Stefan Krüger

A novel strumpellin mutation and potential pitfalls in the molecular diagnosis of hereditary spastic paraplegia type SPG8

Hereditary spastic paraplegia (HSP) is a clinically and genetically heterogeneous, neurodegenerative movement disorder. A total of eight KIAA0196/strumpellin variants have thus far been associated with SPG8, a rare dominant HSP. We present a novel strumpellin alteration in a small family with clinically pure HSP. We corroborated its causality by comparing it to rare benign variants at several levels, and, along this line, also re-considered previous genetic reports on SPG8. These analyses identified significant challenges in the interpretation of strumpellin alterations, and suggested that at least two of the few families claimed to suffer from SPG8 may have been genetically misdiagnosed.

New Insights Into the Flooding Sequence of the Costa Concordia Accident

The tragic accident of the Costa Concordia in January 2012 was one of the most severe large passenger ship accident in Europe in recent times followed by a tremendous public interest. We present the results of an in-depth technical investigation of the flooding sequence which lead to the heeling and grounding of the ship. A fast and explicit numerical flooding simulation method has been developed in the last years to better understand accidents like this one caused by complex and large scale flooding events. The flooding simulation is validated with the help of results from model tests and has been successfully applied to the investigation of several other severe ship accidents. It is based on a quasi-static approach in the time domain which evaluates the hydrostatic equilibrium at each time step. The water fluxes through the openings are computed by a hydraulic model based on the Bernoulli equation. Large and partly flooded openings are taken into account as well as conditional openings like the opening, closing and breaking of doors. The fluxes are integrated in the time domain by a predictor-corrector integration scheme to obtain the water volumes in each compartment involved in the flooding sequence. Due to the fact that the accident happened in calm water at moderate wind speeds close to the shore of the island Giglio this quasi-static numerical flooding simulation can be applied. The results of the technical investigation of the Costa Concordia accident obtained with the help of the developed method are presented. These results match well with the heel and trim motions observed during the accident and the chain of events which lead to the final position of the vessel on the rocks in front of the island Giglio. The explicit and direct approach of the method leads to a fast computational run-time of the numerical method. This allows to study several possible accident scenarios within a short period to investigate for example the influence of the opening and closing of watertight doors and to identify a most likely flooding scenario which lead to this tragic accident.

Computation of Drift Forces for Dynamic Positioning Within the Very Early Design Stage of Offshore Wind Farm Installation Vessels

The German government has decided upon the changeover from fossil and nuclear based electrical power generation to renewable energies. Following from this offshore wind farms are erected in the exclusive economic zones of Germany. For the transportation and installation as well as the maintenance of the wind turbine generators very specialized vessels are needed. The capability of dynamic positioning even in very harsh weather conditions is one of the major design tasks for these vessels. For this reason it is important to know the external loads on the ships during station keeping already in the very early design stage. This paper focuses on the computation of wave drift forces in regular and irregular waves as well as in natural seaway. For validation the results of the introduced calculation procedure are compared to measured drift force data from sea-keeping tests of an Offshore Wind Farm Transport and Installation Vessel.© 2014 ASME

A Fast Sea-Keeping Simulation Method for Heavy-Lift Operations Based on Multi-Body System Dynamics

This paper presents a fast numerical method to analyze heavy-lift operations of ships in short crested waves. For this purpose, a sea-keeping simulation method for the coupled motions of a heavy-lift vessel and a freely suspended load is developed. The method considers the motions of the ship in six degrees-of-freedom and the suspended load as a point mass. The coupling of the multi-rigid-body system of the ship and the suspended load is considered by solving the equation of roll motion together with the Euler-Lagrange equations of the load. This approach allows the simulation of several hours of real time motion in short crested waves within only a few seconds. Consequently, the method is particularly suitable when very long or numerous sea-keeping simulations or statistical results are required. Moreover, the method is applied to evaluate the sea-keeping capabilities of a heavy-lift vessel during a lifting operation conducted offshore in 2013.Copyright

