著者

芦澤 勇暉 岸本 喜直 小林 志好 大塚 年久

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00148-17-00148, 2017 (Released:2017-09-25)

参考文献数

27

---

Replacement of a damaged pipe is important to prevent an accident caused by the pipe. The major damage of the pipe in long-term use is pipe wall thinning. Thus, identification techniques of the location and the thickness of the pipe wall thinning are necessary to decide the appropriate time to replace the pipe. The ultrasonic testing (UT) and the radiographic testing (RT) are currently mainstreams in nondestructive inspections. However, the UT requires the surface preparation of the pipe, and the RT has the risk of the radiation leakage. This study has developed a novel technique of nondestructive identification of location and thickness of pipe wall thinning by using magnetic sensor. This technique aims at only nonmagnetic pipes, and estimates the location and the thickness of the thinning part in the pipe by using the measurement data of the magnetic flux density when the electric current is applied into the pipe. Furthermore, the measurement sensitivity of the magnetic flux density is improved by setting the high magnetic permeability material around the magnetic sensor. In order to verify the validity of the proposed technique, numerical simulations and actual experiments were performed by using specimens with several patterns of the location and the thickness of the thinning part. The results show that the direct analysis values agreed with the measurement data. The inverse analysis results show that the estimated values of the parameters to evaluate the thinning part successfully agreed with the correct values in most of the cases in this study. It is believed that the proposed technique can be applied to practical situations.

著者

吉村 博仁 堀田 恭平 星 幸義 永澤 克浩

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00094-17-00094, 2017 (Released:2017-09-25)

参考文献数

15

被引用文献数

1

---

In recent years, needs for micro drilling are increasing, accompanying the development of higher wiring density of printed circuit board (PCB). When drilling PCB for the purpose of making the electric through holes, it has been said that the drill breakage is caused by being filled the chips of GFRP and copper of PCB in the drill flutes. The aim of this study is to clarify the effect of PCB drilling using DLC coated drill on tool wear, chip evacuation and cutting torque. Series of drilling tests of PCB have been carried out to investigate the amount of drill wear, the chips evacuation behavior out of drilled hole with the drill, the shape of chips produced and the cutting torque using DLC-coated drill and non-coated drill. The chips evacuation behavior out of drilled hole with the drill is filmed by a high-speed motion camera and the shape of chips produced is observed by a microscope. The cutting torque is measured by a dynamometer; Kistler 9329A. The amounts of drill flank wear and margin wear using DLC-coated drill and non-coated drill are almost the same. The chips of GFRP using DLC-coated drill are shorter and smaller than those using non-coated drill. The chips evacuation out of drilled hole with the drill using DLC-coated drill is better than those using non-coated drill, and cutting torque using DLC-coated drill is lower than those using non-coated drill.

著者

福重 真一

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00121-17-00121, 2017 (Released:2017-09-25)

参考文献数

18

被引用文献数

2

---

This paper proposes an interactive image-based re-modeling system for virtual reshaping of real objects via a video see-through display. The system provides a quasi-realistic design environment in which a designer manipulates the shape and location of real products installed in a real living space. A prototype of the proposed system is developed by integrating two sub-systems for solid modeling based on 3D-CAD and visualization based on image-based rendering. A case study of the virtual redesign of real products illustrates that the proposed system allows designers to examine various design changes on the existing products in an immersive and realistic 3D environment.

著者

伊藤 研一郎 西村 秀和 小木 哲朗

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00113-17-00113, 2017 (Released:2017-09-25)

