Recent Japanese Progress on Data Assimilation and Optimal Design by CFD

Digitization has progressed in recent years in response to Covid-19 with considerable advances in the field of CFD. The term ‘digital twin’ is gaining attention as a technology for collecting information in physical space via the ‘Internet of Things (IoT)’, etc., and reproducing physical space in virtual space based on transmitted data. With the advance in IoT technology, numerical information such as measurement and observation data has become readily available. The Kalman filter and the particle filter are well-known methods by which observation data can be included in numerical simulations, modifying the simulated data to approach the observation data. Due in part to the fact that information has become freely available via the Internet, several reference documents on data assimilation methods such as the Kalman filter and the particle filter have been published in Japan over the last decade. With data assimilation, the accuracy of the system equation, i.e. the discretized governing equation that adds the system noise term, depends on the optimal estimated value. It is therefore important to select a high discretization method to obtain highly accurate estimation solution that includes the effects of observed data. At the same time, with the progress of digitization, technology related to resin and metal 3D printers continue to develop. It is now much easier to make objects using a 3D printer, even shapes that are otherwise difficult to manufacture. Many researchers have therefore been directing their attention to techniques of shape optimization and topology optimization with new developments and techniques widely discussed at domestic and international conferences on computational mechanics. Given the above, we have planned a special issue on data assimilation and optimal design in the field of CFD, in which we focus principally on Japanese technologies. We feature here papers submitted by researchers involved in data assimilation and mathematical design based on numerical simulations in the field of CFD. We would like to express our appreciation to all the researchers in this field, and especially thank those who have contributed to this publication by submitting their papers.