Search

[Objectives] The problem of transverse strength of car Ro-Ro ship under racking condition is studied.[Methods] seven kinds of flexible support decks were designed based on the finite element software MSC PATRAN/NASTRAN to study the influence of different flexible support decks on the structural strength of car Ro-Ro ships. According to the guidance document of Det Norske Veritas(DNV), the structural strength of the car Ro-Ro ship cabin of different designs was evaluated. By analyzing the stress magnitude and distribution of the hull structure,the influence of different flexible support deck designs on the strength of the structure of the car Ro-Ro ship cabin was compared.[Results] Results show that different position of the initial layer of the flexible support deck will have a certain impact on the strength of the hull structure,and there is a phenomenon of significantly increased stress in the area between the flexible support deck and the rigid one.[Conclusions] The study in this paper can provide reference for the design and construction of similar ships.

In Variational Mode Decomposition（ VMD）,k belongs to the custom variable,the decomposition result will be different with the change of k,k directly affects the accuracy of the result,which too large or too small will affect the results. Basis on the question above,a method of determining k by kurtosis is proposed. Selecting an integer value of k between 2 and n,every k kurtosis of the maximum correlation coefficient is calculated,and the variation curve of kurtosis is plotted. If the kurtosis of the curve has no peak and monotonically increases,calculating the kurtosis of k is n+1,repeat the steps above. The maximum kurtosis is used as the criterion of optimization,when the kurtosis is maximum,the k is the best. The feasibility of the method is verified by the actual fault signal,a new thinking of the research for VMD is proposed.

As an important part of automobile,the vibration characteristics of automobile transmission have important influence on the performance of the automobile. By studying and analyzing the vibration characteristics of an automobile transmission,the response of different position in different directions of the automobile transmission shell can be obtained. Through the analysis,the dynamic response of the automobile transmission is initial determined,the optimal excitation direction,natural frequency and frequency band of the automobile transmission are obtained. Through the experimental analysis,these parameters are obtained,the inherent characteristics of the automobile transmission is known,the foundation for the next step to analyze and optimize the structural optimization of the automobile transmission is provided.

In order to study the twin joint structure of bird wings,a flapping wing structure based on four-bar mechanism is designed based on the principle of bionics. The brushless motor driving two stage reducer,provides input for four-bar mechanism. The robot has a function of the periodic flapping motion,the frequency change and size of the attitude angle adjustment. According to the range of bird joint angular motion,the output angle of the robot linkage mechanism is determined so that it can move within the expected range. The model is established by MATLAB/SimMechanics,and the four-bar mechanism of the robot is simulated and integrated into the iSIGHT software to optimize the parameters and obtain the design variable value similar to the expected trajectory. The results show that the ornithopter scheme design based on the design of the four-link mechanism is feasible,and the frequency is controllable. In addition,the optimized simulation curve can well approach the given task trajectory. The design method proposed in this paper has the characteristics of fast and efficient,and the result is intuitively visible,which provides a feasible scheme for parameter setting and optimization of other mechanical structure.

The modal of engine,gearbox and frame are tested by the method of hammer excitation,and the modal parameters are obtained. Through interception the vibration signals when the empty light truck on washboard road and obstacles road,the modal test analysis of the vibration signal is carried out,the modal parameters of different stages of the light truck in the working environment are obtained. Finally,the test results are summarized and analyzed,several sensitive modal frequencies are found. Those found would provide theory and technical support for further study on dynamic analysis to estimate the basic reason of the damaging of the engine,gearbox and the frame.

A type of automobile gearbox has box cracking problem,in order to make a structure optimization and precise modal analysis of the automobile transmission shell,with this type of automobile transmission shell as the research object,the automobile characteristics are studied,the optimal excitation direction and frequency band of the dynamic response of the gearbox are obtained,understanding of the inherent characteristics of the transmission shell. Then,by combining the finite element analysis and experimental modal analysis,the modal analysis of automobile transmission shell is carried out,after comparing the obtained data,the reasons for cracking of the transmission shell are analyzed,the foundation for the follow-up of the structural optimization of this type automobile transmission is established.

The cross- term interference caused by multi- modulator and multi- carrier makes it limited the use of the cyclic autocorrelation demodulation. A new method called the MCKD（ Maximum correlated Kurtosis Deconvolution）- cyclic domain demodulation is proposed. Firstly,the strong background noise of the original signal is decreased by the MCKD method in order to extract the interest period component,the above given signal is processed by the cyclic autocorrelation function demodulation. The new method can decrease the cross- term interference caused by multi- modulator and multi- carrier and improve the reliability of the analysis. As the application of the MCKD- cyclic domain demodulation theory in fault diagnosis,the method is used to extract fault feature from vibration signals successfully.

To understand the structure dynamic characteristic problem of a certain type auto transmission housing,taking the type auto transmission housing as the research object,the modal simulation analysis and the experimental modal analysis are respectively carried out on the transmission housing by using the research method combining the technologies of mechanical structure finite element analysis and experimental modal analysis.The dynamic parameters of the transmission housing are extracted,the results of simulation and experiment are compared,it shows the change trend of first six order modal vibration mode have a certain similarity degree,with the relative errors of the same modal frequency are within 8%,it is effectively verified that the results of the structure modal simulation analysis on the transmission housing structure is the reliability. At the same time,the simulation and experiment results can effectively reflect the dynamic characteristics of the transmission housing,a foundation for auto transmission housing structure dynamic optimization is laid.

