Effect of Unbalanced Force Loading on the Safety of Transmission Tower

High-voltage transmission towers, as support points for overhead transmission lines, are often under the condition of unbalanced force loading. Transmission towers can collapse because of the unbalanced forces, leading to the power outage. Therefore, it is of practical importance to set a research on the effect of unbalanced force loading on the safety of transmission tower. In this paper, based on the prototype of 500kV transmission tower, the integral beam element model is established by ABAQUS finite element software for simulation analysis. Static load mode and unbalanced force loading were considered in this simulation model. Through the comparative analysis of the maximum displacement and stress in transmission tower, the safety of the 500kV transmission tower was analyzed. The variations of maximum displacement and Mises stress with the increasing unbalanced force were obtained. The limit of unbalanced force the 500kV transmission tower can sustain was given by comparing the simulated results.

Three-dimensional loading control of a pneumatic three-universal–prismatic–universal robot

Multidimensional force loading has been widely used in the fields of component and material testing. The pneumatic-driven multidimensional force loading parallel mechanism can meet the requirements of complex force loading. A three-dimensional loading robot based on a pneumatic three-universal–prismatic–universal parallel mechanism is designed to apply time-varying three-dimensional loads on a target. Based on the principle of vector superposition, inverse and forward kinematics are deduced. A second-order mathematical model of a metal seal pneumatic cylinder driven by a flow proportional valve is established. Based on the immersion and invariance technique, the leakage flow in the cylinder is taken as the interference term and estimated. Meanwhile, because of the strong nonlinearity of the actuator, based on suitable disturbance estimation, the control rate of the system is designed through the sliding mode surface, and the stability of the control algorithm is analyzed on the basis of the Lyapunov stability theory. The experimental results show that the immersion and invariance controller exhibits a better control performance than the proportional–integral–differential controller: the steady-state control mean square error is reduced by approximately 21% on average and the dynamic (0.2 Hz) tracking mean square error is approximately 10.35 N.

Thermal force loading of an orthotropic cylindrical shell made of a deformationally anisotropic material

Объектами рассмотренных исследований послужил частный случай оболочечных конструкций, а именно оболочка вращения - замкнутая круговая цилиндрическая, так как подобные сооружения весьма часто встречаются при проектировании и строительстве промышленных и гражданских объектов, а также в энергетике. Особенностью конструкции исследуемых оболочек являются материалы, из которых они выполнены, обладают анизотропией двоякого характера. Рассмотрена структурная анизотропия материала уровня ортотропии в совокупности с деформационной, появляющейся в зависимости жесткостных и прочностных свойств от вида напряженного состояния. Оболочка загружается внутренним давлением, которое сводится к равномерно распределенной осесимметричной нагрузки. Кроме того, при постановке задачи строительной механики учтено, что конкретные сооружения эксплуатируются не в идеальном стационаром изолированном пространстве, а в среде с изменяющимися температурными параметрами. При этом учтена вероятность проявления температурного перепада между внутренней загруженной поверхностью оболочки и наружной - свободной от силового воздействия. Известно, что в общем случае температурные и силовые поля взаимосвязаны, а распределение температуры в материале конструкции зависит от напряженного состояния, но как показали многочисленные исследования, связанность термомеханической задачи заметно проявляется только в короткий начальный период температурного изменения до возникновения установившегося перепада. Поэтому в представленной статье задача по термосиловому нагружению цилиндрической оболочки рассматривается в несвязанной постановке, когда общую задачу можно разделить на две независимые: строительной механики и термодинамики. Учитывая, что классические теории термомеханики оболочек, выполненных из материалов, обладающих анизотропией двоякого характера, не позволяют получить достаточно надежные результаты, а большинство известных моделей, предназначенных для указанных материалов, обладают серьезными недостатками, здесь использована методика нормированного тензорного пространства напряжений. В статье представлена система дифференциальных уравнений задачи термоупругости цилиндрической оболочки из материалов с усложненными термомеханическими свойствами. Приведены отдельные решения с наиболее характерными результатами расчета напряженно-деформированного состояния оболочки с их анализом. The objects of the considered studies were a special case of shell structures, namely, the shell of rotation - a closed circular cylindrical one, since such structures are very often found in the design and construction of industrial and civil facilities, as well as in the energy sector. A special feature of the design of the studied shells is the materials, which have anisotropy of a twofold nature. The structural anisotropy of the material of the orthotropy level is considered in conjunction with the deformation one, which appears depending on the stiffness and strength properties of the type of stress state. The shell is loaded with internal pressure, which is reduced to a uniformly distributed axisymmetric load. In addition, when setting the problem of construction mechanics, it is taken into account that specific structures are operated not in an ideal stationary isolated space, but in an environment with changing temperature parameters. At the same time, the probability of a temperature difference between the inner loaded surface of the shell and the outer surface - free from force action-is taken into account. It is known that in the general case, the temperature and force fields are interrelated, and the temperature distribution in the material of the structure depends on the stress state, but as numerous studies have shown, the connectivity of the thermomechanical problem is noticeable only in the short initial period of temperature change before the occurrence of a steady drop. Therefore, in the present article, the problem of thermal force loading of a cylindrical shell is considered in an unrelated formulation, when the general problem can be divided into two independent ones: structural mechanics and thermodynamics. Given that the classical theories of thermomechanics of shells made of materials with anisotropy of a twofold nature do not allow us to obtain sufficiently reliable results, and most of the known models designed for these materials have serious drawbacks, the method of normalized tensor stress space is used here. The article presents a system of differential equations for the problem of thermoelasticity of a cylindrical shell made of materials with complicated thermomechanical properties. Separate solutions with the most characteristic results of calculating the stress-strain state of the shell and their analysis are presented.

