Marine Tower Research Articles

Characteristics of Rain and Sea Spray Droplet Size Distribution at a Marine Tower

The effects of sea spray on open-ocean rainfall measurements-the drop size distribution (DSD) and rainfall intensities-were studied using a state-of-the-art optical disdrometer. The number of rain droplets less than 1 mm in diameter is affected by several factors, including the type of rainfall and seasonality. Over the ocean, small rain and large sea spray droplets co-exist in the same diameter size class (0.072 to 1000 mm); hence, sea spray creates uncertainty when seeking to characterize the drop size distribution (DSD) of rain droplets over the ocean. We measured droplet sizes at a marine tower using a state-of-the-art optical disdrometer, a tipping-bucket rain gauge, a wind anemometer, and a time-lapse camera, over a period that included typhoon Krosa of 2019. The number of rain droplets of diameter less than 1 mm increased monotonically as the horizontal wind speed became stronger. Thus, the shape parameter μ of the Ulbrich distribution decreased. This decreasing trend can be recognized as an increase in sea spray. During no-rainfall hours (indicated by rain gauges on the ocean tower and nearby land), sea spray DSDs were obtained at various horizontal wind speeds. Furthermore, the proportions of sea spray to rainfall at different rainfall intensities and horizontal wind speeds were determined; at a horizontal wind speed of 16 to 20 m s−1, the average sea spray proportions were 82.7%, 19.1%, and 5.3% during total rainfall periods of 2.1 mm h−1, 8.9 mm h−1, and 32.1 mm h−1, respectively. Representation of sea spray DSDs, as well as rainfall DSDs, is a key element of calculating real rainfall intensities over the open ocean.

Atmospheric boundary layer measurements over sea ice in the Sea of Okhotsk

The southernmost part of the Sea of Okhotsk, along the northeastern sea coast of Hokkaido, Japan is usually covered with sea ice from early January through March. There are unstable ice packs, some of which consist of drift ice from the north, while others are locally frozen fast ice. This work reviews our knowledge on sea ice distributions and movements monitored by sea-ice radars and measurements of air-ice drag coefficients over sea ice in the coastal Sea of Okhotsk off Hokkaido. In addition, data from the marine tower standing 6.5 m deep in water and 600 off the shore have been analyzed by the eddy corrlation method to obtain wind stress and heat flux for three separate periods of pre-ice forming, ice forming and ice melt. Variations in drag coefficient and in heat flux coefficient of sea ice and water are shown as a function off wind speed, stability and the surface condition of sea ice. Moreover, surface roughness expressed by backscatter signals from a X-band radar is compared to the micrometeorological roughness, i.e., the air-ice drag coefficient.

横浜マリンタワーのライトアップ

横浜マリンタワーのライトアップ

Wind-induced vibration of tower and practical applications of tuned sloshing damper

Wind-induced vibrations of two actual tall towers were reduced to about half upon installation of newly developed Tuned Sloshing Damper, which utilizes liquid motion in circular container. Vibrations at Nagasaki Airport Tower (height 42 m) and Yokohama Marine Tower (height 101 m) were measured during gusty day, before and after installation of damper. The reduced vibration levels after installation were in the range acceptable from the view point of comfort and serviceability. To further estimate the effects of Tuned Sloshing Damper, the dynamic force frequency response function of STD was experimentally determined. Using this frequency response function, numerical simulation on gust responses was conducted. The results indicate that the amplitude level is reduced to about half and this qualitatively agrees well with observation in the Yokohama Marine Tower.

Wave-induced wind fluctuation over the sea

Simultaneous measurements of the sea surface displacement and the longitudinal component of the wind velocity at several levels are reported. They were obtained at the Marine Tower under various conditions, with the air and the waves moving either in the same or in opposite directions. The spectral analysis was made. The cross-correlation coefficient between the sea surface displacement and the wind velocity is large at the layer adjacent to the surface and decreases with increasing mean wind velocity and height. Below a certain level which is several times or several tens of times higher than the height of the critical level where the wind velocity component in the direction of wave propagation equals the wave velocity, the phase lag of the Fourier component of the wind velocity compared with the surface elevation component is about 160 to 190°. Above this layer the wave-induced wind component is very weak and the phase reversal takes place at the height where the mean wind velocity equals 1·2 to 1·5C, C being the phase velocity of wave. When the wind blows in the opposite direction from that of the wave propagation, the wind fluctuation is in phase with respect to the wave motion and the amplitude of wave-induced wind component is relatively large. Some discrepancies are shown between the observations and the predictions from the theory of inviscid fluids.

Mechanical Handling Aspects of the Tilbury Grain Terminal

The grain terminal for the Port of London Authority (P.L.A.) began commercial operation in April 1969. It is designed for discharge of ships up to about 45 000 ton dead weight (d.w.) at rates up to a maximum of 2000 ton/h. The installation provides two discharging machines of the marine tower type, 105 000 ton of silo storage capacity and an ability to handle from ships to silo, rail, road, coaster or to adjacent flour mills. It also permits loading out to coaster or barge either by direct trans-shipment or from silo. Many alternative handling routes are provided and a very large degree of remote control has been incorporated. The majority of the routes are capable of handling up to 1000 ton/h over a single conveyor. The marine towers are unique in Europe and probably incorporate a greater degree of sophistication than exists in any similar equipment in the world. This paper describes briefly the background leading to the construction of the terminal and the layout of the whole installation. Some of the more interesting points in the mechanical handling control system employed with particular reference to the marine towers, methods of routing, tripper control and dust suppression are described in detail. Comparisons are made between the installation at Tilbury and the installation at present under construction for the Mersey Docks and Harbour Company at Seaforth.