Analisis Perbaikan Stern Tube Poros Propeller Single Screw pada Kapal General Cargo 4192 GT

<p>Dalam proses perencanaan kapal, pada tahap pemasangan poros propulsi di kapal, tentu saja diperlukan penyelarasan yang benar. Kesalahan dapat menyebabkan distribusi beban yang tidak merata pada bantalan, akibatnya menyebabkan abrasi yang tidak normal, kondisi kelebihan beban, kelebihan beban dan kerusakan pada bagian bantalan tertentu, hal tersebut berlaku juga kepada struktur yang mendapat beban statis sebagai tumpuannya. perlunya uji numerik untuk proses analisa terjadinya beban berlebih dalam persiapan reparasi bantalan poros <em>propeller</em> sehingga menunjukan karakter hidrodinamik dan beban yang terjadi ketika bantalan dan poros <em>propeller</em> mulai kontak. Tujuan penelitian ini,menganalisis desain bantalan poros <em>propeller </em>untuk direparasi dan untuk mendapatkan performa terbaik dari sistem kontak antara bantalan dengan poros <em>propeller</em> sehingga merepresentasikan perbandingan kinerja dari <em>propeller</em> sebelum dan sesudah perbaikan. Metode perhitungan dengan metode <em>finite elemen</em> berbasis persamaan matematik merepresentasikan tegangan yang terjadi sesuai karakter material <em>bronze</em> ( AlBr dan CuSn) yang diaplikasikan pada performa bantalan proros <em>propeller</em> kapal tipe <em>general cargo</em> seberat 4192 GT. Hasil analisa menunjukan saat putaran <em>propeller</em> pada rpm mesin yang optimum, tegangan maksimum juga terjadi sesuai dengan hasil percobaan temperatur yang terjadi juga semakin tinggi. Pada beban rpm 525 maka <em>shear stress</em> untuk <em>stern tube</em> material AlBr bernilai 978 Mpa dan pada material SnCu bernilai 948 Mpa. Nilai <em>deflect </em>atau <em>cleareance </em>pada setiap posisi setelah dilakukan perbaikan mengalami peningkatan rata-rata sebesar 24,4 % dari pengukuran awal sebelum dilakukan reparasi. Proses reparasi menunjukan performa yang cukup baik, rata-rata temperatur kerja yang dihasilkan ketika dilakukan pengujian <em>sea trial</em> menurun dari sebelumnya sebesar 7,5%.</p>

Development of AUV MONACA - Hover-Capable Platform for Detailed Observation Under Ice –

The melting of ice and changes in ocean currents in Antarctica must be investigated to understand global climate change. In this regard, the volume changes of sea ice and ice shelves, bathymetry, and ocean currents in the Antarctic Ocean must be measured in three dimensions. Therefore, the use of autonomous underwater vehicles (AUVs), which can directly observe under ice, is being considered. The authors developed an AUV named Mobility Oriented Nadir AntarctiC Adventurer (MONACA) to observe sea ice and the lower region of the ice shelf in the Antarctic Ocean. Herein, we describe MONACA and its basic autonomous navigation methods (altitude control, depth control, and waypoint tracking), as well as report the results of a sea experiment conducted in Shimoda Bay, Japan. During the 5-day sea trial, the MONACA successfully measured bathymetry by tracking 15 waypoints in sequence, switching the control criteria in the -axis direction between 3 m depth and 3 m altitude.