Hydrodynamic Damping and Added Mass of Modern Screw Propellers

The operation of ships with “slow-steaming” poses new problems for the torsional vibration analysis of the drive train. It is well known that the propeller determines the essential part of the mass moment of inertia and the system damping. Both values are determined during the initial design phase by semiempirical methods with have originally been developed by Schwanecke and Grim between 1970 and 1980. Since then, propeller designs have changed significantly and it is unclear if modern propeller designs are still covered by these calculation methods. The paper suggests an extension of Grim’s and Schwanecke’s method for modern screw propellers in homogeneous and unsteady flow. INTRODUCTION The actual trend to operate vessels in the so-called slowsteaming mode has posed a lot of complex problems to the naval architects, as the ships operate far away from their design condition. This is of most importance for the operation of the engine and the propeller. When the propulsion system is operated at low revolutions, it is at the same time operated closer to the torsional vibration resonance, because the drive train is designed with a resonance frequency at low revolutions. During run up or slow down, a so called barred speed range is passed to avoid permanent operation close to the resonance. As a consequence, the layout of the drive train with respect to torsional vibrations must be carried out taking this operational boundary condition into account. With respect to torsional vibrations, the propeller -besides the engineis the main source of excitation as well as the most important damper of the drive train. Furthermore, the mass moment of inertia of propeller – including the so called added mass moment of inertia (MOI) due to forces of the entrained water – dominates the resonance frequency of the drive train. To compute hydrodynamic damping, there are some semiempirical theories available, where the most advanced method was developed by Schwanecke and Grim. Despite the fact that there was a significant development in both numerical and experimental techniques, there are no such applications used for the calculation of propeller damping. Steen [16] has reported that RANS applications can presently not be used to predict propeller damping due to numerical difficulties, and also model tests failed to properly predict propeller damping. Consequently, there are only a very few publications which deal with this problem. Additionally, only a few full scale measurements are available for this problem. For these reasons, the authors have chosen to investigate the Grim/Schwanecke method. The theory of Schwanecke and Grim is based on the established theory of the oscillating airfoil. As the practical application of the theory published by Schwanecke and Grim resulted in complex and time consuming computations, Grim and Schwanecke had introduced some simplifications into the theory. This resulted in quite simple formulae which allowed the computation of hydrodynamic damping and added mass or MOI in an easy way for all six degrees of freedom. However, since these developments screw propellers have been subject to a continuous development, where the aim was mainly to reduce pressure pulses and to increase the efficiency. The most important developments were the introduction of the propeller skew and the application of radially non uniform pitch distributions. Both measures were intended to increase the comfort level of modern propellers, posing the difficulty to the propeller designers to keep the efficiency at least constant. This

Design Aspects of a High Speed Monohull RoPax Ferry

This paper describes the design process of a high speed mono hull RoPax ferry which operates at a Froude number of 0.4. The design task was quite challenging, as two possible transport concepts were in principle possible: Two ships were needed with a total speed of 50knots, which could result in a combination of a 30kn high speed Catamaran plus a conventional 20kn RoPax Ferry or alternatively in two identical sister vessels of 25kn each. The solution with the high speed catamaran plus the conventional RoPax-Ferry defined the total cost budget, which must not be exceeded by the design of the two sister vessels. This resulted in a tough boundary condition and made life cycle cost evaluations necessary.Due to harbor restrictions, the length of the ships was limited by abt. 110m, resulting in a Froude number of abt. 0.4. This resulted in high costs for the propulsion system. The ferries should initially have open RoRo-Cargo spaces for cost reasons, which made the stability requirements (weather criterion plus Stockholm Agreement) quite challenging. This also strongly influenced the design of the final hull form. As the ship is very sensitive to weight, detailed steel structure optimizations had to be carried out to optimize the main grillage systems of the vehicle decks. The hull form and the appendage design required careful optimization to guarantee the required service speed with the engine power which was available in the price budget. As no vessel of comparison was available, the speed power estimation as well as all design tasks had fully to rely on numerical predictions. As the ship had further demanding requirements for course keeping and comfort in waves, the optimization of the hull form must include also these issues.The paper shows that the design of complex ships is actually a holistic task which includes many engineering disciplines. The paper also shows that 1st principle based design methods can support the design process of specialized vessels significantly.© 2015 ASME

