Koji Masaoka

Studies on in-situ full-field measurement for in-plane welding deformation using digital camera

The technique that can measure the transient welding deformation directly is very important for investigating the mechanism of welding deformation. In this study, an in-situ displacement measurement method using digital camera is self developed. This system is non-contact type and it does not need any complicated optical systems but it can measure the in situ displacement over the full field high accuracy using digital image correlation technique. Therefore, it is considered to be useful and easy to apply to practical problems. The number of measuring points that can be obtained at a time is more than 10 million. It is the same as the available pixels of the digital camera. Furthermore, since the active light source is not necessary in this system, the influence of the fluctuation of the atmosphere caused by the high temperature area is small. In this study, the detail of the proposed system is given and it is applied to the transient in-plane deformation problem under very high brightness lightened by welding arc. Through the comparison between the experiment and thermal elastic–plastic finite element analysis, the validity of the transient transverse shrinkage distribution which is measured by the proposed system is verified. The residual deformation is also investigated to check the accuracy and usefulness of the proposed system.

A Method for Reliability-Based Sensitivity Analysis of Ship’s Hull Structures Using Combined Plate and Frame Structure Models

This paper is concerned with reliability-based sensitivity analysis of ship`s hull structures, which are modeled by combined spatial plate and frame elements, based on the ultimate strength analysis. In this paper, at first, a newly proposed system using combined plate and beam elements is presented to offer the expansion of the applicability of the structural reliability-based sensitivity analysis combined with collapse mode analysis. Next, the applicability of the proposed system is demonstrated through a numerical example applied to a simple box girder with longitudinal stiffeners. Finally, features of the structural reliability and sensitivity factors of a high speed ship based on collapse mode analysis are also investigated by successively applying the newly developed system.

Full-field time-series measurement for three-dimensional deformation under welding

Displacement during welding provides important information to understand the mechanisms of welding deformation and residual stress. In particular, if welding deformation can be measured sequentially and the displacement distribution over full field can be measured such as the results obtained by finite element analysis, they can be valuable information. Therefore, in this study, a 3-dimensional (3D) deformation (in-plane and out-of-plane deformation) measurement method is developed using a digital camera, which requires no special equipment. This method is a non-contact method and it can sequentially measure over the entire photographed image. Furthermore, since image analysis is based on the technique of image matching, the method is applicable even when measuring deformation is large. In addition, since it is possible to use all pixels as measuring points, the number of available measuring points at one time is the same as the number of effective pixels of the camera. This is currently more than 15 million points, and the measuring precision is expected to increase as the camera pixel resolution continues to increase. Therefore, this method is expected to have future potential. In this study, the proposed method is applied to the sequential measurement of displacement under the strong lighting levels in arc welding. By comparing the time history of transverse shrinkage, longitudinal shrinkage and angular distortion with the results of FEM thermal elastic-plastic analysis, the qualitative validity of the proposed method is verified. To investigate the measurement precision and usefulness of the method, a 3D shape measurement system (LAT-3D) using a laser displacement gauge and digital caliper are used. The distributions of residual transverse shrinkage and residual angular distortion are measured by the proposed method, LAT-3D and digital caliper. Through the comparison of the results measured by these methods, quantitative validity of the proposed method is also verified.

A study on deterioration of strength and reliability of aged jacket structures

This paper deals with the deterioration of strength for tubular members with a perforation due to corrosion as a part of reliability-based design of aged jacket structures. Firstly, a simplified method is presented for the residual strength of perforated members subjected to combined compressive load and bending moment by applying the reduced Perry-Robertsons or Carlsens method. It is also shown that the above estimation results for effects of the perforation on the ultimate strength deterioration are in comparatively good correspondence to analytical results based on nonlinear finite element method using shell elements. Finally, structures are modeled as a spatial framework and reliability analyses are carried out based on collapsing behavior analysis considering the ultimate strength of cylindrical tubular columns with a perforated damage under the combined loads, using a matrix method combined with a plastic node method. These methods are applied to reliability analysis of a 65m-class damaged structure. Aged effects on the deterioration of reliability level of the structure are also demonstrated through numerical examples.

A study on fatigue behavior of structural steels under multiple repeated loads

This paper deals with fatigue behavior of structure steels under multiple repeated loads as a part of basic studies on fatigue life estimation. First, a testing machine is produced for investigating fatigue behavior of structural steels under multiple repeated loads. Next, fatigue tests are carried out for smooth specimens of structural steel SS400. The fatigue behaviors such as the change of hysteresis loop energy and increasing rate of temperature of specimens under completely reversed tension and compression are investigated with much circumstance. An estimation method of remaining fatigue life is presented by using above results. The applicability of the method is also demonstrated by comparison with experimental results under multiple repeated loads.

