Wave Refraction-Diffraction in the Presence of a Current

-Wave refraction-diffraction due to a large ocean structure and topography in the presence of a 'current are studied numerically. The mathematical model is the mild-slope equation developed by Kirby (1984). This equation is solved using a finite and boundary element method. The physical domain is devid-ed into two regions: a slowly varying topography region and a constant water depth region. For waves propagating in the constant water depth region, without current interfering, the mild- slope equation is then reduced to the Helmholtz equation which is solved by boundary element method. In varying topography region, this equation will be solved by finite element method. Conservation of mass and energy flux of the fluid between these two regions is required for composition of these two numerical methods. The numerical scheme proposed here is capable of dealing with water wave problems of different water depths with the main characters of these two methods.     

Numerical Simulation of Dynamic Response of Towed Systems

In this paper,the dynamic response of undersea -+towed systems is numerically simulated.Atwo body towed system is especially considered in detail.The factors influencing the heave oftowed-bodies,such as the weight of the towed-body(in sea water),the length and the weight(in sea water)per unit length of the cable between towed-bodies and towing ship,are investigated in detail.Calculationsshow that the two-body towed system can greatly increases the stability of the towed system.     

Japan's traditional view of nature and interpretation of landscape

Recently a few Japanese geographers became aware that the concept of nature in modern geography differs from that of traditional Japanese thought. As modern geography in Japan was formed by the influence of European geography, most academic geographers in Japan have followed the occidental view that proposed an opposition between cultural and natural landscapes and that, due to the belief in man's power, sees the former as superior to the latter. From an economic view point, in fact, the European concept of nature which is opposed to culture has contributed to land exploitation that caused the destruction of Japan's natural landscape.The time has come to consider the traditional Japanese idea of nature as Kami (gods) in comparison with the binary opposition of nature/culture which derives from modern rationalism. Kami who represent elements of nature belonged to a Pantheon in ancient Japan. Some examples of the Kami's names and their English explanations are as follows: Amaterasuomikami (godess of sun), Oyamatsumi-no-kami (god of the mountain's spirit), Nozuchi-no-kami (god of the field's spirit). In ancient Japan people believed that natural landscapes were created and inhabited by these Kami, and that the will of these Kami controlled the cultural domain. However, people provided shrines for Kami to placate their reckless domination. In this context, culture is in the hands of nature. This idea of nature's superiority to culture can explain the Japanese geographical concept of landscape.     

A contribution to the geology of the Bahariya Oasis,Western Desert,Egypt

Detailed petrographic investigations of the Upper Cretaceous-Eocene succession exposed at Bahariya Oasis resulted in the recognition of different litho- and biofacies associations, mostly of the carbonate rock type.The litho- and biofacies characters of the Eocene strata reveal comparatively shallow, quiet marine conditions, interrupted by agitated, high energy intervals.During the Maastrichtian age, deeper quiet marine conditions prevailed. The Upper and Lower members of the Campanian strata were deposited under deep quiet marine conditions, relative to shallower agitated conditions that prevailed during the deposition of the middle member.The Lower Cenomanian sediments were deposited under an alternating high and low energy fresh water environment, interrupted with saline (fluviomarine) periods, relative to the comparatively deeper marine conditions that prevailed during the Upper Cenomanian age.The main diagenetic processes recorded are: cementation, aggrading neomorphism, silicification and dolomitization.     

Quality Assessment of Concrete Blocks Exposed in Nature for Eighty Years

The concrete blocks used on a jetty in Shanghai were made in 1909 and 1910. Having been exposed in nature for 80 years, now there are 4600 pieces of blocks left on the jetty. Comprehensive inspections, such as external appearance examination, core-drilling of concrete blocks, ultrasonic detection, nuclear densimeter inspection and in-door and out-door chemical analysis, show that 75% of the blocks are of the rebound number of 21 - 23, and the saturated limit compressive strength and dry limit compressive strength of 10MPa; the carbonized depth of concrete is 1 - 2 mm. Compared with the state of the jetty in 1968, already used for 60 years then, the jetty is expected to serve another 40 years or more after being repaired.     

Hybrid Element Method for Calculation of Harbor Resonance

This paper presents a hybrid element method for calculating harbor resonance in a coastal or offshore harbor under the effects of friction and boundary absorption. The friction term is assumed to be proportional to the flow velocity with a phase difference. The boundary absorption adopts a condition similar to the impedance condition in acoustics. In the near region a variational principle is established. In the far region the solution satisfies the Helmholtz equation. Computation results of harbor resonance by the model show good agreement with experimental data and theoretical result.     

