하드웨어를 이용한 효율적인 인공풍 시뮬레이션 방법

이남경,유관우,백낙훈,Lee, Nam-Kyung,Ryu, Kwan-Woo,Baek, Nak-Hoon 한국정보처리학회 2006 정보처리학회논문지 A Vol.13 No.7

본 논문에서는 자연풍에 비해 상대적으로 작은 영역에 영향을 주는 인공풍을 시뮬레이션하는 방법을 제안한다. 이를 위해 인공풍의 진행 형태를 모델링하는 방법을 제안하고, 제안하는 바람 모델이 시뮬레이션 환경에 미치는 영향을 계산하는 효율적인 방법도 제안한다. 제안하는 방법에서는 인공풍의 영향을 계산하는 수식이 기존의 조명 모델(Illumination Model)에서의 조도 계산식(Intensity Equation)과 유사함을 보이고, 이를 이용하여 바람에 의한 영향을 직접 수식으로 계산하지 않고 집중광선(Spot Light)에 대한 조도 계산식을 사용하여 효과적으로 인공풍의 힘을 계산한다. 제안하는 방법은 실시간 처리가 가능하며, 컴퓨터 게임이나 가상 현실과 같은 다양한 분야에 적용할 수 있다. In this paper, we present a simulation model for artificially generated winds which affect relatively restricted regions in comparison with natural winds. We first propose an artificial wind propagation model, and then propose an efficient way of calculating the effect of this wind model in the simulation environment. Through showing that our wind force calculation equation is similar to the typical intensity equation for illumination models, we can calculate the wind force indirectly by using the intensity equations for spotlights, and hence we can reduce the simulation time. Our method shows real-time capabilities, and thus can be used various real-time applications including computer games, virtual environments, etc.

Hot Data Identification For Flash Based Storage Systems Considering Continuous Write Operation

Seung-Woo Lee(이승우),Kwan-Woo Ryu(유관우) 한국컴퓨터정보학회 2017 韓國컴퓨터情報學會論文誌 Vol.22 No.2

Recently, NAND flash memory, which is used as a storage medium, is replacing HDD (Hard Disk Drive) at a high speed due to various advantages such as fast access speed, low power, and easy portability. In order to apply NAND flash memory to a computer system, a Flash Translation Layer (FTL) is indispensably required. FTL provides a number of features such as address mapping, garbage collection, wear leveling, and hot data identification. In particular, hot data identification is an algorithm that identifies specific pages where data updates frequently occur. Hot data identification helps to improve overall performance by identifying and managing hot data separately. MHF (Multi hash framework) technique, known as hot data identification technique, records the number of write operations in memory. The recorded value is evaluated and judged as hot data. However, the method of counting the number of times in a write request is not enough to judge a page as a hot data page. In this paper, we propose hot data identification which considers not only the number of write requests but also the persistence of write requests.

Block Unit Mapping Technique of NAND Flash Memory Using Variable Offset

Seung-Woo Lee(이승우),Kwan-Woo Ryu(유관우) 한국컴퓨터정보학회 2019 韓國컴퓨터情報學會論文誌 Vol.24 No.8

In this paper, we propose a block mapping technique applicable to NAND flash memory. In order to use the NAND flash memory with the operating system and the file system developed on the basis of the hard disk which is mainly used in the general PC field, it is necessary to use the system software known as the FTL (Flash Translation Layer). FTL overcomes the disadvantage of not being able to overwrite data by using the address mapping table and solves the additional features caused by the physical structure of NAND flash memory. In this paper, we propose a new mapping method based on the block mapping method for efficient use of the NAND flash memory. In the case of the proposed technique, the data modification operation is processed by using a blank page in the existing block without using an additional block for the data modification operation, thereby minimizing the block unit deletion operation in the merging operation. Also, the frequency of occurrence of the sequential write request and random write request Accordingly, by optimally adjusting the ratio of pages for recording data in a block and pages for recording data requested for modification, it is possible to optimize sequential writing and random writing by maximizing the utilization of pages in a block.

비밀자료 삽입용량을 증가시키기 위한 비밀 공유 기반의 이중 이미지 가역 정보은닉 기법

김평한,유관우,Kim, Pyung Han,Ryu, Kwan-Woo 한국멀티미디어학회 2022 멀티미디어학회논문지 Vol.25 No.9

The dual image-based reversible data hiding scheme embeds secret data into two images to increase the embedding capacity of secret data. The dual image-based reversible data hiding scheme can transmit a lot of secret data. Therefore, various schemes have been proposed until recently. In 2021, Chen and Hong proposed a dual image-based reversible data hiding scheme that embeds a large amount of secret data using a reference matrix, secret data, and bit values. However, in this paper, more secret data can be embedded than Chen and Hong's scheme. To achieve this goal, the proposed scheme generates polynomials and shared values using secret sharing scheme, and embeds secret data using reference matrix and septenary number, and random value. Experimental results show that the proposed scheme can transmit more secret data to the receiver while maintaining the image quality similar to other dual image-based reversible data hiding schemes.

