In order to solve the severe vibration problems of an ocean engineering ship with a full-revolving propulsion system, the navigation tests, including forced vibration response test and modal test, are carded out in it...In order to solve the severe vibration problems of an ocean engineering ship with a full-revolving propulsion system, the navigation tests, including forced vibration response test and modal test, are carded out in its stem. It is concluded from the comparison of the time-domain waveform and spectrum from different measurement points that three main factors lead to a high-level stern vibration. Firstly, the specific dynamic stiffness of a water tank is relatively small compared with its neighbor hold, which makes it act like a vibration isolator preventing vibrational energy transmitting to the main hold. Secondly, there exists high-density local modes in the working frequency range of the main engine and thus the local resonance occurs. Thirdly, the abnormal engagement of gears caused by the large deflection of the shaft bearing due to its low mounting rigidity leads to violent extra impulse excitations at high speeds. Then the modification against the dynamic defects is given by simply improving the specific stiffness of the water tanks. And the effect is validated by the FEM calculation. Some important experience is obtained with the problems being solved, which is useful in the design of ships with the same propulsion system. It is also believed that the dynamic consideration is as important as the static analysis for the ships, and that most of the vibration problems may be avoided with a proper acoustic design.展开更多
The Stern-Geary constant(B value)is indispensable to measure the corrosion rate in the microbiologically influenced corrosion(MIC)systems.Linear polarization resistance(LPR)and weight loss methods were used to study t...The Stern-Geary constant(B value)is indispensable to measure the corrosion rate in the microbiologically influenced corrosion(MIC)systems.Linear polarization resistance(LPR)and weight loss methods were used to study the variation of B values for X80 pipeline steel in the presence of Pseudomonas aeruginosa,Acetobacter aceti and Desulfovibrio vulgaris.The results showed that B values in the presence of three different bacteria were 35.60±0.55 mV,33.00±1.00 mV and 58.60±0.55 mV,respectively,suggesting that the change of corrosion system significantly affected the B values of X80 pipeline steel.This work further indicated that the determination of B values is necessary to accurately measure the MIC rate by LPR method.展开更多
Vibration at the stern area is generally the most severe of the entire ship hull,which has always attracted special attention by ship designers and researchers.With reference to a real ship structural layout,a scaled ...Vibration at the stern area is generally the most severe of the entire ship hull,which has always attracted special attention by ship designers and researchers.With reference to a real ship structural layout,a scaled stern model of steel structure was innovatively designed to carry out the mode and response tests.Corresponding finite element(FE)model representing the tested structure was established for verification of commonly-used calculation methods of modal parameters and response.Good agreement between experimental and numerical results demonstrates the credibility of FE method,and some key points of modeling and calculating are discussed.In addition,with the combination of the experiment and calculation,some vibration characteristics of ship stern structure are summarized for future ship design guideline.展开更多
This paper will analyze the identities of Sterne, his two spokesmen - Tristram and Yorick, and the reader of this novel to show their indeterminate identities and the indeterminate relationship between them.
