Experimental Study Of Dynamic Characteristics Research Articles

Experimental study of dynamic characteristics of solid holdup fluctuations in a gas-solid cyclone reactor

Local transient solid holdup signals were measured by using an optical fiber probe at different axial and radial positions in the gas-solid cyclone reactor. The chaotic time series analysis of transient solid holdup was adopted to characterize the dynamic characteristics. The maximum and minimum solid holdup indicates that the high variability of gas-solid interaction. With the increase of the gas / solid ratio, the frequency of solid holdup fluctuation increased while the mean value of amplitude decreased; besides, the level of detail in the power spectrum fluctuations increased. In the diffusion chamber, the overall Kolmogorov entropy (K entropy) and correlation dimension (Dc) were higher indicating the strong chaos characteristic of gas-solid flow. In the agglomeration chamber, higher solid holdup initially reduced gas-solid interaction, decreasing flow randomness, but a subsequent increase led to irregular particle collisions and an upturn of K entropy and Dc. In the annulus chamber, K entropy and Dc were lower around the inner wall and outer wall compared to the middle region. In the separation chamber, K entropy and Dc tended to increase and then decrease as the radial position increased. Finally, the relationship between K entropy, Dc, and time-averaged solid holdup was analyzed.

Экспериментальное исследование динамических характеристик роторов судовых турбогенераторов с опорами на газовой смазке

В статье приводится решение задачи по подтверждению адекватности математической модели, разработанной для исследования динамики роторов на газовых опорах. Газовые подшипниковые опоры имеют многочисленные преимущества перед гидродинамическими подшипниками, работающими на масле. В их число входит повышение механического КПД, повышение надёжности агрегата (ввиду отсутствия системы смазки) и многие другие. Однако газовые опоры имеют повышенные требования к точности изготовления подшипниковых узлов, что усложняет выполнение виброналадки роторов судовых турбогенераторов на таких опорах. В связи с этим, данное исследование направлено на повышение точности определения критических частот роторов турбогенераторов на податливых газовых опорах при проектировании. Для того, чтобы подтвердить адекватность результатов, получаемых с помощью математической модели ротора на податливых газовых опорах, был проведён эксперимент на лабораторной установке. Была получена зависимость первой критической частоты исследуемого ротора от давления наддува в подшипниках для реальной системы. Приведено сравнение результатов физического эксперимента и результатов расчёта при помощи математической модели.. The article provides a solution to the problem of confirming the adequacy of a mathematical model developed to study the dynamics of rotors on gas supports. Gas bearings have many advantages over hydrodynamic bearings running on oil. These include an increase in mechanical efficiency, an increase in the reliability of the unit (due to the lack of a lubrication system) and many others. However, gas supports have increased requirements for the accuracy of manufacturing bearing assemblies, which complicates the implementation of vibration adjustment of the rotors of marine turbogenerators on such supports. In this regard, this study is aimed at improving the accuracy of determining the critical frequencies of turbogenerator rotors on malleable gas supports during design. In order to confirm the adequacy of the results obtained using a mathematical model of a rotor on malleable gas supports, an experiment was carried out on a laboratory installation. The Article provides with obtained dependence of the first critical frequency of the studied rotor on the boost pressure in the bearings for a real system and a comparison of the results of a physical experiment and the results of calculation using a mathematical model. Keywords: Rotordynamics, critical frequencies, gas bearings

Experimental study of dynamic characteristics of an ultra-large jacket offshore wind turbine under wind and wave loads using aero-hydro-structural elastic similarities

