• Journal of Ocean Engineering and Technology
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• v.29 no.3
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• pp.270-282
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• 2015

A submerged body moving near the free surface needs to maintain its attitude and position to accomplish missions. It is necessary to validate the performance of a designed controller before a sea trial. The hydrodynamic coefficients of maneuvering are generally obtained by experiments or computational fluid dynamics, but these coefficients have uncertainty. Environmental loads such as the wave exciting force and suction force act on the submerged body when it moves near the free surface. Thus, a controller for the submerged body should be robust to parameter uncertainty and environmental loads. In this paper, the six-degree-of-freedom equations of motions for the submerged body are constructed. The suction force is calculated using the double Rankine body method. An adaptive control method based on an artificial neural network and proportional-integral-derivative control are used for the depth controller. Simulations are performed under various depth and speed conditions, and the results show the effectiveness of the designed controller.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.9
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• pp.749-757
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• 2021

In transportation missions using quadrotor, the payload may change the model parameters, such as mass, moment of inertia, and center of gravity. Moreover, if position of the payload is constantly changing during flight, the effect can adversely affect the control performances. To handle this issue, we suggest Model Reference Adaptive Control based on Linear Quadratic Regulator(LQR+MRAC) to compensate the uncertainty caused by payload. Firstly, the mathematical modeling with the fixed payload is derived. Second, Linear Quadratic Regulator (LQR) is used to design the reference model and baseline controller. Also, through the Stability method, Adaptive law is derived to estimate the model parameters. To verify the performance of proposed control scheme, we compared LQR and LQR+MRAC in situations where uncertainties exist. And, when the disturbance exist, the classic MRAC and proposed controller is compared to analyze the transient response and robustness.

• Korean Journal of Optics and Photonics
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• v.35 no.2
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• pp.61-70
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• 2024

We demonstrate a laser power meter calibration system based on 12-diode laser sources coupled to single-mode fibres in a wavelength range from 400 to 1,600 nm. In our system, three laser power controllers ensure that the output power uncertainty of all laser sources is less than 0.1% (k=2). In addition, all laser beams are adjusted to have similar beam sizes of approximately 2 mm (1/e²-width) at the measurement position to minimise unmeasured laser power on a detector. As a reference detector, we use an integrating sphere combined with silicon and indium gallium arsenide photodiodes to minimise the non-uniformity and non-linearity of responsivity. The minimum uncertainty of the calibration system is estimated to be 1.1% (k=2) for most laser wavelengths.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.4
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• pp.436-442
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• 2011

To obtain the engine output correctly is basically very important factor for estimating a engine performance. But, it has been reported that the IHP measured from electronic indicator such as MIPS(Mean Indication Pressure System) has a deviation compared to mechanical indicator. It was reported by authors that the uncertainty of crank angle for TDC position could be one of the reasons. In this paper, the uncertainty of crank angle for TDC position and its influence to engine output were investigated respectively about M/E and G/E for marine diesel engines. For the purpose, two sampling methods of pressure in cylinder were considered which were 'angle base sampling' and 'time base sampling'. Angle base sampling is real crank angle acquired from angle encoder which is attached to crank shaft and time base sampling is crank angle calculated by detected revolution with Z-pluse of encoder. Time base sampling is same method of MIPS. This paper concluded that time base sampling method is not suitable for obtaining the output of marine diesel engine on board because of instantaneous speed variation and load fluctuation. Also it is verified that the variation of engine speed by load fluctuation should be one of reasons additionally in case of M/E.

• Journal of the Institute of Convergence Signal Processing
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• v.12 no.1
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• pp.67-75
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• 2011

This paper presents the systematic optimal design of an overlapped ultrasonic sensor ring for high performance obstacle detection using effective beam overlap. Basically, a set of low directivity ultrasonic sensors of the same type are arranged in a circle at regular intervals with their beams overlapped. First, both real and simplified beam patterns of an ultrasonic sensor and several sensor models for obstacle position estimation within its beam pattern are introduced. Second, the obstacle detection range of an overlapped ultrasonic sensor ring and its simple sensor model for obstacle position estimation are described. Third, for both conic and non-conic shaped beam pattern, the design indices of an overlapped ultrasonic sensor ring for minimal positional uncertainty in obstacle detection are defined. Fourth, the constraints imposed on the structural parameters of an overlapped ultrasonic sensor ring to guarantee non empty beam overlap and to avoid excessive beam overlap are derived. Fifth, the optimal number of ultrasonic sensors for a given radius of an overlapped ultrasonic sensor ring and the optimal radius of an overlapped ultrasonic sensor ring are determined. Throughout this paper, the MA40B8 from Murata Inc. is taken as a representative commercial low directivity ultrasonic sensor.

