Seakeeping assessment of fishing vessels in conceptual design stage

The main idea of this paper is to identify functional relations between seakeeping characteristics and hull form parameters of Mediterranean fishing vessels. Multiple regression analysis is used for quantitative assessment through a computer software that is based on the SQL Server Database. The seakeeping attributes under investigation are the transfer functions of heave and pitch motions and of absolute vertical acceleration at stern, while the ship parameters influencing motion dynamics have been classified into two groups: displacement (Δ) and main dimensions (L, B, T), coefficients that define the details of the hull form (C_WP, C_VP, LCB, LCF, etc.).Four multiple regression models having different parameter combinations are here investigated and discussed, giving way to the so-called ‘Simple Model’, ‘Intermediate Model’, ‘Enhanced 1 Model’ and ‘Enhanced 2 Model’. The obtained results are more than satisfactory for seakeeping predictions during the conceptual design stage.     

Subharmonic oscillations in nonlinear rolling

In this paper the rolling motion of a ship is examined with particular regard to the possibility of obtaining oscillations which are subharmonic to the excitation frequency. Three different mechanisms are found to be responsible for this phenomenon, the importance of which has already been recognized in the context of ship stability. The first is related to a strong symmetric or non-symmetric nonlinearity in the righting arm. The second is linked to the harmonic composition of sea waves and the third to the well known parametric excitation caused by coupling between different ship motions in a following sea.The onset of subharmonics is related to a threshold value for the excitation strongly depending on damping. The more appropriate analytical methods for a theoretical study of each mechanism are suggested.     

Velingrad Hydrogeothermal System (Bulgaria): Geochemical Features and Heat Output

Lithology and Mineral Resources - The geothermal and hydrochemical parameters of a large hydrogeothermal system located in the city of Velingrad and its environs (southwestern Bulgaria) are...     

On damping models in free and forced rolling motion

In this paper two different models for the damping moment to introduce in the rolling equation of the ship are proposed. They contain two terms, respectively linear-quadratic and linear-cubic in the angular velocity, and furthermore they foresee a non-linear term representing the dependence of the damping from the heeling angle. These models constitute a generalization of all the models up to now used in the naval literature.With the Bogoliubov-Krilov asymptotic method approximate relations, describing the decay curve of the free oscillations and the maximum roll amplitude in synchronism condition, are obtained. The analysis shows that the choice of the more realistic damping model cannot be based on the simple verification of a good fitting of the free oscillation decay curves. It is necessary to examine also the behaviour of the forced oscillations in synchronism.Finally, a plan of experiments which allows the determination of separate values for the different non-linear damping coefficients is proposed.     

Flexural uplift of the Stara Planina range, central Bulgaria

The Stara Planina is an E–W-trending range within the Balkan belt in central Bulgaria. This topographically high mountain range was the site of Mesozoic through early Cenozoic thrusting and convergence, and its high topography is generally thought to have resulted from crustal shortening associated with those events. However, uplift of this belt appears to be much younger than the age of thrusting and correlates instead with the age of Pliocene–Quaternary normal faulting along the southern side of the range. Flexural modelling indicates the morphology of the range is consistent with flexural uplift of footwall rocks during Pliocene–Quaternary displacement on S-dipping normal faults bounding the south side of the mountains, provided that the effective elastic plate thickness of 12  km under the Moesian platform is reduced to about 3  km under the Stara Planina. This small value of elastic plate thickness under the Stara Planina is similar to values observed in the Basin and Range Province of the western United States, and suggests that weakening of the lithosphere is due to heating of the lithosphere during extension, perhaps to the point that large-scale flow of material is possible within the lower crust. Because weakening is observed to affect the Moesian lithosphere for ≈10  km beyond (north of) the surface expression of extension, this study suggests that processes within the uppermost mantle, such as convection, play an active role in the extension process. The results of this study also suggest that much of the topographic relief in thrust belts where convergence is accompanied by coeval extension in the upper plate (or 'back arc'), such as in the Apennines, may be a flexural response to unloading during normal faulting, rather than a direct response to crustal shortening in the thrust belt.     

