Large Static Loads Research Articles

Identification and Optimization Study of Cavitation in High Power Torque Converter

Aiming at the phenomenon that a high-power torque converter is susceptible to cavitation, which leads to performance degradation, first, a transient flow field model of the torque converter is established, and CFD simulation and experimental research on the torque converter are carried out to find out the speed ratio region where cavitation occurs in the torque converter as well as the rule of occurrence of cavitation, and then the cavitation identification method based on the difference between the inlet and outlet flow of the torque converter is proposed. Then, the transient flow process inside the torque converter is analyzed, and it is pointed out that the angle between the inlet angle of the stator and the outlet angle of the turbine of the torque converter, i.e., the fluid inflow injection deviation angle is an important factor affecting the cavitation phenomenon. By adjusting the key parameters of the stator blade bone line, the fluid inflow deviation angle of the torque converter stator is optimized, so that the speed ratio range of cavitation under large load conditions is greatly reduced from the original 0–0.5 (50%) to 0–0.15 (15%). Meanwhile, in terms of test performance, the nominal torque of the torque converter is greatly improved under the premise of ensuring that the performance is basically unchanged, in which the nominal torque of the test zero speed is increased by 28.7%, and the cavitation of the torque converter has been greatly improved.

Experimental investigations on emission characteristics of heavy-duty hybrid electric vehicles

The emission characteristics under different operating modes (engine mode and hybrid mode) and different test cycles (C-WTVC and CHTC) of a heavy-duty hybrid electric dump truck was investigated on the chassis dynamometer. The emission performance was recorded using Portable Emissions Measurement System (PEMS) and analyzed combined with the characteristic parameters of the test conditions. It is found that the NOx emission under hybrid mode is higher than that under engine mode, while the CO emission under hybrid mode is lower than engine mode. Under engine mode, the NOx emission of CHTC is higher than that of C-WTVC. However, under hybrid mode, the NOx emission of CHTC is lower than C-WTVC. Analysis of CO emission characteristics shows that under engine mode, CO emission is concentrated at low speed and small load condition, while under hybrid mode, CO emission is concentrated at high speed and large load condition.

Performance assessment of steel frame buildings with hybrid self-centering braces under extremely rare far-field earthquakes

This paper investigates the seismic performance enhancement of steel frame buildings using a novel hybrid self-centering braces (HSBs) under extremely rare earthquake events. The hybrid self-centering brace consists of shape memory alloy (SMA) cables and viscoelastic (VE) dampers. A prototype bracing system is designed and fabricated to explore its basic mechanical behavior and working mechanism under cyclic loading, with a focus on its failure modes under large deformation loading condition. A multi-material mechanical model is developed to capture the mechanical behavior and failure of the HSB. Furthermore, five steel frame buildings with different parameterized HSBs are designed and modeled in OpenSees. Nonlinear dynamic analyses and incremental dynamic analyses are conducted on the five case-study frames using 44 far-field ground motions. The risk-based seismic performances of steel buildings with HSB are evaluated to assess the performance of HSB during extremely rare seismic events. The results show that the hybrid self-centering brace exhibits excellent self-centering and energy dissipation capabilities with the maximum equivalent viscous damping ratio reaching 9.4 %. Even under large deformations, VE dampers continue to work effectively after the failure of SMA cables, demonstrating remarkable redundancy. Numerical simulations further reveal that the redundancy of HSB can improve the structural seismic resilience in terms of inter-story drift ratio, residual drift, and floor absolute acceleration. The higher the redundancy of HSB in the case-study frames, the smaller the seismic response and mean annual frequency of exceedance of the engineering demand parameters, thereby indicating a significant improvement in seismic performance.

Error Correction Method of Platform Displacement for Large Load Static Test

The test platform is an indispensable supporting bearing structure in static tests, which is mainly used to fix test products, simulate the real loading boundary, and provide better operation space for measurement. With the large-scale and complicated spacecraft structure, the static test platform tends to be large-scale, and the displacement measurement error of the static test platform under large load conditions cannot be ignored. The conventional error correction method only uses the displacement value of the monitoring point at the corresponding position of the platform to compensate, ignoring the comprehensive influence of the six degrees of freedom displacement for the test platform on the displacement measurement of the specimen. When it is used for the error correction of the static test of large spacecraft structures, there is a large measurement error affected by the structural size. In view of this, according to the static test requirements of a large spacecraft, a large bearing static test platform with a lateral load of 22 T and a longitudinal load of 52 T is designed, and a displacement measurement error correction method based on six degrees of freedom is proposed. Through the static test of a large spacecraft structure, the method can effectively reduce the displacement measurement error caused by the displacement of the test platform, and the error correction rate can reach 20%.

