Shintaro Yamasaki

Magnetic Actuator Design Using Level Set Based Topology Optimization

This paper presents a novel design methodology for optimum structural design of magnetic actuators using a level set based topology optimization method where the level set method can represent the precise boundary shape of a structure and also deal with complex topological changes during the optimization process. The distribution of ferromagnetic material is represented by introducing a level set function into the definition of the magnetic reluctivity. The optimization problem is defined to obtain optimal configurations that maximize the magnetic energy of actuators under a minimum bound of total volume. The movement of the implicit moving boundaries of the structure is driven by a transformation of design sensitivities of the objective and the constraints into speed functions that govern the level set propagation. The proposed method is applied to the structural design of magnetic actuators, and is confirmed to be useful for achieving optimal configurations that deliver higher performance and lighter weight designs.

Design of Compliant Thermal Actuators Using Structural Optimization Based on the Level Set Method

Compliant mechanisms are a new type of mechanism, designed to be flexible to achieve a specified motion as a mechanism. Such mechanisms can function as compliant thermal actuators in Micro-Electro Mechanical Systems (MEMS) by intentionally designing configurations that exploit thermal expansion effects in elastic material when appropriate portions of the mechanism structure are heated. This paper presents a new structural optimization method for the design of compliant thermal actuators based on the level set method and the Finite Element Method (FEM). First, an optimization problem is formulated that addresses the design of compliant thermal actuators considering the magnitude of the displacement at the output location. Next, the topological derivatives that are used when introducing holes during the optimization process are derived. Based on the optimization formulation and the level set method, a new structural optimization algorithm is constructed that employs the FEM when solving the equilibrium equations and updating the level set function. The re-initialization of the level set function is performed using a newly developed geometry-based re-initialization scheme. Finally, several design examples are provided to confirm the usefulness of the proposed structural optimization method.Copyright

Basic Study on the Frost Heave Pressure of Rocks: Dependence of the Location of Frost Heave on the Strength of the Rock

Frost heave in rocks is caused by the frost heave pressure (pore ice pressure) generated by the freezing of pore water, which then cracks the rock. This work attempts to clarify the frost heave pressure of rocks by experiments at four temperature conditions. Ohya tuff and Kimachi sandstone, in which the occurrence of frost heave has previously been confirmed, were used as specimens. Measurements of these experiments were the internal temperature of the rocks during the freezing process and the location where the ice lens formed. These two parameters made it possible to determine the temperature of the location where the ice lens formed. A generalized Clausius-Clapeyron equation was used to calculate the pore ice pressure. The results indicated that the temperature at the location of the ice lens formation depends on the types of rock, but not on the temperature gradient during freezing. It was also confirmed that frost heave in rocks with a higher tensile strength appears at locations with a lower temperature, while that in rocks with a lower tensile strength appears at location of temperatures close to 0°C. These findings suggest that the location and temperature of the ice lens formation are dependent on the strength of the rock.

A New Structural Optimization Method Based on the Level Set Method for Vibration Problems and Heat Conduction Problems

Various structural optimization methods have been proposed for design problems in many industries, such as mechanical, automotive, aerospace and civil industries. Recently, some structural optimization methods based on the level set method have been proposed. Although the previously proposed level set method&b ased structural optimization methods have some benefits, these methods have a difficulty with respect to updating the level set function. Therefore we proposed a new structural optimization method based on the level set method where the level set function is updated based on a simple scheme. In this paper, the newly proposed method is applied to vibration problems and heat conduction problems, and several numerical examples are provided to demonstrate that appropriate optimal structures can be obtained using the newly proposed method.

Acoustic water bottom investigation with a remotely operated watercraft survey system

This paper describes a remotely operated investigation system developed by combining a modern leisure-use fish finder and an unmanned watercraft to survey water bottom topography and other data related to bottom materials. Current leisure-use fish finders have strong depth sounding capabilities and can provide precise sonar images and bathymetric information. Because these sonar instruments are lightweight and small, they can be used on unmanned small watercraft. With the developed system, an operator can direct the heading of an unmanned watercraft and monitor a PC display showing real-time positioning information through the use of onboard equipment and long-distance communication devices. Here, we explain how the system was developed and demonstrate the use of the system in an area of submerged woods in a lake. The system is low cost, easy to use, and mobile. It should be useful in surveying areas that have heretofore been hard to investigate, including remote, small, and shallow lakes, for example, volcanic and glacial lakes.

A Long-Traveling Landslide in Deep Snow Conditions: A Case Study of the Tatsunokuchi Landslide Induced by the 2011 North Nagano Prefecture Earthquake

The 2011 north Nagano Prefecture earthquake (MJMA 6.7) occurred in a deep snow area of Japan that typically has an annual snow cover of more than 2 m. The earthquake induced landslides involving abundant snow. We examined remnant topographies to deduce the landsliding process of one of these landslides, the Tatsunokuchi landslide, which occurred in deep snow conditions. The studied landslide had a displaced mass that included much snow, traveled a long distance, and damaged a wider area than conventional isometric landslides. Our results indicated the following landsliding process: the landslide occurred by the collapse of a rock mass of 5 × 104 m3, rock debris plunged into the abundant snow, a mixture of snow and rock debris formed, and the mixture then traveled on top of snow. Eventually, the displaced mass pushed out nearby snow and thus extended the damage area. The displaced mass having a relatively low proportion of debris probably had a low enough density to be buoyant and therefore easily traveled on top of snow. We estimated the velocity of the landslide using Lenau’s method and obtained a maximum velocity of 14 m/s. Our observations and the clarified landsliding process suggest that landslides will damage a wider area than expected if they occur in deep snow conditions.

A Level Set-Based Topology Optimization Method Targeting Dynamic Characteristics of Rotational Symmetry Structures

In this paper, we present a new level set-based topology optimization method targeting dynamic characteristics of rotational symmetry structures. Rotational symmetry structures are used in rolling mechanism, therefore, dynamic characteristics are often important design criteria. Here, we focus on the lowest eigenfrequency and maximize it based on the level set theory. To guarantee the rotational symmetry of the target structure, we propose to average nodal sensitivities based on the rotational symmetry. We demonstrate the usefulness of our proposed method by a numerical example.

Structural Optimization of Compliant Thermal Micro Actuators Based on the Level Set Method

This paper presents a new structural optimization method for the design of compliant electro thermal micro actuators based on the level set method and the Finite Element Method (FEM). Compliant electro thermal actuator designed to be flexible to achieve a specified motion as a actuator by intentionally designing configurations that exploit thermal expansion effects in elastic material when appropriate portions of the actuator structure are imposed electric voltage. First, an optimization problem is formulated that addresses the design of compliant electro thermal micro actuators considering the magnitude of the displacement at the output location. Based on the optimization formulation and the level set method, a new structural optimization algorithm is constructed that employs the FEM when solving the equilibrium equations and updating the level set function. Finally, a design example is provided to confirm the usefulness of the proposed structural optimization method.