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Repeated lateral impacts on steel grillage structures at room and sub-zero temperatures
Truong, Dac Dung,Shin, Hyun Kyoung,Cho, Sang-Rai Elsevier 2018 International journal of impact engineering Vol.113 No.-
<P><B>Abstract</B></P> <P>This paper presents experimental and numerical investigation results for the plastic response of steel grillages, represented by one longitudinal stiffener and two transverse stiffeners of stiffened plates, used on ships or offshore structures under repeated mass impacts. The repeated mass impact scenario adopted in this paper could represent the repetition of impacted loads on marine structures due to contact with ice floes and floating objects during service. Repeated impact tests on grillage models at room and sub-zero temperatures (−50 °C) were conducted by releasing a knife-edge striker using a drop testing machine. The ends of the grillage models were firmly fixed onto a strong bed with support fixtures. To evaluate the repeated impact performance of the tested models, permanent deflections were measured after each impact test. Additionally, numerical simulations were performed using the commercial software package ABAQUS/Explicit to predict the extent of damage to the tested models caused by repeated impacts. In the calculations, the material properties of tested models were used to determine the strain hardening and strain rate hardening model using the equations recently proposed by the authors. Also, a simple analytical approach has been proposed to predict the damage evolution of the grillage subjected to repeated mass impacts. Reasonable agreement was achieved between the predictions and test results. The results showed that when the structure was repeatedly impacted, permanent deflections of the grillage significantly increased with increasing impact force. The permanent deflections tended to have certain values when the number of impacts increased. Based on the numerical results (which were substantiated with the experimental results), further calculations were then carried out to examine impact responses in greater detail and assess the effects of variations in boundary conditions and strain rate definitions on the response of grillages to repeated mass impacts.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Repeated mass impact tests were performed on four steel grillage structures at room and sub-zero temperatures for different kinetic energies. </LI> <LI> Deflection increments were reduced and contact force increased, but impact duration decreased with an increasing number of impacts. </LI> <LI> An analytical method has been developed in this study to predict the permanent deflections of grillage beam under repeated mass impact. </LI> <LI> There is reasonable agreement between the experimental results and predictions of the numerical and analytical analyses developed in this study. </LI> <LI> The effects of strain rate and boundary conditions on the impact responses of grillages were also numerically investigated. </LI> </UL> </P>
Response of low-temperature steel beams subjected to single and repeated lateral impacts
Dac Dung Truong,Hae-Jung Jung,Hyun Kyoung Shin,Sang-Rai Cho 대한조선학회 2018 International Journal of Naval Architecture and Oc Vol.10 No.6
This paper presents the experimental and numerical investigation results of the response of lowtemperature steel (LT-FH32 grade steel) beams under repeated impacts at room temperature and a single impact at a sub-zero temperature. After conducting tensile tests at room and sub-zero, repeated impact tests were conducted on two clamped single-beam models at room temperature, and singleimpact tests of two other clamped single-beam models were conducted at 50 C. The single and repeated impact tests were conducted by releasing a knife-edge striker using a drop testing machine. The permanent deflection of the model measured after each impact gradually increased with increasing number of impacts. Under the reduced temperature, the permanent deflection of the models slightly decreased. The numerical analyses were also performed to predict the damage response of the tested single-beam models. A comparison of the numerical prediction with those of experiments showed quite reasonable agreement.
Response of low-temperature steel beams subjected to single and repeated lateral impacts
Truong, Dac Dung,Jung, Hae-Jung,Shin, Hyun Kyoung,Cho, Sang-Rai The Society of Naval Architects of Korea 2018 International Journal of Naval Architecture and Oc Vol.10 No.6
This paper presents the experimental and numerical investigation results of the response of low-temperature steel (LT-FH32 grade steel) beams under repeated impacts at room temperature and a single impact at a sub-zero temperature. After conducting tensile tests at room and sub-zero, repeated impact tests were conducted on two clamped single-beam models at room temperature, and single-impact tests of two other clamped single-beam models were conducted at $-50^{\circ}C$. The single and repeated impact tests were conducted by releasing a knife-edge striker using a drop testing machine. The permanent deflection of the model measured after each impact gradually increased with increasing number of impacts. Under the reduced temperature, the permanent deflection of the models slightly decreased. The numerical analyses were also performed to predict the damage response of the tested single-beam models. A comparison of the numerical prediction with those of experiments showed quite reasonable agreement.
