• Journal of the Society of Naval Architects of Korea
• /
• v.57 no.3
• /
• pp.160-167
• /
• 2020

A two-stroke diesel engine and a propeller normally adopted in large merchant ships are regarded as major ship vibration sources. They are directly connected and generate various excitation components proportional to the rotating speed of diesel engine. Among the components, the magnitude of two excitation components with the same frequency generated by both engine and propeller can be compensated by the adjustment of their phase difference. It can be done by the optimization of propeller assembly angle but requires a number of burdensome trials to find the optimal angle. In this paper, the efficient estimation method to determine optimal propeller assembly angle is proposed. Its application requires the axial vibration measurement in sea trial and the numerical vibration analysis for propulsion shafting which can be substituted by additional vibration measurement after one-trial modification of propeller assembly angle. In order to verify the validity of the proposed method, the phase difference between two fifth order excitation components generated by both diesel engine and propeller of a real ship is calculated by the finite element analysis and its result is indirectly validated by the comparison of axial vibration responses at intermediate shaft obtained by the numerical analysis and the measurement in sea trial. Finally, it is numerically confirmed that axial vibration response at intermediate shaft at a resonant speed can be decreased more than 87 % if the optimal propeller assembly angle determined by the proposed method is applied.

• Journal of Advanced Marine Engineering and Technology
• /
• v.19 no.1
• /
• pp.60-70
• /
• 1995

In the field of marine transportation the energy saving is one of the most important factors for profit. In order to reduce the fuel oil consumption the ship's propulsion efficiency must be increased as much as possible. The propulsion efficiency depends upon a combination of an engine and a propeller. The propeller has better efficiency as lower rotational speed. This situation led the engine manufacturers to design the engine that has lower speed, longer stroke and a small number of cylinders. Consequently the variation of rotational torque became larger than before because of the longer delay-time in the fuel oil injection process and an increased output per cylinder. As this new trends the conventional mechanical-hydrualic governors for engine speed control have been replaced by digital speed controllers which adopted the PID control or the optimal control algorithm. But these control algorithms have not enough robustness to suppress the variation of the delay-time and the parameter pertubation. In this paper we consider the delay-time and the perturbation of engine parameters as the modeling uncetainties. Next we design the controller which has zero offset in steady state engine speed, based on the two-degree-of-freedom control theory and $\mu$-synthesis. Thd validity of the controller is investigated through the response simulation. We use a personal computer and an analog computer as the digital controller and the engine (plant) part respectively. And, we certify that the designed controller maintains its performance even though the engine parameters may vary.

• Korean Journal of Radiology
• /
• v.21 no.4
• /
• pp.450-461
• /
• 2020

Objective: We performed a meta-analysis to evaluate the agreement of cardiac computed tomography (CT) with cardiac magnetic resonance imaging (CMRI) in the assessment of right ventricle (RV) volume and functional parameters. Materials and Methods: PubMed, EMBASE, and Cochrane library were systematically searched for studies that compared CT with CMRI as the reference standard for measurement of the following RV parameters: end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), or ejection fraction (EF). Meta-analytic methods were utilized to determine the pooled weighted bias, limits of agreement (LOA), and correlation coefficient (r) between CT and CMRI. Heterogeneity was also assessed. Subgroup analyses were performed based on the probable factors affecting measurement of RV volume: CT contrast protocol, number of CT slices, CT reconstruction interval, CT volumetry, and segmentation methods. Results: A total of 766 patients from 20 studies were included. Pooled bias and LOA were 3.1 mL (-5.7 to 11.8 mL), 3.6 mL (-4.0 to 11.2 mL), -0.4 mL (5.7 to 5.0 mL), and -1.8% (-5.7 to 2.2%) for EDV, ESV, SV, and EF, respectively. Pooled correlation coefficients were very strong for the RV parameters (r = 0.87-0.93). Heterogeneity was observed in the studies (I² > 50%, p < 0.1). In the subgroup analysis, an RV-dedicated contrast protocol, ≥ 64 CT slices, CT volumetry with the Simpson's method, and inclusion of the papillary muscle and trabeculation had a lower pooled bias and narrower LOA. Conclusion: Cardiac CT accurately measures RV volume and function, with an acceptable range of bias and LOA and strong correlation with CMRI findings. The RV-dedicated CT contrast protocol, ≥ 64 CT slices, and use of the same CT volumetry method as CMRI can improve agreement with CMRI.

