Additional Dynamic Loads Research Articles

Estimation of the Service Life of Approach Slabs of Road Bridges Based on the Statistical Modeling Method

The article discusses the durability and reliability of a separate element – bridge approach slab, which is justified by the need to maintain a satisfactory technical condition of Ukrainian bridges in general and traffic safety on public roads with limited funding during martial law. The scope of the research is forecasting the residual service life of bridge elements (on the example of approach slabs) using probabilistic methods. Approach slabs are designed to smoothly and safely connect the road approach embankment with the bridge to gradually equalize the elastic modulus of the carriageway from a less rigid asphalt pavement on an elastic base to a more rigid one on a reinforced concrete slab. The main defects in the destruction of approach slabs are: changes in the longitudinal profile of the road due to the collapse and subsidence of the soil under the approach slabs; longitudinal and transverse cracks in the asphalt concrete pavement on the bridge approaches; and potholes that lead to an increase in the additional dynamic load on the bridge deck.

Assessment of the stress-strain state of slopes in landslide-prone areas where critical infrastructure facilities are located

Purpose. Ensure the integrity of landslide-prone areas through a developed method for assessing the stress-strain state of slopes based on seismic wave registration. The methods. To solve these tasks, the following steps were conducted: calculation of shear stresses and relative deformations of the landslide-prone soil area; registration of seismic vibrations using a MiniMateplus seismograph, determining the amplitudes of mass vibration velocities and frequency characteristics by components (tangential, vertical, radial), and identification of critical points based on shear stress magnitudes and relative deformations that are close to or exceed critical values. Findings. Through the registration of frequency characteristics at specified distances along the entire profile, it is possible not only to assess the hazard level of soil slopes at each point but also to create conditions ensuring necessary stability against additional special loads. The originality. The study introduces a method for monitoring landslide-prone areas based on seismic data analysis. For the first time, the dependency of stress-strain states of slopes in landslide-prone areas on the impact of amplitude frequencies of multiple stepwise free-fall drops of a load (artificial shock) is established through the registration of artificially induced seismic waves. The method considers only those shear stresses and relative deformations whose magnitudes are close to or exceed critical values within the same frequency range. It has been determined that resonance phenomena occur at specific frequencies, which can initiate landslide processes. The slope stability assessment method has further evolved to account not only for the current state of soil slope hazards but also to ensure stability against additional dynamic loads. Practical implementation. Experimental studies have established that to ensure the seismic resistance of critical infrastructure objects, it is necessary to consider not only the mass vibration velocity of soil particles but also the frequency characteristics of the object itself.

Chaotic dynamics of granules-beam coupled vibration: Route and threshold

Although granular materials are the second most processed in industry after water, the theoretical study of granules-structure interactions is not as advanced as that of fluid-structure interactions due to the lack of a unified view of the constitutive relation of granular materials. In the previous work [1], the theoretical model of granules-beam coupled vibration was developed and verified by experiments. However, it was also found that the system exhibits significant stiffness-softening Duffing characteristics even under micro-vibration, which implies that chaotic responses may be reached under certain conditions. To reveal the route and critical conditions for the system to enter chaos, in the present work, the chaotic dynamics of the system are studied. In qualitative analysis, Melnikov method is applied to analyze the instability behavior of the perturbed heteroclinic orbit of the system, thus the critical condition for the system to enter Smale horseshoe chaos, i.e., the Melnikov criterion, is obtained. The validity of the criterion is verified numerically. In experimental studies, the existence of chaotic responses and the route to chaos for granules-beam coupled vibrations is revealed. The experimental results suggest that the system response first experiences symmetry-breaking then undergoes a complete period-doubling cascade, and finally enters single-scroll chaos. In addition, although the Additional Dynamic Load (ADL) generated by granular media is highly complicated, a general and simple evolution pattern of the chaos threshold is found by parametric experiments, which is also supported by the Melnikov criterion. In short, the chaotic dynamics of granules-beam coupled vibration is revealed, which is a contribution to the engineering vibration aspect. On the theoretical side, an impressive result lies in that for the first time, the Melnikov criterion of such fractional-order systems is obtained in a global and closed form, which provides, respectively, improvement suggestions and reference results for the existing and future research on chaotic dynamics of fractional-order systems, especially of the Duffing-type systems.

