Numerical Analysis of Drag Reduction Characteristics of Biomimetic Puffer Skin: Effect of Spinal Height and Tilt Angle.

Based on the migratory phenomenon of the puffer and the cone-shaped structures on its skin, the effects of spinal height and tilt angle on the drag reduction characteristics is presented by numerical simulation in this paper. The results show that the trend of total drag reduction efficiency changes from slow growth to a remarkable decline, while the viscous drag reduction efficiency changes from an obvious increase to steady growth. The total and viscous drag reduction efficiencies are 19.5% and 31.8%, respectively. In addition, with the increase in tilt angle, the total drag reduction efficiency decreases gradually; the viscous drag reduction efficiency first increases and then decreases, finally tending to be stable; and the total and viscous drag reduction efficiency reaches 20.7% and 26.7%, respectively. The flow field results indicate that the pressure drag mainly originates at the front row of the spines and that the total pressure drag can be effectively controlled by reducing the former pressure drag. With the increase in low-speed fluid and the reduction in the near-wall fluid velocity gradient, the viscous drag can be weakened. Nevertheless, the drag reduction effect is achieved only when the decrement of viscous drag is greater than the increment of pressure drag. This work can serve as a theoretical basis for optimizing the structure and distribution parameters of spines on bionic non-smooth surfaces.

Prediction of Welding Deformation and Residual Stress of a Thin Plate by Improved Support Vector Regression.

Thin plates are widely utilized in aircraft, shipbuilding, and automotive industries to meet the requirements of lightweight components. Especially in modern shipbuilding, the thin plate structures not only meet the economic requirements of shipbuilding but also meet the strength and rigidity requirements of the ship. However, a thin plate is less stable and prone to destabilizing deformation in the welding process, which seriously affects the accuracy and performance of the thin plate welding structure. Therefore, it is beneficial to predict welding deformation and residual stress before welding. In this paper, a thin plate welding deformation and residual stress prediction model based on particle swarm optimization (PSO) and grid search(GS) improved support vector regression (PSO-GS-SVR) is established. The welding speed, welding current, welding voltage, and plate thickness are taken as input parameters of the improved support vector regression model, while longitudinal and transverse deformation and residual stress are taken as corresponding outputs. To improve the prediction accuracy of the support vector regression model, particle swarm optimization and grid search are used to optimize the parameters. The results show that the improved support regression model can accurately evaluate the deformation and residual stress of butt welding and has important engineering guiding significance.

Quality Prediction and Control of Assembly and Welding Process for Ship Group Product Based on Digital Twin.

In view of the problems of lagging and poor predictability for ship assembly and welding quality control, the digital twin technology is applied to realize the quality prediction and control of ship group product. Based on the analysis of internal and external quality factors, a digital twin-based quality prediction and control process was proposed. Furthermore, the digital twin model of quality prediction and control was established, including physical assembly and welding entity, virtual assembly and welding model, the quality prediction and control system, and twin data. Next, the real-time data collection based on the Internet of Things and the twin data organization based on XML were used to create a virtual-real mapping mechanism. Then, the machine learning technology is applied to predict the process quality of ship group products. Finally, a small group is taken as an example to verify the proposed method. The results show that the established prediction model can accurately evaluate the welding angular deformation of group products and also provide a new idea for the quality control of shipbuilding.

[GJB2 235delC single allelic mutation modulates the phenotype associated with the mitochondrial A1555G mutation].

OBJECTIVE: To investigate a non-syndromic deafness family in which potential interaction between the GJB2 gene and a mitochondrial gene appeared to be the cause of hearing impairment. METHODS: Audiological examination was performed by pure-tone audiometry (PTA). Blood samples from 8 members of the pedigree were obtained. DNA was extracted from the leukocytes. The coding region of the GJB2 gene and mitochondrial DNA target fragments were amplified by polymerase chain reaction (PCR). The PCR products were analyzed by sequencing. RESULTS: Direct sequencing showed that the proband had both a heterozygous mutation of 235delC in the GJB2 gene and a mitochondrial 1555 A to G mutation. The proband had profound hearing loss. The maternal relatives had sensorineural hearing loss in the higher frequencies or no hearing loss. CONCLUSION: The GJB2 mutations may be an aggravating factor in the phenotypic expression of the non-syndromic hearing loss associated with the A1555G mitochondrial mutation.