A comparison of methods for calculating the motion of a semi-submersible

The 17th ITTC Ocean Engineering Committee undertook the comparison of methods for calculating semi-submersible wave motion, and 34 programs from 28 different organizations participated in the project. The summary of the results are reported in the Technical Report of the 17th ITTC (ITTC, 1984).In this paper, the details of the project are described. Namely, almost all the calculation results of the 34 programs are shown and examined from the viewpoints of the validity of the program itself and of the correlation between the differences in the various calculation methods and the differences in the calculation results. The calculation results are also compared with the experiments, the details of which are also illustrated.     

The effect of the Mt St Helens eruption on tropospheric and stratospheric ions

Balloon-borne observations of electrical conductivity in the troposphere and stratosphere were performed using conductivity sondes at Garmisch-Partenkirchen, West Germany, from June to November, 1980, after the Mt St Helens eruption. A significant decrease of atmospheric ions in the altitudes from the troposphere to lower stratosphere has been detected until several months after the eruption in comparison with the observational results obtained before the eruption. Simulteneous ruby lidar observation a month after the eruption indicates an increased amount of aerosol at nearly the same altitude as that of conductivity decrease. Several months after the eruption it appears that aerosols detected by lidar and those effective in reducing ion concentration have different profiles.     

The K-band Hubble diagram of submillimetre galaxies and hyperluminous galaxies

We present the K -band Hubble diagrams ( K – z relations) of submillimetre-selected galaxies and hyperluminous galaxies (HLIRGs). We report the discovery of a remarkably tight K – z relation of HLIRGs, indistinguishable from that of the most luminous radio galaxies. Like radio galaxies, the HLIRG K – z relation at   z ≲ 3  is consistent with a passively evolving ∼3 L _* instantaneous starburst starting from a redshift of   z ∼ 10  . In contrast, many submillimetre-selected galaxies are ≳2 mag fainter, and the population has a much larger dispersion. We argue that dust obscuration and/or a larger mass range may be responsible for this scatter. The galaxies so far proved to be hyperluminous may have been biased towards higher AGN bolometric contributions than submillimetre-selected galaxies due to the 60-μm selection of some, so the location on the K – z relation may be related to the presence of the most massive active galactic nucleus. Alternatively, a particular host galaxy mass range may be responsible for both extreme star formation and the most massive active nuclei.     

Impact fragmentation experiments of basalts and pyrophyllites

Results of impact fragmentation experiments for basalts and pyrophyllites are reported. Aluminum cylindrical projectiles were impacted on cubic basalt and pyrophyllite targets at velocities of 70 to 990 m/sec. The targets and projectiles were 20 g to 3.3 kg and 2 to 20 g in weight respectively. Weights of the fragments produced by impacts were measured and the size distributions of fragments were examined. Data of the largest fragment mass (m_L) normalized to the original target mass (M_t), m_L/M_t, correlate better with the nondimensional impact stress, P_I, a new scaling parameter introduced by H. Mizutani, Y. Takagi, and S. Kawakami (1984, in preparation) than the conventional projectile's kinetic energy per unit target mass, E/M_t, used in the previous studies. All the m_L/M_t data for basalts obtained in the present study are summarized by m_L/M_t = 2.95 × 10^?2P_I^?1 where P_I = P₀L³/YR³, P₀ = peak shock pressure, L = projectile size, R = target size and Y = material strength of target. For aluminum targets, however, the m_L/M_t is 2.5 orders of magnitude larger than that for brittle targets at impacts with the same P_I. Size distributions of fragments expressed in a log N - log (m/M_t) diagram divided into three regimes bounded by two inflection points. In each regime the curve is expressed by $\text{N (>}\text{m}\text{M}{}_{\mathrm{t}}\text{) = A (}\text{m}\text{M}{}_{\mathrm{t}}\text{)}{}^{\mathrm{?a}}$. The slopes, a, of the log $\text{N -}\text{log}\text{(}\text{m}\text{M}{}_{\mathrm{t}}\text{)}$ curves in the regimes of a large and a medium size range are positively correlated with the nondimensional impact stress, P_I, and expressed as a = C₃ + a₃log P_I. The slopes, a, in the smallest size range are, on the other hand, nearly constant and have values of $\text{0.5}\text{to}\text{0.7 (}\text{1}\text{2}\text{?}\text{2}\text{3}\text{)}$. Present results indicate that the impact fragmentation is scaled well by the new scaling parameter, P_I, of Mizutani, Takagi, and Kawakami and that the present experimental data may shed new light on planetary impact processes.     

