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Optomechanical Design Principles
Published in Anees Ahmad, Handbook of Optomechanical Engineering, 2018
There are two important types of vibration that affect optomechanical systems: periodic and random. Periodic vibration is characterized by a period and amplitude. The amplitude of complex periodic vibration is characterized, statistically, by quantities such as the root-mean-square of the amplitude. Random vibration is also characterized by statistical methods. Random vibration contains all frequencies. One statistical quantity that is often used to describe random vibration is the power spectral density (PSD). The PSD is a measure of the amplitude of vibration contained within some bandwidth, typically 1 Hz. Since PSD is a measure of the area under a curve, it is given in units of area per bandwidth. One such measure is “g2/Hz”, where “g” is a dimensionless acceleration unit (1 g = acceleration of Earth’s surface gravity).
Preliminary Concepts
Published in Hillel Rubin, Joseph Atkinson, Environmental Fluid Mechanics, 2001
Surface water waves develop at the water free surface, which is the interface between the water and air phases. In general, this interface is considered as a discontinuity in the overall distribution of density in the domain. The state of stable equilibrium of the system is represented by water occupying the lowest portions of the domain. Disturbances to the state of equilibrium are represented by surface gravity waves. Such waves propagate only in the horizontal direction, while the restoring gravity force acts in the vertical direction. Therefore there is no preferred horizontal direction of the disturbance propagation, and the waves are isotropic (they may move equally in any horizontal direction). However, waves of different wavelengths penetrate to different depths into the water phase. This phenomenon has an implication with regard to the inertia of the fluid particles that are directly affected by the waves. Therefore waves of different wavelengths have different wave speed. The dependence of the wave speed on the wavelength causes dispersion of the waves.
Global Geoid Determination
Published in Petr Vaníček, Nikolaos T. Christou, GEOID and Its GEOPHYSICAL INTERPRETATIONS, 2020
The incorporation of altimeter data in modeling has been done at NASA/Goddard Space Flight Center, The University of Texas at Austin, and at The Ohio State University. The first Ohio State results were given in Reference 18. Although this solution did not incorporate surface gravity data, it demonstrated the validity of the modeling effort. A second Ohio State computation19 using Geosat altimeter data did incorporate 1° × 1° surface gravity anomalies. The GEM-T3 model12 incorporates altimeter and surface gravity information. Studies at the University of Texas at Austin are described in Reference 24 and at DGFI (Germany)/CNES (France) in Reference 13.
The wavedrifter: a low-cost IMU-based Lagrangian drifter to observe steepening and overturning of surface gravity waves and the transition to turbulence
Published in Coastal Engineering Journal, 2023
F. Feddersen, Andre Amador, Kanoa Pick, A. Vizuet, Kaden Quinn, Eric Wolfinger, J. H. MacMahan, Adam Fincham
where s is the location of the acceleration peak (Figure 2), and the fit-parameters are , s, and . It is useful to note that for a period of s (or ), an acceleration magnitude of implies a vertical oscillation amplitude of mm. Thus, after the initial breach and submergence, the wavedrifter vertical position oscillations are relatively small. When deployed, the wavedrifter will be accelerated vertically by the wave field that is present which will induce small wavedrifter submergences when the sea surface accelerates rapidly. Thus, acceleration variability in a range of frequencies near 2 Hz is expected that should be treated as noise and not as surface gravity waves.
Weighted topology optimization of back-up supporting structures of antennas
Published in Engineering Optimization, 2023
Yuzheng Tan, Shuxin Zhang, Sihao Qian, Jun Song
From the characterization of reflector antennas, the topology optimization of the reflector antenna can be simplified to an overhang Messerschmitt–Bölkow–Blohm (MBB) beam, which is constrained in the centre region. In the following example, by fixing the load node, the direction of the rotational force is equivalent to the force. The problem is described in Figure 6, where the complete design domain, boundary conditions and external loads of the planar array antenna are shown in Figure 6(a). The surface gravity acts on the nodes evenly. Unlike the previous consideration of the vertical direction, the force under a certain angle is decomposed into the longitudinal direction force and the lateral direction force, as shown in Figure 6(b), where the load density is F = 2/a, the design domain is 200 × 20 uniform background element discretization, the specified volume fraction is 0.4, the specified antenna elevation angle is 50°–80° and the angle discretization of stress is 40°–10°. Taking the value uniformly and discretizing it into 11 working conditions, the weight of each working condition is 1/11.
Numerical investigation into motion responses of the intact and damaged DTMB 5415 based on the AMR method in regular waves
Published in Ships and Offshore Structures, 2023
XinLong Zhang, Ping Li, Simone Mancini
The first-order Stokes wave model is approximated to simulate surface gravity waves on a light-heavy fluid interface. A regular wave with a period of 1.2 s and a wave amplitude of 0.08 m are implemented. The theoretical wave elevation equation at a distance of 4 m from the origin is shown as Equation 6. Table 1 shows the effect of three mesh accuracies on the initial position of the wave troughs and crests. The scalar scene shown in Figure 1 visualises the initial position of the wave crest and trough. For the coarse, medium, and fine mesh accuracies, the size of the wave surface is 0.3, 0.2, and 0.1 m. The number of cells of the entire domain is respectively 96000, 174512, and 666444. It can be found that the simulations with three mesh accuracies studied can well capture the waves in the initial state. The maximum error is only 4.2% for the trough position of the coarse case.