• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2003.06a
• /
• pp.1816-1819
• /
• 2003

As a result of milling operation, we expect to have burr at the outward edge of workpiece. Also, it causes undesirable problems such as deburring cost, low quality of machined surface, and bottleneck in manufacturing process. Though it is impossible to totally remove burr in machining, it is necessary to plan a machining process that minimizes the occurrence of burr. In this paper, a scheme is proposed which identifies the tool path of the milling operation with minimum burr. In the previous research, a Burr Expert System was developed where the feature identification, the cutting condition identification, and the analysis on exit burr formation are the key steps in the program. The Burr Expert System predicts which portion of workpiece would have the exit burr in advance so that we can calculate the burr length of each milling operation. Here, the critical angle determines whether the burr analyzed is an exit burr or not. So the burr minimization scheme becomes to minimize the burr with critical angle. By iterating all the possible tool paths in certain milling operation, we can identify the tool path with minimum burr.

• Korean Chemical Engineering Research
• /
• v.58 no.2
• /
• pp.307-312
• /
• 2020

Fluidized bed reactors operated in subatmospheric pressure has been focused because several industrial applications such as vacuum drying and plasma cvd requires reduced pressure fludization. However, the hydrodynamics of fluidized beds in subatmospheric pressure has not been extensively investigated. The pressure drop in the fluidized bed has been measured with variation of downstream pressures from 1.33 to 101.3 kPa in the shallow and deep fluidized beds under the sub-atmospheric pressures. The obtained minimum fluidization velocity of powders is a function of pressure due to the changes of gas density and mean free path. We can experimentally determine the critical Knudsen number and the critical pressure to define the slip regime significantly to influence the hydrodynamics of fluidized beds.

• Proceedings of the KOR-KST Conference
• /
• 1998.10a
• /
• pp.236-244
• /
• 1998

When the capacity and traffic operation at signalized intersections are analyzed in Korea, the unprotected left-turn saturation flow rate, which is an important parameter for the analysis, is estimated form the USHCM model. thus, exact analysis of the left-turn is not possible because of the difference of traffic environments between two contries. In order to improve this problem, it is undertaken in this study to develop techniques for the estimation of unprotected left-turn saturation flows based on Korean drivers' data. As study intersections, signalized or unsignalized intersections on the 6, 4 and 2 lane streets are selected. the data for the saturation flow measurement and gap-acceptance behavior analysis are inputed in a notebook computer on the sites. The critical acceptance gaps of the 6, 4, and 2 lane streets are analyzed to be 6.0 secs, 4.6 secs, and 4.3 secs respectively. the average minimum headway of the left-turn vehicle was observed to be 2.6 secs. As the model to estimate unportected left-turn saturation flows, the drew model is recommended for 6 and 4 lane streets, and a graph is suggested for the 2-lane street. As the values of the parameters of the Drew model, the 2.6 secs of this study is recommended for the average minimum headway of the left-turn. But, the critical acceptance gap varies according to the approach speed of opposing traffic and driver population, it requires field survey to measure the gap of an intersection; however, the values of the gaps studied in this study may be used for the general intersections in urban area in Korean.

• Proceedings of the KIEE Conference
• /
• 1988.07a
• /
• pp.315-318
• /
• 1988

THE STUDY ABOUT CHARACTERISTICS OF PHOTO RESIST ITSELF (MINIMUM RESOLUTION, DEPTH OF FOCUS MARGIN AND CRITICAL DIMENSION CONTROL LATITUDE) WAS DONE AND REPORTED. THREE TYPES OF PHOTO RESISTS WERE TESTED. THE FIRST IS THE LOW MOLECULAR WEIGHT PHOTO-RESIST SHOWING THE NARROW DISTRIBUTION OF MOLECULAR WEIGHT (LOW MOLECULAR WEIGHT CONTROL TYPE), THE SECOND IS A PHOTO-RESIST CONTAINING THE INNER CONTRAST ENCHANCEMENT MATERIAL (INNER CEM TYPE) AND THE THIRD IS A NORMAL PHOTO-RESIST (HIGH MOLECULAR WEIGHT TYPE). THE INNER CEM TYPE AND THE LOW MOLECULAR WEIGHT CONTROL TYPE PHOTO-RESIST ARE MORE IMPROVED PHOTO-RESISTS. IT PROVED THAT THE MINIMUM RESOLUTION WAS IMPROVED BY 0.2 - 0.3 um, THE DEPTH OF FOCUS MARGIN WAS IMPROVED BY 0.8 - 1.2 um AND THE C.D. CONTROL LATITUIDE WAS IMPROVED.