• The Journal of Korean Academy of Orthopedic Manual Physical Therapy
• /
• v.18 no.2
• /
• pp.9-21
• /
• 2012

Background: The purpose of this study was to analysis and to give information about the type of orthopedic manual physical therapy research by KAOMPT Journal from 1995 (Volume 1) to 2011 (Volume 17). The number of research paper were total 212 studies. Method: The studies were analysed with retrospective descriptive study. The results of data analysis was as follow; Results & Conclusion: 1. The studies was analysed 6 study field; manual therapy for disease field (130 studies), the therapeutic (16 studies), the effects of manual therapy education method, learning model (7 studies), medical insurance, history, politics of manual therapy (3 studies), and others (19 studies). 2. In the manual therapy of disease field, there were 4 groups of disease; bone disease (43 studies), soft tissue and muscles disease (57 studies), nerve disease(24 studies), and the others (6 studies). The main disease were low back pain, stroke, HIVD. 3. In the assessment, and intervention field, there were only 5 studies during from 1995 to 2000, but the studies from 2001 to 2011 were more increased 21 studies. 4. In the effects of manual therapy education method, learning model, there were very few studies (7 studies), so it will be needed more studies in this field. 5. In the other fields such as more political issue, history, medical insurance for the manual therapy there were few studies, so it will be needed more advanced studies in this field.

• Tribology and Lubricants
• /
• v.31 no.5
• /
• pp.221-228
• /
• 2015

It is possible to prevent a piston from contacting the cylinder by changing the shape of the piston or by applying micro-textures, such as micro-grooves or micro-holes, over the piston surface. Usually, the minimum radial clearance reaches its minimum value at the beginning of the suction stroke because the pressure around the piston is low and almost axisymmetric such that the net pressure force on the piston is not sufficiently high to support the piston from touching the cylinder. In this study, we apply a series of saw-tooth-shaped grooves on the piston surface, and numerically investigate the effects of groove depth, groove angle, and the number of grooves with radial clearance variations using a finite difference method. We conduct a dynamic analysis of the piston for various changes in groove geometries to obtain the minimum radial clearance variation for the entire compression cycle. The minimum radial clearance increases while friction loss decreases when we apply the series of saw-tooth-shaped grooves on the piston. In addition, we analyze the impact of the change in the groove shape variable due to changes in radial clearance. Leakage variations are relevant to radial clearance, but have almost no effect on the groove parameters.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.33 no.1
• /
• pp.46-58
• /
• 1997

The energy saving is one of the most important factors for profit in marine transportation. In order to reduce the fuel oil consumtion the ship's propulsion efficiency must be increased as possible. The propulsion efficiency depends upon a combination of an engine and a propeller. The propeller has better efficiency as lower rotational speed. This situation led the engine manufacturers to design the engine that has low speed, long stroke and a small number of cylinders. Consequently, the variation of rotational torque became larger than before because of the longer delay-time in fuel oil injection process and an increased output per cylinder. As this new trends the conventional mechanical-hydrualic governors for engine speed control have been replaced by digital speed controllers which adopted the PID control or the optimal control algorithm. But these control algorithms have not enough robustness to suppress the variation of the delay-time and the parameter perturbation. In this paper we consider the delay-time and the perturbation of engine parameters as the modeling uncetainties. Next we design the robust servo controller which has zero offset in steady state engine speed, based on H sub($\infty$) control theory. The validity of the controller was investigated through the response simulation. We used a personal computer and an analog computer as the digital controller and the engine (plant) part respectively. And, we could certify that the designed controller maintains its robust servo performance even though the engine parameters may vary.

• Journal of International Academy of Physical Therapy Research
• /
• v.1 no.2
• /
• pp.107-112
• /
• 2010

The majority of strokes are caused by ischemia and result in brain tissue damage, leading to problems of the central nervous system including hemiparesis, dysfunction of language and consciousness, and dysfunction of perception. The purpose of this study was to investigate the effects of Poly(ADP-ribose) polymerase(PARP) on necrosis in neuronal cells that have undergone needle electrode electrical stimulation(NEES) prior to induction of ischemia. Ischemia was induced in male SD rats(body weight 300g) by occlusion of the common carotid artery for 5 min, after which the blood was reperfused. After induction of brain ischemia, NEES was applied to Zusanli(ST 36), at 12, 24 and 48 hours. Protein expression was investigated using immuno-reactive cells, which react to PARP antibodies in cerebral nerve cells, and Western blotting. The results were as follows: In the cerebral cortex, the number of PARP reactive cells after 24 hours significantly decreased(p<.05) in the NEES group compared to the GI group. PARP expression after 24 hours significantly decreased(p<.05) in the NEES group compared to the GI group. As a result, NEES showed the greatest effect on necrosis-related PARP immuno-reactive cells 24 hours after ischemia, indicating necrosis inhibition, blocking of neural cell death, and protection of neural cells. Based on the results of this study, NEES can be an effective method of treating dysfunction and improving function of neuronal cells in brain damage caused by ischemia.

