• Computers and Concrete
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• v.33 no.1
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• pp.27-39
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• 2024

In this study, the authors investigate the free vibration behavior of three-phases functionally graded sandwich plates using a novel nth-order shear deformation theory. These plates are composed of a homogeneous core and two face-sheet layers made of different functionally graded materials. This is the novel type of the sandwich structures that can be applied in many fields of mechanical engineering and industrial. The proposed theory only requires four unknown displacement functions, and the transverse displacement does not need to be separated into bending and shear parts, simplifying the theory. One noteworthy feature of the proposed theory is its ability to capture the parabolic distribution of transverse shear strains and stresses throughout the plate's thickness while ensuring zero values on the two free surfaces. By eliminating the need for shear correction factors, the theory further enhances computational efficiency. Equations of motion are established using Hamilton's principle and solved via Navier's solution. The accuracy and efficiency of the proposed theory are verified by comparing results with available solutions. The authors then use the proposed theory to investigate the free vibration characteristics of three-phases functionally graded sandwich plates, considering the effects of parameters such as aspect ratio, side-to-thickness ratio, skin-core-skin thicknesses, and power-law indexes. Through careful analysis of the free vibration behavior of three-phases functionally graded sandwich plates, the work highlighted the significant roles played by individual material ingredients in influencing their frequencies.

• Journal of the Ergonomics Society of Korea
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• v.25 no.2
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• pp.125-134
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• 2006

Most users learn new, complex systems through trial-and-error experience rather than referring to the manuals in a cognitive process that is called 'exploratory learning'. While exploring a system, people find prototypical rules for using the system based especially on frequent tasks. The rules are formed from consistent task procedures and well-expected interface elements on the designed system. These rules play the role of the basis of users' knowledge for performing tasks. The decision making to select and apply those rules interacting with an interface can be aided by properly provided hints on the interface. With appropriate hints, users can learn new systems easily and use them with reduced usability problems. This paper first reports an observation of user behavior performing tasks with prototypical interaction rules and finds a sound set of criteria to extract prototypical interaction rules systematically. Two types of hints are defined. Extending hints prompt users to apply prototypical interaction rules beyond well-known tasks. Preventive hints guide users out of possible capture errors by drawing attention to the variation of rules. A systematic and practical method is proposed to identify the opportunities for both types in designing interfaces. It is then verified through a usability test that the proposed method is effective in identifying the locations and types of appropriate hints to reduce or mitigate usability problems.

• Safety and Health at Work
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• v.7 no.4
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• pp.363-371
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• 2016

Background: Seafaring is an inherently stressful environment. Because working time and leisure time is spent in the same confined environment for a prolonged period of time, many stressors present in seafaring can also be conceived of as chronic. We explored the effects of duration at sea, seafaring experience, environmental stressors, and psychological capital (PsyCap) on the sleep quality and fatigue of seafarers. PsyCap is a construct that draws upon ideas from positive psychology and positive organizational behavior, and is intended to capture an individual's psychological capacities that can be developed and utilized for performance improvements. Methods: We collected survey data from a sample of seafarers working in the offshore re-supply industry (n = 402) and a sample of seafarers working on board combined passenger and cargo ships (n = 340). Results: PsyCap emerged as a robust predictor with statistically significant relations to fatigue and sleep quality in both samples. PsyCap also interacted with duration at sea in explaining fatigue in seafarers working on board the passenger and cargo ships. Seafarers on passenger and cargo ships also reported significantly higher levels of fatigue than those working in the offshore re-supply industry. Conclusion: Coupled with emerging research showing that PsyCap is trainable, our results suggest that maritime organizations could have much to gain by being cognizant of and developing routines for continually developing the PsyCap of their employees.

• Geomechanics and Engineering
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• v.15 no.5
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• pp.1047-1059
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• 2018

This paper focuses on the cracking and fragmentation process in rock materials containing a pair of non-parallel flaws, which are through the specimen thickness, under vertical compression. Several numerical experiments are conducted with varying flaw arrangements that affect the initiation and tensile wing cracks, shear crack growth, and crack coalescing behaviors. To obtain realistic numerical results, a parallelized peridynamics formulation coupled with a finite element method, which is able to capture arbitrarily occurring cracks, is employed. From previous studies, crack initiation and propagation of tensile wing cracks, horsetail cracks, and anti-wing cracks are well understood along with the coalescence between two parallel flaws. In this study, the coalescence behaviors, their fragmentation sequences, and the role of an x-shaped shear band in rock material containing two non-parallel flaws are discussed in detail on the basis of simulation results strongly correlated with previous experimental results. Firstly, crack initiation and propagation of tensile wing cracks and shear cracks between non-parallel flaws are investigated in time-history and then sequential coalescing behavior is analyzed. Secondly, under the effect of varying inclination angles of two non-parallel flaws and overlapping ratios between a pair of non-parallel flaws, the cracking patterns including crack coalescence, fragmentation, and x-shaped shear band are investigated. These numerical results, which are in good agreement with reported physical test results, are expected to provide insightful information of the fracture mechanism of rock with non-parallel flaws.

