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ObjectiveThe thermal distribution during the grinding of face gears using a worm grinding wheel is complex, with the heat being concentrated primarily on the surface layer of the wheel teeth, which can lead to thermal deformation and damage. In order to improve the situation, a numerical computational model for the instantaneous grinding temperature of face gears with a worm grinding wheel was established to investigate the distribution and variation patterns of the grinding temperature.MethodsFirstly, based on the geometric contact characteristics between the face gear and the worm grinding wheel during the grinding process, a quadratic surface was employed to approximate the instantaneous contact region and derive a calculation formula for the instantaneous grinding contact area. Secondly, the forces acting on individual abrasive grains during the grinding process were analyzed, taking into account factors such as the number of participating abrasive grains and their average grinding thickness, thereby obtaining the instantaneous tangential and normal forces. Subsequently, the generation and transfer of heat during the grinding process were examined, leading to the development of a numerical analysis model for the instantaneous grinding temperature of face gears with a worm grinding wheel. Finally, the proposed model’s computational accuracy was validated through the test of the grinding temperature.ResultsThe analysis results demonstrate that the instantaneous grinding temperature significantly increases from the inner diameter to the outer diameter at a fixed tooth height position. Moreover, at a constant tooth width position, the temperature gradually rises from the tooth tip to the tooth root, albeit with a small magnitude of variation. Furthermore, the instantaneous grinding temperature rises with increased grinding depth, feed rate, and wheel speed, with the grinding depth and wheel speed exhibiting more pronounced influences.

The crack tip constraint and failure assessment diagram （FAD） in both plate specimen and pipe structure were studied to find out the compatibility and correlation of between the sample and piple.Based on the finite element method, constraints at crack tip of central cracked plate （CCP） specimen and cracked pressure pipe were obtained.It was found that crack tip constraint of CCP specimen under uniaxial loading is better matched with thick-walled pipeline under axial tensile loading, while CCP specimen under biaxial loading is better matched with thin-walled pipeline under internal pressure.In addition, the failure assessment diagram of CCP specimen and pipeline were obtained.It was found that FAD of CCP specimen is less related with thickness, when the thickness of pipe is within the range of thick wall or thin wall; was also pointed out that stress parallel to the crack direction increases the failure assessment curve （FAC） of the structure. Finally, it is found that FAC of the central crack plate specimen is higher than that of the pressure bearing pipeline, for the two structures with the same constraint level，and crack tip mixed mode degree and loading mode. That is, it is unsafe to use FAD of CCP specimen to evaluate pipeline.

In order to investigate the relation between abrasion and crack initiation in the welded zone of rails and axle weight and friction coefficient, through the field measurement of a large number of uneven weld zones, two kinds of typical weld zone uneven data were fitted, and two kinds of typical uneven wheel-rail contact finite element models of upper convex and lower concave weld zones were established. Combined with the friction work model and Archard wear theory, the maximum wear cross section of the welded zone was predicted, and the crack initiation life of the welded zone was predicted based on the Jiang-Sehitoglu model. It is found that with the increase of axle load, the abrasion rate of both the upper convex and lower concave weld zone increases, and the abrasion rate of the upper convex weld zone increases significantly when the axle load reaches 16 t, while the abrasion rate of the lower concave weld zone increases significantly when the axle load reaches 18 t. When the friction coefficient increases from 0.2 to 0.35, the maximal abrasion amount of the two types of weld zones of the upper convex and the lower concave is 1.93 mm and 1.08 mm, respectively. The abrasion rate of the upper convex type increases significantly at a friction coefficient of 0.3, while the abrasion rate of the lower concave type increases significantly at a coefficient of 0.35. When the axle load increases from 12 t to 18 t, the service life of the upper convex weld zone decreases less, while the service life of the lower concave weld zone decreases more. In addition, when the friction coefficient is increased from 0.2 to 0.35, its effect on the service life of the upper convex weld zone is significantly smaller than that of the axle load （12-18 t）. However, when the friction coefficient is increased from 0.2 to 0.35, the effect on the service life of the lower concave weld zone is comparable to that of the axle load （12-18 t）. The results show that with the increase of axle load and friction coefficient, the influence of concave irregularity on the life of rail welding zone is more significant. In the process of engineering maintenance, we should pay attention to the appearance of concave welding zone and mark and repair it in time.

ObjectiveThe existing intelligent fault diagnosis methods face challenges, such as model training relying on a large amount of labeled data, difficulty in obtaining fault data with different occurrence probabilities, and insufficient consideration of the impact of operating conditions. To address these challenges, a novel gearbox diagnosis method for adaptive inter-class and intra-class unbalanced fault data under varying working conditions was proposed.MethodsFirstly, a gated local connection network was utilized to reduce the reliance on the labeled data and extract intrinsic features directly from the original data. Secondly, a parallel mechanism of external and internal attention was designed to consider the distribution differences among inter-class and intra-class faults under different working conditions, adjusting the weights of extracted features accordingly. Finally, focal loss function was employed to focus on minority and challenging samples, enabling high-quality mining of unbalanced diagnostic information.ResultsThe proposed method is demonstrated by six unbalanced gearbox datasets, which shows great effectiveness and superiority in identifying unbalanced fault data.

ObjectiveAiming at the problems of large size, heavy weight and safety of human-machine interaction of traditional rigid wheelchair manipulators, a 6-degree-of-freedom rope driven flexible wheelchair manipulator was designed.MethodsThe manipulator adopted a flexible translation structure, which can keep the end posture unchanged while changing the end position, realized the decoupling of position and posture, and effectively improved the rigidity of the flexible manipulator. The kinematic model of the flexible manipulator was established based on the constant curvature modeling method, and the kinematic analysis between the drive space, joint space, and operation space as well as the decoupling analysis between each flexible joint were carried out. A simulation model based on Adams virtual prototype was established.ResultsBy comparing with the numerical simulation results of Matlab software, the accuracy of the kinematic algorithm is verified, which provides a basis for the subsequent motion control of the manipulator.

ObjectiveThe time-varying mesh stiffness of gear pairs, as one of the most important internal excitation of the gear system, is an important reason for the vibration and noise of the gear system. In previous studies, tooth surface modification and shock absorber were often used to improve the vibration response of the system, but there are few literature on the influence of mesh stiffness fluctuation on the vibration characteristics of the system. In order to improve the vibration characteristics of the helical gear system, a design method of low fluctuation mesh stiffness was proposed.MethodsSince the length of the contact line of the helical gear pair changes during the meshing process, resulting in mesh stiffness fluctuations, the core idea of the design method was to deduce the conditions for the minimum change of the total length of the contact line in the meshing process according to the mesh principle. Then it was compared with the finite element method to verify the correctness and effectiveness of the parameter design method and the analytical mesh stiffness model. A dynamic model of eight-degree-of-freedom helical gear was established. Then the RMS of vibration energy before and after optimization was compared. The loaded static transfer error (LSTE) and dynamic response were analyzed, and two optimization design methods were discussed.ResultsThe results show that appropriate parameter design can significantly reduce the mesh stiffness fluctuation, optimize the LSTE and improve the vibration of the system. The research results provide theoretical support for the vibration reduction design of the gear system.