Owing to the difficulties in the scaled rotor-nacelle assembly (RNA) and support structure design, and alleviation of small scaling effects, the limited dynamic model tests are conducted for the jacket offshore wind turbines (OWTs), which are extensively constructed in the offshore wind farms located in the depth of 40–50 m. To address this limitation, an integrated test method based on aero-hydro-structural elastic similarities is proposed in this study. It comprises a performance-scaled RNA model and a scaled support structure model. A redesigned blade model is adopted in the scaled RNA model to ensure the similarities of aerodynamic thrust loads without modifications of the scaled test winds. Moreover, auxiliary scaled drivetrain and blade pitch control are designed to simulate the operational states of a practical OWT. The scaled model of the OWT support structure is fabricated based on the joint hydro-structural elastic similarity, and the small scaling effects are mitigated by introducing sectional bending stiffness similarities. Subsequently, the dynamic model tests of an ultra-large jacket OWT under wind-only, wave-only, and combined wind and wave conditions are carried out. The accuracy of the fabricated OWT test model is validated based on the recorded responses, and the influence of the dominant frequencies on the dynamic responses of the OWT model is quantitatively evaluated using the wavelet packet-based energy analysis method. Further, the coupling mechanisms of the scaled OWT model under typical wind and wave loads are investigated, and the interactions between the environmental loads and OWT motions are proved.

Modeling and experimental study of dynamic characteristics of the moment wheel assembly based on structural coupling

The microvibration of the satellite moment wheel assembly (MWA) is an essential input for integrated simulation analysis of spacecraft microvibration, which forms the basis for spacecraft vibration suppression. Therefore, it is important to guarantee high-precision data from ground measurements of vibration sources for research into the stabilization accuracy of large space telescopes. In general, a coupled wheel-to-structure disturbance model is more representative of the real environment, and two aspects of the coupling need to be considered: coupling caused by insufficient MWA stiffness and coupling caused by the vibration source installation structure. Therefore, this paper presents the relevant work conducted on these two coupling aspects. First, this paper proposes the amplification factor coefficient, which considers structural coupling based on the classical vibration model of the MWA. The average error in this case could be within 5%. This approach could reduce the computational requirements without affecting the quality of the results. Additionally, as the mass of the MWA is greater and the disturbance output is more obvious. The structural coupling with the installation foundation is unavoidable. In this paper, the effects of installation stiffness on the disturbance measurements are analyzed based on the dynamic mass measurement method and quantitative impedance theory. Finally, based on the above theory, verification testing of the disturbance and transfer models of the MWA is performed and the test results are compared with the simulation results; it is shown that a level of accuracy within ±5% can be achieved.

Experimental study of dynamic characteristics of liquid desiccant dehumidification processes

Liquid desiccant dehumidification is an effective method of removing moisture from the air for air conditioning in built environments. The dehumidifier is a critical component where coupled heat and mass transfer between the desiccant solution and the air occurs. Understanding the dynamic characteristics of the dehumidifier is essential to develop controllers and operation strategies for the liquid desiccant hybrid air-conditioning systems. This article presents an experimental study of the dynamic heat and mass transfer characteristics of a counter-flow packed-type liquid desiccant dehumidifier. Experiments were carried out to investigate the dynamic responses of the outlet air and desiccant solution to various changing inlet conditions. In addition, the influences of typical configuration and operation parameters on the dynamic dehumidification process were analyzed. The results indicate that the settling time of the dynamic process decreases with the air and solution flow rates while increases with the packing height. The experimental results also show that the outlet air humidity ratio stabilizes sooner than the outlet air temperature during the dynamic process. The time constants of the heat and mass transfer processes were obtained, which are valuable to controller design.

Experimental study of dynamic characteristics of single screw expander with compressed air and water steam as working fluid

