Pebble flow in the HTR-PM reactor core by GPU-DEM simulation: Effect of friction

Zhang Zuoyi,Zou Quan,Gui Nan,Xia Bing,Liu Zhiyong,Yang Xingtuan 한국원자력학회 2024 Nuclear Engineering and Technology Vol.56 No.9

The high-temperature gas-cooled reactor (HTGR) with spherical fuel elements contains complex pebble flow. The flow behavior of pebbles is influenced by various factors, such as pebble density, friction coefficient, wall structure, and discharge port size. Using a GPU-DEM numerical model, the effects of the friction coefficient on the cyclic loading and unloading of pebbles in the full-scale HTR-PM are studied. Numerical simulations with up to 420,000 spherical pebbles are conducted. Four sets of friction coefficient values are determined for comparative analysis based on experimental measurements. Discharging speed, residence time, stress, porosity, and velocity distribution are quantitatively analyzed. In addition, a comparison with the CT-PFD experiment is carried out to validate the numerical model. The results show that near-wall retention phenomena are observed in the reactor core only when using large friction coefficients. However, using friction coefficient values closer to the measured experimental values, the pebble bed in HTR-PM exhibited good flow characteristics. Furthermore, the friction coefficient also influences the porosity and velocity distribution of the pebble bed, with lower friction coefficients resulting in lower overall stress in the bed. The discharge outlet’s influence varies with different friction coefficient values. In summary, this study demonstrates that the value of the friction coefficient has a complex influence on the pebble flow in HTR-PM, which provides important insights for future numerical and experimental studies in this field.

디스크 브레이크의 제동마찰 및 마멸특성에 관한 실험적 연구

김청균(Chung Kyun Kim),이병관(Boung Kwan Lee),김한구(Han Goo Kim) 한국트라이볼로지학회 2006 한국윤활학회지(윤활학회지) Vol.22 No.3

This paper presents the braking friction and wears on the rubbing surfaces of a friction pad-disk brake. In this study, four friction disk specimens are sampled from unused and used disks in which are taken from the disk brake system when the friction induced vibration and noise problems have been occurred during a braking period at a running period of 10,000 ㎞, 20,000 ㎞, and 30,000 ㎞ in random. The experimental results indicate that the tribological characteristics of an unused disk brake shows equal and stable as a friction coefficient and temperature distributions during a braking friction/wear test period including a total friction mode from the start to running periods. But the used disk brake shows unstable and uneven friction modes between an outside and inside rubbing surfaces of a disk brake in terms of a friction coefficient and wears. This may lead to a friction induced friction vibration and noise problems of a used disk brake.

주행로봇 제어를 위한 험지의 최대마찰계수 추정

강현석(Hyun-Suk Kang),곽윤근(Yoon Keun Kwak),최현도(Hyun-Do Choi),정해관(Hae-Kwan Jeong),김수현(Soo-Hyun Kim) 제어로봇시스템학회 2008 제어·로봇·시스템학회 논문지 Vol.14 No.10

When mobile robots perform the mission in the rough terrain, the traversability depended on the terrain characteristic is useful information. In the travers abilities, wheel-terrain maximum friction coefficient can indicate the index to control wheel-terrain traction force or whether mobile robots to go or not. This paper proposes estimating wheel-terrain maximum friction coefficient. The existing method to estimate the maximum friction coefficient is limited in flat terrain or relatively easy driving knowing wheel absolute velocity. But this algorithm is applicable in rough terrain where a lot of slip occurred not knowing wheel absolute velocity. This algorithm applies the tire-friction model to each wheel to express the behavior of wheel friction and classifies slip-friction characteristic into 3 major cases. In each case, the specific algorithm to estimate the maximum friction coefficient is applied. To test the proposed algorithm’s feasibility, test bed(ROBHAZ-6WHEEL) simulations are performed, And then the experiment to estimate the maximum friction coefficient of the test bed is performed. To compare the estimated value with the real, we measure the real maximum friction coefficient. As a result of the experiment, the proposed algorithm has high accuracy in estimating the maximum friction coefficient.