ObjectiveThe coaxial dual-output cylindrical gear split-combined-torsion transmission system has the advantages of compact structure, light weight, and strong carrying capacity, and is widely used in aviation, shipbuilding and other fields. Although the coaxial dual-output cylindrical split-combined-torsion transmission system is symmetric in terms of local configuration principle, there is still a problem of uneven load distribution among the branches. The transmission system was analyzed from the perspective of statics.MethodsConsidering factors such as the torsional deformation of the transmission shaft, the support deformation and the meshing deformation of the gear pair, the principle of the meshing phase difference between the two pairs of the gear pair was analyzed, and the time-varying meshing stiffness of the cylindrical gear was calculated. Based on this, combined with the force balance conditions and deformation coordination conditions of the transmission configuration, the influence of the meshing phase difference between the gear pairs on the static load sharing characteristics of the transmission system was studied.ResultsThe results show that the greater the meshing phase difference between the gear pairs is, the worse the static load sharing performance will be; the influence of the combined stage phase difference on the load sharing performance is greater than that of the split torsion stage; for the same stage gear pair, the influence of the phase difference of the right input branch of the inner output shaft branch on the load sharing coefficient is greater than that of the left input branch, and the influence of the phase difference of the left input branch of the external output shaft branch on the load sharing coefficient is greater than that of the right input branch.

ObjectiveThe shotcrete manipulator is an eight-degree-of-freedom redundant manipulator with prismatic joints, and its inverse kinematics is difficult to solve. Therefore, an improved bee colony algorithm was designed.MethodsFirstly, the D-H method was used to establish the kinematics model of the manipulator, and multi-constrained objective functions were constructed with the terminal pose error and best flexibility as optimization objectives. Then, chaotic mapping was introduced to initialize the honey source, and Levy flight was introduced to change the search strategy of the employed bees. The step length of the onlookers was adjusted adaptively, and the population diversity and the algorithm convergence speed were improved. Finally, the Matlab programming was used for simulation verification.ResultsThe results show that the convergence speed and the accuracy of the proposed algorithm are better than the traditional bee colony algorithms, the chaotic bee colony algorithm and the particle swarm algorithm, which proves the feasibility of the proposed algorithm, and has provided a new way to solve the inverse kinematics of the wet spray manipulator.

ObjectiveAt present, there is relatively little research on using micro texture methods to reduce gear meshing noise, and most of it remains at the level of computer simulation and equivalent sample testing. There is no theoretical analysis or bench testing on the noise performance of micro texture gears. It is necessary to understand the influence of micro texture on gear meshing noise under oil lubrication and dry friction conditions.MethodsA gear meshing noise calculation model was built, laser processing technology was used to manufacture micro-textured gears, a gear noise detection platform was built, and the mesh noises of micro-textured gears and non-textured gears were tested and analyzed under oil-lubricated and dry friction conditions.ResultsThe test results show that the micro-texture can help reduce gear meshing noise under both oil lubrication and dry friction conditions, at the same time, and verify the validity of the calculation model of the tooth surface meshing noise.

ObjectiveThe drill power head of the drilling rig often needs to withstand large torque in the working process, and the construction conditions are harsh. The gear material of the power head is often selected 20CrMnTi alloy steel, because the material has excellent hardness and wear resistance. It is also widely used in the preparation of key parts in various transmission devices, such as gears, bearings and drive shafts. However, concerning the power head of the drilling rig often needs to withstand large torque during the working process, the construction conditions are harsh, and the service conditions are complex and harsh, which usually result in a variety of complex abrasive behaviors during use. These will inevitably affect its service performance over time. It is very important to master the failure mechanism of surface abrasion damage of 20CrMnTi alloy steel during actual service.MethodsBased on the wear test device and electrochemical corrosion workstation, the damage behavior and corrosion kinetics of the 20CrMnTi alloy steel at different temperatures (25 ℃/100 ℃) and loads (35 N/55 N/75 N) were studied.ResultsThe test results show that the increase of wear temperature and normal load will aggravate the wear of the material, and then reduce the electrochemical corrosion resistance of the surface. In addition, the abrasion damage mechanism of the 20CrMnTi alloy steel is mainly manifested as abrasive wear and fatigue spalling.

ObjectiveWhen the CVT is running at high speeds, the force relation between its components is very complex, and when the speed exceeds 8 000 r/min, the metal sheet is prone to wear, resulting in a sharp decrease in the service life of the CVT. Studying the strength and wear of metal strips and metal sheets under high-speed conditions is of great significance for the application and development of CVT in electric vehicles.MethodsThe mechanical model of the metal strip under high-speed conditions was established, and the influence of different speed ratios and rotational speeds on the stress and wear of metal sheets was simulated and analyzed by the Ansys Workbench software, and verified by simulation tests.ResultsThe results show that the stress of the metal sheet increases with the increase of the speed ratio at high speed, and the side wear of the metal sheet increases.

ObjectiveThe RV reducer is extensively utilized in the joints of industrial robots due to its advantages such as the high reduction ratio, the low transmission error, and the compact structure. However, the main bearing, being a thin-walled bearing, is prone to significant deformation of the ring during the operation. The transmission error induced by the deformation of the flexible support cannot be neglected. Consequently, it is imperative to investigate the impact of the flexibility and lubrication characteristics of the main bearing on the transmission error of the reducer.MethodsTaking angular contact ball bearings as the research object, the parametric three-dimensional models of main bearings and reducers were established, and the multibody dynamic model of the rigid-flex coupling of main bearings, the elastic lubrication model of main bearings considering the flexible deformation of rings and the dynamic model of RV reducers were constructed. On the basis of studying the dynamic response of key parts of the reducer and the contact characteristics of the main bearing, the influence of the flexible characteristics of the main bearing on the transmission error of the RV reducer was further explored.ResultsThe results show that the transmission error range is -25.2″ to 21.6″ when the flexible characteristics of the main bearing are not considered, and the transmission error range increases to -43.2″ to 45″ after considering the flexible characteristics of the main bearing. With the increasing deformation of the ring, the transmission error of the reducer continues to increase; with the continuous increase of oil film thickness, the transmission error of the reducer first decreases and increases; with the continuous increase of oil film pressure, the transmission error of the reducer is also decreasing first and increases; the influence of the flexible characteristics of the main bearing on the transmission error of the reducer cannot be ignored, and it is of great significance to appropriately improve the supporting stiffness of the main bearing to reduce the transmission error of the RV reducer. The proposed method has certain reference significance for the precision design of RV reducers and main bearings.