Automated cloud tracking system for the Akatsuki Venus Climate Orbiter data

Japanese Venus Climate Orbiter, Akatsuki, is cruising to approach to Venus again although its first Venus orbital insertion (VOI) has been failed. At present, we focus on the next opportunity of VOI and the following scientific observations.We have constructed an automated cloud tracking system for processing data obtained by Akatsuki in the present study. In this system, correction of the pointing of the satellite is essentially important for improving accuracy of the cloud motion vectors derived using the cloud tracking. Attitude errors of the satellite are reduced by fitting an ellipse to limb of an imaged Venus disk. Next, longitude–latitude distributions of brightness (cloud patterns) are calculated to make it easy to derive the cloud motion vectors. The grid points are distributed at regular intervals in the longitude–latitude coordinate. After applying the solar zenith correction and a highpass filter to the derived longitude–latitude distributions of brightness, the cloud features are tracked using pairs of images. As a result, we obtain cloud motion vectors on longitude–latitude grid points equally spaced. These entire processes are pipelined and automated, and are applied to all data obtained by combinations of cameras and filters onboard Akatsuki. It is shown by several tests that the cloud motion vectors are determined with a sufficient accuracy. We expect that longitude–latitude data sets created by the automated cloud tracking system will contribute to the Venus meteorology.     

A comparison of channel-base currents and optical signals for rocket-triggered lightning strokes

A comparative analysis has been performed of the channel-base current and light waveforms for four rocket-triggered lightning strokes. It has been found that the current and light signals at the bottom of the channel exhibit a linear relationship (direct proportionality) in their rising portions. However, just after the peaks the linearity disappears, and the light signals usually decrease faster than the currents during the next several microseconds. Later, this trend is reversed and in some cases the light signals show another rising trend, even when the currents continue to decrease. The linear light/current relationship for the rising portions of the waveforms appears to be the same for different strokes. The findings support the idea of evaluating the variation of return stroke current along the lightning return stroke channel using light signals, provided that evaluation is limited to the rising portions of those signals and assuming that the light/current relationship observed at the bottom of the channel holds at other heights.     

Measurement of lower-stratospheric aerosol by a balloon-borne photometer

Height distribution of the stratospheric aerosol extinction coefficient was measured in the altitude range 10 to 20 km by a balloon-borne multi-color sunphotometer in May 1978. It is demonstrated that detailed structures of the distribution of stratospheric aerosol can be remotely measured by the solar occultation method as well as by lidar andin situ particle counter observations. In the aerosol layer appearing at 18 km altitude the extinction coefficient at 800–1000 nm wavelength reached to 3×10^–7 m^–1, which was reasonable compared with lidar observations. Wavelength dependence of the aerosol optical depth was crudely estimated to be proportional to ^–1.5.     

Design of mooring system of vessels inside breakwater

A method of simulation calculation for a mooring system of vessels inside a breakwater is illustrated. Using a simulation program based on the above method, a test design for a mooring system for oil-storage vessels of total 5.6 million kiloliters was conducted.In order to obtain data for the simulation program, various experiments, such as wind tunnel tests to test wind resistance, and wave tank tests to test the waves transmitted through or over the breakwater, and the motions of vessels inside the breakwater due to waves, were conducted.Some proposals concerning design criteria and safety factors are presented.Finally, the results of the test design under estimated sea and weather conditions are shown, and the design is concluded to be both technically and economically feasible.