参考文献数

25

被引用文献数

3

---

Navigation systems are nowadays widely used for cars though it is yet to be able to say popularized for motorcycles. While motorcycle navigation systems are not popularized yet, previous research indicates motorcyclist's high demand against a useful navigation system. The absence of useful motorcycle navigation system is an issue of current products not capable of providing navigation information efficiently. To work with the issue, information presentation design is necessary to consider the motorcyclist's characterful viewpoint movement of looking at the road surface carefully in a vertical movement. As a solution to this issue, we propose the use of head-up display for information presentation. Previous studies have revealed the amount and positions suitable to present information for motorcyclist while riding, although the timing of information presentation is yet to be discussed. Thus, in this paper, the information presentation timing to provide navigation information has been evaluated. Experiment using an immersive CAVE motorcycle simulator was conducted with the configuration of five timings between 25 m to 85 m prior to the intersection under conditions of urban street with 30 km/h speed limit. Durations of motorcyclist's viewpoint movement and five scale subjective ratings were used for evaluation. The experimental results from 10 subjects showed a statistically significant difference in subjective ratings. In conclusion, suitable information presentation timing of riding in urban streets with 30 km/h speed limit is around 40 m to 55 m prior to the target intersection.

著者

数仲 馬恋典

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00093-17-00093, 2017 (Released:2017-09-25)

参考文献数

24

被引用文献数

2

---

In this paper, a mechanism consisted of a double-cone rolling on two divergent-convergent rails is proposed to be used in the construction of a wave-powered electrical generator. Such divergent-convergent rails, attached to a buoy, can be materialized by using either straight V-rails, or eccentric circular rails. Rotational movement of the buoy, induced by the waves, is transformed into the rotational and translational motion of a magnetized double-cone. In this way, a variable magnetic field is extended over several coils, connected in parallel. Power generation is obtained through the electromagnetic induction effect. Firstly, a geometrical model is proposed to determine the length and radii of contact between the double-cone and the circular rails. Variation of the number of rotations, theoretically obtained, versus the rails eccentricity is validated by tests, where a double-cone, made in S45C carbon steel, is rolling on circular rails, made of A5052 aluminum alloy. Then, a model to evaluate the pressure of contact, and the change of potential energy of the double cone, is advanced. Based on such model, variation of the maximal contact pressure versus the rails eccentricity is clarified, for various loading patterns, corresponding to waves of different heights.

著者

平尾 章成 有田 実花子 金 侖慧 松岡 由幸

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00090-17-00090, 2017 (Released:2017-09-25)

参考文献数

16

---

Person has spent most of the day in a sitting posture. In recent years, there has been a growing attention to the "seating comfort" researches. However, research topics are complicated and vary widely, it is difficult for a designer to use accurately design knowledge during the development of chairs. Therefore, in this study, "seating comfort" researches based on the literatures were systematically analyzed by the elements extracted and classified into spaces of element inter-relationship diagram using Multispace design model. Extracted elements were classified and discussed about change based on timeaxis. And, also the literatures categorized using cluster analysis of the extracted elements. From consideration based on the analysis results, researches about the human mechanism of seating comfort and long-term sitting analysis including the postural change have been proposed as non-research areas for future knowledge expansion.

著者

朝賀 泰男 西垣 英一 青井 一郎 杉浦 豪軌 槇野 浩司

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00088-17-00088, 2017 (Released:2017-09-25)

参考文献数

13

被引用文献数

1

---

As manufacturing has begun to move from mass production to mass customization, manufacturing industries are currently constructing the architecture to provide wide variety of products in countries around the world. Modular design and standardization is effective for mass customization. In recent years, modular design techniques have been researched in vehicle development. Then, car manufacturers have been announcing their own architecture about the car design. We have focused on pipe-based components as the standardized member of body structure. Since the pipe is a general-purpose member, we can get them easily. In this study, we have developed new design techniques for body structure consist of the pipe-based standardized components. Firstly, we have designed base frame layout by topology optimization formulated Min-Max approach for multiple load cases. Secondly, we have calculated cross-sectional design parameters by discrete design value table and fully stressed design. Using these techniques based on modular design rules, we can obtain body structure consisting of standardized components which are subjected to stress lower than the yield strength. As a case study, we have applied our unique modular design techniques to the rear body structure model.

