• Journal of Ocean Engineering and Technology
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• v.27 no.6
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• pp.22-26
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• 2013

The purpose of this study was to improve the design of a mooring line by attaching a lumped mass to it on the seabed. A numerical analysis of the redesigned mooring system is performed to analyze the effect of the weight of the attached lumped mass using the commercial software Orcaflex. The ultimate tension of the mooring system with the lumped mass is compared with that of a bare mooring line in the original design. An appropriately designed weight for the lumped mass is found to induce a critical lifted point in the mooring line by floater motion in the ultimate condition to move toward the floater position from the anchor point, while maintaining a similar safety factor for the mooring line. On the other hand, it is shown that excess weight for the lumped mass induces snapping in a mooring line, resulting in low safety factor for the mooring system. The distance between lumped weights is shown to be a minor parameter affecting the safety of a mooring line, although a shorter line has an advantage from an economic point of view. Using the optimal weight for the lumped mass attached to the mooring line on a seabed reduces the mooring line length and installation area occupied by a mooring system under real sea conditions.

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.6
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• pp.44-52
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• 1997

As part of the effort to reduce the weight of powertrain, a hollow crankshaft has been designed. The mass reduction of the crankshaft changes the dynamic properties of the crankshaft such as moment of inertia, and torsional, bending stiffness. The purpose of this paper is to compare the dynamic behavior of the hollow crankshaft with that of the original, solid crankshaft. Global dynamic behavior of the crankshaft is analyzed bgy the transfer matrix method(TMM). The crankshaft has been modeled by 38 lumped mass and stiffness elements. The dynamic patameters of each lumped element are provided by Finite Element Method(FEM). The responses of the crankshaft from TMM are fed back as loading conditions to the Finite Element model to obtain dynamic stresses for critical areas of the crankshaft.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.333-338
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• 1997

A hollow crankshaft is considered as part of an effort to reduce the weight of the automobile powertrain. Since the resulting mass reduction alters both the inertia and stiffness properties of the crankshaft, the vibration characteristics of the hollow crankshaft needs to be investigated in comparison with the original solid crankshaft. The crankshafts are modeled by 38 lumped mass and stiffness elements, in which the dynamic parameters for each lumped element are obtained by the finite element calculation. The fluid-film bearings supporting the crankshaft give rise to linear spring and damping elements that can be derived from the hydrodynamic bearing model. The transfer matrix method is applied to yield the natural frequencies and mode shapes of the crankshaft vibration. The natural frequencies of the hollow crankshaft are founded to be greater than that of the solid crankshaft, and the incorporation of the bearing stiffness tends to accentuate the difference.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.1
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• pp.29-35
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• 2015

The concept design of a riser for Ocean Thermal Energy Conversion in 10 MW is proposed and its dynamic behaviour characteristics is analyzed with numerical method. A riser pipe with a hollow along its thickness in the cross-section to increase the effective modulus of its cross-section is designed considering the manufacture. The riser pipe without hollows along its thickness needs a lumped weight at the bottom end of a riser in order to keep its vertical hanging configuration from large buoyancy and the strong current. The riser is designed to control its density by inserting materials in high or low density into a hollow. The dynamic behaviour characteristics of the two designed risers is evaluated with the developed numerical analysis tool. The combined stress of the riser with a lumped weight is showed to be dominated by weight of a lumped mass. The riser with no hollow shows large combined stress near sea surface by strong current. Local structural analysis for the cross-section of a hollow riser is needed in detail.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1028-1032
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• 2004

In order to prevent machine tool feed slide system from transient vibrations during operations, machine tool designers usually adopt some typical design solutions; box-in-box typed feed slides, optimizing moving body for minimum weight and dynamic compliance, and so on. Despite all efforts for optimizing design, a feed drive system may experience severe transient vibrations during high-speed operation if its feed rate control is unsuitable. A rough feed rate curve having discontinuity in its acceleration profile causes a serious vibration problem in the feed slides system. This paper presents a feed rate optimization of a ball screw driven machine tool feed slide system for its minimum vibration. Firstly, a ball screw feed drive system was mathematically modeled as a 6-degree-of-freedom lumped parameter system. Next, a feed rate optimization of the system was carried out for minimum vibrations. The main idea of the feed rate optimization is to find out the most appropriate smooth acceleration profile with jerk continuity. A genetic algorithm was used in this feed rate optimization

• Coupled systems mechanics
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• v.6 no.3
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• pp.273-286
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• 2017

We present a simple and easy-to-implement lumped stiffness model to elucidate the load transfer mechanism among all individual tube shells and intertube van der Waals (vdW) interactions in transversely compressed multi-walled carbon nanotubes (CNTs). Our model essentially enables theoretical predictions to be made of the relevant transverse mechanical behaviors of multi-walled tubes based on the transverse stiffness properties of single-walled tubes. We demonstrate the validity and accuracy of our model and theoretical predictions through a quantitative study of the transverse deformability of double- and triple-walled CNTs by utilizing our recently reported nanomechanical measurement data. Using the lumped stiffness model, we further evaluate the contribution of each individual tube shell and intertube vdW interaction to the strain energy absorption in the whole tube. Our results show that the innermost tube shell absorbs more strain energy than any other individual tube shells and intertube vdW interactions. Nanotubes of smaller number of walls and outer diameters are found to possess higher strain energy absorption capacities on both a per-volume and a per-weight basis. The proposed model and findings on the load transfer and the energy absorption in multi-walled CNTs directly contribute to a better understanding of their structural and mechanical properties and applications, and are also useful to study the transverse mechanical properties of other one-dimensional tubular nanostructures (e.g., boron nitride nanotubes).

