• Title/Summary/Keyword: computational model

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Incorporating uplift in the analysis of shallowly embedded pipelines

  • Tian, Yinghui;Cassidy, Mark J.
    • Structural Engineering and Mechanics
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    • v.40 no.1
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    • pp.29-48
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    • 2011
  • Under large storm loads sections of a long pipeline on the seabed can be uplifted. Numerically this loss of contact is extremely difficult to simulate, but accounting for uplift and any subsequent recontact behaviour is a critical component in pipeline on-bottom stability analysis. A simple method numerically accounting for this uplift and reattachment, while utilising efficient force-resultant models, is provided in this paper. While force-resultant models use a plasticity framework to directly relate the resultant forces on a segment of pipe to the corresponding displacement, their historical development has concentrated on precisely modelling increasing capacity with penetration. In this paper, the emphasis is placed on the description of loss of penetration during uplifting, modelled by 'strain-softening' of the force-resultant yield surface. The proposed method employs uplift and reattachment criteria to determine the pipe uplift and recontact. The pipe node is allowed to become free, and therefore, the resistance to the applied hydrodynamic loads to be redistributed along the pipeline. Without these criteria, a localised failure will be produced and the numerical program will terminate due to singular stiffness matrix. The proposed approach is verified with geotechnical centrifuge results. To further demonstrate the practicability of the proposed method, a computational example of a 1245 m long pipeline subjected to a large storm in conditions typical of offshore North-West Australia is discussed.

Tearing of metallic sandwich panels subjected to air shock loading

  • Zhu, Feng;Lu, Guoxing;Ruan, Dong;Shu, Dong-Wei
    • Structural Engineering and Mechanics
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    • v.32 no.2
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    • pp.351-370
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    • 2009
  • This paper presents a computational study for the structural response of blast loaded metallic sandwich panels, with the emphasis placed on their failure behaviours. The fully-clamped panels are square, and the honeycomb core and skins are made of the same aluminium alloy. A material model considering strain and strain rate hardening effects is used and the blast load is idealised as either a uniform or localised pressure over a short duration. The deformation/failure procedure and modes of the sandwich panels are identified and analysed. In the uniform loading condition, the effect of core density and face-sheets thicknesses is analysed. Likewise, the influence of pulse shape on the failure modes is investigated by deriving a pressure-impulse (P-I) diagram. For localised loading, a comparative study is carried out to assess the blast resistant behaviours of three types of structures: sandwich panel with honeycomb core, two face-sheets with air core and monolithic plate, in terms of their permanent deflections and damage degrees. The finding of this research provides a valuable insight into the engineering design of sandwich constructions against air blast loads.

The use of neural networks in concrete compressive strength estimation

  • Bilgehan, M.;Turgut, P.
    • Computers and Concrete
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    • v.7 no.3
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    • pp.271-283
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    • 2010
  • Testing of ultrasonic pulse velocity (UPV) is one of the most popular and actual non-destructive techniques used in the estimation of the concrete properties in structures. In this paper, artificial neural network (ANN) approach has been proposed for the evaluation of relationship between concrete compressive strength, UPV, and density values by using the experimental data obtained from many cores taken from different reinforced concrete structures with different ages and unknown ratios of concrete mixtures. The presented approach enables to find practically concrete strengths in the reinforced concrete structures, whose records of concrete mixture ratios are not yet available. Thus, researchers can easily evaluate the compressive strength of concrete specimens by using UPV values. The method can be used in conditions including too many numbers of the structures and examinations to be done in restricted time duration. This method also contributes to a remarkable reduction of the computational time without any significant loss of accuracy. Statistic measures are used to evaluate the performance of the models. The comparison of the results clearly shows that the ANN approach can be used effectively to predict the compressive strength of concrete by using UPV and density data. In addition, the model architecture can be used as a non-destructive procedure for health monitoring of structural elements.