On the Performance of Hydrostatic Journal Bearings in Air, Water, and Liquid Nitrogen: Measurements and Predictions

Abstract Turbopumps in reusable and low-cost liquid rocket engines require compact and simple hydrostatic (i.e., externally pressurized) bearings to support large static and dynamic loads at high shaft speeds with no bearing DN (diameter in millimeters times rpm) life limitation. Hydrostatic bearings are one of the key mechanical components for cryogenic turbopumps to improve their reliability and reusability. Hydrostatic bearings offer significantly enhanced durability with very low friction and wear while providing accurate rotor positioning as well as large load and static stiffness characteristics even working with low-viscosity liquids. This work measures static load characteristics of hydrostatic journal bearings in air (25 °C), water (from 25 °C to 70 °C), and liquid nitrogen (−197 °C). Air, water, and liquid nitrogen are used as test fluids for the test bearing to evaluate the effects of fluid properties and temperatures on the bearing performance. A complete set of applied static load, bearing eccentricity, and bearing supply pressure for each test fluid (i.e., air, water, and liquid nitrogen) is presented for the test hydrostatic bearing. Measurements show that the applied static load on the test bearing significantly affects the recorded journal eccentricity ratio, bearing flow rate, and bearing static stiffnesses. Predictions are in good agreement with measurements. The predictable performance of hydrostatic journal bearings in air, water, and liquid nitrogen can further their application in various cryogenic turbopumps for liquid rocket engines.

Dry stacking of iron ore tailings: possible particle breakage during compaction

Disposal of iron ore tailings (IOT) in dry stacks is increasingly common in Brazil. IOT are compacted in layers using drum rollers that cause compaction and vibration effects on the ground. Particle breakage is usually observed in granular materials when subjected to large static loads, as can occur depending on the stacking height achieved. This study investigates the breakage behaviour of IOT, simulating load conditions that may arise during compaction of the layers for dry stack construction. Two IOT samples with different amounts of clay-sized particles but similar mineralogy (about 77% quartz and 19% iron oxide – typical of IOT in Brazil) were subject to three different laboratory tests simulating cyclic, compaction and vibration loading. Particle size distribution analyses were performed before and after testing all specimens. Both IOT samples suffered only particle breakage (relative breakage between 0.12 and 0.14 for tailings A and between 0.14 and 0.16 for tailings B) under extremely high pressures (σ′v = 85 MPa) applied by oedometer testing, above those usually found in the field. For the usual pressures applied in the field, the frequency of load and number of cycles were not significant in particle breakage.

Intelligent Health Assessment of Aviation Bearing Based on Deep Transfer Graph Convolutional Networks under Large Speed Fluctuations.

As a critical support and fixed component of aero engines, electro-hydrostatic actuators, and other equipment, the operation of aviation bearings is often subject to high speed, high-temperature rise, large load, and other continuous complex fluctuation conditions, which makes their health assessment tasks more difficult. To solve this problem, an intelligent health assessment method based on a new Deep Transfer Graph Convolutional Network (DTGCN) is proposed for aviation bearings under large speed fluctuation conditions. First, a new DTGCN algorithm is designed, which mainly uses the domain adaptation mechanism to enhance the performance of Graph Convolutional Network (GCN) and the generalization performance of transfer properties. Specifically, order spectrum analysis is employed to resample the vibration signals of aviation bearings and transform them into order spectral signals. Then, the trained 1dGCN is used as the feature extractor, and the designed Dynamic Multiple Kernel Maximum Mean Discrepancy (DMKMMD) is calculated to match the difference in edge distribution. Finally, the aligned features are fed into the softmax classifier for intelligent health assessment. The effectiveness of the proposed diagnostic algorithm and method are validated by using aviation bearing fault data set under large speed fluctuation conditions.

Development and Experimental Analysis of Friction Torque Testing Machine for Planetary Thread Roller Bearing

In order to measure the friction torque of planetary thread roller bearings, a friction torque testing machine was developed based on the principle of transfer method. The test of dynamic friction torque and starting friction torque under axial and radial continuously adjustable large load conditions is realized. The test machine has good stability, and the test data are accurate and reliable, providing data support for in-depth understanding of the friction performance of planetary thread roller bearings.