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.1
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• pp.11-23
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• 1989

This paper presents the results of the numerical analysis on the behaviour of mooring system of offshore guyed tower. Finite element method is used and geometric nonlinearities are considered in the analysis of mooring line. The governing equilibrium equations are derived by the principle of virtual work, and modified Newton-Raphson method and Newmark-${\beta}$ method are employed in response calculations. The drag and inertia effects of fluid are included using a Morrison type equation. The influences of changing typical parameters like initial inclination and tension of line at the guy attachment point, the length of clump weight, its unit weight and the anchor line length are examined. The effects of idealising the clump weight as a point load(lumped clump weight) on the behaviour of mooring lines are also discussed. Numerical examples demonstrate the validity and capability of the mathematical formulation.

• Journal of the Korean Geotechnical Society
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• v.30 no.6
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• pp.23-39
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• 2014

An artificial rainwater reservoir installed in urban areas for recycling rainwater is an eco-friendly facility for reducing storm water effluence. However, in order to recycle the rainwater directly, the artificial rainwater reservoir requires an auxiliary system that can remove non-point source pollutants included in the initial rainfall of urban area. Therefore, the conventional soil filtration technology is adopted to capture non-point source pollutants in an economical and efficient way in the purification system of artificial rainwater reservoirs. In order to satisfy such a demand, clogging characteristics of the sand filter layers with different grain-size distributions were studied with real non-point source pollutants. For this, a series of lab-scale chamber tests were conducted to make a prediction model for removal of non-point source pollutants, based on the clogging theory. The laboratory chamber experiments were carried out by permeating two types of artificially contaminated water through five different types of sand filter layers with different grain-size distributions. The two artificial contaminated waters were made by fine marine-clay particles and real non-point source pollutants collected from motorcar roads of Seoul, Korea. In the laboratory chamber experiments, the concentrations of the artificial contaminated water were measured in terms of TSS (Total Suspended Solids) and COD (Chemical Oxygen Demand) and compared with each other to evaluate the performance of sand filter layers. In addition, the accumulated weight of pollutant particles clogged in the sand filter layers was estimated. This paper suggests a prediction model for removal of non-point source pollutants with theoretical consideration of the physical characteristics such as the grain-size distribution and composition, and change in the hydraulic conductivity and porosity of sand filter layers. The lumped parameter ${\theta}$ related with the clogging property was estimated by comparing the accumulated weight of pollutant particles obtained from the laboratory chamber experiments and calculated from the prediction model based on the clogging theory. It is found that the lumped parameter ${\theta}$ has a significant influence on the amount of the pollutant particles clogged in the pores of sand filter layers. In conclusion, according to the clogging prediction model, a double-sand-filter layer consisting of two separate layers: the upper sand-filter layer with the effective particle size of 1.49 mm and the lower sand-filter layer with the effective particle size of 0.93 mm, is proposed as the optimum system for removing non-point source pollutants in the field-sized artificial rainwater reservoir.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.1
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• pp.22-28
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• 2015

The design on a riser in 1MW OTEC system is performed. The minimum diameter of the riser is decided depending on intake quantity of deep-sea water to supply an OTEC cycle. An applicable pipe material is selected from analyzing the properties of commercial pipes. The selected HDPE pipe with the low density and strength is reinforced with a lumped block attached at the end of and wire ropes along the riser. A lumped block, connected to a floating structure by wire ropes, with 25% and 50% weight of a GFRP riser is designed to be attached the end of a riser. The structural safety of the HDPE riser with wire rope supporting axial loads induced by a lumped block is analyzed under the harsh ocean environmental condition near Hawaii ocean with the numerical method. The final dimension of the riser and accessories is determined considering the economic point of view. The designed riser will be applicable to the construction of the 1 MW OTEC pilot plant.

• Proceedings of the KIEE Conference
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• 2006.07d
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• pp.1834-1835
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• 2006

A robust adaptive position control algorithm is proposed for servomotor drive system with uncertainties and load disturbance. The proposed controller is comprised of a nominal controller and a robust control. The nominal controller is designed in the condition without all the external load disturbance, nonlinear friction and unpredicted uncertainties. The robust controller containing lumped uncertainty approximator using fuzzy-neural network(FNN) is designed to dispel the effect of uncertainties and load disturbance. The interconnection weight of the FNN can be online tuned in the sense of the Lyapunov stability theorem thus asymptotic stability of the proposed control system can be guaranteed. Finally, simulation results verify that the proposed control algorithm can achieve favorable tracking performance for the induction servomotor drive system.