Fractional-order model and experimental verification of granules-beam coupled vibration

Granular media generally exhibit fluid phase, solid phase, or two coexisting phases, and the mechanism of the phase transition is not clear enough. Therefore, unlike the airflow-structure or fluid–structure coupled vibrations, the granules-structure coupled vibrations have not yet been theoretically modeled, and the interest in such coupled vibrations, which has just started in recent years, is mainly focused on experiments and simulations. In order to develop a theoretical model of the coupled vibrations of granular media and beam structures, in this paper, a novel concept called the inertia-viscous effect is introduced in terms of terminology and mathematical expression, and surprisingly, its constitutive relation can be summarized in a unified framework based on fractional calculus, together with Hooke spring, Newtonian dashpot, and Abel sticky pot. Furthermore, the existence of this effect in the granules-beam coupled vibrations is experimentally confirmed, and more importantly, the effect is more suitable for modeling by fractional-order derivatives rather than the conventional integer-order ones due to the frequency-dependent characteristics of the effect. Based on this, the theoretical model of the granules-beam coupled vibrations and the associated parameters identification procedure are successfully developed, in which a fractional-order model is proposed to describe the additional dynamic load (ADL) of the granular media on the beam. The numerical and experimental results suggest that the system response can be accurately predicted by the developed theoretical model without the computational cost as in the discrete element methods, which is the main contribution of this work. Finally, the effectiveness and robustness of the developed theoretical model are further verified by the results of numerous parametric experiments, and importantly, by combining these results with the analytical results, the mechanism of ADL is revealed, thus providing insights for modeling coupled vibrations between other engineering structures and granular media. From another perspective, this work can also be seen as a novel application of fractional calculus in the dynamics of mechanical systems.

The impact of short-wave effects on deterioration of track geometry

Short wavelength rail defects or short-wave effects of rail have a significant influence on the system behaviour of railways. The influence of additional dynamic loads due to short-wave effects on component wear and the general quality behaviour of track is shown by several research papers. However, the described effect cannot yet be quantified comprehensively. This paper attempts to fill this gap. With the help of extensive data analysis, we can show that short-wave effects lead to a track geometry that is up to 50% worse than on average. Furthermore, we show examples illustrating the influence of untreated welded joints on the development of isolated defects of the track geometry. A detailed in-depth analysis of sections with different boundary conditions finally shows that short-wave effects have a significant influence on track geometry if the amplitude of the effect exceeds 0.15 mm. This value can be recommended as a threshold value in Austria and as a reference value in other countries.

Dynamic response assessment of an offshore wind turbine under Peruvian environmental conditions

This paper presents a dynamic response analysis of an offshore monopile wind turbine to be deployed at a near-shore area in the south-centre part of the Peruvian coast (Marcona). It is a 5 MW three bladed wind turbine that operates in an aggressive offshore environment described by its stochastic behaviour. Thus it is necessary to use a statistical approach for its characterization. The operating wind turbine is simulated using an aero-hydro-servo-elastic computational tool (FAST) that allows the simulation of coupled systems. After the simulation, this work analyses relevant dynamic responses (thrust, torque, shear forces, and bending moments). Time series of these responses at critical zones of the wind turbine are presented. The results indicate high variability of the responses and critical fluctuations located at the mudline. It is found that this variability is due to the additional dynamic loads coming from the ocean waves. This is a big issue to consider when designing a monopile offshore wind turbine operating under the Peruvian environmental conditions.