실시간 헬리콥터 시뮬레이션을 위한 회전 깃의 역학적 모델

박수완,유관우,김은주,백낙훈,Park, Su-Wan,Ryu, Kwan-Woo,Kim, Eun-Ju,Baek, Nak-Hoon 한국정보처리학회 2007 정보처리학회논문지 A Vol.14 No.5

물리 기반의 헬리콥터 시뮬레이션은 항공학, 항공역학 등의 분야에서 많이 연구되어 오고 있으나, 복잡한 수식, 많은 계산량 등으로 인해 사실성과 속도를 동시에 추구하는 컴퓨터 그래픽스 분야에는 적용하기 어려웠다. 본 논문에서는 컴퓨터 그래픽스 분야에 적용할 수 있도록 구현하기 쉽고, 실시간 헬리콥터 시뮬레이션을 가능하게 하는 헬리콥터 회전 깃(rotor blades)의 역학적 모델을 제안한다. 헬리콥터는 회전 깃과 공기의 충돌로 발생한 힘을 통해 운동하는데, 이는 유체와 강체가 충돌해서 발생하는 충돌력으로 설명할 수 있다. 이를 근거로 근사화한 회전 깃의 역학적 모델을 도입하면, 기존의 강체 시뮬레이션 방법으로 유체와 강체가 충돌하는 헬리콥터의 움직임을 실시간 시뮬레이션 할 수 있다. 본 논문에서는 실시간 계산이 가능하도록 뉴턴의 양력 계산법을 응용하여 회전 깃의 움직임으로 발생하는 힘을 구한다. 본 논문이 제안하는 방법에 따라 구현된 프로토타입 시스템은 실제와 유사한 헬리콥터 시뮬레이션을 실시간에 처리할 수 있음을 보였다. Physically-based researches on simulating helicopter motions have been achieved in the field of aeronautics, aerodynamics and others. These results, however, have not been appled in the computer graphics area, mainly due to their complex equations and heavy computations. In this paper, we propose a dynamics model of helicopter rotor blades, which would be easy to implement, and suitable for real-time simulations of helicopters in the computer graphics area. Helicopters fly by the forces due to the collisions between air and rotor blades. These forces can be interpreted as the impulsive forces between the fluid and the rigid body. Based on these impulsive forces, we propose an approximated dynamics model of rotor blades, and it enables us to simulate the helicopter motions using existing rigid body simulation methods. We compute forces due to the movement of rotor blades according to the Newton's method, to achieve its real-time computations. Our prototype implementation shows real-time aerial navigation of helicopters, which are murk similar to the realistic motions.

쓰기요청의 연속성과 발생빈도를 고려한 hot data 검증기법

이승우(Seung-Woo Lee),유관우(Kwan-Woo Ryu) 한국컴퓨터정보학회 2019 韓國컴퓨터情報學會論文誌 Vol.24 No.6

Hard disks, which have long been used as secondary storage in computing systems, are increasingly being replaced by solid state drives (SSDs), due to their relatively fast data input / output speeds and small, light weight. SSDs that use NAND flash memory as a storage medium are significantly different from hard disks in terms of physical operation and internal operation. In particular, there is a feature that data overwrite can not be performed, which causes erase operation before writing. In order to solve this problem, a hot data for frequently updating a data for a specific page is distinguished from a cold data for a relatively non-hot data. Hot data identification helps to improve overall performance by identifying and managing hot data separately. Among the various hot data identification methods known so far, there is a technique of recording consecutive write requests by using a Bloom filter and judging the values by hot data. However, the Bloom filter technique has a problem that a new bit array must be generated every time a set of items is changed. In addition, since it is judged based on a continuous write request, it is possible to make a wrong judgment. In this paper, we propose a method using a counting filter for accurate hot data verification. The proposed method examines consecutive write requests. It also records the number of times consecutive write requests occur. The proposed method enables more accurate hot data verification.

