Numerical Simulation of the Post-Tensioned Beams Behaviour Under Impulse Forces Loading

Positioning systems are widely used in space technology products and are most often equipped with linear drives based on screw mechanisms. Currently, the most promising screw mechanisms are planetary roller screw gears (PRSG), which have high efficiency and have high load capacity, rigidity, reliability and durability. This is the basis for their use in the aerospace industry. For high accuracy it is necessary to use backlash-free mechanisms in which the gaps are selected in various ways. For the projected positioning system it is used a backlash-free PRSG with a flexible one-piece nut made in the form of a “short” cylindrical shell and developed ends. The gaps are selected by deforming the flexible nut by bending moments. A structural diagram of the positioning system has been developed, its components (bearings, clutch, etc.) have been selected, the calculation of the power mechanism based on a gas-free gear system has been performed, which has shown high gear operational characteristics. Meanwhile, the PRSG has been calculated for static and dynamic load capacity. Furthermore, the value of the static load capacity of the designed gear has been determined. Prerequisites have been created for the development of design documentation for the components and parts of the positioning system and primarily for the backlash-free PRSG.

The authors conducted a study on superconducting magnetic bearing, which consists of superconducting rotor and stator to apply the flywheel energy-storage system for railways. In this study, high temperature bulk superconductor (HTS bulk) was combined with superconducting coils to increase the load capacity of the bearing. In the first step of the study, the thrust rolling bearing was selected for application by using liquid nitrogen cooled HTS bulk. 60mm-diameter HTS bulks and superconducting coil which generated a high gradient of magnetic field by cusp field were adopted as a rotor and a stator for superconducting magnetic bearing, respectively. The results of the static load test and the rotation test, creep of the electromagnetic forces caused by static flux penetration and AC loss due to eccentric rotation were decreased to the level without any problems in substantial use by using two HTS bulks. In the result of verification of static load capacity, levitation force (thrust load) of 8900N or more was supportable, and stable static load capacity was obtainable when weight of 460kg was levitated.

The implementation method of reinforced concrete construction has progressed very rapidly. This development aims to speed up time and reduce costs. One of the most widely used methods is the precast method, but the less popular precast method is used for simple storey buildings. Therefore, in this study the semi-precast method, which is easy to implement in a simple storey building, was presented. Parts of columns and beams were cast in place with different casting times. Therefore, the connection become non-monolithic. This study presented a comparison between the deflection and the static load capacity that can be received by the connection of reinforced concrete beam-column which is monolithically connected and non- monolithic. 3 sets of specimens were made to represent monolithic and non-monolithic specimens. The nonmonolithic specimens were made with 2 models, i.e. without and with a notch. The beam-column connections were tested experimentally and compared to the monolithic beam-column connection. The results showed that the notch on non-monolithic test specimens can increase the load capacity and reduce deflection compared to the specimen test without notch. The experimental results also showed that the strength and performance of structural non-monolithic beam-column connections were as good as those of monolithic beam-column joints.

This paper uses numerical simulation to study the influences of viscosity ratio on the static characteristics of hydrostatic thrust bearing compensated by various restrictors. The design parameters of open type hydrostatic bearing include: effective area, supply pressure, restriction constants of restrictor and bearing pad, and specific value of average viscosity of the lubricant passing through restrictor and bearing pad film. The optimal design requirements of restrictors and hydrostatic bearing and the corresponding range of design parameters for excellent bearing characteristics can be obtained from the relationships between these design parameters together with their composed parameters and ratios, and the static load capacity and film stiffness and worktable displacement of hydrostatic bearing. Fixing the other design parameters and changing viscosity ratio, the simulation results depict that the lubricant viscosity during restrictor being greater than that in bearing pad film will make the load capacity decrease, but will improve the film static stiffness.