Structural Strength and Fatigue Strength Analysis of Roller Arm

The cone reamer is used for underhole reaming, mainly through the impact crushing and cutting of teeth to complete rock breaking, easy to produce vibration. At the same time, the underground topography is complex and rock materials are changing. Therefore, the force of the cone reamer is complex and easy to damage. According to the statistics of the field use, the main failure form is the failure of the roller arm. The reaming arm consists of two parts: a cone arm and a bearing. As for the reaming arm, it is subjected to the reaction force of rock on teeth and the support force of piston when working. When the teeth eat into the rock alternately, longitudinal vibration will be generated, so that the force of the cone arm is random impact load. Due to the instability of bit weight, additional dynamic load is caused, resulting in the piston support force is also random impact load. Thus causing the fracture of the cone arm. For bearings, reamers are used to drill stepped holes and rely on the outer teeth of the cone as opposed to the cone bit. When the teeth eat into the rock alternately, the longitudinal vibration is generated, and the rock is broken through the impact and cutting of the teeth. And the axial acceleration of the cone reamer is greater than the longitudinal acceleration, so the axial vibration is severe and the bearing bears the impact load. At the same time, the wall morphology and rock material are changing, so the bearing is subjected to random contact fatigue load. The piston cracks under the repeated action of random load, leading to fatigue failure. It can be seen from the structure characteristics and working principle of the cone reamer that the cone arm is the core functional component of the cone reamer. Therefore, abnormal failure of the above components should be avoided as far as possible. Therefore, this paper completed the simulation analysis of the cone arm, obtained the stress and strain distribution of the cone arm, and established the finite element analysis specification and safety evaluation index of the cone arm.

Substantiation of safe parameters for yielding rib pillars in mining technology of ore breaking with induced roof subsidence in complex rockburst-hazardous conditions in Severouralsk bauxite mines

The article discusses VNIMI’s instructional approaches to application of the room-and-pillar systems in the conditions of complex geodynamics in mining rockburst-hazardous bauxite deposits at Severouralsk. The authors describe the determination procedure and resultant parameters of the yielding rib pillars in the mining technology with ore breaking and induced roof subsidence. Stability of structural components experiences high influence of an additional dynamic load initiated by deformation of a blocky structure. In view of the complex shape of the rib pillars, their rockburst hazard is determined using the digital twin PRESS 3D URAL which allows anticipatory assessment of the induced impact exerted by heading and stoping operations on adjacent rock mass. The criterion parameter in the current dynamic hazard prediction is the stress intensity factor at the orebody bottom. The geodynamic safety control using a set of modern powerful hardware/software facilities allows actual reliable and accurate determination and control of the geodynamic behavior of rock masses, as well as the quantitative and qualitative estimation of the geodynamic risks. The timely and reliable prediction and prevention of geodynamic events enables effective managerial decision-making on the improved safety of mines being designed, constructed and operated in difficult geological and geodynamic conditions. The expected result is the enhanced economic efficiency and increased competitive ability of mining companies in the Russian and in the global markets of metals, as well as the higher economic stability of mines.

Analysis of the Vehicle Chassis Axle Fractures.

With the rapid development of the road transport industry, trucks with semi-trailers have become the main means of transporting goods by road. High quality, durability and reliability of the construction are the main requirements for the production of trailers. Trailer and semi-trailer axles are one of the main and most important components of a truck. Due to the fact that semi-trailer axles are subjected to additional static and dynamic loads during operation, their proper construction is extremely important, therefore they should be carefully designed and tested. The durability of the suspension components refers to the duration of the onset of fatigue. This article presents an analysis of damage to the rear axle of the semi-trailer using macroscopic observations of the damage site and dynamic FEA of stress distribution in the axle material. In order to identify the probable cause of the damage, eight cases of loading the semi-trailer axle were considered. Analytical solutions have shown that in various cases the yield point is exceeded and the strength limit of the modeled semi-trailer axle is reached. The risk of damage to the vehicle's suspension system components increases on poor roads (bumps and winding road sections).