• Korean Journal of Materials Research
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• v.19 no.2
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• pp.115-118
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• 2009

The use of dolomite refractories has increased during the past several years in the manufacturing of clean steel during the stainless steelmaking process. However, at the same time, the use of dolomite refractories has led to what is known as the skull formation. In the present work, to understand the skull formation, the wetting characteristics of dolomite substrates by liquid Fe-19wt%Cr-10wt%Ni alloys in various oxygen partial pressures were initially investigated at 1753K using the sessile drop technique. For comparison, the wetting characteristics of alumina substrates were investigated with the same technique. It was found that the wetting index, (1+$cos{\theta}$), of dolomite is approximately 40% higher compared to those of alumina. In addition, the oxygen partial pressure to generate the surface oxide, which may capture the liquid metal on the refractory surface, for dolomite is much lower than that for alumina. From this study, it was concluded that the use of dolomite is much more closely associated with the skull formation compared to the use of alumina due to the stronger wettability and the surface oxide formation at a lower oxygen partial pressure of dolomite.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.3
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• pp.306-320
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• 2010

Modern ultra-large container carriers can be exposed to the unprecedented springing excitation from ocean waves due to their relatively low torsional rigidity. Large deck opening on the deck of container carriers tends to cause warping distortion of hull structure under wave-induced excitation, eventually leading to the higher chance of resonance vibration between its torsional response and incoming waves. To handle this problem, a higher-order B-spline Rankine panel method and Vlasov-beam FE model was directly coupled in the time domain, and the coupled equation was solved by using an implicit iterative method. In order to capture the complicated behavior of thin-walled open section girder, a sophisticated beam-based finite element model was developed, which takes into account warping distortion and shear-on-wall effect. Then, the developed beam model was directly coupled with the time-domain Rankine panel method for hydrodynamic problem by using the fixed-point iteration method. The developed computational scheme was validated through the comparison with the frequency-domain solution on the container carrier model in linear springing regime.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.6
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• pp.143-150
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• 2006

In this paper, a new bushing model for vehicle dynamics analysis using Bouc-Wen hysteretic model is proposed. Bushing components of a vehicle suspension system are tested to capture the nonlinear behavior of rubber bushing elements using the MTS 3-axes rubber test machine. The results of the tests are used to define parameters in Bouc-Wen bushing model, which was employed to represent the hysteretic characteristics of the bushing. Bushing parameters are obtained by using genetic algorithms and sensitivity analysis of parameters are also carried out. ADAMS program was used for the identification process and VisualDOC program was employed to find the optimal parameters. A half-car simulation was carried out to show the usefulness of the developed bushing model.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.54 no.3
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• pp.193-203
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• 2018

Capture efficiencies of commercial shrimp trawls may improve if their designs took into better account behavioral responses of wild shrimp to approaching cod-end of the trawls. Here we report results of water tunnel-based experimental studies of responses of wild California target prawns to several different near-realistic netting configurations over a range of water velocities (0.3-0.7 m/s). Netting panels were oriented at parallel to water flows (FP) on the bottom of test section, vertical (VT) or diagonal sloping backward (DG), bottom to top. Behavioral responses were recorded by video camera and analyzed frame by frame. Measured responses included rates of penetrating through netting by behavioral features and tail-flip frequencies. Frequencies of prawn passing through the nets increased with flow speed for both orientations and were higher at given speeds for sloped nets. Other behavioral features (e.g., passage head-or tail-first) also varied significantly with water velocities and netting orientation. Interactions of penetrating rates between netting orientations and flow speeds also were significantly dependent, except for prawn size. Additional studies are needed of other shrimp species and at higher water velocities more similar to actual field operations using trawls to improve size selectivity.

• Transactions of Materials Processing
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• v.24 no.4
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• pp.280-286
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• 2015

Hemming is used to connect two sheet metal components by folding the edge of an outer panel around an inner panel to create a smooth edge. The minimization of hemming defects is critical to the final quality of automobile products because hemming is one of the last operations during fabrication. Designing the hemmed part is not easy and is influenced by the geometry of the bent part. Therefore, the main problem for automotive parts is dimensional accuracy since formed products often deviate geometrically due to large springback. Few numerical approaches using 3-dimensional finite element model have been applied to hemming due to the small element size which is needed to properly capture the bending behavior of the sheet around small die corner and the comparatively big size of automotive opening parts, such as doors, hoods and deck lids. The current study concentrates on the 3-dimensional numerical simulation of hemming for an automotive door. The relationship between the design parameters of the hemming operation and the height difference defect is shown. Quality improvement of the automotive door can be increased through the study of model parameters.

• Journal of information and communication convergence engineering
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• v.9 no.3
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• pp.325-330
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• 2011

Due to the wide growth and popularity of social network website, large numbers of users discover these social network sites are a place where they can be able to spend their leisure time sharing interests, sharing ideas freely, sharing personal experience, and also to search for new friends or partners. These websites give an opportunity for its users to socialize with new people and to keep in touch or reconnect with current or old friends and families across disperse continents, which traditionally replace the common traditional methods. These social network websites need accurate and careful investigations and findings on the usability issues for effective interactivity and more usability. However, little research might have previously invested on the usability of these social network websites. Therefore, we propose a new framework to study and test the usability of these social network sites. We namely call our framework "Interactivity". This framework will enable developers to assess the usability of the social network sites. It will provide an overview of the user's behavior while interacting in these social network websites. Performance of the framework will be performed using Camtasia software. This software will entirely capture the interactivity of users including the screen and the movements, which the screen and the motion of the user action will undergo to analysis at the end of our research.