The Research and Experiments on Contact Sealing Theory of the Underwater Clamp Connector

With regard to the sealing structure characteristics of the underwater clamp connector, based on the Hertz contact theory, this article studies the method of solving the extreme value of the radius of curvature on the two curved surfaces at the sealing contact point; first, the method of calculating the extreme value of the radius of curvature at any surface point of the rotary part is obtained, and then the equivalent radius of curvature is solved. Using finite element simulation to study the contact sealing characteristics without considering the edge thickness and width of the sealing gasket, it is verified that the Hertz contact theory is applicable to the metal contact theory of underwater clamp connectors. Then, the sealing simulation with the influence of the detailed dimensions of the sealing gasket is compared with the theoretical result of the direct application of the Hertz contact theory in the underwater clamp connector contact, and the theoretical correction coefficient of metal contact seal for underwater clamp connectors is introduced to solve the errors. The pressure sealing experiment is carried out on six-inch flange and metal sealing gasket, which proves that the coefficient can greatly enhance the theoretical calculation accuracy of the contact sealing of the underwater clamp connector.

Nonlinear Dynamics of a Blade Rotor with Coupled Rubbing of Labyrinth Seal and Tip Seal

The dynamic response and its stability of a blade rotor with coupled rubbing in the labyrinth seal and tip seal are investigated. The dynamic equations are established based on the Hertz contact rubbing force at the labyrinth seal and the tip rubbing force considering both the contact deformation of the tip seal and the bending deformation of the blade. Numerical simulations show that the coupled rubbing response includes periodic motions, almost periodic motions, and chaotic motions. Compared with the single rubbing fault, coupled rubbing increases the range of rotation velocity of contact. A new continuation shooting method is used in the solution and stability analysis of the periodic response to give the bifurcation diagrams. The paths of the system for entering and exiting chaos are analyzed.

Contact characteristics of steel-rubber rollers based on modified contact theory considering viscoelasticity

This paper mainly studied the contact characteristics of steel-rubber rollers. First, according to the dynamic mechanical experimental data of rubber, the hyperelastic-viscoelastic composite constitutive model was constructed to accurately describe the properties of rubber. Then, for the contact problem of steel-rubber rollers, the elastic modulus of rubber presents an instantaneous change due to the influence of rubber's viscoelasticity, so the Hertz contact theory was modified through the instantaneous elastic modulus. Next, a dimensionless parameter [Formula: see text] was constructed to judge the viscoelastic influence degree of rubber. Finally, based on modified contact theory and the dimensionless parameter [Formula: see text], the influence of compressive force and rolling speed on the contact characteristics of steel-rubber rollers was analyzed. The research in this paper is helpful to the analysis of dynamic contact problem of rollers structure and the development of contact theory.

Theoretical research on the wear characteristics of rotors in a twin-screw compressor

Thanks to the development and application of coating technology and polymer rotor material, it is an inevitable trend to eliminate synchronous gear for water-injected and dry twin-screw compressors, especially running at a high speed, due to much power consumed by synchronous gears. However, it is not economical and reliable to rely only on coating or rotor material to enhance the wear resistance of rotor. This paper attempts to lighten the rotor wear in twin-screw compressors from the angle of setting driving belt. To achieve this goal, the contact analysis is carried out in this paper, taking the rotor profile of a developed water-lubricated twin-screw air compressor as an example. By the contact analysis, equivalent curvature radius, Hertz contact stress, sliding distance, the value of PH S, and the minimum film thickness of each mesh point on different tooth curve are calculated and discussed. The product of the Hertz contact stress and total sliding distance, PH S, and minimum film thickness are chosen as the evaluation indexes to estimate the wear resistance of all tooth curves. By comparing these indexes of each tooth curve, some suggestions about setting the driving belt are proposed.