ObjectiveThe corrosion fatigue fracture of the wind turbine pitch bearing is a major failure mode, often leading to the blade detachment and shutdown. To this end, a finite element model of replacing the whole pitch bearing with a local one was proposed to investigate the structural fatigue remaining life of pitch bearings after corrosion of the raceways.MethodsA combined method of finite element software Ansys and three-dimensional fracture mechanics software Franc3D was adopted to simulate the corrosion pit by inserting a pre-damage at the location of the maximum equivalent stress in the bearing ring. The crack propagation path and life of the corroded bearing ring were investigated under actual operating conditions.ResultsThe results show that the remaining fatigue life of the corroded bearing ring under actual operating conditions is 2.2×107 cycles, approximately 2.3 years, accounting for 11.6％ of the design life. Through this results, the characteristics of the structural fatigue of the bearing ring affected by the corrosion can be better understood, providing guidance and reference for engineering practices in related fields.

ObjectiveAdding a gravity balance mechanism to robots can effectively improve their dynamic performance.However, there are few existing upper limb rehabilitation training robots that involve end traction balance mechanisms. Based on the analysis of the change law of the center of mass during the cantilever working process of the upper limb rehabilitation robot, a cantilever mechanism of the upper limb rehabilitation robot that can automatically balance gravity was designed to address this issue.MethodsThis institution can achieve gravity balance by determining the position and parameters of the zero length spring, which means that only one spring is needed to meet the self balance of the upper limb rehabilitation robot cantilever in tension and rotation working states. In theory, joint loads generated by gravity can be completely eliminated, energy loss can be reduced, and the working range and system performance of upper limb rehabilitation robots can be improved. And a rehabilitation robot balance model was designed and a prototype test platform was built to verify the accuracy of the model and the feasibility of the design scheme.ResultsThe results show that compared with the traditional traction rehabilitation cantilever, the balance effect of spring gravity balance scheme is significant, the torque required for balance is reduced by 92%, and the joint driving torque is reduced by 85%.

ObjectiveThe modular soft robot has high flexibility and unlimited degrees of freedom in theory, and can adapt to various complex environments and task requirements. Therefore, a kind of honeycomb soft driving unit was designed, which can be connected and composed to realize the modular driving soft robot with different functions.MethodsThe material selection and mechanical analysis of the designed imitation honeycomb soft drive unit were carried out, and a nonlinear relational model between the driving pressure and deformation in the soft drive unit was established; the validity of the model was verified by combining with the finite element simulation. Based on the imitation honeycomb soft body drive unit module, a flexible soft robot and a bidirectional bending soft robot were designed, and finite element simulations on both configurations of soft robots were conducted. Finally, the production of soft robots and test research on the modular driving of soft robots were conducted.ResultsThe simulation results show that the bidirectional bending soft robot has a larger deformation range and better bearing capacity than the flexible soft robot with the same length. The test results show that the bidirectional bending soft robot can realize the linear crawling and turning motion like worm. And the test results of two kinds of soft robot configurations are basically consistent with the simulation results.

ObjectiveThe transmission error is a critical performance indicator in the design of cycloidal pin wheel reducers. The influence of design parameters for crank bearings and output shaft pins on this error is frequently neglected in existing research. To address the issue, a method for calculating transmission error based on the kinematic and mechanical analysis was introduced, thereby offering theoretical foundation for the optimization of design and the enhancement of performance in cycloidal pinwheel reducers.MethodsFirstly, the motion locus of the meshing point between cycloidal gear teeth and pin teeth was obtained based on the instantaneous motion locus of the cycloidal pin gear mechanism and the meshing interval between them. Subsequently, the design range for the distribution circle radius of crank bearing and output shaft pin was defined. A contact force analysis model for the crank bearing and the output pin was established, and their respective force influences were calculated. Finally, by Masta software, the influence of distribution circle radius on transmission error of cycloidal pinion reducers was analyzed.ResultsThe results show that within the design range for distribution circle radius of the crank bearing and the output shaft pin, the larger values result in smaller transmission errors but greater forces exerted on these components. This study provides valuable insights for designing and optimizing domestic cycloidal reducers.

ObjectiveThe application of deep learning methods in the field of rolling bearing fault diagnosis is very effective, but traditional neural networks cannot extract features at multiple scales due to the use of a single scale convolution kernel, and do not consider the importance of different features in fault diagnosis. Therefore, it is difficult to extract fault features of rolling bearing signals under noise interference. A rolling bearing fault diagnosis method based on parameter-optimized variational mode decomposition (VMD) noise reduction and GoogLeNet network with improved attention mechanism was proposed.MethodsThe local minimal envelope entropy was used as the fitness function, and the sparrow search algorithm (SSA) was used to optimize the VMD parameter combination; the optimized VMD algorithm was used to decompose the bearing vibration signals to obtain several modal components, and the signals were reconstructed by filtering the modal components with rich fault features according to the envelope entropy and kurtosis; the reconstructed signals were used to construct the feature matrix and input into the improved GoogLeNet network to complete the diagnosis.ResultsThe test results show that the diagnostic accuracy of the method is 95.5% to 99.8% under different noise backgrounds, which is better than other methods in terms of noise robustness.

In order to clarify the influence of different working conditions on the wear of tapered roller bearings, the wear state of tapered roller bearings was carried out.A quasi-statics model of tapered roller bearings including roller balance equation and inner ring balance equation was established, and a wear depth calculation model suitable for wear analysis of tapered roller bearings was derived based on Archard wear theory.The wear distribution characteristics of bearing inner and outer raceways and roller elements under light load, medium load and heavy load conditions were comparative analyzed.The results show that the wear depths of the tapered roller and the inner/outer raceways on the contact line show bimodal distribution characteristics, and the wear distribution of the outer raceway is closely related to the positions of the rolling elements.For light load condition, the peak wear depth of bearing raceways and roller elements increases by 20% as bearing speed increases 25%, and for heavy load condition, the peak wear depth of bearing raceways and roller elements increases more than 17% as bearing load increases 16%.The comparison of bearing wear peaks under the three working conditions shows that the product of the equivalent load and the speed of the bearing is not the determining factor controlling bearing wear，and the load change has a significant impact on the bearing wear.

ObjectiveAiming at the problem that the working plane of inspection robots equipped with precision instruments can’t always maintain stable when moving on complex road surfaces such as bosses and trenches, an innovative design of the robot’s mobile chassis structure was proposed based on the contradiction analysis method and the material field model.MethodsA floating structure design was proposed and obstacle crossing analysis and driving smoothness analysis under complex road conditions such as bosses and trenches were conducted on the floating mobile chassis. The comparative simulation of the original structure chassis and improved mobile chassis moving under complex road conditions was conducted in Admas simulation software. A floating mobile chassis test prototype was built to conduct motion tests under complex road conditions.ResultsThe test results indicate that the floating mobile chassis has strong adaptability, and the working plane can maintain stable when crossing obstacles.