• Journal of Korean Physical Therapy Science
• /
• v.5 no.4
• /
• pp.785-794
• /
• 1998

We have made a survey of 40 patients in the university hospitals and oriental medical centers in Seoul from Sep. 1, 1997 to Mar. 1, 1998. We sampled 25 of them and the result shows that there were 12 MCA damaged patients(48%), 5 SAH(20%), 5 ACA(20%), 2 PCA (8%), 1 PCOA(4%). The number of MCA patients were the most. 1. As the cause of each disease, 4 of the 12 MCA damaged patients(33.35%) have infarction and cerebral hemorrhage, 2 of 5 SAH patients(40%) have cerebral hemorrhage and head injury, 3 ACA damaged patients have cerebral hemorrhage. 11 of 25 brain bloodvessel damaged patients(44%) were hemorrhage patients. 2. Rt. hemiparesis was the main symptom of 6 of 12 MCA damaged patients(50%) and 3 of 5 SAH patients(60%), and the main symptom of 3 of 5 ACA patients(60%) was Lt. hemiparesis. The main symptom of 13 of 25 brain bloodvessel damaged patients(52%) was Lt. hemiparesis 11 of them(44%) Rt. hemiparesis, and 1 of them(8.3%) Quadriplegia. 3. Language was the most well preserved function. 12 MCA damaged patients could understand language. 4. Retraction of shoulder girdle, among VIE flexor synergy, was the most frequent element because 9 of 12 MCA damaged patients had it. Among VIE flexor synergy, 5 SAH patient's most frequent synergy was Elbow flexion because all of them had it. All of 5 ACA damaged patients have shoulder girdle elevation, shoulder joint, hyperextension, abduction, and external rotation among VIE flexor synergy. 5. 7 of 12 MCA damaged patients(58.3%) were stereognosis handicapped patients, 3 of 5 SAH patients(60%) have handicap of position sense, light touch, and temperature, 3 of 5 ACA patients(60%) have position handicap. 13 of brain bloodvessel damaged patients(52%) have light touch handicap. 6. 8 of MCA damaged patients(66.7%) have facial palsy, 4 of SAH damaged patients(80%) have memory and action decline, and 3 of ACA damaged patients(60%) have action decline and facial palsy. The problem of Hemiplegia is very extensive from muscle weakness, atrophy, or deformation to psychical problems. Therefore physical therapists should have sufficient interest in psychological handicap as well as physical handicap as they deal with adult hemiplegia.

• Journal of Sensor Science and Technology
• /
• v.31 no.1
• /
• pp.51-56
• /
• 2022

In this study an efficient method for detecting and monitoring engine misfiring, focusing on minute speed changes in the crankshaft is proposed., Its validity is verified using various misfiring cases. Typically, the crankshaft speed fluctuates around the normal value depending on the engine misfiring status. Even a minute speed change in the crankshaft can be estimated by measuring the rotation time of each tooth of the 118-tooth flywheel attached to the crankshaft with a 2-MHz timer. Therefore, a speed pattern for an in-line six-cylinder engine consists of 236 tooth rotation speeds corresponding to the two rotations of the crankshaft, in which all the cylinders complete four-stroke cycle. FFT analysis can reduce the number of components of a speed pattern from 236 to just four major components: - fundamental frequency_(f), 2f, 3f, 6f., - This makes the comparison of the misfiring cases simpler and faster. In the experiment, five engine status cases (one normal firing and, four misfiring cases) were simulated. While the 6f component was the largest for the normal case, the f component increased as misfiring occurred one, two apart, and two consecutive times. The 3D FFT pattern comprising the ratio of f, 2f, and 3f, 6f showed that the distance between the misfiring and normal states was larger

• Journal of the Society of Naval Architects of Korea
• /
• v.35 no.3
• /
• pp.71-78
• /
• 1998

Recently, modern long-stroke diesel engines with small number of cylinders have been installed for energy saving and simpler maintenance. These kinds of low speed diesel engine produce large torsional vibration in the shafting, which induces the excessive vibratory stresses in the shafting and large propeller thrust variation. This thrust variation excites vibrations of the shafting and superstructure in the longitudinal direction. Up to now the deteriministic analysis of coupled vibration of marine shafting system has been performed. In this paper probabilistic analysis method of the marine diesel propulsion shafting system under coupled axial and torsional vibrations is presented. For the purpose of this work, the torsional and axial vibration excitations of engine and propeller are assumed to be probabilistic while the lateral excitation is assumed to be deterministic. The probabilistic analysis is based on a response surface and Monte-Carlo simulation. Numerical results based on the proposed method are compared with results calculated using the conventional deterministic analysis method. The results obtained make it clear that the proposed method gives a substantial increase in information about shafting behaviour as compared with the deterministic method.