Dynamic Coefficient Research Articles

DYNAMIC LOADS IN ELASNIC ELEMENTS/ROPES OF CONSTRUCTION CRANES ANALYSIS AND OPTIMIZATION

In the study, an analysis of the dynamic model of construction cranes’ load lifting mechanism, proposed by professor Loveikyn V.S. and others, was carried out. In order to determine the dynamic loads in the elastic rope, a dynamic model is used, in which all sections of the shafts are considered rigid, and only the cable is elastic. Bringing the engine rotor masses, brake pulley, gears, drum and load to the rope branchers that are wound on the drum, allows the original complex multi-mass tech-nical system to be reduced to a simplified (two-mass) crane lifting mechanism dynamic model, which is comprehensively and in detail analyzed in transition-type modes (for example, in the start-up mode). 
 An established and substantiated criterion for the movement quality of the hoisting crane load mechanism, at which rope system dynamic stresses are minimized in the starting mode, as well as the dynamic coefficient for different ways of lifting the load: 1) “from the weight”; 2) “with a pick up”/ “from the base” − typical during cranes real work in cargo lifting/lowering operations (loading and unloading). 
 Classical variational calculus methods usage (Euler-Poisson equation) allows to determine the conditions, according to which the above-mentioned criterion for the movement quality of the load lifting mechanism can be implemented.
 The movements laws of the load cargo and the drive crane mechanism are also defined, as well as law of dynamic coefficient change in time, for which there is no oscillation nature of time dependence, and the specified time functions have a mono-tonically growing character over time.
 The results obtained in the work allow (when using mechatronic control systems for the cargo lifting process) prevent overloading of the crane rope system and possible emergency situations, which lead to breaks in the elastic elements of the load lifting mechanisms (i.e. ropes), and also clarify and improve the existing engineering methods of similar complex technical systems calculations in their real operation modes.

Analysis on the dynamic characteristics of spiral groove dry gas seal based on the gas film adaptive adjustment model

PurposeThis study aims to acquire the influence mechanism of gas film adaptive adjustment (GFAA) acted on the dynamic characteristics of spiral groove dry gas seal (S-DGS) and then propose a sealing stability enhancement measure.Design/methodology/approachThe gas film dynamic stiffness and damping of S-DGS are obtained by numerically solving the transient Reynolds equation based on perturbation method and finite difference method. The dynamic coefficients in GFAA model and constant gas film thickness (CGFT) model are compared and analyzed.FindingsThere is the risk to misestimate the instability of DGS with rotational speed or medium pressure grows under the condition of CGFT assumption. Based on GFAA model, increasing balance ratio B properly is an effective measure to improve the stability of DGS. The balance ratio can stimulate the sensitivity of gas film dynamic coefficients to the variation of rotational speed. Increasing medium pressure in small balance ratio range will be conducive to reducing the risk of angular instability.Originality/valueThe influence mechanism of GFAA on S-DGS dynamic characteristics is analyzed. The interactions between rotational speed and balance ratio, medium pressure and balance ratio acted on gas film dynamic characteristics are explored based on the GFAA model.

Theoretical calculation method for critical buckling load of locally stiffened U-shaped steel sheet pile using the dynamic coordination coefficient method

In order to solve the problem that U-shaped steel sheet piles (USSSPs) are prone to buckling when inserted, we propose a local stiffened U-shaped steel sheet pile destabilization critical load calculation method, namely ‘dynamic alignment coefficient method’, and analyze the influence of stiffening area, stiffening position and number of stiffening plates on the stiffening effect.The study shows that when the total stiffening area is certain, there is a scheme of stiffening plate arrangement to maximize the critical load value of USSSPs with determined length,and reveals the law of local instability caused by the small width of single stiffening plate when the number of blocks is too large. The critical load value of the member can be increased by 13.55% with the variation of the single stiffener plate arrangement position for 10 m long USSSPs, and the optimized theoretical scheme of stiffener plate arrangement for 10 m and 30 m long USSSPs with different total stiffener area is obtained.

