YoungSoon Yang

A comparative study on reliability-index and target-performance-based probabilistic structural design optimization

Abstract Probabilistic structural design optimization enables designers and engineers to quantitatively take into account the uncertainties observed in the structural and environmental properties. In this paper, two approaches to determine the satisfaction of probabilistic constraints are discussed. One is the conventional reliability-index-based approach and the other is a more recently proposed target-performance-based approach. An algorithm, which detects and eliminates the excessive zigzagging iterations during the searches for the most probable failure point and the minimum performance target point, was incorporated. The number of iterations required by the two approaches was investigated in three examples: a cantilever beam, a three-bar truss and a ten-bar truss structure. Based on the results, the target-performance-based approach was found to be superior to the reliability-index-based one in view of both computational efficiency and numerical stability.

Axiomatic design approach for marine design problems

Abstract The axiomatic design approach proposed by N.P. Suh consists of the Independence Axiom and the Information Axiom. The Independence Axiom assists a designer in generating good design alternatives by considering the relationships between the functions and the physical product using a hierarchical mapping procedure. The Information Axiom, which is related to the probability of achieving the given functional requirements, can be used as a criterion for the selection of the best solution among the proposed alternatives in the conceptual or preliminary design stage. In the early stages of marine design, especially ship design, there exists a lot of uncertainty because of the size and complexity of a marine vehicle. This uncertainty often leads to a probabilistic approach rather than a deterministic approach. Ship designs are often routine, requiring small modifications of an existing, successful design. The availability of axiomatic design in this marine design field has been investigated through four examples: a conceptual thruster design, a foil-strut optimization problem, a main engine selection problem, and a barge design problem. By these examples, the possibility of the application of Design Axioms in marine design has been illustrated.

Establishing the methodologies for human evacuation simulation in marine accidents

Abstract Recently, many lives are lost around the world due to passenger ships accidents. The International Maritime Organization (IMO) developed guidelines in May 1999 for the evacuation analysis of ro–ro passenger ships to prevent loss of life in maritime accidents. However, IMO considered these guidelines only as an interim measure and allocated 3 years for their improvement and further development as very limited experience and data were available. In this paper, the requirements of IMO and current research works for evacuation from ship are reviewed. Also the applicable evacuation models are presented and several experimental methods to obtain data of human behavior with consideration to ship list and dynamics are evaluated. In addition, the features of evacuation model, which is being developed by KRISO, are finally given.

A Flexible and Robust Approach for Preliminary Engineering Design Based on Designer's Preference

This study proposes a new set-based design approach for preliminary engineering design that intrinsically contains various sources of uncertainties. The goal is to achieve design flexibility and robustness while capturing designers preference. The proposed design approach includes three computational methods: (1) set representation method to specify the varying degree of desirability of a ranged set of design solutions and performance requirements, thereby enabling the manipulation of uncertain design solutions and requirements based on designers preference structure; (2) set propagation method to obtain performance possibilities achievable by uncertain design solutions, thus exploring a broader design possibilities; (3) set narrowing method to generate a ranged set of feasible solutions (i.e., robust and flexible solution set) instead of single point solution that satisfies changing sets of performance requirements by eliminating infeasible and inferior subsets of solutions, thus allowing designs to be readily adapted to changing conditions. Finally, the proposed design approach is illustrated with a successful implementation of real industrial design problem (i.e., vehicle side-door structure design) in the simulation-based design environment.

Implementing linear models in genetic programming

This paper deals with linear models of genetic programming (GP) for regression or approximation problems when given learning samples are not sufficient. The linear model, which is a function of unknown parameters, is built through extracting all possible base functions from the standard GP tree by utilizing a symbolic processing algorithm. The major advantage of a linear model in GP is that its parameters can be estimated by the ordinary least square (OLS) method and a good model can be selected by applying the modern minimum description length (MDL) principle, while the nonlinearity necessary to handle the given problem is effectively maintained by indirectly evolving and finding various forms of base functions. In addition to a standard linear model consisting of mathematical functions, one variant of a linear model, which can be built using low-order Taylor series and can be converted into the standard form of a polynomial, is considered in this paper. With small samples, GP frequently shows the abnormal behaviors such as extreme large peaks or odd-looking discontinuities at the points away from sample points. To overcome this problem, a directional derivative-based smoothing (DDBS) method, which is incorporated into the OLS method, is introduced together with the fitness function that is based on MDL, reflecting the effects of DDBS. Also, two illustrative examples and three engineering applications are presented.

A trial application of FSA methodology to the hatchway watertight integrity of bulk carriers

Abstract Formal safety assessment (FSA) is a formal, structured and systematic methodology, aimed at enhancing maritime safety, including protection of life, property and marine environment, by using risk and cost–benefit assessments. For the application of this methodology to the rule-making process, the International Maritime Organization (IMO) presented the Interim Guidelines, which describe procedures of FSA and inputs/outputs of each procedure in detail. This paper basically deals with an application of FSA methodology according to the IMOs Interim Guidelines to the hatchway watertight integrity of bulk carriers, which was carried out as a cooperative research between Korean Register of Shipping and Seoul National University. As results of this application study, 18 hazards are identified and 32 risk control measures are devised to reduce the associated risks. Potential risks, costs and benefits when some Risk Control Options are introduced are evaluated in monetary unit of US

Differences in Regional Glucose Metabolism of the Brain Measured with F-18-FDG-PET in Patients with Essential Tremor According to Their Response to Beta-Blockers.

