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Tuesday, 26 May 2015

One accident doesn't mean a thing is risky...

A while ago I wrote about a new section of bike lane that I use on the way to work. It was created one year ago with the ambition to improve, but “done with sudden turns (radius 2 meters) were I and other bikers (two-way) are supposed to [as we are turning and keeping our eyes on the cars] share a lane less than 2 meters wide. It is also marked out with curb stones immersing the bike lane risking striking down bikers”.

Today at the very spot described above there was an accident involving at least two bikers (the slow careful types judging by their appearance) and a car. One person looked to be injured enough to be waiting for an ambulance. This is otherwise a quite spot and a lot of people where helping so I hope everything worked out just for the best.
All intersections can have an accident, even in their first year. This without proving that the intersection is a bad one (about this one I however have my doubts).

Monday, 18 May 2015

Comparison between different survivability measures on a generic frigate

New published article in International Journal of maritime Engineering:

Choosing suitable survivability measures is a demanding task that has to start early in the ship design process. Throughout the design process there is a need for compromises that will define and sometimes limit future operations or capabilities. In this study generic survivability measures are compared. The study also examines the sensitivity of the calculated probabilities to changes in the threat description. The result shows that it is important to investigate the total effect of a hit over a set of relevant ship functions defined for example by survivability levels. The calculations for different threat definitions show that the changes in survivability are substantial when the threat definition is changed. Moreover, the effects of different hit assumptions differ between weapon types. This must be treated as an uncertainty which also should be reflected in the output and weighted into the decisions made, based on the survivability analysis.
Authors: Hans Liwång, Swedish Defence University and Chalmers University of Technology, Henrik Jonsson, Royal Swedish Navy.

Saturday, 16 May 2015

Survivability of an ocean patrol vessel – Analysis approach and uncertainty treatment

New published article in Marine Structures:

Abstract (somewhat extended)

Military ocean patrol vessels (OPVs) are today an increasingly common type of naval ship. To facilitate the wide range of tasks with small crews, OPVs represent several ship design compromises between, for example, survivability, redundancy and technical endurance. Some of these compromises are new to military ships.
The aim of this study is to examine how the design risk control options in relation to survivability, redundancy and technical endurance can be linked to the operational risks in a patrol and surveillance scenario where the ship can be attacked by a suicide bomber with an IED in a small boat. The ship operation for a generic OPV, including the actions of the threat, is modeled with a Bayesian network describing the scenario and the dependency among different influences. The probabilities for the consequences to the crew, ship buoyancy and maneuverability as a result of a possible attack are calculated.
The scenario is described with expert data collected from subject matter experts. The approach includes an analysis of uncertainty using Monte Carlo analysis and numerical derivative analysis.
The results show that it is possible to link the performance of specific ship design features to the operational risk. Being able to propagate the epistemic uncertainties through the model is important to understand how the uncertainty in the input affects the output and the output uncertainty for the studied case is small relative to the input uncertainty. The study shows that linking different ship design features for aspects such as survivability, redundancy and technical endurance to the operational risk gives important information for the ship design decision-making process.

Author: Hans Liwång
Department of Military Studies, Swedish Defence University, 11593, Stockholm, Sweden.