Advanced studies for probabilistic optimal power flow in active distribution networks: A scientometric review

In the active distribution networks (ADNs), the emerging trend of high penetration of sustainable energy sources such as wind turbines, photovoltaics, and the forthcoming integration of energy storage devices and additional dynamic loads like plug-in-electric vehicles (PEVs) influences to change the nature of electric distribution networks. Consequently, it deteriorates power quality and reliability in terms of unacceptable voltage rise-drop, harmonic distortion, voltage unbalance, and excessive power loss. In this context of transition into the active distribution network, the probabilistic optimal power flow (P-OPF) in the ADN is considered an important tool that helps the distribution grid operators for defining the optimal settings of the system's control variables. However, the optimal solution of P-OPF becomes highly complex while considering the multiple variables, time-varying characteristics and operational uncertainties associated with sustainable resources, consumer behaviour and electricity market prices. This review aims at promoting the research and discussion of P-OPF studies in the context of ADNs characteristics and challenges. First, we perform a data-driven and visualized scientometric analysis of 1988 quality documents retrieved from the Scopus during the last ten years using VOSviewer software. Second, an in-depth investigation of the recent and emerging techniques for solving the P-OPF problem is presented. Third, a set of recommendations and highlights of future challenges for P-OPF in ADNs are offered. The review findings showed high interest among the scientific community in sustainable energy source integration, given the recent rise in publications and citations. Also, there is still a lack of innovative optimization techniques that can adequately handle the current issues associated with P-OPF and objectives with fair computational efficiency and accuracy. Finally, this paper offers a guide for P-OPF researchers to navigate the recent studies considering the sustainable sources, spot the new research frontiers, and identify the most impactful countries and publishers.

Dynamic response of unsaturated poroelastic ground underlying uneven pavement subjected to vehicle load

In this study, the dynamic response of unsaturated ground coupled with an uneven model due to vehicle load is investigated. The governing equation of the unsaturated poroelastic ground is established by extending Biot's theory. The uneven pavement is simplified as a Kirchhoff small-deflection thin plate. The vehicle is modeled as a spring–mass damping system, while considering the effect of the uneven pavement. The dynamic wheel-uneven pavement force is calculated by regarding the pavement roughness as a sinusoidal wave. The solutions in the wavelength domain are presented by applying a double Fourier transform. Subsequently, the corresponding numerical results in the space domain are obtained by employing the numerical method of the double inverse Fourier transform. Next, the stress paths of the unsaturated soil element caused by the vehicle load are calculated and analyzed. The numerical results show that the additional dynamic load caused by the uneven pavement is affected by pavement roughness and vehicle velocity. The increasing vehicle velocity slightly affects the vertical normal stress, shear stress, and stress path. However, the peaks of the horizontal normal stresses increase, and the vertical displacement decreases. The ground dynamic response is significantly and positively correlated with the axle load. As saturation increases, the vertical displacement and dynamic stresses of the ground soil decrease slightly, and the stress path is reduced.

Prognostics of unsupported railway sleepers and their severity diagnostics using machine learning

Railway sleepers are safety–critical components of a railway structure. They support ballasted track superstructure and are a critical factor in track geometry and track components’ deterioration. Unsupported sleepers are a common issue incurred after tracks have been utilized. When unsupported sleepers are present, they cause differential settlements of track superstructures, additional dynamic loading, and excessive train-track vibrations which affect passenger comfort, safety, and maintenance cost. This study is the world's first to develop new machine learning models to prognose and better diagnose defect severities of unsupported sleepers aligned with practical track inspection guidelines. Data used to develop machine learning models are based on a verified finite element model with actual field measurements, enabling unbiased full data ranges that govern all defect conditions. Different conditions of unsupported sleepers can be explored by varying locations of unsupported sleepers and the number of unsupported sleepers. Also, other operational parameters can be addressed such as speeds of rolling stock, the roughness of rail surface, and vertical stiffness of wheel-rail contact. In total, 2016 data sets have been obtained. Axle box accelerations are adopted as key indicators for machine learning models. Machine learning techniques used in the study are the convolutional neural network, recurrent neural network, ResNet, and fully convolutional neural network. Data fusion and assimilation have been conducted since the data points are dependent on the train speeds. Our new results reveal a breakthrough essential for real-world applications that the convolutional neural network model provides the best accuracy in both unsupported sleeper prognostics and severity identification. The accuracies of detection and severity identification are 99.34% and 97.02% respectively.