A fatigue crack growth prediction model for cracked specimen under variable amplitude loading

The objective of this study was to propose a crack growth prediction model for cracked specimens under large and variable amplitude loading conditions. In this study, the concept of change in net-section strain energy was applied to simulate elastic–plastic fracture behavior, and three-dimensional fitting of the results with respect to changes in the net-section strain energy, load ratio, and crack growth rate was performed to create the crack growth prediction model. The validity of the generated model was examined using comparisons with experimental data as well as simulation results from existing crack growth models under several variable loading conditions.

Functional readiness and properties of the nervous system peculiarities of art specialties’ future teachers

Background and purpose. The future professional work of students of the Faculty of Arts is characterized by an insufficient level of physical activity of a dynamic nature in combination with a large static load and highly coordinated finger work. Representatives of these specialties have their own psychological characteristics. Purpose: to reveal the peculiarities of the properties of the nervous system and the functional potential of the cardiovascular system of students - future teachers of fine arts and music and, based on the obtained data, to develop recommendations for physical education and sports.
 Material and methods. Students of Pedagogical University took part in the study. The total number of students was 812. 24 of them were students of the Faculty of Arts. Future specialists in physical education and sports took part in the number of 25 people. 763 students were representatives of other faculties. Properties of the nervous system were determined using psychophysiological testing. During psychophysiological testing, the reaction time and the number of errors were determined for each test. The indicators of the orthostatic test were used as indicators of functional readiness. In the orthostatic test, the heart rate was measured in the lying position and in the standing position and the difference between these indicators. Statistical analysis involved comparing students of the Faculty of Arts with students of other faculties using parametric methods, since all samples corresponded to a normal distribution.
 Results. Future teachers of creative specialties have reliably the least mobility in combination with the highest stability of nervous processes in comparison with representatives of other pedagogical specialties. Reliable differences were found between the indicators of orthostatic reactions of students of the Faculty of Arts and the faculty where future sports coaches are trained. Orthostatic regulation is significantly better in students of the Faculty of Physical Education and Sports.
 Conclusions. It is necessary to adjust the program of physical education of students of creative specialties to increase the interest of students and to match physical exercises to the features of the nervous system of students of the Faculty of Arts. Future teachers of creative specialties can be recommended to engage in any kind of sport or motor activity, but the most suitable for them are exercises that require the development of endurance in combination with the inclusion of cognitive processes and concentration: walks with observation of nature and the city, exercises performed to music, exercises with a concentration on various natural images, etc.

On the Pneumatic Hammer of Hybrid Gas Bearings: Measurements and Predictions

Abstract Hybrid bearings integrating an external pressurizing source are widely used in high-speed turbomachinery due to their notable advantages, including low friction and wear, enhanced reliability and durability, and accurate rotor positioning, as well as large static stiffness and load carry capacity even lubricated with low viscosity liquids. This paper reports experimental data and predictions to identify the characteristics of pneumatic hammer of hybrid gas bearings, 60 mm in diameter, with increasing feed gas pressures. Pneumatic hammer characteristics with static load stiffnesses and flow rates of the test bearing are recorded for increasing static loads with various shaft center positions. A computational program for modeling of hybrid gas bearings predicts static load characteristics of the test bearings. Predictions show a remarkable agreement with measurements. Comparisons of measurements and predictions reveal that calculated reduced damping factors and damping coefficients of hybrid bearings, relying on volume ratio between recess and fluid film, are reliable indicators to estimate the onset condition of pneumatic hammer instability.

Tough Engineering Hydrogels Based on Swelling-Freeze-Thaw Method for Artificial Cartilage.