Due to their vanishingly low air friction, high wear resistance, and environmental friendliness, aerostatic bearings are used in machines, machine tools, and devices that require high accuracy of micro-movement and positioning. The characteristic disadvantages of aerostatic bearings are low load capacity, high compliance and an increased tendency for instability. In radial bearings, it is possible to use longitudinal microgrooves, which practically exclude circumferential air leakage, and contributes to a significant increase in load-bearing capacity. To reduce compliance to zero and negative values, inlet diaphragm and elastic airflow regulators are used. Active flow compensation is inextricably linked to the problem of ensuring the stability of bearings due to the presence of relatively large volumes of gas in the regulator, which have a destabilizing effect. This problem was solved by using an external combined throttling system. Bearings with input flow regulators have a number of disadvantages-they are very energy-intensive and have an insufficiently stable load capacity. A more promising way to reduce compliance is the use of displacement compensators for the movable element. Such bearings also allow for a decrease in compliance to zero and negative values, which makes it possible to use them not only as supports, but also as active deformation compensators of the technological system of machine tools in order to reduce the time and increase the accuracy of metalworking. The new idea of using active flow compensators is to regulate the flow rate not at the inlet, but at the outlet of the air flow. This design has the energy efficiency that is inherent to a conventional bearing, but the regulation of the lubricant output flow allows the compliance to be reduced to zero and negative values. This article discusses the results of a theoretical study of the static and dynamic characteristics of a two-row radial aerostatic bearing with longitudinal microgrooves and an output flow regulator. Mathematical modeling and theoretical study of stationary modes have been carried out. Formulas for determining static compliance and load capacity are obtained. Iterative finite-difference methods for determining the dynamic characteristics of a structure are proposed. The calculation of dynamic quality criteria was carried out on the basis of the method of rational interpolation of the bearing transfer function, as a system with distributed parameters, developed by the authors. It was found that the volumes of the microgrooves do not have a noticeable effect on the bearing dynamics. It is shown that, in this design, the external combined throttling system is an effective means of maintaining stability and high dynamic quality of the design operating in the modes of low, zero and negative compliance.

To reveal nonlinear dynamic rules of low viscosity fluid-lubricated tilting-pad journal bearings (TPJBs), the effects of design parameters on journal center orbits and dynamic minimum film thicknesses of water-lubricated TPJBs with and without static loads are investigated. The hydrodynamic bearing force used in the nonlinear dynamic analysis is an approximate analytical solution including the turbulence effect. The results reveal the methods for vibration suppression and load capacity improvement and give an optimal pivot offset and clearance ratio that can maximize the minimum film thickness. The results also show that four-pad TPJBs with loads between pads are preferred due to good dynamic performance and load capacity. This study would provide some guidance for nonlinear design of low viscosity fluid-lubricated TPJBs under dynamic loads.

To expand the application scope of gas bearings in oil-free turbomachinery, this paper presents a novel porous tilting pad gas thrust bearing (PTPGTB) with umbrella-type dampers (UDs) incorporating viscoelastic material. This damper, fabricated using additive manufacturing, can shrink like an umbrella to squeeze the viscoelastic material from all directions so as to dissipate more energy. A comprehensive theoretical model is proposed by coupling the PTPGTB model and the UD model. Dynamic load tests and load capacity tests are carried out. The experimental results generally agree with the predicted results. The effects of nominal clearance, supply pressure, rotational speed, and UD geometry parameters are discussed. The variations of hydrostatic and hydrodynamic effects in PTPGTBs with different parameters are revealed. The results show that smaller clearances, lower rotational speeds, higher supply pressures, and greater axial stiffness increase the load capacity of PTPGTBs. The research can provide a new design idea and theoretical guidance for improving the load capacity of gas thrust bearings.