著者

明石 一希 森永 英二 若松 栄史 倉橋 龍 荒井 栄司

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00084-17-00084, 2017 (Released:2017-09-25)

参考文献数

10

被引用文献数

2

---

With recent globalization in industries, the number of failures and troubles of products caused by using them in unexpected ways has increased. In order to avoid such troubles, it is necessary not only to assume various ways of use thoroughly, but also to verify whether the design plan can fulfill required functions when the product is utilized in those ways. From this point of view, the authors proposed a functional verification method considering ways of use based on qualitative modeling of behavior of entities and cause-and-effect relationships among physical phenomena using Petri nets. It is, however, impossible to detect failures concerning to specification which requires dealing with quantitative information. This paper provides a method for quantitative modeling of behavior of entities and cause-and-effect relationships among physical phenomena. Two types of tokens were defined for dealing with positive and negative values and four types of arcs were for controlling changes of those values. These new elements of Petri net made it possible to represent behavior of entities and cause-and-effect relationships quantitatively. Application of this new modeling method to the functional detection method enables automatic detection of failures concerning to both functions and specification. The detection method using this modeling method was applied to an example, and its effectiveness was proven.

著者

史 金星 大村 渓一朗 下田 昌利

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00077-17-00077, 2017 (Released:2017-09-25)

参考文献数

28

---

Because of their superior mechanical, structural, and electronic properties, carbon nanomaterials (CNs) (e.g. graphene sheets and carbon nanotubes) are supposed to be base materials for nanoelectromechanical systems (NEMS). In the present work, we propose a structural optimization method of carbon nanomaterials by introducing topological defects, which consists of the molecular mechanics method, the free-form optimization method, the Phase-Field-Crystal (PFC) method, Voronoi tessellation, and molecular dynamics (MD) simulation. The C-C bonds of CNs are simulated as equivalent continuum beams by a combination of molecular and continuum mechanics, so the atomic structures of CNs can be treated as frame structures. We adopt the free-form optimization method for frames to determine the optimal shapes of CNs in stiffness maximization problem. For obtaining the stable atomic structures of the optimal shapes of CNs, topological defects are introduced in the optimal shapes of CNs using a combination of PFC method, Voronoi tessellation, and MD simulation. The numerical results show that the compliance of CNs can be significantly reduced according to the structural optimization method, which is helpful for designing CNs components in NEMS.

著者

江川 翔一 瀬島 吉裕 佐藤 洋一郎 渡辺 富夫

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00076-17-00076, 2017 (Released:2017-09-25)

参考文献数

27

---

We have already developed an embodied communication system with the pupil response and demonstrated that the pupil response plays an important role in realizing smooth human interaction and communication. Therefore, the pupil response has possibilities to enhance a sharing of empathy and to convey rich affects such as a pleasure with laugh. Hence, in order to develop communication systems which enhance empathy, it is desired to design the media representation of pupil response. In this paper, focusing on the laugh with pleasure emotion as a typical pleasure affect, we analyzed the relation between laugh and pupil response using a pupil measurement device, and developed a pupil response system for inducing empathy by laugh response based on speech input. In addition, we evaluated the pupil response with the laugh by using the developed system. The results demonstrated that the dilated pupil response with the laugh is effective for enhancing empathy.

著者

小野寺 誠 針谷 昌幸 金剛 力 新谷 政樹 何 祺

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00073-17-00073, 2017 (Released:2017-09-25)

参考文献数

19

被引用文献数

1

---

This paper proposes an advanced mesh generation technique that reuses the proven analysis models by similar sub-part search. The purpose of this development is to reduce interactive mesh improvement work time and to comply with the mesh specifications. The number of product specifications is increasing due to global business development and diversification of needs. Hence, the execution frequency of simulation is increasing. Therefore, it is necessary to reduce the working hours. Furthermore, quality improvement and standardization of analysis models are required because the general designers have learned to manage V&V. This technique consists of two distinctive techniques. First, it is the technique to search the sub-parts from newly design CAD where have similar shape with the archived feature sub-parts contained in the proven CAD models. In this technique, the similar sub-parts are retrieved from a CAD model described by boundary representation and made correspondence relation surface pairs of a retrieval model (proven model) and a target model (CAD of new design). A similarity score is based on the attributed graphs of a retrieval model and a target model. And, this score is calculated by a geometrical similarity and topological similarity. Second, mesh can be generated automatically by arranging and merging the mesh of similar sub-parts. Experimental results show that this technique can efficiency achieve mesh generation without interactive mesh improvement operation.