Semi-Lagrangian 이류항 계산의 추적법 개선

박수완,백낙훈,유관우,Park, Su-Wan,Baek, Nak-Hoon,Ryu, Kwan-Woo 한국정보처리학회 2009 정보처리학회논문지 A Vol.16 No.6

일반적으로 사실성 있는 유체를 시뮬레이션하기 위해 Navier-Stokes 방정식을 사용한다. Euler 구조에서 Navier-Stokes 방정식을 풀 때, 이 류항은 비선형이어서 계산이 복잡하기 때문에 근사화한 모델로 Semi-Lagrangian 방법을 사용한다. Semi-Lagrangian 방법에서는 먼저 이류하 는 위치를추적하고, 추적한 위치에서 값을 보간해서 사용한다. Stam이 제안한 방법으로 계산할 경우, 이 과정에서 수치적 소실이 많이 발생하 기 때문에 수치적 소실을 보정하려는 노력들이 있어 왔다. 그러나 대부분의 경우에 보간하는 과정에서의 소실을 줄이려는 노력이거나, 입자를 같이 사용하는 방법이었다. 따라서 본 논문에서는 Euler 구조에서 다른 추가나 변형을 가하지 않고 이류항의 연산에서 추적법을 개선함으로 수 치적 소실을 줄이는 방법을 제안한다. 우리의 방법에서는 현재 격자의 속도로 역추적하는 기존의 방법이 아니라, 현재의 격자로 오게 될 속도 를 가진 격자를 찾아서, 그 격자의 물리량들을 선형 보간하여 사용한다. 이는 직관적으로 생각할 때, 어느 지점의 물리량은 그 지점의 속도로 인해 다음 단계에 다른 지점에 있게 된다는 사실을 그대로 적용한 것이다. 본 논문에서 제안한 방법으로 기체를 시뮬레이션 했을 때 수치적 소 실이 줄었으며, 그로 인해 사실성을 높이면서도 실시간 처리가 가능했다. To realistically simulate fluid, the Navier-Stokes equations are generally used. Solving these Navier-Stokes equations on the Eulerian framework, the non-linear advection terms invoke heavy computation and thus Semi-Lagrangian methods are used as an approximated way of solving them. In the Semi-Lagrangian methods, the locations of advection sources are traced and the physical values at the traced locations are interpolated. In the case of Stam's method, there are relatively many chances of numerical losses, and thus there have been efforts to correct these numerical errors. In most cases, they have focused on the numerical interpolation processes, even simultaneously using particle-based methods. In this paper, we propose a new approach to reduce the numerical losses, through improving the tracing method during the advection calculations, without any modifications on the Eulerian framework itself. In our method, we trace the grids with the velocities which will let themselves to be moved to the current target position, differently from the previous approaches, where velocities of the current target positions are used. From the intuitive point of view, we adopted the simple physical observation: the physical quantities at a specific position will be moved to the new location due to the current velocity. Our method shows reasonable reduction on the numerical losses during the smoke simulations, finally to achieve real-time processing even with enhanced realities.

효율적인 대화형 천 시뮬레이션 기법

정대현,김구진,백낙훈,유관우,Jeong Dae Hyun,Kim Ku Jin,Baek Nakhoon,Ryu Kwan Woo 한국정보처리학회 2005 정보처리학회논문지 A Vol.12 No.4

We present an interactive cloth simulation method based on the mass-spring model, which is the most widely used one in the field of cloth animation. We focus especially on the case where relatively strong forces are applied on relatively small number of mass-points. Through distributing the forces on some specific points to the overall mass-points, our method simulates the cloth in pseudo-real time. Given a deformed cloth, we start from resolving the super-elasticity effect using Provot's dynamic inverse method [9]. In the next stage, we adjust the angles between neighboring mass-points, to finally remove the unexpected zigzags due to the previous super-elasticity resolving stage. 본 논문에서는 질점-스프링 모델(mass-spring model)에 기반한 대화형 천 시뮬레이션(interactive cloth simulation) 기법을 제시하며, 특히 소수의 질점들(mass-points)에 상대적으로 강한 힘이 가해졌을 경우 사실적으로 천을 시뮬레이션하는 방법에 초점을 맞추었다. 본 논문에서 제시하는 방법은 소수의 점들에 대해 가해진 힘을 모든 질점들에 분산시킴으로써 의사 실시간(pseudo real-time) 내에 시뮬레이션을 수행하며, 이는 기존의 방법들에 비해 수행속도 면에서 매우 효율적이다. 또한, Provot[9]의 역동역학 방법(inverse dynamic method)을 사용하여 초탄성(super-elasticity) 현상을 해결한 뒤, 인접한 질점 간의 각도를 조정함으로써 초탄성 효과에 의해 발생하는 지그재그(zigzag) 현상을 제거하여 사실적으로 천을 시뮬레이션한다.

