Nghiên cứu xác định đáy chạy tàu hợp lý trong trường hợp có bùn loãng tại một số luồng hàng hải ở việt nam tt tieng anh

MINISTRY OF EDUCATION & TRAINING MINISTRY OF AGRICULTURE & RURAL DEVELOPMENT VIETNAM ACADEMY FOR WATER RESOURCES NGUYEN ANH TUAN STUDY AND DEFINE REASONABLE NAUCTICAL BOTTOM IN FLUID MUD ENVIRONMENT AT SEVERAL VIETNAMESE CHANNELS Major: Hydraulic Construction Engineering Code: 9-58-02-02 PhD THESIS SUMMARY Hanoi, 2020 This thesis has been accomplished at: VIETNAM ACADEMY FOR WATER RESOURCES SCIENTIFIC SUPERVISORS: Supervisor 1: Prof.Dr Nguyen Ngoc Hue Supervisor 2: Assoc.Prof.Dr Nguyen Khac Nghia Member of Thesis committee 1: Dr Trần Văn Sung Member of Thesis committee 2: Assoc.Prof.Dr Tran Thanh Tung Member of Thesis committee 3: Prof.Dr Lê Văn Nghị The PhD thesis shall be defensed at the institual thesis committee of Vietnam Academy for Water Resources at h on The thesis could be referenced at the library of: Vietnam Academy for Water Resources INSTRODUCTION The necessity of the study At present, there are 45 publics and 34 specialized navigational channels with total length of about 1,200 km Almost of these channels are suffering from sedimentation, therefore, for the maintenance of nautical depth, dredging works must be conducted yearly with large consumption of governmental budget In many channels, during dredging process, fluid mud has been recorded Basing on practical experience, shipping in fluid mud environment has been conducted in several areas by reducing under keel clearance However, this solution is lack of scientific basis and suffered from a lot of risks Besides, in some important channels, there is a fact that giant vessels are often required to reduce load and wait for tidal for safety of shipping traffic This solution causes expense increase and decrease of channel operation efficiency The utilization of fluid mud in shipping would help reducing under keel clearance, upsizing vessel capacity or transportation load, thereof, maximizing the efficiency of channel operation From the above mentioned reasons, the study on fluid mud and the utilization of fluid mud in shipping (reasonable nautical depth in fluid mud environment) is regarded of high necessary and practical feasibility Study purposes - Clarifying theory basis of utilizing fluid mud in shipping; - Analyzing the characteristics of estuaries and natural condition to evaluate the possibility of fluid mud occurrence in Vietnamese channels; - Establishing methodology for the definition of fluid mud thickness and nautical bottom; - Establishing methodology for the calculation of monthly sedimentation and defining reasonable dredging time for the maximization of channel operation efficiency Study subject and scope: Study the sediment rule and the formation of fluid mud in several channels in Vietnam, conduct specific calculation for characteristic channels in the northern and southern regions Methodology The following methodology has been applied: - General study: analyzing relevant researches, paper works and information; - Field investigation: field measuring and collecting data for analysis; - Mathematical modeling; remote sensing image interpretation; - Statistic methodology: multi variable regression and Fourier analysis Scientific and practical meanings 5.1 Scientific meanings - Establishing scientific and technological base for the selection of criteria in the definition of fluid mud utilization in shipping and reasonable nautical bottom; - Clarifying several scientific aspects on sedimentation in channels with the occurrence of fluid mud, applying reasonable equipment and methodology to define exactly which channels meet the conditions and requirements for shipping in fluid mud; - Establishing methodology for the calculation of fluid mud thickness in correlation with hydraulic and sediment factors; - Analyzing period sediment rule basing on statistic data; defining reasonable nautical bottom and dredging time 5.2 Practical meanings - Applying to evaluate the shipping in