著者

西垣 英一 朝賀 泰男

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00065-17-00065, 2017 (Released:2017-09-25)

参考文献数

13

---

This paper describes a modularization method based on the creation of a new layout structure by combining topology optimization using beam elements and clustering analysis. By setting candidates for frame members in smaller units than parts and performing topology optimization using beam elements, a frame structure of new layouts as an aggregate of fine frame members can be created. For each fine frame member, connectivity as a structure in the entire frame structure is expressed as Design Structure Matrix (DSM). By performing hierarchical clustering on this DSM, clusters of fine frame members are formed as parts, and modules as these aggregate can be found out. Since this is hierarchically determined as a dendrogram, it is possible to determine the number of module divisions of the product configuration depending on the granularity of the cluster. Furthermore, by advancing each fine cluster towards the trunk above the tree diagram, an assembly process with less rework is obtained. Unlike the method of deriving the optimal solution for the product with existing structure, this research proposes a method to derive concurrently the new frame structure and construction of parts and module decomposition which minimizes rework. By validation analysis using a simple box structure, the effectiveness of this proposed method has been confirmed.

著者

一文字 正幸 見村 勇樹 池田 和徳 永田 寿一 平手 利昌 平井 匡平 平野 俊夫 淵本 遼 塩飽 宣貴 荒川 雅生

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00056-17-00056, 2017 (Released:2017-09-25)

参考文献数

7

---

Dynamic FEM analysis is valid for designing rotating machinery to reduce its vibration problem when we may ensure enough accuracy of the analysis. Surrogate multiple objective optimization method is one of the most effective methods for structural identification improving the FEM analysis model of a structure to adjust the natural frequency analysis results to the experimental results. In this study the structural identification method is applied to stator end-windings of a turbine generator to determine the Young's modulus of the principal components on the FE model minimizing the analysis errors of the natural frequencies of the 2-lobe and 4-lobe circular modes to the corresponding experimental results. The accurate FE model of the end-windings is obtained by this method.

著者

木村 弘之 藤谷 高寛

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00205-17-00205, 2017 (Released:2017-09-25)

参考文献数

15

---

Vibration suppressors are used to change the natural frequency of an elevator rope and prevent resonance. The displacement of the parts of the elevator rope at both the ends is small compared to that of the center part of the rope; therefore, it is not necessary to set the vibration suppressors in the parts on either ends. The elevator rope is generally modeled using a string, and linear string vibration is well researched. However, the vibration of the string equipped with vibration suppressors encounters geometric nonlinearity, and hence, its characteristics have been studied under a few conditions. Furthermore, in the case in which the vibration suppressor is located except for both ends part of the string, no exact solution has yet been obtained for the free vibration of the string. In this paper, an exact solution is presented for the free vibration of a string when the vibration suppressors are located except for both ends part of the string. In the analysis for determining the exact solution, the problem of free vibration with vibration suppressors is transposed to a problem of forced vibration. Further, to verify the validity of the exact solution, a finite difference analysis of the string vibration with vibration suppressors is performed. The calculated results obtained from the finite difference analysis are in good agreement with the results of the exact solution.