Multi-Layers Composite Plasma Coatings Based on Oxide Ceramics and M-Croll

The paper considers the influence of the parameters of the plasma spraying process on the technological characteristics of multilayer coatings based on nickel-chromium, nickel-chromium-aluminum-yttrium materials, oxide ceramics, intended for operation at high temperature and additional dynamic loads. The design of plasma coatings during their application (with subsequent high-energy processing) under such conditions requires a comprehensive solution – both the use of high-quality powder ingredients and the optimization of technological parameters. The plasma process of applying powder materials has been improved to obtain the maximum values of their utilization factors. The technological characteristics that affect the properties of plasma coatings are optimized, namely: the flow rates of the plasma-forming and materials-transporting gases, the flow rate of supplied powder materials, the current and voltage of the electric arc of the plasma torch, the distance from the plasma torch nozzle exit to the substrate. The paper presents the results of studies of the structure of coatings, performed using scanning electron microscopy. Their analysis has made it possible to form general regularities obtained by the action of radiation of compression plasma flows on coatings formed by air plasma. The considered structures are created using the processes of melting, compaction and high-speed cooling of plasma coatings. The main optimization indicators are the maximum local compaction and spillage of the obtained compositions with the absence of defects and destruction from the impact of compression plasma flows. The main effect during the action of radiation of a compression plasma flow on previously formed coatings is thermal. It contributes heating of the near-surface layer. When the coating is exposed to radiation of compression plasma flows, a remelted layer of oxides with a thickness of about 12–15 µm is created, smoothing the relief of the formed surface and creating a network of cracks on the surface, diverging into the depth of the coating. The liquid-phase processes occurring in the molten phase of the near-surface layers after exposure to compression plasma radiation change the structure of the layers and contribute to the modification of their mechanical properties. By smoothing the surface, increasing the density of the surface crystallized layer and minimizing macro-defects – pores or macrocracks – the mechanical characteristics of the coatings increase.

Modern geomechanical assessment of influence of rockbursts in tectonic areas on mine stability in the North Urals Bauxite Mine

Experience of the North Urals Bauxite Mine shows that the current conditions, namely, mining technologies and rates per extraction panels, as well some other geotechnical factors not always and not in full conform with the actual geology and geomechanics, which affects mining safety. VNIMI accomplished the research aimed at efficiency evaluation of room-and-pillar mining in complicated geodynamic conditions of the North Urals Bauxite Mine. It is found that stability of mine support elements is greatly affected by additional dynamic load induced by deformation of block rock mass. Mining-initiated reactivation of healed faults leads to liberation of large amounts of accumulated energy, which results in dynamic failures in mines. The quantitative estimation of such energy was carried out using Russian software PRESS 3D URAL. The computer modeling results point at the additional concentration of dynamic stresses during slippage along the healed faults, which should be taken into account in mine support design. Before and during actual stoping in extraction panels, it is required to implement geodynamic zoning to update the local tectonic structure, as well as the anticipatory computer-aided prediction (using the adapted anticipatory computerized simulation in PRESS 3D URAL) of the stress–strain behavior and geodynamic safety of rock mass with regard to the widely varying geological factors, their complication with growing depth, as well as aggravation of geodynamic regime and rockburst hazard.