Development of three-dimensional welding deformation measurement based on stereo imaging technique

Due to the rapid improvement of digital cameras, especially the pixel resolution, digital image correlation (DIC) has been introduced to measure the deformation and strain of structures. Using digital cameras for the DIC technique is an easy and fast method for obtaining structural information, represented as all the pixel points in a photo. Because a wide range of structural deformation can be obtained with high accuracy, this method has the potential to be very useful. Currently, DIC can execute a measurement with high accuracy only when the out-of-plane displacement is small. When the out-of-plane displacement is large, the deformation causes the measurement error. Therefore, a stereo imaging method using two digital cameras is proposed in this study. The proposed method can measure not only in-plane deformation but also out-of-plane deformation with high accuracy without calibration of the errors caused by the out-of-plane displacement. In this paper, the measurement accuracy of the proposed method for in-plane deformation and out-of-plane deformation is discussed through the application of a bead-on-plate welding test. The proposed method can measure transverse shrinkage and angular distortion with high accuracy. In contrast to the vernier caliper and laser distance metre measurement methods, which can measure only a few points at a time, the proposed method using two digital cameras can measure the full field in a short time. These results confirm that the proposed method is more advantageous than other methods.

A Study on Efficient Methods for Estimating Load Effects and Reliability and Their Application to Preliminary Structural Design of Rectangular-VLFS: 1st Report

This paper is concerned with efficient methods for estimating load effects and reliability and their application to preliminary structural design of box-type VLFS supposed as a floating airport, which is to be put in the west area of the Inland Sea of Japan (“Setonaikai”). In this study, as the first report, structural responses in oblique waves are investigated by using the efficient method based on Weighted Residual Method combined with thin plate and shallow water approximation presented by Tsubogo (2004). Effects of wavelength and wave incident angles on characteristics of the structural response are clarified from results obtained by numerical calculation. These results can be used to evaluate the load effect and the reliability in next report.Copyright

A method for estimating strength and reliability of stiffened plates for pontoon-type VLFS

This paper deals with a simplified method for estimating strength and reliability of stiffened plates for pontoon-type very large floating structures (VLFS), which are supposed floating airport, as a part of studies on reliability based preliminary design systems. Firstly, limit state conditions are shortly presented for the buckling and ultimate collapse strength of stiffened plates under combined compression, shear and lateral pressure in the deck, bulkhead and bottom parts of VLFS, especially, by using a simplified estimation formula. Next, the validity is shown by nonlinear finite element method. Finally, the reliability level is investigated through numerical examples for a 5,000 m-class VLFS under a trial design.

A Method for Structural Design of Pontoon Type VLFS Based on Collapse Behavior and Reliability Analysis

This paper deals with a simplified method for the preliminary design of pontoon-type very large floating structures (VLFS), which are supposed floating airport, based on collapse behavior and reliability analysis in irregular waves. Firstly, a simplified estimation method is presented for the probabilistic load effect model of VLFS under irregular sea-state conditions. Next, limit state conditions are shortly presented for the buckling and ultimate collapse strength of stiffened plates under combined compression, shear and lateral pressure in the deck, bulkhead and bottom parts of VLFS, especially, by using a simplified estimation formula. Then, the validity is shown by non-linear finite element method. Finally, dominant limit state modes of 5,000m-class VLFS under combined loads with bending moment, shear force and lateral pressure are obtained by applying the above methods. Then, the features of the collapse behavior and reliability level are investigated by using above calculation results. Effects of design parameters such as yield stress, plate thickness, stiffener and bulkhead space are also investigated using sensitivity analysis.© 2004 ASME

A Study on Structural Design of Huge Barge Structures Based on Collapsing Behavior and Reliability Analysis

This paper deals with the limit state and reliability analysis of huge barge structures (HBS) which are supposed floating refuse storage and incineration plant based on collapsing behavior analysis in irregular waves as a part of studies on structural reliability-based design methods. First, a limit state and reliability analysis method is shortly presented for the buckling and ultimate collapse strength of deck, bulkhead and bottom panels of HBS. Next, a simplified method is briefly introduced for collapsing behavior and reliability analysis of HBS under extreme sea loads by using a developed system combined with a finite element method and plastic node method using hexahedral element models. Moreover, a simplified estimation method is shortly introduced for the probabilistic load model considering the hydro-elastic response of the structure in irregular waves. Finally, dominant limit state modes of 1,000m-class HBS under combined loads with bending moment, shearing force and lateral pressure are obtained by applying the above methods. Then, the features of the collapsing behavior and reliability level are investigated by using above calculation results. Effects of statistical values such as reduction of thickness due to corrosion, yield stress and design parameters are also investigated using sensitivity analysis.Copyright