Junji Sawamura

Study on Heat Transfer Between Gas Flame and Plate During Line-Heating Process

This paper discusses how the transient 3-dimensional distribution plate surface of the spot heating gas flame is measured in detail by a high performance L.I.F. measurement system. It has been found that the thermal-flow field within the combustion flame remains almost unchanged regardless of the temperature increase in the steel plate. A new hypothesis on the heat transfer during line heating process is built up based on the results of the L.I.F. experiment. This hypothesis is that the distribution of gas temperature near plate surface and local heat transfer coefficient depend only on the distance from the torch. The appropriateness of this hypothesis is proven by the performance of an inverse heat conduction analysis of a spot heating experiment.

Development of a New Fatigue Testing Machine for High Frequency Fatigue Damage Assessment

A new simple fatigue testing machine, which can carry out fast and low-cost fatigue tests of welded joints subject to wave with high frequency vibration, has been developed. This machine is designed for plate bending type fatigue tests, and wave load is applied by using motors with eccentric mass. Springing vibration is superimposed by attaching an additional vibrator to the test specimen, and whipping vibration is superimposed by an intermittent hammering.Fatigue tests which simulate springing and whipping by a conventional servo-type fatigue testing machines are very expensive and use a large amount of electricity. If one uses these conventional machines, it is difficult to simulate superimposed stress wave forms at high speed, and it takes long hours of testing to examine the high frequency effect. In contrast, it is found that fatigue tests can be carried out in fast, i.e. waves with 10Hz or higher frequency for out-of-plane gusset welded joint specimens with 12mm plate thickness by using the developed machine. The electricity to be used for fatigue tests could be minimal, for example one thousandth of that needed for conventional machines. These results demonstrate the superiority of the developed machine.Copyright

Study of Heattransfer During Piercing Process of Oxyfuel Gas Cutting

The heat transfer parameters, the local heat transfer coefficient, α, and the gas temperature adjacent to the plate, TG, are nearly unchanged with time during preheating for oxyfuel gas cutting. A genetic algorithm (GA)-based identification technique for α and TG is proposed. The validity of the proposed technique and the accuracy of the identified parameters are examined by comparing the measured and calculated plate back face temperatures during spot heating tests. Hydrogen-LP mixed gas and LPG are used as preheating gases in these tests. It is considered that the plate temperatures during preheating for piercing can be calculated by using α and TG identified in spot heating tests. The minimum piercing time is estimated by calculating the time until the plate heating face temperature reaches the kindling temperature. The validity of the above assumption is examined by comparing the estimated and measured minimum piercing times for hydrogen-LP mixed gas and LPG. As a result, the following are found: 1) The plate temperatures during spot heating tests calculated by using the identified heat input parameters agree well with the ones measured. This demonstrates the accuracy of the identified parameters and the validity of the proposed heat transfer simulation technique. 2) The heat flux of a hydrogen-LP mixed gas flame around the preheating gas ejection hole is 40 % greater than that of a LPG flame, while the total calorific value of hydrogen-LP mixed gas is 25 % lower than that of LPG. This result shows that it is not appropriate to evaluate the thermal effect of the preheat flame only from the total calorific value alone. 3) The calculated time for the plate face temperature to exceed the steel’s kindling temperature almost agrees with the minimum piercing time observed in piercing tests. For the first time, it is possible to anticipate the piercing time by numerical simulation.

Experimental Study on High Frequency Effect on Fatigue Strength of Welded Joints by Using Plate-Bending-Vibration Type Fatigue Testing Machines

Fatigue strength of out-of-plane gusset welded joints subject to springing and whipping superimposed wave loadings is examined by using Plate-Bending-Vibration (PBV) type fatigue testing machines developed in the previous reports [Osawa, N. et al. (2013) Proc. OMAE2013, Paper OMAE2013-11582, Osawa N. et al. (2013) Proc. PRADS2013, pp.550–556]. Springing vibration is superimposed by attaching an additional vibrator to the test specimen, and whipping vibration is superimposed by intermittent hammering. ‘Enlargement counting’ method, in which the stress history is approximated by a waveform with the low frequency component’s period and the enlarged total amplitude, is proposed. Fatigue damages and equivalent stress ranges are calculated by enlargement and rainflow cycle counting methods. It is found that the fatigue life under high frequency superimposed loads can be predicted with acceptable accuracy by the modified Miner rule when enlargement or rainflow stress counting is performed and the S-N curve is modified so that it fits the equivalent stress range’s Ps = 50% curve. Based on test results, a simplified assessment method for high frequency effect on fatigue strength of ship’s welded joints is proposed. The validity of the proposed assessment method should be further examined by carrying out fatigue tests with realistic stress histories which emulate intermittent occurrence of springing and whipping in ship structure.© 2014 ASME