Disaster mitigation based on smart structures and materials
As serious disasters have occurred around the world in recent years, a large number of people have been lost despite rapid advancements in science and technology. Furthermore, my personal experience of the 11 March 2011 Japanese earthquake and tsunami prompted me to think about realizing disaster mitigation strategies through novel ideas and methodologies. To that end, I have brought together a number of enthusiastic people from various fields to build a platform and create new technologies and products for disaster mitigation. In addition to disaster mitigation, our new concept—‘disaster mitigation and sustainable engineering’—is sustainable, and has high reliability and low costs. Moreover, this platform is made possible because of the innovative field of smart structures and materials.1, 2
Several projects have already been undertaken to try and meet this challenge of disaster mitigation, some of which have been commercialized. These smart products include the Hitachi Zosen Corporation's neo RiSe® (no energy, no operation, rising seawall) land-mounted movable flap-gate-type seawall, which can be autonomously deployed using the force of tsunamis.3 The MOSE (experimental electromechanical module) project,4 Aqua Dam,5 and Water-Gate6 flood protection schemes have also been developed. In addition, Takenaka Corporation has proposed the so-called breakwater and breakwater group approach.7
The basis of our disaster mitigation and sustainable engineering concept is illustrated in Figure 1. Although serious disasters may not occur for long periods of time, the structures necessary for disaster mitigation require vast construction and maintenance costs. It is thus beneficial to use these same structures daily to produce something useful, such as energy. The energy that is generated can then be used for the monitoring, maintenance, corrosion suppression, and repair of these structures, as well as for many other purposes (e.g., lighting, charging, and drones). As the mitigation structures need to be available continuously (i.e., mostly for periods without disasters), their compactness is useful from an aesthetic point of view and their daily usage is indispensable for commercialization. In addition to the examples shown in Figure 1, many other ideas (e.g., ‘smart shelter’ and ‘smart furniture’) have been proposed to protect valuable items from damage during disaster situations (see Figure 2). In this work,8 we introduce several additional examples to demonstrate our disaster mitigation and sustainable engineering concept more comprehensively.
For protection against tsunamis, rigid and fragile structures are unsuitable. Strong, light, and flexible structures are preferred instead. We have therefore been developing a multilayered flexible and deployable structural material system—see Figure 2(a) and Figure 3—which can be used to diminish the force of a tsunami. This system can also be used to dissipate the tsunami's energy by separating water flows and letting them conflict with each other.
Our second example—artificial and multifunctional forests—is illustrated in Figure 2(c). Natural forests present several problems, including low fractions of trees, low visibility of ocean waves, low strength, and long periods of growth. With our proposed artificial forests, we therefore intend to have a better ability to mitigate against high waves and tsunamis. We can achieve an ideal state for this forest by optimizing various parameters (e.g., configuration, density, and material). So far, we have used a water channel set up (see Figure 4) to examine a couple of these experimental parameters. We are also considering multifunctional designs for the artificial forests.
Another of our examples—see Figure 2(b) and Figure 5—is a new smart honeycomb-based structure, which can be used to protect against flooding. We have demonstrated the possibility of automatically deploying this proposed structure in response to increased water levels. This autonomous height-controlled river or anti-flooding bank system can thus be regarded as a smart structure. We are also currently investigating the use of energy-harvesting materials and systems to improve the autonomy of this structure and to fully realize the concept.
Several different aspects of ongoing research are also being conducted with my various collaborators. For example, we are pursuing applications of piezoelectric polymers for electrical power generation with the use of ocean waves.9 In addition, we are investigating the dynamic deployment of smart inflatable tsunami bags for tsunami mitigation purposes.10 Novel underwater inflatable structures for smart coastal disaster mitigation are also being studied.11 In other work, we are examining structural health monitoring of pipelines for environment pollution mitigation.12 The Italian Space Agency's geodetic satellite LARES (Laser Relativity Satellite) is also being used to study global climate change.13 Finally, we are investigating smart disaster mitigation strategies in both Italy14 and in Thailand.15
In summary, we have developed a new concept of disaster mitigation and sustainable engineering that is based on smart structures and materials. To illustrate this approach, we have discussed three potential examples of projects for protection against tsunamis and river flooding. As part of a large international collaboration we are also continuing to conduct research in a number of different areas related to disaster mitigation and sustainable engineering. As part of our future work, I will be working with international executive members of the collaboration to establish a research committee. This committee will also include several researchers from Chiba University and members of the Japan Society of Mechanical Engineers. Most recently,16 we have started to explore other innovative ideas and challenges (e.g., offshore megafloating structures with energy harvesting and dissipation functions). We welcome requests for information and collaboration possibilities.
The work shown in Figure 3 was performed in collaboration with M. Kubo, Y. Maruyama, and G. Tanaka from Chiba University, Japan.
Hiroshi Asanuma obtained his Dr. Engineering degree from the University of Tokyo, Japan. He then worked as a research associate at the Institute of Industrial Science, University of Tokyo, and as an assistant professor and an associate professor at Chiba University. He has also worked as a visiting professor at the University of Wollongong, Australia, and Sapienza University of Rome, Italy. Since then he has been a professor at Chiba University. He has also served as the chair of the Japan Society of Mechanical Engineers (JSME) Materials and Processing (M&P) division, and he is the chair of the Active Material System technical section of the JSME M&P division. In addition, he is a fellow of JSME and the Institute of Physics. He has received several awards, including the Excellent Achievement Medal, International Medal, and Excellent Performance Medal from the JSME M&P division.