Articular cartilage, which exhibits toughness and ultralow friction even under high squeezing pressures, plays an important role in the daily movement of joints. However, joint soft tissue lesions or injuries caused by diseases, trauma, or human functional decline are inevitable. Poly(vinyl alcohol) (PVA) hydrogels, which have a water content and compressive strength similar to those of many tissues and organs, have the potential to replace tough connective tissues, including cartilage. However, currently, PVA hydrogels are not suitable for complex dynamic environments and lack rebound resilience, especially under long-term or multicycle mechanical loads. Inspired by biological tissues that exhibit increased mechanical strength after swelling, we report a tough engineered hydrogel (TEHy) fabricated by swelling and freeze-thaw methods with a high compressive strength (31 MPa), high toughness (1.17 MJ m-3), a low friction coefficient (0.01), and a low energy loss factor (0.22). Notably, the TEHy remained remarkably resilient after 100 000 cycles of contact extrusion and remains intact after being compressed by an automobile with a weight of approximately 1600 kg. The TEHy also exhibited excellent water swelling resistance (volume and weight changes less than 5%). Moreover, skeletal muscle cells were able to readily attach and proliferate on the surface of TEHy-6, suggesting its outstanding biocompatibility. Overall, this swelling and freeze-thaw strategy solves the antifatigue and stability problems of PVA hydrogels under large static loads (>10 000 N) and provides an avenue to fabricate engineering hydrogels with strong antifatigue and antiswelling properties and ultralow friction for potential use as biomaterials in tissue engineering.

Active vibration control of heavy platform-struts structure

To tackle the active control problem of the heavy platform-struts structure, this paper designs a kind of hydraulic servo actuator that can withstand large static load and generate high-precision, small-amplitude dynamic forces as well, and develops a multi-channel cross-coupling suppression control algorithm that can consider the strong coupling effect in structure. Subsequently, combining the designed actuators with the control algorithm, this paper puts forward an active heavy platform-struts structure vibration control method. By embedding the designed actuators into the support struts, a platform-struts structure experimental system is constructed to assess the vibration suppression effect of the proposed method. Excited by the amplitude-varying disturbing force, four different kinds of experiments are conducted. The experimental results show that the distributed multi-channel adaptive active control method without considering the coupling effect will lead to the instability, and the vibration attenuation of the proposed method in this paper exceeds 90%. The proposed method therefore has an important potential in addressing the problem of vibration suppression in the practical engineering. In addition, it has strong convergence and robustness.

Self-adaptive macroslip array for friction force prediction in contact interfaces with non-conforming meshes

The steady-state nonlinear forced response (NFR) of finite element (FE) models with friction joints is usually computed in the frequency domain through the combination of node-to-node contact elements and the Harmonic Balance Method (HBM). In the current state of the art, rare are the cases where the friction forces are estimated for contact interfaces with non-conforming mesh grids. This need is nowadays taking place due to the improving capability of commercial FE software to manage any kind of boundary condition (i.e., either coupling or contact), without requiring coincident pairs of nodes at the joint interfaces. Such an advantage becomes a drawback when the analysts are requested to investigate the NFR of the assembly by using build-in codes, where the contact forces prediction usually requires node-to-node contact elements whose parameters (i.e., the contact stiffnesses and friction coefficients) can be easily identified by means of experiments. This paper addresses the mentioned limitation, and proposes a novel self-adaptive macroslip array (SAMA) model for the estimation of the nonlinear friction forces on FE contact interfaces with non-conforming meshes. The SAMA model consists on a set of node-to-node contact elements ordered in parallel, whose contact parameters and normal preloads are identified through a step-by-step self-adaptive weighting algorithm that depends on the topology of the meshes in contact. The goodness of the proposed model is assessed on the calculation of the NFR of a bladed disk with shroud contacts, under the hypotheses of cyclic symmetry and HBM. The nonlinear dynamic behavior of the bladed disk is evaluated in two different cases. First, in the case of lack of node-to-node congruence at the contact interface for the structure being in its undeformed configuration, and second, in the case of a relevant static misalignment of the contact interfaces due to the application of large static loads.

Research of Reinforcement Deployment Mechanism of Automatic Sampler for Lunar Sample Return Mission

Chang’E-5 detector has successfully completed the lunar sample return mission, and accomplished the first extraterrestrial object drilling sampling detection of China. The deploying process is a key point for the whole mission and the design of the deployment mechanism is significantly important for the system. Compared to traditional deployment, low gravity surface operation and heavy load is the characteristics of this mission. In this paper, a design of reinforcement deployment mechanism suitable for lunar low gravity environment, large load condition is proposed. In this scheme, the planetary force augmentation and fulcrum separation method is adopted, the arm of force is introduced to achieve large load driving by small torque, and the design parameters are determined. The performance of the deployment mechanism is vindicated by dynamic simulation analysis and experimental verification. The research results demonstrate that the deployment mechanism can meet the demand of driving large load with small torque. The deployment mechanism designed based on this scheme has been employed by Chang’E-5 detector and performed perfectly on the moon.

