Influence Of Thermal Deformation Research Articles

Analysis of friction vibration characteristics of the end face of a T-slot sealing ring under thermal deformation

Aiming at the friction vibration problem caused by dry friction contact during the start-stop process of a dry gas sealing device, this paper takes the end face of a T-slot dry gas sealing ring as the research object and establishes a numerical calculation model of the end face of the T-slot sealing ring. The thermal coupling method is used to obtain the thermal deformation law of the seal ring end face. The transient dynamics analysis method was applied to study the frequency and vibration mode of the friction vibration instability of the seal ring end face under thermal deformation. A vibration test bench was set up for the friction ring, and the friction vibration signals of the test pieces were collected, and the characteristic frequencies were extracted. The results show that: After thermal deformation, the end face of the sealing ring changes from a parallel surface to an inward converging surface, and the friction system of the sealing ring will become unstable. When considering the influence of thermal deformation, there are more unstable frequencies and lower frequency values that are most prone to frictional vibration. As the thermal deformation of the sealing ring increases, the frictional vibration becomes greater. In areas where the characteristic frequency values of frictional vibration are concentrated during thermal deformation, the occurrence rate of frictional vibration noise is higher.

Thermal optimization of a high heat load liquid-metal-bath cooled mirror at the Hefei Advanced Light Facility.

Within the beamlines of diffraction-limited storage rings, the liquid-metal-bath cooling scheme is a prevalent choice for the cooling of high-heat load mirrors. This study employs the finite element analysis method to evaluate the thermal deformations of liquid-metal-bath horizontally deflecting mirrors in the Hefei Advanced Light Facility. In particular, we introduce a novel optimization strategy to obtain the optimal thermal deformation scenario, which also satisfies mechanical design requirements. Moreover, a concurrent optimization approach across multiple structural parameters of mirrors is adopted to attain globally optimal thermal deformation. Following the optimization of the mirror's structural parameters, the curvature radius increases to 227 km, while the residual slope error decreases to 36.3 nrad at 6eV in the meridian direction. The ray tracing analysis of the beam demonstrates a considerable reduction in the influence of thermal deformation on the beam's focal point. This work proposes an optimization method for designing cooling schemes under mechanical constraints.

Probabilistic analysis of homogenized elastic property for resin products fabricated by additive manufacturing based on three-dimensional random field modeling of microstructure

Additive manufacturing (AM) techniques have been used in several fields of science and industry, and fabrication techniques are being updated. For this fact, especially, for industrial use, mechanical property evaluation methodologies for AM products and standards for product quality assessment should also be well established. In this paper, a probabilistic evaluation of the homogenized elastic properties of a resin product fabricated by a material extrusion-based AM technique is attempted by considering the randomness of both material and microscopic geometrical quantities. This AM method fabricates a resin structure by piling up melted resin, and to decrease consumed material and influence of thermal deformation, the inner structure of the fabricated products will include many pores and its geometry is difficult to be well controlled. From this fact, the products will be regarded as a heterogeneous material with complex random microstructure. This will cause difficulty in the evaluation of its apparent material properties and therefore a probabilistic homogenization analysis is attempted for their quantitative estimation in this study. In particular, to investigate probabilistic properties of microscopic geometry, a random field modeling technique is employed for the evaluation of autocorrelation of the microscopic geometrical parameter, and the results of the autocorrelation identified by experimental observation are introduced to the probabilistic homogenization analysis. The two-dimensional or three-dimensional random field modeling is attempted, and the effectiveness of this approach is investigated by comparing it with the experimental result.