著者

亀谷 均 堀江 克明 幸田 憲明 久間 英樹 松本 浩介 内村 和弘 小森 健一 増木 新呉 東 裕人

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00147-17-00147, 2017 (Released:2017-09-25)

参考文献数

7

---

Lower to middle tier regions of dam reservoirs often fall into the anoxic states in summer. When the anoxic state is reached, living things die, heavy metals such as manganese and iron, hydrogen sulfide and methane are eluted from mud deposited on the lakebed. Since it is not possible to release heavy metals exceeding environmental standards, an improvement of dissolved oxygen concentration in dam lakebed is required. So far, there is no system that can automatically improve the dissolved oxygen, in the lower to middle tier regions of dam lakebed. This study was carried out for developing an automatic system to improve the lakebed dissolved oxygen concentration to 6mg/L or more. The developed oxygen dissolution apparatus can diffuse a high concentration oxygen water horizontally at a rate of 1km per day. Thus, by raising and lowering this oxygen dissolution apparatus in water, a system that creates 3 - dimensional spreading of the dissolved oxygen not only to the lower tier but also to the middle tier regions was developed. The demonstration experiments, reported of the effectiveness of the system that can raise the dissolved oxygen concentration from the low oxygen-free state to the target of 10 mg / L in 5 days. Moreover, the system demonstrated its ability to automatically raise the dissolved oxygen concentration to 10mg/L in the 10m region from the bottom of lakebed.

著者

瓜生 耕一郎 長舩 司 村上 隆則 中村 守正 射場 大輔 船本 雅巳 森脇 一郎

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00156-17-00156, 2017 (Released:2017-09-25)

参考文献数

11

被引用文献数

2

---

Taper shaped skiving cutters are commonly used in gear skiving because they provide clearance angles under a simple gear arrangement and they could have lower cutting resistance than cylindrical skiving cutters. Their tooth flanks are generally ground by the same method of generation grinding with a trapezoidal wheel as ones for pinion cutter tooth flanks for gear shaping. In gear skiving, however, the process of tool-face re-grinding could increase profile deviations of cut gears due to the lack of an appropriate change in cutter profiles along the facewidth. In the present paper, computer programs were developed to simulate the generation grinding and the skiving with the cutting edges ground by the method. Skiving with a cutter ground by the method were carried out and skived tooth forms were compared with those calculated by the developed program. As a result, the comparisons could guarantee the reliability of the program. Furthermore, the program has revealed that the increase in a helix angle of a cutter yields the increase in tooth profile deviations of skived gears after regrinding the tool faces. Therefore, taper shaped cutters should be applied to internal gear skiving with extra caution.

著者

長田 拓也 鈴木 拓央 中内 靖

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00118-17-00118, 2017 (Released:2017-09-25)

参考文献数

9

---

Since medicine treatment is one of the most major and effective cure methods, many patients take medicine every day. On the other hand, patients sometimes have serious accidents because some of them do not follow correct medicine dosing method (i.e. taking medicine without enough quantity of water). Though it may result serious accidents, in general, their doctors cannot notice the above-mentioned facts. In this paper, we propose a sensor-embedded intelligent cup that provides instructions for correct dosing and a medicine instruction support system using it. The proposed cup is the dual structure of a tumbler equipped with water level and acceleration sensors. The cup can detect if enough quantity of water is in it before a user takes medicine by using the water level sensor. We developed a calibration method for the water level sensor and implement it so that the quantity of water can be measured on any temperature. The cup can also detect if a user has taken medicine with the enough quantity of water from the cup by SVM (Support Vector Machine) using data of the acceleration sensor. Furthermore, the cup can also detect the quantity of water left in the cup using the acceleration sensor. The system will also provide the dosing history (i.e. when the dosing has conducted) to a user's caregivers (care giver and family in distant) through web interface. We conducted experiments and confirmed the positive effect of the proposed intelligent medicine cup.

著者

吉村 博仁 拜野 賢太 渡邉 英人 永澤 克浩

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.16-00374-16-00374, 2017 (Released:2017-09-25)

