Journal of Engineering and Thermal Sciences
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Adaptive mesh refinement method for optimal control based on Hermite-Legendre-Gauss-Lobatto direct transcription
Get PDFDirect transcription has been employed to transcribe the optimal control problem into a nonlinear programming problem. This paper presents a trajectory optimization method based on a combination of the direct transcription and mesh refinement algorithm. Hermite-Simpson method has the advantage of reasonable accuracy with highly sparse Hessian matrix and constraint Jacobians, and the pseudospectral method provides spectral accuracy for optimal control problems. The optimal control problem is discretized at a series of Legendre-Gauss-Lobatto points, then the trajectory states are approximated by using local Hermite interpolating polynomials. Thus, the method produces significantly smaller mesh size with a higher accuracy tolerance solution. The derived relative error estimation is then used to trade the number of mesh polynomials degree within each mesh interval with the number of mesh intervals. As a result, the suggested method can produce more small mesh size, requires less computation solution for the same optimal control problem. The simulation experiment results show that the suggested method has many advantages
Numerical computation for the impact of flow rate and rotational speed on the flow-induced noise of the centrifugal pump
Get PDFThis paper adopted an indirect mixed method (computational fluid dynamics + boundary element method) based on computational fluid dynamics + Lighthill acoustic analogy theories to compute the flow field and flow-induced noise of the centrifugal pump, and experimentally verified the correctness of computational results. The pressure distribution of the centrifugal pump through an unsteady computation showed that there were obvious separation vortexes at the outlet of the centrifugal pump and pressure at the edge of impellers was obviously more than that of other parts. There were many peak noises on the sound pressure level curve at the outlet of the centrifugal pump. The sound pressure level gradually decreased with the increased frequency. However, sound pressure levels will be a stable value when the analyzed frequency was more than 3000 Hz. Sound pressures at the inlet and outlet of the centrifugal pump were relatively large. Sound pressures at the inlet pipeline gradually decreased from outside to inside and sound pressures of outlet pipeline gradually decreased from inside to outside. The structure of the centrifugal pump was not completely symmetrical, and the sound field was not symmetrical. In addition, the radiation noises in the external field at the inlet and outlet of the centrifugal pump were similar to the radiation of many point sound sources. Peak values of flow-induced noises at the outlet of the centrifugal pump were more than those at the inlet of the centrifugal pump under the working condition of different rotational speeds and flow rates. In the meanwhile, sound pressure levels at the inlet and outlet of the centrifugal pump did not show many differences in amplitudes when the rotational speed was small. When the rotational speed reached up to 3000 r/min, the sound pressure at inlet was more than that at outlet within 1500 Hz-4500 Hz. At many peak frequency points, peak noises at outlet were obviously more than those at inlet, which thus proved that fluid caused large pressure fluctuations due to the interaction between impellers and volutes after flowing through the centrifugal pump and flow-induced noises caused by pressure fluctuations were mainly reflected in blade frequency. The change of the rotational speed and flow rate would not only increase the flow-induced noise in the centrifugal pump, but also seriously affect the external radiation sound field of the centrifugal pump
Sequential fault detection for sealed deep groove ball bearings of in-wheel motor in variable operating conditions
Get PDFSealed deep groove ball bearings (SDGBBs) are employed to perform the relevant duties of in-wheel motor. However, the unique construction and complex operating environment of in-wheel motor may aggravate the occurrence of SDGBB faults. Therefore, this study presents a new intelligent diagnosis method for detecting SDGBB faults of in-wheel motor. The method is constructed on the basis of optimal composition of symptom parameters (SPOC) and support vector machines (SVMs). SPOC, as the objects of a follow-on process, is proposed to obtain from symptom parameters (SPs) of multi-direction. Moreover, the optimal hyper-plane of two states is automatically obtained using soft margin SVM and SPOC, and then using multi-SVMs, the system of intelligent diagnosis is built to detect many faults and identify fault types. The experiment results confirmed that the proposed method can excellently perform fault detection and fault-type identification for the SDGBB of in-wheel motor in variable operating conditions
Impact of road surface roughness and magnetic force on the in-wheel motor magnet gap
Get PDFFor an in-wheel-motor drive electric vehicle, the driving motors are directly mounted in the wheels. Using this chassis structure, the road excitation can cause a magnet gap deformation in the motor. The magnet gap deformation will lead to magnetic force which not only has a negative impact on vehicle dynamics but also affects the magnet gap deformation in turn. To further analyze the impact of the road and the magnetic force on the motor magnet gap, a test platform was built, and used to simulate cases of road and composite excitation. The results show that 1) road excitation can cause motor magnet gap deformation, and when the excitation frequency is increased for a constant amplitude, the deformation degree also increases. 2) For the same road excitation frequency, the deformation degree increases with the motor speed. This not only proves the existence of the magnetic force but also indicates that the size of the magnetic force is related to the motor rotating frequency. 3) A comparison between the simulated and experimental results not only confirms the validity of the theoretical derivation and analysis but also lays the foundation for subsequent vibration control of in-wheel-motor drive electric vehicles
