Determining the Onset and Strength of Unforced Wave Breaking in A Numerical Wave Tank

A numerical wave tank is used to investigate the onset and strength of unforced wave breaking, and the waves have three types of initial spectra： constant amplitude spectrum, constant steepness spectrum and Pierson-Moscowitz spectrum. Numerical tests are performed to validate the model results. Then, the onset of wave breaking is discussed with geometric, kinematic, and dynamic breaking criteria. The strength of wave breaking, which is always characterized by the fractional energy loss and breaking strength coefficient, is studied for different spectra. The results show how the energy growth rate is better than the initial wave steepness on estimating the fractional energy losses as well as breaking strength coefficient.

聚酯缆动力学行为计算方法研究

The dynamic stiffness of polyester rope presents a complex mechanical performance,and the search for an appropriate calculation method to simulate this property is important.Distorted simulation results eventually yield inaccurate line tension and vessel offset predictions,with the inaccuracy of vessel offset being particularly large.This paper proposes a flexible calculation method for the dynamic behavior of polyester rope based on the dynamic stiffness model.A real-time varying stiffness model of polyester rope is employed to simulate tension response through rope strain monitoring.Consequently,a simulation program is developed,and related case studies are conducted to explore the differences between the proposed method and analytical procedure of the DNV standard.Orcaflex is used to simulate the results of the latter procedure for comparison.Results show the convenience and straightforwardness of the procedure in the selection of an approximate dynamic stiffness model for polyester rope,which leads to an engineering-oriented approach.However,the proposed method is related to line property,which can directly reflect the dynamic behavior of polyester rope.Thus,a flexible calculation method may provide a reference for the simulation of the dynamic response of polyester mooring systems.

KNOT STRENGTH OF INDUSTRIAL TEXTILE FIBRES

In this paper, the knot strengths of the seven strands which were made of polyethleneterephthalate(PET), nylon 6, polyvinyl formal fibre, polypropylene and polyethylene with differentspecification used for industrial purposes were tested and discussed. The results of experimentshow: the knot strength loss does not only depend on the breaking elongation and the diameter ofsample, but also on the shape of the load-extension curve and twist factor of sample and other fac-tors; the range of the knot strength loss and the breaking energy loss vary in a wide range, in thepresent case. the former is from 2.7% to 58.14% and the latter from 16.36% to 78.76%. Thestrength loss of the polypropylene filament is the least among the samples investigated.

Effects of L-arginine,guanidinoacetic acid and L-citrulline supplementation in reduced-protein diets on bone morphology and mineralization of laying hens

The alterations in feed ingredients and the nutrient matrix to produce reduced-protein diets may affect bone morphology and mineralization in laying hens.This study was implemented to determine the effects of L-arginine(Arg),guanidinoacetic acid(GAA),and L-citrulline(Cit)supplementation to Argdeficient reduced-protein diets on bone morphology,strength,and mineralization status of laying hens.Individually housed Hy-Line Brown laying hens were evenly distributed to five dietary treatments with 25 replicates per treatment from 20 to 40 wk of age.Treatments consisted of a standard protein diet(17%crude protein,SP),a reduced-protein diet deficient in Arg(13%crude protein,RP),and RP supplemented with Arg(0.35%Arg,RP-Arg),GAA(0.46%GAA equivalent to 0.35%Arg,RP-GAA),or Cit(0.35%Cit equivalent to 0.35%Arg,RP-Cit)to reach the Arg level of SP diets.Birds fed the SP diet had similar bone weight,ash,length,width,Seedor index,breaking strength,and serum mineral concentration,but higher toe B level(P<0.001)compared to those fed the RP diet at wk 40.Birds fed the SP diet consumed more but also excreted more K and B compared to those fed the RP diet(P<0.01).Birds fed the SP diet had lower Cu digestibility(P=0.01)and higher B retention(P<0.01)compared to those offered the RP diet.Supplementation of Arg,GAA,and Cit to the RP diet increased relative femur weight and length(P<0.001).Citrulline supplementation also increased relative tibia and femur ash,and Zn digestibility(P<0.05).Supplementation of GAA to the RP diet decreased serum Ca,P,and Mg levels,decreased tibia Fe and Mg levels and toe Mg level,but increased Al,Fe,Zn,and Mn digestibility(P<0.05).The current findings demonstrated the capacity of laying hens to adapt to low mineral intake by increasing mineral utilization.Overall,bone morphology and breaking strength,and serum mineral level in laying hens were not influenced by dietary CP levels.Dietary Arg,GAA,or Cit supplementation were effective in improving bone morphology and mineralization in laying hens fed Arg-deficient RP diets.

Degradability evaluation for natural material fibre used on fish aggregation devices(FADs)in tuna purse seine fishery

Purse seiners deploy large amounts of drifting fish aggregation devices(FADs)in all tropical oceans to catch tunas.These FADs are constructed with porous synthetic fibre netting,which are responsible for incidental mortality of sea turtles and sharks through entanglement,and can engage in ghost fishing if they are lost and abandoned.The use of natural or biodegradable materials to build FADs can effectively mitigate marine pollution and bycatch issues,and as such they are currently promoted by fisheries management organizations.This study evaluated the degradability of ropes made of common natural fibres;cotton rope(3-strand,96-thread,twisted,S-lay),jute rope(3-strand,13-thread,twisted,Z-lay)and sisal rope(3-strand,8-thread,twisted,Z-lay).Degradability was evaluated by measuring the breaking strength(cN/dtex)and retention ratio of rupture elongation.Results showed that jute rope and sisal rope experienced rapid reduction of strength which over the first month soaking in the sea fell by 66.8%and 46.9%,respectively.Cotton rope exhibited the most inert degradation behavior,with breaking strength maintained at half of the initial value at 10 months.The retention ratio of rupture elongation for jute ropes and sisal ropes fluctuated considerably in the following months after deployment,compared to the relatively stable change for cotton rope.Results suggested that among these congeners,cotton rope would be most preferable component for Bio-FADs with a 10-month minimum durability that matches the required lifetime of FAD fishing strategies.