The study of thermal-structural coupling deformation analysis for flexible space manipulator in orbit

Abstract The space manipulator can assist astronauts to accomplish space activities, including docking, fixing, and grasping. It is subjected to thermal radiation and produces thermal deformation during orbit operation, which makes the operation of the space manipulator deviate from the predetermined trajectory and further affects its positioning accuracy. Therefore, to solve the problem of bidirectional coupling thermal-structure deformation analysis and positioning accuracy for space manipulator, based on the thermal-structural bidirectional coupling deformation analysis, a method of its thermal deformation on the output positioning accuracy of space flexible manipulator is proposed. It analyzes the bidirectional coupling relationship between the temperature and its thermal deformation for the manipulators. Then, the influence of thermal deformation on the output joint error and end positioning accuracy of the space manipulator are analyzed. Finally, the validity of this method is verified by numerical analysis. Compared with the unidirectional coupling model, the bidirectional coupling model comprehensively considers the structure, deformation and temperature of manipulators. It is closer to the real system. Thermal deformation will reduce the reliable runtime of the space manipulator in orbit. The study provides a theoretical basis for its thermal design and control.

Research on thermal characteristics modeling for feed system of CNC machine tool considering thermal parameter correction

Feed system is an essential part of machine tools for controlling cutting. The thermal characteristics of the feed system has a significant impact on the machining accuracy for machine tool. To predict the temperature distribution of the feed system accurately, a dynamic thermal analytical approach for feed system is proposed in this paper, which considers the dynamic change process of the bearing and nut heat source affected by thermal deformation. Taking the feed system of machine tool as the research object, the heat source calculation method and stress modeling process considering the influence of thermal deformation is proposed. The thermal-structural coupling analysis of the feed system and the corresponding experimental data are presented. With the comparison of the simulation and test results, it is concluded that the simulation result of the feed system thermal characteristics analysis is in good agreement with the experimental data, and the established model and method can effectively improve the simulation accuracy of the feed system.

Accurate Data Match and Call Method for the Thermal Compensation Database of the Reflector Antenna

Abstract The influence of thermal deformation on the performance of reflector antennas has become increasingly significant with the increasing aperture and working frequency. The use of a thermal compensation database is an efficient method to compensate for the deformation caused by the non-uniform temperature distribution. However, how to efficiently and accurately match and call the database remains as one of the tough challenges for the antenna thermal compensation system to achieve real time compensation. Therefore, this study proposes a data match and call method for the thermal compensation database of the reflector antenna, matching the database from three aspects: the overall rms match of temperature data, the similarity area match of each data sample, and the key area match of key structural positions. The validation of this method is demonstrated in an example. The difference between the pointing adjustment amount calculated by the matched data and the collected data was found to be less than 1″, which satisfied the requirements of practical engineering, thus achieving real-time thermal compensation of the antenna.

Research on thermal design and thermal optical performance of space telescope based on multidisciplinary integration

This paper first analyzes the external heat flow of a low-orbit space telescope in different flight attitudes, and determines the position of the heat dissipation surface and the thermal analysis cases. Then, the detailed thermal design of each component of the telescope is completed to reduce the influence of thermal deformation of optical elements and supporting structures caused by temperature changes on the imaging quality of telescope. Especially for the thermal control difficulties of CCD detectors such as large heat generation in a short time and one-dimensional movement in a narrow space, a segmented proprietary cold chain with flexible section is designed to transfer the heat to the radiant cold plate. Finally, the thermal/structure/optical integrated simulation analysis under extreme cases is carried out. It is concluded that the average modulation transfer function (MTF) of the optical system at the cutoff frequency satisfies the design requirement greater than 0.3. The analysis results show that the thermal control system designed in this paper can ensure the optical performance of the telescope, which has important reference significance for the thermal design of other space telescopes.

Dynamic of Grating Thermal Deformation on Beam Quality for Spectral Beam Combining

For spectral beam combining, an experimental system of dynamic beam quality caused by the thermal deformation of a grating has been designed and established. According to the theoretical model established, the distribution of the temperature field, as well as the thermal deformation of the grating, has been analyzed. Further, the combined beam quality and the intensity distribution have been numerically calculated in detail. The results show that the maximum temperature and the grating thermal deformation increase with the extension of irradiation time, resulting in side lobes appearing in the intensity distribution. In the experiment, the measured combined beam quality factor Mx2 was 1.29 without the thermal deformation. When the grating was heated by pump lasers at different times, Mx2 can arrive at 1.34, 1.37, and 1.41, respectively. The results reveal that the combined beam quality increases with the increase in irradiation time and changes rapidly at the beginning of heating, consistent with the theoretical analysis. The discussion and analysis of the dynamic beam quality are potentially valuable for reducing the influence of thermal deformation on the beam quality.