A topology optimization method of multiple load cases and constraints based on element independent nodal density

  • Yi, Jijun;Rong, Jianhua;Zeng, Tao;Huang, X.
    • Structural Engineering and Mechanics
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    • v.45 no.6
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    • pp.759-777
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    • 2013
  • In this paper, a topology optimization method based on the element independent nodal density (EIND) is developed for continuum solids with multiple load cases and multiple constraints. The optimization problem is formulated ad minimizing the volume subject to displacement constraints. Nodal densities of the finite element mesh are used a the design variable. The nodal densities are interpolated into any point in the design domain by the Shepard interpolation scheme and the Heaviside function. Without using additional constraints (such ad the filtering technique), mesh-independent, checkerboard-free, distinct optimal topology can be obtained. Adopting the rational approximation for material properties (RAMP), the topology optimization procedure is implemented using a solid isotropic material with penalization (SIMP) method and a dual programming optimization algorithm. The computational efficiency is greatly improved by multithread parallel computing with OpenMP to run parallel programs for the shared-memory model of parallel computation. Finally, several examples are presented to demonstrate the effectiveness of the developed techniques.

A Study on Dynamic Characteristics of Single Lap Joints with Different Joining Methods (체결방법에 따른 랩조인트의 동특성 해석)

  • Jung, Y.D.;Park, M.K.;Bahk, S.M.;Choi, Y.S.
    • Proceedings of the KSME Conference
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    • 2001.06b
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    • pp.624-629
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    • 2001
  • Two types of bolted lap joints, one with a viscoelastic layer and the other without the viscoelastic layer were chosen to analyze the dynamic characteristics of the joints with the mechanical properties of the bolts of the joints being taken as computational variables. The finite element method was used along with the impact hammer technique to verify the FEM model. The results in the bolted lap joints reveal that the higher the Young's Modulus for the bolts are the higher the natural frequencies results for the joints. However, the natural frequency differences in the first and second mode are not substantial but become noticeable in the higher modes. Lower natural frequencies were obtained for the bolted lap joints with the viscoelastic layer when compared with those of the bolted lap joints without the viscoelastic layer. And the differences in the natural frequencies for the two types of joints are relatively small in the first and second mode whereas in the higher mode the differences become significant. The loss factors were observed to be significant especially in the second mode for the bolted lap joints with the viscoelastic layer.

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Design and Control of a Wearable Robot (Wearable Robot Arm의 제작 및 제어)

  • Jeong, Youn-Koo;Kim, Yoon-Kyong;Kim, Kyung-Hwan;Park, Jong-Oh
    • Proceedings of the KSME Conference
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    • 2001.06b
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    • pp.277-282
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    • 2001
  • As human-friendly robot techniques improve, the concept of the wearability of robotic arms becomes important. A master arm that detects human arm motion and provides virtual forces to the operator is an embodied concept of a wearable robotic arm. In this study, we design a 7 DOF wearable robotic arm with high joint torques. An operator wearing this robotic arm can move around freely because this robotic arm was designed to have its fixed point at the shoulder part of the operator. The proposed robotic arm uses parallel mechanisms at the shoulder part and the wrist part on the model of the human muscular structure of an upper limb. To reduce the computational load in solving the forward kinematics and to prevent singularity motions of the parallel mechanism, yawing motion of the parallel mechanisms was separated using a slip ling mechanism. The total weight of the proposed robotic arm is about 4 kg. An experimental result of force tracking test for the pneumatic control system and an application example for VR robot are described to show the validity of the robot.

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Development of the Linear Piston Pump Driven by the Hydraulic Power for the Solid Transferring (고형물 이송을 위한 유압구동 선형 피스톤 펌프의 개발)

  • Kim, Bong-Hwan;Ahn, Kook-Chan;Chung, Sung-Won;Kim, Young-Hoon
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.8 no.3
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    • pp.82-89
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    • 2009
  • The purpose of this study is to investigate the actual field application of the linear piston pump for the solid transferring driven by the hydraulic power unit. In this paper, the numerical analysis and performance evaluating experiments were performed. CFX program has been used to obtain the solutions for the problems of three-dimensional, turbulent water flow in the linear piston pump. The velocity and the pressure distributions are obtained using the turbulent $k-\varepsilon$ model. To evaluate the performance of the linear piston pump, the performance test stand and data acquisition system were manufactured. The numerical predictions agree favorably with experimental results within 7% error. Speed of the piston which is satisfied the flow rate 3,000l/min which considers from basic design became 0.33m/s. This paper could be applied to the design of the linear piston pump for the fish transferring.

