Pneumatic and similar breakwaters

1955 ◽  
Vol 231 (1187) ◽  
pp. 457-466 ◽  
Keyword(s):  
Small Amplitude ◽  
Wave Motion ◽  
Surface Current ◽  
Water Velocity ◽  
Air Injection ◽  
Air Bubbles ◽  
Surface Currents ◽  
Damping Effect ◽  
Water Jets ◽  
Set Up

The process of calming waves by injecting air bubbles beneath the surface has been known to civil engineers for nearly 50 years. It has been little used for its results have been erratic, its method of working was unknown and its effect could not be predicted. The investigation described in this paper has shown that the surface currents set up by air injection, and the distribution of the water velocity within the currents, can be matched by currents set up by water jets, and that the two currents so matched have almost the same wave-damping effect whether they are set up by water jets or by air. It is concluded that the bubbles as such have at most a very small effect on the wave motion. It is found that waves of small amplitude are stopped in the way predicted theoretically, but that as the amplitude increases the surface current necessary to stop waves of a given length increases.

The action of a surface current used as a breakwater

1955 ◽  
Vol 231 (1187) ◽  
pp. 466-478 ◽  
Keyword(s):  
Surface Current ◽  
Water Current ◽  
Air Bubbles ◽  
Surface Currents ◽  
Mean Velocity ◽  
Uniform Velocity ◽  
Sea Bottom ◽  
The Mean ◽  
Perforated Tube ◽  
A Current

The conditions under which an outward-flowing surface current can prevent the passage of waves coming in from the sea are investigated mathematically. Two types of current are considered: ( a ) a current with uniform velocity extending to a depth h ; ( b ) a current with velocity decreasing uniformly and vanishing at depth h . They have very similar effects. The mean velocity required to stop waves of given frequency is rather greater in case ( a ) than in case ( b ). The water current produced by a curtain of air bubbles from a perforated tube on the sea bottom is investigated theoretically on the assumption that the bubbles are very small. Evans (1955) has measured the surface currents produced in a tank by a bubble curtain and finds them smaller than predicted. The discrepancy is partly due to the fact that the bubbles were not very small.

Effect of Air Fraction on Force Coefficients in Oscillatory Flow

2021 ◽  
Author(s):  
Malene Hovgaard Vested ◽  
Erik Damgaard Christensen
Keyword(s):  
High Speed ◽  
Offshore Structures ◽  
Air Injection ◽  
Wave Loads ◽  
Morison Equation ◽  
Force Coefficients ◽  
Air Content ◽  
Set Up ◽  
High Level ◽  
Spilling Breakers

Abstract The forces on marine and offshore structures are often affected by spilling breakers. The spilling breaker is characterized by a roller of mixed air and water with a forward speed approximately equal to the wave celerity. This high speed in the top of the wave has the potential to induce high wave loads on upper parts of the structures. This study analyzed the effect of the air content on the forces. The analyses used the Morison equation to examine the effect of the percentage of air on the forces. An experimental set-up was developed to include the injection of air into an otherwise calm water body. The air-injection did introduce a high level a turbulence. It was possible to assess the amount of air content in the water for different amounts of air-injection. In the mixture of air and water the force on an oscillating square cylinder was measured for different levels of air-content, — also in the case without air. The measurements indicated that force coefficients for clear water could be use in the Morison equation as long as the density for water was replaced by the density for the mixture of air and water.

An Approach for Efficient CFD Simulations of an Ejector Air Injection System for Active Aerodynamic Compressor Stabilization

2017 ◽  
Author(s):  
Sebastian Brehm ◽  
Felix Kern ◽  
Jonas Raub ◽  
Reinhard Niehuis
Keyword(s):  
Large Scale ◽  
Armed Forces ◽  
Air Injection ◽  
Injection System ◽  
Cfd Simulations ◽  
Data Set ◽  
Numerical Effort ◽  
Enhance Efficiency ◽  
Set Up ◽  
Novel Concept

