Construction of a finite element model of the Japanese koto
A. Kimi Coaldrake · The Journal of the Acoustical Society of America · 2017
This paper presents the steps in developing a finite element model of the Japanese koto (13-stringed zither) in Comsol Multiphysics® v5.2a and some of the issues encountered. As the instrument is 1.8 meters in length and hand crafted there are many internal irregular shapes. Early attempts at creating a geometry were unsatisfactory. To address this issue a CT scan with 2400 cross-sections was used to measure the internal details. A mesh was created from the scan using Simpleware® software. The result was a mesh with 430,000 elements for the instrument alone, placed in a sphere of air resulting in over 7 million degrees of freedom. This new model therefore has required the use of high performance computing to produce a second of acoustic output. The issue of the physical properties of paulownia, the less well-characterized highly anisotropic wood used to construct the koto, has proven more intractable. Scanning electron microscopy, frequency response and acoustic camera studies of the original instrument provided important insights into paulownia in particular and developing the model in general. A number of studies have been undertaken to validate the model including comparing it with the original instrument. Further studies of the acoustics of the koto are in progress.