ObjectiveAiming at the work problem of installation quality acceptance of horizontal glass insulators in 500 kV transmission lines, a design scheme of a robot mechanism for insulator installation quality acceptance was proposed.MethodsFirstly, a three-dimensional model of the insulator acceptance robot was established based on the operating environment. The D-H parameter method was used to conduct forward kinematics analysis of the detection structure. Then, in order to solve the problem of the robot’s stable crawling on insulator strings with different tilt angles, the optimization of the robot’s driving structure was carried out, and kinematic simulations were carried out on insulator strings with three different tilt angles of 5°, 10° and 15°. Finally, the longitudinal and lateral stability of the optimized crawler robot were analyzed, and the force of the shock absorbing spring was simulated and analyzed.ResultsThe simulation results show that compared with the multi-wheeled drive structure, the stability of the robot’s center of mass in the crawler drive structure in the Z-axis speed is increased by 84.73％, 75.76％, and 73.70％ respectively; the stability of the X-axis offset distance is increased by 40.47％, 44.21％, and 74.14％ respectively, verifying that the optimized robot has better stability. The proposed scheme provides theoretical support for the overall design of the subsequent insulator robot.

ObjectiveIn order to solve the problem of insufficient parameters optimization with multiple constraints in the current research of cat-like robots, a method of dimension optimization using the grey wolf algorithm was proposed. The sizes of the key components of the cat-like robot were optimized in the method, and higher stability and flexibility of the robot were obtained under the restriction of many constraints.MethodsFirstly, the mechanics of the cat-like robot model was analyzed, and the multi-constraints and objective function were acquired comprehensively. Secondly, the grey wolf algorithm was used to optimize the size of the leg and waist of the robot. Lastly, the simulation analysis of the cat-like robot was carried out in Matlab and Adams software.ResultsThe results show that the stability index is improved by 31.15％, and the flexibility index is improved by 11.28%. It verifies the rationality of the optimization scheme of the robot.

ObjectiveThe excessive wear of the scraper conveyor sprocket and the over-life working condition will lead to the occurrence of the stuck chain, broken chain and other faults, which will adversely affect the normal operation of the conveyor equipment. In order to guide users to replace the sprocket that is not suitable for further use and reduce the incidence of equipment failure, a mining scraper conveyor sprocket replacement and repair evaluation method was proposed.MethodsBased on the Archard wear theory, firstly, the hardness characteristics of the quench hardness layer of the sprocket were studied, and then the dynamic simulation analysis on the meshing transmission process of the ring chain drive system under different wear degree of the sprocket was carried out. The dynamic characteristics of the scraper conveyor were tested to verify the accuracy of the simulation analysis.ResultsThe test results show that when the wear depth of the sprocket chain socket reaches the maximum quenching hardness layer depth, the performance of the sprocket has decreased significantly, and the sprocket should be replaced. When the speed fluctuation, the contact force and the tension increase abnormally in the ring chain drive system, the sprocket should also be replaced in time to ensure the stable operation of the equipment. The proposed method provides a basis for the maintenance and replacement of the scraper conveyor sprocket.

Lattice structures have become a research highlight in the fields of aviation, aerospace and automobile because of its high specific strength and stiffness. The development of additive manufacturing technology makes it possible to manufacture mechanical metamaterials with complex geometric shapes and special mechanical properties. However, traditional additive manufacturing processes are difficult to coordinate the contradiction between the cost, geometric size and accuracy of such structures.In view of this, a mechanical metamaterial structure concept of reversible assembly and the connection method of its basic voxels were proposed, which can effectively overcome the size limitation of manufacturing equipment, and can construct a macro lattice structure with rich mechanical properties through different combination sequences. Aiming at the basic voxel type of reversible assembly, the influence of voxel geometric parameters, relative density and voxel numbers on its mechanical properties through parametric modeling method was analyzed, and the experimental results were compared. The results show that the three basic voxels have great rigidity difference, and Poisson’s ratio covers the range from negative to positive.Therefore, different combination sequences of these three basic voxels can produce macro structures with different mechanical property distributions, which proves the rationality of using these three basic voxels as the basic voxels of the reversible-assembly structure.In addition, the mathematical relationship between geometric parameters and mechanical properties can provide guidance for the engineering application of such mechanical metamaterials.

A two-degree-of-freedom collision system with gap and elastic constraint was used as the research object, and the regional distribution and transitions of the periodic motion of the system under low frequency conditions were studied by numerical simulation.It was obtained that with the decrease of excitation frequency, the p/1 periodic motion occurs with grazing bifurcation transitions to （p+1）/1 periodic motion.When the number of collisions was large enough, the Chattering-impact characteristics were presented.Then a circuit model that was completely equivalent to the collision system was established and simulation experiments were carried out.The results show that the results generated by establishing the equivalent circuit are consistent with those generated by numerical simulations, and the equivalent circuit is more efficient in simulation experiments, which can realize fast modal transitions and parameter adjustments，making it more convenient and providing a research method for the study of nonlinear dynamics.

The planetary gear system is widely used in aircraft transmission equipment because of its small size, light weight and large load capacity，but the problem of bias load caused by various errors cannot be avoided, and a serious bias load condition will lead to under utilization of the advantages of the planetary system cannot be fully exploited.The influence mechanism of the flexible change of the inner gear ring on the bias load behavior of the system was investigated by taking a certain type of aeronautical planetary gear system as the research object.The deflection，stress and strain of the inner gear ring were measured by experiments with different number of planets and different rim thicknesses, and the mechanism of bias load was analyzed and the degree of influence of the number of planets and rim thickness on the bias load behavior of the system was evaluated.The advanced simulation calculation and analysis of a large aeronautical planetary system was completed by using a hierarchical finite element model to quantify the influence mechanism of the variation of inner gear ring flexibility on the load distribution and gear ring deflection of the system.The accuracy of the simulation results was evaluated by fitting the experimental and simulation results to the same parameter range for comparison.The research results provide targeted structural optimization guidance for the development and design of internal gear rings of large aeronautical planetary gear systems, which can greatly reduce the cost of this type of large aeronautical equipment in the design and iteration process.