Physical Layer Secrecy Performance of RF-EH Networks with Multiple Eavesdroppers
Truong, Tien-Vu,Vo, Nhan-Van,Ha, Dac-Binh,Tran, Duc-Dung The Korea Institute of Information and Commucation 2016 Journal of information and communication convergen Vol.14 No.3
In this study, we investigate the physical layer secrecy performance of RF energy harvesting (EH) networks over Rayleigh fading channels. The RF-EH system considered here consists of one power transfer station, one source, one destination, and multiple passive eavesdroppers. The source harvests energy from the power transfer station and transmits the information to the destination by using a time switching-based relaying protocol. The eavesdroppers try to extract the transmitted information without an active attack. By using the statistical characteristics of the signal-to-noise ratio (SNR), the exact closed-form expressions of the existence probability of the secrecy capacity and the secrecy outage probability are derived. Further, we analyze the secrecy performance of the system with respect to various system parameters, such as the location of the system elements and the number of eavesdroppers. Finally, the equivalent Monte Carlo simulation results are provided to confirm the correctness of our calculations.
Secrecy Performance of Energy Harvesting Wireless Networks in the Presence of Multiple Eavesdroppers
Tien-Vu Truong,Nhan-Van Vo,Dac-Binh Ha,Duc-Dung Tran 한국정보통신학회 2016 2016 INTERNATIONAL CONFERENCE Vol.8 No.1
This paper investigates the physical layer secrecy performance of radio frequency energy harvesting wireless networks over Rayleigh fading channels. The considered RF-EH system consists of a power transfer station, a source and a destination in the presence of multiple passive eavesdroppers. By using statistical characteristics of the signal-to-noise ratio (SNR), the exact closed-form expressions of existence probability of secrecy capacity is derived. Finally, simulation results are provided to confirm the correctness of our calculation.
A study on accumulated damage of steel wedges with dead-rise 10° due to slamming loads
Seo, Byoungcheon,Truong, Dac Dung,Cho, Sangrai,Kim, Dongju,Park, Sookeun,Shin, Hyunkyoung The Society of Naval Architects of Korea 2018 International Journal of Naval Architecture and Oc Vol.10 No.4
This paper presents the results of experimental investigation on the elastic-plastic response of steel unstiffened wedges with dead-rise $10^{\circ}$ subjected to repeated impulsive pressure loadings. Repeated drop tests were performed with both wedge thickness and drop height varied. The pressure and histories were recorded during the tests and the permanent deflections were measured after every drop. Using the recorded test result, the effects of flexibility of wedges and repetition have been investigated. From the pressure history obtained from the tests the characteristics of the impulses were identified. Numerical simulations of the tests were made using the measured pressure history and the permanent deflection predictions were compared with those of the experiments.
A study on accumulated damage of steel wedges with dead-rise 10 due to slamming loads
Byoungcheon Seo,Dac Dung Truong,Sang-Rai Cho,Dongju Kim,Sookeun Park,Hyun Kyoung Shin 대한조선학회 2018 International Journal of Naval Architecture and Oc Vol.10 No.4
This paper presents the results of experimental investigation on the elasticeplastic response of steel unstiffened wedges with dead-rise 10 subjected to repeated impulsive pressure loadings. Repeated drop tests were performed with both wedge thickness and drop height varied. The pressure and histories were recorded during the tests and the permanent deflections were measured after every drop. Using the recorded test result, the effects of flexibility of wedges and repetition have been investigated. From the pressure history obtained from the tests the characteristics of the impulses were identified. Numerical simulations of the tests were made using the measured pressure history and the permanent deflection predictions were compared with those of the experiments.