Path Analysis for Hybrid Rigid–Flexible Mechanisms

Hybrid rigid–flexible mechanisms are a type of compliant mechanism that combines rigid and flexible elements, being that their mobility is due to rigid-body joints and the relative flexibility of bendable rods. Two of the modeling methods of flexible rods are the Cosserat rod model and its simplification, the Kirchhoff rod model. Both of them present a system of differential equations that must be solved in conjunction with the boundary constraints of the rod, leading to a boundary value problem (BVP). In this work, two methods to solve this BVP are applied to analyze the influence of external loads in the movement of hybrid compliant mechanisms. First, a shooting method (SM) is used to integrate directly the shape of the flexible rod and the forces that appear in it. Then, an integration with elliptic integrals (EI) is carried out to solve the workspace of the compliant element, considering its buckling mode. Applying both methods, an algorithm that obtains the locus of all possible trajectories of the mechanism’s coupler point, and detects the buckling mode change, is developed. This algorithm also allows calculating all possible circuits of the mechanism. Thus, the performance of this method within the path analysis of mechanisms is demonstrated.

Osteosynthesis With Elastic Titanium Nail For Fractures Of Long Bones Of The Lower Extremities In Children

In recent years, approaches have been used to treat diaphyseal fractures in children and adolescents, which make it possible to shorten immobilization and hospitalization time as soon as possible, as well as return to normal life as soon as possible. In a retrospective study, the conservative treatment of diaphyseal hip fractures was compared with the closed elastic method of rod fixation. In the period from 2014 to 2019. In our clinic, 11 diaphyseal fractures of the femur and 16 tibia were treated. In all cases, elastic rod osteosynthesis was used. Conservative treatment gave more complications (difference in limb length and inaccurate reduction). In case of the closed fracture fixation with the help of flexible rods the consolidation and fast mobilization with small number of complications was achieved.

Optimization of design solutions for main pipeline projects in conditions of island and intermittent permafrost

Представлены результаты численных экспериментальных исследований по оптимизации проектных решений при прокладке участков магистральных трубопроводов в условиях распространения прерывистой и островной мерзлоты. Обоснована нецелесообразность использования надземного способа прокладки трубопровода на опорах при незначительной протяженности зон многолетнемерзлых пород. В качестве альтернативы указан метод подземного закрепления участков с помощью специально разработанных анкерных опор на гибких тягах. При расчете конструкции опор учитываются особенности знакопеременных сезонных нагрузок, возникающих при различных вариантах оттаивания траншей в мерзлых породах под действием температуры окружающей среды и самого трубопровода. С целью оценки напряженно-деформированного состояния отклонившихся от проектного положения подземных участков трубопровода разработана многофакторная конечно-элементная модель, позволяющая рассчитать допустимые нагрузки и определить места опасных сечений для выбора максимального шага расстановки опор. В результате расчетов подтверждена нецелесообразность использования теплоизоляции, вес которой многократно увеличивает уровень напряженности на опасных сечениях как при всплытии, так и при провисании трубопровода в оттаившей траншее. Для трубопровода диаметром 1200 мм определены допустимые значения протяженности пролетов - максимальный шаг расстановки подземных опор. Проведены оптимизационные расчеты для различных сочетаний постоянных и переменных нагрузок, по результатам которых подтверждена возможность сокращения количества опорных конструкций путем исключения теплоизоляции, ограничения температуры монтажа и укладки упругим изгибом в направлении, обратном направлению стрелы прогнозируемого прогиба оси трубопровода. The results of numerical experimental studies on optimization of construction of main pipelines in areas of intermittent and seasonally melting permafrost are presented. The paper is devoted to inexpediency of an aboveground method of laying the pipeline on supports in small areas of island permafrost zones characterized by solid ice lenses and heaving mounds. Alternatively, the method of underground anchoring of sections using specially designed anchor supports on flexible rods is proposed. The design of these supports takes into account the features of alternating seasonal loads that occur in various variants of thawing trenches in frozen rocks under the influence of ambient temperatures and the pipeline itself. In order to assess the stress-strain state of underground sections that deviated from the design position, a multi-factor finite element model was developed that allows to calculate the permissible loads and determine the places of dangerous cross-sections for selecting the maximum step of placement of supports. As a result of calculations performed using the developed mathematical model in ANSYS, it was confirmed that it is not practical to use thermal insulation, the weight of which repeatedly increases the level of tension at dangerous sections, both when surfacing and when sagging sections in a thawed trench. For a pipeline with a diameter of 1200 mm, the permissible values of spans are defined - the maximum step of placement of underground supports. Using the developed model, optimization calculations were performed for various combinations of constant and variable loads, during which the possibility of reducing the number of support structures by eliminating thermal insulation, limiting the installation temperature and laying the underground section with an elastic bend in the direction opposite to the predicted deflection of the pipeline axis during thawing of the soil was confirmed.

Synthesized Optimal Control of Group Interaction of Quadrocopters Based on Multi-Point Stabilization

The study examines the problem of optimal control of group interaction of three quadrocopters. A group of three quadrocopters must move the load on flexible rods from one point in space to another one without hitting obstacles, one quadrocopter being not able to complete the task due to the weight of the load. To solve the problem, the method of synthesized optimal control based on multi-point stabilization was used. The method is called synthesized, since the problem of synthesizing the stabilization system for each robot is first solved. At the next stage, the problem of the optimal location of stabilization points in the state space is solved in such a way that when these points are switched from one to another, at a given time interval, the quadrocopters move the load from the initial position to the final one with the optimal value of the quality criterion. The network operator method is used to solve the synthesis problem. All phase constraints describing group interaction and obstacles are included in the quality criterion by the method of penalty functions. An evolutionary particle swarm optimization algorithm was used to find the positions of points

Attitude control of nanosatellite with single thruster using relative displacements of movable unit

The attitude dynamics of a nanosatellite (NS) with one movable unit changing its angular position relative to a main body of the nanosatellite is considered. This relative movability of the unit can be implemented with the help of flexible rods of variable length connecting the unit with the main body. Change of the relative position of the movable unit shifts the center of mass of the entire mechanical system. The NS has a single jet engine rigidly mounted into the NS main body. The shift of the mass center creates an arm of the jet-engine thrust and a corresponding control torque. Schemes to control the attitude dynamics of the satellite using the movability of its unit are developed, using both the torque from the engine and inertia change.