Thermal Stability Design of Asymmetric Support Structure for an Off-Axis Space Camera

With the development of space optical remote sensing technology, especially off-axis space cameras, the thermal dimensional stability of the support structure has become increasingly demanding. However, the asymmetry of the camera structure has not been fully considered in the past design of the thermal stability of off-axis cameras. In order to solve this problem, a support structure with very low thermal deformation in the asymmetric direction is presented in this paper for an off-axis TMA camera. By means of the negative axial thermal expansion coefficient of carbon-fiber-reinforced plastics (CFRP), a composite laminate with near zero-expansion was obtained by adjusting the direction of fiber laying, and the asymmetric feature of the off-axis remote sensing camera structure was fully considered, thus enabling the support structure to have good thermal dimensional stability. We carried out a thermal load analysis and an optical analysis of the whole camera in the case of a temperature rise of 5 °C. The results show that the zero-expansion support structure has good thermal stability, and the thermal deformation in the asymmetric direction of the camera is obviously smaller than that of the isotropic laminate support structure. Compared with the isotropic support structure, the influence of thermal deformation on MTF is reduced from 10.43% to 2.61%. This study innovatively incorporates the asymmetry of the structure into the thermal sta-bility design of an off-axis TMA camera and provides a reference for the thermal stability design of other off-axis space cameras.

Influence of the Bearing Thermal Deformation on Nonlinear Dynamic Characteristics of an Electric Drive Helical Gear System.

Based on the statics and quasi-statics analysis methods, the thermal deformation calculation model of a deep-groove ball bearing was constructed for the helical gear transmission system of a high speed electric drive, and the radial and axial bearing stiffness values of the bearing were calculated under the thermal deformation in this study. The obtained radial and axial stiffness values were introduced into the established dynamics model of helical gear system, and the influence of changed bearing stiffness, resulting from the thermal deformation, on the nonlinear dynamic characteristics of gear pair was analyzed using the Runge–Kutta method. The results show that the axial and radial deformations of bearing occur due to the increase of working speed and temperature, in which the axial stiffness of bearing is improved but the radial stiffness is reduced. The decreasing degree of axial stiffness and the increasing degree of radial stiffness decrease with the gradually increasing working rotational speed. When considering the influence of thermal deformation on the bearing stiffness, the helical gear system will have nonlinear behaviors, such as single periodic, double periodic, and chaotic motion with the change of working speed. Therefore, in order to improve the nonlinear dynamic characteristics of high speed electric drive gear systems, the influence of bearing stiffness change on the dynamic performance of a gear system should be considered in the industrial applications.

The influence of thermal deformations on clearance in a turbine seal of a liquid rocket engine’s turbopump

The influence of thermal deformations on clearance in a turbine seal of a liquid rocket engine’s turbopump

Modeling and Analysis of the Composite Stiffness for Angular Contact Ball Bearings

As a core component of the motorized spindle, the dynamic stiffness of the angular contact ball bearing directly affects the dynamic characteristics of machinery. A modified quasistatic model of the ball bearing is established considering the influences of thermal deformation, centrifugal deformation, and elastohydrodynamic lubrication (EHL). Then, the film stiffness model considering spin motion is constructed. On this basis, the composite stiffness model of the ball bearing is proposed, and the effects of different factors on dynamic characteristic parameters are investigated. The results show that different factors have different effects on the dynamic parameters. With the increase in preload, the contact stiffness and composite stiffness increase. Considering EHL, the radial contact stiffness and composite stiffness increase while the axial and angular contact stiffness and composite stiffness decrease. Considering the thermal effect and centrifugal effect, the radial contact stiffness and composite stiffness increase while the axial and angular contact stiffness and composite stiffness decrease. The film stiffness and composite stiffness increase with the consideration of the spinning motion.

