THE INFLUENCE OF CENTRE BOW LENGTH ON SLAMMING LOADS AND MOTIONS OF LARGE WAVE-PIERCING CATAMARANS

The effect of various centre bow lengths on the motions and wave-induced slamming loads on wave-piercing catamarans is investigated. A 2.5 m hydroelastic segmented model was tested with three different centre bow lengths and towed in regular waves in a towing tank. Measurements were made of the model motions, slam loads and vertical bending moments in the model demi-hulls. The model experiments were carried out for a test condition equivalent to a wave height of 2.68 m and a speed of 20 knots at full scale. Bow accelerations and vertical bending moments due to slamming showed significant changes with the change in centre bow, the longest centre bow having the highest wave-induced loads and accelerations. The increased volume of displaced water which is constrained beneath the bow archways is identified as the reason for this increase in the slamming load. In contrast it was found that the length of centre bow has a relatively small effect on the heave and pitch motions in slamming conditions.

DETERMINATION OF WAVE SLAMMING LOADS ON HIGH-SPEED CATAMARANS BY HYDROELASTIC SEGMENTED MODEL EXPERIMENTS

A 2.5m hydroelastic segmented catamaran model has been developed based on the 112m INCAT wave-piercer catamaran to simulate the vibration response during the measurement of dynamic slam loads in head seas. Towing tank tests were performed in regular seas to measure the dynamic slam loads acting on the centre bow and vertical bending moments acting in the demihulls of the catamaran model as a function of wave frequency and wave height to establish the operational loads acting on the full-scale 112m INCAT catamaran vessel. Peak slam forces measured on the bow of the model are found to approach the weight of the model, this being similar to the findings of full-scale vessel trials. A review of the motions of the hydroelastic segmented catamaran model found that the heave and pitch motions give a good indication of slamming severity in terms of the dimensionless heave and pitch accelerations. The dynamic wave slam forces are closely related to the relative motion between the bow and the incident wave profile.

Application of 3D-Modeling in Medicine in Preparation for 3D-Printing

3D-modeling in the medical field can be used to create medical models (eg, tissues and human organs) using 3D-printing or used for digital 3D visualization of the necessary structures. Medical 3D-printing is used when the work on prostheses that should perfectly match the patient's anatomy is needed. In addition, thanks to 3D-modeling technology, it is possible to develop peculiar medical tools. It is also possible to perform trial surgeries on 3D-models before the actual operation. There is special software for creating medical 3D-models for further printing. The purpose of this work is to determine the functions of 3D-modeling in preparation for 3D-printing in the process of creating medical models and comparative analysis of software for 3D-modeling used in the medical field. There is a common workflow that can be used to convert volumetric medical imaging data (created by computer tomography (CT), or other imaging techniques) into physical models printed on a 3D-printer. This process is divided into three stages: image segmentation, polygon mesh refinement, and 3D-printing. 3D-modeling programs are used at the stage of polygon mesh refinement. They allow almost unlimited manipulations to refine the mesh to make the model printable. The main manipulations for post-processing of a segmented model using 3D-modeling are: 1) reparation - correction of errors and discrepancies that sometimes occur in the process of segmentation and images export; 2) smoothing - correction of errors that occur during segmentation due to inappropriate resolution of the original medical image via softening by smoothing the surface of the model; 3) adding elements - combining a segmented model with other structures or removing unnecessary parts from the segmentation. As a result of a comparative analysis of 3D-modeling software used in the medical field, it was found that for 3D-modeling can be used software specifically designed for medical 3D-modeling and regular 3D-modeling software. When using regular software, you need third-party software to get the correct model file format. The choice of software depends on the goal: to work with implants and create patient-specific devices, it is possible to use specially designed programs for these purposes, such as Within Medical and Medical Design Studio; if high accuracy is required, it is possible to use D2P created for working with DICOM-images at the image segmentation stage; to achieve fast results, when maintaining of maximum accuracy is not needed, a mobile version of the software, such as Ossa 3D, can be used; common 3D-modeling software, such as Cinema 4D and Blender, can be used to develop peculiar tools and medical equipment.

Analysis of Force Distribution of Four Rows of Bolts in Aircraft Fitting Joint

With the help of 3D modeling software and finite element analysis software, the force distribution of four rows of bolts in the aircraft fitting joint is obtained in this paper. In 3D modeling software, the solid model is segmented according to the area and height of the center of gravity of the cross-section. In finite element analysis software, the beam elements are used to replace the segmented model to obtain the internal force applied at the end of the segmented model and the stress-strain state of each segment is calculated according to the internal force applied at the end of each segment. Finally, the force distribution of the four rows of bolts is obtained according to the average force difference on the center section between the bolt rows. In order to ensure the validity of this step-by-step calculation result, it was compared with the entire calculation result. It can be concluded that the force distribution of the two calculations is consistent. Under the working conditions of the fitting joint (130 MPa), the force distribution coefficients of the four rows of bolts are 0.182, 0.215, 0.197, and 0.12. Therefore, it is feasible to use the step-by-step method to calculate the force distribution of the four rows of bolts in the fitting joint. Compared with the entire calculation, the step-by-step calculation has the advantages of less calculation amount and faster calculation speed.