• Wind and Structures
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• v.22 no.1
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• pp.17-41
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• 2016

To address the uncertainty of the flight trajectories caused by the turbulence and gustiness of the wind field over the roof and in the wake of a building, a 3-D probabilistic trajectory model of flat-type wind-borne debris is developed in this study. The core of this methodology is a 6 degree-of-freedom deterministic model, derived from the governing equations of motion of the debris, and a Monte Carlo simulation engine used to account for the uncertainty resulting from vertical and lateral gust wind velocity components. The influence of several parameters, including initial wind speed, time step, gust sampling frequency, number of Monte Carlo simulations, and the extreme gust factor, on the accuracy of the proposed model is examined. For the purpose of validation and calibration, the simulated results from the 3-D probabilistic trajectory model are compared against the available wind tunnel test data. Results show that the maximum relative error between the simulated and wind tunnel test results of the average longitudinal position is about 20%, implying that the probabilistic model provides a reliable and effective means to predict the 3-D flight of the plate-type wind-borne debris.

• The Journal of Engineering Geology
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• v.33 no.1
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• pp.201-211
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• 2023

This study investigated the damage range of the debris flow to predict the amount of collapsed soil in a landslide event. The height of the collapsed slope and the distance traveled by the collapsed soil were used to predict the total trajectory distance using a random walk model. Debris flow trajectory probabilities were calculated through 10,000 Monte Carlo simulations and were used to calculate the damage range as measured from the landslide scar to its toe. Compiled information on debris flows that occurred in the Cheonwangbong area of Mt. Jirisan was used to test the accuracy of the proposed random walk model in estimating the damage range of debris flow. Results of the comparison reveal that the proposed model shows reasonable accuracy in estimating the damage range of debris flow and that using 10 m × 10 m cells allows the damage range to be reproduced with satisfactory precision.

• Wind and Structures
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• v.13 no.2
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• pp.191-206
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• 2010

Windborne debris is a major cause of structural damage during severe windstorms and hurricanes owing to its direct impact on building envelopes as well as to the 'chain reaction' failure mechanism it induces by interacting with wind pressure damage. Estimation of debris risk is an important component in evaluating wind damage risk to residential developments. A debris risk model developed by the authors enables one to analytically aggregate damage threats to a building from different types of debris originating from neighboring buildings. This model is extended herein to a general debris risk analysis methodology that is then incorporated into a vulnerability model accounting for the temporal evolution of the interaction between pressure damage and debris damage during storm passage. The current paper (Part I) introduces the debris risk analysis methodology, establishing the mathematical modeling framework. Stochastic models are proposed to estimate the probability distributions of debris trajectory parameters used in the method. It is shown that model statistics can be estimated from available information from wind-tunnel experiments and post-damage surveys. The incorporation of the methodology into vulnerability modeling is described in Part II.

• Wind and Structures
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• v.13 no.2
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• pp.95-108
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• 2010

This review paper discusses research from the last few years relating to windborne debris risk models and the essential elements of engineering damage prediction models. Generic types of windborne debris are discussed. The results of studies of debris trajectories that are relevant to damage models are described - in particular the horizontal component of debris velocity as a function of distance travelled. The merits of impact momentum versus impact kinetic energy as a relevant parameter for predicting damage are considered, and how published data from generic cannon Impact tests can be used in risk models. The quantitative variation of debris impact damage with wind speed is also discussed. Finally the main elements of previously-proposed debris damage models are described.

• Wind and Structures
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• v.35 no.2
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• pp.109-120
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• 2022

The force coefficients of rotating plates in the acceleration stage will vary with rotation rate from 0 to stable rotation rate w₀, which are important for quasi-steady theory of plate-like windborne debris to simulate the trajectory. In this paper, a wind tunnel experiment is carried out to study the effects of geometry and the Reynolds number on the variations of mean force coefficients of rotating plates. The rotational lift coefficients are sensitive to both geometry effect and Reynolds number effect, while the rotational drag and moment coefficients are only sensitive to geometry effect. In addition, new empirical formulas for the rotational lift coefficient and moment coefficients are proposed. Its accuracy is verified by comparing the predicted results with existing test data. Based on the experimental data of rotating plates, a new rotational force model for quasi-steady theory, which can be applied to a wider scope, is proposed to calculate the trajectory of plate-like windborne debris. The results show that the new model provides a better match with the tested trajectories than previous quasi-steady theories.

