Crown Wall Research Articles

Comparison of new large and small scale overtopping tests for rubble mound breakwaters

Many breakwaters are, due to functional requirements, designed for small wave overtopping discharges. From the EC-research projects OPTICREST and CLASH it is known that overtopping discharges determined from conventional Froude scale models of rubble mound breakwaters are smaller than measured in corresponding prototypes. The present study examines this scale effect by comparing overtopping discharges in small scale and large scale tests. The length scale ratio between the models was 5.7. The reason for using a large scale model instead of a prototype is the difficulties in accurate reproduction of prototype conditions for waves and structure in the model, as prototype conditions are not known in sufficient details. The model was designed to avoid as many model effects as possible. Despite this some differences in wave kinematics were detected, most probably due to differences in wave generation hardware and software. This demonstrates that, even under controlled conditions, it is very difficult to reproduce similar conditions. From the present test results it is concluded, despite the model effect, that a significant scale effect on small overtopping discharges exists also when wind effects are absent. The scale effect seems to be very dependent on the top geometry of the breakwater with much larger scale effects for a low crown wall than for a high one. The paper presents an explanation of this difference.

3D instability analysis of an underground geological repository—an Indian case study

Conceptual geological repositories are generally used for disposing spent nuclear wastes containing both high and low level of nuclear radiation and heat. Due to its long-lasting effect, it is imperative to analyze its long-term effect on the surrounding rock. Before analyzing radiation and thermal effect, it is important to have structurally stable cavern because designing an opening in rock is a more difficult problem than designing the structure made of steel. Underground rocks are under stress because of the weight of the overlying rock, and in addition, an underground opening will produce a stress concentration and stress relaxation in the surrounding rock. If the induced stress in the surrounding rock exceeds its strength, the opening will fail either by fracturing or by deforming more than the tolerable limit. In this paper, the stability of four different shapes of excavation has been examined for conceptual geological repositories in Indian context. This has been done using equivalent continuum numerical model which has been incorporated in the commercial finite difference code-FLAC-3D. Effects of opening shapes on stress distribution, subsidence of crown and side wall, and their stability have been analyzed and discussed. The validation of FLAC3D software for its applicability in conceptual underground geological repositories has been done with a published literature.

混相流研究の進展 ４ 液滴・液膜衝突に及ぼす液膜厚さおよび衝突角度の影響

Two-dimensional interface tracking simulations and photographic experiments were carried out to investigate the effects of film thickness and impingement angle on the splashing event during single-drop impact onto a plane liquid surface. For sufficiently small values of liquid film depth, liquid originally included in the inner region of liquid crown was not transported to the outer region. As a result, the pressure rise at the impact neck became significant, a thin liquid crown was formed, and the crown wall was broken into many secondary drops. Numerical results showed that the pressure rise induced on the bottom wall by drop impact is significantly mitigated if the impacted wall is covered with the liquid film whose thickness is comparable to the primary drop size. With respect to the effect of impingement angle, pressure rise in liquid was equally dependent on the normal and tangential components of impact velocity for slightly and moderately oblique impacts; however, the pressure rise was mitigated for very oblique impacts.

Wave run-up and overtopping over smooth and rock slopes of coastal structures without crown walls

The Journal of the National Science Foundation of Sri Lanka publishes the results of research in all aspects of Science and Technology. The journal also has a website at http://www.nsf.gov.lk/. 2020 Impact Factor: 0.515The JNSF provides immediate open access to its content on the principle that making research freely available to the public supports a greater global exchange of knowledge.

Fracture behaviour of zirconia ceramic cantilever fixed dental prostheses in vitro

Objective. Evaluation of the fracture resistance of all-ceramic cantilever fixed dental prostheses (FDPs) manufactured from zirconia frameworks and veneered with a press ceramic. Material and Methods. Two mandibular premolars were prepared either with a box inlay cavity or with a full crown chamfer preparation and then duplicated. 40-three-unit cantilever FDPs replacing one premolar, with a group size of eight for each design, were manufactured. In group i-i the cantilever FDPs were retained by two inlays, in group i-c by an inlay–crown combination, and in group c-c by two crowns. The frameworks in groups i-c-R and c-c-R were reinforced by an additional shoulder on the oral side of the zirconia frameworks. All FDPs were subjected to thermal cycling (TC) and 600,000 cycles of mechanical loading (ML) with 50 N. The load to fracture was measured and fracture sites were evaluated. Results. The mean fracture values ranged from 172 N to 792 N. Fracture-strength values were significantly lower for the i-i retained FDPs than for the i-c and c-c combinations. There was no significant effect of the reinforcing shoulder in groups i-c-R and c-c-R. For FDPs with a crown on the terminal tooth, fractures were usually within the distal wall of the distal crown. Conclusions. Inlay–inlay retained cantilever FDPs cannot withstand the mastication forces expected. Fracture load values for inlay–crown and crown–crown-retained FDPs encourage further clinical investigation. The mode of fracture indicates that reinforcement of the distal crown wall might enhance fracture resistance.

감육 곡관의 붕괴거동에 미치는 곡관 굽힘각의 영향

The purpose of this study is to investigate the effect of bend angle on the collapse behavior of locally wall thinned pipe bends. For this purpose, the present study performed three-dimensional finite element analysis on the 30-, 60-, and 90-degree pipe bends with local wall thinning at the center of intrados, extrados, and crown, and evaluated the collapse moment for different thinning dimensions under closing- and opening-mode bending with a constant internal pressure. The results showed that, for intrados and extrados wall thinning, the reduction in the collapse moment due to local wall thinning became significant with decreasing bend angle of pipe bends. This effect of bend angle was enhanced with increasing thinning dimensions, and it was clearer for opening-mode bending than for closing-mode bending. For crown wall thinning, however, the effect of bend angle was unclear and was less sensitive to the change of wall thinning shapes.

