

A linear stability analysis for establishing the combined effect of joint flexibility and an elastic bracing system on the buckling load of steel plane frames is presented herein. Based on the beam-to-column model of Eurocode 3, the subsequent study shows that joint flexibility is a very important parameter that needs to be incorporated into the stability analysis of frames with semi-rigid connections. It was found that assuming flexible connections in such frames always leads to a reduction of their buckling load, which is proven to be significant in many characteristic cases. Numerical results for simple elastically braced or unbraced frames with semi-rigid connections, in tabular and graphical form, reveal the pronounced effect of joint flexibility and elastic bracing on their buckling load. The results presented herein can be readily used for the design of simple frames against buckling, while the flexible connection concept can be applied to all types of steel frames.

Precision tracking control of a horizontal arm coordinate measuring machine in the presence of dynamic flexibilities

One of the major sources that affect measurement ac- curacy and limit the use of high motion speeds in coordinate measuring machines (CMM) is the position error. In fact, static and dynamic probe errors are more direct factors in measur- ing machine accuracy, but are not the subject of this research. However the accuracy of acquisition of component position er- rors using a CMM in motion is also of importance, hence the dynamics of a CMM need to be considered. Therefore, this re- search aims to model the dynamics of a horizontal arm CMM by considering drive flexibility at joints and evaluates the char- acteristics of the system for fine motion control purposes. De- sign of a precision tracking controller (PTC) to perform supe- rior tracking for enhancing the measurement accuracy and the probing speed in providing less inspection time at high mo- tion speeds is carried out. A dynamic model for the CMM is developed including drive flexibilities represented with lumped springs at the joints. Due to the non-collocated nature of the control scheme in the flexible CMM dynamics, a non-minimum phase system is observed in the proposed CMM model. Using the derived CMM model with joint flexibilities, tracking motion control simulations are conducted at different probing speeds for the cases where a PI controller and a feedback PTC are em- ployed. A comparison of the PI controller with the feedback PTC is also performed. Results demonstrate that the effects of joint flexibilities on the contour error and probing speeds are sig- nificant and the PI controller is not capable of providing good accuracy during challenging tasks such as corner tracking. How- ever, the simulation results indicated that by using the proposed feedback precision tracking controller, contour errors in corner tracking that are caused by joint flexibilities can be reduced effectively.

The effect of joint flexibility on the free elastic vibration characteristics of steel plane frames

The present work offers a simplified approach for establishing the effect of joint flexibility on the free vibration characteristics of steel plane frames. Based on the beam-to-column model of Eurocode 3, the presented analysis shows that within the elastic range and under certain combinations of the parameters involved, a transition to a higher vibration mode may occur, a finding of great importance for structural design purposes. Numerical results of an L-shaped steel frame, considered either rigid or semi-rigid, in tabular and graphical form, reveal the pronounced effect of the joint’s stiffness and its specific role especially on higher vibration modes, implying that the actual flexible joint behavior should be accounted for, even in the elastic range.

Effect of joint flexibility on walking economy in middle-aged and older people.

Effect of joint flexibility on walking economy in middle-aged and older people.

Effect of joint flexibility on walking economy in middle‐aged and older people

Purpose: The purpose of the present study was to clarify the effect of joint flexibility on walking economy.Methods: Forty‐one healthy people (20–79 years) were divided into old (n = 13, 67 ± 5 years), middle (n = 11, 54 ± 3 years) and young groups (n = 17, 23 ± 3 years). Each group was asked to measure maximal walking speed, flexibility (trunk, ankle and hip joint), oxygen uptake during treadmill walking (60, 80 and 100 m/min) with and without stretching.Results: All variables measured (except flexibility of ankle joint) in older groups (n = 24) were significantly lower than those in the young (P < 0.05–0.001). However, there was no difference in mean values between the two older groups. Although stretching improved flexibility in all groups (P < 0.01–0.001), oxygen uptake during walking decreased only in the older groups (P < 0.05–0.01). Maximal walking speed in the older groups positively correlated only with flexibility of hip joint (r = 0.52; P < 0.01) and negatively with oxygen uptake during walking (r = –0.37 to –0.41 (P < 0.05)). The only flexibility that showed significant correlations with oxygen uptake during walking was that of the hip joint in the older groups (older: r = –0.44 to –0.55; P < 0.05–0.01; young: r = –0.11 to 0.08).Conclusion: These data suggest that the increase of flexibility, especially flexibility of the hip joint, induces improvement of walking economy in older adults, but not in young adults, and that increasing the flexibility of the hip joint could contribute a beneficial effect to maintaining and improving walking ability in middle‐aged and older adults.