• Biomaterials and Biomechanics in Bioengineering
• /
• v.3 no.2
• /
• pp.71-84
• /
• 2016

The finite element method is wide used in simulation in the biomechanical structures, but a lack of studies concerning finite element mesh quality in biomechanics is a reality. The present study intends to analyze the importance of the mesh quality in the finite element model results from humeral structure. A sensitivity analysis of finite element models (FEM) is presented for the humeral bone and cartilage structures. The geometry of bone and cartilage was acquired from CT scan and geometry reconstructed. The study includes 54 models from same bone geometry, with different mesh densities, constructed with tetrahedral linear elements. A finite element simulation representing the glenohumeral-joint reaction force applied on the humerus during $90^{\circ}$ abduction, with external load as the critical condition. Results from the finite element models suggest a mesh with 1.5 mm, 0.8 mm and 0.6 mm as suitable mesh sizes for cortical bone, trabecular bone and humeral cartilage, respectively. Relatively to the higher minimum principal strains are located at the proximal humerus diaphysis, and its highest value is found at the trabecular bone neck. The present study indicates the minimum mesh size in the finite element analyses in humeral structure. The cortical and trabecular bone, as well as cartilage, may not be correctly represented by meshes of the same size. The strain results presented the critical regions during the $90^{\circ}$ abduction.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.10 no.1
• /
• pp.187-194
• /
• 2002

It has been reported that cracks in mechanical joints is generally under mixed-mode and there is critical inclined angle at which mode I stress intensity factor becomes maximum. The crack propagates in arbitrary direction and thus the prediction of crack growth path is needed to provide against crack propagation or examine safety. In order to evaluate the fatigue life of cracks in mechanical joints, horizontal crack normal to the applied load and located on minimum cross section is major concern but critical inclined crack must also be considered. In this paper mixed-mode fatigue crack growth test is performed far horizontal crack and critical inclined crack in mechanical joints. Fatigue crack growth path is predicted by maximum tangential stress criterion using stress intensity factor obtained from weight function method, and fatigue crack growth rates of horizontal and inclined crack are compared.

• Proceedings of the KIEE Conference
• /
• 2009.07a
• /
• pp.1491_1492
• /
• 2009

The impedance of a vertical grounding electrode is not lowered by expanding the dimension of the grounding electrode, and the length of thr vertical grounding electrode which shows the minimum value of the grounding impedance for each condition of frequency and soil characteristics is existent, and it is defined as Critical length. In this paper, the critical lengths for the vertical grounding electrodes are calculated by using the distributed parameter circuit model. The adequacy of the simulations has been confirmed by comparing the simulated results with the measured results.

• 제어로봇시스템학회:학술대회논문집
• /
• 2001.10a
• /
• pp.131.4-131
• /
• 2001

A lot of path planning algorithms have been developed to find the collision-free path with minimum cost. But most of them require complicated computations. In this paper, a thinning method, which is one of the image processing schemes, was adopted to simplify the path planning procedure. In addition, critical points are used to find the shortest-distance path among all possible paths from the start to the goal point. Since the critical points contain the information on the neighboring paths, a new path can be quickly obtained on the map even when the start and goal points change. To investigate the validity of the proposed algorithm, various simulations have been performed for the environment where the obstacles with arbitrary shapes exist. It is shown that the optimal paths can be found with relative easiness.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.5 s.176
• /
• pp.1231-1237
• /
• 2000

Dynamics of a rotating cantilever beam near its critical angular speed is investigated in this paper. The external, force is idealized as a periodic function which has the same period as the rotati ng frequency of the beam. The equations of motion are derived and transformed into a dimensionless form. A prescribed spin-up motion is employed for the rotating motion. Numerical study shows that the steady state and the transient responses of the beam are affected by the spin-up time constant and there exists a time constant at which the maximum transient response becomes minimum.

• Nuclear Engineering and Technology
• /
• v.34 no.1
• /
• pp.68-79
• /
• 2002

The approach for evaluating the critical heat flux (CHF) margin using the departure from nucleate boiling ratio (DNBR) concept has been widely applied to PWR core design, while DNBR in this approach does not indicate appropriately the CHF margin in terms of the attainable power margin-to-CHF against a reactor core condition. The CHF power margin must be calculated by increasing power until the minimum DNBR reaches a DNBR limit. The Critical Power Ratio (CPR), defined as the ratio of the predicted CHF power to the operating power, is considered more reasonable for indicating the CHF margin and can be calculated by a CPR orrelation based on the heat balance of a test bundle. This approach yields directly the CHF power margin, but the calculated CPR must be corrected to compensate for many local effects of the actual core, which are not considered in the CHF test and analysis. In this paper, correction of the calculated CPR is made so that it may become equal to the DNB overpower margin. Exemplary calculations showed that the correction tends to be increased as power distribution is more distorted, but are not unduly large.