Aiming at the research on intelligent identification of caving coal and gangue, in order to provide a complete and effective vibration signal acquisition scheme of coal and gangue, an optimal layout strategy of tail beam sensors of caving coal hydraulic supports based on vibration characteristics of coal and gangue was proposed. Firstly, the modal analysis of the tail beam model was carried out, extracting the vibration mode matrix， and the effective independent method was used to select the measuring points. Secondly, the vibration signals of coal falling and gangue falling at the corresponding primary measuring points from the tail beam test bench were obtained, and the feature extraction was carried out. Thirdly, the extracted features were visualized by t-distributed stochastic neighbor embedding （t-SNE） dimensionality reduction, and five features which were sensitive to the distinction between coal and gangue signals were selected as target features. Finally, the probability density functions of target features were estimated by the kernel density estimation method. The K-L（Kullback-Leibler） divergence was used to evaluate the approximation between combined signal of each measuring point and the complete signal and the difference between characteristics of coal and gangue. The evaluation indexes of coal and gangue vibration signals were constructed. Combined with Fisher information matrix criterion, a comprehensive evaluation index was formed to determine the optimal scheme of tail beam sensor arrangement. The results show that the sensor arrangement scheme determined by this method not only reduces the number of sensors on the basis of satisfying modal observability, but also makes the measured vibration signals have better coal gangue difference and information integrity.

Considering the actual excitation load, the nonlinear dynamics characteristics of the bolted structure have a certain impact on the whole mechanical system. The dynamics model of actual bolted structure is more complex with considering joint surface morphology parameters and plasticity index. Therefore, with considering the influence of the surface mopography parameters, plastic index on the normal contact stiffness, contact damping and under the various conditions such as external harmonic excitation, the existing normal contact model of bolted structure was modified, and the obtained nonlinear normal contact stiffness and nonlinear contact damping were applied to the dynamics response characteristics analysis of forced vibration of bolted joints structure. The influences of surface morphology parameters and plasticity index on the dynamics characteristics of bolted structure were studied.

The torsional vibration of reciprocating compressor crankshaft system can cause major problems such as burnt bearings and shaft fracture.In order to understand the torsional vibration response of the compressor rotor system, a torsional vibration mechanics solution method for the flexible rotor system of the compressor considering the bushing-pin collision clearance and the oil film clearance of the crankshaft-bearing was proposed, which provided a new idea and method to avoid the natural frequency of the crankshaft system.Based on the multi-body dynamics and Hertz contact theory，the torsional dynamic response of the crankshaft system with collision clearance was solved.The results show that the torsional vibration amplitude of the 4th column crank pin is the largest, the torsional angular displacement amplitude is 0.051°, and the dynamic angular velocity peak value is 156.026 rad/s.Based on this, the crankshaft-bearing oil film clearance was considered, the oil film pressure of sliding bearings was calculated by the finite difference method and the over-relaxation iterative method, and the dynamic characteristic coefficients of bearings were solved according to pressure perturbation method.The effects of the bushing-pin collision clearance and the crankshaft-bearing oil film clearance on the dynamic response of the crankshaft system were comprehensively considered in the modal analysis of the crankshaft system under preload.The resonance of the crankshaft with and without oil film clearances was compared. The results show that the natural frequencies of the 3rd and 8th orders of the crankshaft system decreases by 44.64% and 21.23%, and when considering the reduction of the resonant speed point of the crankshaft with comprehensive clearance in the same speed range, the 2nd order critical speed is reduced by 38.55%, and the probability of resonance increases.

In order to solve fatigue fracture problem of the transverse stabilizer bar link of a pickup truck, taking the measured load spectrum as support, the fatigue analysis and structural improvement of bar link was carried out based on multi-body dynamics load decomposition method. The load spectrum acquisition test of stabilizer bar link was carried out, and the correlation analysis between sensor signals was conducted, and the validity of the collected signals was verified. Through the kinematics compliance（KC） test, the accuracy of suspension dynamics model was verified, by using virtual iteration method, the accuracy of the vehicle dynamic model is verified by the measured load spectrum signal as excitation. The critical load of bar link was obtained by means of multi-body dynamics load decomposition method, compression rod instability theory method and bench test method respectively, the strength of link was checked and compared with the measured load value, and the accuracy of the three methods was evaluated. The results show that multi-body dynamics load decomposition method can accurately predict the critical load, the bench test method have some errors, and the the compression rod instability theory cannot be directly used for strength check of link. Fatigue simulation and optimization of link were carried out by combining nominal stress method and load spectrum of multi-body dynamics decomposition. The fatigue mileage predicted by simulation is 12 143 km, the relative error value with real life is 14%, which proves validity of simulation method. The structural improvement of the dangerous part of link body port eliminates stress concentration of it, and makes the design life of link meet the service requirements.

In response to the challenging task of fault feature classification in the current working conditions of pumping units，which results in poor adaptability and low recognition rate of the established diagnosis model. The dynamometer card was pretreated by mathematical morphology through the analysis of the motion state of the pumping unit valve and the sucker rod. Then, two methods of obtaining valve opening and closing points and load variation characteristics were proposed, and 54 new features of global faults of pumping units were extracted, and the characteristic database of working conditions of the pumping unit was established.Finally, the algorithm of decision tree, logistic regression and support vector machine was used to verify that the feature database has good classification effect under different working conditions. The characteristic indexes of different fault conditions were evaluated, and the private rule database of each working condition was obtained. The research results demonstrate that the proposed features in this study are capable of effectively identifying comprehensive faults in pumping units, exhibiting a high level of recognition accuracy.

Based on the low temperature tensile test data of the rubber, Ansys software was used to fit the Mooney-Rivlin hyperelastic constitutive model of rubber material parameters, and the thermo-solid coupling simulation was carried out on the U-shaped rubber outer windshield according to three real working conditions, and the influence of different working conditions on the U-shaped rubber deformation was studied.The low temperature test was carried out on U-shaped rubber outer windshield and three rubber samples with different batten thicknesses， the influence of temperature and batten thickness on its deformation was studied.The results show that the U-shaped rubber deformation is mainly caused by the temperature change, the U-shaped rubber height decreases obviously, and the shape variable of the side wall thickness and the rubber length is small.In addition, the batten thickness has a greater influence on the rubber shape variable at the bolt hole.Compared with the batten of 5 mm and 6 mm thickness, the 4 mm batten produces a larger deformation under the bolt preload action, resulting in a larger deformation at the bolt hole, and then increasing the batten thickness can effectively reduce the hole removal risk.Comparing the finite element simulation data with the low temperature test results, it is found that the two results are basically consistent，which indicates the finite element analysis feasibility and the low temperature test reliability.The research results provide some guidance basis for the U-shaped rubber outer windshield under low temperature application reliability.