Computation of Long-Term Statistical Properties of Wave Agitation in Harbors

In this paper,the long-term statistical properties of wave height in an idealized square harborwith a partial opening are studied.The incident waves are propagated into the harbor numerically by the fi-nite/infinite element method using three different wave models:(1)monochromatic wave train,(2)long-crested random wave train,and(3)short-crested random wave train.This study shows that for a giv-en incident wave,the wave height in the harbor is affected by the wave model used.For long-term estima-tion of wave height exceedance probability,it is recommended that the waves be propagated into the har-bor using the random wave model,and that wave heights be computed by use of the Rayleigh probabilitydistribution.     

Analysis and Research of Ice Loads Acting on Offshore Structures

- Usually, the action of sea ice on offshore engineering structures is one of the controlling loads in cold waters engineering structure design. The reasonable selection of environmental condition and the physical mechanical properties of ice in the region are directly related to the structure design, operation and safety. In this paper, the sea ice force acting on the structure, the physical mechanical properties of ice and the selection of parameters in calculation are discussed. Some suggestions are proposed as to the calculation of various kinds of ice loads acting on the structure.     

Bacteriogenic sulfur isotopic ratios in geology

Stable sulfur isotopes may aid in distinguishing sulfides of a magmatic hydrothermal origin from sulfides containing biogenic sulfur. For those sulfide ore depositis that are intimately associated with the intrusive body from which it is inferred their ore solutions were derived, the variation in S³⁴ values is generally less than ± 5 permil. Biogenic sulfides, on the other hand, exhibit a broad spread in S³⁴ values that is rately less than a few permil. The reason for this is that the sulfur produced, as hydrogen sulfide by anaerobic bacteria, is isotopically fractionated by variable amounts resulting in a relatively broad spread in S³⁴ values.Raw culture experiments have illustrated the isotopic effects resulting from reduction of sulfate to hydrogen sulfate by sulfate reducing bacteria. The characteristics of enrichment of S³² to a highly variable extent in hydrogen sulfide is verified by these experiments.In addition, a series of closed system raw culture experiments resulted in fractionation factors between 1.043 to 1.062 which are similar to variations in S³⁴ between juxtaposed sulfides in nature produced by bacteriogenic processes.Speech delivered on October 1, 1965, on the occasion of the colloquy concerning Sulphurisotopes organized by the Deutsche Forschungsgemeinschaft at Bad Sooden-Allendorf.     

Die Paläogeographische Entwicklung des Mittelamerikanisch-Westindischen Raumes

Zusammenfassung Die geologische Überlieferung des Untersuchungsgebietes beginnt im Jungpaläozoikum, in dem der Kern Mittelamerikas durch zwei Orogenesen geprägt wurde. Kartographische Darstellung der Paläogeographie ist aber erst vom oberen Jura an mit einiger Zuverlässigkeit möglich. Es zeichnen sich folgende Gebiete unterschiedlicher tektonischer und paläogeographischer Entwicklung ab: Das Kerngebiet des nördlichen Mittelamerikas, sein nördliches Vorland mit Vortiefe und Yucatán-Plattform, das Orogen des südlichen Mittelamerikas, das Antillenorogen mit Großen Antillen, Inseln vor und unter dem Winde, das Orogen der venezuelanischen Küstenkordillere und die karibischen Meeresbecken.Nach einer weitreichenden jurassisch-kretazischen Transgression führt die laramische Orogenese zur Landbildung, die im nördlichen Mittelamerika auf weite Gebiete endgültig ist, während die Antillen und das südliche Mittelamerika schon im Alttertiär wieder überflutet werden. Die Antillen verdanken ihre heutige Gestalt jungtertiärer Faltung und an Brüche gebundener Hebung. Das südliche Mittelamerika durchläuft von Eozän bis Miozän die Entwicklung von Geosynklinale und Orogenese. Erst vom Pliozän an ist die Festlandsbrücke geschlossen. Das karibische Meeresbecken wird als jungmesozoischer Festlandsblock aufgefaßt, um den herum sich Geosynklinalen ausbilden konnten. Mit der laramischen Orogenese begann er zur heutigen Tiefsee abzusinken.