In order to understand the vibration of an automotive transmission system,taking the type automotive transmission as the research object,the vibration signal tests and analysis of the automotive transmission under multi- conditions are carried out,and a greater contribution to vibration frequencies of the transmission are obtained. Comparing the vibration frequency with the modal test results of the transmission,the frequency which is easy to cause the resonance of the transmission is confirmed. The results can lay a foundation for taking measures to avoid the resonance frequency,to reduce the vibration and the optimized design of vehicle structure.

A gear- box is the important continuously variable transmission in light truck. The structure and shape of a gear- box is particular complex and the phenomenon of stress concentration exists. And the high stress caused by stress concentration will directly affects the lifetime of a gear- box,even leads to crack. The structure strength of gear- box is studied through the experiment of static torque loading. The data of stress-strain characteristics of the cast aluminum shell is collected. And those data are analyzed with unidirectional stress method to find the stress concentration positions of a gear- box in its practical working conditions. Those analysis provide an important experimental basis for designing and manufacturing gearboxes.

According to the problem that a certain type of automotive transmission case in the sale is easy to crack,the finite element modal analysis and operational modal tests of automotive transmission are carried out and the modal parameters of transmission are obtained. Then,the reliability of the results is verified by the modal correlation matrix. On this basis,through comparing the results between simulation and experiment,the correctness and reliability of the simulation analysis are proved. The mode shapes which prone to fatigue cracking are analyzed. Finally,from the perspective of the frequency shift,the installation type of the powertrain is optimized,the overall stiffness of the transmission is improved,the test results provide method and theoretical basis for avoiding the transmission case cracking.

Through the experiment of the vibration modal of gearbox shell,the gearbox shell vibration state is analyzed and the stability of its operation is evaluated.By using DASP（Data Acquisition& Signal Processing）software,the vibration modal of the HW25505 TCL type aluminum alloy gearbox shell is tested.By the contrast between ERA method and PloyLSCF method,the reliable 14order of frequency and damping are obtained,and thus the vibration mode analysis is carried out.By using modal correlation matrix of modal to test and verify,through the comparison with calculating modal,the validity and reliability are proved.Applied DASP to vibration modal test of gearbox shell,not only the gearbox shell high order frequency,damping,vibration mode,and vibration condition can be acquired,but also the vibration problem of similar shell gearbox in operation can be solved,The theoritical basis for the improvement of the gearbox shell structure characteristics and the fault diagnosis of gearbox shell are provided,and had better promotion value in engineering practice.

Due to the complexity of light truck powertrain vibration shape,the structure weak parts is easy to motivate and cause resonance phenomenon.In order to obtain the powertrain dynamic characteristics,by using the finite element method and PolyMAX method,simulation and experiment modal analysis for light truck powertrain are respectively carried out.By analyzing and comparing the results of both,the dynamic characteristic of the light truck powertrain is effectively reflected,the reliability and rationality are proved.The theory basis for the fault diagnosis and dynamic optimization design of the light truck powertrain are provided.

The manifold learning algorithm is a method of nonlinear data dimensionality reduction and can get available low dimensional geometry,it is also better reflects the nature of things. In order to improve the classification ability of gearbox vibration signals,a new feature extraction method from fault signals of gearbox vibration based on the manifold learning method（ MLM） is proposed. The results show that the fault feature information of gearbox vibration can be MLM effectively extracted and the different types of fault feature information can be separated. The diagnostic accuracy of features extracted by MLM is higher than that of the time domain statistical method.

Scratch is widely used as an introductory educational tool for computer programming. However, little is known about how the action of adding favorite projects on Scratch social media influences programming skill improvement. On Scratch social media, learners select personally intriguing projects to view and learn from. Favorite projects both motivate users to participate on social media and serve as scaffolding material for learners. In this study, we analyzed a dataset of 50,786 users from 5 years of longitudinal activities on Scratch social media using the Zones of Proximal Flow theory. To understand how favorite projects influence learners, we compared the frequency of social media use and programming skill improvement between users who did and did not add favorite projects, and we found a significant difference in programming skill improvement. Among users with favorite projects, there is a proximal difference of two to five Dr. Scratch scores of the favorite project above users' capability level, which maximizes the frequency of social media use and programming skill improvement.

Abstract Background In a natural environment, contextual noise frequently occurs with a signal sound for detection or discrimination in a temporal relation. However, the representation of sound frequency by auditory cortical neurons in a noisy environment is not fully understood. Therefore, the purpose of this study was to explore the impact of contextual noise on the cortical tuning to signal sound frequency in order to better understand the mechanism of cortical frequency coding in a complex acoustical environment. Results We compared the excitatory frequency-level receptive fields (FLRFs) of neurons in the rat primary auditory cortex determined under both quiet and preceding noise conditions. Based on the changes of minimum threshold and the extent of FLRF of auditory cortical neurons, we found that the FLRFs of a cortical neuron were modulated dynamically by a varying preceding noise. When the interstimulus interval between noise and the probe tone was constant, the modulation of the FLRF increased as the level of noise was increased. If the preceding noise level was constant, the modulation decreased when the interstimulus interval was increased. Preceding noise sharpened the bandwidth of the FLRFs of 47.6% tested neurons. Moreover, preceding noise shifted the CFs of 47.6% neurons by more than 0.25 octaves, while the CFs of the rest of the neurons remained relatively unchanged. Conclusions The results indicate that the cortical representation of sound frequency is dynamically modulated by contextual acoustical environment, and that there are cortical neurons whose characteristic frequencies were resistant to the interference of contextual noise.