Influence of the elastic and elastic-plastic material parameters on the mechanical properties of slewing bearings

Slewing bearings are critical components of rotating equipment. Large structure sizes and heavy working load conditions require an extremely high load-bearing capacity and reliability. Overall and local contact finite element models of slewing bearings are verified by the empirical formula and Hertz contact theory. Validated finite element models are used to analyse the influence of the elastic material (E 1) and elastoplastic material parameters (EP 1, EP 2 and EP 3) on the load carrying capacity. The following conclusions are obtained by comparing the maximum contact load, the contact stress, the load distribution and the full-circle deformation. The influence of the material parameters on the slewing bearing is investigated to improve the analysis accuracy of the carrying capacity of the slewing bearings.

A Passive Vibration Isolator Integrated a Skyhook Damper or a Groundhook Damper

Presented in this paper is a passive vibration isolator integrated a skyhook damper or groundhook damper. The dynamic behavior of the isolator supporting a lumped mass is investigated using force and displacement transmissibility of the isolator. Force and displacement transmissibility are derived by modelling the new isolator a two-degree-of-freedom system. Numerical simulation and parameter studies of the isolator were performed. It reveals that the new isolator is a passive linear isolator, without any non-linear elements, spring or damper. However, it can bear a large static load and, at the same time, achieve greatly improved vibration isolation without employing high damping element, which is difficult to achieve in practices. Moreover, the implementation of such an isolator in practice is convenient. All these make the isolator attractive for engineering application.

Optimization of ultrasonic nanocrystal surface modification for surface quality improvement of directed energy deposited stainless steel 316L

Ultrasonic nanocrystal surface modification (UNSM) technology can be used for the surface treatment of specimens produced by additive manufacturing using directed energy deposition. We investigated the change in the surface quality characteristics of the treated specimens with respect to the UNSM process variables. The roughness and waviness of the deposited surface were adopted as the objective functions and the optimal process conditions were determined by the response surface method (RSM). The surface waviness and roughness were determined to be most affected by the static load, with the scanning speed having the least effect. It was observed that a smaller inter-path interval decreased the surface waviness and roughness, and an excessively large or small static load deteriorated the surface modification results. The finally optimized conditions consisted of a static load of 45 N, inter-path interval of 10 μm, and scanning speed of 2600 mm/min. These conditions produced a surface waviness of 1.8097 μm and roughness of 0.3297 μm, which represent improvements of 80% and 72%, respectively, compared with the untreated specimen. It was further observed that UNSM significantly refined the material grains and considerably increased the martensite. This resulted in a surface microhardness increase of up to 71.2%.

Theoretical and Experimental Study on Contact Characteristics of Spiral Bevel Gears under Quasi-Static and Large Loading Conditions

The precise mathematical model for the tooth surface and transition surface of spiral bevel gears is derived. Taking a pair of spiral bevel gears of a heavy vehicle as an example of calculation and analysis, a finite element model of spiral bevel gears transmission system is established. Through the finite element tooth contact analysis under quasi-static loading and high loading condition, the influences of torque on the root stress distribution, contact stress, and transmission error are discussed, and the results are compared with the empirical formula results. Finally, a contact performance test bench of spiral bevel gear pair is developed, then the root bending stress, contact pattern, and transmission error tests are carried out. These experiment results are compared with analyzed ones, which showed a good agreement.

A Robust $H_\infty$ Multivariable Stabilizer Design for Droop Based Autonomous AC Microgrid

The autonomous microgrid (MG) with multiple voltage source inverters (VSI) is operated in droop mode to share the load proportionally. These VSI controllers require higher droop constants if the feeder lines connecting the VSI to microgrid has a low X/R ratio. The higher droop gains and large loading conditions in the microgrid may exhibit instability with the low frequency power modes (LFPM). This paper details a systematic multivariable plant model of the MG using dynamic phasor modeling of power flow transfer functions to analyze the LFPM. Further, a robust supplementary multivariable controller is developed to stabilize the developed plant model, damp LFPM and improve transient power sharing performance of VSIs without affecting their steady-state power sharing. This stabilizer is developed based on Glover-McFarlane H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> loop shaping robust stabilization technique with an additional pole placement constraints formulated in linear matrix inequality framework. A laboratory scale experimental validation is presented to evaluate the performance of proposed stabilizer under various operating conditions and uncertainties in the autonomous MG. Moreover, the transient power sharing performance of DGs with proposed controller was compared with that of widely used derivative droop controller.