The misalignment of the dual-rotor system for the aero-engine will lead to abnormal increase of the vibration which results in the rotor-stator rubbing and affects the safty and stability of the rotor operation.The dual-rotor system was taken as the research object.Considering the combination misalignment-rubbing fault, the dynamic model of the rotor system is established based on the lumped mass method.The differential equation of the system motion was established according to the Lagrange equation, and the Range-Kutta method was used to solve it.The influence mechanism of the key parameters such as the speed, the misalignment angle and the coupling misalignment on the nonlinear dynamic characteristics of the system was studied.The results show that the system presents complex dynamic characteristics such as periodic, multi-periodic, quasi-periodic and chaotic motion with the increase of the rotor’s speed.When the speed is in the range of 1 500-2 200 rad/s, the system switches between periodic 2 motion and chaotic state through multiple paroxysmal bifurcations and paroxysmal inverted bifurcations.There are nonlinear phenomena such as jump in the bifurcation diagram of the vibration response with the change of the parallel misalignment of the coupling.As the misalignment angle of the bearing increases, the chaotic interval of the high speed decreases, and the stable periodic motion interval increases.

An online measurement method of a dynamic unbalance force of the geotechnical centrifuge was carried out based on monitoring the change of the axial preload of anchor bolts. Firstly, the change model of the axial preload of the anchor bolt under different unbalanced force states was deduced theoretically, which proved the feasibility of indirectly measuring the unbalanced force of the centrifuge. Then, the typical testing case was carried out on the TLJ-500 centrifuge, and the law of the dynamic unbalance moment changing with the counterweight was obtained. By fitting the change of the axial force at the measuring point, the relation between the axial force at the measuring point and the unbalance mass and the running gravitational acceleration g value of the centrifuge was established.Finally, the relation between the change of the axial preload of anchor bolts, acceleration of the centrifuge and counterweight mass were obtained by measuring the preload change of one anchor bolt and fitting the response surface. The results show that it is feasible to obtain the unbalanced force of the centrifuge operation by monitoring the change of anchor bolts’ pre-tightening force， and the centroids of different counterweights should be kept consistent in the test. When calculating the counterweight mass to balance the rotating arm according to the fitting formula, a larger acceleration should be used as far as possible to reduce the error caused by the centrifuge not being leveled.

In order to determine the sensitive vibration characteristic parameters of coal and gangue in the process of top coal caving and improve the intelligent identification accuracy of coal and gangue, the dynamic characteristics of the tail beam of the hydraulic support were studied. Firstly, the rigid-flexible coupling dynamic model of top coal caving hydraulic support and coal gangue was established, and the vibration acceleration of the tail beam of the hydraulic support in the process of coal caving was calculated. Secondly, the acceleration response was decomposed by variational mode decomposition (VMD) to obtain the intrinsic mode function (IMF), and the time domain and frequency domain characteristics of each IMF component were analyzed. Thirdly, the t-distributed stochastic neighborhood embedding (t-SNE) method was used to reduce the dimension of these features, and the average silhouette coefficient (ASC) of different features was calculated. The vibration characteristics of the tail beam under the impact of coal gangue were compared and studied. Finally, the bench of the top coal caving hydraulic support was built to verify the calculation results of the model. The results show that the energy, singular value, mean frequency, peak frequency, spectral centroid and frequency variance in the IMF component of the vibration acceleration of the tail beam are sensitive to the characteristics of coal and gangue, which can be used as the characteristic parameters of the coal and gangue identification.

In order to avoid large vibration response and transcritical motion instability of ultra-high speed centrifugal impeller rotor system caused by unbalanced excitation, the unbalanced excitation response of ultra-high speed centrifugal impeller rotor system was analyzed by using Ansys rotor dynamics response analysis module and comprehensively considering the stiffness and damping of sliding bearing, the dynamic response of ultra-high speed centrifugal impeller rotor system under different unbalanced excitation was obtained.At the same time, DEWESoft vibration test system was used to track and record the rotating frequency vibration value of ultra-high speed centrifugal impeller rotor system, and compared with the unbalanced response analysis results, it was concluded that the dynamic balance accuracy level of the ultra-high speed centrifugal impeller rotor system should be better than G1 level. The unbalanced excitation response analysis and control method has been well verified by tests, which has important engineering application significance.

ObjectiveIn order to quantitatively work out operating parameters and relation of parts of multi-power system coupled with planetary gears, a mathematical mapping analysis method was proposed.MethodsThe method was discussed by analyzing the hybrid system coupled with planetary gears of one truck, the kinematic and mechanical relations of parts of the system were deduced; a mathematical map was constructed with Matlab software; the switching order of modes and the path planning in start-up acceleration were quantitatively analyzed; the optimal cruising fuel consumption under different slopes and speeds was quantitatively analyzed; based on the above analysis, three system architecture optimizations were proposed, and compared to the original system in performance with simulation.ResultsThe switching order of modes, the path planning and the optimal fuel consumption point under cruising conditions could be intuitively and quantitatively figured out. The optimizations are verified by simulation to have a certain effect in performance improvement, which is useful for the development of control strategy and calibration of the system.

Abstract In recent years, IoT technologies have made our daily lives more convenient and comfortable. In particular, these technologies are being actively utilized in our living environments through the development of various smart home appliances. As the pace of Digital Transformation (DX) quickens and digital platforms become integrated into diverse residential settings, the notion of the home we inhabit is taking on greater significance beyond merely a place for rest. Therefore, this paper explains the development of user-friendly interfaces for smart home systems used in our living rooms. An appropriate service can be provided accordingly if the user’s intent is specifically understood. Therefore, this paper explores the relationship between the user’s gaze and the control targets of the smart home using Mixed Reality (MR) devices. In this study, we introduce a novel smart home control system from a range of options. Our proposed system enables user analysis and remote control through the utilization of an MR device capable of tracking a user’s gaze. In addition, we investigate the perception of user interfaces and analyze the survey results conducted after using the interface system, discussing the validity of the proposed system.

The welding process aims at joining materials, especially metals or thermoplastic for certain purposes. It melts the materials in the joining process. In some cases, such material is difficult to be joined with the welding process. Therefore, an appropriate flux is needed in this process. The effect of adding borax in the welding process of OAW is the focus of this research. The research was conducted using the experimental method of adding 1 gram, 3 grams, and 5 grams of borax to the brass and ST42 steel welding process. Borax was added to aid the adhesion process between brass and steel as both have different properties. This research results in the highest elongation value in 1 gram of borax addition; the elongation is 3.9935 cm. Meanwhile, adding 1 gram of borax also affects the welding joints’ ultimate tensile strength (UTS). It results in the highest UTS value of 9.961779 kN/mm2 among the other weight variations of borax addition. It indicates that the borax addition with proper weight in the welding process affects the joints. Moreover, the borax addition in the welding process influences the elongation values, ultimate tensile strength, and modulus of elasticity of the welding joints.