The Institute of Jet Propulsion at the University of the German Federal Armed Forces Munich has developed and patented a novel concept of air injection systems for active aerodynamic stabilization of turbo compressors. This so-called Ejector Injection System (EIS) utilizes the ejector effect to enhance efficiency and impact of the aerodynamic stabilization of the Larzac 04 two-spool turbofan engine’s LPC. The EIS design manufactured recently has been subject to CFD and experimental pre-investigations in which the expected ejector effect performance has been proven and the CFD set-up has been validated. Subsequently, optimization of the EIS ejector geometry comes into focus in order to enhance its performance. In this context, CFD parameter studies on the influence of in total 16 geometric and several aerodynamic parameters on the ejector effect are required. However, the existing and validated CFD set-up of the EIS comprises not only the mainly axisymmetric ejector geometry but also the highly complex 3D supply components upstream of the ejector geometry. This is hindering large scale CFD parameter studies due to the numerical effort required for these full 3D CFD simulations. Therefore, an approach to exploit the overall axissymmetry of the ejector geometry is presented within this paper which reduces the numerical effort required for CFD simulations of the EIS by more than 90%. This approach is verified by means of both experimental results as well as CFD predictions of the full 3D set-up. The comprehensive verification data set contains wall pressure distributions and the mass flow rates involved at various Aerodynamic Operating Points (AOP). Furthermore, limitations of the approach are revealed concerning its suitability e.g. to judge the response of the attached compressor of future EIS designs concerning aerodynamic stability or cyclic loading.

scholarly journals Characteristic Mode Analysis of surface current distributions on metallic structures exposed to HIRF- and DCI-excitations

2020 ◽  
Vol 18 ◽  
pp. 33-41
Author(s):  
Jan Ückerseifer ◽  
Frank Gronwald
Keyword(s):  
Three Dimensional ◽  
Surface Current ◽  
Resonance Region ◽  
Mode Analysis ◽  
Surface Currents ◽  
Characteristic Mode ◽  
Metallic Structures ◽  
Current Distributions ◽  
Characteristic Modes ◽  
Physical Quantities

Abstract. This paper treats Characteristic Mode Analyses of three-dimensional test objects in the context of EMC. Based on computed Characteristic Modes and mode-specific physical quantities, series expansions for HIRF- and DCI-induced surface currents are deduced. The contribution of single Characteristic Modes to surface currents at different test frequencies is analyzed. HIRF- and DCI-excitations are compared with regard to their surface current distributions in their resonance region determined by Characteristic Mode Analysis.

scholarly journals A New Small Drifter for Shallow Water Basins: Application to the Study of Surface Currents in the Muggia Bay (Italy)

2016 ◽  
Vol 2016 ◽  
pp. 1-5 ◽  
Author(s):  
Carmelo Nasello ◽  
Vincenzo Armenio
Keyword(s):  
Free Surface ◽  
Shallow Water ◽  
Coriolis Force ◽  
Surface Current ◽  
Meteorological Conditions ◽  
Water Current ◽  
Surface Currents ◽  
Water Basin ◽  
Surface Circulation ◽  
The City

A new small drifter prototype for measuring current immediately below the free surface in a water basin is proposed in this paper. The drifter dimensions make it useful for shallow water applications. The drifter transmits its GPS location via GSM phone network. The drifter was used to study the trajectory of the surface current in the Muggia bay, the latter containing the industrial harbor of the city of Trieste (Italy). The analysis has been carried out under a wide variety of wind conditions. As regards the behavior of the drifter, the analysis has shown that it is well suited to detect the water current since its motion is marginally affected by the wind. The study has allowed detecting the main features of the surface circulation within the Muggia bay under different meteorological conditions. Also, the study has shown that the trajectory of the surface current within the bay is weakly affected by the Coriolis force.

Quantization of a Free Particle in a Dissipative Medium: Interaction of Charged Particles With Matter

2005 ◽  
Author(s):  
Eqab M. Rabei ◽  
Abdul-Wali Ajlouni ◽  
Humam B. Ghassib
Keyword(s):  
Wave Function ◽  
Energy Loss ◽  
Free Particle ◽  
Canonical Quantization ◽  
Charged Particles ◽  
Dissipative Medium ◽  
Nonconservative Systems ◽  
Damping Effect ◽  
Free Particles ◽  
Set Up

Following our work on the quantization of nonconservative systems using fractional calculus, the canonical quantization of a system of free particles in a dissipative medium is carried out according to the Dirac method. A suitable Schro¨dinger equation is set up and solved for the Lagrangian representing this system. The wave function is plotted and the damping effect manifests itself very clearly. This formalism is then applied to the problem of energy loss of charged particles when passing through matter. The results are plotted and the relation between the energy loss and the range agrees qualitatively with experimental results.