The research and development of novel high-efficient devices used for thermal energy conversion of low-temperature heat source (blow 230°C) is of great significance for energy saving. Single screw expander is a novel expander with a lot of advantages, such as a good axial and redial force balance, a long working life which is twice of double screw, a high pressure ratio which is up to 15 for single stage, a highest volumetric efficiency which can reach 92%, 4% higher than that of double screw, a relatively high efficiency under part load condition, a simple structure, a lowest noise which is 10dB lower than the double screw, and an oil free lubrication. In this paper, an experimental system used for testing the performance of a single screw expander whose diameter is 117 mm was designed and established. The number of screw head is 6 and the number of star wheel teeth is 11. The compressed air and the water steam were used as the working fluid to experimentally study the dynamic characteristics of single screw expander. In the experiment, the inlet temperature, the outlet temperature, the inlet pressure, the outlet pressure, the flow rate of the working fluid, the torque, the speed, and the power of the single screw expander were measured. When compressed air was used as the working fluid, the valve is fully open and the outlet pressure of the air compressor is set to be 0.75–0.85 MPa. From the experimental results, it can be seen that the single screw expander has an optimal power output working condition when the speed is about 2500–3500 r/min, and an optimal temperature drop working condition when the speed is about 2180–2700 r/min. The maximum torque was 4.4 kW when the speed of expander reached 2700 r/min. The maximum inlet flow rate was 32.9 m3/h. The initial inlet temperature of the expander was 22.7°C, and the final inlet temperature is 28.7°C. The variation of the inlet temperature is due to the inadequate heat dissipation caused by the long-time running of the air compressor. The lowest outlet temperature of the single screw expander reached - 20°C. The maximum temperature drop between inlet and outlet of expander reached 45°C. The lowest gas consumption rate was 55.2 kg/(kW h), the highest reached 187 kg/(kW h), and the average was 77.5 kg/(kW h). The maximum total efficiency of expander reached 58.8% and the average was 45.8%. Moreover, the irreversible loss increases first and then decreases with the increase of speed and with the increase of expansion ratio. The highest irreversible loss reached when the speed was 1200 r/min and the expansion ratio was 6.2. With the increase of the speed, the outlet pressure gradually increased and the expansion ratio gradually decreased. The gas consumption rate of the single screw expander first increased and then decreased with the increase of the speed. When water steam was used as the working fluid, the maximum power of expander was up to 3.9 kW. The lowest gas consumption rate was 22.5 kg/(kW h), and the maximum total efficiency of expander reached 66%.

Experimental Study of Dynamic Characteristics on Composite Foundation with CFG Long Pile and Rammed Cement-Soil Short Pile

Based on the idea of optimization design of pile type, the two kinds of the typical pile type are selected, which containing flexibility pile (e.g. rammed cement-soil pile is for short RCSP), and rigid pile (e.g. cement-flyash-gravel pile is for short CFGP). The three kinds of the composite foundation are designed, which are CFGP, CFG long pile and CFG short pile (for short CFGLP-CFGSP), CFG long-short pile and rammed cement-soil short pile (for short CFGLP-RCSSP). Natural earthquake is simulated by using the engineering blasting; the dynamic characteristics and dynamic response of the composite foundation are studied through field test. CFGLP-RCSSP is closed to linear relation. The bearing capacity of the four composite foundation of the CFGP, CFGLP-CFGSP, and CFGLP-RCSSP in the site are 225 kPa, 179 kPa, and 197 kPa, separately increases 150%, 98.8% and 119% compared to the natural foundation. The vibration main frequency is mainly depended on properties of foundation soil and piles between vibration source and measuring point, pilling load value. Horizontal vibration main frequency greater than the vertical vibration main frequency and the vertical vibration main frequency close to the first-order natural frequency of composite foundation. With the pilling load increasing, the CFGLP-RCSSP pile composite foundation combined frequency decreased. Under the same blast energy, the acceleration peak on the CFG pile composite foundation is less than CFGLP-CFGSP the corresponding values, as the load increases, the peak acceleration gently. CFG pile composite foundation is favorable on seismic. The distribution of peak acceleration is consistent within 4 m from pile top in the CFGLP_RCSSP composite foundation. The maximum of the horizontal acceleration peak along the pile body occurs at a distance of pile top 4 m or the pile top, and that of vertical acceleration peak occurred at a pile top.

РАЗРАБОТКА И ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ СТЕНДА СТОХАСТИЧЕСКОЙ ДВУХМАССОВОЙ ЭЛЕКТРОМЕХАНИЧЕСКОЙ СИСТЕМЫ

Разработан стенд стохастической двухмассовой электромеханической системы. Проведены экспериментальные исследования динамических характеристик стенда стохастической двухмассовой электромеханической системы с типовым и робастным регуляторами. Показано, что система с робастным регулятором имеет меньшую ошибку по сравнению с системой с типовым регулятором. Ил.: 6. Библиогр.: 9 назв.