ObjectiveThe vibration analysis is an effective and widely used technology for monitoring the state of the rotating machinery. To better manage the health condition of various components in gear transmission systems, a vibration state monitoring framework for gear transmission systems based on the digital twin technology was proposed.MethodsFirstly, the functionality and logical relation of each module in this technology framework were introduced from the physical layer, the data layer, the model layer, and the application layer, respectively. Secondly, the construction of the performance model and the behavior model for the gear transmission system was detailed. The performance model was used to simulate vibration signals, while the behavior model was utilized for updating the digital twin model. Finally, using a two-stage fixed-axis gear transmission system as an example, its digital twin system was established. Theoretical analysis and verification of various key technologies were conducted.ResultsThe digital twin system achieves online vibration monitoring of the gear transmission system. The simulation response of the digital twin model shows close agreement with the measured vibration data, validating the effectiveness of both the performance and behavior models. This study provides valuable data support for the fatigue life prediction and reliability assessment of key components in the gearbox, contributing to the advancement of digital twin technology in the monitoring of rotating machinery.

ObjectiveThe industrial robot industry has put forward higher requirements for RV reducers, and the precision life reflects the ability of the reducer to maintain transmission accuracy, which is one of the most important design criteria and usage indicators. To improve the precision performance of precision reducers, it is crucial to evaluate their reliability. Therefore, the degradation characteristics of precision reducers were analyzed.MethodsTaking the RV80E reducer as an example, a random degradation model based on Gamma process was proposed. Combined with the performance degradation data of the reducer transmission accuracy, the model parameters were estimated based on the matrix method and the maximum likelihood estimation method. A Gaussian process regression model optimized by genetic algorithm was established using vibration characteristic data to optimize the prediction of transmission accuracy.ResultsThe results show that the prediction accuracy based on Gaussian process regression model is significantly better than that of traditional regression model. The posterior distribution parameters of the random degradation model are updated by using the algorithm to predict the results, which can effectively evaluate the reliability of the accuracy life of RV reducer and lay the foundation for further reliability optimization design of accuracy life.

Abstract Grease is extensively used in rolling bearings due to its inherent sealing properties. However, mechanical degradation typically occurs, resulting in a significantly shorter lifespan for the grease compared to the bearing. Investigating aging mechanisms is essential. This study utilized rolling bearings to obtain mechanically aged greases. The aged samples were then subjected to do rheological test, FTIR test and friction test to examine the effects of aging time, radial load, and rotational speed. An innovative disk-ball-disk device was developed to study the friction characteristics of aged grease in rolling bearings. Additionally, a grease lubrication and friction model were proposed to further evaluate the lubrication performance of aged grease, using measured rheological parameters and the kinematic velocities of the disk-ball-disk device as inputs. The calculated friction coefficients matched well with disk-ball-disk experimental results. FTIR analysis revealed that the non-soap thickener's structure remained stable, but additives depleted at high speeds. The structure of lithium soap thickener decomposed severely, leading to oil bleeding and a shortened replenishment duration. Over aging time, both greases had lower friction and viscosity due to gradual thickener breakdown, releasing bled oil and extending replenishment. Radial load minimally affected the properties of aged grease. This study may provide valuable insights into the aging mechanisms of grease and the enhancement of rolling bearing lubrication.

Abstract Despite significant progress in the Prognostics and Health Management (PHM) domain using pattern learning systems from data, machine learning (ML) still faces challenges related to limited generalization and weak interpretability. A promising approach to overcoming these challenges is to embed domain knowledge into the ML pipeline, enhancing the model with additional pattern information. In this paper, we review the latest developments in PHM, encapsulated under the concept of Knowledge Driven Machine Learning (KDML). We propose a hierarchical framework to define KDML in PHM, which includes scientific paradigms, knowledge sources, knowledge representations, and knowledge embedding methods. Using this framework, we examine current research to demonstrate how various forms of knowledge can be integrated into the ML pipeline and provide roadmap to specific usage. Furthermore, we present several case studies that illustrate specific implementations of KDML in the PHM domain, including inductive experience, physical model, and signal processing. We analyze the improvements in generalization capability and interpretability that KDML can achieve. Finally, we discuss the challenges, potential applications, and usage recommendations of KDML in PHM, with a particular focus on the critical need for interpretability to ensure trustworthy deployment of artificial intelligence in PHM.

Abstract Many experiments have supported the contact models, such as the GW and MB models, but the majority of previous validations have been performed under light loads, resulting in a linear relationship between normal force and contact area. However, the real contact area fraction should never equal one; there must be a limit smaller than the apparent area, implying that the real contact area cannot increase linearly indefinitely. In this paper, the real contact area between two polymethylmethacrylate (PMMA) blocks under heavy load is measured using the total reflection method, and the contact area is analyzed using the image processing method. The results show that the real contact area increases with normal load linearly in light loads but non-linearly in heavy loads; the number of contact spots increases with load linearly in light loads but also non-linearly in heavy loads, synchronous with the change in the real contact area. The GW, MB, and Zhao, Maietta, and Chang (ZMC) models were used to predict the experiment results, but none of them predicted the non-linear stage. A revised GW model based on the bulk deformation hypothesis performs better in predicting the non-linear stage. The study’s findings can be applied to PMMA or other similar materials, and they can serve as a useful reference for future research on the contact mechanisms of other materials.

Abstract We are currently developing a suit that assists human running motion based on the Smart Suit (SS). The SS is a wearable assistive device that intervenes in trunk kinetic chain movements by linking trunk rotation to hip flexion and extension through elastic belts. By intervening in the trunk kinetic chain, our goal is to enhance stiffness, thereby improving running economy and speed. The purpose of this study is to acquire fundamental insights into the changes in leg and trunk rotational stiffness induced by the SS, as well as the underlying mechanisms. We defined the SS torque intervention rate $$p_{ss}$$ p ss , which focuses on the magnitude of force, and the peak time difference index, $$e_{lag}$$ e lag , between SS and humans, which focuses on the timing of force, and analyzed the relationship between the stiffness change rate due to SS wearing. The results of the analysis suggest that SS affects human running sensitively rather than mechanically. We also confirmed that the degree of adaptation to SS, assessed by the timing gap between SS exertion and human exertion, contributes significantly to changes in trunk rotation stiffness.

MethodsThe finite element model of spherical steel projectile penetrating 2024-T42 aluminum alloy target was established based on Ansys/Workbench software and Johnson-Cook material model, and its effectiveness was verified. In addition, the response characteristics of aluminum alloy circular tubes with different radii and thicknesses under normal impact of spherical steel bullets were simulated, and the deformation and damage of the circular tubes were analyzed.ResultsThe results show that the anti penetration ability of the upper and lower walls of aluminum alloy circular tubes is different, and the anti penetration ability of the upper convex structure wall is better than that of the lower concave structure wall; The smaller the radius of an aluminum alloy circular tube, the better the anti penetration performance of its upper pipe wall, while the lower pipe wall is weaker than the upper pipe wall, and its ballistic limit velocity difference gradually weakens with the radius; For aluminum alloy circular pipes with the same radius, the thicker they are, the more linearly the ballistic limit velocity of the upper and lower pipe walls increases.