Dynamic simulation model for mixed-loop planar robots with flexible joint drives

A dynamic simulation model for mixed-loop planar robots with flexible joint drive and servo-motor control is developed. The motion of the links is coupled with the deflection of the drive shaft at the joints. The virtual work method is used for the derivation of the mathematical model. The drive signal at the motor is based on the error between the desired and actual motions using proper position and velocity gains. Different motion programs are considered in the simulation for the time histories of the angular displacements and velocities of the links and motors. The driving torques and the total error produced at the end-effector are computed. The simulation results for a five-link, three degrees of freedom manipulator show that the model presented is capable of simulating the coupling effect of joint flexibility and rigid body motion for planar robots.

Design of force/position control laws for constrained robots, including effects of joint flexibility and actuator dynamics

In this paper, a mathematical representation of constrained robot systems in the form of a differential-algebraic equation model is first considered. This model in modified further to include the joint flexibility between the linkages of the robot, and the actuator dynamics. The objective is to design a feedback control law for the system so that the position output variables (typically the end-effector position) and the force output variables (typically the contact force between the robot's end-effector and the contact surface) of the robot follows the desired position and the desired force trajectories, respectively, despite the presence of joint flexibility and actuator dynamics. A systematic procedure is developed for designing a feedback control law which ensures that the position variables track the desired position trajectories exponentially, and the force variables track the desired force trajectories exponentially. Since the development of the control law is based on the model of a constrained robot system which includes the effects of actuator dynamics and joint flexibility, it is possible to achieve better tracking performance using the force/position control law developed in this paper in cases where such effects are significant.

Effect of joint flexibility in adhesively bonded composite panel-to-flange joints

An experimental and numerical study was conducted to investigate the postbuckling induced failure in adhesively bonded composite postbuckled panel-to-flange (ABPTF) joints. Each ABPTF joint structure consists of two laminated flanges bonded to a long laminated panel. When the ABPTF joint structure is loaded in compression, the long panel buckles and then generates a relatively large peel stress in the joints. To understand the effects of joint flexibility on the buckling load, failure load and the failure mechanism, a variety of specimens were manufactured using two different stacking sequences for the long panel lay-up, i.e. ( ± 45/0/90)s and (0/90/ ± 45)s, and seven different stacking sequences for the flange lay-up, i.e. ( ± 45/0/90)2s, ( ± 45/0/90)s, ( ± 45)s, ( ± 45)2s, (0/90/ ± 45)2s, (0/90/ ± 45)s and (0/90)s. Typical buckling and postbuckling behaviour for all specimens was observed and then correlated with the numerical predictions. The failure surfaces were studied using a scanning electron microscope (SEM), and features of failure were identified. It is revealed that flexible joints have reduced peel stress and consequently provide higher joint efficiency while stiff joints have relatively large peel stress and thus give lower joint efficiency. Here joint efficiency is defined as the ratio of the maximum stress outside joint to its associated strength allowable when joint fails.

Flexible rotor beam element for the manipulators with joint and link flexibility

This paper presents a new flexible rotor beam element to study the dynamic behaviour of manipulators with flexible links and joints. Both link and joint flexibility are incorporated together by using the element model which is the combination of a finite element model for links and a torsional spring model for joints. The coupling terms of link and joint flexibility are considered in the dynamic equations of the manipulator. A planar 3R manipulator with flexible links and joints is analyzed as an example. The results of numerical simulation show the significant effect of joint flexibility in the dynamics of compliant manipulators.