Investigation of Fracture Width Change under Closure Pressure in Unconventional Reservoir Based on the Hertz Contact Theory

To describe the fracture width is crucial for the flow conductivity evaluation, which influences the exploitation efficiency of unconventional oil and gas resources. Commonly, as the proppants fill in the fracture, the deformation will happen under the closure pressure to resist the fracture width change. Therefore, it is significant to develop the theoretical model to predict the variation. In this work, the mathematical model for the propping behavior of proppants in the fracture under closure pressure is established based on the Hertz contact theory. Compared with the existing models, the developed model considers both the proppant insertion and the elastic compression among the proppants, which is closer to the actual physical process. Furthermore, the experimental cases with different proppant sizes are taken to verify the model, and the good conformity presents its rationality. The parameter sensitivity analysis of this model shows that the fracture width change increases with the increase of the average diameters of proppants ( D ) and it declines with the improving of proppant elasticity modulus ( E 1 ) and Poisson’s ratio ( v 1 ).

A novel tooth tip relief method for reducing micro-pitting of spur gears

Micro-pitting is a common fatigue failure mode of spur gears. To reduce it, this paper proposes a novel tooth tip relief method. Gear meshing simulation is firstly performed considering the actual contact path, showing that there are four Hertz contact stress peaks in the transition areas of the tooth flank. Equations are then developed for the novel tooth tip relief method: one focuses on the smooth transition between the involute profile and the tip relief region, the other on the smooth transition between the tip relief region and the tooth tip. The results of curvature radius and Hertz contact stress show that the proposed novel method can effectively reduce the Hertz contact stress peaks, which indicates this tip relief method could benefit for reducing the micro-pitting. Finally, both wear simulations and bench tests are conducted, verifying the effectiveness of the proposed method for reducing the micro-pitting of spur gears.

A Dynamic Damage Model for the Rock-Shed Roof Under the Rockfall

The dynamic response of the rock-shed roof under the rockfall is a complicated mechanical process, which mainly includes the following three deformation stages, e.g. the elastic compression, plastic damage compression and elastic resilience stages of the rock-shed roof. However, the existing models based on Hertz elastic-perfectly plastic contact theory cannot perfectly reflect the above mechanical process. Therefore, on basis of the classical Hertz contact theory, the damage of the rock-shed roof induced by the rockfall is firstly introduced to consider its effect on the material elastic modulus, and then the revised Hertz contact theory considering the damage is proposed. Secondly, in view of the existing calculation method of the maximum rockfall impact force based on the theorem of impulse, a new calculation method is proposed by combining the revised Hertz contact theory. Thirdly, according to the dynamic mechanical response process of the rock-shed roof under the rockfall and in view of the revised Hertz contact theory, a dynamic damage model for the rock-shed roof under the rockfall is proposed, which can perfectly illustrate the variation law of the impact force with the deformation of the rock-shed roof during the rockfall. Finally, the proposed model is verified with other models for the maximum rockfall impact force. In all, the proposed model can perfectly describe the dynamic mechanical behavior of the rock-shed roof under the rockfall, which can be referred for the engineering design.

Analysis of Contact Deformations in Support Systems Using Roller Prisms

This article presents the results of finite element analyses of the influence of reaction forces on stresses and strains at the contact points of the rollers of prism supports with cylindrical surfaces of the main journals of large-sized crankshafts. The analyses of strains and stresses, as well as the depth of their occurrences, in the case of the shaft journal and support rollers were carried out using Hertz contact theory and the finite element method. These calculation results proved to be highly consistent. Additionally, they provide a basis for stating that, in the case under consideration, permanent deformations do not significantly affect the values of the measured geometrical deviations nor the profile forms of the supported main crankshaft journals.

A Novel Tooth Tip Relief Method for Reducing Micro-Pitting of Spur Gears

Micro-pitting is a common fatigue failure mode of spur gears. To reduce it, this paper proposes a novel tooth tip relief method. Gear meshing simulation is firstly performed considering the actual contact path, showing that there are four Hertz contact stress peaks in the transition areas of the tooth flank. Equations are then developed for the novel tooth tip relief method: one focuses on the smooth transition between the involute profile and the tip relief region, the other on the smooth transition between the tip relief region and the tooth tip. The results of curvature radius and Hertz contact stress show that the proposed novel method can effectively reduce the Hertz contact stress peaks, which indicates this tip relief method could benefit for reducing the micro-pitting. Finally, both wear simulations and bench tests are conducted, verifying the effectiveness of the proposed method for reducing the micro-pitting of spur gears.