Research on the community electric carbon emission prediction considering the dynamic emission coefficient of power system

Based on the counted power system emission factors of North China Power Grid, a community carbon emissions sample database is constructed. The support vector regression (SVR) model is trained to forecast the power carbon emissions, which is optimized by genetic algorithm (GA). A community carbon emission warning system is designed according the results. The dynamic emission coefficient curve of the power system is obtained by fitting the annual carbon emission coefficients. The time series SVR carbon emission prediction model is constructed, while the GA is improved to optimize its parameters. Taking Beijing Caochang Community as an example, a carbon emission sample database is generated based on the electricity consumption and emission coefficient curve to train and test the SVR model. The results show that the GA–SVR model fits well with the training set and the testing set, and the prediction accuracy of the testing set reaches 86%. In view of the training model in this paper, the carbon emission trend of community electricity consumption in the next month is predicted. The carbon emission warning system of the community is designed, and the specific strategy of community carbon emission reduction is proposed.

Comparative Research on Corrosion Resistant Non-Skid Al and Al-3%Ti Coating Fabricated by Twin Wire arc Spraying

To ensure the lifetime of marine constructions and the safety of workers and pedestrians, corrosion protective non-skid coating is an effective solution. However, the conventional polymer-based coating has some limitations. In this study, newly-suggested Al and Al-3%Ti coatings were deposited on high strength low alloyed steel substrate using twin wire arc spraying (TWAS). The static and dynamic friction coefficients of the Al-based coatings under dry and wet conditions were measured using portable friction testers. To evaluate the corrosion behavior under sea water conditions, a cyclic potentiodynamic polarization test (CPDP) and salt solution immersion test (SSIT) were performed with a 3.5% NaCl solution. To confirm the coating degradation, mechanical properties (Vickers hardness and adhesion strength) were compared before and after SSIT. The results showed that the TWAS Al-based coatings were well fabricated on HSLA steel and had the general microstructure of a thermal spray. The coatings provided excellent corrosion protection for the steel substrate and greatly increased the friction coefficient of the surface. The Vickers hardness slightly increased and adhesion strength decreased after SSIT. The microstructure observation revealed that the TWAS coatings had a bimodal structure induced by non-uniform droplet generation at the TWAS tips. After SSIT, some oxides formed on the surface and porous regions of the coatings. This indicated that the TWAS coating successfully provided corrosion protection and non-skid properties.

Effect of StaticMagneticand Pulsated Electromagnetic Fields On the Dynamic and Kinematic Viscosity of Metal Cutting Fluids

In this paper, authors investigated the difference between the influenceof staticmagnetic field and pulsating electromagnetic field on metal cutting fluids. Two essential physical parameters of the cutting fluids, dynamic and kinematic viscosity coefficients were analyzedduring the experiment in the same laboratory condition.The results obtained from the experimental researchshow thatthe influence of thestatic magnetic field onsample metal cutting fluids is greaterthanthe influence ofthe pulsating electromagnetic field.Such as, after magnetizing cutting fluids under the effect of three various static magnetic field strengths, the kinematic and dynamic viscosity havedecreased about 17%and 6% respectively,while they declined about 7% and 4% after magnetizing the fluidsunder the effect of the same electromagnetic magnetic field strengths. Moreover, special magnetizing devices have beendesigned to magnetize different types offluids intheirflowing condition.