fluid mud environment with the aim of increasing transportation capability and improving the efficiency of channel operation; - Applying for government authority in maritime management and planning for port and channel operation efficiency Content of the thesis - Generally studying and evaluating the possibility of occurring fluid mud at several channels in Vietnam; - Studying the methodology of defining the thickness of fluid mud by applying multi variable regression function, defining reasonable nautical bottom in fluid mud environment; - Studying yearly sediment rule in Vietnamese channel by applying Fourier analysis basis; defining reasonable dredging time for the maximization of channel operation efficiency CHAPTER 1: OVERVIEW OF STUDY ON SHIPPING IN FLUID MUD ENVIRONMENT Chapter represents overview of study objects, methodology and general results of both foreign and domestic studies, thereof, analyzing Vietnam’s conditions and clarifying study content of the thesis Foreign studies: 1.1 Study content: In order to evaluate the feasibility of safety shipping traffic in channels with fluid mud, foreign studies have been conducted on the following issues: - Characteristics of fluid mud and criteria to define fluid mud; - Nautical bottom and methodology of nautical bottom definition in channels with fluid mud; - Scientific comprehension and methodology of defining nautical depth in fluid mud situation; - Feasibility of shipping traffic in fluid mud situation; - Methodology of fluid mud treatment 1.2 Methodology: In order to study the above issues, the following study methods have been applied: - Field investigation and data analysis: field survey (by echo –sounder with multi frequencies), laboratory analysis and modeling; - Physical modeling: study on models, simulation equipment and real shipping - Mathematical model: applying mathematical models developed for specific projects or commercial program (model of Tian-Jian Hsu and Peter A Traykovski, MIKE models…) 1.3 Study results - Fluid mud: According to McAnally et al., fluid mud is a highconcentration suspension of water and clay- and silt-sized particles, typically defined as particles (< 62,5 μm in diameter) in which settling is substantially hindered by the close proximity of sediment particles and flocs, but which has not formed an interconnected matrix of bonds (gelling concentration) strong enough to eliminate the potential for mobility Fluid mud is described by specific charecteristics:: (1) (Rheology), (2) (Density) Fluid mud typically exhibits bulk densities between 1,080 and 1,200 kg/m3 Formation of fluid mud: Fluid mud formation is conducted by physical, chemical and biological processes The formation of fluid mud is affected by fluid dynamic characteristics The causes of fluid mud formation are studied and generally recognized in (1) paper works of William H.McAnally and (2) Jianyi XU and Jianzhong YUAN - Physical characteristics: From a hydrological point of view, suspended load, as a pre-stage of fluid mud, stands between the rule of Newton (100% classical fluid) and the rule of Hooke (classical soil mechanics) - Nautical bottom: A joint PIANC-IAPH working group (PIANC, 1997) defined the nautical bottom as ‘the level where physical characteristics of the bottom reach a critical limit beyond which contact with a ship’s keel causes either damage or unacceptable effects on controllability and manoeuvrability’ most harbour and waterways authorities that have introduced the nautical bottom concept make use of a density criterion: 1,151 -1,317 kg/m3 (Zeebrugge – Belgium) and 1,200 – 1,300 kg/m3 (Yianjing Xingang – China) - Other issues relating fluid mud: Nautical Depth Definition, Active Nautical Depth, Aerobic Agitation, Sediment Traps, Gates and Dikes, Channel Separations, Placement in confined disposal facilities or offshore … 1.4 Domestic studies: In Vietnam, due to sediment characteristics as well as channel operation features, the study on fluid mud and shipping in fluid mud environment has important