Application of traction balance analysis to increase operating efficiency of road-building machines

Operation of road-building machines is attributed to accelerations, especially in case of speeding-up or taking-off. Established accelerations in machine assemblies and interfaces, as well as in their units, cause additional dynamic loads that increase parts wear and decrease their service life. Acceleration is facilitated by vibration that increases deformation of parts and assemblies, which infringes specified settings and disturbs the process flow, making it unstable. Besides, the engine power utilization factor and machine capacity decrease, fuel consumption increases, which eventually affects economic parameters. It has been demonstrated in practice that optimum conditions of road-building equipment operation, in terms of occurring accelerations and vibrations, take place when unit driving force and the sum of motion resistance forces are approximately equal. Analysis of the traction balance curve of a machine under review, as related to adherence parameters, reveals areas that can be used to determine the maximum traction that can be generated by this machine under particular operating conditions. For instance, in case of low adherence values, a machine is unable to take off and the wheels will be slipping, until the balance point is reached. Further, as the balance point is exceeded, the machine can overcome motion resistance, unless it exceeds the difference between the maximum driving force and the sum of resistance forces, i.e. in case of normal operation. In case of operation within the high adhesion area, a machine engine can stall. Traction balance analysis results of a particular machine can be used to anticipate reasonable conditions and efficiency of road-building machines operation.

Construction of theoretical models for the lifting mechanism of the foundry crane

In the lifting drive of the foundry crane, there are emergency situations provoked by failures of bolted connections in the insert of the split drum. The latter is explained by the appearance of unequal gaps in the gearboxes of the «left» and «right» electromechanical systems driven by asynchronous motors with short-circuited rotors powered by individual frequency converters. With high rigidity of the mechanical characteristics of the engines, small deviations in nominal slides can cause a significant variation in engine loads and, as a result, unequal loading of gearboxes and a skew in the loading of the insert. This leads to a violation of the stability of the speed regime of both parts of the drum and to the appearance of additional dynamic loads in the lifting ropes and vibrations of the bucket with metal. The proposed design schemes of the lifting mechanism of the foundry crane allow tracing the nature of simplifications and focusing on possible emergency situations. Lifting models of electromechanical systems make it possible to study their dynamics in typical operating modes. The presence of a gap in the insert when one of the motors is switched off leads to an oscillatory process in electromechanical systems; this especially affects the movement of the insert elements — there are areas of gap opening, which leads to additional dynamic loads in bolted connections and their premature failure. It is recommended to take the elastic moment in the insert as a diagnostic value, by the nature of the change of which it is possible to judge the development of an emergency situation in electromechanical lifting systems.

Towards the dynamic coefficient

For the first time, this paper studies the fundamental conditions of the dynamics of bridge spans under non-stationary oscillations with regard to the mass inertia of the span–vehicle system. Based on the dynamic analysis of the stress-strain state of spans under changing live load, the mechanical and energy principles of additional dynamic load characterized by the dynamic coefficient, are formulated and substantiated. It is found that the dynamic coefficient slightly depends on the system vibrations due to the temporary nature of its application. The amplitudefrequency characteristics of the dynamic stress-strain state are considered in the mode of stable oscillations only. Theoretical and experimental studies of road bridges of various designs and lengths confirm the relationship between the dynamic coefficient and the parameters of damping and resonance. It is found that the dynamic coefficient reflecting the energy balance of the system allows considering the critical ratios of the equilibrium amplitudes and dynamic stiffness of the spans under the changing effect of the live load as well as the presence of road defects and span bearing elements in terms of the well-known Hurwitz criterion.

Забезпечення енергоефективності трансмісій автомобілів і тракторів при модернізації зі зміною числа циліндрів ДВЗ