Optoacoustic quantitative in vitro detection of diabetes mellitus involving the comprehensive impacts based on improved quantum particle swarm optimized wavelet neural network

The high accurate detection of blood glucose level (BGL) is very important for non-invasive monitoring of diabetes mellitus. In this work, the optoacoustic (OA) quantitative in vitro detection of diabetes mellitus involving the comprehensive impacts of multiple factors (irradiation energy, concentration, temperature, flow rate and vessel depth) was firstly studied. To achieve this aim, a set of OA in vitro detection system of blood glucose with the comprehensive influence of five factors was constructed. The real-time OA signals of 625 rabbit whole blood were obtained at the characteristic wavelength of 750 nm, as well as peak-to-peak values (PPVs). Results show that the accurate detection of BGL was very difficult due to the complicated OA signals. To accurately predict the BGL under the comprehensive impacts of five factors, wavelet neural network (WNN) was employed to train BGL of 500 training set blood. The mean square error (MSE) of BGL for 125 testing set blood was 6.5782 mmol/L. To decrease the MSE, WNN optimized by quantum particle swarm optimization (QPSO), i.e., QPSO-WNN algorithm was utilized. The MSE of BGL based on QPSO-WNN was 0.37485 mmol/L, which was superior to 0.48005 mmol/L of PSO-WNN. Particularly, to further decrease MSE, a novel nonlinear dynamic shrinkage coefficient (DSC) strategy was proposed, and compared with other four kinds of DSC strategies and the fixed one. With the optimal parameters, the MSE of BGL was decreased to 0.3088 mmol/L. Comparison results of seven algorithms and research works demonstrate that OA technology combined with QPSO-WNN algorithm and the novel nonlinear DSC strategy has excellent performance in the quantitative detection of diabetes mellitus involving in the comprehensive impacts.

Shimizu–Morioka's chaos synchronization: An efficacy analysis of active control and backstepping methods

This research study inspects the effectiveness of synchronization methods such as active control and backstepping control from systematic design procedures of a synchronized Shimizu–Morioka system for the same parameter. It aimed to achieve synchronization between the state variables of two identical Shimizu–Morioka chaotic systems by defining the proposed varieties of the error dynamics coefficient matrix. Furthermore, this study also aimed to designed an active controller that enables the synchronization of these systems. The use of designed recursive backstepping nonlinear controllers was based on the Lyapunov function. Furthermore, it also demonstrated the stability of the synchronization of the nonlinear identical Shimizu–Morioka system. The new virtual state variable and establishment of Lyapunov functionals are used in the backstepping controller to stabilize and reduce errors between the Master (MS)/Drive (DS) systems. For comparison, the complexity of active controllers is verified to be such that the designed controller's effectiveness based on backstepping is attainable in engineering applications. Finally, numerical simulations are performed to demonstrate the effectiveness of the proposed synchronization strategy with the Runge–Kutta (RK-4) algorithm of fourth order through MatLab Simulink.

Operating characteristics of supercritical carbon dioxide high speed tilting pad bearings considering inertia effect

Some degree of inertia effect on the bearing film is inevitable for high density supercritical carbon dioxide (S-CO2) working as a lubricant in high speed rotor operating conditions. This paper aims to reveal the influence of inertia effect on static and dynamic performances of the S-CO2 tilting pad bearings. Numerical results demonstrate that inertia effect on the lubricating film of the top pad is more pronounced. The peak pressure of all pads is increased at a high reduced Reynolds number compared with the inertialess condition, while the influence of inertia effect on the dynamic coefficient is weak. The theoretical model including inertia effect presented in this study can more accurately evaluate the performance of high speed S-CO2 tilting pad bearings.

Study on Friction and Wear Properties of 3D Braided Carbon Fiber

In this paper, the friction and wear properties of 3D braided carbon fiber wet friction material at 2550r/min, 3800r/min and 5100r/min were studied with MM3000 friction and wear tester, and the wear mechanism was studied with SEM. The results show that the average static friction coefficient of friction materials is 0.153; With the increase of rotating speed, the dynamic friction coefficient decreases from 0.095 to 0.087; The volume wear rate decreased from 9.46*10−8cm3/J to 2.58*10−8cm3/J; The friction torque curves at three different speeds are relatively stable, showing the material has good braking stability. 3D braided carbon fiber friction material has fiber fracture and crack on the raised surface of the material after 1500 times of jointing at three different speeds. The mechanism of friction and wear is abrasive wear and fatigue wear.

