Dynamic Load Positioning for Subsea Installation via Adaptive Neural Control

How, Bernard Voon Ee,Ge, Shuzhi Sam,Yoo Sang Choo IEEE 2010 IEEE JOURNAL OF OCEANIC ENGINEERING - Vol.35 No.2

<P>In this paper, positioning control is investigated for the installation of subsea systems, with attached thrusters, under time-varying irrotational ocean current. Backstepping in combination with adaptive feedback approximation techniques is employed in the design of the control, with the option of high-gain observer for output feedback control. The stability of the design is demonstrated through Lyapunov analysis where semiglobal uniform boundedness of the closed-loop signals is guaranteed. The proposed adaptive neural control is able to capture the dominant dynamic behaviors without exact information on the hydrodynamic coefficients of the structure and current measurements. Comparative simulations with linear proportional derivative (PD), PD with adaptive term, and model-based controls are carried out. The proposed technique is found to be effective and robust and reduces tracking error of the subsea module.</P>

Concrete crack rehabilitation using biological enzyme

How-Ji Chen,Pang-Hsu Tai,Ching-Fang Peng,Ming-Der Yang 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.19 No.4

Concrete is a material popularly used in construction. Due to the load-bearing and external environmental factors during utilization or manufacturing, its surface is prone to flaws, such as crack and leak. To repair these superficial defects and ultimately and avoid the deterioration of the concrete’s durability, numerous concrete surface protective coatings and crack repair products have been developed. Currently, studies are endeavoring to exploit the mineralization property of microbial strains for repairing concrete cracks be the repairing material for crack rehabilitation. This research aims to use bacteria, specifically B. pasteurii, in crack rehabilitation to enhance the flexural and compression strength of the repaired concrete. Serial tests at various bacterial concentrations and the same Urea-CaCl2 medium concentration of 70% for crack rehabilitation were executed. The results prove that the higher the concentration of the bacterial broth, the greater the amount of calcium carbonate precipitate was induced, while using B. pasteurii broth was for crack rehabilitation. The flexural and compression strengths of the repaired concrete test samples were the greatest at 100% bacterial concentration. Compared to the control group (bacterial concentration of 0%), the flexural strength had increased by 32.58% for 1-mm crack samples and 51.01% for 2-mm crack samples, and the compression strength had increased by 28.58% and 23.85%, respectively. From the SEM and XRD test results, a greater quantity of rectangular and polygonal crystals was also found in samples with high bacterial concentrations. These tests all confirm that using bacteria in crack rehabilitation can increase the flexural and compression strength of the repaired concrete.

Novel fuzzy based model on analysis of invasiveness due to dispersal related traits of plants

HOW Peiris,S. Chakraverty,SSN Perera,SMW Ranwala 원광대학교 기초자연과학연구소 2017 ANNALS OF FUZZY MATHEMATICS AND INFORMATICS Vol.13 No.3

Invasive Alien Species (IAS) can be considered as a serious threat to the existence of the biodiversity as they alter physical, chemical and biological components of the environment. Invasive potential of species can be recognized by their biological traits. Therefore, it is very important, if a model could be developed to measure the biological risk of plant species before introducing to a new environment. This work aims to incorporate dispersal related biological traits into a mathematical model to evaluate the risk of plant species. To build up the model, four factors of dispersal traits have been considered and grade of important weights of these traits towards invasiveness was assigned as explained in Chang's extent analysis and Buckly's methods (Column geometric mean method). The present model is found to be a better tracking system for identifying potential invaders compared to the conventional manually conducted risk assessment methods when incorporated with important weights as per Chang's extent analysis.

Strength and durability of concrete in hot spring environments

How-Ji Chen,Tsung-Yueh Yang,Chao-Wei Tang 사단법인 한국계산역학회 2009 Computers and Concrete, An International Journal Vol.6 No.4

In this paper an experimental study of the influence of hot springs curing upon concrete properties was carried out. The primary variables of the investigation include water-to-binder ratio (W/B), pozzolanic material content and curing condition. Three types of hot springs, in the range 40-90oC, derived from different regions in Taiwan were adopted for laboratory testing of concrete curing. In addition, to compare with the laboratory results, compressive strength and durability of practical concrete were conducted in a tunnel construction site. The experimental results indicate that when concrete comprising pozzolanic materials was cured by a hot spring with high temperature, its compressive strength increased rapidly in the early ages due to high temperature and chloride ions. In the later ages, the trend of strength development decreased obviously and the strength was even lower than that of the standard cured one. The results of durability test show that concrete containing 30-40% Portland cement replacement by pozzolanic materials and with W/B lower than 0.5 was cured in a hot spring environment, then it had sufficient durability to prevent steel corrosion. Similar to the laboratory results, the cast-inplace concrete in a hot spring had a compressive strength growing rapidly at the earlier age and slowly at the later age. The results of electric resistance and permeability tests also show that concrete in a hot spring had higher durability than those cured in air. In addition, there was no neutralization reaction being observed after the 360-day neutralization test. This study demonstrates that the concrete with enough compressive strength and durability is suitable for the cast-in-place structure being used in hot spring areas.