• THE INTERNATIONAL COMMERCE & LAW REVIEW
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• v.17
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• pp.251-293
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• 2002

The study is a comparative and analytical study which comprises of the analysis of the rules of the buyer's right to withhold performance where the seller delivers defective goods or documents of three legal systems; the CISG, English law and Korean law. The purposes underlying this study are twofold. The first is to clarify the current position as to the right of withholding performance in the event of the seller's tender of defective goods or documents in Korean law, CISG and English law so that it may assist the parties in drafting the buyer's right to withhold performance in their own contract. The second is to compare the rules of one jurisdiction with those of other jurisdictions and to evaluate the rules in light of the practical functions and benefits of the right to withhold performance and the discipline of comparative law the basic question of which is whether a solution from one jurisdiction may facilitate the systematic development and reform of another jurisdiction. It shows that each jurisdiction does not have any provision or case law specifically dealing with the buyer's right to withhold performance where the seller delivers the goods which are defective in terms of quality or quantity. The absence of such provision or case in each jurisdiction has resulted in either disputes or uncertainty. However, the study executed in light of the primary functions and benefits of the right in practice and the discipline of comparative law reveals that, first, the view in English law which is against recognizing the right may not be justified when one considers the practical importance of having the right and the position taken by the CISG as a well developed and modernized law, second, the view in Korean law which argues that the principle of specific goods dogma on which it is based is extended even to substitutable or repairable goods cannot be also justified on the ground of one's ordinary expectation and the position under the CISG and English law which imposes a contractual duty to deliver non-defective goods on the seller insofar as the buyer's payment is deemed to be made in exchange for the seller's delivery of non-defective goods and they are substitutable or repairable. Regarding the right to withhold performance in the event of the seller's tender of defective documents, the study shows that the relatively detailed rules in English law may be utilized as a guideline to fill the gap in the CISG and Korean law in terms of the practicability and appropriateness to govern documentary sales. Furthermore, it is found that the position in English law which confers on the buyer the right to withhold performance for a trivial defect in documents may be unreasonable in terms of one's need to enable justice to be done in individual cases.

• Journal of the Korean Magnetics Society
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• v.12 no.6
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• pp.206-211
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• 2002

We have constructed a new kind of magnetic motion capture sensor based on the pulse magnetic field method. 3-orthogonal magnetic pulse fields were generated in turns only one period of sinusoidal waveform using 3-orthogonal magnetic dipole coils, ring counter and analog multiplier. These pulse magnetic fields were measured with 3-orthogonal search coils, of which induced voltages by the x-, y-, and l-dipole sources using S/H amplifier at the time position of maximum induced voltage. Using the developed motion capture sensor, we can measure position of sensor with uncertainty of ${\pm}$0.5％ in the measuring range from ${\pm}$0.5 m to ${\pm}$1.5 m.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.2
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• pp.185-198
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• 2016

In this work, experimental errors from an impact hammer test were investigated to develop a statistic-based technique for updating a finite element model. Digital signal processing was analyzed by using theoretical models and experiments when errors occurred during the experimental procedure. First, the duration time and peak level of the excitation signal, the stiffness and position of elastic springs connecting the specimen as well as the support, position and mass of the accelerometer were considered as error factors during the experiment. Then the picket fence effect, leakage, and exponential window function were considered as candidate error factors during the digital signal processing. Finally, methods to reduce errors are suggested.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.10
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• pp.116-122
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• 2016

This paper proposes a practical object shape reconstruction method using an underwater imaging sonar. In order to reconstruct the object shape, three methods are utilized. Firstly, the vertical field of view of imaging sonar is modified to narrow angle to reduce an uncertainty of estimated 3D position. The wide vertical field of view makes the incorrect estimation result about the 3D position of the underwater object. Secondly, simple noise filtering and range detection methods are designed to extract a distance from the sonar image. Lastly, a low pass filter is adopted to estimate a probability of voxel occupancy. To demonstrate the proposed methods, object shape reconstruction for three sample objects was performed in a basin and results are explained.

• Journal of Advanced Navigation Technology
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• v.23 no.5
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• pp.352-360
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• 2019

This paper proposes a docking assessment algorithm for an autonomous underwater vehicles (AUVs) with sensor uncertainties. The proposed algorithm consists of two assessments, state assessment and probability assessment. The state assessment verifies the reachability by comparing forward distance to the docking station with expected distance to reach same depth as the docking station and necessity for correcting its route by comparing calculated inaccessible areas based on turning radius of the AUV to position of the docking station. When the AUV and the docking station is close enough and the state assessment is satisfied, the probability assessment is conducted by computing success probability of docking based on the direction angle, relative position to the docking station, and sensor uncertainties of the AUV. The final output of the algorithm is decided by comparing the success probability to threshold whether to try docking or to correct its route. To verify the validation of the suggested algorithm, the scenario that the AUV approaches to the docking station is implemented through Matlab simulation.