ObjectiveStructural optimization of wind turbine blades is one of the most important ways to enhance performance, reduce mass and lower costs. Currently, the research on structural optimization focuses on the blade size or layup scheme, and the overall configuration inside the blade is relatively fixed, but it also limits the structural innovation to a certain extent.MethodsTherefore, Abaqus softwave topology optimization module was adopted to optimize the design of the blade web structure to seek for the optimal material layout, to obtain a new blade structural configuration to achieve the purpose of lightweighting.ResultsThe results show that the mass of the web plate is reduced by about 4.56% after optimization; the optimization of the blade web topology does not affect the overall mass distribution and stiffness distribution of the blade, and maintains good vibration resistance; the maximum stress of the optimized web plate increases, but it does not yet exceed the maximum permissible stress of the material; the flexure factor of each order decreases, which is due to the reduction of the material of the web plate to weaken the role of its support for the surface of the blade, but it still remains in the safe range.

A high velocity is rarely accessible in water streams such as rivers, canals, and outlets of sewage and common effluent treatment plants. However, an average velocity of 0.5 - 1.0 m/s is reported to be available in many water streams most of the time. Hydrokinetic (HK) turbines can extract power from the flowing water in these streams. Considering the small quantum of power generated, the economic factor is more significant than efficiency. A Savonius-type HK turbine can generate energy from low-velocity magnitudes of around 0.5 m/s, although it remains a low-speed and low-efficiency turbine. In this study, an attempt has been made to computationally investigate the performance of the Savonius turbine in a water stream channel. It is observed that the performance of the Savonius turbine is not significant, and the generated power cannot be utilized constructively for different applications. Therefore, it is necessary to develop and investigate variant constructive systems to enhance turbine performance. This manuscript focuses on exploring these variant systems and understanding their performance characteristics. Four variant systems have been selected: (i) System-1: Solely Savonius turbine, (ii) System-2: Savonius turbine with a flume, (iii) System-3: Deflector section used before the flume, and (iv) System-4: Deflector section used before the turbine. The investigation was carried out for these four variant systems using the Fluent commercial code. The results indicate that the Coefficient of performance (Cp) is low for System-1, solely Savonius turbine, with a value of 0.052. For the other variants, Cp values were found to be 0.357, 1.385, and 0.579 for the turbine with a flume, deflector before the flume, and deflector before the turbine respectively at the Tip Speed Ratio (TSR) is 1. Moreover, the study also extends to optimizing Cp under different TSR for the different variant systems. The intention is to use this study to install an HK turbine with an optimum constructive structure for maximizing and stabilizing the power that can be used for an isolated application.

The performance of the settling chamber was examined in two scenarios in this study. In case 1, the settling chamber collection efficiency and flow characteristics were predicted without a baffle plate. In case 2, the settling chamber performance was predicted with the baffle plates. In case 2, two baffle plates were placed between the inlet and exit nozzle. The experimental set up was fabricated with the baffle plates to measure the performance. Moreover, the efficiency of the settling chamber was determined for the different inlet velocities. The Variable Frequency Drive (VFD) controller was adopted with the suction fan to vary the inlet velocity. The Reynolds Stress Model (RSM) was used to forecast the settling chamber flow characteristics. In cases 1 and 2, the best capture efficiency results were achieved at 2.5 m/s inlet velocity. The experimental study shows that the settling chamber gathering efficiency was 45% at 52.35µm. It is 44.4% higher than case 1. In CFD analysis, the settling chamber efficiency was 43%. The variation between the experimental and CFD results was 4.4%. The observations show that the pressure drop for the baffle plate setting chamber was increased 4.37 % compared to case1. The maximum settling velocity of the case 1 and case 2 chambers is 1.62 m/s and 2.81 m/s respectively. It indicates that the baffle plate chamber has highest setting velocity. Moreover, the hopper region has highest tangential velocity when introducing the baffle plate. The observations show that the radial velocity is increased in the rectangular wall region compared to hopper region due to the baffle plate.

The intricate and complex flow structures of three-dimensional unsteady incompressible turbulence surrounding bluff bodies have garnered considerable attention from numerous researchers. Using computational fluid dynamics (CFD) methodologies, the underlying mechanism by which a wavy trailing edge (TE) design for a D-shaped bluff body achieves drag reduction was explored. The wavy TE was in the form of a cosine wave with two design parameters: amplitude and wavelength. To ascertain optimal control parameters, we employed an improved delayed detached eddy simulation (IDDES) technique for a comprehensive parametric analysis, focusing on the amplitudes and wavelengths of the cosine wave. Furthermore, to gain a more holistic understanding of the factors influencing the design of wavy TE structures, we conducted parametric studies on three distinct groups of wavy structures. After identifying the optimal amplitude, wavelength, and wave type, we further investigated the control mechanism of the wavy structures in reducing the drag and mitigating lift fluctuations for Reynolds numbers in the range 3.6×105–3.6×106. Present investigation revealed that compared with the original D-shaped bluff body, the wavy TE structures significantly reduced the average drag coefficient, with a maximum drag reduction of 60.2%. Moreover, it effectively curtailed the fluctuations in the lift coefficient. With careful parameter adjustments, the wavy TE significantly enhanced the characteristics of the flow field. This improvement was evident in the reduction in vortex scales, enhancement of instability characteristics in separated shear layers, and effective suppression of periodic vortex shedding.

Microchannel heat sinks (MCHS) are capable of removing exceptionally high heat fluxes through liquid-to-vapor phase transition, making them suitable for various applications, including the thermal management of high-power microelectronics. However, their commercial applicability is hindered by the flow boiling instability associated with chocking of the micro-passage as the vapor bubbles grow. The present study addresses the research gap in literature pertaining to the impact of microchannel depth on flow boiling instability in terms of amplitude of heated surface temperature and pressure drop oscillations, and their influence on heat transfer performance. Experiments are conducted using dielectric water boiling in multiple parallel microchannels with mass fluxes of 220 and 320 kg/m²s and wall heat fluxes ranging from 25 kW/m² to 338 kW/m². Two different MCHS, fabricated from oxygen-free copper substrate, were examined, each comprising 44 parallel microchannels with nominal depths of 500 µm and 1000 µm, and a consistent nominal width of 200 µm. Heat transfer coefficients were measured using an array of embedded T-type thermocouples on the substrate to measure temperature gradients. The findings reveal that increasing the microchannel depth results to a significant increase in the amplitude of wall temperature fluctuations under fixed wall heat flux conditions, which in turn diminishes heat transfer performance. Additionally, the study demonstrates a notable dependence of pressure drop on coolant flow and both microchannel sizes. This research provides new insights into optimizing MCHS design for enhanced thermal management, highlighting the critical role of microchannel depth in mitigating flow boiling instability and improving overall heat transfer efficiency.