The Impact of the Surgeon on the Current Status of ERAS in Asia

How Kwang Yeong 대한외과학회 2019 대한외과학회 학술대회 초록집 Vol.2019 No.10

Feasibility of utilizing oven-drying test to estimate the durability performance of concrete

How-Ji Chen,Hsien-Sheng Peng,Chao-Wei Tang 사단법인 한국계산역학회 2011 Computers and Concrete, An International Journal Vol.8 No.4

The increasing concern for reinforced concrete structure durability has been justifying in many ways in the last few decades. However, there is no perfect durability test method till now. In this research an alternative method, which is based on the cumulative moisture loss percent of the concrete specimens after oven-drying, was proposed to estimate the durability performance of the concrete. Two temperatures were considered for the oven-drying tests: 100°C and 200°C. Test results showed that oven-drying at 200°C was obviously an unsuitable procedure to preserve the fragile microstructure of cement-based materials. By contrast, experimental results through oven-drying at 100°C allowed estimating the moisture loss percent of cement-based materials in a more rational manner. Moreover, the magnitudes of the cumulative moisture loss percent obtained from oven-drying tests at 100°C for 48 hours have good correlations with the data of other well-known methods, namely, electrical resistance test, water permeability test, and mercury intrusion porosimetry test. This investigation established that regarding the oven-drying test as one of the tests for evaluating the potential durability of concrete is considerably practicable.

Numerical modeling of drying shrinkage behavior of self-compacting concrete

How-Ji Chen,Te-Hung Liu,Chao-Wei Tang 사단법인 한국계산역학회 2008 Computers and Concrete, An International Journal Vol.5 No.5

Self-compacting concrete (SCC), characterized by the high flowability and resistance to segregation, is due to the high amount of paste (including cement and mineral admixtures) in contrast with normal concrete (NC). However, the high amount of paste will limit the volume fractions of coarse aggregate, and reduce the tendency of coarse aggregate to suppress drying shrinkage deformations. For this reason, SCC tends to produce higher values of drying shrinkage than NC for the most part. In order to assess the drying shrinkage of SCC quantitatively for application to offshore caisson foundations, the formulas presented in the literatures (ACI 209 and CEB-FIP) are used to predict the values of drying shrinkage in SCC according to the corresponding mix proportions. Additionally, a finite element (FE) model, which assumes concrete to be a homogeneous and isotropic material and follows the actual size and environmental conditions of the caisson, is utilized to simulate stress distribution situations and deformations in the SCC caisson resulting from the drying shrinkage. The probability of cracking and the behavior of drying shrinkage of the SCC caisson are drawn from the analytic results calculated by the FE model proposed in this paper.

Influence of high-cycle fatigue on the tension stiffening behavior of flexural reinforced lightweight aggregate concrete beams

How-Ji Chen,Te-Hung Liu,Chao-Wei Tang,Wen-Po Tsai 국제구조공학회 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.40 No.6

The objective of this study was to experimentally investigate the bond-related tension stiffening behavior of flexural reinforced concrete (RC) beams made with lightweight aggregate concrete (LWAC) under various high-cycle fatigue loading conditions. Based on strain measurements of tensile steel in the RC beams, fatigue-induced degradation of tension stiffening effects was evaluated and was, compared to reinforced normal weight concrete (NWC) beams with equal concrete compressive strengths (40 MPa). According to applied load-mean steel strain relationships, the mean steel strain that developed under loading cycles was divided into elastic and plastic strain components. The experimental results showed that, in the high-cycle fatigue regime, the tension stiffening behavior of LWAC beams was different from that of NWC beams; LWAC beams had a lesser reduction in tension stiffening due to a better bond between steel and concrete. This was reflected in the stability of the elastic mean steel strains and in the higher degree of local plasticity that developed at the primary flexural cracks.

Time-dependent properties of lightweight concrete using sedimentary lightweight aggregate and its application in prestressed concrete beams

How-Ji Chen,Wen-Po Tsai,Chao-Wei Tang,Te-Hung Liu 국제구조공학회 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.39 No.6

We have developed a lightweight aggregate (LWA) concrete made by expanding fine sediments dredged from the Shihmen Reservoir (Taiwan) with high heat. In this study, the performance of the concrete and of prestressed concrete beams made of the sedimentary LWA were tested and compared with those made of normal-weight concrete (NC). The test results show that the lightweight concrete (LWAC) exhibited comparable time-dependent properties (i.e., compressive strength, elastic modulus, drying shrinkage, and creep) as compared with the NC samples. In addition, the LWAC beams exhibited a smaller percentage of prestress loss compared with the NC beams. Moreover, on average, the LWAC beams could resist loading up to 96% of that of the NC beams, and the experimental strengths were greater than the nominal strengths calculated by the ACI Code method. This investigation thus established that sedimentary LWA can be recommended for structural concrete applications.

Urinary tract infection among clean room workers

How-Ran Guo 한국환경보건학회 2006 한국환경보건학회 학술대회 자료집 Vol.2006 No.-