scientific meaning and high feasibility However, Vietnam has been still lack of comprehensive and professional studies on this issue, except several individual and specific proposals 6 1.5 Analysis of issues needed to be studied - From the results of foreign and domestic studies on fluid mud, it can be seen that many countries have established specific criteria for nautical bottom definition basing on geography, density, stress and visco-elastic data However, due to different natural hydrological characteristics as well as regional physic-mechanical characteristics of sediment, it is impossible to apply exactly the above foreign study results in any specific channel in Vietnam - With specific characteristics of Vietnamese channel, this paper has clarified study orientation as following: (1) Evaluating the feasibility of shipping in fluid mud environment at several channels in Vietnam; (2) Applying multi linear regression analysis, numerical models and GIS remote sensing image precessing technology to propose the methodology for fluid mud thickness definition; (3) Establising criteria of channel operation efficiency in order to clarify nautical bottom and reasonable dredging time in case of occuring fluid mud CHAPTER 2: LITERATURE REVIEW, METHODOLOGY FOR THE DEFINITION OF FLUID MUD AND NAUTICAL BOTTOM IN FLUID MUD ENVIRONMENT Chapter represents the following literature: - Theory of fluid mud transportation under the effect of coastal wave: Density of fluid mud is between 1.08  1.20 g/cm3 Under the effect of stable wave, the variation of fluid mud density occurs correspoindingly 7 At the same wave slope, the lower the fluid mud density is, the bigger  is and vice versa Besides, fluid mud also transports according to wave transmission direction The higher the fluid mud density is, the smaller  is, and relative stress increases In natural condition, the density of fluid mud is higher than 1.2g/cm3, and may reach 1.4 g/cm3 Therefore, the transportation of fluid mud is basically at suspended mode - Disordering and stirring up of fluid mud under the influence of single direction flow:: Fluid mud is of low concentration, suffered from flow influence The influence of single direction flow causes the occurance of displacement in mud surface; mud is disordered and flew in the direction of water flow This flow velocity value is called displacement flow velocity Flow velocity causes mud to be floated and sedimented mud is sturred up, that is call stir-up flow velocity Displacement flow velocity and stir-up flow velocity of fluid mud have close relationship with the density of surface mud - Mud concentration within mud area under the effect of tidal and wave: Value of mud concentration has close relationship with ”flow velocity” term:  Vw  Vtb S   z  gh      n (2.1) in which: S  Average concentration of mud; Vtb  V b  Vl velocity combining wind and tidal Vb  Average velocity in a specific period: Vb = 0,0205 W (W – wind velocity) (2.2) Vw  Average flow velocity due to wave, can be determined as following: Vw  0,2CH s h (2.3) C  Wave transmission velocity; s  Particular weight of mud, s = 2.650ks/m3 Relationship (2.1) is tended to be a straight line Therefore, it can be defined n=2;  = 0,0273 - Mud transportation equation: was established by Teisson in 1991 and has been used in Mike 21MT model In this equation, deposition process is regarded as sedimentation process Sedimentation process can be divided into two separated processes, including: deposition process and sedimentation process - Fourier analysis theory: is statistic analysis method using actual measurement data Actual measurement curve is separated into several single curves (theory) of sin, cosine type with defined cycle Time function f(t) can be represented according to Fourier integral as following: ∞ F(t) = ∫−∞ 𝐹(𝜎)𝑒 2𝜋𝑖𝜎𝑡 𝑑𝜎 ∞ F(𝜎) is spectrum density function F(𝜎) = ∫−∞ 𝑓(𝑡)𝑒 −2𝜋𝑖𝜎𝑡 𝑑𝑡 For calculation with discrete time series, Fourier formula is rewrited as following: F(t) = 𝐴0 𝜋𝑘𝑡 )∆𝑡 𝑁 + ∑∞ 𝑘=1 𝐴𝑘 𝑐𝑜𝑠( 𝜋𝑘𝑡 )∆𝑡 𝑁 + 𝐵𝑘 