Quantifying The Impact That Coxswain Behaviour Has on Whole Body Vibration - Simulator Trial

A common risk to personnel is from Whole Body Vibration (WBV) and shock when transiting at speed in heavy seas, and much research has been done by maritime organisations to reduce this risk and the associated health impacts. It is well known that coxswain ‘driving style’ can radically affect exposure levels for a given sea state and sustained transit speed. A data-driven approach to define what makes a good coxswain from a WBV perspective is currently being developed by the Naval Design Partnering team (NDP). In phase 1, a systematic coxswain behaviour tracking methodology has been developed and demonstrated using a motion platform-based fast craft simulator at MARIN. The performance of several experienced volunteer coxswains from MOD, RNLI and KNRM has been evaluated based on a set pattern of tests. The advantages of using the simulator, over a sea trial, have been demonstrated: it is more repeatable, more controllable, accurate and more accessible. The potential disadvantages of the approach are also discussed with reference to feedback gathered from coxswains. Analysis has shown effective throttle control is much more important than steering to reduce WBV. Several interesting trends in WBV reduction potential have been shown which it is thought, with further validation, could aid mission planning, mission execution and provide data for training autonomous feedback/control algorithms. Further work is required before the findings of this study can be fully exploited. These subsequent phases, which include sea trials, aim to provide validation and further evidence to support the initial findings.

Experimental Results of Underwater Acoustic Communication with Nonlinear Frequency Modulation Waveform

In this paper, we propose underwater acoustic (UWA) communications using a generalized sinusoidal frequency modulation (GSFM) waveform, which has a distinct ambiguity function (AF) and correlation function characteristic. For these reasons, it is more robust in multipath channels than the conventional chirp spread spectrum (CSS) with a linear frequency modulation (LFM) waveform. Four types of GSFM waveforms that are orthogonal to each other are applied for each symbol in the proposed method. To evaluate the performance of the proposed method, we compared the performances of the proposed method and conventional method by conducting diverse experiments: simulations, lake trials and sea trials. In the simulation results, the proposed method shows better performance than the conventional method. The lake trial was conducted with a distance of 300~400 m between the transmitter and receiver. As a result of the experiment, the average bit error rate (BER) of the proposed method is 3.52×10−2 and that of the conventional method is 3.52×10−1, which shows that the proposed method is superior to the conventional method. The sea trial was conducted at a distance of approximately 20 km between the transmitter and receiver at a depth of 1500 m, and the receiver was composed of 16 vertical line arrays (VLAs) with a hydrophone. The proposed method had a BER of 0.3×10−2 in one channel and was error free in the other.

Energy Consumption Modeling for Underwater Gliders Considering Ocean Currents and Seawater Density Variation

Energy management is a critical and challenging factor required for efficient and safe operation of underwater gliders (UGs), and the energy consumption model (ECM) is indispensable. In this paper, a more complete ECM of UGs is established, which considers ocean currents, seawater density variation, deformation of the pressure hull, and asymmetry of gliding motion during descending and ascending. Sea trial data are used to make a comparison between ECMs with and without the consideration of ocean currents, and the results prove that the ECM that considers the currents has a significantly higher accuracy. Then, the relationship between energy consumption and multiple parameters, including gliding velocity relative to the current, absolute gliding angle, and diving depth, is revealed. Finally, a simple example is considered to illustrate the effects of the depth-averaged current on the energy consumption.

Dynamic Landing Control of a Quadrotor on the Wave Glider

Aiming at the problems of difficult attitude stabilization, low landing accuracy, large external disturbance and slow dynamic response during the quadrotor dynamic landing on the wave glider, an improved series active disturbance rejection control method for the quadrotor is proposed. The quadrotor controller with inner-loop attitude angular velocity control and outer-loop position control based on the active disturbance rejection controller (ADRC) is designed by analyzing the dynamic model of the quadrotor. A tracking differentiator (TD) is adopted to track the input signal, and an expansive state observer (ESO) is used to estimate the total disturbance. Moreover, a nonlinear law state error feedback (NLSEF) is used to generate the virtual control volume of the system to realize the control of the quadrotor, and the stability of the cascaded self-turbulent controller is verified by Lyapunov’s theory. The simulation verifies that the proposed controller can accurately control the attitude and the position with better anti-interference capability and faster tracking speed. According to the final sea trial, a combination of an active disturbance rejection controller optimized with improved crow search algorithm (ICADRC) and April Tag visual reference system is used to land the quadrotor efficiently and successfully even under the surface float attitude uncertainty.