Research Regarding the Improving of the Machining Parameters in the Field of Grinding Process

Grinding is one of the most important machining processes that confer the final size and surface finish for the workpiece. The paper presents a theoretical study regarding the manner in which the quantity of heat that results during grinding process is transmitted to the technological elements. The study reveals as well the influence of thermal deformations on the dimensional accuracy of the workpiece. Experimental data regarding the influence of cutting speed on the temperature in the machining zone for different cutting processes are distinguished.

Effect of Ferritic Hot Rolling Process on Microstructure and Properties of IF Steel

The effect of ferritic hot rolling process on microstructure and properties of Ti microalloyed IF steel was investigated. The hot rolling-coiling, cold rolling and continuous annealing processes of ferritic zone were physically simulated. The influence of thermal deformation (finishing rolling temperature, coiling temperature) on the structure, texture and forming properties of Ti-If steel was studied through tensile test, EBSD, XRD and other analytical methods. The results showed that the recrystallization occurred after hot rolling and coiling in the ferritic region. Weak α-fiber and weak γ-fiber were obtained in the central layer of hot rolling plates, and the strength of γ-fiber was higher when finished rolling at low temperature. α-fiber and weak γ-fiber were strengthened after cold rolling. After annealing, the α-fiber was weakened and the γ-fiber was strengthened, and the γ-fiber became the main texture. The larger and more uniform grain size and better mechanical properties were obtained by IF steel finished rolling and coiling at high temperature and after continuous annealing, reaching yield strength of 106 MPa, tensile strength of 297 MPa, elongation rate of 52%, n value of 0.26 and r value of 2.3. The hot rolling texture is hereditary. If the more γ-fiber is formed after hot rolling, the more γ-fiber recrystallization texture is formed after cold rolling and annealing.

Thermal Deformation Analysis of Water Cooling Doubly Salient Brushless DC Generator With Stator Field Winding

Thermal deformation changes the length of a variable reluctance machine's air gap; this change has a significant effect on the machine's power density and efficiency. The variable reluctance machine usually has a small air gap, which may cause scrapping failure (due to thermal deformation). Therefore, it is necessary to study the influence of thermal deformation on air gap length in order to avoid scrapping failure and to choose an optimal air gap length. The doubly salient brushless dc (DSBLDC) generator is a variable reluctance machine with stator field winding. Water cooling is the usual method for cooling a DSBLDC generator (as all excitation sources are mounted on the stator). In this paper, a water-cooling DSBLDC generator is employed to analyze thermal deformation. First, the configuration of the DSBLDC generator is introduced and the thermal distribution characteristics of the water-cooling DSBLDC generator are given. Second, the DSBLDC generator is separated into a yoke and pole in order to investigate its thermal deformation. A theoretical calculation model and a three-dimensional finite-element model are then proposed to analyze the thermal deformation. The influence of thermal deformation on the stator, rotor, and air gap length is further analyzed under different temperature distribution conditions. Finally, thermal deformation's influence on output performance is discussed and the calculation and analysis of thermal deformation are verified through experimental results.

Dynamic characteristics of beam perveance under thermal deformation for a three-grid ion thruster

In this study, the dynamic characteristics of beam perveance under thermal deformation in a three-grid ion thruster are analyzed and discussed by a combination of theory and experiment. Beam extraction in the apertures of the grids is simulated by the particle-in-cell–Monte Carlo collision method. The influences of thermal deformation on ion density thresholds in underperveance and overperveance conditions are analyzed and calculated. Finally, a verification experiment is performed. The simulated and experimental results show the gradually increasing underperveance threshold but decreasing overperveance threshold with the grid gap widening. Unlike under normal perveance in the cold state, the extracted beam exhibits a local anomalous perveance under thermal deformation with overperveance or underperveance occuring in the middle or edge area, respectively. The simulation and experimental results agree well with a maximum relative error of less than 4.1%. This work offers a reference for uniformity of optimization of beam density for ion thrusters.