Influence of oil film nonlinearity on identification accuracy of dynamic characteristic coefficient of heavy-duty sliding bearing

Influence of oil film nonlinearity on identification accuracy of dynamic characteristic coefficient of heavy-duty sliding bearing

Dynamical friction due to fuzzy dark matter on satellites described by axisymmetric logarithmic potentials

A plausible dark matter candidate is an ultralight bosonic particle referred to as fuzzy dark matter. The equivalent mass-energy of the fuzzy dark matter boson is ∼ 10-22 eV and has a corresponding de Broglie wavelength of kiloparsec scale, thus exhibiting wave behaviour in scales comparable to a galactic core, which could not appear in conventional cold dark matter models. The presence of fuzzy dark matter in galactic clusters will impact the motion of their members through dynamical friction. In this work, we present simulations of the dynamical friction on satellites traversing an initially uniform fuzzy dark matter halo. We focus on the satellites whose shapes are beyond spherical symmetry described by ellipsoidal and logarithmic potentials. We find that the wakes created on the fuzzy dark matter halo due to the passage of such satellites are qualitatively different from those generated by spherically symmetric ones. Furthermore, we quantify the dynamical friction coefficient for such systems, finding that the same satellite may experience a drag differing by a factor of 5 depending on its ellipticity and the direction of motion. Finally, we find that the dynamical friction time-scale is close to Hubble time, assuming a satellite of 1011 M ⊙ traversing at 103 km/s a FDM halo whose mean density is ∼ 106 M ⊙ kpc-3.

UAV Dispatch Planning for a Wireless Rechargeable Sensor Network for Bridge Monitoring

Due to the breakthrough of wireless power transfer technology, wireless rechargeable sensor networks (WRSNs) have the potential to provide sustainable work. Most existing researches on WRSNs usually focus on the cases that mobile charging vehicle moves freely through the sensors. However, for some applications, such as bridge monitoring, WRSNs are implemented in a three-dimensional space with obstacles, so the charging path may be blocked by the obstacles. To cope with this problem, charging scheduling to replenish a wireless rechargeable sensor network for bridge monitoring by an unmanned aerial vehicle (UAV) is studied. The problem is formulated as an optimization problem through optimizing UAV navigation path and sensor energy allocation collaboratively. This optimization problem is hard to be solved as both path navigation and energy allocation are required to be optimized simultaneously. To circumvent this challenge, an improved ant colony system algorithm (IM-ACS) is proposed to plan the trajectory of the UAV between sensors. By integrating enhancement factors and dynamic pheromone intensity coefficients, the convergence of the algorithm is accelerated. Then, a two-stage algorithm is proposed to schedule charging sequence and assign energy with limited energy carried by the UAV in each charging period. Experiments and simulations show that the proposed approach achieves shorter feasible trajectory paths and longer network lifetime than those obtained by the compared methods.

Bearing Capacity of Steel Trusses with Local Damage Considering the Exclusion Time

To ensure the safety of buildings and structures, they must maintain their bearing capacity in case of local damage. The article is devoted to the study of the robustness of damaged steel trusses, as well as the time during which local destruction of the trusses occurs. Finding a solution to this problem is one of the key stages in the development of a practical methodology for calculating steel trusses’ resistance to the local destruction of elements. The time from the beginning of destruction to the complete failure of the element is proposed to be called the exclusion time. Based on the performed theoretical and numerical studies, for the quasi-static calculation it is recommended to use the values of the dynamic coefficient for the considered steel trusses. In the numerical formulation, the work of steel trusses as part of the building frame was investigated along with local destruction of individual elements of the truss. Numerical studies have shown that the shorter the failure time of the truss element, the greater the dynamic forces arising in the structure. The frame of the building is considered as a spatial system. A numerical dynamic analysis of the spatial coverage is carried out, taking into account the local failure of one of the truss elements. The distribution of the dynamic coefficient over the steel trusses is obtained. This made it possible to study the effect of local failure on the intact load-bearing structures. The article presents the results of a series of experimental studies of flat trusses aimed at determining the time of failure of a steel truss element. Based on the results obtained, the failure time of the damaged rod and the redistribution of efforts to the neighboring elements of the truss were calculated. In accordance with the calculated failure time, recommendations were formulated to reduce the value of the dynamic coefficient used in the static calculation, depending on the types of damage to the truss.