𝑠𝑖𝑛( This sum has 𝑁⁄2- terms with sin function, and 𝑁⁄2 terms with cosin function because AN/2 always be The above formula can be rewrited as following: 2𝜋 2𝜋 𝑁/2 X = 𝑋̅ + ∑𝑖=1 (𝐴𝑖 𝑠𝑖𝑛 𝑃 𝑖𝑡 + Bi cos 𝑃 it) To calculate exactly the contribution of ith function using 𝐶𝑖2 variance, Nth function with variance shall be calculated according to 𝐶𝑖2 formula With this value, the curve representing the contribution of each function shall be established - Multi variable regression model theory: During linear regression process, forecasting term Y is represented by linear combinatorics of forecasting terms X1, Xm2, , Xm in the following equation: Y  a0   a j X j j 1 In which: a0, a1 , am – regression coefficients, defined by: m a0  y  a jx j j 1 m a R j 1 j jk  Ryk , k  1, 2, , m Rjk – correlation momentum between terms Xj and Xk (j,k=1,2, ,m); y, x j - Average value of Y and Xj Linear regression equation between Y and Xi is defined through step – by – step regression method: 10 Step 1: Calculate general correlative coefficients ryi between Y and Xi (i=1 m) and select the coefficient with maximum absolute value Step 2: Calculate particular correlative coefficients ryi.1 (i=2 m) and select the coefficient with maximum value Step 3: Compare surplus standard error value to determine regression equation as following: Y ( k )  a0( k )  a1( k ) x1   ak( k ) xk Data base for study - Topographic data: Topographical data (both single and multi frequency) in monthly maritime notice, yearly dredging work acceptance report, paper works and researches at several channels in Vietnam, as well as actual measured data in 2018 - Hydrographic and muddy data: hydrographic data is collected for calculation, model establishment and examination - Remoting sensor image data: collected at https://earthexplorer.usgs.gov/ Methodology - Site survey: Topographic measurement (using echo sounder at the frequency of 200 KHz, 33KHz, and Echotrac MKIII single beam double frequency echo sounder), Hydro Pro software…; hydrographic measurement, sediment sample study … - Statistic analysis: + Fourier analysis: establish specified formula to define average thickness of fluid mud on the basis of the above mentioned Fourier theory Monthly sediment calculation is as following: F(t) = 𝐴0 𝜋𝑘𝑡 )∆𝑡 𝑁 + ∑∞ 𝑘=1 𝐴𝑘 𝑐𝑜𝑠( 𝜋𝑘𝑡 )∆𝑡 𝑁 + 𝐵𝑘 𝑠𝑖𝑛( 11 Using Fotran program language, establishing calculation program, separating a time - variable synthetic curve into several curves with clarified cycle Evaluating the contribution of each curve to define the important ones Establishing the formula defining the thickness of sediment by comparing and selecting the formula which gives forecasting value closed to actual measured value + Multi variable regression model: establishing the correlation between fluid mud thickness and several hydrographic factors According to the equation of Teisson, 1991, the formation and development of fluid mud at channel shall be represented by two main factor groups, including: dynamic factor (velocity) and muddy factor (density and particle size) There are parameters: Water Turbidity (SPM); Maximum Flow Velocity, Mean Flow Velocity; Tidal Amplitude (H); Bottom Topography or Slope; Maximum Tension Coefficient and Mean Tension Coefficient (Cdmax; Cdmean); Mud Net Weight (Net) Method to define these parameters is presented in part 3.2 Forecasting variables used in regression equation shall be filtered through step – by – step regression method to select the most related factors to establish forecasting equation Basing on the above mentioned theory of multi variable regression analysis, establish automation program, analyzing multi variable regression model and establishing correlation between parameter couples Final result shall be a regression equation, in which the left side is fluid mud thickness and the right one is main parameters CHAPTER 3: CONDITIONS FOR SHIPPING ON FLUID MUD, FOURIER ANALYSIS AND MULTI VARIABLE 12 REGRESSION MODEL FOR THE DEFINITION OF SEDIMENTATION RULE AND FLUID MUD THICKNESS Chapter