A215 高速ビデオカメラを用いたMarangoni不安定によるクラウンの崩壊過程の観察

When a viscous drop impacts onto a thin film of ethanol on a solid surface, a lot of hole formations can be observed on the eject crown. The holes are caused by the Marangoni instabilities, which occur at a point where ethanol droplets contact at crown wall of viscous drop. The high-speed video camera, of which frame rate is a million frames per second, is employed for detailed observations.

一層被覆型消波ブロックを用いた護岸の水理特性について

The hydraulic characteristics of block mound seawall with single armor layer are investigated by 2-D model tests. The differences in thickness of armor layer are discussed on wave reflection, wave overtopping and wave force on crown wall. Based on the test results, the necessary height and width of the crown wall can be obtained for the design conditions. The stability of HAMA-BITE, newly developed block for single armor layer, is examined by wave force and stability tests. For thepractical design of block mound seawall with single armor layer, the stability number of HAMA-BITE is formulated as the function of the relative damage level and the number of wave action.

Wave loads on rubble mound breakwater crown walls

Crown walls are primarily built to reduce wave overtopping of mound breakwaters. Several methods have been proposed to calculate wave loads on the crown wall, e.g., Iribarren and Nogales [Iribarren, R., Nogales, C., 1964. Obras Marı́timas. Dossat (Ed.), Madrid, 376 pp.], Jensen [Jensen, O.J., 1984. A Monograph on Rubble Mound Breakwaters. Danish Hydraulic Institute] and Günbak and Gökce [Günbak, A.R., Gökce, T., 1984. Wave screen stability of rubble-mound breakwaters. International Symposium of Maritime Structures in the Mediterranean Sea. Athens, Greece, pp. 2.99–2.112]. In this paper, a new method based on those previous results, and on further experimental work, using monochromatic waves, is presented. The application of the new method requires waves breaking on the armour layer; i.e., only broken waves will reach the crown wall. The method is extended to irregular waves via the hypothesis of equivalence introduced by Saville [Saville, T., 1962. An approximation of the wave run-up frequency distribution. Proc. 8th International Conference on Coastal Engineering, Mexico City] and is applied to the crown walls of Gijón and Bilbao breakwaters in Spain. The comparison of the probability force distributions obtained by the present method to that measured by Burcharth et al. [Burcharth, H.F., Frigaard, P., Berenguer, J.M., Gonzalez, B., Uzcanga, J., Villanueva, J., 1995. Design of the Ciervana breakwater, Bilbao. In: T. Telford (Ed.), Proc. 4th Coastal Structures and Breakwaters, Chap. 3. Institution of Civil Engineers] and Jensen (1984) is relatively good.

Effect of Armor Layer and Crown Wall on Wave Overtopping of Rubble Mound

Recently, randomly placed special armor blocks with single unit versus double unit width are being gradually used for protecting rubble mound breakwaters. With this in mind, we conducted a series of experiments to examine wave overtopping of various types of rubble mound breakwaters. Results indicate that (i) differences in width and void ratio of the armor layer affect both wave energy dissipation on the armor layer and in turn the wave overtopping and wave forces on the crown wall, and (ii) wave overtopping is affected by differences in the height of the armor layer relative to the crown wall height. Also discussed is an alternative design of the crown wall using a perforated wall concept to reduce wave overtopping.

Vertical Clearance Modification of Two Railroad Tunnels

Two century old rock tunnels required increased vertical clearance to accommodate double-stacked container cars. At the Haverstraw and Kingston Tunnels, located on Consolidated Rail Corporation9s River Line up to two ft (0.6 m) of rock was removed from the crown of each tunnel. A survey was conducted at each tunnel to determine the existing vertical clearance, and tunnel mapping and rock mass characterization were performed to assess the stability of the tunnel crown and side walls. Rock reinforcement and rock support were designed based on the field mapping and rock mass characterization. Construction involved removing rock from the crown by smooth wall blasting techniques and installing rock reinforcement and rock support.

WAVE OVERTOPPING ON RUBBLE MOUND BREAKWATERS

The paper gives the results of an extensive series of hydraulic model tests carried out in a random wave flume, in order to study the effects on wave overtopping of the main geometric parameters of a typical rubble mound breakwater with crown wall. The results have been compared with those from other studies and analyzed with different methods. Generalized design diagrams and formulae for the prediction of overtopping discharges are finally given for a large number of popular breakwater configurations.

Variation of Heat Flux through a Combustion Chamber Wall of Pre-chamber type Diesel Engine : Heat Flux through Piston Crown, Cylinder Head, Suction Valve, Exhaust Valve, Pre-combustion Chamber and Exhaust Port Wall

The heat flux through the combustion chamber wall varies periodically with thermodynamical cycle of engine and locally according to various places of the wall. In this research project the heat flux was measured at the walls of piston crown, cylinder head, suction valve, exhaust valve, pre-combustion chamber and exhaust port, and the result was compared with the calculated value of heat loss based on cooling water. The heat flux at any point and at any period during the cycle depends on gas temperature, the surface temperature of wall and gas flow. Especially, it is affected by a jet flow from the pre-chamber and the arrival of a burning flame at these points. The percentage of heat loss from piston crown is about 7%, from cylinder head 4%, from prechamber wall 4%, from suction valve 1%, from exhaust valve 0.5% and from exhaust port 5% of the heat energy supplied by fuel at full load.