The article investigates the energy efficiency of motor-transmission units when using internal combustion engines with different numbers of cylinders. Transmissions, those in a unit with piston internal combustion engines are loaded with uneven torque, which is the cause of torsional vibrations of their parts. Torsional vibrations create additional dynamic loads on the transmission elements, and also reduce its efficiency. To ensure a high level of energy efficiency of the engine-transmission unit, the elastic-inertial parameters of the transmission must be matched with the amplitude-frequency characteristics of the torque of the installed engine. When replacing a serial internal combustion engines with an engine with output characteristics different from the prototype, it is necessary to assess the vibration resistance of the modernized engine-transmission unit, which was done in this work. As a criterion for vibration resistance of the modernized machine unit, the cyclic elastic efficiency of the transmission was used. This factor takes into account the natural frequency of the transmission input shaft, as well as the amplitude and frequency of vibration of the engine torque. The decisive influence on the vibration characteristics of the engine is exerted by the rotational speed of its crankshaft and the number of cylinders. When conducting a comparative assessment of the energy efficiency level of the modernized engine-transmission unit, it was assumed that before the modernization the transmission was in a unit with a single-cylinder internal combustion engine. As a result of the study, the conditions for ensuring the vibration resistance of engine transmission units have been determined, a method has been developed for comparative analysis of the energy efficiency indicators of engine transmission units with different numbers of internal combustion engine cylinders, and possible ways to increase the energy efficiency of engine units of cars and tractors during modernization with a change in the number of internal combustion engine cylinders are indicated.

ANALYSIS OF THE REVERSING MECHANISM OF LIGHT INDUSTRY EQUIPMENT

To create reliable and highly efficient, en- ergy-saving machines for light industry, it is necessary to study the dynamic processes of movement of the links of the mechanisms of which they are composed. Especially such studies should be given attention for machines, the mechanisms of which have a cyclic nature of action. During the execution of a technological operation in light industry machines with a periodic cyclic movement of the working bodies, an uneven movement of the main shaft occurs. This is caused by the movement of the links of the mechanism with certain accelerations and taking into account the periodic nature of the action of technological loads, which vary in magnitude and direction. The uneven nature of the movement leads to the appearance of additional loads in the kinematic pairs of mechanisms, mechanical vibrations in the mechanical trans- mission systems of motion, leads to the appearance of vibrations and violations in the positioning of the working bodies, affects the techno- logical process of the equipment. Uniform and stable tension of the threads is the key to a high-quality performance of the loop formation process in knitwear. Additional dynamic loads affect the technological tension of textile threads during equipment operation. These loads are caused by the accelerated movement of the links of the mechanism, which is especially important for technological equipment with the pres- ence of a reverse working stroke of its links. In such mechanisms, the values of the angular acceleration of the links and the linear accelera- tion of their individual points can acquire critically permissible values. It is possible to ensure the movement of the working bodies of the machine according to the law for which the tension of the threads will be optimally necessary. To do this, you need to choose the right type of mechanism that sets them in motion. The aim of the work is to conduct a structural-kinematic research of the mechanism of the reversible movement of the needle drum of a knitting machine, which will justify the selection of the required type of mechanism for such equipment. The confirmation of the improvement of the conditions for the formation of loops when knitting on a knitting machine with a reversible needle drum movement, made on the basis of a rocker mechanism, has been obtained.

Analysis of the influence on the hydraulic lifting circuit of the boom crane when the characteristics of the steel wire rope changes

In the process of lifting and landing of large hydraulic crane fully loaded, the working condition conversion makes the stress of steel wire rope change frequently and generate additional dynamic load, which makes the movement of the crane unstable and affects the working stability of the hydraulic system, and also leads to the fatigue damage of the tower structure and reduces the effective working life of the tower crane. In order to find the optimal dynamic characteristics of hydraulic system, the initial tension force, stiffness of hoisting wire rope and rigidity of variable amplitude wire rope of hoisting wire rope are studied respectively by means of machine-liquid integration simulation based on the AMESim, a kind of simulation software. The lifting mechanism of a type of closed hydraulic system is modelled and simulated. The results show that the maximum dynamic load of hoisting mechanism is reduced by 92.6% and the stabilization time is reduced by 49%. The optimized stiffness of hoisting wire rope reduces the dynamic load and peak pressure of hoisting mechanism by 5.2% and 4.3% respectively. The stiffness of the variable amplitude steel wire rope has little effect on the dynamic characteristics of lifting.