represents the results of the thesis including: (1) Conditions for shipping on fluid mud in Vietnamese channels, (2) Multi variable regression model for the definition of fluid mud thickness (3) Calculation model of monthly sedimentation 3.1 Conditions for shipping in fluid mud environment in Vietnamese channels - Transportation condition: At channels with high demand of transportation, the shipping traffic of oversized vessels exceeds the capacity of channel dredging and maintaining work With current status of important channels in Vietnam, the increase of nautical depth shall directly affect the efficiency of operation - Natural condition: It is said that the formation and existance of fluid mud is closely related to the following factors: (1) Physico-mechanical characteristic of bottom sediment, (2) Water turbidity, (3) Others: hydrometeorological characteristics (flow, tidal, flood, moonsoon); shipping activity; dredging work; salinity instrution, biochemical factors …Basing on foreign experience and domestic observation, the natural conditions for the occurance of fluid mud in Vietnamese channels include: + Within muddy, sandy estuaries; + Strong tidal and great river flow; + High shipping traffic Basing on Vietnamese coastal geomorphological and dynamical zoning, as well as the conditions of fluid mud occurance, it can be seen that the possibility of fluid mud occurance is much higher in channels 13 within muddy, sandy, funnel-shaped estuaries with combined river – sea factor: - Hai Phong area (Cam river, Bach Dang, Lach Huyen, Chanh river, Pha Rung, Cai Trap); - Do Son – North of Thanh Hoa area (Diem Dien, Hai Thinh); - Vung Tau – Tien Giang area (Vung Tau – Thi Vai, Soai Rap, Sai Gon – Vung Tau, Dua river …); - Tien Giang – Ca Mau area (Dinh An, Quan Chanh Bo, Duyen hai – Tra Vinh) 3.2 Multi variable regression model for fluid mud definition - Input parameters: - Establish distribution map of fluid mud in site area basing on actual measurement data - Recover turbidity field and sediment volume by the method of GIS remoting sensor image analysis: using satellite Landsat image and Nechad 2010 algorithm Run the turbidity field recovering program to have input data for regression analysis - Recover dynamic field within site area by mathematical modeling on the basis of actual measurement data (topography, water level, velocity, flow) - Establish specified formula to define the thickness of fluid mud by multi variable regression model: input data is synchronized in grid, each grid mesh has values, including forecasting value and forecasting parameters - Calculation automation program: using Fotran 90 program language - Analyze correlation calculation result and establish specified formula for fluid mud thickness calculation: basing on the output 14 result of the program, analyse the correlation between parameters for filtering and defining specified formula, in which the left side is fluid mud thickness and the right one is main parameters - Calculating result of specified formular for Soai Rap channel: Basing on the output result of running multi variable regression model (11,237 samples) for Soai Rap channel, the table of correlation between variables has been made By analyzing the correlation between variables, the equation of fluid mud thickness is rewrited as following: Y = -0.00328 + 112.95918 × X5 – 0.00076 × X7 – 29.18383 × X4 In which: X5: tension coefficient, X7: concentration (mg/l) and X4: maximum tension coefficient Maximum average error: (MAE) = 0.08m (~ 30%); Standard error: 0.11211 Multiple correlation coefficient: R2 = 0.5 - Examine specified formula: using actual data measured by multi frequency equipment in 2018, making comparision with the result of specified formula The error is defined to be about 30% 3.3 Establish calculation model of monthly sediment variation Establish calculation sofeware, using Fotran program language on the basis of Fourier analysis theory to separate monthly actually measured sediment volume chart into single curves with