One of the important issues in the system identification and the spectrum analysis is the frequency resolution, i.e., the capability of distinguishing between two or more closely spaced frequency components. In the mo...One of the important issues in the system identification and the spectrum analysis is the frequency resolution, i.e., the capability of distinguishing between two or more closely spaced frequency components. In the modal identification by the empirical mode decomposition （EMD） method, because of the separating capability of the method, it is still a challenge to consistently and reliably identify the parameters of structures of which modes are not well separated. A new method is introduced to generate the intrin- sic mode functions （IMFs） through the filtering algorithm based on the wavelet packet decomposition （GIFWPD）. In this paper, it is demonstrated that the CIFWPD method alone has a good capability of separating close modes, even under the severe condition beyond the critical frequency ratio limit which makes it impossible to separate two closely spaced harmonics by the EMD method. However, the GIFWPD-only based method is impelled to use a very fine sampling frequency with consequent prohibitive computational costs. Therefore, in order to decrease the computational load by reducing the amount of samples and improve the effectiveness of separation by increasing the frequency ratio, the present paper uses a combination of the complex envelope displacement analysis （CEDA） and the GIFWPD method. For the validation, two examples from the previous works are taken to show the results obtained by the GIFWPD-only based method and by combining the CEDA with the GIFWPD method.展开更多
For Al 6k21-T4 overlap weld joint,the shear-tensile strength by using the weaving laser was improved as compared to the case of linear laser.For the specimen of low strength,the porosity was distributed continuously a...For Al 6k21-T4 overlap weld joint,the shear-tensile strength by using the weaving laser was improved as compared to the case of linear laser.For the specimen of low strength,the porosity was distributed continuously along the intersection between the plates and fusion line.However,for the optimized welding condition,large oval-shaped porosities were located only in the advancing track of the concave part.Therefore,the continuity of cracks and porosities played a key role to determine the strength.And,the weaving width was also the important parameter to control the strength.Furthermore,the concave part had more significant hot and cold cracking in the weld and heat-affected zone（HAZ）,respectively,than the convex part.展开更多
Past research has demonstrated that a static, three-dimensional （3D） object scene can be directly recorded as a complex digital hologram. However, numerical reconstruction of the object scene, which may comprise mul...Past research has demonstrated that a static, three-dimensional （3D） object scene can be directly recorded as a complex digital hologram. However, numerical reconstruction of the object scene, which may comprise multiple sections located at unknown distances from the hologram, is a complicated and computation-intensive process. To the best of our knowledge, we propose, for the first time, a low complexity method that is capable of recon- structing a complex hologram, such that sections at different depths in the 3D object scene can be automatically reconstructed at the correct focal distances and merged into a single image for an extended depth of field. We demonstrate an order of magnitude increase of the depth of field for binary objects. With the use of a graphical processing unit, the reconstruction of a 512 × 512 complex hologram can be accomplished in about 100 ms, equivalent to around 10 frames per second.展开更多
基金supported by the State Key Program of National Natural Science of China (No. 11232009)the Shanghai Leading Academic Discipline Project (No. S30106)
文摘One of the important issues in the system identification and the spectrum analysis is the frequency resolution, i.e., the capability of distinguishing between two or more closely spaced frequency components. In the modal identification by the empirical mode decomposition （EMD） method, because of the separating capability of the method, it is still a challenge to consistently and reliably identify the parameters of structures of which modes are not well separated. A new method is introduced to generate the intrin- sic mode functions （IMFs） through the filtering algorithm based on the wavelet packet decomposition （GIFWPD）. In this paper, it is demonstrated that the CIFWPD method alone has a good capability of separating close modes, even under the severe condition beyond the critical frequency ratio limit which makes it impossible to separate two closely spaced harmonics by the EMD method. However, the GIFWPD-only based method is impelled to use a very fine sampling frequency with consequent prohibitive computational costs. Therefore, in order to decrease the computational load by reducing the amount of samples and improve the effectiveness of separation by increasing the frequency ratio, the present paper uses a combination of the complex envelope displacement analysis （CEDA） and the GIFWPD method. For the validation, two examples from the previous works are taken to show the results obtained by the GIFWPD-only based method and by combining the CEDA with the GIFWPD method.
基金supported by a grant from the Ministry of Knowledge Economy,Republic of Koreaby NCRC (National Core Research Center) Program through the National Research Foundation of Korea funded by the Ministry of Education,Science and Technology (2010-0001-222)
文摘For Al 6k21-T4 overlap weld joint,the shear-tensile strength by using the weaving laser was improved as compared to the case of linear laser.For the specimen of low strength,the porosity was distributed continuously along the intersection between the plates and fusion line.However,for the optimized welding condition,large oval-shaped porosities were located only in the advancing track of the concave part.Therefore,the continuity of cracks and porosities played a key role to determine the strength.And,the weaving width was also the important parameter to control the strength.Furthermore,the concave part had more significant hot and cold cracking in the weld and heat-affected zone（HAZ）,respectively,than the convex part.
基金partially support by the MSIP(Ministry of Science,ICT and Future Planning),Korea,under the ITRC(Information Technology Research Center)support program(IITP-2015-R0992-15-1008)supervised by the IITP(Institute for Information&communications Technology Promotion)
文摘Past research has demonstrated that a static, three-dimensional （3D） object scene can be directly recorded as a complex digital hologram. However, numerical reconstruction of the object scene, which may comprise multiple sections located at unknown distances from the hologram, is a complicated and computation-intensive process. To the best of our knowledge, we propose, for the first time, a low complexity method that is capable of recon- structing a complex hologram, such that sections at different depths in the 3D object scene can be automatically reconstructed at the correct focal distances and merged into a single image for an extended depth of field. We demonstrate an order of magnitude increase of the depth of field for binary objects. With the use of a graphical processing unit, the reconstruction of a 512 × 512 complex hologram can be accomplished in about 100 ms, equivalent to around 10 frames per second.
