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The most effective method for surveying underwater archeological sites is visually identifying areas with relics or remains through diving surveys. However, during underwater excavations, it is difficult to obtain images in turbid water. Furthermore, on-site diving is costly and time-consuming. Marine acoustic geophysical survey equipment is not significantly affected by underwater turbidity, and underwater excavations often rely on geophysical equipment for surface inspections. This study aimed to improve existing underwater excavation imaging through the application of acoustic survey methods. Underwater surveys were conducted via acoustic marine geophysical survey devices at three historically significant underwater sites in South Korea: Dangampo, Nakwoldo Island, and the Battle of Myeongnyang. At the Dangampo site, surveys were conducted using three different sonar devices—side scan sonar, multibeam echo sounder, and scanning sonar—and the results were compared, scanning sonar was the most effective. The methodology was further refined during excavations at the Nakwoldo and Myeongnyang sites. Results show that the scanning sonar can produce images that are more accurate than on-site drawings produced during underwater excavations, even in turbid underwater environments. Moreover, applied in conjunction with high-frequency geophysical exploration techniques, scanning sonar can significantly increase the reliability of investigations of buried underwater remains and relics.

Bathymetric changes were studied in the southern sea off the Jinwoo-do Island, which is one of the deltaic barrier is- lands surrounding the Nakddong river estuary. In this study, 16 bathymetry data sets were obtained from June 2006 to April 2015. Two narrow channels, the one lying between Jinwoo-do and Shinja-do, and the other one lying between Nulcha-do and Jinwoo-do extended into the eastern and western parts of the study area, respectively. The eastern extension of the channel con- tained a passage of mixed estuarine waters of seawater and river water discharged from the Nakdong river barrier and the west Nakdong River. The western channel connected the Nakdong River estuary with the Busan New Port via a connecting pier. Total volumetric changes of sediments in study area and discharge flow of the Nakdong river barrier were analyzed. Bottom topographical changes occurred mainly in the eastern extension of the channel. These changes were initially characterized by gradual erosion or deposition followed by rapid restoration. The total volume of sediment gradually increased from June 2006 to March 2013, but experienced a sudden decrease in October 2013 because of typhoon Danas. Few fluctuations were observed from October 2013 to April 2015. Analysis of the cross-sectional bathymetry of the north-south direction showed that the deep- est point of the eastern channel moved 100-130 m westward and 200 m northward between June 2006 and April 2015.

The design and buckling behavior of earth retaining system supported by high strength steel pipe and PHC pile under compression is presented in this study. Buckling analysis of various strut system was investigated according to the strut total length(30m, 60m, 90m), three types of built-up columns and connection condition. Buckling loads calculated by F.E analysis was compared with the theoretical solution corresponding to diagonal buckling mode, local and global buckling mode of main strut. The design of the built-up column struts are performed based on design guide for high strength steel pipes and P-M diagram for built-up column with two PHC pile section.

Holed-Incrementally Prestressed Concrete (H-IPC) girders are designed using the following new design concepts. At first, web openings reduce the self-weight of the girder, and also diffuse prestressing tendon anchorages. The reduced end anchoring forces decrease the web thickness of the end sections. Additionally, precast technology help to improve the quality of concrete and to reduce the construction period at the site. For experimentally verification, two 50 m full-scale H-IPC girders are manufactured with different concrete strength of 55 MPa and 80 MPa. The safety, stiffness, ductility, serviceability and crack development of H-IPC girder are measured and compared with each other for different strengths. Both girders show enough strength to carry live load and good stiffness to satisfy the design criteria. The experimental result shows the advantages of using high strength concrete and adopting precast girder. The test data can be used as a criterion for safety control and maintenance of the H-IPC girder.