defined cycle Calculate and evaluate the contribution of each curve, then establish specified formula of monthly sediment variation Following are the calculating results of Lach Huyen and Bach Dang channel: - Input data: On the basis of input data, including monthly average sediment data series at Lach Huyen and Bach Dang channels (in 05 15 years from 2012 – 2017), the chart of actual measured sediment volume shall be established - Calculation automation program On the basis of Fourier analysis theory and the above mentioned algorihm diagram, establish a program named SBThang.exe on Fotran program language - Calculation procedure: Step 1: Prepare input data, in type of thickness sediment data under timing variation (average monthly data) Step 2: Run program, then the curve of 12 month actual measurement shall be separated into single curves, all parameters of each single curve shall be extracted into text file Step 3: Analyse and establish formula basing on output result Step 4: Establish formula by filtering meaningless function, using forecasting result and correlation coefficient between forecasting result and actual measurement data R2 - Calculation result for Lach Huyen and Bach Dang channels: - Lach Huyen channel - Set up monthly average sediment chart at Lach Huyen channel - Running Sbthang program, the curve of actual measurement is separated into single curves The formula defining the thickness of sediment at Lach Huyen channel is rewrited as following: 2𝜋 2𝜋 2𝜋 X = 0.24+ 0.04[cos (t-5.94)] + 0.03[cos (t-1.69)] + 0.01[cos (t2.74)] + 0.05[cos 2𝜋 (t-1.12)] Basing on the value of variance ratio, select 03 formulas to clarify the optimum one:: 2𝜋 (1) X = 0.24 + 0.04[cos (t-5.94)] 16 (2) X = 0.24 + 0.04[cos (3) X = 0.24+ 0.05[cos 2𝜋 (t-5.94)] + 0.03[cos 2𝜋 (t-1.69)] 2𝜋 (t-1.12)] Basing on the evaluation of correlation coefficient R2 between actual measurement data in 2016 and the result of forecasting formula (1), (2), (3), it can be seen that, the formula (1) gives maximum correlation coefficient R2 with the value of 0,82 Therefore, the formula (1) shall be selected to be the formula forecasting the thickness of sediment in Lach Huyen channel area - Bach Dang channel: Similar procedure is applied for Bach Dang channel, the following formula is defined: 2𝜋 2𝜋 2𝜋 X = 5.016+ 5.1[cos 12 (t-6.6)] + 0.6[cos 12 (t-0.6)] + 0.4[cos 12 (t-2.0)] (This formula shall be used to calculate reasonable dredging time in part 4.2) CHAPTER 4: APPLICATION OF STUDY RESULTS 4.1 Application of specified formula calculating the thickness of fluid mud and defining reasonable nautical bottom and dredging bottom in Soai Rap – Hiep Phuoc channel 4.1.1 Calculating the thickness of fluid mud and defining reasonable nautical bottom (Soai Rap channel from 49 to 57 float) Applying mathematical model and remoting sensor image analysis as described in part 3.2 chapter 3, the velocity, tension coefficient and turbidity have been calculated Using the formula forecasting the thickness of fluid mud in chapter 3: 17 Y = -0,00328 + 112,95918 × X5 – 0,00076 × X7 – 29,18383 × X4 The result of calculating the average thickness of fluid mud is represented as following: a) b) a) Calculating result of fluid mud distribution; b) Longitudinal section of channel Forecasted thickness of fluid mud in each section: Accumulated Fluid mud distance (m) thickness hbl (m) P01 to P10 1,000 0.25 – 0.35 P11 to P88 1,800 0.15 – 0.25 P 29 to P42 4,200 0.15 - 0.24 P43 to P52 5,200 0.2 – 0.25 P53 to P79 7,900 0.13-0.22 No Section 4.1.2 Defining nautical bottom and designed dredging bottom level Nautical bottom level is defined according to the following formula: CĐĐCT = MNCT – h h: designed nautical depth: ℎ = 𝑇 + ∑ Z𝑖 In which: T: designed draft; ∑ ∆𝑍𝑖 including: z1: wave response allowance 18 z2: Allowance for dynamic heel due to wind and turning (m) z3: Allowance for trim or turning, z3 = 0.5Btsinα - z1 (m) z0 > 0.5z1 (m) α: deflection angle due to trim or turning, α = 4o (dry cargo ship) z4: Allowance for bed level uncertainties (m) Designed nautical bottom is calculated as following: CĐĐ = CĐĐCT – z = MNCT – z5 – h (z5 is sedimentation allowance between two dredging periods) (m) In case of fluid mud occurence hbl: CĐĐ = MNCT – z5 – h + hbl Calculation is made for section from P49 to 57 of Soai Rap channel: - Designed for container vessel size of post panamax 70.000 DWT, with draft T=13.8m Nautical bottom selected in accordance with standard condition at the frequency P% = 50% is +2.9 (chart datum) The result is as following: v T z1 z2 z3 Z4 Nautical (m/s) (m) (m) (m) (m) (m) depth, h (m) 0.49 0.91 0.55 15.7 4.12 13 Dredging level is defined by formula (4.4) with z5 = 0,4 m; Nautical level = +2,9 (at frequency P% = 50%): CĐĐ = + 2,9 m -15,7m – 0,4m = -13.2 (chart datum) The dredging bottom level counting fluid mud occurrence is calculated as following: MNCT Channel section h (m) hbl Z5 CĐĐ (m) (m) From P01 to P10 +2.9 15.7 0.4 0.25 -12.95 P11 to P18 +2.9 15.7 0.4 0.15 -13.05 19 P19 to P28 +2.9 15.7 0.4 0.25 -12.95 P 29 to P42 +2.9 15.7 0.4 0.15 -13.05 P43 to P52 +2.9 15.7 0.4 0.2 -13.0 P53 to P79 +2.9 15.7 0.4 0.1 -13.1 Note: Due to difference in fluid mud distribution, the minium thickness of fluid mud is selected to take in to calculation - The specialized formula of fluid mud distribution in chapter can be applied for: + Forecasting the distribution and thickness of fluid mud in studied channel section according to affecting factors that have been defined in the formula + Conducting adjustment for channel depth notification, dredging bottom level in order to improve the efficiency of dredging work and channel opperation 4.2 Defining reasonable dredging time for the maximization of Bach Dang channel operation efficiency The formula to calculate the thickness of monthly sedimentation in Bach Dang channel (Chapter 3): 2𝜋 2𝜋 2𝜋 X = 5.016+ 5.1[cos 12 (t-6.6)] + 0.6[cos 12 (t-0.6)] + 0.4[cos 12 (t-2.0)] Nautical bottom level is defined as following: CĐĐCT = MNCT – (hhbl) in which, hbl is the thickness of fluid mud The expense of dredging work is selected to be target function The efficiency of channel operation is depended on how much the dredging depth is higher than the designed nautical bottom level The value of hcl is the sediment allowance value remaining at the tth month after finishing dredging work 20 Calculating reasonable dredging time to maximize the efficiency of vessel size > 10.000 DWT, with the assumption that the channel is dredged once a year, within one month, hdt = 60 cm: 12 Hcl(t) = hdt -∑ 𝑡=1 0.6)] + 0.4[cos 5.016 + 5.1[cos 2𝜋 (t − 12 2𝜋 (t 12 − 6.6)] + 0.6[cos 2𝜋 (t 12 − 2.0) The value of Hcl at tth month is equal to hdt minus the accummulated total of months from dredging completion to the month right before the one selected to calculate Hcl The calculated result of Hcl and Hhd value according to the formula of average sediment speed at Bach Dang channel is represented in detail in Chapter of the thesis The result shows that the selection of dredging time causes great affect to the total time of maintaining sediment allowance at tth month If this total value of a year is called Hhd, it shall be in direct proportion to the efficiency of channel operation If Hhd is called added efficiency value, by trial method for each month, the month with maximum value of Hhd could be defined In case of Bach Dang channel section, maximum value of Hhd is Hhd= 438cm when dredging work is performed on August CONCLUSION The occurence of fluid mud in several channels in Vietnam has already been recorded, besides, its popularity has also been recognized The solution of utilizing partly fluid mud in shipping has been applied to reducing under keel upsizing vessel, increasing cargo load and improving the efficiency of marine transportation In term of science, this issue is relatively novel and under insufficient study 21 This thesis has generated and analyzed the most basic contents relating fluid mud and the utilization of fluid mud in shipping in the world and Vietnam; applying statistic