Application of the GWPS for Machining of a Transmission Housing

2000 ◽  
Author(s):  
Suren B. Rao ◽  
Gary L. Neal ◽  
Edward C. DeMeter ◽  
Martin W. Trethewey
Keyword(s):  
Reference Frame ◽  
Surface Current ◽  
Prototype System ◽  
Specific Information ◽  
Accuracy And Precision ◽  
Machining System ◽  
Housing Component ◽  
Set Up ◽  
Novel Concept ◽  
Machining Operations

Abstract One component of a modern machining system that has remained virtually unchanged, since time immemorial, is part location. The fundamental basis of current methods of part location is the concept of a physical datum surface, which is created in the first machining operation and conducting all the further machining operations with reference to this physical surface. Current workpiece positioning practice utilizes physical contacts between the fixture and workpiece for location. Due to contact feature variations, the positioning is inconsistent and variable for sequential machining set-ups. Consequently, geometric errors are induced in machined features. This paper proposes a novel concept, the Global Workpiece Positioning System (GWPS), for datum establishment. Precision artifacts are strategically located on the rough workpiece and a part reference frame is defined, with respect to these artifacts, at a qualification station. This part specific information now travels with the part to the machining station. At the machining station a probe is used to locate the artifacts on the part and determine their location with reference to the machine tool’s reference frame. Since the part reference frame is known with respect to the artifacts, its location can be derived with respect to the machine tool’s reference frame. The part program can then be modified to reflect the actual location of the part and the machining of the features carried out with a greater degree of accuracy and precision. A prototype system using the GWPS concept is implemented and presented. Experimental results validate the GWPS concept. A three-hole pattern is drilled and bored in an aircraft transmission housing component in a two set up operation. The GWPS located workpieces retained a hole center location accuracy within the required drawing specification without the use of the traditional location fixtures that are typically used for the two operational set-ups.

scholarly journals Dynamics of the Land–Sea Breeze System and the Surface Current Response in South-West Australia

2020 ◽  
Vol 8 (11) ◽  
pp. 931
Author(s):  
Syeda Rafiq ◽  
Charitha Pattiaratchi ◽  
Ivica Janeković
Keyword(s):  
Surface Current ◽  
Field Measurements ◽  
Sea Breeze ◽  
Wind Forcing ◽  
Current Response ◽  
Surface Currents ◽  
The South ◽  
Wind Speeds ◽  
North East ◽  
South West

The land–sea breeze (LSB) system, driven by the thermal contrast between the land and the adjacent ocean is a widely known atmospheric phenomenon, which occurs in coastal regions globally. South-west Australia experiences a persistent and one of the strongest LSB systems globally with maximum wind speeds associated with the LSB system often exceeding 15 ms−1. In this paper, using field measurements and numerical simulations, we examine: (1) the local winds associated with the land–sea breeze with an emphasis on the ocean; and, (2) the response of the surface currents to the diurnal wind forcing. The measurements indicated that the wind speeds decreased between midnight and 0400 and increased rapidly after 1100, reaching maxima >10 ms−1 around 1800) associated with the sea breeze and decreased to midnight. Wind directions were such that they were blowing from south-east (120°) in the morning and changed to almost southerly (~200°) in the afternoon. Decomposition of the wind record to the diurnal and synoptic components indicated that the diurnal component of winds (i.e., LSB) was oriented along the south-west to north-east axis. However, the stronger synoptic winds were from the south-east to south quadrant and in combination with the LSB, the winds consisted of a strong southerly component. We examined the evolution, horizontal extent, and propagation properties of sea breeze fronts for characteristic LSB cycles and the sea breeze cell propagating offshore and inland. The results indicated that the sea breeze cell was initiated in the morning in a small area, close to 33° S, 115.5° E, with a width of ~25 km and expanded onshore, offshore and alongshore. The sea breeze cell expanded faster (30 kmh−1) and farther (120 km) in the offshore direction than in the onshore direction (10 kmh−1 and 30–40 km). Winds during the LSB cycle followed a counterclockwise rotation that was also reflected in the surface currents. The winds and surface currents rotated anticlockwise with the surface currents responding almost instantaneously to changes in wind forcing but were modified by topography. The diurnal surface currents were enhanced due to the resonance between the LSB forcing and the inertial response.

The Experimental Study of the Magnetic Fluid Damper Based on the Principle of Second-Order Buoyancy

2012 ◽  
Vol 512-515 ◽  
pp. 1459-1463 ◽  
Author(s):  
Yi Ding ◽  
De Cai Li ◽  
Qing Lei Wang ◽  
Hai Na Zhang ◽  
Zhi Li Zhang
Keyword(s):  
Experimental Study ◽  
Magnetic Fluid ◽  
Second Order ◽  
Test Rig ◽  
Damping Effect ◽  
Fluid Damper ◽  
Reduction Effect ◽  
Set Up ◽  
The Relationship

Two different structure of dampers based on the principle of second-order buoyancy were designed in this paper. In order to verify the reduction of the vibration, a test rig was set up. On the test rig, the reduction effect of two different dampers was studied by adjusting the amount of the magnetic fluid. The experiment results indicate the relationship between the damping effect of magnetic fluid damper and the amount of magnetic fluid and this analysis result is benefit to the design of the dampers.

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