Abstract: Because micro-vibration environment of the high resolution remote sensing satellite makes great influence on image quality, it is necessary to design micro-vibration measurement equipment to accurately measure the micro-vibration parameters which impact the CCD imaging quality. The paper proposes a set of template to design the parameters of the micro-vibration on board. Starting from the change of CCD modulation transfer function (MTF) due to the micro-vibration, we can build the model, analyze the relationship of the CCD MTF and the frequency and the amplitude, and then we can determine the minimum of the angular displacement and the angular velocity. Finally design and conclude a set of logical, realizable and optimal template, which can afford facilities for the design on the parameters of measuring micro-vibration on the other high resolution remote sensing satellites.
Abstract: Our contribution in this work is to detect, localize and quantify the noise sources radiated by a spur gear transmission mechanism. The imaging technique is used; it is based on the acoustic inverse frequency response function (IFRF). The IFRF is based on the inversion of the transfer matrix built between the source points represented by their complex source strengths and listening points represented by the complex pressures measured by the hologram. The measurements were performed in a semi-anechoic room where the floor is concrete and the walls are covered with glass wool. The complex acoustic pressures are measured by an antenna with microphones regularly spaced; it is placed above the noisy mechanism. The reconstruction problem is therefore an inverse problem and is said ill-posed; thus, regularizations are needed to stabilize and to find the best solutions. As regularization technique, the Tikhonov method is applied and the regularization parameters are chosen according to the L-curve method. The goal is to reconstruct as accurately as possible the acoustic field radiated by the transmission mechanism on a fictive and tangent plane to the noisy mechanism considered open and sometimes closed. The results obtained showed that the sources were located with good approximation. The IFRF method is able to reconstruct the sound sources responsible for the noise radiated by the mechanism without any a priori information of the sources distribution, and the visualization of spatial acoustic fields facilitate the understanding of the complex phenomena of radiation.
Abstract: Structural stability of satellites is of vital significance for the operation of sophisticated payload systems. Therefore manufacturers of satellite components, such as reaction wheels, make huge efforts to assure the convenient vibration behavior of their products. To meet that demand a device for the detection of mechanical oscillations with very small amplitudes was developed. The described micro-vibration test-bench allows the detection of vibrations with amplitudes > 10 5 Newton in a frequency range of < 20 kHz generated by a test item with a mass up to 30 kg. The quality of the thereby obtained data makes it possible to identify the sources of the observed vibration. The high information content of the measurements originates from a set of high resolution force sensors, variably arranged on a mechanically isolated platform. The sensitivity of the used equipment (charge cables, charge amplifiers and signal analyzers) and its resistance to ambient disturbances allow the high accuracy of the measurement as mentioned above. The described micro-vibration test-bench additionally provides opportunity to detect production errors non-destructively and helps to reduce the inherent noise of the item under test. It therefore represents a reliable measurement device to quantify and assess detrimental vibrations.
Abstract: Magnetic bearings support a body by mechanical pulling forces without any mechanical contact. They consist of an electromagnetic actuator, position sensors, power amplifiers and feedback controller. All of these components are characterized by nonlinear behavior and hence the entire system is inherently nonlinear. This paper presents a mathematical model for the vibrations of a non-Jeffcott type rotor supported on a non-linear bearing. The model can be used as a reference for systems supported on nonlinear bearings like magnetic bearings.
Abstract: Study the effect of the blade’s aspect ratio and thickness on rotating vibration according as modulating frequency can reduce the resonance vibration of the blades. Research the modal analysis of the blades of the aero-engine. Apply the software of a finite element method (FEM) to simplify calculating process. Establish three finite element models of the blade. Calculate and analyze the natural frequency and mode of each blade. Analyze the local resonance which is caused by the wake flow exciting force in the different conditions of the engine. The structure of the blades should be right for the engine conditions which make the vibration frequency of the blades out of the resonance vibration scope.
Abstract: The problem brake squeal is one of the important areas of application in the automotive industry. Most brake squeal is produced by vibration (resonance instability) of the brake components, especially the pads and discs are known as force-coupled excitation. Until now have many research about predict vibration and noise of disc brake but unfortunate the results is not satisfied. This paper presents model for prediction stability of disc brake for a model four degrees of freedom. The result shows stability of system and when occurrence brake squeal.
Abstract: A Fourier Transform method is applied to determine the displacements of a cantilever beam subjected to a multi-frequency excitations at the base. To dampen the displacements of the beam, a point mass is attached to the beam. The position of the mass on the beam is determined such that the overall deflections of the beam are minimal. It is shown that these attachments to the beam are effective in reducing the vibrations of the beam but their position is frequency dependent. It is shown that the low frequency component of the external excitation is most important in finding the optimal position of the mass.
Abstract: The flow past a circular cylinder at a subcritical Reynolds number 3900 was simulated by the method of detached-eddy simulation (DES). The objective of this present work is not to investigate the physical phenomena of the flow but to study modeling as well as numerical aspects which influence the quality of DES solutions in detail. Firstly, four typical spanwise lengths are chosen and the results are systematically compared. The trend of DES results along the span increment is different from previous large-eddy simulation (LES) investigation. A wider spanwise length does not necessary improve the results. Then, the influence of mesh resolution is studied and found that both too coarse and over refined grids will deteriorate the performance of DES. Finally, different orders of numerical schemes are applied in the inviscid fluxes and the viscous terms. The discrepancies among different schemes are found tiny. However, the instantaneous flow structures produced by 5th order WENO with 4th order central differencing scheme are more abundant than the others. That is, for the time-averaged quantities, the second-order accurate schemes are effective enough, whereas the higher-order accurate methods are needed to resolve the transient characteristics of the flow.
Abstract: Granular materials flow is discussed by different models. These models are 2D and each of them includes some special effects of two phase flow. For simulating the 3D flow of granular materials in rotary kilns, a model based on finite volume method (FVM) is presented which includes axial and rotational motion and also all of the effects of two phase flow such as: viscosity effect, particle size, rotating velocity of kiln, kiln tilt, etc. This method is used according to a real kind of rotary kiln and hypothetical clogging inside of kiln. The simulation results in both 2D and 3D views are presented in this article. These results are compared with Kramer’s model and they are acceptable. Also in this simulation, granular flow over the clogging is reviewed by using hypothetical clogging in the rotary cement kiln.
Abstract: By using the Perturbation Theory and solidification coefficient method, based on the interpolation parameters for optimal control feedback matrix, the design of optimal roll control system for a small solid rocket is achieved. The hardware-in-the-loop simulation platform built with DSPACE real-time simulator and high-precision three axis turntable is designed to validate the optimal control law. As for no feedback device of the steering gear, the radios are used to transfer the signals between the devices in the closed loop simulation system. Finally, through the flight-testing, the results confirm a good stability of the roll control system and the high reliability of the hardware-in-the-loop simulation platform.