Experimental Study of Dynamic Characteristics of Dry Friction Damping of Turbine Blade Steel

For lot of structures, especially turbine blades, damper can dissipate the vibration energy by friction. Investigating the property of metal dry friction damping can give many usable data for response analysis of damping blade which is important in damped blade designs. The paper constructs an experimental rig and carries out experiment with pieces having radius of curvature 6mm, 12mm and 24mm. The relative displacement between contact surfaces and the friction force changed with time were obtained for different initial pressure and frequency of exciting force. Hysteresis curves of dry friction damper were derived. The variations of friction coefficient of stick-slip area, equivalent stiffness and equivalent damping were calculated based on experimental data.

451 クリアランスを有する往復振動系の動特性に関するシミュレーション及び実験的研究(OS6-1 非線形振動,OS6 振動解析と制振)

451 クリアランスを有する往復振動系の動特性に関するシミュレーション及び実験的研究(OS6-1 非線形振動,OS6 振動解析と制振)

Actuation and Control of a Micro Electrohydraulic Digital Servo Valve

Structure of the micro digital servo valve is given. A micro stepper motor is used as electrical-to-mechanical interface of the valve. A special mechanical device is designed to convert the rotation of the stepper motor into the linear motion of the spool. This moving conversion device functions through an eccentric ball head rigidly connected to the axis of the stepper motor and plugged into a slot at the central spool land. While the stepper motor rotates, the eccentric ball head will actuate the spool to make a linear motion. Unlike conventional servo or proportional valves, in which the spool is forced to central position by a spring force, when the current supply is switched off, the digital valve has a program to control the spool to its central position each time the electrical power supply is switched on or off. The two end screws are used to adjust the position of the sleeve to sustain a mechanical central position coincided with electrical central position given by the stepper motor after initialization. The adjustment has to be carried once before the first time the servo valve is put into service. This paper presents theoretical analysis and experimental study of dynamic characteristics of the proposed micro digital servo valve. Experimental results demonstrated that the valve takes the advantage of high accuracy and fast response.

Dynamic Characteristics and Effective Stiffness Properties of Honeycomb Composite Sandwich Structures for Highway Bridge Applications

In this paper, a combined analytical and experimental study of dynamic characteristics of honeycomb composite sandwich structures in bridge systems is presented, and a relatively simple and reliable dynamic experimental procedure to estimate the beam bending and transverse shear stiffness is proposed. This procedure is especially practicable for estimating the beam transverse shear stiffness, which is primarily contributed by the core and is usually difficult to measure. The composite sandwich beams are made of E-glass fiber and polyester resins, and the core consists of the corrugated cells in a sinusoidal configuration. Based on the modeling of equivalent properties for the face laminates and core elements, analytical predictions of effective flexural and transverse shear stiffness properties of sandwich beams along the longitudinal and transverse to the sinusoidal core wave directions are first obtained. Using piezoelectric sensors, the dynamic response data are collected, and the dynamic characteristics of the sandwich structures are analyzed, from which the flexural and transverse shear stiffness properties are reduced. The experimental stiffness results are then compared to the analytical stiffness properties, and relatively good correlations are obtained. The proposed dynamic tests using piezoelectric sensors can be used effectively to evaluate the dynamic characteristics and stiffness properties of large sandwich structures suitable for highway bridge applications.

Analytical and Experimental Study of Dynamic Characteristics of Turbopumps : 3rd Report, Experimental Study of Dynamic Characteristics of a Centrifugal Pump

Analytical and Experimental Study of Dynamic Characteristics of Turbopumps : 3rd Report, Experimental Study of Dynamic Characteristics of a Centrifugal Pump

Analytical and Experimental Study of Dynamic Characteristics of Turbopumps : 2nd Report, Analytical Study of Dynamic Characteristics

Analytical and Experimental Study of Dynamic Characteristics of Turbopumps : 2nd Report, Analytical Study of Dynamic Characteristics

Analytical and Experimental Study of Dynamic Characteristics of Turbopumps : 1st Report, Analysis of Oscillating Flow through Cascades

Analytical and Experimental Study of Dynamic Characteristics of Turbopumps : 1st Report, Analysis of Oscillating Flow through Cascades