We analyze the spin coincidence experiment considered by Bell in the derivation of Bells theorem. We solve the equation of motion for the spin system with a spin Hamiltonian, Hz, where the magnetic field is only in th...We analyze the spin coincidence experiment considered by Bell in the derivation of Bells theorem. We solve the equation of motion for the spin system with a spin Hamiltonian, Hz, where the magnetic field is only in the z-direction. For the specific case of the coincidence experiment where the two magnets have the same orientation the Hamiltonian Hz commutes with the total spin Iz, which thus emerges as a constant of the motion. Bells argument is then that an observation of spin up at one magnet A necessarily implies spin down at the other B. For an isolated spin system A-B with classical translational degrees of freedom and an initial spin singlet state there is no force on the spin particles A and B. The spins are fully entangled but none of the spin particles A or B are deflected by the Stern-Gerlach magnets. This result is not compatible with Bells assumption that spin 1/2 particles are deected in a Stern-Gerlach device. Assuming a more realistic Hamiltonian Hz + Hx including a gradient in x direction the total Iz is not conserved and fully entanglement is not expected in this case. The conclusion is that Bells theorem is not applicable to spin coincidence measurement originally discussed by Bell.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.51109131)
文摘In order to solve the severe vibration problems of an ocean engineering ship with a full-revolving propulsion system, the navigation tests, including forced vibration response test and modal test, are carded out in its stem. It is concluded from the comparison of the time-domain waveform and spectrum from different measurement points that three main factors lead to a high-level stern vibration. Firstly, the specific dynamic stiffness of a water tank is relatively small compared with its neighbor hold, which makes it act like a vibration isolator preventing vibrational energy transmitting to the main hold. Secondly, there exists high-density local modes in the working frequency range of the main engine and thus the local resonance occurs. Thirdly, the abnormal engagement of gears caused by the large deflection of the shaft bearing due to its low mounting rigidity leads to violent extra impulse excitations at high speeds. Then the modification against the dynamic defects is given by simply improving the specific stiffness of the water tanks. And the effect is validated by the FEM calculation. Some important experience is obtained with the problems being solved, which is useful in the design of ships with the same propulsion system. It is also believed that the dynamic consideration is as important as the static analysis for the ships, and that most of the vibration problems may be avoided with a proper acoustic design.
基金financially supported by the National Natural Science Foundation of China (Nos.U1660118 and 51871050)the National Environmental Corrosion Platform (NECP) of China and Shenzhen Science and Technology Research Funding (JCYJ20160608153641020)
文摘The Stern-Geary constant(B value)is indispensable to measure the corrosion rate in the microbiologically influenced corrosion(MIC)systems.Linear polarization resistance(LPR)and weight loss methods were used to study the variation of B values for X80 pipeline steel in the presence of Pseudomonas aeruginosa,Acetobacter aceti and Desulfovibrio vulgaris.The results showed that B values in the presence of three different bacteria were 35.60±0.55 mV,33.00±1.00 mV and 58.60±0.55 mV,respectively,suggesting that the change of corrosion system significantly affected the B values of X80 pipeline steel.This work further indicated that the determination of B values is necessary to accurately measure the MIC rate by LPR method.
文摘Vibration at the stern area is generally the most severe of the entire ship hull,which has always attracted special attention by ship designers and researchers.With reference to a real ship structural layout,a scaled stern model of steel structure was innovatively designed to carry out the mode and response tests.Corresponding finite element(FE)model representing the tested structure was established for verification of commonly-used calculation methods of modal parameters and response.Good agreement between experimental and numerical results demonstrates the credibility of FE method,and some key points of modeling and calculating are discussed.In addition,with the combination of the experiment and calculation,some vibration characteristics of ship stern structure are summarized for future ship design guideline.
文摘This paper will analyze the identities of Sterne, his two spokesmen - Tristram and Yorick, and the reader of this novel to show their indeterminate identities and the indeterminate relationship between them.
文摘We analyze the spin coincidence experiment considered by Bell in the derivation of Bells theorem. We solve the equation of motion for the spin system with a spin Hamiltonian, Hz, where the magnetic field is only in the z-direction. For the specific case of the coincidence experiment where the two magnets have the same orientation the Hamiltonian Hz commutes with the total spin Iz, which thus emerges as a constant of the motion. Bells argument is then that an observation of spin up at one magnet A necessarily implies spin down at the other B. For an isolated spin system A-B with classical translational degrees of freedom and an initial spin singlet state there is no force on the spin particles A and B. The spins are fully entangled but none of the spin particles A or B are deflected by the Stern-Gerlach magnets. This result is not compatible with Bells assumption that spin 1/2 particles are deected in a Stern-Gerlach device. Assuming a more realistic Hamiltonian Hz + Hx including a gradient in x direction the total Iz is not conserved and fully entanglement is not expected in this case. The conclusion is that Bells theorem is not applicable to spin coincidence measurement originally discussed by Bell.