효과적인 가역 정보은닉을 위한 픽셀의 차이 값을 이용한 개선된 보간법

김평한,정기현,윤은준,유관우,Kim, Pyung Han,Jung, Ki Hyun,Yoon, Eun-Jun,Ryu, Kwan-Woo 한국멀티미디어학회 2021 멀티미디어학회논문지 Vol.24 No.6

The reversible data hiding technique safely transmits secret data to the recipient from malicious attacks by third parties. In addition, this technique can completely restore the image used as a transmission medium for secret data. The reversible data hiding schemes have been proposed in various forms, and recently, the reversible data hiding schemes based on interpolation are actively researching. The reversible data hiding scheme based on the interpolation method expands the original image into the cover image and embed secret data. However, the existing interpolation-based reversible data hiding schemes did not embed secret data during the interpolation process. To improve this problem, this paper proposes embedding the first secret data during the image interpolation process and embedding the second secret data into the interpolated cover image. In the embedding process, the original image is divided into blocks without duplicates, and the maximum and minimum values are determined within each block. Three way searching based on the maximum value and two way searching based on the minimum value are performed. And, image interpolation is performed while embedding the first secret data using the PVD scheme. A stego image is created by embedding the second secret data using the maximum difference value and log function in the interpolated cover image. As a result, the proposed scheme embeds secret data twice. In particular, it is possible to embed secret data even during the interpolation process of an image that did not previously embed secret data. Experimental results show that the proposed scheme can transmit more secret data to the receiver while maintaining the image quality similar to other interpolation-based reversible data hiding schemes.

TMA 모델을 이용한 해양파 시뮬레이션 방법

이남경,백낙훈,김구진,유관우,Lee Nam-Kyung,Baek Nakhoon,Kim Ku Jin,Ryu Kwan Woo 한국정보처리학회 2005 정보처리학회논문지 A Vol.12 No.4

컴퓨터 그래픽스 분야에서는 해양파(ocean waves)를 표현하기 위한 여러가지 방법들이 있지만, 완전한 해결책은 아직까지 제시되지 못하고 있다. 해양파는 여러가지 원인에 의해 생성되지만, 가장 지배적인 요소는 바람과 중력에 의한 표면 중력파(surface gravity waves)이다. 본 논문에서는 해앙학 분야의 정밀한 해양파 모델에 기초하여, 실시간에 표면 중력파를 시뮬레이션하는 방법을 제시한다. 기존 연구들은 수심이 무한대라고 가정하는 Pierson-Moskowitz(PM) 모델[1]을 사용하여, 얕은 바다를 시뮬레이션하기에는 무리가 따랐다. 본 논문에서는 좀더 정밀한 Texel-Marsen-Arsloe(TMA) 모델[2]을 사용하여 더욱 사실적인 해양파를 표현할 수 있다. TMA 모델을 분석한 후, 3차원 컴퓨터 그래픽스 프로그램들에서 사용할 수 있는 실제적인 구현 모델(implementation model)을 정립하였고, 이를 구현한 프로토타입 시스템은 펜티엄-4 1.6GHz PC들에서 초당 30프레임 이상을 표시할 수 있음을 보였다. 본 논문에서 제안하는 방법은 기존 연구들에 비해, (1) 사용자가 제어할 수 있는 매개변수들이 더욱 다양해짐으로써, 사용자 요구에 적합한 파형(wave shape)들을 다양하게 생성할 수 있고, (2) 정밀한 해양파 모델을 사용하여, 얕은 바다에서도 더욱 사실적인 파도를 표현할 수 있다. In the field of computer graphics, we have several research results to display the ocean waves on the screen, while we still not have a complete solution yet. Though ocean waves are constructed from a variety of sources, the dominant one is the surface gravity wave, which is generated by the gravity and the wind. In this Paper, we Present a real-time surface gravity wave simulation method, derived from a precise ocean wave model in the oceanography. There are research results based on the Pierson-Moskowitz(PM) model[1], which assumes infinite depth of water and thus shows some mismatches in the case of shallow seas. In this paper, we started from the Texel, Marsen and Arsloe(TMA) model[2], which is a more precise wave model and thus can be used to display more realistic ocean waves. We derived its implementation model for the graphics applications and our prototype implementation shows about 30 frames per second on the Intel Pentium 4 1.6GHz-based personal computer. Our major contributions to the computer graphics area ill be (1) providing more user-controllable parameters to finally generate various wave shapes and (2) the improvement on the expression power of waves even in the shallow seas.