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Numerical Simulation of Flow and Heat Transfer in Cooling Channel with a Staggered V-shaped Rib (엇갈린 V-형 리브가 부착된 냉각유로에서의 열유동 수치해석)

  • Myong, Hyon-Kook;Kim, Kwang-Yong
    • Proceedings of the KSME Conference
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    • 2008.11b
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    • pp.2448-2453
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    • 2008
  • The present study numerically investigates the flow and heat transfer characteristics of rib-induced secondary flow in a cooling channel with staggered V-shaped ribs, extruded on both walls. The rib-height-to-hydraulic diameter ration (h/$D_h$) is 0.17; the rib pitch-to-height ratio (p/h) equals 2.8; the Reynolds number is 50,000. Shear stress transport (SST) turbulence model is used as a turbulence closure. The present results are compared with those for a continuous V-shaped rib. Computational results show that, for average heat transfer rate the staggered V-shaped rib gives about 2.5 times higher values than the continuous V-shaped rib, while, for the streamwise pressure drop the former gives about 5 times higher values than the latter. Consequently, for the thermal performances, based on the equal pumping power condition, the staggered one gives about 2 times higher values than the continuous one. Also, for the staggered V-shaped rib, complex secondary flow patterns are generated in the duct due to the snaking flow in the streamwise direction, and more uniform heat transfer distributions are obtained.

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Numerical Analysis on Longitudinal Heat Conduction in Printed Circuit Heat Exchanger (인쇄기판형 열교환기의 유동방향 전도열전달에 관한 수치해석 연구)

  • Oh, Dong-Wook;Kim, Young;Choi, Jun Seok;Yoon, Seok Ho
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.26 no.12
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    • pp.600-604
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    • 2014
  • Longitudinal heat conduction is known to be an important factor in the design of a printed circuit heat exchanger(PCHE) for cryogenic applications. Parasitic heat conduction through the heat exchanger frame needs to be considered because it is known to decrease the effectiveness of the heat exchanger. In this paper, a conjugate heat transfer problem in a simple counter-flow PCHE is analyzed by a computational fluid dynamics simulation. The effect of longitudinal conduction in a straight channel is compared with the theoretical effectiveness-NTU relationship that assumes a "thin" heat exchanger frame. The calculation results suggest that the theoretical model is valid in the present calculation conditions where NTU is < 13.

A Numerical Study on Solidity Characteristics of the Cross-flow Power Turbine(CPT) (횡류형 파워 터빈(CPT)에서 솔리디티 영향에 관한 수치해석 연구)

  • Chung, Kwang-Seop;Kim, Chul-Ho
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.22 no.8
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    • pp.562-566
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    • 2010
  • Wind energy is one of the most general natural resources in the world. However, as of today, generating electricity out of wind energy is only available from big wind generator, Furthermore, an axial-flow turbine is the only way to produce electricity in the big wind generator. This paper is for the guidance of drawing impact fact about power turbine using cross-flow type transferring wind energy to electricity energy. It will find the ideal value which enables to make cross-flow power turbine(CPT) using computational fluid dynamics(CFD) code. This study tries to analyze the "Solidity" characteristics. We can find out turbine-blade number through CFD. CFD is using "Fluent_ver 6.3.16", and the data from its result will judge fan-blade performance through specific torque and specific power from each "Solidity" model. Based upon the above, we will make cross-flow power turbine of multi-blade centrifugal fan instead of axial-flow type.