Density currents formed by buoyancy discharges from rivers are numerically studied using non-dimensional two layer model including Coriolis acceleration, bottom stress, interfacial friction. Some typical numbers such as Froude number, densimetric Froude number and Kelvin number are obtained and some characteristic scales are defined as a result of non-dimensionalization of the governing equations. Besides the Coriolis effect, the configurations of bottom topography, bottom friction coefficient and interfacial friction are found to significantly affect the propagation of the warm water plume. Frontal position can fastly propagate in the case of large density difference between the two layers and small interfacial friction. Left side boundary current is easily formed under the small interfacial friction. With large Kelvin number, both right and left side boundary currents are formed. Wave-like disturbances and eddies are easily formed under the high Froude number.

Since distribution and preservation of cultural artifacts in the submarine sediments are directly affected by not only ocean currents and tides, but also their composition, it is very important to investigate geological characteristics of sediments and ocean-sediment interactions for maritime archaeological survey. Physical properties of submarine sediments, which are collected by grab sampler and vibro-corer, are analyzed in order to investigate effects of submarine environment on development of maritime archaeological survey techniques. Result of physical property analysis showed that bulk density, shear strength, and magnetic susceptibility increase with depth, while water contents and porosity decrease with depth. Since the magnetic susceptibility of bedrock is about 40 times that of submarine sediments, it might impact greatly on the response of magnetic survey. Physical properties of sediments with depth and sediment classification by Folk’s ternary diagram indicate that submarine sediment mainly consists of silt, and cultural artifacts can not penetrate no deeper than 1.5 m in sediments.

The parametric analysis on ultimate behavior of buried cylindrical GFRP(Glass Fiber Reinforced Polymer) septic tank was presented. Two kinds of F.E. analysis model(soil-spring model and 3D full model) was constructed. The ultimate behavior of septic tank was investigated according to the size of stiffened steel ring and properties of underground soil. Ramberg-Osgood model and Druker-Prager model were used for material nonlinear characteristics of GFRP septic tank and soil, respectively. The diameter and thickness of stiffened steel ring inside septic tank, elastic modulus and internal friction angle of soil were selected for parametric variables. The ultimate behavior of septic tank, load-displacement, axial and hoop strain, were calculated and investigated.

In order to study geology and sediment characteristics in Danghang Bay area, surface geological survey, SBP (sub-bottom profiler) survey, an d sediment analysis were conducted. Danghang Bay area has a closing coast surrounded by land, and surface layer are covered by mud and sandy mud. Sedimentary facies of t he surface layer consists of Mm and Mms facies. A SBP seismic survey shows that gas bearing sediments might be spread throughout the sediment layers, so that it seem s to be hard to find acoustic basement and gas seeps are easily found throughout the survey lines. The gas trapped in the sediments may be related to the high organic contents of the sediment, and the thick mud layer may restrain the gas from releasing. Key words: Danghang Bay area, Sediments, SBP (Sub-bottom profiler), Gas be aring sediments †교신저자(동아대학교 에너지·자원공학과, E-mail:jkim@dau.ac.kr, Tel: 051-200-7790)1 동아대학교 대학원 에너지·자원공학과2 동아대학교 대학원 해양공학과3 동아대학교 에너지·자원공학과 1. 서 론 한반도의 남부 연안은 수많은 섬들과 소규모의 만들로 이루어져 있으며, 매우 복잡한 해안선을 갖고 있다. 지금까지 남해안 일대에 분포하는 퇴적물의 특성 및 퇴적작용에 관한 연구는 많이 수행되었다. 이들 연구들에 의하면 한반도 남부해역 만 내에는 현생 세립질 퇴적물이 널리 분포하고 있으며, 지난 빙하기 이후 해수면 상승과 더불어 활발한 퇴적 작용으로 인해 비교적 두꺼운 퇴적층이 형성된 것으로 보고되고 있다. 만 내에 분포하는 세립질 퇴적물들은 주로 낙동강이나 섬진강에 의해 이 지역에 공급되는 것으로 보인다[1-3].