Application of Energy Saving Fins on Rudders

Due to rising fuel oil prices in the last decade as well as rising design speeds, it has become common practice to build rudders with twisted leading edges to minimize resistance and cavitation risk. The next step in this development is the application of fins on to the rudder. The aim is to generate a distinct amount of thrust through the fins by retrieving rotational kinetic energy from the propeller slipstream. This paper presents a fast method to design and calculate rudder fins in the propeller slipstream, which has been implemented in the ship design environment E4.Because of his working principle, the propeller induces velocities to its slipstream. In the usual setup, the rudder is placed behind the propeller to generate higher steering forces caused by the higher inflow speed in the slipstream. In this arrangement, propeller and rudder together are forming a rotor–stator system. The gains of the stator can be maximized by adding fins to the rudder. The main challenge of a fin design is the maximization and prediction of the regained thrust from the propeller slipstream. In order to do this, a steady, three dimensional, direct panel method is used to calculate the flow around the rudder and fin bodies, from which later the pressures and forces are evaluated. A lifting line method is used to predict the inflow velocities caused by the vortex dominated propeller slipstream on each panel. A special focus is on the treatment of the vortex wake, as crossing wake elements can lead to numerical instabilities and a wrong wake alignment produces bad thrust predictions.For the purpose of rudder design steady computation should be preferred over fully unsteady computation, since only time average integral values are of interest and the degrees of freedom are reduced to the relevant ones. For example, it is not necessary to know the fluctuation of the angle of attack for the basic design of the profile respective the leading edge of the foil, only the mean value is needed.In the industrial practice, rudder fins are not often used because the calculation is difficult. Until now it is more expensive to design and build the fins than the savings earned by the ship owner. This phenomenon will change in the next years due to better calculations and rising fuel oil prices.Copyright

Analysis of the German Navy Stability Standard BV 1030 With Respect to Operability in Heavy Weather

The stability standard of the German Navy — the BV 1030 — was developed in the mid-sixties of the last century in close cooperation with the German Navy Authorities (now BAIINBw) and the University of Hamburg. Other than the stability standards used for commercial shipping, the BV 1030 is based on righting and heeling lever balances for each individual loading condition of each individual ship. Different types of heeling moments have to be assumed in several combinations and they have to be balanced against the righting levers of the ship. Not only the still water stability curve is subject to this lever balance, but also wave crest and wave trough situations are subject to the stability analysis. The BV 1030 stability standard further requires a minimum stability if the ship is on the wave crest. Since this stability standard is in force, the German Navy never experienced a stability accident. The development of new hull forms with the focus on fuel efficiency has widely brought up new problems in heavy weather, for example the vulnerability for parametric rolling. It was therefore of interest for the German Authorities (BAIIN) whether the existing stability standard has sufficient safety to cover also these phenomena connected to more modern hull forms. Therefore an analysis was carried out in close cooperation between BAIINBw, MARS and TUHH where the operability of several ships of the German Navy was analyzed with numerical sea keeping computations. The nonlinear sea keeping code E4ROLLS was used which allows the computation of time series of the ship motions in irregular, short crested seas. From these computations, operational limits could be derived, or, vice versa, the required stability to guarantee a certain operability. The results showed that the concept of the German BV 1030 stability standard provides a significantly higher safety level compared to IMO standard for commercial ships. The results did also show that for modern hull forms, some adjustments to the existing safety standard were found to be useful to better cope with righting arm fluctuations in longitudinal waves.Copyright