Influence of thermal deformation in cavity mirrors on beam propagation characteristics of high-power slab lasers

Owing to their good diffusion cooling and low sensitivity to misalignment, slab-shape negative-branch unstable-waveguide resonators are widely used for high-power lasers in industry. As the output beam of the resonator is astigmatic, an external beam shaping system is required. However, the transverse dimension of the cavity mirrors in the resonator is large. For a long-time operation, the heating of cavity mirrors can be non-uniform. This results in micro-deformation and a change in the radius of curvature of the cavity mirrors, and leads to an output beam of an offset optical axis of the resonator. It was found that a change in the radius of curvature of 0.1% (1 mm) caused by thermal deformation generates a transverse displacement of 1.65 mm at the spatial filter of the external beam shaping system, and an output power loss of more than 80%. This can potentially burn out the spatial filter. In order to analyze the effect of the offset optical axis of the beam on the external optical path, we analyzed the transverse displacement and rotational misalignments of the spatial filter. For instance, if the transverse displacement was 0.3 mm, the loss in the output power was 9.6% and a sidelobe appeared in the unstable direction. If the angle of rotation was 5°, the loss in the output power was 2%, and the poles were in the direction of the waveguide. Based on these results, by adjusting the bending mirror, the deviation angle of the output beam of the resonator cavity was corrected, in order to obtain maximum output power and optimal beam quality. Finally, the propagation characteristics of the corrected output beam were analyzed.

Influence of Thermal Deformation on Exchange Bias in FeGa/IrMn Bilayers Grown on Flexible Polyvinylidene Fluoride Membranes

We investigated the influence of thermal deformation on the magnetic properties of flexible FeGa/IrMn exchange-biased (EB) bilayers grown on polyvinylidene fluoride (PVDF) membranes with the pinning direction parallel to the thermal deformation directions $\alpha _{31}$ and $\alpha _{32}$ of PVDF. Because with increasing temperature, the uniaxial anisotropy is reoriented from the $\alpha _{32}$ to $\alpha _{31}$ directions by the thermally induced compressive strain along the $\alpha _{32}$ direction, both the coercive field $H_{c}$ and the loop squareness $M_{r}/M_{s}$ of FeGa/IrMn bilayers display a complex temperature-dependent behavior. The EB field $H_{c}$ decreases with increasing temperature. A modified Stoner–Wohlfarth model was employed to account for the temperature dependence of magnetic properties in the flexible FeGa/IrMn bilayers.

Influence of thermal deformation on irradiance of a collimating optical system used in radiometric calibration

In order to solve the problem of prodigious temperature fluctuation for a collimating optical system used in radiometric calibration in simulated space application, the study on influence of thermal deformation on irradiance of the collimating optical system composed of an off-axis paraboloidal reflector is presented in this paper. Firstly, the mechanical model for the optical system is initiated by SOLIDWORKS. Next, the thermo-mechanical coupling analysis of optical and mechanical structures is performed by means of finite-element method via ANSYS. Then, the geometric model for the deformed optical system is established due to the analysis result. Finally, the irradiance of this deformed optical system is analyzed by the Monte-Carlo ray-tracing analysis. The results indicate that the irradiance change induced by surface deformation of the off-axis paraboloidal reflector with a PV error of 0.161λ and a RMS error of 0.026λ (λ=632nm) is less than 0.4%. It is found that the influence of the rigid body displacement of the paraboloidal reflector on the irradiance change is larger, and in the edge of the region where the grid irradiance is weaker, the irradiance change is about 3%.

Development of Methods for Determining the Coefficients of Linear Thermal Expansion for End Measures of Length

We propose and have tested a method of determining linear thermal expansion coefficients, which is not affected by the influence of thermal deformation of structural elements of the measuring system on the results determining these coefficients. We present recommendations for the application of the developed methodology.