Seismic data is often contaminated with high-energy, spatially aliased noise, which has proven impractical to attenuate using Fourier techniques. Wavelet filtering, however, has proven capable of attacking several types of localized noise simultaneously regardless of their frequencies. In this study a 2-D stationary wavelet transform is used to decompose seismic data into its wavelet components. A threshold is applied to these coefficients to attenuate high amplitude noise, followed by an inverse transform to reconstruct the seismic trace. The stationary wavelet transform minimizes the phase-shift errors induced by thresholding that occur when the conventional discrete wavelet transform is used.

An improved shear deformable curved beam theory to overcome the drawback of currently available beam theories is newly proposed for the spatially coupled stability analysis of thin-walled curved beams with nonsymmetric cross sections. For this, the displacement field is introduced considering the second order terms of semitangential rotations. Next the elastic strain energy is newly derived by using transformation equations of displacement parameters and stress resultants and considering shear deformation effects due to shear forces and restrained warping torsion. Then the potential energy due to initial stress resultants is consistently derived with accurate calculation of the Wagner effect. Finally, equilibrium equations and force–deformation relations are obtained using a stationary condition of total potential energy. The closed-form solutions for in-plane and out-of-plane buckling of curved beams subjected to uniform compression and pure bending are newly derived. Additionally, finite-element procedu...

For spatial stability analysis of shear deformable thin-walled curved beams with non-symmetric cross-sections, an improved analytical formulation is proposed. Firstly the displacement field is introduced considering the second order terms of semi-tangential rotations. Next an elastic strain energy is derived by using transformation equations of displacement parameters and stress resultants and considering shear deformation effects due to shear forces and restrained warping torsion. And then the potential energy due to initial stress resultants is consistently derived with accurate calculation of Wagner effect. In addition, closed-form solutions for in-plane and lateral-torsional buckling loads of curved beams subjected to uniform compression and pure bending are newly derived. In the companion paper, FE procedures are developed by using curved and straight beam elements with arbitrary thin-walled sections. In numerical examples, to illustrate accuracy and validity of this study, closed-form solutions for in-plane and out-of-plane buckling loads are presented and compared with those obtained from analytical solutions by other researchers.

In a companion paper, transformation rules of Rodriguez' finite rotations and semitangential rotations are derived, respectively, and their rotational properties are discussed. The shear deformable displacement field of nonsymmetric thin-walled space frames is introduced based on semitangential rotations and the potential energy corresponding to semitangential internal moments are consistently derived using the proposed displacement field. In this paper, for spatial postbuckling analysis of thin-walled space frames, the elastic strain energy including bending-torsion coupled terms and shear deformation effects is derived using transformations of displacements and stress resultants defined at the centroid and the centroid-shear center, respectively. Tangent stiffness matrices of the frame element are derived by using Hermitian polynomials including shear effects, and an improved corotational formulation is presented by separating rigid body motions and pure deformations from incremental displacements, calc...

A consistent finite element formulation is presented for the free vibration and spatial stability analysis of thin-walled tapered beams and space frames. The kinetic and potential energies are derived by applying the extended virtual work principle, introducing displacement parameters defined at the arbitrarily chosen axis and including second order terms of finite semitangential rotations. As a result, the energy functional corresponding to the semitangential rotation and moment is obtained, in which the elastic strain energy terms are coupled due to axial–flexural–torsional coupling effects but the potential energy due to initial stress resultants has a relatively simple expression. For finite element analysis, cubic polynomials are utilized as the shape functions of the two-noded Hermitian space frame element. Mass, elastic stiffness, and geometric stiffness matrices for the unsymmetric thin-walled cross-section are precisely evaluated, and load-correction stiffness matrices for off-axis concentrated and distributed loadings are considered. In order to illustrate the accuracy and practical usefulness of this formulation, finite element solutions for the free vibration and lateral–torsional buckling problems of thin-walled tapered beam-columns and space frames are presented and compared with available solutions.