The modal analysis of three-dimension gun barrel using isogeometric analysis and its application to optimization
Get PDFIn this paper, the Isogeometric Analysis (IGA) is applied to make the modal analysis for 3D gun barrel. The geometry of IGA is modeled by None-Uniform Rational B-Splines (NURBS) which is exact and smooth even at the coarsest mesh level. The first 9 natural frequencies were calculated respectively by IGA and traditional finite element method (ABAQUS), and compared with the test results. The maximum relative error between numerical value and experimental value is less than 3.6 % which verifies the feasibility of numerical model. Six different refinement schemes were analyzed to compare the computational accuracy and efficiency of IGA and ABAQUS. To achieve the credible results, the CPU time of ABAQUS is more than twice of IGA. On this basis, the IGA method is used for the structural shape optimization of gun barrel. The first natural frequency is increased by 6.96 % and the barrel mass is reduced by 4.9 %
Seismic fragility analysis of continuous bridges with UDCMEJ under the excitation of seismic sequence
Get PDFPounding and unseating have been repeatedly observed during severe earthquakes. Residual displacement between adjacent components may have already existed after the mainshock and it will get further destroyed with series of aftershocks. The uniform drift cable-sliding modular expansion joints (UDCMEJ) are constructed by connecting the supporting bars and the fuse boxes with elastic cables avoiding the excessive relative displacement between girders. The seismic analysis of bridges with UDCMEJ under the excitation of seismic sequence is conducted on a continuous beam bridge and a probabilistic assessment is introduced in this study. Conclusions are drawn from comparing fragility curves with and without UDCMEJ. It reveals that the UDCMEJ can avoid pounding between girders and the relative displacement is limited to cables’ free movement. With the contribution of the expansion joints, all of the girders work together and get a balance between displacement and force causing decreased damage probability
Kinematics simulation analysis and trajectory planning of a moving robot based on ADAMS
Get PDFThe study of kinematics modeling and simulation of industrial robots is the basis of robot development and optimization. According to the configuration characteristics of a moving robot, the coordinate system and the kinematics equation of the connecting rod are established based on the DH coordinate transformation method. The kinematics positive solution problem is solved in detail. The moving robot is established by the joint simulation of Solid works and ADAMS The motion model of the moving robot is verified by the kinematic analysis, and the displacement and angle curve of the end point are obtained. The rationality of the kinematics model of the moving robot is verified. The trajectory planning of the moving robot is carried out according to the actual situation, the results show that the moving robot is running smoothly and meets the requirements, which provides an important basis for the subsequent control research
An analytical modeling for high-velocity impacts on woven Kevlar composite laminates
Get PDFIn this paper, an analytical model, which based on energy balance, is built to study the process of high velocity impacts on woven Kevlar composite laminates by a cylindrical projectile. Four different mechanisms, such as laminate crushing, linear momentum transfer and tensile fiber failure, and shear plugging, is absorbed by the laminate while impacting. Then, simplification of the model is done to obtain the residual velocity and ballistic limit. The analytical results are validated with the results of experiment, and the perturbation analysis is done to analyze the reason of error
Test my product using sine or random?
Get PDFAs you know, in the vibration world, there are quite a few test “types” to which you can expose your product. The major choices are Sine, Random, Classical Shock, Transient Shock, Field Recorded Time History, Sine-on-Random, Random-on-Random and Sine-and- Random-on-Random. Frequently, our customers will request advice on which of these types of test to run on their product, and in particular, how to choose between the two most common test types: sine or random. Their desire is to know which test, sine or random, is best to most quickly pinpoint flaws in their product. If they can only run one test, either sine or random, which should it be? Recently, I received an even more specific request from a customer. This customer (Don) presented both a sine test and a random test and wanted to know, given both a sine test and a random test, how he could determine which is the most severe? Let’s take a look at the two tests and decide how to answer to his question. Here is Don’s question: How would the following specifications compare with regard to amplitude/severity
Propagation of rotational waves in a block geomedium
Get PDFOn the base of assumption that the rotational movements of the chain of the crust blocks and the corresponding rotational waves characterizing the redistribution of tectonic stresses are described by the sine-Gordon equation with dissipation, the dispersion properties of this equation are analyzed. It is shown that the dispersion is manifested in the low-frequency range at high values of the dissipation factor. The presence of anomalous dispersion has been revealed for all values of the dissipation factor. Influence of this factor on dispersion is investigated. Some features of propagation of a stationary shock wave in a geomedium are studied. It has been found that the shock wave front width is directly proportional to the nonlinear wave velocity and to the dissipation factor of the medium, but it is inversely proportional to the nonlinearity coefficient