参考文献数

11

---

Recently, the diameter of through hole on printed circuit board (PCB) has become smaller with downsizing of electric devices. However, the drilling small diameter through hole includes some problems such as hole position accuracy and hole bending. Entry sheet is used to improve drill centering, drill guidance and reduction of burrs when drilling PCB. Series of drilling tests of PCB are carried out to investigate the effect of entry sheet on hole position accuracy, hole bending and chip-evacuation using three kinds of materials of entry sheet; aluminum, aluminum clad with lubricant and resin. The thrust during drilling entry sheet and the wear of the drill are measured. The hole position accuracy and hole bending examined after the drilling tests. The chips evacuation behavior out of drilled hole with the drill is filmed by a high-speed motion camera and the shape of chips produced is observed by a microscope. The amount of chisel wear and flank wear of the drill is not almost affected by the kinds of sheets. The hole position accuracy of entry side is worse as the maximum thrust during drilling entry sheet is increasing. The rate of increase of the amount of hole bending to the hit number of hole when using high rigid and high lubricant entry sheet decreases rather than that when using low rigid and low lubricant entry sheet. The evacuation out of drilled hole with the drill in case of drilling with aluminum clad with lubricant is better than that in case of drilling with aluminum.

著者

石塚 尚子 野口 悠暉 山田 崇恭 泉井 一浩 西脇 眞二

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00185-17-00185, 2017 (Released:2017-09-25)

参考文献数

19

被引用文献数

1

---

The uniformity of deposition thickness in electroplating processes is vital to the realization of desirable surface qualities of many products. The thickness distribution of deposits varies according to numerous factors, such as the arrangement and shapes of auxiliary cathodes, anodes and shields, and the detailed configuration of the plating process. In recent years, computer analyses such as the Finite Element Method (FEM) have become widespread. Such analytical tools can predict thickness distributions, search for optimal process configurations, and avoid production problems, to some extent, but the selection of the most effective analytical conditions still depends on skilled analysts. This study presents a topology optimization method to achieve uniform deposition thickness, applied to the design of the shields placed in an electroplating bath. The proposed method uses level set boundary expressions and the FEM to analyze the electrochemical field. The Kreisselmeier-Steinhauser (KS) function for the current density distribution on a cathode is employed as an objective function, since current density is nearly proportional to the thickness of the resulting electroplating. The magnitude of the current density on the cathode is set as a constraint so that it does not fall below a certain value, to avoid lengthy plating times that would occur if the current density were too low. Numerical examples are presented to confirm the utility of the proposed method and the results demonstrate that the proposed method can obtain appropriate shapes and arrangements of shields.

著者

前田 慎市 吉木 一秀 菅野 祥一郎 冨田 啓太 小原 哲郎

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.852, pp.17-00019-17-00019, 2017 (Released:2017-08-25)

参考文献数

26

---

Shock-induced combustion around a spherical body was experimentally investigated by launching the projectile at supersonic speed into a combustible mixture. This study focused on occurrence conditions for an unsteady combustion which was characterized as combustion instabilities with an oscillating combustion front. A spherical body of 4.76 mm dimeter was used as the projectile, and its flight Mach numbers were ranged from 3.5 to 7.5. Four types of combustible mixtures, which were stoichiometric hydrogen-oxygen and ethylene-oxygen mixtures diluted with argon or nitrogen (2H2 + O2 + 3Ar, 2H2 + O2 + N2, C2H4 + 3O2 + 12Ar, C2H4 + 3O2 + 2.5N2), were used and their initial pressures were varied between 25 and 100 kPa. The combustion regimes around the projectile were observed by using a schlieren optical system and high-speed camera. The combustion regimes generally varied from the steady combustion with smooth combustion front to the unsteady combustion with oscillating combustion front, when the projectile Mach number or the initial pressure increased. The occurrence conditions for the unsteady combustion were expressed by the two dimensionless parameters; dimensionless heat release rate, q*t* and dimensionless induction length, lind*, which were defined by the post-shock state and flow velocity on the stagnation streamline of the projectile and by assuming the chemical reaction as a constant-volume explosion. The q*t* included a temperature gradient in a reaction zone, and represented the strength of the pressure wave driven by the heat release reaction. The lind* included an induction time, and represented the distance between the shock wave and the location where the heat release reaction started. The unsteady combustion occurred when these two dimensionless parameters were above the critical values, and the trend of occurrence condition of the two combustion regimes could be explained by introducing the parameters.