The theoretical considerations of the post-buckling analyses of thin-walled space frames with non-symmetric cross sections are presented based on the semitangential rotation and semitangential moment. The nature of the Rodriguez's rotations and semitangential rotations are discusssed, and the improved displacement field is introduced based on the second order terms of semitangential rotations. By defining all the displacement parameters at the centroid and introducing the normalized warping functions defined at the centroid and the shear center, respectively, the elastic strain energy including bending-torsion coupled terms due to the non-symmetry of cross-section is clearly derived. Also, the total potential energy consistently derived, without unreasonable assumption, based on semitangential rotations corresponds to semitangential bending and torsional moments. It is proved that the conventional potential energy due to stress resultants corresponds to the quasitangential internal bending and torsional moments, and the potential energy considering the effects of the second order terms of semitangential rotations includes the energy terms transforming quasitangential moments to semitangential moments.

A consistent finite-element formulation is presented in order to analyze the spatial stability of shear deformable thin-walled space frames and circular arches. The displacement field of unsymmetric thin-walled cross sections is introduced based on the inclusion of second-order terms of Rodriguez's finite rotations, and the potential energy corresponding to the semitangential moments is consistently derived. For finite-element analysis, cubic Hermitian polynomials including shear deformation effects due to flexural and restrained warping shear stress are utilized as shape functions. Load correction stiffness matrices for the different types of moments and off-axis loadings are taken into account. For spatial buckling behaviors of space frames and circular arches, finite-element solutions using the two-noded straight frame element are presented and compared with the analytical solutions and the results in the literature.

A clearly consistent finite element formulation for spatial stability analysis of thin-walled space frames is presented by applying linearized virtual work principle and introducing Vlasov's assumption. The improved displacement field for unsymmetric thin-walled cross-sections is introduced based on inclusion of second-order terms of finite rotations, and the potential energy corresponding to the semitangential moments is consistently derived. In the present formulation, displacement parameters of axial and bending deformations are defined at the centroid axis and parameters of lateral and torsional deformations at the shear centre axis, and all bending-torsional coupling effects due to unsymmetric cross-sections are taken into account. For finite element analysis, cubic Hermitian polynomials for the flexural beam with four types of end conditions are utilized as shape functions of Hermitian space frame element. Also, load correction stiffness matrices for off-axis point loadings are derived based on the second-order rotation terms. Finite element solutions for the spatial buckling analysis of thin-walled space frames are compared with available solutions and other researcher's results.

In a companion paper,1 equations of motion and closed-form solutions for spatial stability and free vibration analysis of shear flexible thin-walled elastic beams were analytically derived from the linearized Hellinger–Reissner principle. In this paper, elastic and geometric stiffness matrices and consistent mass matrix for finite element analysis are evaluated by using isoparametric and Hermitian interpolation polynomials. Isoparametric interpolation functions with 2, 3 and 4 nodes per element are utilized in isoparametric beam elements, and in Hermitian beam elements, the third- and fifth-order Hermitian polynomials including shear deformation effects are newly derived and applied for the calculation of element matrices. In order to verify the validity of the finite element formulation, both analytic and numerical solutions for spatial buckling and free vibration problems including shear effects are presented and compared.

The experiment and FE analysis of ultimate behavior of GFRP cylindrical shell structure stiffened by steel pipe ring instead of rectangular cross-section ring was presented. Four kinds of test models were designed and flexural failure experiment was performed to investigate ultimate behavior characteristic according to the size of cross section of steel pipe ring and diameter of GFRP shell. Material properties of specimens were experimented by bending, tensile and compressive test. Displacements and strains were measured to evaluate failure behavior of steel pipe ring and GFRP shell structure. The experimental results were compared with the FEA results by commercial program ABAQUS. It is observed that GFRP shell structure stiffened by steel ring have enough ductility to bending failure, and an increase of bending rigidity of steel ring is very effective to increase of failure strength of GFRP shell structure.