With the evolution of casing drilling technology, connections are subjected to increasingly stringent well conditions. These conditions include higher pressures, higher temperatures, and higher mechanical loads for longer drilling periods. As a result, the performance of the connector under these conditions is of increasing concern. Most recent casing connection evaluation test programs are based on ISO 136791 requirements. However, API RP72 is the dominant testing program for drill stem applications. Drilling with casing applications combine drilling and casing concerns. As a result, a new test program is required to adequately characterize connection performance when used in casing drilling applications3. As part of the test program, the static and dynamic connector capacities are individually evaluated to benchmark the design. Based on these results, additional testing is conducted todetermine the connector static capacity after dynamic loading for an expected drilling period at an expected maximum build rate. This testing demonstrates the connector performance under drilling with casing application conditions. This testing program may be utilized to better define connector performance limits when used in drilling with casing applications leading to increased operational safety and lower overall risks. A better understanding of how connection tolerances impact connection performance under combinations of static and dynamic loading conditions will aid in connector selection for drilling with casing applications and may allow the technology to be used in broader applications. The paper includes results, observations, and conclusions from a subject test per the testing program. The subject test is currently being conducted on a 9-5/8" 53.50ppf P-110 drilling with casing connector. Introduction The objective of this project is to evaluate the connection performance for casing drilling application. Tests were conducted in four phases, each with distinctive goals.Phase I: Design SelectionPhase II: Fatigue to Failure TestPhase III: Static Capacity TestPhase IV: Post-fatigue ISO Series B Test The objective of Phase I test was to find the best connection and thread compound combination. Three samples with different thread compounds were tested. DWC/C and DWC/C-SR connections were fatigue tested with the same loading condition. All samples were threaded to nominal tolerances and subsequent capped-end pressure test determined the best design for Phase II test. Phase II was to generate the SN curve for DWC/C-SR connection. Three ISO configurations, with three samples in each group, were tested at different stress levels. Connections were fatigued to failure with different stress range. Fatigue performance with respect to sample configuration was investigated. ISO 2 configuration is the worst-case for fatigue. Phase III was the static capacity verification test. Three ISO configurations, identical as tested in Phase II, were tested with ISO Series B service load envelope (SLE). The configuration with the best pressure containability was chosen for Phase IV test. Phase IV included the post-fatigue ISO Series B test. The specimens were fatigued to pre-determined cycles at a certain stress level, followed by an ISO Series B testing. The testing format was modified based on ISO 13679 requirement.

Anion-exchange membranes were evaluated for the capture of a small protein (α-lactalbumin, 3.5-nm diameter) and a large protein (thyroglobulin, 20-nm diameter). The static binding capacity equaled the dynamic binding capacity and increased with increasing protein size. This result was in agreement with calculations based on monolayer coverage on the membrane surface and an absence of mass-transfer limitations. In contrast, for anion-exchange beads, the static capacity was the same for both proteins, and the dynamic capacity decreased strikingly with increasing protein size. These observations were attributed to very slow intrapore diffusion for large proteins in the beads, resulting in surface binding only. This work has important applications in the selection of chromatography media for the purification of viruses and plasmid DNA. Specifically, membranes with a high capacity for large biomolecules (20−300 nm) and a low capacity for small host-cell proteins and endotoxin contaminants are preferable to beads for the purification of such biomolecules.

Wire-race bearings are a non-conventional type of bearings where the rolling process takes place over a race shaped in a wire. This design allows building the rings with lighter materials and innovative ring designs. Despite the wide range of applications where wire-race bearings can be the best option, no specific analysis tools have been developed yet. There are several analytical tools for conventional bearings, which obtain the stiffness, the effect of the preload and the static load capacity among others. In this work a simplified analytical model is proposed for a wire-race ball bearing, and comparatively validated via Finite Element Analysis.