Evidence from the Mesta half-graben, SW Bulgaria, for the Late Eocene beginning of Aegean extension in the Central Balkan Peninsula

The ENE-tilted Mesta half-graben contains a 3-km-thick section of Priabonian (Late Eocene) to Oligocene sedimentary and volcanic rocks that rest unconformably on basement metamorphic rocks along its west side. Basal strata dip 50–60° E and dip at progressively lower angles upward, indicating synrotational deposition. The southern part of the half-graben contains nested volcanic caldera complexes, formed during the deposition of the middle part of the sedimentary sequence, which have been rotated by about half the total rotation of the sedimentary succession. The half-graben is bounded on the east by a fault that steepens from more deeply exposed structural levels in the south (8–18° W) to shallower exposed structural levels in the north (70° W) and together with the rotation of Paleogene strata during deposition indicate the Mesta half-graben is underlain by a listric detachment fault, the Mesta detachment. Subhorizontal Middle Miocene strata that unconformably overlie tilted Paleogene strata yield an upper age limit to the extension. West and northwest of the Mesta half-graben are many other NNW-trending NE-tilted Paleogene half-grabens which we suggest are part of an important extended area in SW Bulgaria and eastern Macedonia that lies above one or more west-dipping detachment faults and date the beginning of Aegean extension in the southern Balkan region as at least as old as Priabonian. The Mesta detachment is oblique to the trend of a contemporaneous Paleogene magmatic arc in the southern Balkans and the origin of the detachment is probably related to gravitationally induced spreading of thickened hot arc crust and Hellenic trench roll back.     

Geomorphic change in high mountains: a western Himalayan perspective

Globally significant interactions between climate, surface processes, and tectonics have recently been proposed to explain climate change and mountain building. Assessing climate-driven erosion processes and geomorphic change in high-mountain environments, however, is notoriously difficult. In the western Himalaya, the coupling of climate, surface processes, and tectonics results in complex topography that frequently records the polygenetic nature of topographic evolution over the last 100 ka. Depending upon the erosional history of a particular landscape, temporal overprinting of geomorphic events can produce unique topographic properties which define the spatial complexity of the topography. Field work coupled with analysis of the topography using digital elevation models (DEMs) enable low- and high-frequency spatial patterns and scale-dependent properties of the topography to be detected and associated with geomorphic events caused by climate and tectonic forcing. We conducted spatial analysis of the topography at Nanga Parbat in northern Pakistan to demonstrate the utility of geomorphometry and to characterize dramatic geomorphic change over the past 100 ka. Results indicate rapid river incision, extensive glaciation, and variable denudation rates by mass movement, glaciation, and catastrophic flood flushing. Furthermore, topographic and chronologic evidence indicate that glaciation is strongly controlled by the southwestern monsoon, and that modern fluvial systems are still responding to tectonic forcing and deglaciation. Scale-dependent analysis of the topography revealed that different erosion processes uniquely alter the spatial complexity of the topography, such that the greatest mesoscale relief appears to be caused by glaciation. Collectively, our results indicate that topographic development in the western Himalaya is inherently polygenetic in nature, with glaciation, fluvial and slope processes all playing important roles at different times, and that they can do so sequentially on the same portion of the landscape. Given the rapidity of major changes in climate and glaciation over the last 100 ka, the landscape cannot be in steady-state.     

The Sub-Balkan graben system of central Bulgaria

The Sub-Balkan graben system in central Bulgaria forms the present northern boundary of the Aegean extensional region. This east-trending graben system lies along the southern flank of the Stara Planina range and consists mainly of half-grabens. The sedimentary fill in the grabens ranges in age from late Miocene to Recent and records the initiation and evolution of the graben system. The sedimentary fill in the grabens is oldest in the central graben and becomes progressively younger to the west and east, indicating a diachronous development of the grabens. Grabens are formed in the hangingwalls of south-dipping low-angle normal faults which have been displaced by younger higher angle normal faults along the foot of the Stara Planina. Hangingwall rocks have been complexly faulted and rotated such that some graben fill has been rotated down-to-the-north. The Sredna Gora range south of the grabens is part of a complexly faulted and rotated hangingwall block bounded on the south by south-dipping normal faults forming the northern boundary of the Thracian Basin. The Stara Planina range has been formed by uplift and rotation due to footwall unloading along the low-angle normal faults and forms the northern margin of the graben system. Most of the topography of Bulgaria south of the Sub-Balkan graben system is the result of late Miocene to Recent extensional processes linked to the Aegean region that have been superposed on convergent features and earlier extensional features that extend back to late Eocene time.     

Nonlinear dynamics of an elastic cable during laying operations in rough sea

A numerical approach for predicting motion and tension of extensible marine cables during laying operations in a rough sea is presented here. The solution methodology consists of dividing the cable into straight elements, which must satisfy an equilibrium equation and compatibility relations. The system of nonlinear differential equations is solved by the Runge–Kutta method, taking the effect of regular and/or irregular waves into account explicitly.

Illustrative applications of the method are given for a typical cable laying ship. The results are presented as rms values of the cable dynamic tension and corresponding dynamic factor for two different types of cable and several values of cable stiffness. The effect of axial deformation on the maximum tension at the shipboard pulley location is highlighted.