Rotor vibration control via integral magnetorheological damper

Despite of wide applications of damping support structures in rotor vibration reduction, their performance is generally unsatisfactory in the high-frequency range. A new method of oil-film zoning control for a novel integral magnetorheological damper (IMRD) with a compact design and enhanced performance is proposed to extend the rotor vibration reduction to the high-frequency range. To demonstrate the feasibility of the proposed IMRD, firstly, a nonlinear dynamic model is established by using the Lagrange equation and introduced into a flexible rotor system. Then, the dynamic behaviors of the system are investigated in framework of the Newmark-β method, upon which the influence of different oil-film zones is evaluated. Finally, experiments are conducted to investigate the vibration reduction performance of the IMRD on rotor system. The results show that there are at least three pressure zones for IMRD in operating conditions, of which one can produce negative normal oil-film force. Moreover, different pressure zones have different effects on dynamic coefficients of IMRD, which makes the proposed IMRD capable of achieving excellent vari-stiffness and vari-damping effects through oil-film zoning control, and leads to the vibration reduction of rotor system not only in the resonance range by providing effective damping but also in the high-frequency range by softening the support stiffness. This work demonstrates a new strategy for dampers in rotor systems to broaden the vibration reduction bandwidth and provides guidance for the implementation of IMRD.

Study on the shear-slip process and characteristics of fracture in shale

To clarify the shear-slip process and characteristics of fault, we conducted triaxial shear tests driven by displacement on shale samples with prefabricated sawcut and natural fractures, and the acoustic emission (AE) technology was used to monitor the shear-slip process in real-time. According to the test results, the shear-slip process and mechanical characteristics of sawcut and natural fractures were analyzed. The test results indicate that the shear-slip process of fractures can be divided into four stages, improving the confining pressure will cause more serious plastic failure in the shear-slip process, and the increase of roughness will make the phenomenon of “stress drop” more obvious, which is closely related to the earthquake occurrence. Confining pressure and roughness all have implications for the stress thresholds of each stage. With the transition of shear-slip stages, the effects of confining pressure and roughness on the shear-slip of fractures are more drastic. The maximum static friction coefficient μ0 increases with initial roughness increasing and is independent of confining pressure. Due to the strain-strengthening effect of fracture slip, the average value of dynamic friction coefficient μd under simple shear deformation is greater than the maximum static friction coefficient μ0. Based on AE response characteristics, microcracks development, and rupture scale during the shear-slip process were also explored. AE events are mainly distributed along the inclined fracture. The AE response in different shear-slip stages displays pronounced differences, and the AE evolution and macro mechanical characteristics of fractures show significant time-synchronization. The variation of peak frequency can reflect the rupture scale transformation and the influence of confining pressure and roughness. Additionally, the differences in the morphological evolution of sawcut and natural fractures are mainly reflected in the wear pattern, degree and the rock debris attach amount. Finally, we also discussed the micro-deformation mechanism of asperities during the shear-slip process. This work may provide a reference for the research of fault activation and slip in shale reservoirs.