Dynamic response of hollow section frames with bolted moment connections

The behaviour of moment-resisting steel frames under various types of loads is dependent on the type of beam-to-column connections and their flexibilities. The extended end-plate connection is a practical field bolted moment connection that can be adopted in moment-resisting steel frames with hollow structural steel (HSS) columns, by using high strength blind bolts. The objective of this work was to study the behaviour of blind bolted extended end-plate connections for HSS columns under cyclic loading. With proper detailing and modelling of such connections, it has been possible to investigate the effect of joint flexibility on the response of the frame when subjected to dynamic loading and then to compare its response to that of a rigid frame. It is concluded that the proposed bolted joint behaves in a predictable manner that can be modelled and analysed using standard frame analysis programmes. The study also showed that the inclusion of the connection flexibility in frame analysis is essential to obtain a more realistic frame behaviour.

Control of constrained robots including effects of joint flexibility and actuator dynamics

AbstractWe consider mathematical representations of constrained robot systems in which the effects of joint flexibility and actuator dynamics are significant. The objective is to design a feedback control law so that the position output variables and the force output variables of the robot follows the desired position and the desired force trajectories respectively despite the presence of joint flexibility and actuator dynamics. A systematic procedure is developed for designing a feedback control law which ensures that the position variables track the desired position trajectories exponentially, and the force variables track the desired force trajectories exponentially. The development of the control law is based on the model of a constrained robot system which includes the effects of actuator dynamics and joint flexibility. Thus using the force/position control law developed in this paper one can achieve better tracking performance in cases where such effects are significant.

Connection element method for the analysis of semi-rigid frames

A general procedure for incorporating the effects of joint flexibility into standard methods for the analysis of frames is presented. The method can allow for joint flexibility associated with all six degrees of freedom normally considered when analysing three-dimensional frames, including coupling between deformations. It can also allow for the finite size and exact location of connections. Simple examples using the moment distribution technique, slope deflection equations and matrix stiffness method illustrate the application of the proposal. Additional examples to illustrate the effects of connection length on the frame moment distribution, lateral drift and column load capacities are also present.

Decoupling force and motion control in industrial robots

Abstract A theoretical approach to force control design for industrial robots involved in surface-following tasks is described in this paper, assuming an infinitely stiff environment. Independent Joint Control techniques, based on standard (PID) algorithms, are adopted for position control. Force control acts as an outer loop, by adding a bias to the position set points in the joint space. A simple model and compensation of the joint flexibility effects, that play an important role in determining the dynamic behavior of the system, are also presented, leading to a force control decoupled from motion control. Some experimental results are discussed, with reference to the industrial robot SMART.

Dynamic Control of Redundant Manipulators with Joint Flexibility

A general dynamic model of a redundant rigid/flexible-joint manipulator is introduced. Using this model and the pseudo-inverse approach, a Cartesian space control scheme for rigid/flexible-joint redundant manipulators is developed where redundancy is resolved to compensate for the effect of joint flexibility. To avoid possible algorithmic singularities, a modified damped least-squares approach is incorporated in the control scheme. Issues concerning the compensation capability are also discussed. Finally, computer simulations are given to illustrate the application of the proposed control scheme.

Decoupling Force and Motion Control in Industrial Robots

A theoretical approach to force control design for industrial robots involved in surface following tasks is described in this paper, assuming an infinitely stiff environment. Independent Joint Control techniques, based on standard (PID) algorithms, are adopted for position control. Force control acts as an outer loop, by adding a bias to the position set points in the joint space. A simple model and compensation of the joint flexibility effects, that play an important role in determining the dynamic behavior of the system, are also presented, leading to a force control decoupled from motion control. Some experimental results are discussed, with reference to the industrial robot SMART.

Seismic performance of moment resisting frames with flexible joints

An analytical study was conducted to investigate the effect of joint flexibility, in particular extended end-plate joints, on the response of moment resisting frames. Eight storey frames having extended end-plate joints and with joints detailed according to different design criteria, were analysed for different earthquake records using a step-by-step time history analysis. Realistic models developed from an extensive experimental research program were used to simulate the joint response. An evaluation of the frames' performance in terms of lateral deflection, inter-storey shear, drift, and the inelastic rotational demands imposed upon the beams, columns and joints was carried out. It is concluded that joint behaviour is an important consideration in a frame's response. Also, its performance can be much improved by properly designing and detailing the joints.