Advanced non-dimensional dynamic influence function method considering the singularity of the system matrix for accurate eigenvalue analysis of membranes

An advanced non-dimensional dynamic influence function method (NDIF method) for highly accurate free vibration analysis of membranes with arbitrary shapes is proposed in this paper. The existing NDIF method has the weakness of not offering eigenvalues and eigenmodes in the low frequency range when the number of boundary nodes of an analyzed membrane is increased to obtain more accurate result. This paper reveals that the system matrix of the membrane becomes singular in the lower frequency range when the number of the nodes increases excessively. Based on this fact, it provides an efficient way to successfully overcome the weaknesses of the existing NDIF method and still maintain its accuracy. Finally, verification examples show the validity and accuracy of the advanced NDIF method proposed.

Advanced NDIF Method for Eigenvalue Analysis of Arbitrarily Shaped Acoustic Cavities With the Partially Pressure-Release Boundary

In this paper, an advanced non-dimensional dynamic influence function method (NDIF method) for eigenvalue analysis of arbitrarily shaped two-dimensional acoustic cavities with the mixed boundary consisting of the pressure-release and rigid-wall boundaries is proposed. The existing NDIF method has the weakness of having to calculate the singularity of the final system matrix of an analyzed acoustic cavity in the frequency band of interest to obtain the eigenvalues of the cavity because the final system matrix is dependent on the frequency. The newly proposed NDIF method in this paper provides an efficient way to extract accurate eigenvalues and eigenmodes by successfully overcoming the above weaknesses. Finally, the validity and accuracy of the proposed method are shown through verification examples.

Comparative Study on Stress Intensity Factors for Surface Cracks in Welded Joint and Flat Plate by Using the Influence Function Method

Welding is an effective method for joining metallic structures which are very common in the construction of ships and offshore platforms. However, welded joints are prone to fatigue failure under cyclic loading due to the associated high residual stresses. In order to assess the fatigue crack propagation (FCP) accurately, precise evaluation of stress intensity factors (SIFs) is a key parameter. The residual stress distribution on the crack face of welded joints is usually non-uniform and also depends on boundary conditions. Therefore, an efficient technique is required to calculate SIFs for welded joints under non-uniform stress distribution. In this study, SIFs of semi-circular surface cracked welded joints are calculated by using the influence function method (IFM). The IFM has been introduced as an efficient method to evaluate SIFs under arbitrary stress distribution. The influence coefficient databases (ICDB) are developed for welded joints and flat plate models using IFM in this study. As the crack face traction (CFT) integral is employed in this developed influence coefficients (IC), the SIFs given by IFM are more accurate compared to the previously established solutions without CFT-integral. The ICDB and SIFs evaluated by using welded joint and flat plate models are compared and discussed. This study reveals the difference between ICDB of flat plates and welded joints, and estimation error of calculated SIFs for welded joints by using flat plate ICDB.