Динамические силы воздействия колеса на рельс при безбалластной конструкции пути RHEDA 2000

Purpose: Experimental determination of vertical dynamic forces of wheel impact on a rail at ballastless construction of railway track RHEDA2000 upper structure with subsequent analysis of obtained data; definition of main factors affecting vertical dynamic force value; identification of dependence of change in the value of wheel vertical dynamic force impact on a rail from motion speed and rolling stock type; calculation of coefficients of vertical dynamics at ballastless construction of rail upper structure. Methods: Measurement of wheel vertical dynamic force impact on a rail was carried out by strain-gauge method (Schlumpf method). Numerical values of those, obtained in the course of experiment, were processed by mathematical statistics method, in its turn, probability level was taken equal to 0.994. Results: The values of vertical dynamic forces of wheel impact on a rail for ballastless structure of RHEDA2000 type at rolling stock different types and various ranges of motion speed have been determined. The dependence of change in the value of wheel vertical dynamic force impact on a rail from motion speed and rolling stock type has been graphically built. Comparison of vertical dynamics coefficients of ballastless construction of railway RHEDA2000 upper structure with the construction of a track on a ballast has been carried out. Practical significance: The obtained results can be used in projection, construction, reconstruction and repair of railway track where track ballastless upper composition is provided.

Mixed reality-integrated soft wearable biosensing glove for manipulating objects

Recent advances in flexible sensors and wireless electronics have driven the development of lightweight and ergonomic wearable sensing gloves. Such gloves can be employed in mixed reality (MR) environments to give haptic capabilities during interactions with various objects. However, no prior study shows a quantitative measurement of physical user interactions of object manipulation in MR. Here, we report an MR-integrated soft bioelectronic system on a glove for quantifying the changes in the user's pinching tasks. We use nanomanufacturing techniques to fabricate flexible sensors, wireless circuits, and stretchable interconnectors seamlessly integrated with a wearable glove. The wearable biosensing glove with an integrated capacitive pressure sensor evaluates how users interact directly and indirectly interact with objects. The direct mode describes a user's direct touching and manipulating objects in MR. In contrast, in the indirect mode, objects are located far away and touched via a narrow light beam. The virtual object measurement parameters include mass, movement latency, dynamic friction coefficient, angular drag coefficient, and linear drag coefficient. The experimental results with human subjects show positive, linear relationships between pinching force and dynamic friction coefficient and mass parameters during the direct manipulation mode. Collectively, the MR-enabled wearable biosensing glove system offers unique advantages in detecting physical interactions and sensory feedback for various rehabilitation applications and MR human-machine interfaces.

A Research on the Impact of Global Stock Market Co-movement during Covid-19 Epidemic

Covid-19 has brought huge fluctuations to world economy and such volatilityis evidently indicated by global stock market. In light of econometric hypotheses, this paper explained the comovement mechanism of global stock markets, made descriptive statistical analysis to the market returns of sample countries with VAR and DCC-GARCH models, and examined the comovement of market returns. The result shows that stock market in Brazil was the most volatile among all sample countries. Meanwhile, after the outbreak, VIX and WTI’s influence on dynamic correlation coefficients increased, showing a positive and significant impact and thereby strengthening the comovement of global stock markets.  

Transition to Equilibrium and Coherent Structure in Ideal MHD Turbulence

Transition of ideal, homogeneous, incompressible, magnetohydrodynamic (MHD) turbulence to near-equilibrium from non-equilibrium initial conditions is examined through new long-time numerical simulations on a 1283 periodic grid. Here, we neglect dissipation because we are primarily concerned with behavior at the largest scale which has been shown to be essentially the same for ideal and real (forced and dissipative) MHD turbulence. A Fourier spectral transform method is used to numerically integrate the dynamical equations forward in time and results from six computer runs are presented with various combinations of imposed rotation and mean magnetic field. There are five separate cases of ideal, homogeneous, incompressible, MHD turbulence: Case I, with no rotation or mean field; Case II, where only rotation is imposed; Case III, which has only a mean magnetic field; Case IV, where rotation vector and mean magnetic field direction are aligned; and Case V, which has nonaligned rotation vector and mean field directions. Dynamic coefficients are predicted by statistical mechanics to be zero-mean random variables, but largest-scale coherent magnetic structures emerge in all cases during transition; this implies dynamo action is inherent in ideal MHD turbulence. These coherent structures are expected to occur in Cases I, II and IV, but not in Cases III and V; future studies will determine whether they persist.