Hiroshi Ohmori

Computational Morphogenesis Its Current State and Possibility for the Future

Computational morphogenesis is the word generally used for expressing those techniques or ways of thought by which the configuration or the system of structures is generated mainly through the usage of computers, which is realized on the firm foundation of both FEM as a tool of numerical analysis and various methods based on relatively newly-developed algorithms for structural optimization. Recently, it has been gaining a considerable number of users such as structural engineers or architects for the structural design of actual buildings as well as proposals for architectural competitions. Here we present the state of the art in computational morphogenesis especially in Japan as well as the future prospects for computational morphogenesis.

Development of membrane stress measurement equipment for membrane structures: proposal of measuring method and its experimental verification

One of the most important issues in keeping membrane structures in good condition is to maintain the proper tension distribution over the membrane. However, it is not easy to determine the real stress level in the membrane quantitatively after completion of the structures. Fluttering by strong wind or ponding caused by rain water may cause severe damage to the membrane structure itself. Therefore, it is very important to know the magnitude of existing stress in membrane structures for their maintenance and management. In this paper, the authors propose a new method that can measure membrane stress using sound waves, and hold experimental tests of membrane stress measurement that use the sound external excitation with sine wave and white noise.

Dynamic Structural Analysis of Deployment of Scissors Structure in Space

The objective of the present study is to investigate the dynamic motion of a deployable structure, which is composed of a scissors mechanism assumed to be deployed in space with a self-balancing moment by actuators. For this purpose, the present paper focuses on how to calculate the dynamic motion of deployment of the scissors mechanism in space with a self-balancing moment, in consideration of its mass and rotational friction around the joints, and showing its numerical results. The present paper also checks the stress and deflection of the frame, as a problem of the structural analysis of an unstable structure without outer boundaries.

Transformable Linked Panels

The objective of the present paper is to show a new concept different from the ‘2D-deployable flat-panel structure’ which was previously proposed by us, and to simulate its rigid body motion. The new concept consists mainly of square panels which are linked by rotational actuators and can be deployed and extended like a scissors mechanism. This is simpler than the previously proposed ‘2D-deployable flat-panel structure’ composed mainly of a scissors mechanism, square panels, and tilted rotational axes. We propose a new system for realization of a solar power satellite as a huge flat construction in space.

Light-weight telescope structure optimized by genetic algorithm

We designed the optics supporting structure (OSS) of a 3.8 m segmented mirror telescope by applying genetic algorithm optimization. The telescope is the first segmented mirror telescope in Japan whose primary mirror consists of 18 petal shaped segment mirrors. The whole mirror is supported by 54 actuators (3 actuators per each segment). In order to realize light-weight and stiff telescope structure, we have adopted full truss structure as OSS of the telescope. We optimized its design by a newly developed software program incorporating genetic algorithm. The program automatically generates new OSS design step-by-step by optimizing the OSS parameters for realizing both light-weight structure and homologous deformation of the mirror surface supported by the OSS against the telescope elevation change simultaneously. The program successfully generated an ultra light-weight OSS design whose weight is only 8 tons including the optical elements and actuators (4 tons) with an eigen frequency of 9.5 Hz. The deviations of the 54 nodes from their original configuration of the designed OSS are less than 100 μm in the range of elevation angle 20 - 90 degrees. A real model of the OSS is under test construction. We also report the results of static test and deformation performance of this OSS model.

Performance Improvement of Membrane Stress Measurement Equipment through Evaluation of Added Mass of Membrane and Error Correction

One of the most important issues in keeping membrane structures in stable condition is to maintain the proper stress distribution over the membrane. However, it is difficult to determine the quantitative real stress level in the membrane after the completion of the structure. The stress relaxation phenomenon of the membrane and the fluttering effect due to strong wind or ponding caused by precipitation may cause severe damage to the membrane structure itself. Therefore, it is very important to know the magnitude of the existing stress in membrane structures for their maintenance. The authors have proposed a new method for separately estimating the membrane stress in two different directions using sound waves instead of directly measuring the membrane stress. The new method utilizes the resonance phenomenon of the membrane, which is induced by sound excitations given through an audio speaker. During such experiment, the effect of the surrounding air on the vibrating membrane cannot be overlooked in order to assure high measurement precision. In this paper, an evaluation scheme for the added mass of membrane with the effect of air on the vibrating membrane and the correction of measurement error is discussed. In addition, three types of membrane materials are used in the experiment in order to verify the expandability and accuracy of the membrane measurement equipment.

EFFECT OF PHASE OF INPUT EARTHQUAKE WAVE ON DYNAMIC RESPONSE OF BUILDINGS WITH SPINDLE-SHAPED RESPONSE CURVE

地震応答解析に基づいて構造設計を行う場合,告示が定める加速 度応答スペクトル(以下,告示スペクトル)に適合する地震波(以 下,告示波)を用いることが,建築基準法等によって定められてい る)。しかし,告示波の作成で必要となる位相特性は建築基準法 等で定められていない。このため,構造設計では,例えば神戸位 相,八戸位相,乱数位相などを用いて告示波が作成されているが, 設計者によって位相特性が異なっている現状がある。 一般に,建物の最大応答変位に着目すれば,中小規模地震ならば 概ね線形弾性範囲内に留まるので位相が応答値に与える影響は無視 できる。しかし,大規模地震では建物の応答は線形弾性範囲を超え るため,同じ応答スペクトルに適合する地震動でも,位相特性に よって建物の最大層間変形角は異なる例えば),。 ここで,実務設計における建物の最大層間変形角と地震荷重の関 係について考察を行う。静的な構造設計(ルート設計)では,Ai分 布を用いて動的な地震力を静的な地震荷重に置換する。また,地震 応答解析に基づく構造設計(大臣認定)でも,予備応答解析による 層せん断力分布に基づいて静的な設計用層せん断力分布を定め,静 的に建築物の設計(設計用応力の算定,部材の断面算定等)を行 う。この静的な設計の検証として再度応答解析を行い,設計者はそ の結果を大臣認定書に記載する。また,静的な設計では地震荷重に よって層間変形角が決まる。従って,結果として層間変形角の大き さは地震荷重の大きさを表していることになる。 現行法では告示波の位相特性を定めていないため,建物の地震荷 重は設計者が選択する位相特性に依存する。このため,設計者が恣 意的に地震荷重を決めることも可能である。これを避けるために, 建設省告示第1461号によって複数の告示波を用いて耐震性の検証を 行うことが義務づけられている)と考えられる。しかし,この規定 でも限られた告示波を例示的に用いて耐震性の検証しているに過ぎ ず,全ての位相に対し耐震性を検証を行ったことにはならない。 また,ベンチマークとなる最大もしくは最小応答変位を与える告 示波(以下,最大・最小応答告示波)が分からなければ,設計に用 いた告示波について客観的な評価(例えば最小告示波の倍の応答 値を与える告示波)もできないが,実用的な最大・最小応答告示波 を定める手法を筆者らは知らない。 計算コストを無視すれば,無限に存在する告示スペクトルに適合 する告示波の中から,ランダムサーチで最大・最小応答告示波を探 索することはできるが,この手法は現実的ではない。また,探索空 入力地震波の位相特性が紡錘型履歴特性建物の応答に与える影響 -遺伝子的アルゴリズムによる最大・最小応答値を与える位相の探索EFFECT OF PHASE OF INPUT EARTHQUAKE WAVE ON DYNAMIC RESPONSE OF BUILDINGS WITH SPINDLE-SHAPED RESPONSE CURVE GA Search of Phase for Maximum-Minimum Response -