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Central America and the West Indies belong to the zone of circum-Pacific orogens and consists of the following units which are of different paleogeographic development: Northern Central America, the Southern Central American Orogen, the Orogen of the Greater Antilles, the Orogen of the Leeward Islands, the chain of the volcanic Lesser Antilles and the Caribbean Sea Regions.In the mountain chains of Northern Central America a Paleozoic core crops out. The question as to its continuation in the Antilles has often been discussed, but not yet been answered. After a stratigraphic hiatus which probably comprises the whole Triassic and locally parts of the Jurassic there followed another period of continental sedimentation. Marine beds of the Neocomian indicate a new transgression which reaches its culmination in the Albian. During the Upper Cretaceous regression began and at the end of the Cretaceous, the marine sedimentation zone had been driven back in an northern direction. The regression took place in connection with partially strong laramic folding.The development of the Southern Central American Orogen started in the Upper Cretaceous with the deposition of thick submarine volcanic and clastic rocks indicating the formation of a geosyncline. Orogenic movement, acompanied by regression followed in the Upper Cretaceous but in the Lower Tertiary most parts of Southern Central America built a marine trough filled by thick volcanic sediments. In Upper Miocene this trough was folded and general uplift of the isthmus began.In the Orogen of the Greater Antilles the Middle Jurassic Formation of Cuba preface the development of the Antillean geosyncline, which following the Lower Cretaceous extended from Cuba to the Virgin Islands. At the end of the Cretaceous, the Antillean geosyncline was caught up in the Laramide orogenesis which was followed in the major part of the West Indies by regional uplift and rapid erosion. In the Middle Eocene, there began a new and widespread marine transgression, which left the Antilles as a few small, scattered islands and deposited a cover of massive, neritic limestone over most of the region. A major deformation began in the Miocene, with folding of the Lower Tertiary sediments and uplifting of the cores of the present-day islands. During Late Miocene and Pliocene, extensive peneplains were formed, which, as a result of the youngest crustal movements in the Antilles, now stand at elevations as great as 2.000 meters, or 6.600 feet.In the Lesser Antilles, volcanic activity began in the Eocene and continued with interruptions into the Recent. The Leeward Islands are remanents of a Late Cretaceous geosyncline.The hypotheses on the geological development of the Caribbean Sea are contradictory:Schuchert considered it to be an old basin, others were of the opinion, that until the end of the Cretaceous, a continental landmass occupied the position of the present-day Caribbean Sea, finally,Woodring considered that during the Cretaceous, it was a volcanic archipelago. The writer favours the idea, that a Caribbean continent was in existance during the Mesozoic, nethertheless it must be pointed out, that the results of refraction seismographic research support an opposite view.

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Résumé On peut classifier l'Amérique Centrale et les Antilles dans des régions différentes qui ont achevé un développement paléographique dinstinct. En Amérique Centrale nucléaire les plus anciennes formations datées paléontologiquement, contiennent des fossiles du Carbonifère supérieur. Là-bas le plissement paléozoique a produit une importante masse continentale. En conséquence, le Trias et le Jurasique sont continentaux. Une nouvelle invasion marine se produit au Crétacé inférieur. Au Crétacé supérieur, la mer se retire vers le Nord. En conséquence d'une orogénèse laramienne l'Amérique Centrale nucléaire reste continent aussi pendant le Tertiaire et le Pléistocéne, exceptées les régions du bord.Le développement de l'Amerique Centrale isthmique est tout à fait différent. La série stratigraphique, qui débute au Crétacé, a été affecté par des mouvements laramiens. Depuis commença une invasion marine dans l'Eocène. Il se forma une géosynclinal. Vers la fin du Miocène des mouvements se produisent en Amérique Centrale isthmique. Les chaînes de montagnes d'aujourd'hui commençèrent alors à se lever de la mer. L'isthme panamien a émergé complètement à la fine du Pliocène.L'histoire géologique des Antilles commença avec l'Oxfordien supérieur de Cuba. Au Crétacé une sédimentation marine et volcanique est connue dans l'ensemble des Antilles, à l'éxception des Petites Antilles. L'orogénèse laramienne est très générale dans les Antilles. A cause d'elle des grandes régions se convertirent en continent et îles. Une transgression éocène s'est produite dans la plupart des îles. Puis la sédimentation calcaire s'est étendue très loin. Dans le Miocène moyen il y a eu des mouvements orogéniques. A cause d'eux les nouyaux des îles d'aujourd'hui sont sortis. Dans le Pliocène et le Pléistocène les montagnes s'elèvèrent dans les lignes de fracture.La situation de la mer des Antilles est problematique. Quelques auteurs la considerent comme un continent enfoncé, des autres comme un vieux océan. Une troisième opinion suppose qu'au Crétacé la mer des Antilles était un archipel volcanique.

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