• The Journal of Engineering Geology
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• v.23 no.1
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• pp.57-65
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• 2013

We developed a computer program (CDFlow v. 1.0) to design countermeasures against debris flows in natural terrain. The program can predict the probability of landslides occurring in natural terrain and can estimate the zone of damage caused by a debris flow. It can also be used to design the location and size of countermeasures against the debris flow. The program is run using the ArcGIS Engine, which is one of the most well-known Geographic Information System (GIS) tools for developers. The quasi-dynamic wetness index and the infinite slope stability equation were applied to predict landslide probability as a type of slope safety factor. The calculated safety factor was compared with the required safety factor, and areas of high probable potential for landslides were then selected and represented on the digital map. The volume of debris flow was estimated using these areas of high probable potential for landslides and soil depth. The accumulated volume of debris flow can be calculated along the flow channel. To assess the accuracy of the program, it was applied to a real landslide site at Deoksan-ri, Inje-gun, Kangwon-Province, where four debris barriers have been installed in the watershed of the site. The results of soil tests and a field survey indicate that the program has great potential for estimating probable landslide areas and the trajectory of debris flows. Calculation of the capacity volume of existing debris barriers revealed that they had insufficient capacity to store the calculated amount of debris flow. Therefore, this program enables a rational estimation of the optimal location and size of debris barriers.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.4
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• pp.354-363
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• 2012

Now there are a lot of expired satellites or space debris around the earth orbit and they threaten the operating satellites and manned space missions. KOMPSAT-2 that scheduled to operate the mission by July, 2013 also has to consider the space debris. This paper introduces the '25 years rules' that must be re-entered within 25 years after the space mission for LEO satellites and describes the removal trajectory design that satisfies the '25 years rules' and minimizes fuel consumption. And this paper suggests monte-carlo simulation for risk analysis that causes the approaching object to the removal trajectory. The result shows that the collision probability of worst case presents 6.0741E-07 and it need to more analysis about precise satellite safety during removal maneuver because there is no information about the object size that approaching to the satellites.

• Wind and Structures
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• v.17 no.2
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• pp.185-202
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• 2013

The goal of this study was to investigate the vulnerability of roof tile systems and metal shutters to roof tile debris. Three phases addressed the performance of tile roof systems and metal shutters impacted by roof tile debris. The first phase experimentally evaluated the tile fragment size and quantity generated by a tile striking a tile roof system. The second phase experimentally quantified the puncture vulnerability of common metal panel shutter systems as a function of tile fragment impact speed. The third phase provided context for interpretation of the experimental results through the use of a tile trajectory model. The results provide supporting evidence that while metal panel window shutters provide significant protection against a prevalent form of windborne debris, these systems are vulnerable to tile fragment puncture in design level tropical cyclones. These findings correlate with field observations made after Hurricane Charley (2004).

• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.6
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• pp.745-753
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• 2019

Recently, with the development of long-range / high-altitude guided weapon system for defense against ballistic missile, test range and firing altitude for guided weapons are increasing. Due to the increase in the test range and the intercepting altitude, it is expected to increase the range of safety area required for the firing test. Comparing to the foreign countries which have many desert or non-residence, in the domestic circumstances where the population is concentrated and distributed, it is more important to predict the falling area and to set the safety area for safely carry out the long-range / high-altitude intercept test. In this paper, we consider the following three points. The first is the booster fall trajectory modeling, the second is the shroud fall trajectory modeling, and finally, the debris dispersion modeling for the missile intercept. Especially, the AUTODYN model was used to predict debris falling area which produced in the high-speed guided missile intercepting test.

• Journal of Ocean Engineering and Technology
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• v.37 no.4
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• pp.145-157
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• 2023

Due to a recent increase in maritime activities in South Korea, the frequency of maritime distress is escalating and poses a significant threat to lives and property. The aim of this study was to validate a drift trajectory prediction technique to help mitigate the damages caused by maritime distress incidents. In this study, OpenDrift was verified using satellite drifter data from the Korea Hydrographic and Oceanographic Agency. OpenDrift is a Monte-Carlo-based Lagrangian trajectory modeling framework that allows for considering leeway, an important factor in predicting the movement of floating marine objects. The simulation results showed no significant differences in the performance of drift trajectory prediction when considering leeway using four evaluation methods (normalized cumulative Lagrangian separation, root mean squared error, mean absolute error, and Euclidean distance). However, leeway improved the performance in an analysis of location prediction conformance for maritime search and rescue operations. Therefore, the findings of this study suggest that it is important to consider leeway in drift trajectory prediction for effective maritime search and rescue operations. The results could help with future research on drift trajectory prediction of various floating objects, including marine debris, satellite drifters, and sea ice.