Pitch and yaw bearings are essential to the safe and efficient operation of wind turbines. They are classified as a large bearing, and they suffer from much more severe operational conditions compared to small bearings used for general industrial applications; in particular, they are subjected to greater external forces in each direction, very thin lubrication film thickness during operation, and so on. Furthermore, because they are installed on the wind turbine blade or a tower top of high altitude, it is costly and time consuming to repair or replace them in the field. Therefore, a laboratory-scale test is required for ensuring the performance of the pitch and the yaw bearings before application in the field. A test rig is developed to verify the performance of the pitch and the yaw bearings, including their fatigue life and static loading capacity. The test rig can reproduce actual operational conditions such as 6 degree of freedom (DOF) dynamic loadings and rotation of bearings for both directions. The mounting interfaces of the test rig are also the same as those used in the original environment, and various sizes of bearings can be applied by using a changeable adaptor. This high reproducibility of actual loading, driving, and mounting conditions simultaneously as well as applicability to wide size ranges are distinctively advantageous characteristics compared to previous test rigs. A structural analysis and preliminary friction torque test showed the suitability of the developed rig for use in pitch and yaw bearings of 2.0–3.0 MW class wind turbines.

Robotics is a relatively new and evolving technology being applied to manufacturing automation and is fast replacing the special-purpose machines or hard automation as it is often called. Demands for higher productivity, better and uniform quality products, and better working environments are primary reasons for its development. An industrial robot is a multifunctional and computer-controlled mechanical manipulator exhibiting a complex and highly nonlinear behavior. Even though most current robots have anthropomorphic configurations, they have far inferior manipulating abilities compared to humans. A great deal of research effort is presently being directed toward improving their overall performance by using optimal mechanical structures and control strategies. The optimal design of robot manipulators can include kinematic performance characteristics such as workspace, accuracy, repeatability, and redundancy. The static load capacity as well as dynamic criteria such as generalized inertia ellipsoid, dynamic manipulability, and vibratory response have also been considered in the design stages. The optimal control problems typically involve trajectory planning, time-optimal control, energy-optimal control, and mixed-optimal control. The constraints in a robot manipulator design problem usually involve link stresses, actuator torques, elastic deformation of links, and collision avoidance. This paper presents a review of the literature on the issues of optimum design and control of robotic manipulators and also the various optimization techniques currently available for application to robotics.

Analysis of aerostatic porous rectangular thrust bearings with offset loads

An improved nonlinear vibration isolator is proposed in this paper. It uses the exact solution derived load-displacement hysteresis curve formula based on energy method to calculate disc spring, combined with the finite element analysis. The static load capacity and dynamic mechanical property of this new type disc spring vibration isolator is validated through the static load tests or fatigue analysis. Compared with the rubber vibration isolator, the conclusion can be found: the new type vibration isolator has wider scope of vibration isolation, and is better in low frequency vibration isolation. These research achievements are of significant importance in the vibration isolation of heavy load and great shock mechanical equipment.

Gas foil bearings (GFBs) find widespread usage in oil-free turbo expanders, APUs and micro gas turbines for distributed power due to their low drag friction and ability to tolerate high level vibrations, including transient rubs and shaft misalignment, static and dynamic. The static load capacity and dynamic forced performance of GFBs depends largely on the material properties of the support elastic structure, i.e. a smooth foil on top of bump strips. Conventional models include only the bumps as an equivalent stiffness uniformly distributed around the bearing circumference. More complex models couple directly the elastic deformations of the top foil to the bump underlying structure as well as to the hydrodynamics of the gas film. This paper details two FE models for the top foil supported on bump strips, one considers a 2D shell anisotropic structure and the other a 1D beam-like structure. The Cholesky decomposition of the stiffness matrix representing the top foil and bump strips is performed off-line prior to computations coupling it to the gas film analysis governed by Reynolds equation. The procedure greatly enhances the computational efficiency of the numerical scheme. Predictions of journal attitude angle and minimum film thickness for increasing static loads and two journal speeds are obtained for a GFB tested decades ago. 2D FE model predictions overestimate the minimum film thickness at the bearing centerline, while underestimating it at the bearing edges. Predictions from the 1D FE model compare best to the limited tests data; reproducing closely the experimental circumferential wavy-like minimum film thickness profile. The 1D top foil model is recommended due to its low computational cost. Predicted stiffness and damping coefficients versus excitation frequency show that the two FE top foil structural models result in slightly lower direct stiffness and damping coefficients than those from the simple elastic foundation model.