Experimental investigation of friction noise on lubricated contact

남재현,백종수,도현철,강재영 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.12

In order to remove friction noise, a lubricant is normally applied on the friction surface either after cleansing the contact surface or without any surface treatment. As the friction continues, the lubrication performance deteriorates and the friction noise can reoccur in the both cases, but the cause of friction noise may be different. This study originally investigates the mechanism of friction noise under a lubricant on either the clean or contaminated surface. During the friction noise test, the vibration and sound pressure, the changes in friction coefficient and the characteristics of the contact surfaces are measured for the two lubrication scenarios. Particularly, the surface image and chemical state on the contact area are measured by SEM/EDS analysis in sequence. The results show that friction noise under the lubrication on the clean surface is induced by the reduction of the lubricant causing the increase of friction coefficient. For the lubrication on the contaminated surface by wear debris, the lubricant is mixed and contaminated with wear debris, and then friction noise eventually occurs with the negative slope of the friction-velocity curve in the absence of the increase of friction coefficient.

마찰계수의 비접촉 추정을 위한 영상정보 활용방법

김두규(Doo-gyu Kim),김자영(Ja-young Kim),이지홍(Jihong Lee),최동걸(Dong-Geol Choi),권인소(In-So Kweon) 大韓電子工學會 2010 電子工學會論文誌-SP (Signal processing) Vol.47 No.4

본 논문에서는 마찰계수의 비접촉 추정을 위한 영상정보 활용방법을 제안한다. 마찰계수는 이동체의 도로주행 또는 장애물 극복에 있어 매우 중요한 요소이다. 이동체가 이동경로의 마찰계수를 미리 알 수 있다면 이동성향상을 기대할 수 있다. 본 논문의 마찰계수 추정방법은 영상정보를 활용하기 때문에 이동체가 지면과 접촉하기 전에 마찰계수를 추정 할 수 있다는 장점이 있다. 마찰계수의 비접촉 추정을 위한 영상정보 활용방법은 마찰계수측정실험과 물질그룹생성을 포함한 학습단계와 물질그룹 분류과정과 마찰계수 함수 활용을 포함한 마찰계수 추정단계로 구성되어 있으며 물질 조성비를 생성하는 영상처리는 두 단계에 모두 포함된다. 이 과정을 통해 얻은 마찰계수는 무인이동로봇이 이동경로 진입 전에 미끄러움을 판단하여 미끄럼지역을 회피 할 수 있도록 하며, 저속으로 이동이 가능한 경우 미끄럼이 발생하지 않는 적정속도를 계산하는데 확용 가능하다. 본 논문에서 사용한 지형의 마찰계수와 영상정보는 마찰계수 측정실험을 통해 취득하였다. 마찰계수 추정방법을 평가하기 위해 실험지형의 실제 마찰계수와 추정 마찰계수의 차이를 비교하였다. In this paper, we proposed an algorithm for utilizing visual information for non-contact predicting method of friction coefficient. Coefficient of friction is very important in driving on road and traversing over obstacle. Our algorithm is based on terrain classification for visual image. The proposed method, non-contacting approach, has advantage over other methods that extract material characteristic of road by sensors contacting road surface. This method is composed of learning group(experiment, grouping material) and predicting friction coefficient group(Bayesian classification .prediction function). Every group include previous work of vision. Advantage of our algorithm before entering such terrain can be very useful for avoiding slippery areas. We make experiment on measurement of friction coefficient of terrain. This result is utilized real friction coefficient as prediction method. We show error between real friction coefficient and predicted friction coefficient for performance evaluation of our algorithm.

Estimation of the Road Friction Coefficient Using a Particle Filter

Do Ui Hong,ChanHo Park,GiSung Gwak,Sung-Ho Hwang 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.춘계 No.-

In vehicle driving safety, the friction coefficient is the important factor in deciding braking distance. The road friction coefficient manifests non-Gaussian states. In this paper, we use a particle filter, which is a simulation-based approach and which approximates the posterior Probability Density Function (PDF), to estimate the road friction coefficient. We derive the equation of the friction coefficient from the Free Body Diagram (FBD) of the vehicle. Using this equation, we find the μ-slip curve for each different road condition. Through the μ-slip curve, we can determine the road friction coefficient by interpolation. We perform the simulation by Carsim, and the result shows that the particle filter tracks the friction coefficient more accurately than before.