Active Loading Control Design for a Wearable Exoskeleton with a Bowden Cable for Transmission

Exoskeletons with a Bowden cable for power transmission have the advantages of a concentrated mass and flexible movement. However, their integrated motor is disturbed by the Bowden cable’s friction, which limits the performance of the force loading response. In this paper, we solve this problem by designing an outer-loop feedforward-feedback proportion-differentiation controller based on an inner loop disturbance observer. Firstly, the inner loop’s dynamic performance is equivalent to the designed nominal model using the proposed disturbance observer, which effectively compensates for the parameter perturbation and friction disturbance. Secondly, based on an analysis of the stability of the inner loop controller, we obtain the stability condition and discuss the influence of modeling errors on the inner loop’s dynamic performance. Thirdly, to avoid excessive noise from the force sensors being introduced into the designed disturbance observer, we propose the feedforward-feedback proportion-differentiation controller based on the nominal model and pole configuration, which improves the outer loop’s force loading performance. Experiments are conducted, which verify the effectiveness of the proposed methods.

Does cellular adaptation to force loading rate determine the biphasic vs monotonic response of actin retrograde flow with substrate rigidity?

The transmission of cytoskeletal forces to the extracellular matrix through focal adhesion complexes is essential for a multitude of biological processes such as cell migration, differentiation, tissue development, cancer progression, among others. During migration, focal adhesions arrest the actin retrograde flow towards the cell interior, allowing the cell front to move forward. Here, we address a puzzling observation of the existence of two distinct phenomena: a biphasic relationship of the retrograde flow and cell traction force with increasing substrate rigidity, with maximum traction force and minimum retrograde flow velocity being present at an optimal substrate stiffness; in contrast, a monotonic relationship between them where the retrograde flow decreases and traction force increases with substrate stiffness. We propose a theoretical model for cell-matrix adhesions at the leading edge of a migrating cell, incorporating a novel approach in force loading rate sensitive binding and reinforcement of focal adhesions assembly and the subsequent force-induced slowing down of actin flow. Our model unravels both biphasic and monotonic responses of the retrograde flow and cell traction force with increasing substrate rigidity, owing to the cell’s ability to sense and adapt to the fast-growing forces. Moreover, we also elucidate how the viscoelastic properties of the substrate regulate these nonlinear responses and alter cellular behaviours.

The glycocalyx affects force loading-dependent mechanotransductive topography sensing at the nanoscale

ABSTRACTThe cell/microenvironment interface is the starting point of integrin-mediated mechanotransduction, but many details of mechanotransductive signal integration remain elusive due to the complexity of the involved (extra)cellular structures, such as the glycocalyx.We used engineered nano-bio interfaces with extracellular matrix nanotopography-mimicking features to analyse the impact of the glycocalyx on nano-mechanosensing. Our data demonstrates that the glycocalyx configuration affects spatiotemporal nanotopography-sensitive mechanotransductive events at the cell/microenvironment interface. Opposing effects of glycocalyx removal were observed, when comparing flat and specific nanotopographical conditions (i.e., 15 nm root-mean-square (rms) roughness). In fact, the excessive force loading and retrograde actin flow speed, characteristic for the 15 nm rms nanotopography in the presence of native glycocalyx, are strongly reduced in its absence. Conversely, on the flat substrate, these parameters increased upon glycocalyx-targeting enzymatic treatment.Our results highlight the importance of the glycocalyx configuration in a molecular clutch force loading-dependent cellular mechanism for nano-mechanosensing of the topography.