analysis, site survey, mathematical model, remoting sensor images and other methods to study the following contents: conditions to apply shipping in fluid mud environment in Vietnam, methodology to define sediment rule, fluid mud thickness and reason nautical bottom in case of fluid mud The results of this thesis shall bring general scientific basis for initial solutions of the following issues: - Scientific and technical base for the selection of criteria defining the feasibility of fluid mud utilization in shipping and reasonable nautical bottom; - Clarify several scientific issues relating sedimentation at channels with fluid mud, using reasonable methods and technology to define conditions for specific channel whether the utilization of fluid mud in shipping can be applied; - Establish program and planning to improve the efficiency of channel operation, determining reasonable dredging time and cycle in case of fluid mud Results - Analyse natural charactistics and operation characteristics of specific channels to evaluate the possibility of fluid mud occurance and the conditions to apply shipping in fluid mud environment; - Establish multi variable regression equation to determine the thickness of fluid mud basing on actual measurement data; - Evaluate the rule of variation in channel depth, using statistic data and Fourier spectrum theory to establish the formula to calculate the thickness of monthly sediment; 22 - Basing on the basic formula defining nautical bottom and the results of calculating yearly average fluid mud thickness, establish the methodology and examine the reasonable nautical bottom in case of fluid mud; - Establish the methodology defining reasonable dredging time basing on statistic data and the value of Hhd which is added efficiency value Novel contributions - Establish the methodology to evaluate the occurance of fluid mud and the feasibility of shipping in fluid mud environment - Establish the methodology and calculation procedure of fluid mud thickness according to dynamic and muddy factors; - Establish the methodology to define the thickness of monthly sediment basing on Fourier analysis theory - Establish the methodology for the definition of reasonable nautical bottom in case of fluid mud - Establish the efficiency criteria of channel maintainance in order to define reasonable dredging time 23 PUBLICATIONS Nguyen Anh Tuan (2019) Vietnamese coastal geomorphological and dynamical zoning, and the conditions of fluid mud occurance in Vietnamese navigable channels, Water Resource Science and Technology Magazine, 56: 99-107 Nguyen Anh Tuan (2019) Application of Fourier statistic data analysis in evaluating the rule of nautical depth reduction, Transportation Magazine, 06: 106-108 Nguyen Anh Tuan (2019) Forecasting the thickness of fluid mud in navigable channel by dynamic and multi variables regression model, Transportation Magazine, 08: 98-103 Nguyen Ngoc Hue, Nguyen Anh Tuan and Mac Van Dan (2018) Application of Landsat remoting sensor image in studying and forcasting the volume of suspended sediment flowing through river cross section, Transportation Magazine, 12: 140-144 Nguyen Ngoc Hue, Nguyen Anh Tuan (2014) Mathematic model on suspended sediment flow due to vessel propeller operation, Transportation Magazine, 7: 28-30 Nguyen Anh Tuan (2015) Modeling of suspended sediment contrentation due to dredging by cutter suction dredger, Sea and Coastal Magazine, 4: 30-36 ... of Thesis committee 2: Assoc.Prof.Dr Tran Thanh Tung Member of Thesis committee 3: Prof.Dr Lê Văn Nghị The PhD thesis shall be defensed at the institual thesis committee of Vietnam Academy for... mud in Vietnamese channels include: + Within muddy, sandy estuaries; + Strong tidal and great river flow; + High shipping traffic Basing on Vietnamese coastal geomorphological and dynamical zoning,... soil mechanics) - Nautical bottom: A joint PIANC-IAPH working group (PIANC, 1997) defined the nautical bottom as ‘the level where physical characteristics of the bottom reach a critical limit