메조페이스 핏치계 탄소/탄소 복합재료의 제조 및 마찰 마모특성

박종규,이진용,하헌승,임연수,이승구 한국세라믹학회 1998 한국세라믹학회지 Vol.35 No.9

This study is concerned with the production of carbon fiber reinforced carbon(C/C) with polyaromatic mesophase pitch as matrix precursor and with the investigation of friction-wear characteristics in ambient air using a constant speed type of friction tester. The main problem in using the polyaromatic mesophase as the matrix precursor is the high viscosity which may limit the complete impregnation of the fiber preform in the vacuum. To solve these problems two dimensional carbon fiber fabrics were infiltrated with meso-phase pitch in the pitch impregnator. After the impregnation and the heat treatment process. C/C com-posites were characterized by density porosity to monitor the influence of high pressure and temperature. It showed that the bulk density was increased and the apparent porosity and the density increasing rate was reduced as repeating the impregnation the carbonization and the heat treatment. The friction-wear charac-teristics of C/C composites were investigated by measuring the average friction coefficient and the specific wear rate as functions friction speed and friction pressure using a constant speed type of friction tester. C/C composite4s showed the average friction coefficient to be reduced as increasing the friction speed and the friction pressure.

FRICTIONAL CHARACTERISTICS OF STEEL SHEETS USED IN AUTOMOTIVE INDUSTRY

T. TRZEPIECI SKI,A. BAZAN,H. G. LEMU 한국자동차공학회 2015 International journal of automotive technology Vol.16 No.5

In this paper the results of experimental tests aimed to determine the friction coefficient in sheet metal forming operations for various sheet metal materials and at different operative conditions are presented. The research has considered the frictional characterization of three kinds of drawing quality steels that are commonly used in automotive industry. These are a drawing quality steel (DQ), a deep drawing quality steel (DDQ), and extra deep drawing quality steel (EDDQ). For measurement of the sheet surface topography, a 3D stylus instrument Alicona InfiniteFocus was used. To determine the friction coefficient three tribological tests, i.e. a strip drawing test, a draw bead test and a pin-on-disc tribometer, have been conducted. The experimental results have ascertained several relationships showing the effect of sheet metal surface roughness, lubricant conditions and sheet orientation on the value of friction coefficient in sheet metal forming processes. The results further showed that the surface topography and sample orientation in the rolling direction of the sheet are significant factors that influence the friction coefficient. It was found that the tested steel sheets, selected from automotive industry applications, exhibit anisotropic resistance to the friction corresponding to the measured orientation in relation to the rolling direction of the sheet.

D2 공구강과 접촉시의 두 자동차체용 강판의 마찰 거동

김종민(Chongmin Kim),이정욱(Jeong-Uk Lee),Frederic Barlat,이명규(Myoung-Gyu Lee) 한국소성가공학회 2013 한국소성가공학회 학술대회 논문집 Vol.2013 No.5

The application of advanced high strength steels generally makes it necessary to use higher tool-sheet contact pressures compared with those used for forming low-strength steel, and it will lead to changes in frictional behavior significantly, which in turn change the final product characteristics. In order to understand frictional behaviors between steel sheets and tool materials under high contact stresses present in real stamping conditions, a novel friction tester was conceived, fabricated and used. This tester can generate high normal loads, as high as 625 MPa, whereas traditional friction testers were limited to 10 MPa or less. A mild steel and a TRIP780 steel were paired with Cr-coated D2 tool steel, and friction behaviors were observed under various conditions, including the use of lubricants, different sliding speeds and different normal contact stresses. The coefficient of friction decreased at a low contact pressure as the sliding velocity increased. The contact pressure had a significant effect, albeit too complex to be explained by simple models. The magnitude of change of friction constant due to changes in experimental conditions was enough to affect spring-back of automotive body panels significantly, thereby revealing the inadequacy of the traditional Coulomb’s Law of Friction. It was also evident that lubricant effects must be studied coupled with the contact pressure and sliding speed.

브레이크 패드에 함유된 아라미드 섬유와 미네랄 섬유의 마찰특성 연구

공지운(Ji Woon Kong),박정환(Jung Hwan Park),정진오(Jin Oh Chung),김향래(Hyang Rae Kim) 한국자동차공학회 2007 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

Friction characteristics of automotive friction materials according to the types of fiber were investigated by using a 115 scale brake dynamometer. fiber materials used in the study are aramid, mineral fiber respectively, while keeping other ingredients, such as binders, lubricants, abrasives, fillers the same. In the entire mode of friction test the friction coefficients of all the specimens show different among different pads even under the same temperature condition. In the effectiveness test, friction coefficients decrease with increase in the mineral fiber and aramid-containing friction material FB4 shows the highest coefficients. In the 1st fade test, fade phenomena is decreased with increase in the mineral fiber. The fade rate of FB1(scotching) is higher than the FB1. And 2nd fade rate is higher than 1st fade rate for each specimen. All the specimens tested showed a good recovery rate. The standard deviations of friction coefficient during entire mode for all the specimens were more stable with increase in the mineral fiber and FB1(scotching) is more stable than FB1.