. Finally, some discussions and recommendations based on experiences are also given for both future work and better application of this FSA methodology to the rule-making process.

Reflections of Two Parallel Pathways between the Hippocampus and Neocortex in Transient Global Amnesia: A Cross-Sectional Study Using DWI and SPECT

Objective In this study, there was an investigation as to whether there is a functional difference in essential tremor (ET), according to responses to beta-blockers, by evaluating regional changes in cerebral glucose metabolism. Materials and Methods Seventeen male patients with ET were recruited and categorized into two groups: 8 that responded to medical therapy (group A); and 9 that did not respond to medical therapy (group B). Eleven age-sex matched healthy control male subjects were also included in this study. All subjects underwent F-18 fluorodeoxyglucose (FDG)-PET, and evaluated for their severity of tremor symptoms, which were measured as a score on the Fahn-Tolosa-Marin tremor rating scale (FTM). The FDG-PET images were analyzed using a statistical parametric mapping program. Results The mean FTM score 6 months after the initiation of propranolol therapy was significantly lower in group A (18.13 > 8.13), compared with group B (14.67 = 14.67). The glucose metabolism in group A in the left basal ganglia was seen to be decreased, compared with group B. The ET showed a more significantly decreased glucose metabolism in both the fronto-temporo-occipital lobes, precuneus of right parietal lobe, and both cerebellums compared with the healthy controls. Conclusion Essential tremor is caused by electrophysiological disturbances within the cortical-cerebellar networks and degenerative process of the cerebellum. Furthermore, ET may have different pathophysiologies in terms of the origin of disease according to the response to first-line therapy.

Left dominance of EEG abnormalities in patients with transient global amnesia

Objectives Two parallel pathways have been proposed between the hippocampus and neocortex. Recently, the anterior and posterior hippocampus showed distinct connectivity with different cortical areas in an fMRI study. We investigated whether the two parallel pathways could be confirmed in patients with transient global amnesia (TGA) which is a natural lesion model of a perturbation of the hippocampus. In addition, we evaluated the relationship between the location of the hippocampal lesion and various clinical variables. Methods A consecutive series of 37 patients were identified from the TGA registry database of Seoul National University Bundang Hospital. Based on the location of the diffusion-weighted imaging (DWI) lesion along the anterior-posterior axis of the hippocampus, they were divided into the following three groups: head (n = 15), body (n = 15) or tail (n = 7). To evaluate which cortical regions showed hypoperfusion according to the location of the DWI lesion, their SPECT images were compared between two groups using statistical parametric mapping. We performed hierarchical cluster analysis to group demographic and clinical variables, including the location of the DWI lesion, into clusters. Results Statistical parametric mapping analyses revealed that more anterior DWI lesions were associated with hypoperfusion of the anterior temporal and frontal areas, whereas more posterior lesions were associated with hypoperfusion of the posterior temporal, parietal, occipital and cerebellar areas. The difference was most prominent between the group of hippocampal lesions on the head and tail. Hierarchical cluster analysis demonstrated that vomiting was related to female gender and hippocampal head lesions, whereas vascular risk factors were related to male gender and hippocampal body lesions. Conclusions We confirmed the parallel pathways between the hippocampus and neocortex with DWI and SPECT images of patients with TGA. Patients with hippocampal head lesions and body lesions were clustered within different groups of clinical variables.

Clinical characteristics according to depression screening tools in patients with Alzheimer's disease: View from self, caregiver-reported and drug-intervention pattern

PURPOSE Transient global amnesia (TGA) is a syndrome of unknown etiology. Electroencephalographic (EEG) abnormalities in TGA have been reported previously. We analyzed the frequency and characteristics of EEG abnormalities in patients with TGA. METHODS We collected EEGs of patients with a clinical diagnosis of TGA who had visited the emergency room or the outpatient clinic over a period of 8 years and compared clinical and demographic characteristics of the patients with normal EEGs with those with abnormal EEGs. RESULTS EEG abnormalities were found in 35 (22.9%) out of 153 patients and epileptiform discharges were seen in 26 (74.3%) out of these 35 patients. Spikes or sharp waves were detected on the left side only (48.6%) or on both sides (25.7%), but none of the patients showed spikes or sharp waves on right side only. In six patients the EEG had normalized within three months of presentation, in ten within six months, and in twelve by one year. The EEG remained abnormal in eleven out of the 23 patients one year after presentation. CONCLUSION In this largest consecutive EEG study at one center, the proportion of patients with TGA in whom epileptiform discharges were demonstrated within days of the episode of TGA was significantly higher than in the previous literature. EEG abnormalities such as spikes or sharp waves spontaneously disappeared in almost half of cases over one-year of follow-up. There was a clear left dominance of EEG abnormalities in patients with TGA.